Experimental Demonstration of Room-Temperature Spin Transport in n-Type Germanium Epilayers

次世代半導体材料ゲルマニウムにおける室温スピン伝導を世界で初めて実現.京都大学プレスリリース. 2015-04-27.We report an experimental demonstration of room-temperature spin transport in n-type Ge epilayers grown on a Si(001) substrate. By utilizing spin pumping under ferromagnetic resonance, which inherently endows a spin battery function for semiconductors connected with a ferromagnet, a pure spin current is generated in the n−Ge at room temperature. The pure spin current is detected by using the inverse spin-Hall effect of either a Pt or Pd electrode on n−Ge. From a theoretical model that includes a geometrical contribution, the spin diffusion length in n−Ge at room temperature is estimated to be 660 nm. Moreover, the spin relaxation time decreases with increasing temperature, in agreement with a recently proposed theory of donor-driven spin relaxation in multivalley semiconductors

Efficient room-temperature magnetization direction detection by means of the enhanced anomalous Nernst effect in a Weyl ferromagnet

Spintronic phenomena exhibiting a longitudinal resistance change under magnetization reversal are a quite novel feature in nanoscience, which has been intensively studied in hopes of realizing all-electrical magnetization direction detection devices, where no reference ferromagnetic layer is required. However, cryogenic temperatures and/or high magnetic fields have been required to achieve noticeable effects. Here, the high heat-to-charge conversion efficiency of the Heusler alloy Weyl semimetal Co₂MnGa is exploited in single layer nanoscaled wires at room temperature to produce at least two orders of magnitude enhancement of the resistance change ratio, when compared with conventional ferromagnets. Such resistance change under magnetization reversal is consistently explained through temperature distribution simulations and direct thermoelectric measurements of the large anomalous Nernst effect (ANE) in this topologically nontrivial material. Although many reports consider ANE signals as perturbations or undesired artifacts, we demonstrate that they are dominant in this system and can be seized for nonvolatile memory readout, as shown in a prototype device. These results open up new horizons of using enhanced thermoelectric voltages in novel materials for magnetization direction detection in any system where significant temperature gradients exist

Features in constructing a certificate of strength of extraterrestrial material by the example of the Chelyabinsk meteorite

© 2017, Pleiades Publishing, Ltd. The mechanical properties of various components of the Chelyabinsk meteorite are studied. A measurement technique allowing one to obtain a strength certificate of the material by a minimum necessary number of samples with allowance for defectiveness is developed. Universal expressions for the chondritic component and impact melting have been obtained. The expressions allow one to make general estimates of the strength boundaries for LL type meteorites

Strongly anisotropic spin relaxation in graphene/transition metal dichalcogenide heterostructures at room temperature

Graphene has emerged as the foremost material for future two-dimensional spintronics due to its tuneable electronic properties. In graphene, spin information can be transported over long distances and, in principle, be manipulated by using magnetic correlations or large spin-orbit coupling (SOC) induced by proximity effects. In particular, a dramatic SOC enhancement has been predicted when interfacing graphene with a semiconducting transition metal dechalcogenide, such as tungsten disulphide (WS$_2$). Signatures of such an enhancement have recently been reported but the nature of the spin relaxation in these systems remains unknown. Here, we unambiguously demonstrate anisotropic spin dynamics in bilayer heterostructures comprising graphene and WS$_2$. By using out-of-plane spin precession, we show that the spin lifetime is largest when the spins point out of the graphene plane. Moreover, we observe that the spin lifetime varies over one order of magnitude depending on the spin orientation, indicating that the strong spin-valley coupling in WS$_2$ is imprinted in the bilayer and felt by the propagating spins. These findings provide a rich platform to explore coupled spin-valley phenomena and offer novel spin manipulation strategies based on spin relaxation anisotropy in two-dimensional materials

Gate-Tunable Spin-Charge Conversion and the Role of Spin-Orbit Interaction in Graphene

次世代スピントロニクス材料であるグラフェンにおいてスピンを電圧に変換する新しい機能を発見. 京都大学プレスリリース. 2016-05-18.The small spin-orbit interaction of carbon atoms in graphene promises a long spin diffusion length and the potential to create a spin field-effect transistor. However, for this reason, graphene was largely overlooked as a possible spin-charge conversion material. We report electric gate tuning of the spin-charge conversion voltage signal in single-layer graphene. Using spin pumping from an yttrium iron garnet ferrimagnetic insulator and ionic liquid top gate, we determined that the inverse spin Hall effect is the dominant spin-charge conversion mechanism in single-layer graphene. From the gate dependence of the electromotive force we showed the dominance of the intrinsic over Rashba spin-orbit interaction, a long-standing question in graphene research

Giant spin Hall angle in the Heusler alloy Weyl ferromagnet Co2MnGa

ワイル強磁性体の新しいスピン機能の開拓 --ワイル強磁性体Co2MnGaにおける巨大なスピン流＝電流変換効率を発見--. 京都大学プレスリリース. 2021-02-02.Weyl semimetals are playing a major role in condensed-matter physics due to exotic topological properties, and their coexistence with ferromagnetism may lead to enhanced spin-related phenomena. Here, the inverse spin Hall effect (ISHE) in the ferromagnetic Weyl semimetal Heusler alloy Co2MnGa was investigated at room temperature by means of electrical spin injection in lateral spin valve structures. Spin transport properties such as spin polarization and spin diffusion length in this material were precisely extracted in order to estimate the spin Hall angle θSH, which was found to be −0.19±0.04 and is among the highest reported for a ferromagnet. Although this value is on the same order of magnitude of known heavy metals, the significantly higher resistivity of Co2MnGa implies an improvement on the magnitude of detection voltages, while its ferromagnetic nature allows controlling the intensity of SHE through the magnetization direction. It was also shown that Onsager's reciprocity does not hold for this system, which is in part attributable to a different spin-dependent Hall conductivity for spin-up and spin-down carriers