掲載種別：研究論文（学術雑誌）   国際・国内誌：国際誌  

担当区分：責任著者   掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

DOI： 10.1063/5.0056724

担当区分：責任著者   掲載種別：研究論文（国際会議プロシーディングス）   共著区分：共著   国際・国内誌：国際誌  

担当区分：責任著者   掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.5129188

担当区分：責任著者   掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

We report the spin current properties in a pigment-red (perylene-3,4,9,10-tetracarboxylic dianhydride: PTCDA) film prepared by thermal evaporation. In a palladium(Pd)/PTCDA/Ni80Fe20 tri-layer sample, a pure spin-current is generated in the PTCDA layer by the spin-pumping of the Ni80Fe20. The spin current is absorbed into the Pd layer, converted into a charge current with the inverse spin-Hall effect in Pd, and detected as an electromotive force. This is clear evidence for the pure spin current in a PTCDA film, and it is confirmed that a PTCDA film is useful not only as a robust protection layer material but also as a spintronic material.

担当区分：責任著者   掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

The spin transport in thermally-evaporated tetracene films and 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) films by using the spin-pumping-induced spin injection method was challenged at room temperature. The spin transport in the TIPS-pentacene films was demonstrated, while the spin transport in tetracene films was not succeeded. For tetracene films, reconstruction of the prepared films was occurred due to the high vapor pressure and it might be caused the deformation of ferromagnetic material as the spin injector.

DOI： 10.1109/TMAG.2018.2856275

担当区分：責任著者   掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

The inverse spin-Hall effect (ISHE) is produced even in a “single-layer” ferromagnetic material film. Previously, the self-induced ISHE in a Ni80Fe20 film under the ferromagnetic resonance (FMR) was discovered. In this study, we observed an electromotive force (EMF) in an iron (Fe) and a cobalt (Co) single-layer films themselves under the FMR. As origins of the EMFs in the films themselves, the ISHE was main for Fe and dominant for Co, respectively 2 and 18 times larger than the anomalous Hall effect. Thus, we demonstrated the self-induced ISHE in an Fe and a Co single-layer films themselves under the FMR.

DOI： 10.1063/1.5006102

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

Thin films of weak charge-transfer (CT) complexes (pyrene/dimethylpyromellitdiimide or pyrene/pyromellitic dianhydride) were prepared on an interdigitated platinum electrode by vacuum vapor deposition. Their photoconductivity and magnetoconductance (MC) effects were investigated, and mobile triplet excitons (probably CT excitons) were detected by time-resolved ESR (TRESR) at room temperature. The MC effect on the photocurrent was observed and analyzed by quantum-mechanical simulation assuming two types of collision mechanisms between the electron and hole carriers and between the trapped triplet excitons and mobile carriers. A successful simulation was achieved when the parameters (g, D, E, and polarization) determined by TRESR and the effective hyperfine splitting estimated from an ab initio molecular-orbital calculation were used.

DOI： 10.1039/c7cp02781h

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

A d-orbital electron has an anisotropic electron orbital and is a source of magnetism. The realization of a two-dimensional electron gas (2DEG) embedded at a LaAlO3/SrTiO3 interface surprised researchers in materials and physical sciences because the 2DEG consists of 3d-electrons of Ti with extraordinarily large carrier mobility, even in the insulating oxide heterostructure. To date, a wide variety of physical phenomena, such as ferromagnetism and the quantum Hall e_ect, have been discovered in this 2DEG system, demonstrating the ability of d-electron 2DEG systems to provide a material platform for the study of interesting physics. However, because of both ferromagnetism and the Rashba field, long-range spin transport and the exploitation of spintronics functions have been believed di_cult to implement in d-electron 2DEG systems. Here, we report the experimental demonstration of room-temperature spin transport in a d-electron-based 2DEG at a LaAlO3/SrTiO3 interface, where the spin relaxation length is about 300 nm. Our finding, which counters the conventional understandings of d-electron 2DEGs, highlights the spin-functionality of conductive oxide systems and opens the field of d-electron spintronics.

担当区分：責任著者   掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

The spin current relaxation time (tau) in thermally evaporated pentacene films was evaluated with the spin-pump-induced spin transport properties and the charge current transport properties in pentacene films. Under an assumption of a diffusive transport of the spin current in pentacene films, the zero-field mobility and the diffusion constant of holes in pentacene films were experimentally obtained to be ~8.0*10^-7 m²/Vs and ~2.0*10^-8 m²/s, respectively. Using those values and the previously obtained spin diffusion length in pentacene films of 42±10 nm, the tau in pentacene films was estimated to be 150±120 ns at room temperature. This estimated tau in pentacene films is long enough for practical use as a spintronic material.

担当区分：責任著者   掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

We report the electromotive force (EMF) properties generated in 3d-transition ferromagnetic metal (FM = Fe, Co, and Ni80Fe20) films themselves under their ferromagnetic resonance (FMR). For Fe and Co films, the EMF due to the anomalous-Hall effect is dominantly generated under their FMR. Meanwhile, for a Ni80Fe20 film, the EMF due to the inverse spin-Hall effect in the Ni80Fe20 film itself under the FMR is mainly generated. This tendency is qualitatively explained with differences of the spin polarization, the spin Hall conductivity, the anomalous Hall conductivity, the magnetization saturation, and the resistivity of the FM films.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

In this paper, we report on the investigation of (i) the transport properties of multicarriers in semimetal Bi and (ii) the spin conversion physics in this semimetal system on a ferrimagnetic insulator, yttrium-iron-garnet. Hall measurements reveal that electrons and holes coexist in the Bi, with electrons being the dominant carrier. The results of a spin conversion experiment corroborate the results of the Hall measurement; in addition, the inverse spin Hall effect governs the spin conversion in the semimetal/insulator system. This study provides further insights into spin conversion physics in semimetal systems.

DOI： 10.1103/PhysRevB.93.174428

担当区分：責任著者   掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

We report the spin-pump-induced spin transport properties of a pentacene film prepared by thermal evaporation. In a palladium(Pd)/pentacene/Ni₈₀Fe₂₀ tri-layer sample, a pure spin-current is generated in the pentacene layer by the spin-pumping of Ni₈₀Fe₂₀, which is independent of the conductance mismatch problem in spin injection. The spin current is absorbed into the Pd layer, converted into a charge current with the inverse spin-Hall effect in Pd, and detected as an electromotive force. This is clear evidence for the pure spin current at room temperature in pentacene films prepared by thermal evaporation.

担当区分：責任著者   掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

Spin pumping controlled with the ferromagnetic resonance of an Ni₈₀Fe₂₀ thin film annealed in a magnetic field was performed in order to investigate the simple and efficient generation method of the pure spin current. At the spin-pumping using the Ni₈₀Fe₂₀ on an annealed Pd/Ni₈₀Fe₂₀ stacked structure, the electromotive force due to the inverse spin-Hall effect (ISHE) in the Pd was found to be 30% stronger than that without annealing. When the angle between the directions of localized magnetic moments in the Ni₈₀Fe₂₀ film and the external magnetic field in the spin-pumping is zero, the spin injection efficiency into the Pd layer, i.e., the spin current density generated in the Pd layer can be the maximum. The annealing in a magnetic field is a convenient technique for increasing the spin current density generated by the spin pumping.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

Inverse spin Hall effect (ISHE) allows the conversion of pure spin current into charge current in nonmagnetic materials due to spin-orbit interaction (SOI). In ferromagnetic materials (FMs), SOI is known to contribute to anomalous Hall effect, anisotropic magnetoresistance, and other spin-dependent transport phenomena. However, SOI in FM has been ignored in ISHE studies in spintronic devices, and the possibility of “self-induced ISHE” in FM has never been explored until now. In this paper, we demonstrate the experimental verification of ISHE in FM. We found that the spin-pumping-induced spin current in permalloy (Py) film generates a transverse electromotive force (EMF) in the film itself, which results from the coupling of spin current and SOI in Py. The control experiments ruled out spin rectification effect and anomalous Nernst effect as the origin of the EMF.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

Spin Hall angle and spin diffusion length in amorphous bismuth (Bi) are investigated by using conversion of a pure spin current to a charge current in a spin pumping technique. In Bi/Ni₈₀Fe₂₀/Si(100) sample, a clear direct current (DC) electromotive force due to the inverse spin Hall effect of the Bi layer is observed at room temperature under a ferromagnetic resonance condition of the Ni₈₀Fe₂₀ layer. From the Bi thickness dependence of the DC electromotive force, the spin Hall angle and the spin diffusion length of the amorphous Bi film are estimated to be 0.02 and 8 nm, respectively.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

The generation, propagation, and control of spin current have attracted a great deal of attention because of the possibility of realizing dissipation-free information propagation. Although electrical generation of spin current originally made significant advances in spin-current devices, novel spin-current-generation approaches without the application of charge current, such as dynamical methods, have also been gaining importance. However, the low spin-current generation efficiency associated with dynamical methods has impeded further progress towards practical spin devices. Here we show that by introducing a single-crystalline ferromagnetic material, Fe₃Si, pure spin currents can be generated about 20 times more efficiently when using a dynamical method. This achievement paves the way to the development of different spin-based devices.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

In this study, the temperature dependence of the spin Hall angle of palladium (Pd) was experimentally investigated by spin pumping. A Ni₈₀Fe₂₀/Pd bilayer thin film was prepared, and a pure spin current was dynamically injected into the Pd layer. This caused the conversion of the spin current to a charge current owing to the inverse spin Hall effect. It was found that the spin Hall angle varies as a function of temperature, whereby the value of the spin Hall angle increases to ca. 0.02 at 133 K.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

Large linear magnetoresistance (MR) in electron-injected p-type silicon at very low magnetic field is observed experimentally at room temperature. The large linearMRis induced in electron-dominated space-charge transport regime, where the magnetic field modulation of electron-to-hole density ratio controls the MR, as indicated by the magnetic field dependence of Hall coefficient in the silicon device. Contrary to the space-charge-induced MR effect in unipolar silicon device, where the large linear MR is inhomogeneity-induced, our results provide a different insight into the mechanism of large linear MR in nonmagnetic semiconductors that is not based on the inhomogeneity model. This approach enables homogeneous semiconductors to exhibit large linear MR at low magnetic fields that until now has only been appearing in semiconductors with strong inhomogeneities.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

The conductance mismatch problem limits the spin-injection efficiency significantly, and spin injection into graphene usually requires high-quality tunnel barriers to circumvent the conductance mismatch. We introduce an approach which enables the generation of pure spin current into single-layer graphene (SLG) that is free from electrical conductance mismatch by using dynamical spin injection. An experimental demonstration of spin-pumping-induced spin current generation and spin transport in SLG at room temperature was successfully achieved, and the spin coherence length was estimated to be 1.36 μm by using a conventional theoretical model based on the Landau-Lifshitz-Gilbert equation. The spin coherence length is proportional to the quality of SLG, which indicates that spin relaxation in SLG is governed by the Elliot-Yafet mechanism, as was reported.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

Spin pumping enables the vertical transport of pure spin current through Al in a Pd/Al/ Ni₈₀Fe₂₀(Py) trilayer film, in which the Py acts as a spin battery. The spin current injected into the Al flows through the Al to reach the Pd, resulting in the generation of electromotive forces due to the inverse spin Hall effect in the Pd. The electromotive forces decreased with increasing thickness of the Al layer. A simple model based on the theory by Tserkovnyak et al., allows an estimation of the spin coherence of the vertical spin transport in the Al of 61 nm. This comparatively short coherence is attributed to a reduction in spin pumping efficiency because of the roughness of the Al/Py interface.

担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

A spin battery concept is applied for the dynamical generation of pure spin current and spin transport in p-type silicon (p-Si). Ferromagnetic resonance and effective s-d coupling in Ni₈₀Fe₂₀ results in spin accumulation at the Ni₈₀Fe₂₀/p-Si interface, inducing spin injection and the generation of spin current in the p-Si. The pure spin current is converted to a charge current by the inverse spin Hall effect of Pd evaporated onto the p-Si. This approach demonstrates the generation and transport of pure spin current in p-Si at room temperature.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

We demonstrate dynamical spin injection into p-type germanium (Ge) at room temperature (RT) using spin pumping. The generated pure spin current is converted to a charge current by the inverse spin-Hall effect (ISHE) arising in the p-type Ge sample. A clear electromotive force due to the ISHE is detected at RT. The spin-Hall angle for p-type Ge is roughly estimated to be 9.6*10#u-4#ur at RT.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

A novel magnetoelectric effect is found to appear in a C₆₀-Co nanocomposite. Although Co is well-known as a ferromagnet, its nanoparticles embedded in a C₆₀ matrix can exhibit multiferroic-like behavior, i.e., an electric field controls magnetic alignment of the nanoparticles and a magnetic field controls their charged states. This novel effect enables a strong magnetic switching effect for which the on/off ratio is ca. 10⁴. Such an effect has been expected to exist and these findings show this magnetoelectric coupling for the first time.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

We report a significant lowering of the Schottky barrier height (SBH) in nickel (Ni)/rubrene devices by the insertion of a tetrafluoro-tetracyanoquinodimethane (F₄TCNQ), molybdenum trioxide (MoO₃), or tetracyanoquinodimethane (TCNQ) layers at the device junction. Devices with F₄TCNQ and MoO₃ layers show ohmic-like characteristics, whereas the device with the TCNQ layer shows a low SBH (0.26 eV). The SBH of Ni/rubrene device without the acceptor layers is 0.56 eV. We explain the SBH lowering by the electron accepting properties of the thin layers. Such layers can be used to fabricate molecular spintronics devices with ohmic contacts for effective electrical spin injection.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

The underlying physics of the inverted Hanle effect appearing in Si was experimentally investigated using a Si spin valve, where spin transport was realized up to room temperature. No inverted-Hanle-related signal was observed in a nonlocal four-terminal scheme, even when the same ferromagnetic electrode was used, whereas the signal was detected in a nonlocal three-terminal scheme. Although the origin of the inverted Hanle effect has been thought to be ascribed to interfacial roughness beneath a ferromagnetic electrode, our finding is inconsistent with the conventional interpretation. More importantly, we report that there were two different Hanle signals in a nonlocal three-terminal scheme, one of which corresponds to the inverted Hanle signal while the other is ascribed to spin transport. These results strongly suggest that (1) there is room for discussion concerning the origin of the inverted Hanle effect, and (2) achievement of spin transport in a nonlocal four-terminal scheme is indispensable for further understanding of spin injection, spin transport, and spin coherence in Si. Our findings provide a strong platform for future discussion of the physical essence of Hanle-related spin phenomena.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

We investigated the effect of spin drift on spin accumulation in highly doped silicon (Si) by using a non-local three-terminal (NL-3T) and four-terminal (NL-4T) methods, and have clarified that the spin accumulation voltages in a NL-3T device were modulated due to spin drift and that spin lifetime can be accurately extracted by employing a modified spin drift-diffusion equation. The extracted spin lifetime is 4-7 ns, which is slightly shorter than the intrinsic spin lifetime (8 ns) measured in the NL-4T method in the same Si device because of spin drift. It is elucidated that the spin drift effect should be considered for the precise estimation of spin lifetime in Si by NL-3T method.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

The electronic properties of Eu_2.75C₆₀ are studied using magnetic susceptibility and electron spin resonance (ESR) from 2 to 300 K. Both themagnetic susceptibility and the ESR parameters clearly show an anomaly around the valence transition temperature, T_V = 70 K. The magnetic susceptibility shows weak temperature dependence above T_V, while it changes drastically to Curie-Weiss behavior below T_V. The low-temperature susceptibility can be reproduced by assuming the moment of free Eu²⁺ ions. This result reveals that Eu_2.75C₆₀ changes from the intermediate valence state to the divalent state below T_V. Although ESR signals above T_V should be attributed to conduction electrons, the ESR intensity below T_V follows the Curie-Weiss law with a distinct increase in the g-factor. This should be associated with a strong localization of π electrons. We also found that, below ∼17 K, the isothermal magnetization exhibits a weak hysteresis and thermoremanent magnetization appears. These results suggest that valence-ordered Eu_2.75C₆₀ undergoes antiferromagnetic ordering with a weak ferromagnetic component at the N´eel temperature, T_N = 17 K.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

A systematic investigation of spin transport properties in silicon at 8 K by using a nonlocal geometry is presented. The spin injection signal in the nonlocal scheme is found to increase in proportion to the evolution of bias electric currents. Theoretical fittings using the Hanle-type spin precession signals reveal that the spin polarization of the transported spins in the Si is much less affected by the change in the bias electric current compared with the cases in the other spin devices. It is also revealed that the bias current dependence of the spin accumulation voltages exhibits good accordance with that of the spin polarization.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

The electronic structure of the interface between rubrene (C₄₂H₂₈) single crystal and ferromagnetic Ni is studied using an electrical method from a viewpoint of spintronics applications of organic single crystals. The Schottky barrier height at the interface is estimated to be 0.56 eV, and our finding is compared with previous results in spectroscopic method. This study clarifies the importance of electrical investigations of the Schottky barriers for various ferromagnet/organic systems and suggests that functionalization and carrier doping to rubrene single crystals are potential for obtaining the thinner barriers and yielding conclusive electrical spin injection.

担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

A high resistance ferromagnetic oxide Fe_2.5Mn_0.5O₄ (FMO) property as a novel spin injector was investigated with a structure of a magnetic tunneling junction (MTJ) composed of FMO/Al–O/Ni₈₀Fe₂₀, in order to reduce an impedance mismatch problem on molecular spintronics. A tunneling magnetoresistance (TMR) effect in the MTJs was observed. The maximum TMR ratio observed in the MTJs was approximately 0.85% at room temperature (RT), and the spin-polarization of FMO was estimated to be at least 0.94% at RT.

担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

Organic light-emitting devices (OLEDs) with a phosphorescent molecule Ir(ppy)₃ as the emitter and with an Fe cathode as the spin injector were fabricated for the observation of the large degree of circular polarization. The OLED structure was a glass-substrate/ITO/a-NPD/CBP doped with Ir(ppy)₃/BCP/Aloxide/Fe/Al. The mixing ratio of CBP and Ir(ppy)₃ in the emissive layer was optimized for high luminescence efficiency. The OLEDs showed circular polarization, and the maximum degree of circular polarization of the OLEDs was 0.4% at the applied magnetic field of 1.6 T at room temperature. On the other hand, no circular polarization was observed from the OLEDs with an Al cathode.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

We describe an alternative method for realizing a carbon nanotube spin field-effect transistor device by the direct synthesis of single-walled carbon nanotubes (SWNTs) on substrates by alcohol catalytic chemical vapor deposition. We observed hysteretic magnetoresistance (MR) at low temperatures due to spin-dependent transport. In these devices, the maximum ratio in resistance variation of MR was found to be 1.8%.

DOI： 10.1088/1468-6996/9/2/025019

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

The magnetization and the coercivity of Co and Fe thin films in the thickness range 10–200 nm deposited onto GaAs(0 0 1) substrate were studied. Coercivity of Co and Fe thin films increases with increase in film thickness. Coercivity increased from 10 to 80 Oe as thickness of Co films increased from 50 to 100 nm. In the Fe/GaAs system, coercivity increased from 30 to 180 Oe as thickness of Fe films increased from 40 to 100 nm. The surface roughness measurements of Fe films indicate that enhancement of coercivity is due to surface roughness of the film. On the other hand, it was observed from the AFM study that the enhancement of coercivity was not due to surface roughness of Co film. It is speculated that the enhanced coercivity of Co/GaAs is due to a special interaction between Co film and GaAs substrate, since the enhancement of coercivity did not appear in Co films deposited on Si(0 0 1) substrate.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

Transport properties of C₆₀ field-effect transistors (FETs) have been investigated in the temperature range between 160 and 300 K. Activation energy was estimated from temperature dependence of resistance at the linear region and of current at the saturation region for various channel lengths. Variation of activation energy values is attributed to carrier injection barrier at contact between source electrode and C₆₀ channel, and barriers to carrier hopping between trap states in the channel of C₆₀.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

We have fabricated carbon nanotube (CNT) field-effect transistors FETs by direct growth of single-wall CNTs between the source and drain electrodes, and investigated their device characteristics. The FETs show ambipolar operation. The temperature and bias voltage dependence of device characteristics are consistent with device operation of the Schottky-type FET. The carrier injection barrier heights for both the electron and hole carriers show small values of 17–74 meV, without any additional specific treatment after device fabrication.

担当区分：最終著者   掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

We report transport properties of C₆₀ thin film field-effect transistors (FETs) with a channel length of several-ten nanometers. Nonlinear drain current I_D versus source-drain voltages V_DS characteristics were observed at room temperature. We discuss this phenomenon in terms of the crossover from a diffusive conductance in bulk regime to a coherent one in the nanometer scale.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

C60 field-effect transistors (FETs) have been fabricated with source/drain electrodes of three different materials, indium tin oxide (ITO), Au, and Pt. High field-effect mobility µ_FE of FETs with ITO electrodes, 1.6*10⁻¹ cm² /V s, shows that ITO is a potential material for the electrodes of organic electronics. Although the highest Schottky barrier and the lowest µ_FE were expected, µ_FE of FET with Pt electrodes (1.4*10⁻¹ cm²/Vs) is higher than that of FET with Au electrodes (9.6*10⁻² cm²/Vs). The result suggests that modification of local electronic structure at the interface between electrodes and C60 affects device performance.

担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

Electroluminescence (EL) properties of organic light-emitting diodes (LEDs) under an external magnetic field were investigated for observation of spin-polarized luminescence. When an external magnetic field was applied to organic LEDs with an Fe cathode, circularly polarized light was observed, while devices with an Al cathode did not show such behavior. In order to confirm whether the circularly polarized light was certainly due to spin injection or not, photoluminescence (PL) property of Alq₃ (tris-(8-hydroxyquinolinato)-aluminum) film on Fe and that of Alq₃ film on Al under an external magnetic field were investigated. In the case of Alq₃ on Fe film, the degree of circular polarization from EL was much higher than that from PL. This suggested that circular polarization on EL was mainly due to spin injection.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

We report the dependence of growth yield of single-walled carbon nanotubes (SWNTs) on heat-treatment time and catalyst film thickness by the alcohol catalytic chemical vapor deposition method. Three types of heat-treatment, synthesis of 30 min, synthesis of 30 min after annealing of 30 min, and synthesis of 60 min, were investigated. Thickness of Co catalyst film was varied from 1 to 10 nm. In the case of thinner Co film less than 3 nm, long synthesis time of 60 min is favorable for the effective SWNT growth, because of the small amount of Co catalyst. In the case of thicker Co film more than 3 nm, an amount of grown SWNTs by 30 min synthesis after 30 min annealing and by 60 min synthesis was much higher than that by 30 min synthesis without annealing, showing that total heat-treatment time of 60 min is important for the SWNT growth. Results suggest that the conversion from the thicker film of Co to nano-particle which acts as catalyst takes place during the first 30 min.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

Local transport properties of a carbon nanotube (CNT) thin-film transistor (TFT) have been investigated by conducting atomic force microscopy. The current in a CNT bundle is almost constant, whereas it drastically decreases at the contacts between CNTs. Current drops at the contacts are reduced with increasing negative gate voltage VG. The results show that the contact resistance between CNTs can be modified by VG, and the operation of CNT-TFT is mainly governed by the modulation of contact resistance.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

Field-effect transistor (FET) devices with thin films of perylene have been fabricated with various metal electrodes exhibiting work function φ from 2.5 to 5.1 eV. All perylene FET devices show p-channel FET properties. The p-channel field-effect mobility µ_p and the on-off ratio in the perylene FET increase with an increase in φ of the metal electrodes. The n-channel conduction is also observed for the FET devices with Eu and Sr electrodes exhibiting small φ. These results can be reasonably explained on the basis of energy barrier for hole or electron.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

Field-effect transistor (FET) device with thin films of C₆₀ has been fabricated with Eu electrodes exhibiting small work function. The C₆₀ FET device shows n-channel FET properties with high field-effect mobility, 0.50 cm² V⁻¹ s⁻¹. Furthermore, nonvanishing drain current, i.e., normally on, is observed in this FET device. This originates from small energy barrier for electron from Eu source electrode to lowest unoccupied molecular orbital of C₆₀.

担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

We investigated the luminescence properties of organic light-emitting devices under an external magnetic field. Circularly polarized light was observed from the devices with an Fe cathode, whereas those with an Al cathode did not show such behavior. The degree of circular polarization on the device with an Fe cathode increased with increasing applied magnetic field and decreased with increasing emissive layer thickness. These phenomena can be well explained in terms of the recombination of spin-polarized electrons injected from a ferromagnetic cathode. Consequently, spin diffusion length in the emissive layer, tris-(8-hydroxyquinolinato)-aluminum was estimated to be less than 60 nm from the thickness dependence of the degree of circular polarization.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

The authors report size dependence of characteristics of C₆₀ field-effect transistors (FETs). The transport properties of the channel and the contact resistance between the channel and electrodes are extracted from size dependence. Contact resistances are comparable to those of channel resistances, and the gate voltage dependence of contact resistance is greater than that of channel resistance even at linear region. Results show that the Schottky barriers between the channel and the electrodes still affect device characteristics in the on state of C₆₀ FETs.

掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

We report the transport properties of C₆₀ thin film field-effect transistors (FETs) with a channel of several-hundred nanometers. Asymmetrical drain current I_D versus source-drain voltage V_DS characteristics were observed. This phenomenon could be explained in terms of the high contact-resistance between the C₆₀ thin film and the source/drain electrodes. This device showed a current on/off ratio >10⁵.

担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

The electroluminescence and conduction properties of organic light emitting devices (OLEDs) with Al_q3 emissive layer and with Fe cathode were investigated. The relative luminescence intensity for the device became lower than that with Al cathode. Time resolved photoluminescence of Al_q3 was measured to investigate the electronic state of the interface between Fe and Al_q3 layer of OLEDs. The difference of luminescence intensities of OLEDs could not be explained only due to the work functions, but also due to the essential increase of quenching centers.

担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国内誌  

Layered perovskites (RNH₃)₂CuCl₄ were synthesized, where R was C₆H₅(CH₂)-, C₆H₅(CH₂)₂ -, 1-C₁₀H₉(CH₂)-, 2-C₁₀H₉(CH₂)-, 1-C₆H₅N=NC₆H₄O(CH₂)₃-, and 1-C₆H₅COC₆H₄O(CH₂)₃-. These complexes showed ferromagnetism with different Curie temperature, T_C, depending on the structure of the molecules. These T_C seem to be independent of the distance of interlayer space between CuCl-bases layers, The complexes with naphthalene showed lower T_C than those with benzene, the degree of electronic state mixing between the organic and the inorganic layers might change and affect the interlayer magnetic interaction J’.

担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国際誌  

Layered perovskites (RNH₃)₂CuCl₄, where R was methyl-benzene C₆H₅-CH₂, 1-methyl-naphthalene 1-C₁₀H₉-CH₂, 1-propyl-naphthalene 1-C₁₀H₉-O(CH₂)₃ and 1-butyl-naphthalene 1-C₁₀H₉-O(CH₂)₄, were synthesized. These complexes showed ferromagnetism, with different Curie temperatures, T_C, depending on the structure of the molecule. The change of T_C by taking into account the overlap of the electronic states between the organic and the inorganic layers were discussed.

担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   共著区分：共著   国際・国内誌：国内誌  

Organic-inorganic complex magnets (RNH₃)₂CuCl₄ were synthesized, where R is a simple alkylammonium molecule (CH₃(CH₂)₁₇), a 1-methyl-naphthalene (1-C₁₀H₉-CH₂), a 1-propyl-naphthane (1-C₁₀H₉-O(CH₂)₃), or a 1-butyl-naphthane (1-C₁₀H₉-O(CH₂)₄), M is a 3d transition metal element, and X is a halide element (Cl). Their complexes had a layered perovskite structure checked by XRD. The distance of interlayer space between MCl-based layers was shorter for the complexes with 1-butyl-naphthane than for those with 1-propyl-naphthane. When R was a simple alkylammonium molecule, a 1-methyl-naphthalene and a 1-propyl-naphthalene, its Cu complexes showed ferromagnetism and it Mn complexes antiferromagnetism. However, Cu and Mn complexes with a 1-butyl-naphtalene did not show ferromagnetism and antiferromagnetism, respectively. The absorption spectra of Cu complexes were also measured. When R was a simple alkylammonium molecule, a 1-methyl-naphthalene and a 1-propyl-naphthalene, Cu complexes showed a D_4h structure for inorganic layers, while the structure for the complex with a 1-butyl-naphthalene was D_2d.

担当区分：筆頭著者   掲載種別：記事・総説・解説・論説等（国際会議プロシーディングズ）   共著区分：共著   国際・国内誌：国際誌  

Circular polarization of organic light-emitting diode with a ferromagnetic metal Fe cathode and with a phosphorescent molecule Ir(ppy)₃ was observed. The maximum degree of circular polarization was 0.4 % at constant voltage operation and 0.6 % at constant current operation. Degree of circular polarization was independent of device degradation process. Both the maximum degrees of circular polarization were much smaller than the value expected from the spin-polarization at Fermi energy of the Fe cathode. Efficient spin-injection and spin transport into emissive molecules are expected to improve the degree of circular polarization.

担当区分：筆頭著者   掲載種別：記事・総説・解説・論説等（学術雑誌）   共著区分：単著   国際・国内誌：国内誌  

Recently, research field of organic molecular spintronics has attracted much attention. One of important issues in this field is to clarify mechanisms of spin injection from ferromagnetic materials into organic molecules. The flatter interface between an organic molecular layer and a ferromagnetic electrode as a spin injector is, the more efficiently spin-polarized carriers are injected. In our study, a planer-type structure that had the flatter interface was adopted. By using electron beam lithography, photolithography and vacuum vapor deposition, Ni₈₀Fe₂₀/tris-(hydroxyquinolinato)-aluminum(Alq₃)/Ni₈₀Fe₂₀ junctions were fabricated and the magnetoresistance (MR) effect was investigated. Devices having shorter distance between Ni₈₀Fe₂₀ electrodes showed the MR effect. Origins of the MR were investigated by the devices with nonmagnetic electrodes, by the devices with tunnel barriers at the interface between the Alq₃ and the Ni₈₀Fe₂₀, and by the devices with another molecule. As the result, it was suggested that the MR was mainly originated from a local magnetic state on the Ni₈₀Fe₂₀ surface.

担当区分：筆頭著者   共著区分：共著   国際・国内誌：国際誌  

This study investigated magnetic properties of multifilms, Fe/Al–O(Al-oxided), Fe/Al_q3(tris-(8-hydroxyquinolinato)-aluminum), and Fe/Al–O/Al_q3, using vibrating sample magnetometer and ferromagnetic resonance. In the case of Fe/Al_q3-films, the decrease of magnetization value of Fe was observed compared with the other two. It was explained with diffusion of Fe atoms from the
underlayer into the Al_q3 layer, and those diffused Fe atoms worked as quenching centers in the
luminescence process of Al_q3.

Metal halide-based layered perovskites, (RNH₃)₂MCl₄, self-organized organic/inorganic multilayer structure were synthesized, where R is a simple alkylammonium molecule with a long chain length, (CH₃(CH₂)₁₇) or a l-methyl-naphthalene (C₁₀H₉CH₂), M is 3d transition metal elements. Its layered perovskite structure was checked by a FT-IR method. The perovskites of CH₃(CH₂)₁₇NH₃ with Cu and Cr showed ferromagnetism (T_C= 10 K and 42 K, respectively), and Mn and Fe antiferromagnetism (T_N=41 K and 95 K, respectively). These results roughly corresponded to the results for methyl and ethyl ammonium complexes reported. The naphthalene complex with Cu also showed ferromagnetism, however, the Curie temperature became low. It was considered that the relative large chromophore might disturb the Jahn-Teller distortion of CuCl₆ octahedra. l-methyl-naphthylamine- hydrochloride was luminous with the wavelength of 350 nm under ultraviolet light irradiation, but its Cu complex was quenched.

会議種別：ポスター発表  

開催地：仙台  

講演番号：21a-P02-10

会議種別：ポスター発表  

開催地：Okinawa  

Poster No.1-11

会議種別：ポスター発表  

開催地：Okinawa  

Poster No.1-78

会議種別：ポスター発表  

開催地：Okinawa  

Poster No.1-12

会議種別：口頭発表（招待・特別）  

開催地：オンライン  

会議種別：口頭発表（一般）  

会議種別：口頭発表（一般）  

会議種別：口頭発表（一般）  

会議種別：口頭発表（一般）  

会議種別：ポスター発表  

会議種別：ポスター発表  

会議種別：口頭発表（一般）  

Molecular materials are promising on the viewpoint of the spin transport because of their weak spin-orbit interaction. The spin transport in thermally-evaporated pentacene films at room temperature (RT) was achieved with the spin-pumping driven by the ferromagnetic resonance (FMR), although the spin transport mechanism was unclear. In this study, to clarify the mechanism, the spin transport in evaporated tetracene films and TIPS-pentacene films were tried by the spin-pumping. Since a tetracene molecule has less pai-electrons per molecule than pentacene, the spin transport mechanism can be considered on a viewpoint of the pai-electron number difference. A TIPS-pentacene, which is a pentacene-derivative molecule, was focused to investigate the spin transport mechanism from another viewpoint of the film crystallinity difference. Pd(10)/molecules(0 to 100)/Ni₈₀Fe₂₀(25 nm in thick) tri-layer samples were formed on SiO₂ substrates by using EB deposition or thermal evaporation. To avoid breaking the samples during Ni₈₀Fe₂₀ depositions, the substrate temperature was kept under 270 K. When the FMR of the Ni₈₀Fe₂₀ is excited with an ESR system, a pure spin current is injected from the Ni₈₀Fe₂₀ layer into the Pd layer via the molecular film. Then, the spin current is converted to a charge current due to the inverse spin-Hall effect (ISHE) in the Pd layer and detected as an electromotive force. For a control experiment, samples with a Cu layer instead of the Pd layer were formed since Cu has weaker spin-orbit interaction than Pd. The spin transport in a tetracene film has not been achieved yet because it was hard to form continuous tetracene films by thermal evaporation due to the high saturated vapor pressure. On TIPS-pentacene samples with a Pd layer, output voltages were observed under the FMR of the Ni₈₀Fe₂₀ and the voltage sign was inverted at the magnetization reversal of the Ni₈₀Fe₂₀. Meanwhile, no output voltages from the TIPS-samples with a Cu layer were observed under the FMR of the Ni₈₀Fe₂₀. These indicate that the output voltage observed from the TIPS-samples with a Pd is due to the ISHE. That is, the spin transport in evaporated TIPS-pentacene films by the spin-pumping was achieved at RT.

会議種別：ポスター発表  

スピントロニクスにおいて、スピン流を外場で制御するスピン流スイッチの実現は重要な課題である。本研究では、遷移金属酸化物である二酸化バナジウム(VO2)に着目した。VO2はある温度付近で抵抗値が急激に変化する金属絶縁体転移という特性を持つ[1]。スピントロニクスにおけるスピン流スイッチを実現する手段として、VO2が持つ特性である金属絶縁体転移を利用し、温度によってスピン流を制御する熱スイッチングが可能なデバイスの創成が期待できる。本研究では、Ni80Fe20/VO2二層接合における強磁性共鳴下での起電力の温度依存性を評価することを目的とした。 Fig.1に、Ni80Fe20/VO2二層接合の試料構造を示す。真空蒸着装置を用いて、TiO2(001)基板上に、VO2はパルスレーザー堆積法、Ni80Fe20とPdは電子ビーム蒸着法を用いて作製した。Pdは電圧計によって起電力を測定する際の電極として用いた。 Fig.2に膜厚10 nmのVO2薄膜(Ni80Fe20無し)の抵抗値の温度依存性を示す。試料の温度は2 K/minで変化させた。抵抗値が急激に変化していることから、金属絶縁体転移が発生していることがわかる。 続いて、二層接合に対し、Ni80Fe20の強磁性共鳴(FMR)を励起し、スピンポンピングによってVO2薄膜へスピン注入を行った。注入されたスピン流は、VO2薄膜中で逆スピンホール効果(ISHE)[2]によって電流に変換される。この電流をVO2の抵抗を介して起電力として検出することにより、VO2薄膜へのスピン注入特性を評価した。ベクトルネットワークアナライザから伝送線路に流れる高周波電流による高周波磁界と電磁石によって発生する静磁界を組み合わせることによって、FMRを励起した。Fig.3に、Fig.1の試料におけるFMR下での起電力(VFMR)の温度依存性を示す。VO２薄膜の抵抗値は温度によって変化するため、VO2薄膜の抵抗値(RVO2)で規格化した。温度上昇によりVO2薄膜の抵抗値が急激に減少すると、VISHE/RVO2は増加した。また、Fig.2と同様に加熱時と冷却時でヒステリシスが確認された。以上のことから、金属絶縁体転移を利用し、温度によってスピン注入効果を制御できる可能性が示唆された。学会時には、研究の詳細について議論する。

会議種別：ポスター発表  

近年、分子スピントロニクスが注目されている［1-3］。これまでにスピンポンピングにより様々な有機半導体中でのスピン輸送が達成されている[1-3］。本研究で扱うPTCDA([4],Fig.1)は、剛直なペリレンのπ共役骨格を有し、その薄膜上に金属を蒸着する際に高耐久性が期待できるので、有機半導体としての特性を最大限に発揮したデバイスの作製が可能となる。本研究ではスピンポンピングによるPTCDA薄膜のスピン輸送の実証とその特性評価を目的とした。 Pd(膜厚10nm)/PTCDA(dnm)/Ni₈₀Fe₂₀(25 nm)の三層構造を真空蒸着により作製した。Pd、Ni₈₀Fe₂₀は電子ビーム蒸着法、PTCDAは抵抗加熱法を用いた。基板には表面に酸化被膜付きSi基板を使用した。Ni₈₀Fe₂₀層の強磁性共鳴(FMR)を励起し、PTCDA層にスピン流を生成し、それをPd層における逆スピンホール効果(ISHE)[5]により起電力として検出することでスピン輸送特性を評価した。FMRの励起には電子スピン共鳴装置を使用し、起電力の検出にはナノボルトメ－タを用いた。測定は全て室温条件下で行った。 Fig.3にPTCDAの膜厚d= 30nmの試料における(a)FMRスペクトルと(b)FMR磁場付近におけるPdからの出力電圧特性を示す。この時、200mWのマイクロ波を印加した。FMR磁場付近で起電力が検出され、静磁場の方向を反転させると検出される起電力も反転した。また、マイクロ波パワ－を0～200mWの範囲において変化させた時の起電力はマイクロ波パワ－に比例した。スピンポンピングにより励起されたスピン流から変換されるISHE起因の起電力はマイクロ波パワ－に比例することが示されており[1-3]、この結果はその特長と一致する。以上のことから、Pdで検出された起電力はISHEによるものであると推測する。学会時には対照実験を含む研究の詳細について議論する。

会議種別：口頭発表（一般）  

会議種別：口頭発表（招待・特別）  

We developed an evaluation method of the spin transport property in materials with ferromagnetic resonance (FMR), called as “the spin-pumping method” [1]. First, this method was developed to achieve the spin transport at room temperature (RT) in an inorganic semiconductor material, p-type Si in 2013 [1] and then applied for a lot of materials. The spin-pumping is a generation method of a pure spin current which is a flow of spin angular momenta [2]. In a “ferromagnetic metal (FM) / target material / paramagnetic metal (PM)” tri-layer junction, a spin-pump-induced pure spin current, JS, driven by the FMR of the FM layer (for example, Ni80Fe20) is generated in the target material. This JS is absorbed into the PM layer (for example, Pd), converted into a charge current due to the inverse spin-Hall effect (ISHE) in the PM layer [3], and detected as an electromotive force (EMF) via the sample resistance. Thus, if the EMF due to the ISHE in the PM is detected under the FMR of the FM, it is clear evidence for spin transport in the target material. In 2014, the spin transport in conductive polymer PBTTT films formed by a solution process was achieved at RT with the spin-pumping [4] and it was suggested that the polarons mainly carry spins in the PBTTT films. In 2015, we achieved the spin transport in thermally-evaporated pentacene films by using the spin-pumping [5], and its spin diffusion length and the spin current relaxation time were evaluated to be about 40 nm and 150 ns at RT, respectively [5, 6]. However, a question “what carries the spins in pentacene films?” has been remained because a pure pentacene film is basically an insulator. Recently, we tried the spin-pumping-induced spin transport at RT in thermally- evaporated tetracene films possessing less -electron numbers per a molecule than pentacene, and in TIPS-pentacene films having higher crystallinity than pentacene. For tetracene, the making of thermally-evaporated films has not been succeeded yet because of its high vapor pressure. Meanwhile, we successfully demonstrated the spin-pump-induced spin transport in evaporated TIPS-pentacene films at RT [7]. The detail will be discussed in the presentation. [1] E. Shikoh, M. Shiraishi, et al., Phys. Rev. Lett., 2013, 110, 127201-1 – 4. [2] S. Mizukami, Y. Ando, T. Miyazaki, Phys. Rev B, 2002, 66, 104413-1 – 9. [3] E. Saitoh, M. Ueda, H. Miyajima, G. Tatara, Appl. Phys. Lett., 2006, 88, 182509-1 – 3. [4] S. Watanabe, et al., Nat. Phys., 2014, 10, 308 – 313. [5] Y. Tani, Y. Teki, E. Shikoh, Appl. Phys. Lett., 2015, 107, 242406-1 – 4. [6] Y. Tani, T. Kondo, Y. Teki, E. Shikoh, Appl. Phys. Lett., 2017, 110, 032403-1 – 4. [7] Y. Tanaka, Y. Teki, E. Shikoh, IEEE Trans. on Magnetism, 2019, 55, 1400304-1 – 4.

会議種別：口頭発表（招待・特別）  

スピントロニクスを用いたスマートエネルギー技術身が注目されている。我々は革新的スピントロニクスデバイスとして、強磁性共鳴状態の強磁性金属単層薄膜に生成される起電力を利用するデバイスの創製を目指している。これにより電子デバイスにおける局所的な創エネを実現するとともに、その起電力を蓄電して利用する畜エネ技術開発も行う。強磁性金属(FM)の薄膜に静磁界Hと高周波磁界を印加すると強磁性共鳴(FMR)が励起され、即ち、FM薄膜内の微小磁石Mが歳差運動を行う。FMRはFM薄膜が一様に磁化されていればMの一斉回転モデルにより、H、高周波の周波数およびFM薄膜の飽和磁化MSで決まる共鳴条件を満たす際に最も強く励起される。通常FM薄膜は保持するための基板上に形成される。このときFM薄膜内の磁気緩和特性が、基板との界面側と膜表面側(空気との界面側)とで異なるため、膜全体のMは一様には回転せず、回転の位相が異なる。そのため基板に保持されているFM薄膜にはそのFMR下でスピン角運動量の流れである純スピン流が膜面の法線方向に生じる。これまでに鉄(Fe), コバルト(Co)およびニッケル(Ni)-Fe合金(Ni80Fe20)薄膜において、Hの方向と純スピン流の方向の双方に直角な方向に起電力が生成されることを見出した。この起電力の起源は、スピン流がFMのスピン軌道相互作用によって電流へと変換される逆スピンホール効果が主であり他に異常ホール効果等のいくつかの現象も含まれることを定量的に評価した。本稿では、まず、これまでの成果の概要を紹介し、次に実用化への展望および課題を述べる。真空蒸着装置を用い、絶縁体基板上にFe, Co, NiおよびNi80Fe20等のFM薄膜を形成した。膜厚dは実験パラメータであり、マイクロ波の表皮効果とこれまでの研究実績から50 nm以下とした。FMRの励起には、電子スピン共鳴装置を用いる方法あるいは、ベクトルネットワークアナライザにより伝送線路に高周波電流を印加し、それにより高周波磁界を発生させる方法を用いた。起電力の検出にはナノボルトメータを用いた。全ての評価は室温で行った。 FeおよびCo薄膜ともFMRが観測され、HFMR付近で起電力が観測された。ここで注目すべきは主たる起電力Vの符号である。まずHの印加方向が反転するとVsymの符号も反転する点は逆スピンホール効果の重要な特徴であり、Fe、Coともに観測された。更に興味深い点が、原子番号が一つしか違わないFeとCoの間で起電力の符号が異なる点である。これは強磁性体を、3d電子数の異なる常磁性体的に捉えたリジッドバンドモデルによる理論的考察と一致しない。FeとCoは、NiやNi80Fe20と比べてMSが大きいため、FMR条件のHが小さく、実用化に向いている。即ち、このVsymの符号の起源の解明が、その絶対値制御とともに喫緊の課題である。 FMRの励起においてHの制御の容易さの点から、数GHz～十数GHzの高周波が利用される。近年、この周波数帯域の電波が環境に多く存在する (PCや無線LAN、スマートフォン等)。そこで、デバイス中にFM薄膜とHの発生機構を内蔵し、環境に存在する高周波を用いてFMRを励起することにより、局所的な起電力を発生させる。この起電力をそのままデバイスの電源として用いてもよいが、電源を常時接続する必要が無い点にも着目する。例として建物内部の非常用照明の電源として用いる(そのままでは起電力が小さいため、コンデンサを接続し、蓄電して利用)。あるいはウェアラブルデバイスのようにバッテリーの軽量化が必要な分野に展開する。 従来GHz帯の電磁波(高周波)のセンシングあるいは同周波数帯の高周波による送電技術には、高周波の電界成分を利用し、アンテナ技術を用いていたが、アンテナ長は電磁波の波長と相関、即ち、周波数と相関するため、周波数の連続可変への対応は困難である。一方、本研究では電磁波の磁界成分を用い、GHz帯域の高周波だけでなく、原理的にはTHz帯域まで周波数連続で利用可能になる(FMR励起のための静磁界の制御は必要)。将来応用として、環境に存在するあらゆる周波帯域の高周波を利用し、発電する新技術を開発中である。

会議種別：ポスター発表  

The magnetic anisotropy of a ferromagnetic film deposited on a flexible substrate is changed　by deformation of　the　films[1]. It is also expected for increasing magnetic anisotropy to affect output voltage　properties　due to inverse spin-Hall effect (ISHE) induced by　the spin-pumping.This is because the spin-pumping is caused　by the ferromagnetic resonance (FMR). In this study, a Ni80Fe20/Pd bilayer sample, which has quite small magnetocrystalline anisotropy, was formed on a PET substrate and the FMR and ISHE voltage properties of the films were investigated under a mechanical strain. A Ni80Fe20(25)/Pd (10 nm in thick) bilayer samples were prepared on a PET substrate by using an electron-beam deposition under the vacuum of 10-6Pa. After the depositions, the samples were bent along pedestals having curvature radius is 7.5, 10.0, or 12.5 mm. By this operation, different strains were applied to the samples.The FMR was excited by an electron spin resonance system. When the FMR of the Ni80Fe20 of samples was excited, a spin current was generated in the Pd layer by the spin-pumping. Then, the spin current was converted to a charge current due to the ISHE in the Pd layer, and detected as an electromotive force.All measurements were performed at room temperature. The FMR field was shifted to the higher magnetic field side as the strain increased. And the output voltage due to the ISHE of samples placed along the 7.5 mm pedestal was 5.83µV, while that of the non-strained sample was 6.71µV. Thus, the output voltage became 0.87 times by applying the strain compared without any applying strain. The output voltages depended on the magnitude of the strain. These results indicated that the output voltage due to the ISHE was decreased by increasing　the magnetic anisotropy due to deformation of the films. [1]Z. Tang, et al., Appl. Phys. Lett. 105, 103504 (2014).

会議種別：ポスター発表  

Cu is a promising material for spintronics because it is industrial friendly and has long spin diffusion length. Previously, spin transport in Cu was achieved by an electrical spin injection method from Ni80Fe20(Py), which had very small anisotropy, to Cu directly [1]. In that method, thin wire structure samples had to be prepared for matching the interface resistances between materials, which was not easy to form and needed lithography systems. Meanwhile using the spin-pumping method induced by ferromagnetic resonance(FMR), we donʼt need making the wire samples. Using this method and Y3Fe5O12(YIG), spin transport in Cu was achieved [2]. However, YIG was needed a district condition to induce a pure spin current, and it was difficult to find the condition, especially on industries. In this study, we demonstrate successful vertical spin transport in the Cu layer of Py/Cu/Pd tri-layer films by using the spin pumping at room temperature. A Py (10)/Cu (10-50)/Pd (10 nm in thick) tri-layer sample was prepared on a Si/SiO2 substrate by using electron beam deposition under the vacuum of 10-6 Pa. The Cu layer was easily oxidized, so Cu and Py layers were sequentially formed without breaking the vacuum after the Pd deposition. The pure spin current is generated in the Cu layer by the spin pumping with the FMR of the Py film. The generated spin current is absorbed into the Pd layer. Then the spin current is converted into a charge current by the inverse spin-Hall effect(ISHE) in the Pd layer, and detected as an electromotive force. An electromotive force was observed from the samples under the FMR of the Py film, and the sign of the electromotive force was inverted at the magnetization reversal of the Py film, which is a typical behavior of the ISHE. That is, we successfully demonstrated the vertical spin transport in the Cu layer by the spin-pumping. The electromotive force exponentially decayed as the thickness of the Cu layer in samples became thick. Concerning this, the spin diffusion length of the Cu was estimated to be 34.5nm which was short comparing to the preceding study [1]. [1] T. Kimura, et al., Phys. Rev. Lett. 98, 249901 (2007) [2] Chunhui Du, et al., Phys. Rev. Appl. 1.044004 (2014)

会議種別：ポスター発表  

Organic semiconductors(OSs) have unique properties, and are often used in recent spintronics. We achieved spin transport in thermally evaporated pentacene films[1]. In this study, we investigate spin transport properties of OS films using tetracene as a poly-acene and 6,13-bis (triisopropylsilylethynyl) pentacene (TIPS-pentacene) having a structure in which part of pentacene is substituted. Spin transport is observed in Pd(10 nm in thick) / OS(50~200 nm) / Ni80Fe20(25 nm) trilayer samples. All films were formed by vacuum evaporation, under a vacuum pressure of < 10-6 Pa. The ferromagnetic resonance(FMR) is excited in the Ni80Fe20 using an ESR system, and a pure spin current is injected into the OS by the spin-pumping, which is independent of the conductance mismatch problem at the interface. The pure spin current transported through the OS is detected with a nanovoltmeter as an electromotive force(EMF) caused by the inverse spin Hall effect(ISHE) in Pd. All measurements were implemented at room temperature. In the TIPS-pentacene sample, an EMF was detected in the Pd layer, under the FMR of the Ni80Fe20. When the direction of the static magnetic field for exciting the FMR was reversed, the detected EMF was also inverted. In a control experiment in which Pd was changed to Cu, the EMF detected in the Cu was become about 1/10 of that in Pd. We think that the ISHE in pure Cu is very weak, but the ISHE in oxidized Cu causes relatively large EMF and the latter was detected in this experiment. Thus, we concluded that the spin transport in TIPS-pentacene films was achieved. We also conducted a similar experiment using tetracene films. When a magnetic field was applied by the ESR system, any FMR signal was not observed. At measuring the magnetization curve of Ni80Fe20 on a tetracene sample, the residual magnetization was small. By using AFM, it was found that the surface of the Ni80Fe20 film on a tetracene was very rough. So, the Ni80Fe20 film was not uniform on a tetracene film, compared with that on a regular pentacene film. [1] Yasuo Tani, Yoshio Teki, Eiji Shikoh, Appl.Phys.Lett. 107, 242406 (2015).

会議種別：ポスター発表  

最近、スピン流の生成や検出が比較的容易になり、従来とは異なる動作原理を持つスピンデバイスへの応用が期待されている。一方で近年のデバイスの小型化、軽量化への需要に伴い、フレキシブル基板の使用例が増大しており、デバイス化において、基板が変形しても素子の動作を保証する必要がある。しかし、強磁性薄膜はひずみによりその磁気異方性が変化するので、スピン流の生成、検出に影響を与えることが懸念される。よって本研究の目的は、ひずみを印加した強磁性薄膜にスピンポンピングを励起し、生成されるスピン流由来の起電力を観測し、その特性評価を行うことである。 Pd (膜厚 10 nm) / Ni80Fe20(25 nm)の二層構造を電子ビーム蒸着法により作製した。基板にはPET基板を使用した。作製した試料を、曲率半径の異なる半円を持つ台座に沿わせ、固定することで、試料にひずみを印加した。測定には曲率半径7.5 mm, 10.0 mm, 12.5 mmを持つ3つの台座を使用した。 以上のように試料にひずみが印加された状態下において、電子スピン共鳴（ESR）装置を用いてNi80Fe20層にFMRを励起し、Pd層における逆スピンホール効果（ISHE）により起電力を検出することで、ひずみによる起電力特性の変化を評価した。試料に印加したマイクロ波パワーは200 mWであり、測定は全て室温で行った。 ひずみの増加に伴ってFMRスペクトルの半値幅が増大した。学会時には、研究の詳細について議論する。

会議種別：口頭発表（招待・特別）  

In spintronics, carbon-based materials are promising from the viewpoint of the spin transport because their spin-orbit interaction is generally weak. In this study, a pentacene thin film prepared by thermal evaporation is focused as a candidate material for spin transport. Pentacene has good crystallinity, even in thermally-evaporated films, and shows relatively high electrical conductivity without any dopants. Moreover, pentacene shows photo-conductivity, that is, the spin transport can be controlled by light irradiation. Previously, spin transport in pentacene films was studied using a spin-polarized charge current. However, in the electrical spin injection, there is a conductance mismatch problem between the ferromagnetic electrode as a spin injector and pentacene, which causes lowering the spin injection efficiency. In this study, clear evidence for spin transport in pentacene films at room temperature (RT) is shown by using a spin-pump-induced pure spin current. In the spin-pump which is a dynamical spin injection method, the conductance mismatch problem is negligible. By using EB deposition or resistance heating deposition, Pd(10 nm in thick)/pentacene (d: 0 ~ 100 nm)/Ni80Fe20(25 nm) tri-layer structure samples were prepared. Spin transport properties in pentacene films are observed as follows: A spin-pump-induced pure spin current, JS, driven by the ferromagnetic resonance (FMR) of the Ni80Fe20 film is generated in the pentacene layer. This JS is absorbed into the Pd layer, converted into a charge current as a result of the inverse spin-Hall effect (ISHE) in Pd, and detected as an electromotive force (EMF) via the sample resistance. Thus, if the EMF due to the ISHE in Pd is detected under the FMR of Ni80Fe20, it is clear evidence for spin transport in pentacene films. Output voltages from samples were observed under the FMR of the Ni80Fe20 film, and the voltage sign was inverted at the magnetization reversal of the Ni80Fe20 film. This sign inversion of voltage in Pd associated with the magnetization reversal in Ni80Fe20 is a characteristic of the ISHE. The output voltage increases in proportion to the microwave power of the ESR system, which is also the characteristic of the ISHE. Meanwhile, no clear output voltages from samples with a Cu layer instead of a Pd layer were observed under the FMR of the Ni80Fe20 film. The above results suggest that the output voltages observed in samples with a Pd layer under the FMR of the Ni80Fe20 film are mainly due to the ISHE in Pd. That is, spin-pump-induced spin transport in evaporated-pentacene films was achieved at RT [1]. Using the d dependence of the EMF, the spin diffusion length in evaporated pentacene films, , was evaluated to be 42±10 nm at RT [1]. By using the  and the mobility in films, the spin current relaxation time in pentacene films was evaluated to be 150±120 ns at RT [2]. [1] Y. Tani, Y. Teki, E. Shikoh, Appl. Phys. Lett., 2015, 107, 242406-1 – 242406-4. [2] Y. Tani, T. Kondo, Y. Teki, E. Shikoh, Appl. Phys. Lett., 2017, 110, 032403-1 – 032403-4.

会議種別：ポスター発表  

Thin films of weak charge-transfer (CT) complexes (pyrene/pyromellitic dianhydride or pyrene/dimethylpyromellitdiimide) were prepared on an interdigitated platinum electrode by vacuum vapor deposition. Their photoconductivity and magnetoconductance (MC) effects were investigated, and mobile triplet excitons (probably CT excitons) were detected by time-resolved ESR (TRESR) at room temperature. The MC effect on the photocurrent was observed and analyzed by quantum-mechanical simulation assuming two types of collision mechanisms and mobile carriers. A successful simulation was achieved when the parameters (g, D, E and polarization) determined by TRESR and the effective hyperfine splitting estimated from an ab initio molecular-orbital calculation were used.

会議種別：ポスター発表  

有機半導体における光電流の磁場効果は固相中のスピンを持つキャリアの挙動を反映するため、磁場効果を解析することで有機デバイスの励起状態における輸送特性の解明／制御に繋がると期待される。弱い電荷移動CT錯体は光励起することで効率的に電荷分離を引き起こすことが知られており 1) 、電荷分離によるキャリアの生成過程や励起子とキャリアの衝突が磁場効果を示すと予想される 。 本研究では弱いCT錯体としてピレン／ピロメリット酸無水物およびピレン／ジメチルピロメリットジイミドを選択し、その結晶の時間分解ESRを測定することにより電荷分離状態または三重項励起子を観測した。また、それぞれのCT錯体を櫛形電極に真空蒸着した蒸着膜において窒素雰囲気下、キセノンランプ白色光照射条件で電圧を10V印加することで 光電流を観測した。さらに、200 mTの磁場を印加することでその光電流が約1.2%増加することを見出した。この磁場効果の磁場強度依存性をトラップされた三重項励起子とキャリアの衝突によりキャリアがトラップされる過程と電荷分離状態からホールと電子が生成 し、拡散していく過程をStochastic Liouville方程式により量子力学的シミュレーションを行った。時間分解ESRによって決定されたゼロ磁場分裂パラメータ（g値、 D 値、 E 値） および動的スピン分極と分子軌道計算から推定された超微細結合定数を用いることでシミュレーションは磁場効果の振る舞いを図１に示したように良好に再現できた2) 。 1 J. Krzystek J. U. Von Schütz, Triplet Excitons in Weak Organic Charge Transfer Crystals, Advances in Chemical Physics, Wiley VCH, Weinheim, Germany, 1993 , vol. 86. 2 K Kato, S Hagi, M Hinoshita, E Shikoh Y Teki, Phys . Chem . Chem . Phys ., 2017 , Advance Article . DOI:10.1039/C7CP02781H.

会議種別：ポスター発表  

In spintronics, carbon-based materials are promising from the viewpoint of the spin transport because their spin-orbit interaction is generally weak. In this study, a pentacene thin film prepared by thermal evaporation is focused as a candidate material for spin transport. Pentacene has good crystallinity, even in thermally-evaporated films, and shows relatively high electrical conductivity without any dopants. Moreover, pentacene shows photo-conductivity, that is, the spin transport can be controlled by light irradiation. Previously, spin transport in pentacene films was studied using a spin-polarized charge current. However, in the electrical spin injection, there is a conductance mismatch problem between the ferromagnetic electrode as a spin injector and pentacene, which causes lowering the spin injection efficiency. In this study, clear evidence for spin transport in pentacene films at room temperature (RT) is shown by using a spin-pump-induced pure spin current. In spin injection by the spin-pump, the conductance mismatch problem is negligible. Figure 1 shows schematic illustrations of our sample structure and experimental set-up. By using EB deposition or resistance heating deposition, Pd(10 nm in thick)/pentacene (d: 0 ~ 100 nm)/Ni80Fe20(25 nm) tri-layer structure samples were prepared. Spin transport properties in pentacene films are observed as follows: A spin-pump-induced pure spin current, JS, driven by the ferromagnetic resonance (FMR) of the Ni80Fe20 film is generated in the pentacene layer. This JS is absorbed into the Pd layer, converted into a charge current as a result of the inverse spin-Hall effect (ISHE) in Pd, and detected as an electromotive force (EMF) via the sample resistance. Thus, if the EMF due to the ISHE in Pd is detected under the FMR of Ni80Fe20, it is clear evidence for spin transport in pentacene films. FMR was excited by using a conventional ESR system. Figures 2 (a) and (b) show a main experimental result. Under the FMR of the Ni80Fe20 film, output voltages from samples were observed, and the voltage sign was inverted at the magnetization reversal of the Ni80Fe20 film. This sign inversion of voltage in Pd associated with the magnetization reversal in Ni80Fe20 is a characteristic of the ISHE. The output voltage increases in proportion to the microwave power of the ESR system, which is also the characteristic of the ISHE. Meanwhile, as shown in Fig. 2 (c) and (d), no output voltages from samples with a Cu layer instead of a Pd layer were clearly observed under the FMR of the Ni80Fe20 film. The above results suggest that the output voltages observed in samples with a Pd layer under the FMR of the Ni80Fe20 film are mainly due to the ISHE in Pd. That is, spin-pump-induced spin transport in evaporated-pentacene films was achieved at RT [1]. Using the d dependence of the EMF due to the ISHE, the spin diffusion length in evaporated pentacene films, , was evaluated to be 42±10 nm at RT [1]. By using the estimated , the spin current relaxation time, , in pentacene films was evaluated to be 150±120 ns at RT [2]. The detail of this study is shown in the meeting. Refs. [1] Y. Tani, Y. Teki, E. Shikoh, Appl. Phys. Lett., 107, 242406 (2015). [2] Y. Tani, T. Kondo, Y. Teki, E. Shikoh, Appl. Phys. Lett., 110, 032403 (2017).

会議種別：ポスター発表  

近年、スピントロニクスでは有機分子材料が注目されている[1-4]。これまでにスピンポンピングのような動力学的手法を用いたペンタセンなどの有機半導体でのスピン輸送が達成されている[1,2]。本研究では6,13bis-TriIsoPropylSilylethynyl-ペンタセン（C44H54Si2、Fig.1）（以下TIPSペンタセンとする。）を扱う。TIPSペンタセンはペンタセンよりも安定度と易動度が高いとされる有機半導体で、より高い結晶性を有する[4]。この様々な性質から、効率的なスピンの輸送の材料として期待ができる。これまでにTIPSペンタセン薄膜に対し、スピン偏極電流を用いたスピン輸送の研究はあるが[4]、コンダクタンスミスマッチの問題[5]を排除できていない。よって、本研究ではコンダクタンスミスマッチ問題を無視できるスピンポンピングを用いてTIPSペンタセン薄膜のスピン輸送の実証と特性評価を目的とした。 Pd (膜厚10 nm) / C44H54Si2 (d nm) / Ni80Fe20 (25 nm) の三層構造を真空蒸着装置により作製した。Pd, Ni80Fe20は電子ビーム蒸着法、TIPS ペンタセンは抵抗加熱法を用いた。基板は表面に酸化被膜の付いたSi基板を使用した。強磁性体であるNi80Fe20層で強磁性共鳴（FMR）を起こし、TIPSペンタセン層でスピンを輸送し、Pd層における逆スピンホール効果（ISHE）[6]により起電力を検出することでスピン輸送特性を評価した。FMRを励起させる方法としては電子スピン共鳴（ESR）装置を使用し、ナノボルトメーターで起電力を検出した。印加するマイクロ波のパワーは0~200mWで測定した。今回の測定は全て室温条件下で行った。 Fig.3 に印加するマイクロ波パワーを200mWにしたTIPSペンタセンの膜厚d = 100 nmの試料のFMRスペクトル(a)とPdで検出された起電力を示す(b)。強磁性共鳴が励起される磁場付近で起電力が検出された。印加する静磁場の方向を反転させると検出される起電力も反転し、対称性が見られた。また、起電力はマイクロ波パワーの大きさを変化させると、それに比例し起電力の大きさも変化した。これはISHEにより発生する起電力の特性と一致している[1,2,6]。以上のことから、Pdで検出された起電力はISHEによるものであると推測する。dを変えて測定を行ったところ、d = 50 nmと100 nmの時の起電力の大きさにあまり変化は見られていない。TIPSペンタセンは結晶性の有機半導体であるため結晶の構造によりスピンの輸送の特性が変化したと考える。 以上をふまえて、学会時には実験方法・結果の詳細について、TIPSペンタセンの結晶性と起電力の関係性とともに議論する。 [1] S.Watanabe, et.al., Nature Phys., 10,308(2014). [2] Y.Tani, et.al., Appl.Phys.Lett., 107,242406(2015). [3] V.Dediu, et.al., Splid State Comm., 122(2002) 181-184. [4] S.Mooser, et.al., Phys.Rev.B, 85,235202(2012). [5] G.Schmidt, et.al., Phys.Rev.B, 67,R4790(2000). [6] E.Saitoh, et.al., Appl.Phys.Lett., 88,182509(2006).

会議種別：ポスター発表  

The purpose of our study is development of a local power generation system by using ferromagnetic resonance (FMR). In spintronics, studies aiming at reducing energy loss and power saving have been widely conducted. On the other hand, our study is focused on the aspect of generating electromotive force (EMF) from the viewpoint of energy creation. The inverse spin-Hall effect (ISHE) is observed even in a ferromagnetic metal (FM) Ni80Fe20 “single-layer” without non-magnetic metal layers under the FMR [1]. However, except for the Ni80Fe20 [1], the EMF property generated in a “single-layer structure” FM film itself under the FMR has not been investigated yet. So, in this study, in order to observe the EMFs in iron (Fe) and cobalt (Co) single-layer films under the FMR condition and clarify the origins of the EMFs in FMs under their FMR, the voltage properties generated in FM an Fe and a Co films under the respective FMR condition were investigated at room temperature. Fig. 1 shows the sample structure. FM films with the thickness of 25 nm were prepared on Si/SiO2-substrates by using an electron beam deposition system. After film formation, the sample substrates were cut to be the sample area size of 1.5 × 4.0 mm2. Leading wires for measuring the EMFs in the FM films were directly connected to the both edges of the films by using silver paste. We succeeded to observe the EMFs in the Fe and Co single-layer films under the FMR [2]. The saturation magnetization calculated with FMR condition is 1330 emu/cc for Fe, and 1169 emu/cc for Co, respectively. We used equations (1) and (2) to analyze three following effects; ISHE, anomalous Hall effect (AHE), and planer Hall effect (PHE) [1], As the analyzing results, as origins of the EMF, the self-induced ISHE in Fe and Co single-layer films was dominant, and respectively 2.1 and 18 times larger than the AHE which is one origin of the simultaneously observed EMFs under the FMR as shown in Fig. 2. When we set the calculated ISHE is respectively 7.1 and 73 times larger than the calculated PHE by eq. (2), we could explain experimental data well as shown in Fig. 3. Thus, we concluded that the ISHE was main in EMFs observed in the Fe and Co single-layer films under the FMR.

会議種別：ポスター発表  

Thin films of pyrene-oxoverdazyl (PyrOV) radical and its precursor were prepared on an interdigitated platinum electrode by vacuum vapor deposition. There thin films showed the bias voltage dependence of the photo-current, which was linear to the applied bias. The wavelength dependence was measured using the band pass filters at CWL 400, 450, 500, 550, 600, 650 and 700 nm, which compare between the absorption spectra and the action spectra, in which the photo-current magnitude divided by the light intensity. The action spectra were corresponding well to the absorption spectra, meaning that the origin of the matter. The much larger photo-current was detected in PyrOV than that in precursor.

会議種別：口頭発表（一般）  

In spintronics, carbon-based materials are promising from the viewpoint of the spin transport because their spin-orbit interaction is generally weak. In this study, a pentacene thin film prepared by thermal evaporation is focused as a candidate material for spin transport. Pentacene has good crystallinity, even in thermally-evaporated films, and shows relatively high electrical conductivity without any dopants. Moreover, pentacene shows photo-conductivity, that is, the spin transport can be controlled by light irradiation. Previously, spin transport in pentacene films was studied using a spin-polarized charge current. However, in the electrical spin injection, there is a conductance mismatch problem between the ferromagnetic electrode as a spin injector and pentacene, which causes lowering the spin injection efficiency. In this study, clear evidence for spin transport in pentacene films at room temperature (RT) is shown by using a spin-pump-induced pure spin current. In the spin-pump which is a dynamical spin injection method, the conductance mismatch problem is negligible. By using EB deposition or resistance heating deposition, Pd(10 nm in thick)/pentacene (d: 0 ~ 100 nm)/Ni80Fe20(25 nm) tri-layer structure samples were prepared. Spin transport properties in pentacene films are observed as follows: A spin-pump-induced pure spin current, JS, driven by the ferromagnetic resonance (FMR) of the Ni80Fe20 film is generated in the pentacene layer. This JS is absorbed into the Pd layer, converted into a charge current as a result of the inverse spin-Hall effect (ISHE) in Pd, and detected as an electromotive force (EMF) via the sample resistance. Thus, if the EMF due to the ISHE in Pd is detected under the FMR of Ni80Fe20, it is clear evidence for spin transport in pentacene films. Output voltages from samples were observed under the FMR of the Ni80Fe20 film, and the voltage sign was inverted at the magnetization reversal of the Ni80Fe20 film. This sign inversion of voltage in Pd associated with the magnetization reversal in Ni80Fe20 is a characteristic of the ISHE. The output voltage increases in proportion to the microwave power of the ESR system, which is also the characteristic of the ISHE. Meanwhile, no output voltages from samples with a Cu layer instead of a Pd layer were clearly observed under the FMR of the Ni80Fe20 film. The above results suggest that the output voltages observed in samples with a Pd layer under the FMR of the Ni80Fe20 film are mainly due to the ISHE in Pd. That is, spin-pump-induced spin transport in evaporated-pentacene films was achieved at RT [1]. Using the d dependence of the EMF, the spin diffusion length in evaporated pentacene films, , was evaluated to be 42±10 nm at RT [1]. By using the estimated , the spin current relaxation time in pentacene films was evaluated to be 150±120 ns at RT [2]. [1] Y. Tani, Y. Teki, E. Shikoh, Appl. Phys. Lett., 107, 242406 (2015). [2] Y. Tani, T. Kondo, Y. Teki, E. Shikoh, Appl. Phys. Lett., 110, 032403 (2017).

会議種別：ポスター発表  

Carbon-based molecules are promising materials from the viewpoint of the spin transport because their spin-orbit interaction is generally weak. In this study, a pentacene molecular film prepared by thermal evaporation is focused as a candidate material for spin transport. Pentacene has good crystallinity, even in films formed by thermal evaporation, and shows relatively high electrical conductivity without any dopants. Previously, spin transport in pentacene films has been studied using a spin-polarized charge current, as distinct from pure spin current. However, in the electrical spin injection, there is a conductance mismatch problem between the ferromagnetic electrode as a spin injector and pentacene, which causes lowering the spin injection efficiency at the interface. In this study, clear evidence for spin transport in pentacene films at room temperature (RT) is shown by using a pure spin current induced with the spin-pump, which is a dynamical spin injection. In this case, the conductance mismatch problem related to spin injection with the spin-pump is negligible. Pd/pentacene/Ni80Fe20 tri-layer samples were prepared as follows: On a thermally-oxidized Si substrate, a Pd layer (the thickness of 10 nm) was formed by an EB deposition under a vacuum of <10-6 Pa. Next, under a vacuum of <10-6 Pa, pentacene molecules were thermally evaporated. The pentacene layer thickness, d, was varied in the range from 0 to 100 nm. Finally, a Ni80Fe20 layer (25 nm) was formed by using an EB deposition under a vacuum of <10-6 Pa. To prevent samples during the Ni80Fe20 deposition, the sample substrate temperature was kept at below 270 K. As a control experiment, samples with a Cu layer, instead of the Pd layer, were prepared because the Cu has smaller spin-orbit interaction than the Pd. Spin transport properties in pentacene films are observed as follows: A spin-pump-induced pure spin current, JS, driven by the ferromagnetic resonance (FMR) of the Ni80Fe20 film is generated in the pentacene layer. This JS is then absorbed into the Pd layer. The absorbed JS is converted into a charge current as a result of the inverse spin-Hall effect (ISHE) in Pd and detected as an electromotive force (EMF). That is, if the EMF due to the ISHE in Pd is detected under the FMR of Ni80Fe20, it is clear evidence for spin transport in pentacene films. A sample is set into a microwave TE011-mode cavity in an ESR system to excite the FMR in Ni80Fe20 and a nano-voltmeter to detect EMFs from the samples was connected. Output voltages from samples with a Pd layer were observed under the FMR of the Ni80Fe20 film and the output voltage sign was inverted at the magnetization reversal of the Ni80Fe20 film. This sign inversion of voltage in Pd associated with the magnetization reversal in Ni80Fe20 is a characteristic of the ISHE. The output voltage increases in proportion to the microwave power of the ESR system, which is also the characteristic of the ISHE. Meanwhile, no output voltages from the sample with a Cu layer were clearly observed under the FMR of the Ni80Fe20 film. The above results suggest that the output voltages at the FMR field observed in samples with a Pd layer are mainly due to the ISHE in Pd. That is, spin-pump-induced spin transport was achieved in evaporated-pentacene films at RT.[1] By using the d dependence of the output voltages, the spin diffusion length of pentacene films, lamda, was estimated to be 42±10 nm at RT.[1] Using the estimated lamda, the spin current relaxation time in pentacene films was evaluated to be 150±120 ns at RT [2], which is long enough as a candidate material for future spintronics devices. On the meeting, the detail of the above is introduced. 1. Y. Tani, Y. Teki, and E. Shikoh, Appl. Phys. Lett., 107, 242406 (2015). 2. Y. Tani, T. Kondo, Y. Teki, and E. Shikoh, cond-mat:arXiv, 1609.07869 (2016).

会議種別：口頭発表（一般）  

近年、スピンポンピングを用い、分子材料のスピン輸送特性を評価する研究が注目されている[1-3]。我々は応用展開の観点から、真空蒸着法によって作製された分子薄膜のスピン輸送に注目している。低分子材料の一つ、ペンタセンは、蒸着膜でも高い結晶性を有し、分子材料の中では高い導電性を有する[4]。従来、スピン偏極電流によるペンタセン薄膜中のスピン輸送が試みられたが[5]、外的要因の排除が困難だった。本研究では純スピン流を生成することができ、かつ、異種材料界面でのコンダクタンスミスマッチ[6]が無視できるスピンポンピングを用い、ペンタセン蒸着膜のスピン輸送特性を室温で評価した。更に、そのスピン輸送の緩和時間を評価した。 真空蒸着法を用いて「Ni80Fe20(膜厚25 nm)/ペンタセン(d:0~100 nm)/ Pd(10 nm)」三層構造試料を作製した。強磁性共鳴FMRを用いたスピンポンピングによりNi80Fe20からペンタセンへ純スピン流JSが生成され、その生成されたJSはPdへと吸収される。Pdに吸収されたJSはPd中で逆スピンホール効果ISHE[7]により起電力に変換されることが期待できるため、PdにおいてISHEによる起電力が観測できればペンタセン蒸着膜中のスピン輸送の証拠になる。FMR励起にはESR装置を、起電力検出にはナノボルトメータを用いた。 dの異なる各試料において、Ni80Fe20のFMR磁場付近で、静磁場に対し反転対称性を示す出力電圧が観測された。また、観測された出力電圧はESRの高周波出力に比例した。対照実験としてPdの代わりにCuを用いたところ、Cu膜を有する試料からは明確な出力電圧が観測されなかった。以上より、Pd膜を有する試料にて観測された出力電圧はPdのISHEによる起電力と結論、即ち、ペンタセン蒸着膜の室温スピン輸送に成功した[8]。また、d依存性より、ペンタセン膜の室温スピン拡散長を42±10 nmと評価した[8]。更にJSの緩和時間を150±120 nsと評価した[9]。学会時には以上の詳細を議論する。 [1] Z. Tang, et.al., Phys. Rev. B 87, 140401(R) (2013)., [2] S. Watanabe, et.al., Nature Phys. 10, 308 (2014)., [3] M. Kimata, et.al., Phys. Rev. B 91, 224422 (2015)., [4] H. Cheng, et.al., Appl. Phys. Lett. 90, 171926 (2007)., [5] T. Ikegami, et.al., Appl. Phys. Lett. 92, 153304 (2008)., [6] G. Schmidt, et.al., Phys. Rev. B 67, R4790 (2000)., [7] E. Saitoh, et.al., Appl. Phys. Lett. 88, 182509 (2006)., [8] Y. Tani, Y. Teki, and E. Shikoh, Appl. Phys. Lett., 107, 242406 (2015)., [9] Y. Tani, T. Kondo, Y. Teki, and E. Shikoh, Appl. Phys. Lett., 110, 032403 (2017).

会議種別：口頭発表（一般）  

分子材料は一般にスピン軌道相互作用が弱いので、スピントロニクスにおいてスピン輸送材料として有望である。本研究ではペンタセン分子の蒸着膜に着目する。ペンタセン薄膜は蒸着膜でも高い結晶性を有し、不純物をドープすることなく高い導電性を示す。以前に、電気的なスピン注入を用いて、ペンタセン薄膜中のスピン輸送が評価されていた[1]。しかしながら電気的なスピン注入では、スピン注入源の強磁性体とペンタセン薄膜間の伝導度に大きな差があり、その差によって、スピン注入効率の低下を引き起こす。本研究ではスピンポンピングという、材料の伝導度の差の問題を回避してスピン注入が可能な、動力学的スピン注入法を用い、ペンタセン蒸着膜の室温スピン輸送特性とその緩和特性を評価することを目的とした。 図1に試料構造と評価方法の概要を示す。真空蒸着法を用い、熱酸化膜付きSi基板上に、パラジウム(Pd; 膜厚, 10 nm)/ペンタセン(d, 0 ~ 100 nm)/強磁性金属Ni80Fe20(25 nm)という３層構造試料を作製した。この試料基板をESR装置にセットし、Ni80Fe20の強磁性共鳴(FMR)を誘起する。Ni80Fe20をFMR状態にすると、隣接するペンタセン層にスピンポンピングによるスピン流JSが生成され、そのJSはペンタセン層を流れ、Pd層に吸収される。吸収されたJSは、Pdのスピン軌道相互作用を原理とする逆スピンホール効果(ISHE)によって電流へと変換され、Pdの抵抗を介して、起電力Eとして検出できる。即ち、Ni80Fe20のFMR下で、PdのISHEによる起電力が検出できれば、ペンタセン薄膜中のスピン輸送の明確な証拠となる。 図2にdが50 nmの試料の(a) FMR特性および (b)出力電圧特性を示す。ESRのマイクロ波出力Pは200 mWである。強磁性共鳴磁場HFMRにおいて、試料膜に対する外部磁場Hの印加方向 が0 でも180°でも起電力が観測された。そしてその起電力の符号は が0 と180°とで反転、即ち、Ni80Fe20の磁化反転によって、起電力の符号が反転した。これはISHEによる起電力の特徴の一つである。また、その起電力はPの大きさに比例して増加した。更に対照実験として、Pd層の代わりに、スピン軌道相互作用の小さなCu層を導入したところ、明確な起電力は観測されなかった。以上により、Pd層を有する試料において、Ni80Fe20のFMR下で観測された起電力は、主にISHEによるものであり、即ち、スピンポンピングによって生成したスピン流を用いて、ペンタセン蒸着膜の室温スピン輸送を達成した[2]。また、その起電力のd依存性を評価することにより、ペンタセン蒸着膜の室温スピン拡散長を42±10 nmと見積もった[2]。更に、ペンタセン蒸着膜のの値から、スピン流の室温での緩和時間を150±120 ns と見積った[3]。この時間は、例えばスピン流を外場で制御する際に、充分に長い時間であり、スピントロニクスにおいて、ペンタセン蒸着膜が有望であることを示す。学会時には以上の詳細を講演する。 [1] T. Ikegami, et al., Appl. Phys. Lett., 92, 153304 (2008). [2] Y. Tani, Y. Teki, E. Shikoh, Appl. Phys. Lett., 107, 242406 (2015). [3] Y. Tani, T. Kondo, Y. Teki, and E. Shikoh, Appl. Phys. Lett., accepted for publication. (See also, cond-mat:arXiv, 1609.07869.)

会議種別：ポスター発表  

Recently, it has been discovered that the inverse spin-Hall effect (ISHE) occurs in a ferromagnetic metal (FM) Ni80Fe20 monolayer without non-magnetic metal layers under the ferromagnetic resonance (FMR) [1]. In this study, in order to clarify the origins of the electromotive forces in ferromagnetic metals under their FMR, the electromotive forces properties generated in ferromagnetic metal Fe, Co and Ni80Fe20 films under the respective FMR condition were investigated at room temperature. Figure 1 shows a schematic illustration of a sample in this study. Ferromagnetic films with the thickness of 25 nm were prepared by using a DC sputtering system. After the film formation, the sample substrates were cut to be the sample area size of 1.5 × 4.0 mm2. Leading wires for measuring the electromotive forces in the ferromagnetic metal films were directly connected to the both edges of the films by using silver paste. The sample was set into a microwave cavity of an electron spin resonance system to excite the FMR. Figures 2 (a)-(c) show the FMR spectra of samples with an external magnetic field orientation angle θ of 0°, under the microwave power (PmW) of 200 mW to excite the respective FMR. The saturation magnetization (MS) calculated with the FMR condition is 1061 emu/cc for Fe, 1094 emu/cc for Co, and 472.8 emu/cc for Ni80Fe20, respectively. Electromotive forces (EMFs) were observed for all ferromagnetic metal samples under the respective FMR. Figs. 2 (d)-(f) show the EMF signals of each FM metals at the θ of 0° and 180°, with the PmW of 200 mW for the excitation of the respective FMR. The obtained EMFs were analyzed by using an equation including the ISHE and the anomalous Hall effect (AHE) terms. The EMF due to the ISHE (VISHE) and the EMF due to the AHE (VAHE) are 34.0 μV and -73.1 μV for Fe, -0.939 μV and -5.85 μV for Co, and 12.4 μV and 0.544 μV for Ni80Fe20, respectively. From the above analysis, the value of |VISHE/VAHE| is 0.466 for Fe, 0.161 for Co, and 22.8 for Ni80Fe20, respectively. For Fe and Co films, the EMF due to the AHE is dominantly generated under the FMR. Meanwhile, for Ni80Fe20 films, the EMF due to the ISHE in the Ni80Fe20 film itself under the FMR is mainly generated. This tendency is explained with differences of the spin polarization, the spin Hall conductivity, the anomalous Hall conductivity, the MS, and the resistivity of the FM metals [2]. [1] A. Tsukahara, et al., Phys. Rev. B 89, 235317 (2014). [2] K. Kanagawa, et al, cond-mat.arXiv:1610.06695.

会議種別：ポスター発表  

会議種別：口頭発表（招待・特別）  

Carbon-based molecules are promising materials from the viewpoint of the spin transport because their spin-orbit interaction is generally weak. In this study, a pentacene molecular film prepared by thermal evaporation is focused as a candidate material for spin transport. Pentacene has good crystallinity, even in films formed by thermal evaporation, and shows relatively high electrical conductivity without any dopants. Previously, spin transport in pentacene films has been studied using a spin-polarized charge current, as distinct from pure spin current, although there is a conductance mismatch problem between the ferromagnetic electrode as a spin injector and pentacene, which causes lowering the spin injection efficiency at the interface. In the present study, clear evidence for spin transport in pentacene films at room temperature (RT) by using a pure spin current induced by spin-pump is shown. In this case, the conductance mismatch problem related to spin injection with spin-pump is negligible. Figure 1 shows the sample structure and experimental set up. Palladium(Pd; thickness, 10 nm)/pentacene(d, 0 ~ 100 nm)/Ni80Fe20(25 nm) tri-layer samples were prepared on SiO2-substrates by using EB deposition and thermal evaporation under a vacuum. Spin transport in pentacene films is observed with an ESR system to excite the ferromagnetic resonance (FMR) in Ni80Fe20 and a nano-voltmeter to detect electromotive forces (EMFs) from the samples, as follows: A spin-pump-induced pure spin current, JS, driven by the FMR of the Ni80Fe20 film is generated in the pentacene layer. This JS is then absorbed into the Pd layer. The absorbed JS is converted into a charge current as a result of the inverse spin-Hall effect (ISHE) in Pd and detected as an electromotive force, E. That is, if the EMF due to the ISHE in Pd is detected under the FMR of Ni80Fe20, it is clear evidence for spin transport in pentacene films. Figure 2 show the FMR spectrum and output voltage properties of a sample with the d of 50 nm, under a microwave power (P) of 200 mW. Output voltages are observed at the resonance field HFMR at  of 0 and 180°. Notably, the output voltage changes the sign between theta of 0 and 180°. This sign inversion of voltage in Pd associated with the magnetization reversal in Ni80Fe20 is a characteristic of the ISHE. The EMF increases in proportion to the increase in the P, which is also the characteristic of the ISHE. For a control experiment, samples with a Cu layer, where the spin-orbit interaction is relatively weak, instead of the Pd layer. No clear EMF from samples with a Cu layer was observed at theta of 0 and 180°. The above results suggest that the EMFs at the FMR field observed for the sample with a Pd layer are mainly due to the ISHE in Pd, that is, spin-pump-induced spin transport is achieved in evaporated-pentacene films at RT.[1] By using the d dependence of the EMF, the spin diffusion length of the pentacene film was estimated to be 42±10 nm at RT.[1] On the meeting, the detail of the above is introduced. 1. Y. Tani, Y. Teki, and E. Shikoh, Appl. Phys. Lett., 107, 242406 (2015).

会議種別：ポスター発表  

近年、強磁性金属Ni80Fe20の単層薄膜に対し、その強磁性共鳴(FMR)下において、薄膜自身に起電力が生成されることが発見された[1]。その起電力の起源として、薄膜中の磁気ダンピングの不均一性によってスピン流が生成され、それが逆スピンホール効果(ISHE)によって起電力として検出されるという機構が提唱された[1]。そこで本研究では、様々な強磁性単層薄膜に対し、それぞれのFMR下で生成される起電力特性を評価し、その起源を解明することを目的とした。 　Fig. 1に試料構造と評価方法の概要図を示す。試料サイズは1.5×4.0 mm2、膜厚は25 nmである。強磁性体(FM)としてFe, Co, Ni80Fe20の三種類を用い、Si/SiO2基板上にDCスパッタリングによって成膜した。また、起電力の検出のために、リード線を試料の両端に銀ペーストを用いて直接取り付けた。FMRの励起には電子スピン共鳴装置を用い、起電力はナノボルトメータを用いて測定した。評価はすべて室温で行った。 Fig. 2に各強磁性単層薄膜のFMRスペクトル及び起電力特性を示す(マイクロ波パワーPmW = 200 mW)。各強磁性体の飽和磁化は、FMR特性からFe, Co, およびNi80Fe20それぞれ、1061 emu/cc, 1094 emu/cc, および472.8 emu/ccと見積もった。また、起電力特性の解析により、起電力の共鳴磁場に対する対称成分Vsym及び反対称成分Vasymは、Fe, Co, そしてNi80Fe20それぞれにおいて、43.0 μV及び-73.2 μV, -1.19 μV及び-5.94 μV, そして、14.7 μV及び0.836 μVと算出した。したがって|Vsym/Vasym|はFe, Co, およびNi80Fe20それぞれ、0.588, 0.200, および17.5となり、Fe及びCo薄膜において生成される起電力は反対称成分(異常ホール効果等)が主であり、Ni80Fe20薄膜については対称成分(ISHE等)が主であった。この傾向は強磁性金属中の3d電子と4s電子の合計数に基づくスピンホール伝導度の理論的研究[2]と定性的に一致する。学会時には研究の詳細を議論する。 [1] A. Tsukahara, et al., Phys, Rev. B 89, 235317 (2014)., [2] T. Naito, et al., Phys, Rev. B 81, 195111 (2010).

会議種別：口頭発表（一般）  

近年、純スピン流を用いた分子材料のスピン輸送の研究が注目され、これまでにスピンコート法で作製された高分子薄膜等においてスピン輸送が達成されている1, 2)。本研究では応用展開の観点から、一般的な真空蒸着法で成膜可能な低分子量材料のスピン輸送に注目する。ペンタセン分子（分子構造をFig. 1.に示す）の薄膜は蒸着法による膜でも高い結晶性を有し、比較的高い導電性を有する3)。これまでにスピン偏極電流を用いたペンタセン薄膜のスピン輸送が試みられたことがあるが4)、外的要因の排除が困難だった。本研究では純スピン流を生成可能で、且つ、異種材料界面でのコンダクタンスミスマッチ5)が無視できるとされるスピンポンピング（動力学的スピン注入法）を用い、ペンタセン蒸着膜のスピン輸送特性を室温で評価した6)。 電子ビーム蒸着法および抵抗加熱蒸着法を用いてFig. 1に示す「パラジウムPd(膜厚10 nm)/ペンタセン(d)/ Ni80Fe20(25 nm)」の三層構造試料を作製した。強磁性共鳴FMRを用いたスピンポンピングによりNi80Fe20からペンタセンへ純スピン流JSが生成され、そのJSはPdへと吸収される。吸収されたJSはPd中で逆スピンホール効果ISHE7)により起電力Eに変換される。そのため、Ni80Fe20のFMR下において、PdのISHEによる起電力が観測されればペンタセン薄膜のスピン輸送達成の証拠になる。FMRの励起には電子スピン共鳴装置を、起電力の検出にはナノボルトメータを用いた。評価は全て室温で実施した。 Fig. 2にd = 50 nm試料の(a)FMRスペクトルと(b)FMR磁場付近におけるPdからの出力電圧特性を示す。高周波の出力は200 mWである。FMR磁場付近において、静磁場Hに対する反転対称性を示す出力電圧特性が観測されている。また、観測された出力電圧は高周波出力に比例した。一方、比較のためにPdの代わりに、スピン軌道相互作用の小さなCuを用いたところ、その試料からは明確な起電力が得られなかった。以上により観測された出力電圧はPdのISHEによる起電力と結論した。すなわち、ペンタセン蒸着膜のスピン輸送に成功、しかも室温で達成した6)。更に起電力のペンタセン膜厚依存性の評価により、ペンタセン蒸着膜のスピン拡散長を約42 nmと見積もった6)。学会時には以上の詳細と併せて薄膜の結晶性の影響についても議論する。 1) S. Watanabe, et al., Nature Phys. 10, 308 (2014). 2) M. Kimata, et al., Phys. Rev. B 91, 224422 (2015). 3) H. Cheng, et al., Appl. Phys. Lett. 90, 171926 (2007). 4) T. Ikegami, et al., Appl. Phys. Lett. 92, 153304 (2008). 5) G. Schmidt, et al., Phys. Rev. B 67, R4790 (2000). 6) Y. Tani, Y. Teki, E. Shikoh, Appl. Phys. Lett. 107, 242406 (2015). 7) E. Saitoh, et al., Appl. Phys. Lett. 88, 182509 (2006).

会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

１．はじめに 講演題目は「基礎から学ぶスピントロニクス材料」となっているが、講演時間中に全てを網羅するのは不可能である。そこで講演では、１）スピントロニクスとは？、そして２）研究紹介、を行うこととし、１）ではスピントロニクスの概要を、２）では講演者らの最近の研究紹介を行う。 ２．スピントロニクスとは？ [1-5] 　電子の持つ２つの自由度（電荷とスピン）は少し前まで別々に制御してきた。電荷自由度を積極的に制御（電気伝導を制御）する半導体工学分野では電子デバイスを産み出し、一方で、スピン自由度を積極的に制御（磁石、あるいは磁石に準ずる概念であるスピンの向きを制御）する磁気工学分野では磁気デバイス（またはスピンデバイス）を産み出してきた。スピントロニクス（“スピン”＋“エレクトロニクス”）はそれらの２つを融合（両自由度を積極的に制御）し、学理の解明および新しいデバイス創製を目指している分野である。細かく言えば、スピン自由度も制御した電気伝導（“スピン偏極電流”）や、電荷自由度を伴わずにスピン自由度の伝搬のみ（後述の“純スピン流”）を制御することにより、新しい展開を切り開くことを目指している。 ３、最後に 　以上はスピントロニクスを理解する上で、必要不可欠の概念や現象等である。皆様の理解の助けに少しでもなれば幸いである。 参考文献 [1] 宮崎照宣 “スピントロニクス” （日刊工業新聞社）(2004). [2] 井上順一郎、伊藤博介 “スピントロニクス” （共立出版）(2010). [3] 宮崎照宣、土浦宏紀 “スピントロニクスの基礎” （森北出版）(2013). [4] 齊藤英治、村上修一 “スピン流とトポロジカル絶縁体” （共立出版）(2014). [5] 大谷義近ら “固体物理” Vol.50, No.11 (特集号「スピントロニクスの新展開～スピン変換現象を中心に～」) （アグネ社）(2015).

会議種別：口頭発表（一般）  

Spin transport in the nondegenerate p-type Si with the carrier concentration N of 1.0×10¹⁷ ~ 1.0×10¹⁹ cm^-3 has recently been achieved at room temperature [1]. In this study, the N dependence of spin transport characteristic in the p-Si was studied including a degenerate Si with the N of 1.0×10²⁰ cm^-3. A Ni80Fe20 (25 nm in thick) film as the spin current generator and a Pd (10 nm) wire as the spin current detector on p-Si substrates were separately formed by using laser lithography and electron-beam deposition systems. The gap length between the Pd wire and Ni80Fe20 film L was set to be below 1 μm. When the ferromagnetic resonance FMR of the Ni80Fe20 was excited, a spin current was generated in the p-Si by the spin-pumping and the spin current was transport through the p-Si and absorbed into the Pd. Then, the spin current was converted to a charge current by the inverse spin-Hall effect (ISHE) in the Pd, and detected as an electromotive force. For the sample with the L of 586 nm, the output voltage of 0.25 μV from the Pd wire was obtained under the FMR of the Ni80Fe20 film with the microwave power of 200 mW. However, no inversion symmetry of the voltage signs to the magnetization reversal of the Ni80Fe20 film as an evidence of the ISHE has been shown. This phenomenon may be caused by high career doping concentration and/or thermal effect. The spin diffusion length of the p-Si with the N of 1.0×1020 cm-3 was estimated to be 119 nm under an assumption of an exponential decay of the spin signals and its value was almost consistent with the values of other p-Si [1]. [1] E. Shikoh, et al, Phys. Rev. Lett., 110, 127201 (2013).

会議種別：口頭発表（一般）  

Spintronics in organic semiconductors attracts a lot of interests because organic semiconductors could generate artificially and have low spin couple interaction and interesting behaver, such as photo-conductivity. High vapor deposition makes high purity film. The conductance mismatch have important influence on injecting spin current of electrical method, but not spin pumping. In this study, spin transport characteristic of C22H14, which is known as a p-type organic semiconductor and deposited filmhas high conductivity and crystal orientation, is investigated by using spin pumping under ferromagnetic resonance (FMR). Pd/C22H14/Ni80Fe20 trilayer samples are deposited on Si/SiO2 substrate under vacuum of 10^-6. Pd and Ni80Fe20 layer were deposited by using EB deposition, C22H14 is deposited by using resistance heating vapor deposition. For this sample, the pure spin current is injected into Pd from Ni80Fe20 layer under the FMR. Then, the spin current is converted to a charge current via inverse spin-Hall effect (ISHE) in Pd layer and the voltage is detected. The change of angular of applied magnetic field changes the angular of the voltage. Cu/C22H14/Ni80Fe20 sample was also made because the amplitude of voltage due to ISHE is extremely small in Cu. All experiments are performed at RT. The peak of output voltage in Pd was observed at the FMR magnetic field. The angular of peak of voltage in this sample is inverted when the angular of magnetic field was inverted. In contrast, the peak of output voltage in Cu wasn’t observed at the FMR magnetic field. The amplitude of voltage in Pd of Pd/C22H14/Ni80Fe20 is proportional to power of microwave. These indicate that the peak of output voltage that observed in Pd at the FMR magnetic field is due to ISHE and spin transport in C22H14 is succeeded. The spin diffusion length was estimated by investigating C22H14 thickness dependence of voltage[1].

会議種別：口頭発表（一般）  

In ferromagnetic Ni80Fe20 films, an electromotive force due to the inverse spin-Hall effect (ISHE) in the Ni80Fe20 film itself is generated under the ferromagnetic resonance (FMR) of the Ni80Fe20 film [1]. This can be used as a new power-saving technology of electronics devices by using high frequency electromagnetic waves in general environments. In this study, the characteristics of electromotive forces generated in ferromagnetic metal Fe, Co and Ni80Fe20 films under the respective FMR conditions were investigated at room temperature. Rectangular-shaped thin film samples with the thickness of 25 nm were formed by using a DC sputtering system. Conducting wires for measuring the electromotive forces generated in the ferromagnetic films were directly connected to the both edges of the rectangular samples by using silver paste. A sample was set into a microwave cavity of an electron spin resonance system to excite the FMR. Electromotive forces were observed for all ferromagnetic metal samples under the respective FMR conditions. The obtained electromotive forces were analyzed by using an equation taking into account the ISHE, the anomalous Hall effect (AHE) in the ferromagnetic film, and so on. The AHE was dominantly detected from the Fe films, while the ISHE was dominant for the Ni80Fe20 films. This tendency was almost consistent with a theoretical study of the spin-Hall conductivity of 3d-transition metals [2]. The characteristic of electromotive forces generated in Co films was strongly affected to the experimental conditions [3]. [1] A. Tsukahara, E. Shikoh, et al., Phys. Rev. B 89, 235317 (2014). [2] T. Naito, et al., Phys. Rev. B 81, 195111 (2010). [3] J. Kötzler, et al., Phys. Rev. B 72, 060412(R) (2005).

会議種別：口頭発表（一般）  

近年、分子材料を用いたスピントロニクスが注目されている[1-4]。これまでにスピンコート法により作製された高分子薄膜へのスピン注入[1]および、高分子薄膜中のスピン輸送[2]が確認されている。しかしながらデバイス化を目指す場合、スピンコート法では用途が限定される。一方、パターニングのしやすさなどの点で有利な真空蒸着法を用い、これまでに低分子材料ペンタセン(C22H14, 図1)のスピン輸送特性が、電気的スピン注入法を用いて試みられた[3, 4]。ペンタセンは蒸着膜でも高い結晶性を有し、有機分子材料の中では高い導電性を有する材料である[5]。一方、従来[3, 4]は局所磁気抵抗効果法、即ちスピン偏極電流によるスピン輸送が試みられたが、この手法では外的要因の排除が困難だった。そこで本研究では純スピン流を生成することができ、かつ、異種材料界面でのコンダクタンスミスマッチ問題[6]が極めて小さい動力学的スピン注入、即ちスピンポンピングを用い、ペンタセン蒸着膜のスピン輸送特性を評価した。 図2に示す「Ni80Fe20(膜厚25 nm)/ペンタセン(d)/パラジウムPd(10 nm)」三層構造の試料を作製した。Ni80Fe20とPdの成膜には電子ビーム蒸着法を、ペンタセンの成膜には抵抗加熱蒸着法をそれぞれ用いた。強磁性共鳴FMRを用いたスピンポンピングによりNi80Fe20からペンタセンへ純スピン流が生成され、その生成されたスピン流はPdへと吸収される。Pdに吸収された純スピン流はPd中で逆スピンホール効果ISHE[7]により起電力に変換されることが期待されるため、Pdにおいて起電力が観測できれば、ペンタセン蒸着膜中のスピン輸送の証拠になる。FMRの励起には電子スピン共鳴ESR装置を、起電力の検出にはナノボルトメータを用いた。全ての測定は室温で行った。 図3にd = 50 nmの試料の、(a)FMRスペクトルと(b)FMR磁場付近におけるPdからの出力電圧特性を示す。高周波出力は200 mWである。FMR磁場付近において、外部静磁場に対する反転対称性を示す出力電力特性が観測されている。また、観測された出力電圧は高周波出力に比例した。更に、Pdの代わりにスピン軌道相互作用の小さなCuを用いた試料からは明確な起電力が得られなかった。以上により、観測された出力電圧はPdのISHEによる起電力と結論した。即ち、ペンタセン蒸着膜のスピン輸送に成功した。学会時には以上の詳細について、起電力のペンタセン膜厚依存性の実験等とともに議論する。 [1] K. Ando, et.al., Nature Mat., 12, 622 (2013). [2] S. Watanabe, et.al., Nature Phys., 10, 308 (2014). [3] T. Ikegami, et.al., Appl. Phys. Lett., 92, 153304 (2008). [4] T. Shimada, et.al., Jpn. J. Appl. Phys., 47, 1184 (2008). [5] H. Cheng, et.al., Appl. Phys. Lett., 90, 171926 (2007). [6] G.Schmidt, et.al., Phys. Rev. B 67, R4790 (2000). [7] E.Saitoh, et.al., Appl.Phys. Lett., 88, 182509 (2006).

会議種別：ポスター発表  

近年、分子材料を用いたスピントロニクスが注目されている[1-4]。これまでにスピンコート法により作製された高分子薄膜へのスピン注入[1]および、高分子薄膜中のスピン輸送[2]が確認されている。しかしながらデバイス化を目指す場合、スピンコート法では用途が限定される。一方、パターニングのしやすさなどの点で有利な真空蒸着法を用い、これまでに低分子材料ペンタセン(C22H14, 図1)のスピン輸送特性が、電気的スピン注入法を用いて試みられた[3, 4]。ペンタセンは蒸着膜でも高い結晶性を有し、有機分子材料の中では高い導電性を有する材料である[5]。一方、従来[3, 4]は局所磁気抵抗効果法、即ちスピン偏極電流によるスピン輸送が試みられたが、この手法では外的要因の排除が困難だった。そこで本研究では純スピン流を生成することができ、かつ、異種材料界面でのコンダクタンスミスマッチ問題[6]が極めて小さい動力学的スピン注入、即ちスピンポンピングを用い、ペンタセン蒸着膜のスピン輸送特性を評価した。 図2 に示す「Ni80Fe20(膜厚25 nm)/ペンタセン(d)/パラジウムPd(10 nm)」三層構造の試料を作製した。Ni80Fe20 とPd の成膜には電子ビーム蒸着法を、ペンタセンの成膜には抵抗加熱蒸着法をそれぞれ用いた。強磁性共鳴FMR を用いたスピンポンピングによりNi80Fe20 からペンタセンへ純スピン流 が生成され、その生成されたスピン流はPd へと吸収される。Pd に吸収された純スピン流はPd 中で逆スピンホール効果ISHE[7]により起電力に変換されることが期待されるため、Pd において起電力が観測できれば、ペンタセン蒸着膜中のスピン輸送の証拠になる。FMR の励起には電子スピン共鳴ESR 装置を、起電力の検出にはナノボルトメータを用いた。全ての測定は室温で行った。 図3 にd = 50 nm の試料の、(a)FMR スペクトルと(b)FMR磁場付近におけるPd からの出力電圧特性を示す。高周波出力は200 mW である。FMR 磁場付近において、外部静磁場に対する反転対称性を示す出力電力特性が観測されている。また、観測された出力電圧は高周波出力に比例した。更に、Pd の代わりにスピン軌道相互作用の小さなCu を用いた試料からは明確な起電力が得られなかった。以上により、観測された出力電圧はPd のISHE による起電力と結論した。即ち、ペンタセン蒸着膜のスピン輸送に成功した。学会時には以上の詳細について、起電力のペンタセン膜厚依存性の実験等とともに議論する。 [1] K. Ando, et.al., Nature Mat., 12, 622 (2013). [2] S. Watanabe, et.al., Nature Phys., 10, 308 (2014). [3] T. Ikegami, et.al., Appl. Phys. Lett., 92, 153304 (2008). [4] T. Shimada, et.al., Jpn. J. Appl. Phys., 47, 1184 (2008). [5] H. Cheng, et.al., Appl. Phys. Lett., 90, 171926 (2007). [6] G. Schmidt, et.al., Phys. Rev. B 67, R4790 (2000). [7] E. Saitoh, et.al., Appl. Phys. Lett., 88, 182509 (2006).

会議種別：ポスター発表  

[はじめに] 純スピン流の効率良い生成は新規スピントロニクスデバイス創製のために欠かせないものである。この純スピン流の生成方法としてスピンポンピングがある。強磁性共鳴を用いたスピンポンピングによる純スピン流の生成効率向上は種々のパラメータに依存し、当研究室では強磁性体の質の向上に着目する。この強磁性体の質向上に関して本研究では、スピンポンピングの研究でよく用いられ、成膜の容易なNi80Fe20薄膜を磁場中熱処理することで高品質化し、比較的容易にスピン流生成功率を向上させることに成功した[1]。そこで更なる生成効率向上を目指し、磁場中熱処理時の温度依存性を調査し、スピンポンピングのための磁場中熱処理温度の最適化を目的とした。 [実験方法] 図1に試料構造及び評価方法の概要を示す。まず、熱酸化膜付Si基板上に電子ビーム蒸着法を用いてNi80Fe20/Pd二層膜を形成した。その全てを形成後に磁場中熱処理した。ここで、磁場中熱処理時の最高温度は可変とし、冷却速度は1時間あたり150℃で固定とした。また、熱処理時の磁場強度は30 mT, 真空度は1×10-2 Pa以下とした。この試料で、Ni80Fe20の強磁性共鳴を用いたスピンポンピングによりPd膜に純スピン流を注入し、注入された純スピン流をPdの逆スピンホール効果による起電圧として検出した。この検出された起電力の温度依存性を評価した。 [実験結果] 図2に、非熱処理試料での結果で規格化された、FMRスペクトルから見積もられたスピン流密度(図2a)とPdにおける逆スピンホール効果電圧(図2b)の熱処理温度依存性を示す。この結果、磁場中熱処理時の最高温度が400℃のときに、出力電圧が最大(約1.3倍)を示した。学会時には、更なる詳細について議論する。 [1] Hideki Shimogiku, Naoyuki Hanayama, Yoshio Teki, Hiroaki Tsujimoto, Eiji Shikoh, cond-mat:arXiv.1407.7028.

会議種別：口頭発表（招待・特別）  

The research field of the silicon (Si) spintronics has attracted much attention [1-4] because the Si is a pivotal material in today’s semiconductor electronics industry. For n-type Si, the first demonstration of the spin transport was achieved in 2007 using the hot electron transistor method, at low temperature. [1] In 2011, the room temperature spin transport in degenerate n-Si was demonstrated by using the non-local four-terminal method. [2] And recently, the gate modulated spin transport in non-degenerate n-Si with a spin-MOSFET structure was demonstrated. [3] Meanwhile, to achieve the spin transport in p-type Si, the spin-pump, [5, 6] which is a dynamical method to create pure spin current, was applied as shown in figure 1 [4] : the spins pumped from a ferromagnetic Ni80Fe20 film propagate in the p-Si as a pure spin current JS, are absorbed in a non-magnetic palladium (Pd) wire onto the p-Si, where the JS is converted to a charge current JC due to the inverse spin Hall effect (ISHE) [7]. To detect the JC in the Pd as an electromotive force corresponds to achieve the spin transport in the p-Si. Figure 2(a) shows a schematic illustration of the Ni80Fe20/p-Si/Pd&Cu sample, and the definition of the static magnetic field angle H. L is the gap length between the Ni80Fe20 film and the Pd or Cu wire. Figure 2(b) shows the H dependences of the electromotive force V(H) in the Pd wire (purple circles), and that in the Cu wire (green circles) of the Ni80Fe20/p-Si/Pd&Cu sample, evaluated at around the ferromagnetic resonance magnetic field HFMR under a microwave excitation of 200 mW, by using an ESR system. The electromotive force in the Pd wire depending on the H was observed, but in the same sample no signals were observed in the Cu wire, which has smaller the spin-orbit interaction than Pd. This strongly indicates that the output voltage in the Pd wire can be attributed to the ISHE in the Pd. Moreover, the carrier doping concentration in the p-Si and the temperature dependences of the electromotive forces in the Ni80Fe20/p-Si/Pd samples were investigated, and these also showed decisive evidence of spin transport in the p-Si. That is, the spin transport in the p-Si was demonstrated by using the spin-pump. [4] From the experimental data, the spin diffusion length in the p-Si was estimated to be ca. 150 nm. [4] This spin-pump method, which is a simple and strong technique to study the spin transport properties in solid state materials, has widely been utilized, for instance, to observe the spin transport in the aluminum [8], graphene [9], and GaAs [10]. 1. I. Appelbaum, et al., Nature (London) 447, 295 (2007). 2. T. Suzuki, et al., Appl. Phys. Express 4, 023003 (2011). 3. T. Sasaki, et al., Phys. Rev. Appl. 2, 034005 (2014). 4. E. Shikoh, et al., Phys. Rev. Lett. 110, 127201 (2013). 5. Y. Tserkovnyak, et al., Phys. Rev. Lett. 88, 117601 (2002). 6. S. Mizukami, et al., Phys. Rev. B 66, 104413 (2002). 7. E. Saitoh, et al., Appl. Phys. Lett. 88, 182509 (2006). 8. Y. Kitamura, et al., Sci. Rep. 3, 1739 (2013). 9. Z.Y. Tang, et al., Phys. Rev. B 87, 140401(R) (2013). 10. A. Yamamoto, et al., Phys. Rev. B 91, 024417 (2015).

会議種別：ポスター発表  

[はじめに]　純スピン流を効率よく生成することは新規スピントロニクスデバイス創成にとって非常に魅力的である。この純スピン流の生成方法としてスピンポンピングがある。強磁性共鳴を用いたスピンポンピングによる純スピン流の生成効率の向上は種々のパラメータに依存するが、我々は強磁性体の質の向上に着目する。これまでに、Fe-SiやFe-N等を用いることで、スピン流の生成効率が向上することが報告されている[1, 2]。しかしそれらの形成にはエピタキシャル成長技術や反応性スパッタ等の特殊な装置が必要である。本研究では、スピンポンピングの研究でよく用いられ、成膜の容易なNi80Fe20薄膜を磁場中熱処理により高品質化し、スピン流生成効率を向上させることを目的とした。 [実験方法]　図1に試料構造及び評価方法の概要を示す。まず、熱酸化膜付きSi基板上に、電子ビーム蒸着法を用いてNi80Fe20/Pd二層膜を形成した。その全てを形成後に試料を磁場中熱処理した。この試料を電子スピン共鳴装置にセットし、Ni80Fe20の強磁性共鳴を用いたスピンポンピングによりPd膜に純スピン流を注入し、注入された純スピン流をPdの逆スピンホール効果による起電圧として検出した。この検出された起電力の大きさを、磁場中熱処理を施した試料と施さなかった試料とで比較することにより、磁場中熱処理効果を評価した。 [実験結果]　図2にNi80Fe20の強磁性共鳴磁場HFMR付近の出力電圧特性を示す。 = 0°, 180°の両方において磁場中熱処理を行った試料の方が大きな電圧を得ることが出来た。解析の結果、逆スピンホール効果による起電圧は、 = 0°においては、磁場中熱処理無しが約1.94 V、磁場中熱処理有りが約2.60 Vとなり、磁場中熱処理により出力電圧が約1.3倍向上した。また、 = 180°においては約1.4倍向上した。学会時には、以上の詳細に加え、熱処理時の印加磁場方向依存性や、Pdの代わりにPtやCuを用いた実験結果も交えて議論する。 [1] Y. Ando, et al., Phys. Rev. B, 88, 140406(R) (2013). [2] S. Isogami, et al., Appl. Phys. Exp., 6, 063004 (2013).

会議種別：口頭発表（招待・特別）  

[はじめに] スピントロニクス分野においてシリコン(Si)は、そのスピンコヒーレンスを生かし、Siスピントランジスタ1)や新方式の論理演算素子2)の創製が期待されている材料である。また、Siのスピントロニクス応用には、従来エレクトロニクスでのインフラがそのまま使用できる利点がある。即ち、基礎研究と産業応用の双方において、Siスピントロニクスの展開が注目されている。近年n型Si (n-Si)に対し、非局所四端子法を用いることにより、室温でのスピン輸送が実証された3)。本研究では、p型のSi (p-Si)に対し、動力学的スピン注入法であるスピンポンピングを用いることにより、世界で初めてスピン輸送を実証、しかも室温で成功した4)。 [実験方法] Fig. 1(a)に試料構造を示す。電子線リソグラフィおよび真空蒸着装置を用い、p-Si基板上に強磁性金属Ni80Fe20(Py)薄膜および、スピン軌道相互作用の大きな非磁性金属であるPdの細線を距離Lだけ離して配置した。この試料に対し、Pyの強磁性共鳴(FMR)を用いたスピンポンピングにより、p-Si基板中に純スピン流を生成させる。p-Si中に生成された純スピン流はp-Si中を流れ、Pd線に吸収される。そしてPd線に吸収された純スピン流は、Pdにおける逆スピンホール効果による起電力として観測される。この起電力を検出することにより、p-Si中のスピン輸送特性を評価した。一方、比較のため、スピン軌道相互作用の小さな金属であるCuの細線も作製し、Pd線と同様に評価した。測定には電子スピン共鳴(ESR)装置およびナノボルトメータを用いた。 [実験結果] Fig. 1(b)にPy薄膜のFMR磁場HFMR付近における各細線の起電力特性を示す。Hは静磁場Hの印加方向である。HFMR付近にて、Pd線からはHに対して反転対称性を示す起電力が観測され、その電圧の大きさはESR装置のマイクロ波の出力に比例した。一方、Cu線からは、起電力は観測されなかった。以上により、Pd線における起電力の起源はPdにおける逆スピンホール効果による起電力と結論した。即ち、p-Si中の室温スピン輸送を世界で初めて達成した4)。この成果により、先に達成済みのn-Siに対する室温スピン輸送と併せ、 p、n両方のSiでの室温スピン輸送が実証されたこととなり、Siスピントロニクスの更なる展開が大いに期待できることを示した。学会時には研究の詳細について、Siのキャリア濃度依存性や測定温度依存性等も交えて講演する。 1) S. Sugahara, M. Tanaka, Appl. Phys. Lett., 84, 2307 (2004). 2) H. Dery, P. Dalal, L. Cywinski, L. J. Sham, Nature, 447, 573 (2007). 3) T. Suzuki, T. Sasaki, T. Oikawa, M. Shiraishi, Y. Suzuki, K. Noguchi, Appl. Phys. Exp., 4, 023003 (2011).　 4) E. Shikoh, K. Ando, K. Kubo, E. Saitoh, T. Shinjo, M. Shiraishi, Phys. Rev. Lett., 110, 127201 (2013).

会議種別：口頭発表（招待・特別）  

本稿はスピントロニクスという言葉の定義の確認から始める。というのも、分野によってスピントロニクスの捉え方が異なり、それが誤解を招くことがあるからである。インターネットで「スピントロニクス」という言葉を検索すると大抵は「電子の電荷自由度のみならず、スピン自由度も制御し、それを応用する分野」という説明がなされている。この説明に間違いはないと思う。それでは、次のような説明も出てくるのだが、「元々は“スピン”と“エレクトロニクス”の造語である“スピンエレクトロニクス”から来ている」というのはどうだろうか。後者については、そもそもスピントロニクスという言葉が生まれるきっかけとなった巨大磁気抵抗効果（GMR効果）やトンネル磁気抵抗効果（TMR効果）の発見、実証に起因する。それらGMR効果やTMR効果を示す試料（あるいは素子）の最も基本的な構造は「強磁性薄膜／非磁性薄膜／強磁性薄膜」という三層を成す（本稿では、強磁性以外の性質を有するものを非磁性と呼ぶことにする）。三層のうち２つの強磁性薄膜が電極であり、今、その三層に電流を流し、電極間の電気抵抗が磁場中でどのように変化するのかを考える。GMR効果やTMR効果とは、両強磁性電極の磁化同士が互いに成す角度によって試料全体の電気抵抗が変化する現象である。詳細には、一方の強磁性薄膜電極からスピン偏極した電子がそれぞれ、非磁性体や薄い絶縁体を介して対向する強磁性体電極へと伝導する際に、電子の有するスピンの向きに依存して電子の流れやすさが異なるために電気抵抗が変化する現象である。GMR効果やTMR効果における抵抗変化の割合は、一つの強磁性電極の中でのみ生じる磁気抵抗効果（いわゆる異方性磁気抵抗効果：AMR効果）よりもかなり大きい。要するにAMR効果のような材料単体の電気抵抗を磁場中で測定した際に生じる現象はスピントロニクスという言葉が誕生するずっと以前から知られている現象である。これに対しGMR効果および、TMR効果を示すためには、構造が複数層（GMR効果やTMR効果の例では少なくとも三層）で構成される試料が必要である。要はこれらの効果の原理だけがスピントロニクスとする考えもあり、その主張はその２つの効果が発見された金属磁性分野や無機半導体分野において強い。つまり「スピントロニクス」という言葉のコアな捉え方は、“電荷が複数の材料間をそのスピン自由度に依存して伝導する際に生じる物理現象を取り扱う分野”である。この捉え方を最近では“狭義のスピントロニクス”と呼び、一方で、先のAMR効果も含めて、「電子の電荷自由度とスピン自由度の両方を制御する分野」という意味で用いる場合には“広義のスピントロニクス”と呼ぶほうが誤解は少なそうである。では、有機スピントロニクスと一般に呼ばれる分野（似た意味で用いられる分子スピントロニクス、有機分子スピントロニクスなどもこれに含める）ではどのような感じなのか紹介したい。狭義のスピントロニクス研究者は少なく、それだけではこの会合が成り立たないのが実情である。つまり有機スピントロニクスの分野では、広義のスピントロニクスが優勢である。 本稿では狭義のスピントロニクスにフォーカスする。大きく分けて２つの指向がある。一つは有機分子材料をスピン輸送材料と考えてスピン依存輸送を目指すタイプであり、もう一つは有機分子材料からスピンに依存する新機能の創出を目指すタイプである。大切なことは、材料のスピン状態の観点から考えた場合、その２つの指向に求められる性質が、一般には相反することである。スピン輸送を狙うのであれば、スピン散乱の本質的な要因となるスピン軌道相互作用はできるだけ弱いほうがよい。他方、スピン機能の創出を目指すならば、スピン依存機能の本質的要因であるスピン軌道相互作用はできるだけ強いほうがよい。もちろん輸送と機能創出の両方可能な材料も、使い方次第で有用である。どちらを目指すのでも研究例や研究者人口はまだまだ少ないので、新たな方々の参入と分野展開が楽しみである。

会議種別：口頭発表（一般）  

はじめに シリコン(Si)は、そのスピンコヒーレンスを生かし、Siスピントランジスタ1)や、新方式の論理演算素子2, 3)の創製が期待されている半導体材料である。また、Siのスピントロニクス応用には、従来エレクトロニクスでのインフラがそのまま使用できる利点がある。即ち、基礎科学と産業面の双方より、Siスピントロニクスの展開が注目されている。近年n型Siに対し非局所四端子法を用いることにより、室温でスピン輸送が実証された4)。一方、p型Si(p-Si)についてもスピンポンピングを用いて室温スピン輸送が実証された5)。本研究ではSiのスピン輸送機構の解明を目指し、p-Siにおけるスピンコヒーレンスの温度依存性を評価した。 実験方法 詳細は文献5)と同様である。本研究ではイオン注入を用いて、キャリア濃度NAが1×10¹⁷ ~ 1×10¹⁹ cm^-3のp-Si基板を準備した。電子線リソグラフィおよび電子線蒸着装置を用い、各p-Si基板上にNi₈₀Fe₂₀ (Py)薄膜とPd細線を、ギャップ長Lだけ離して形成した。p-Siのスピン輸送特性の評価には、Pyからスピンポンピングを用いてp-Si中にスピン流を生成し、そのスピン流をPd細線での逆スピンホール効果(ISHE)による起電力として検出する手法を用いた。スピンポンピングには温度可変機構付き電子スピン共鳴装置を用いた。起電力の測定にはナノボルトメータを用いた。各測定は、測定温度が十分に安定してから実行した。 実験結果 Fig. 1にp-SiのNAが1×10¹⁹ cm^-3、L = 580 nmの試料における(a)Pyの強磁性共鳴(FMR)特性の温度依存性および、(b)Pdにおける起電力の温度依存性を示す。起電力は低温ほど増大し、その極性はPyの磁化反転により逆転した。この電圧の極性反転は、得られた起電力の主因がISHEであることを示唆した5)。講演時にはNAの異なるp-Siに対する温度依存性の評価とともに、p-Siにおけるスピンコヒーレンスの詳細について議論する。 1) S. Sugahara, M. Tanaka, Appl. Phys. Lett. 84, 2307 (2004). 2) H. Dery, P. Dalal, L. Cywinski, L. J. Sham, Nature 447, 573 (2007). 3) H. Dery, Y. Song, P. Li, I. Zutic, Appl. Phys. Lett. 99, 082502 (2011). 4) T. Suzuki, T. Sasaki, T. Oikawa, M. Shiraishi, Y. Suzuki, K. Noguchi, Appl. Phys. Exp. 4, 023003 (2011).　 5) E. Shikoh, K. Ando, K. Kubo, E. Saitoh, T. Shinjo, M. Shiraishi, Phys. Rev. Lett. 110, 127201 (2013).

会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

半導体素子の更なる高度集積化において、いわゆるBeyond-CMOS技術の開発が必要である。 講演者らはそれをスピントロニクスの視点で目指している。特にシリコン(Si)でそれを達成することは、従来エレクトロニクス産業との親和性の点から非常に期待されている。 最近、講演者らは動力学的スピン注入法であるスピンポンピングを用いてp型Siにおけるスピン輸送を室温で実証した。これにより先に達成済みのn型Siでの室温スピン輸送と併せて、スピントロニクスを用いた新しいタイプの省エネ論理演算素子等の創製が期待される。また、同手法により、グラフェンや金属アルミニウム中の室温スピン輸送にもそれぞれ成功した。 セミナーではそれらの詳細を講演する。

会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

A spin battery concept is applied for the dynamical generation of pure spin current and spin transport in p-type silicon (p-Si). Ferromagnetic resonance and effective s-d coupling in Ni80Fe20 results in spin accumulation at the Ni80Fe20=p-Si interface, inducing spin injection and the generation of spin current in the p-Si. The pure spin current is converted to a charge current by the inverse spin Hall effect of Pd evaporated onto the p-Si. This approach demonstrates the generation and transport of pure spin current in p-Si at room temperature.

会議種別：口頭発表（招待・特別）  

Spin transport in inorganic semiconductors provides an indispensable building block for realizing the so-called beyond-CMOS technologies. Since the spin-orbit interaction in silicon (Si) is essentially small, Si-based functional devices using the spin degree of freedom is recognized to be promising with respect to spin coherence. Although spin transport at room temperature (RT) in n-Si has been reported [1], spin transport in p-Si has not been experimentally realized, which is an important and unexplored issue in spintronics. Successful observations of spin transport in n- and p-Si are significant for constructing future spin-based logic systems, such as for the case of the charge transport in Si for operating conventional logic circuits. We experimentally demonstrated spin-pumping-induced spin current generation and spin transport in p-Si at RT. In the experiments, a ferromagnetic metal Ni80Fe20 film and a paramagnetic metal palladium (Pd) wire were separately formed with the gap distance of ~500 nm on a p-Si substrate with a doping concentration of 1  1019 cm-3, by using electron beam lithography and electron beam deposition. The sample was placed at the center of a microwave cavity in an electron spin resonance system. In the ferromagnetic resonance condition of the Ni80Fe20 film, a spin current was generated in the p-Si by the spin pumping [2, 3], and the spin current was absorbed into the Pd wire, which was transferred to a charge current by the inverse spin-Hall effect [4] in the Pd wire. The output voltage of 1.4 V by the charge current at the spin pumping was detected in the Pd wire at RT, under the microwave power of 100 mW, and the voltage sign was inverted by the magnetization reversal of the Ni80Fe20 film. Meanwhile, in the case of samples with a copper wire instead of the Pd wire, no output voltages were observed. This indicated that we successfully observed the spin transport in the p-Si at RT [5]. The spin diffusion length in the p-Si was estimated to be ca. 150 nm at RT [5]. [1] T. Suzuki, et al., Appl. Phys. Exp., 4, 023003 (2011). [2] Y. Tserkovnyak, et al., Phys. Rev. Lett. 88, 117601 (2002). [3] S. Mizukami, et al. Phys. Rev. B, 66, 104413(2006). [4] E. Saitoh, et al., Appl. Phys. Lett., 88, 182509 (2006). [5] E. Shikoh, et al., cond-mat. arXiv:1107.0376.

会議種別：口頭発表（一般）  

Spin transport in inorganic semiconductors provides an indispensable building block for realizing the so-called beyond-CMOS technologies. Since the spin-orbit interaction in silicon (Si) is essentially small, Si-based functional devices using the spin degree of freedom is recognized to be promising with respect to spin coherence. Although spin transport at room temperature (RT) in n-Si has been reported [1], spin transport in p-Si has not been experimentally realized, which is an important and unexplored issue in spintronics. Successful observations of spin transport in n- and p-Si are significant for constructing future spin-based logic systems, such as for the case of the charge transport in Si for operating conventional logic circuits. We experimentally demonstrated spin-pumping-induced spin current generation and spin transport in p-Si at RT. In the experiments, a ferromagnetic metal Ni80Fe20 film and a paramagnetic metal palladium (Pd) wire were separately formed with the gap distance of ~500 nm on a p-Si substrate with a doping concentration of 1  1019 cm-3, by using electron beam lithography and electron beam deposition. The sample was placed at the center of a microwave cavity in an electron spin resonance system. In the ferromagnetic resonance condition of the Ni80Fe20 film, a spin current was generated in the p-Si by the spin pumping [2, 3], and the spin current was absorbed into the Pd wire, which was transferred to a charge current by the inverse spin-Hall effect [4] in the Pd wire. The output voltage of 1.4 V by the charge current at the spin pumping was detected in the Pd wire at RT, under the microwave power of 100 mW, and the voltage sign was inverted by the magnetization reversal of the Ni80Fe20 film. Meanwhile, in the case of samples with a copper wire instead of the Pd wire, no output voltages were observed. This indicated that we successfully observed the spin transport in p-Si at RT [5]. The spin diffusion length and spin coherent time in the p-Si were estimated to be 130 nm and 94 ps, respectively, under an assumption of an exponential-like decay of spin-signals in the p-Si [5]. [1] T. Suzuki, et al., Appl. Phys. Exp., 4, 023003 (2011). [2] Y. Tserkovnyak, et al., Phys. Rev. Lett. 88, 117601 (2002). [3] S. Mizukami, et al. Phys. Rev. B, 66, 104413(2006). [4] E. Saitoh, et al., Appl. Phys. Lett., 88, 182509 (2006). [5] E. Shikoh, et al., cond-mat. arXiv:1107.0376.

会議種別：口頭発表（招待・特別）  

有機分子材料を用いたスピントロ二クスすなわち、有機スピントロ二クスの研究分野において、分子のスピン自由度を制御することにより、新奇な輸送現象および光学特性の創成が期待されている[1]。このうちスピン輸送特性の制御は応用展開にダイレクトにつながるために、分子材料を用いたデバイスの磁気抵抗効果の研究が多数行なわれている[1]。しかしながら磁気抵抗効果の実験には強磁性電極自身の磁気抵抗効果などの外的要因を含むため、分子材料の本質的特性の抽出が難しい。他方、光学特性には分子のスピン状態が直接反映されるため、スピンに依存する本質的特性を評価しやすい。それゆえ、スピン依存する光学特性評価は、有機スピントロ二クスの詳細な理解と、スピン依存の光学デバイスへの応用展開の両方において、強力なツールである。 有機ＥＬ素子(OLED)からのスピン依存発光の研究すなわち、再結合励起子の生成確率の制御や円偏光発光の研究は、その良い例である[2-7]。OLEDのスピン機能としてスピン注入による円偏光発光の達成は、無機半導体を用いたspin-LED[8]のようなチャレンジである。有機分子の発光色は発光分子の官能基を制御することにより細かくチューニングできるため、OLEDによる可視光でのスピン依存円偏光発光の達成は、3次元表示可能なフレキシブルフルカラーディスプレイデバイス等への応用展開が期待される。 以下にOLEDを用いた講演者らの研究[4-7]の一端を紹介する。陰極MにFeを用いた素子からは外部磁場に線形応答する円偏光特性が観測された。この磁場への線形応答性はFe陰極薄膜の磁化過程を反映すると考察した。また、円偏光度の大きさは、Fe陰極表面での磁気光学効果(外的要因)よりも十分に大きかった。一方、Alを陰極に用いた素子からは円偏光は観測されなかった。以上より、Fe陰極素子において観測された円偏光は、主にFe陰極から発光分子へのスピン注入に起因すると結論した。この一連の研究は有機分子にスピンが入った数少ない成功例の一つである。講演時には以上の実験の詳細だけでなく、他グループから報告されている信頼性の高い有機スピントロ二クス研究も紹介し、分野の現状と今後の展開について議論したい。 [1] M. Shiraishi & T. Ikoma, Physica E, 43, 1295 (2011). [2] A.H. Davis & K. Bussmann, J. Appl. Phys., 93, 7358 (2003). [3] E. Arisi, et al., J. Appl. Phys., 93, 7682 (2003). [4] E. Shikoh, et al., J. Magn. Magn. Mater., 272, 1921 (2004). [5] E. Shikoh, et al., Jpn. J. Appl. Phys., 45, 6897 (2006). [6] E. Shikoh, et al., J. Magn. Magn. Mater., 310, 2052 (2007). [7] E. Shikoh, et al., Synth. Met., 160, 230 (2010). [8] Y. Ohno, et al., Nature, 402, 790 (1999).

会議種別：口頭発表（招待・特別）  

Spin transport and accumulation in inorganic semiconductors provide an indispensable building block for realizing so-called beyond-CMOS technologies. Since the spin-orbit interaction in Si is essentially smaller than in GaAs, Si-based functional devices using the spin degree of freedom is recognized to be very promising with respect to spin coherence. Whereas spin transport at room temperature (RT) in n-type Si has been reported previously, spin transport in p-type Si has not been experimentally realized, which is an important and unexplored milestone in spintronics. Successful observations of spin transport in n- and p-type Si are significant for constructing future spin-based logic systems, such as for the charge transport in Si for operating conventional logic circuits. Here we show experimental demonstration of spin-pumping-induced spin current generation and spin transport in p-type Si at RT.

会議種別：口頭発表（一般）  

Spin transport in inorganic semiconductors provides an indispensable building block for realizing so-called beyond-CMOS technologies. Since the spin-orbit interaction in Si is essentially small, Si-based functional devices using the spin degree of freedom is recognized to be promising with respect to spin coherence. Whereas spin transport at room temperature (RT) in n-Si has been reported [1], spin transport in p-Si has not been experimentally realized, which is an important and unexplored milestone in spintronics. Successful observations of spin transport in n- and p-Si are significant for constructing future spin-based logic systems, such as for the case of the charge transport in Si for operating conventional logic circuits. We experimentally demonstrated spin-pumping-induced spin current generation and spin transport in p-Si at RT, as follows: a ferromagnetic Ni80Fe20 and a paramagnetic metal were separately formed with the gap distance of ~490 nm on a p-Si with a doping concentration of ~1  1019 cm-3, by using electron beam lithography and electron beam deposition. The sample was placed near the center of a microwave cavity in an electron spin resonance system. In the ferromagnetic resonance (FMR) condition of the Ni80Fe20, a spin current was generated in the p-Si by the spin pumping, and the spin current was injected into the paramagnetic metal, which was transferred to a charge current by the inverse spin-Hall effect [2] in the paramagnetic metal. The output voltage of 1.4 V by the charge current at the spin pumping was obtained at RT, under the microwave power of 100 mW, and the voltage sign was inverted by the magnetization reversal of the Ni80Fe20. The spin diffusion length and spin coherent time in the p-Si were estimated to be at least 130 nm and 94 ps, respectively. That is, we successfully observed the spin transport in p-Si at RT [3]. [1] T. Suzuki, et al., Appl. Phys. Exp., 4, 023003 (2011). [2] E. Saitoh, et al., Appl. Phys. Lett., 88, 182509 (2006). [3] E. Shikoh, et al., arXiv:1107.0376 .

会議種別：口頭発表（招待・特別）  

Spin injection and transport in graphene, based on generation of a pure spin current, is discussed. Spin injection is achieved by using a non-local 4-terminal measurement technique at room temperature. Bias current dependence of the spin signals are so unique that the spin signals are less affected by the bias electric current, which indicates the spin polarization of the transported spins are robust. The bias dependence under positive and negative bias currents can be plausibly explained by taking spin drift in graphene into account.

会議種別：口頭発表（招待・特別）  

In the field of molecular spintronics [1-11] which combines spintronics [12] and molecular electronics [13], novel transport and optical properties of molecular materials are expected to be produced by controlling the spin degree of freedom. The optical properties can easily be assigned to their origin in general, and directly reflect the spin-related phenomena, compared with the transport properties. Therefore, the production of spin-dependent optical properties is one powerful technique for both detailed characterization of molecular spintronics and application to optical devices. Spin-dependent luminescence from the organic light-emitting diodes (OLEDs) is good examples [1-5]: as a spin function of OLEDs, the realization of circular polarization is a great challenge [3-5], and will be a milestone in the molecular spintronics, as in the case of inorganic spintronics [14]. Circular-polarization P, of the light emission from OLEDs, which consist of glass-sub./ITO/-NPD/CBP+Ir(ppy)3/BCP/ Al-O/Fe, was observed at room temperature[5]. Here, Fe is a ferromagnetic cathode in the OLEDs. The P in the OLEDs increased with increasing the magnetic field. The maximum P was 0.4% at 1.6 T. Meanwhile, no circular polarization was observed from OLEDs with a cathode of Al. These results indicate that the ferromagnetic cathode certainly causes the P [5]. Using another optical method [4], it has been confirmed that the origin of the P is mainly due to spin injection from the Fe cathode. That is, the spin injection into organic molecule has been successfully observed, by using an optical method. Details of the above study and recent our approaches in molecular spintronics are introduced and discussed in the presentation. The author thanks to Prof. M. Shiraishi in Osaka University, and Prof. A. Fujiwara in JASRI/SPring-8. This research was partly supported by a Grant-in-Aid for Scientific Research from MEXT of Japan, and by the industrial Technology Research Grant from NEDO of Japan. References: [1] A.H. Davis, K. Bussmann, J. Appl. Phys. 2003., [2] E. Arisi, et al., J. Appl. Phys. 2003., [3] E. Shikoh, et al., Jpn. J.Appl. Phys. 2006., [4] E. Shikoh, et al., J. Magn. Magn. Mater. 2007., [5] E. Shikoh, et al., Synth. Met. 2010., [6] K. Tsukagoshi, et al., Nature 1999., [7] V. Dediu, et al., Solid State Commun. 2002., [8] Z. H. Xiong, et al., Nature 2004., [9] T.S. Santos, et al., Phys. Rev. Lett. 2007., [10] V. Dediu, et al., Phys. Rev. B 2008., [11] C. Barraud, et al., Nat. Phys. 2010., [12] S.A. Wolf, et al., Science 2001., [13] J.R. Heath, M.A. Ratner, Phys. Today 2003., [14] Y. Ohno, et al., Nature 1999.

会議種別：口頭発表（招待・特別）  

In the research field of spintonics, studies using group IV elements have recently attracted much attention. Our group has been focusing not only the graphene spintronics, but also the spintronics using other carbon materials and Si. The gigantic MR effect (1.4 million % at 2K) in C60(fullerene)-Co nanocomposites was observed. That MR effect was well explained with our original theory including the Coulomb Blockade regime. The spin transport properties in Si, such as the bias-current dependence of spin polarization in Si, were observed at room temperature. Those researches are also introduced in addition to our topics in graphene spintronics.

会議種別：口頭発表（基調）  

Recently, circularly polarized luminescence due to the spin injection was observed from the organic light-emitting device (OLED) with Alq3 molecule as the emitter and Fe cathode as the spin injector [1, 2]. In this study, to efficiently produce circular polarization, the Ir(ppy)3 molecule having large spin-orbit interaction was used as the emitter. The OLEDs were fabricated by using the thermal evaporation and the electron beam deposition under the high vacuum (< 10-5 Pa). The device structure was a glass-substrate / ITO (thickness, 150 nm) / a-NPD (40 nm) / CBP(90%) + Ir(ppy)3(10%) (20 nm) / BCP (40 nm) / Al-O (2 nm) / M(M = Al, Fe) (20 nm) / Al (120 nm). The devices with nonmagnetic Al cathode were also investigated for comparison. All measurements were performed under an atmospheric condition without device passivation. The threshold voltages of the OLED with M = Al and Fe were 14.3 V and 14.6 V, respectively. At the drive current density of 12.5 mA/cm2, the initial luminances of the OLED with M = Al and Fe were 300 cd/m2 and 250 cd/m2, respectively, and the half-life of luminance was over 1 hr, in the both devices. [1] E. Shikoh et al., Jpn. J. Appl. Phys. 45, 6897 (2006). [2] E. Shikoh et al., J. Magn. Magn. Mater. 310, 2052 (2007).

会議種別：口頭発表（一般）  

Recently, circularly polarized luminescence due to the spin injection was observed from the organic light-emitting device (OLED) with Alq3 molecule as the emitter and Fe cathode as the spin injector [1, 2]. However, even under the external magnetic field of 2 T, the degree of circular polarization was only about 1 %, which was much smaller than the value expected from spin polarization at the Fermi energy of Fe. The reason of small degree of circular polarization is not only low efficiency of spin injection into the Alq3 molecule, but also small spin-orbit interaction in the luminescence process of the Alq3 molecule. The improvement of the efficiency of spin injection and the efficient production of circular polarization cause the increase of the degree of circular polarization. In this study, to efficiently produce circular polarization, the Ir(ppy)3 molecule having large spin-orbit interaction was used as the emitter. The OLEDs were fabricated by using the thermal evaporation and the electron beam deposition under the high vacuum (< 10-5 Pa). The device structure was a glass-substrate / ITO (thickness, 150 nm) / -NPD (40 nm) / CBP(90%) + Ir(ppy)3(10%) (20 nm) / BCP (40 nm) / Al-O (2 nm) / M(M = Al, Fe) (20 nm) / Al (120 nm). The devices with nonmagnetic Al cathode were also investigated for comparison. All measurements were performed under an atmospheric condition without device passivation. The threshold voltages of the OLED with M = Al and Fe were 14.3 V and 14.6 V, respectively. At the drive current density of 12.5 mA/cm2, the initial luminances of the OLED with M = Al and Fe were 300 cd/m2 and 250 cd/m2, respectively, and the half-life of luminance was over 1 hr, in the both devices. The half-life of OLEDs over 1 hr is long enough to characterize properties of circularly polarized luminescence from OLEDs (total measurement time in our optical equipment is 0.5 hr). [1] E. Shikoh et al., Jpn. J. Appl. Phys. 45, 6897 (2006). [2] E. Shikoh et al., J. Magn. Magn. Mater. 310, 2052 (2007).

会議種別：口頭発表（招待・特別）  

Recently, circularly polarized luminescence due to the spin injection was observed from the organic light-emitting device (OLED) with Alq3 molecule as the emitter and Fe cathode as the spin injector [1, 2]. However, even under the external magnetic field of 2 T, the degree of circular polarization was only about 1 %, which was much smaller than the value expected from spin polarization at the Fermi energy of Fe. The reason of small degree of circular polarization is not only low efficiency of spin injection into the Alq3 molecule, but also small spin-orbit interaction in the luminescence process of the Alq3 molecule. The improvement of the efficiency of spin injection and the efficient production of circular polarization cause the increase of the degree of circular polarization. In this study, to efficiently produce circular polarization, the Ir(ppy)3 molecule having large spin-orbit interaction was used as the emitter. The OLEDs were fabricated by using the thermal evaporation and the electron beam deposition under the high vacuum (< 10-5 Pa). The device structure was a glass-substrate / ITO (thickness, 150 nm) / a-NPD (40 nm) / CBP(90%) + Ir(ppy)3(10%) (20 nm) / BCP (40 nm) / Al-O (2 nm) / M(M = Al, Fe) (20 nm) / Al (120 nm). The devices with nonmagnetic Al cathode were also investigated for comparison. [1] E. Shikoh et al., Jpn. J. Appl. Phys. 45, 6897 (2006). [2] E. Shikoh et al., J. Magn. Magn. Mater. 310, 2052 (2007).

会議種別：口頭発表（招待・特別）  

炭素等の軽元素で構成される有機分子は一般にスピン軌道相互作用が小さいため，スピン情報を保った伝導が期待できる．一方，有機分子は，分子一つでも発光等の機能を発現する．そのため，単一分子へのスピン注入により新機能の創出が可能であり，無機材料とは質的に異なるスピントロニクスデバイス創製への展開が期待できる．しかしながら現状ではデバイス作製技術が未熟なため，無機材料に比べて有機材料を用いたスピントロニクスの研究が遅れている．現在の有機スピントロニクスの課題は，1)強磁性電極から有機分子へのスピン注入方法の確立と，2)分子内および分子間のスピン伝導機構の解明が挙げられる．これらに対するアプローチとして，電界効果トランジスタ(FET)のような平面型構造素子を用いる方法がある[1]．この構造では，基板裏面からゲート電圧を印加することにより有機分子のキャリア密度を制御できるので，強磁性電極と有機分子間のエネルギーバンドミスマッチを解消でき，効率の良いスピン注入が期待できる．また別のアプローチ方法として，強磁性電極間の有機分子膜の厚さを容易に制御できる積層型構造素子を用いる方法がある[2]．この構造では，有機分子膜の厚さをナノメートルオーダーで制御することにより，分子の大きさやスピン拡散長を考慮したスピン伝導機構の解明を行なうことが期待できる．我々はこれまでに積層型素子の一つである有機電界発光素子(有機EL素子)を用い，その強磁性陰極から発光分子層へ注入されたスピン偏極電子と，ホールとの再結合による円偏光特性を解析することにより，発光分子層のスピン拡散長を評価することに成功した[3]．その成果の一端をここに紹介する． [1] K. Tsukagoshi, B. W. Alphenaar and H. Ago: Nature 401 (1999) 572. [2] Z. H. Xiong, Di Wu, Z. V. Vardeny and J. Shi: Nature 427 (2004) 821. [3] E. Shikoh, A. Fujiwara, Y. Ando and T. Miyazaki: Jpn. J. Appl. Phys. 45 (2006) 6897.

会議種別：口頭発表（一般）  

炭素等の軽元素で構成される有機分子は一般にスピン軌道相互作用が小さいため，長いスピン拡散長が期待できる．一方，有機分子は，分子一つでも発光等の機能を発現する．そのため，単一分子へのスピン注入により新機能の創出が可能であり，無機材料とは質的に異なるスピントロニクスデバイス創製への展開が期待できる．現在の有機スピントロニクスの課題は，1)強磁性電極から有機分子へのスピン注入方法の確立と，2)分子内および分子間のスピン伝導機構の解明が挙げられる．これらに対するアプローチとして，電界効果トランジスタ(FET)のような平面型構造素子を用いる方法がある[1]．この構造では，基板裏面からゲート電圧を印加することにより有機分子のキャリア密度を制御できるので，強磁性電極と有機分子間のエネルギーバンドミスマッチを解消でき，効率の良いスピン注入が期待できる．また別のアプローチ方法として，強磁性電極間の有機分子膜の厚さを容易に制御できる積層型構造素子を用いる方法がある[2]．この構造では，有機分子膜の厚さをナノメートルオーダーで制御することにより，分子の大きさやスピン拡散長を考慮したスピン伝導機構の解明を行なうことが期待できる．我々はこれまでに積層型素子の一つである有機電界発光素子(有機EL素子)を用い，その強磁性陰極から発光分子層へ注入されたスピン偏極電子と，ホールとの再結合による円偏光特性を解析することにより，発光分子層のスピン拡散長を評価することに成功した[3]．その成果の一端をここに紹介する． [1] K. Tsukagoshi, B. W. Alphenaar and H. Ago: Nature 401 (1999) 572. [2] Z. H. Xiong, Di Wu, Z. V. Vardeny and J. Shi: Nature 427 (2004) 821. [3] E. Shikoh, A. Fujiwara, Y. Ando and T. Miyazaki: Jpn. J. Appl. Phys. 45 (2006) 6897.

会議種別：口頭発表（招待・特別）  

Recently, research field of organic molecular spintronics has attracted much attention. One of important issues in this field is to clarify mechanisms of spin injection from ferromagnetic materials into organic molecules. The flatter interface between an organic molecular layer and a ferromagnetic electrode as a spin injector is, the more efficiently spin-polarized carriers are injected. In our study, a planer-type structure that had the flatter interface was adopted. By using electron beam lithography, photolithography and vacuum vapor deposition, Ni80Fe20/tris-(hydroxyquinolinato)-aluminum(Alq3)/Ni80Fe20 junctions were fabricated and the magnetoresistance (MR) effect was investigated. Devices having shorter distance between Ni80Fe20 electrodes showed the MR effect. Origins of the MR were investigated by the devices with nonmagnetic electrodes, by the devices with tunnel barriers at the interface between the Alq3 and the Ni80Fe20, and by the devices with another molecule. As the result, it was suggested that the MR was mainly originated from a local magnetic state on the Ni80Fe20 surface.

会議種別：口頭発表（一般）  

On recent experiments of organic spintronics, stacking-type devices have often been employed [1, 2]. However, it’s hard to control the interface state between the upper ferromagnetic electrode and organic molecular layer because the surface of organic molecular layer is very rough and material of upper electrode might penetrate into the organic molecular layer during deposition. Therefore, those cause low efficiency of spin injection from ferromagnetic electrode into organic molecular layer. In this study, for more efficient spin injection, planer-type devices which had flatter interface between the electrode and molecular layer were adopted. By using electron beam lithography, photo lithography, electron beam deposition and vacuum vapor deposition, Ni80Fe20/Alq3(tris-(hydroxy-quinolinato)-aluminum)/Ni80Fe20 planer-type devices were fabricated and the magnetoresistance effect was investigated. One ferromagnetic electrode had different aspect ratio from another one, in order to make mutually different coercivity hold. The devices in which the distance between ferromagnetic electrodes d was less than or equal to 50 nm showed magnetoresistance effect. On the other hand, in the case that d was more than 100 nm, the devices didn’t show the effect. Those results suggest that spin diffusion length of Alq3 channel is in the range from 50 to 100 nm and this is consistent with the previous report by stacking-type devices (about 60 nm) [2]. [1] Z. H. Xiong et al., Nature 427, 821 (2004) [2] E. Shikoh et al., Jpn. J. Appl. Phys. 45, 6897 (2006)

会議種別：口頭発表（招待・特別）  

On recent experiments of organic spintronics, stacking-type devices have often been employed [1, 2]. In this study, for more efficient spin injection, planer-type devices which had flatter interface between the electrode and molecular layer were adopted. By using electron beam lithography, photo lithography, electron beam deposition and vacuum vapor deposition, Ni80Fe20/Alq3(tris-(hydroxy-quinolinato)-aluminum)/Ni80Fe20 planer-type devices were fabricated and the magnetoresistance effect was investigated. One ferromagnetic electrode had different aspect ratio from another one, in order to make mutually different coercivity hold. The devices in which the distance between ferromagnetic electrodes d was less than or equal to 50 nm showed magnetoresistance effect. On the other hand, in the case that d was more than 100 nm, the devices didn’t show the effect. Those results suggest that spin diffusion length of Alq3 channel is in the range from 50 to 100 nm and this is consistent with the previous report by stacking-type devices (about 60 nm) [2]. [1] Z. H. Xiong et al., Nature 427, 821 (2004) [2] E. Shikoh et al., Jpn. J. Appl. Phys. 45, 6897 (2006)

会議種別：口頭発表（招待・特別）  

はじめに：炭素等の軽元素で構成される有機分子は一般にスピン軌道相互作用が小さいため，スピン情報を保った伝導が期待できる．一方，有機分子は，分子一つでも発光等の機能を発現する．そのため，単一分子へのスピン注入により新機能の創出が可能であり，無機材料とは質的に異なるスピントロニクスデバイス創製への展開が期待できる．しかしながら現状ではデバイス作製技術が未熟なため，無機材料に比べて有機材料を用いたスピントロニクスの研究が遅れている．現在の有機スピントロニクスの課題は，1)強磁性電極から有機分子へのスピン注入方法の確立と，2)分子内および分子間のスピン伝導機構の解明が挙げられる．これらに対するアプローチとして，電界効果トランジスタ(FET)のような平面型構造素子を用いる方法がある[1]．この構造では，基板裏面からゲート電圧を印加することにより有機分子のキャリア密度を制御できるので，強磁性電極と有機分子間のエネルギーバンドミスマッチを解消でき，効率の良いスピン注入が期待できる．また別のアプローチ方法として，強磁性電極間の有機分子膜の厚さを容易に制御できる積層型構造素子を用いる方法がある[2]．この構造では，有機分子膜の厚さをナノメートルオーダーで制御することにより，分子の大きさやスピン拡散長を考慮したスピン伝導機構の解明を行なうことが期待できる．我々はこれまでに積層型素子の一つである有機電界発光素子(有機EL素子)を用い，その強磁性陰極から発光分子層へ注入されたスピン偏極電子と，ホールとの再結合による円偏光特性を解析することにより，発光分子層のスピン拡散長を評価することに成功した[3]．その成果の一端をここに紹介する． 有機EL 素子へのスピン注入：構成「ガラス基板/透明陽極ITO(膜厚40 nm)/ホール輸送層TPD(45 nm)/発光層Alq3(d)/Al 酸化膜(1 nm)/強磁性陰極Fe(20 nm)/陰極保護膜Al(120 nm)」の有機EL 素子からの発光に対し，円偏光度を評価した．今後は，様々な発光分子のスピン拡散長の評価を通して，有機分子のスピン伝導機構を解明する研究展開が期待できる．講演では，ここで紹介した研究の解説に加え，最近の我々の研究成果と有機スピントロニクスの将来展望について述べる． [1] K. Tsukagoshi, B. W. Alphenaar and H. Ago: Nature 401 (1999) 572. [2] Z. H. Xiong, Di Wu, Z. V. Vardeny and J. Shi: Nature 427 (2004) 821. [3] E. Shikoh, A. Fujiwara, Y. Ando and T. Miyazaki: Jpn. J. Appl. Phys. 45 (2006) 6897.

会議種別：口頭発表（招待・特別）  

炭素等の軽元素で構成される有機分子は一般にスピン軌道相互作用が小さいため，長いスピン拡散長が期待できる。一方，有機分子は，分子一つでも発光等の機能を発現する．そのため，単一分子へのスピン注入により新機能の創出が可能であり，無機材料とは質的に異なるスピントロニクスデバイス創製への展開が期待できる．現在の有機スピントロニクスの課題は，1)強磁性電極から有機分子へのスピン注入方法の確立と，2)分子内および分子間のスピン伝導機構の解明が挙げられる．これらに対するアプローチとして，電界効果トランジスタ(FET)のような平面型構造素子を用いる方法がある[1]．この構造では，基板裏面からゲート電圧を印加することにより有機分子のキャリア密度を制御できるので，強磁性電極と有機分子間のエネルギーバンドミスマッチを解消でき，効率の良いスピン注入が期待できる．また別のアプローチ方法として，強磁性電極間の有機分子膜の厚さを容易に制御できる積層型構造素子を用いる方法がある[2]．この構造では，有機分子膜の厚さをナノメートルオーダーで制御することにより，分子の大きさやスピン拡散長を考慮したスピン伝導機構の解明を行なうことが期待できる．我々はこれまでに積層型素子の一つである有機電界発光素子(有機EL素子)を用い，その強磁性陰極から発光分子層へ注入されたスピン偏極電子と，ホールとの再結合による円偏光特性を解析することにより，発光分子層のスピン拡散長を評価することに成功した[3]．その成果の一端とその物理的原理を紹介する． [1] K. Tsukagoshi, B. W. Alphenaar and H. Ago: Nature 401 (1999) 572. [2] Z. H. Xiong, Di Wu, Z. V. Vardeny and J. Shi: Nature 427 (2004) 821. [3] E. Shikoh, A. Fujiwara, Y. Ando and T. Miyazaki: Jpn. J. Appl. Phys. accepted for publication.