arXiv subjects

Eiji Shikoh

Publications and source records attributed to Eiji Shikoh.

At least 19 recordsLinked to original sources

arXiv2026

Spin-pump-induced spin transport demonstration in a photoconductive PTCDA molecular thin film with a transparent spin current detector

We demonstrate spin-pump-induced spin transport in a photoconductive PTCDA (3,4,9,10-perylene-teracarboxylic dianhydride) molecular thin film with a transparent ITO (In2O3 + SnO2) film as a spin current detector. In a tri-layer stacking structure sample composed of ITO/PTCDA/Ni80Fe20, pure spin current is generated in the PTCDA layer by using the spin pumping driven by the ferromagnetic resonance of the Ni80Fe20 layer. The generated spin current is absorbed into the ITO layer, converted to a charge current due to the inverse spin-Hall effect of the ITO layer, and detected as an electromotive force via the ITO resistance. Also, the light irradiation effect on spin transport in PTCDA films is investigated.

cond-mat.mtrl-sci↗

arXiv2024

Electromotive force generation in a ferromagnetic metal thin film under the ferromagnetic resonance excitation with permanent magnets

Ferromagnetic resonance (FMR) excitation of a ferromagnetic metal single-layer film was tried by using a couple of permanent magnets as the source of the uniform static magnetic field and by using a co-planer waveguide connected with a network analyzer as the source of the radiofrequency (RF) magnetic field. A typical FMR spectrum of a ferromagnetic Ni$_{80}$Fe$_{20}$ thin film was successfully obtained and a clear electromotive force (EMF) was generated in the Ni$_{80}$Fe$_{20}$ thin film under the FMR excitation with the permanent magnets. That is, we achieved EMF generation in a Ni$_{80}$Fe$_{20}$ thin film under the FMR excitation with the permanent magnets, which can be applied as a simple energy transduction technology from ambient RF energy to electrical energy.

physics.app-ph↗

arXiv2023

Spin current relaxation time in thermally evaporated naphthyl diamine derivative films

The spin relaxation time (tau) on the spin transport in thermally evaporated thin films of a naphthyl diamine derivative: N, N'-Bis(naphthalen-1-yl)-N, N'-bis(phenyl)-2,2'-dimethylbenzidine (a-NPD) was evaluated with the spin-pump-induced spin transport properties and the electrical current-voltage properties in a-NPD films. The zero-bias mobility and the diffusion constant of charges in a-NPD films were obtained to be about 1.2*10-3 cm2/Vs and about 3.0*10-5 cm2/s, respectively. Using these values and the previously evaluated spin diffusion length in a-NPD films of about 62 nm, the tau in a-NPD films was estimated to be about 1.9 micro-second at room temperature, under an assumption of diffusive transport of the spin current in a-NPD films. This estimated tau in a-NPD films is long enough for practical use as a spintronic molecular material.

cond-mat.mtrl-sci↗

arXiv2022

Spin transport properties in a naphthyl diamine derivative film investigated by the spin pumping

We report the spin transport properties in a thin film of a naphthyl diamine derivative: N,N'-Bis(naphthalen-1-yl)-N,N'-bis(phenyl)-2,2'-dimethylbenzidine (alpha-NPD). In a palladium(Pd)/alpha-NPD/Ni80Fe20 tri-layer structure sample, a pure spin current is generated in the alpha-NPD layer with the spin pumping driven by ferromagnetic resonance (FMR). The generated spin current is absorbed into the Pd layer, and converted into a charge current with the inverse spin-Hall effect (ISHE) in Pd. An electromotive force due to the ISHE in the Pd layer is observed under the FMR of the Ni80Fe20 layer, which is clear evidence for the spin transport in an alpha-NPD film. The spin diffusion length in an alpha-NPD film is estimated to be about 62 nm at room temperature, which is long enough as a spin transport material for spintronic devices.

cond-mat.mtrl-sci↗

arXiv2022

Glass-patternable notch-shaped microwave architecture for on-chip spin detection in biological samples

We report a notch-shaped coplanar microwave waveguide antenna on a glass plate designed for on-chip detection of optically detected magnetic resonance (ODMR) of fluorescent nanodiamonds (NDs). A lithographically patterned thin wire at the center of the notch area in the coplanar waveguide realizes a millimeter-scale ODMR detection area (1.5 x 2.0 mm^2) and gigahertz-broadband characteristics with low reflection (about 8%). The ODMR signal intensity in the detection area is quantitatively predictable by numerical simulation. Using this chip device, we demonstrate a uniform ODMR signal intensity over the detection area for cells, tissue, and worms. The present demonstration of a chip-based microwave architecture will enable scalable chip integration of ODMR-based quantum sensing technology into various bioassay platforms.

physics.app-ph↗

arXiv2021

An energy harvesting technology controlled by ferromagnetic resonance

We have successfully demonstrated electrical charging using the electromotive force (EMF) generated in a ferromagnetic metal (FM) film under ferromagnetic resonance (FMR). In the case of Ni80Fe20 films, electrical charge due to the EMF generated under FMR can be accumulated in a capacitor; however, the amount of charge is saturated well below the charging limit of the capacitor. Meanwhile in the case of Co50Fe50, electrical charge generated under FMR can be accumulated in a capacitor and the amount of charge increases linearly with the FMR duration time. The difference between the Ni80Fe20 and Co50Fe50 films is due to the respective magnetic field ranges for the FMR excitation. When the FM films were in equivalent thermal states during FMR experiments, Co50Fe50 films could maintain FMR in a detuned condition, while Ni80Fe20 films were outside the FMR excitation range. The EMF generation phenomenon in an FM film under FMR can be used an energy harvesting technology by appropriately controlling the thermal conditions of the FM film.

cond-mat.mtrl-sci↗

arXiv2021

Spin injection into vanadium dioxide films from a typical ferromagnetic metal, across the metal-insulator transition of the vanadium dioxide films

A vanadium dioxide VO2 film shows metal-insulator transition (MIT) induced by changing environmental temperature. We report the temperature dependence of electromotive force properties generated in VO2/Ni80Fe20 bilayer junctions under the ferromagnetic resonance (FMR) of the Ni80Fe20 layer. An electromotive force generated in a VO2/Ni80Fe20 bilayer junction under the FMR showed a small change across the MIT temperature of the VO2 film, while the VO2 film resistance drastically changed. This behavior was not only explained with the temperature dependence of the electromotive force property generated in the Ni80Fe20 film itself under the FMR, but also with the generated electromotive forces due to the inverse spin-Hall effect (ISHE) in the VO2 film under the FMR of the Ni80Fe20 film. That is, we successfully demonstrated the spin injection from a Ni80Fe20 film into a VO2 film across the MIT temperature of the VO2 film.

cond-mat.mtrl-sci↗

arXiv2019

Pure spin current in a robust pigment-red film

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.

cond-mat.mtrl-sci↗

arXiv2017

Strong evidence for d-electron spin transport at room temperature at a LaAlO3/SrTiO3 interface

A d-orbital electron has an anisotropic electron orbital and is a source of magnetism. The realization of a 2-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 effect, have been discovered in this 2DEG systems, demonstrating the ability of the 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 difficult to implement in the d-electron 2DEG systems. Here, we report the experimental demonstration of room-temperature spin transport in the d-electron-based 2DEG at a LaAlO3/SrTiO3 interface, where the spin relaxation length is ca. exceeding 200 nm. Our finding, which counters the conventional understandings to d-electron 2DEGs, opens a new field of d-electron spintronics. Furthermore, this work highlights a novel spin function in the conductive oxide system.

cond-mat.mtrl-sci↗

arXiv2017

Spin current relaxation time in thermally evaporated pentacene films

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 ~8.0x10^-7 m^2/Vs and ~2.0x10^-8 m^2/s, respectively. Using those values and the previously obtained spin diffusion length in pentacene films of 42{plus-minus}10 nm, the [tau] in pentacene films was estimated to be 150{plus-minus}120 ns at room temperature. This estimated [tau] in pentacene films is long enough for practical use as a spintronic material.

cond-mat.mtrl-sci↗

arXiv2016

Electromotive forces generated in 3d-transition ferromagnetic metal films themselves under their ferromagnetic resonance

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.

cond-mat.mtrl-sci↗

arXiv2016

Transport and spin conversion of multi-carriers in semimetal bismuth

In this paper, we report on the investigation of (1) the transport properties of multi-carriers in semi-metal Bi and (2) the spin conversion physics in this semimetal system in a ferrimagnetic insulator, yttrium-iron-garnet. Hall measurements reveal that electrons and holes co-exist 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.

cond-mat.mtrl-sci↗

arXiv2015

Spin-pump-induced spin transport in a thermally-evaporated pentacene film

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.

cond-mat.mtrl-sci↗

arXiv2014

Spin pumping using an Ni80Fe20 thin film annealed in a magnetic field

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.

cond-mat.mtrl-sci↗

arXiv2014

Self-induced inverse spin Hall effect in permalloy at room temperature

Inverse spin Hall effect (ISHE) allows the conversion of pure spin current into charge current in nonmagnetic materials (NM) due to spin-orbit interaction (SOI). In ferromagnetic materials (FM), SOI is known to contribute to anomalous Hall effect (AHE), anisotropic magnetoresistance (AMR), 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.

cond-mat.mes-hall↗

arXiv2013

Temperature Dependence of Spin Hall Angle of Palladium

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 123 K.

cond-mat.mtrl-sci↗

arXiv2013

Bipolar-Driven Large Magnetoresistance in Silicon

Large linear magnetoresistance (MR) in electron-injected p-type silicon at very low magnetic field is observed experimentally at room temperature. The large linear MR is 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 non-magnetic 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.

cond-mat.mtrl-sci↗

arXiv2013

Vertical Spin Transport in Al with Pd/Al/Ni80Fe20 Trilayer Films at Room Temperature by Spin Pumping

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., [Phys. Rev. B, 66, 224403 (2002)] allows an estimation of the spin coherence of the perpendicular 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.

cond-mat.mtrl-sci↗