Dynamic nuclear polarization and Knight shift measurements in a breakdown regime of integer quantum Hall effect

Nuclear spins are polarized electrically in a breakdown regime of an odd-integer quantum Hall effect (QHE). Electron excitation to the upper Landau subband with the opposite spin polarity flips nuclear spins through the hyperfine interaction. The polarized nuclear spins reduce the spin-splitting energy and accelerate the QHE breakdown. The Knight shift of the nuclear spins is also measured by tuning electron density during the irradiation of radio-frequency magnetic fields.Comment: 3 pages, 2 figures, EP2DS-1

Half-Metallic Heusler Alloy/GaN Heterostructure for Semiconductor Spintronics Devices

Because spin-orbit coupling in wurtzite semiconductors is relatively weak compared with that in zincblende ones, the III-nitride semiconductor GaN is a promising material for high-performance optical semiconductor spintronic devices such as spin lasers. For the purpose of reducing the operating power of spin lasers, it is necessary to demonstrate highly efficient electrical spin injection from a ferromagnetic material into GaN with a low-resistance contact. Here, an epitaxial half-metallic Heusler alloy Co2FeAlxSi1−x(CFAS)/GaN heterostructure is developed by inserting an ultrathin Co layer between the CFAS and GaN. The CFAS/n+-GaN heterojunctions clearly show tunnel conduction with very small rectification and a low resistance-area product of ≈3.8 kΩµm2, which is several orders of magnitude smaller than those reported in previous work, at room temperature. Nonlocal spin signals and a Hanle effect curve are observed at low temperatures using lateral spin-valve devices with the CFAS/n+-GaN contacts, suggesting pure spin current transport in bulk GaN. The spin transport is observed at temperatures as high as room temperature, with a high spin polarization of 0.2 at a low bias voltage less than 2.0 V. This study is expected to open a path to GaN-based spintronic devices with highly spin-polarized and low-resistance contacts.Yamada S., Kato M., Ichikawa S., et al. Half-Metallic Heusler Alloy/GaN Heterostructure for Semiconductor Spintronics Devices. Advanced Electronic Materials 9, 2300045 (2023); https://doi.org/10.1002/aelm.202300045

The antiphase boundary in half-metallic Heusler alloy Co2Fe(Al,Si) : atomic structure, spin polarization reversal, and domain wall effects

Atomic resolution scanning transmission electron microscopy reveals the presence of an antiphase boundary in the half-metallic Co2Fe(Al,Si) full Heusler alloy. By employing the density functional theory calculations, we show that this defect leads to reversal of the sign of the spin-polarization in the vicinity of the defect. In addition, we show that this defect reduces the strength of the exchange interactions, without changing the ferromagnetic ordering across the boundary. Atomistic spin calculations predict that this effect reduces the width of the magnetic domain wall compared to that in the bulk

Room-temperature local magnetoresistance effect in n-Ge devices with low-resistive Schottky-tunnel contacts

Two-terminal local magnetoresistance (MR) effect in n-type germanium (Ge) based lateral spin-valve (LSV) devices can be observed at room temperature. By using phosphorus δ-doped Heusler-alloy/Ge Schottky-tunnel contacts, the resistance-area product of the contacts is able to be less than 0.20 kΩ μm 2 , which is the lowest value in semiconductor based LSV devices. From the one-dimensional spin drift-diffusion model, the interface spin polarization of the Heusler-alloy/Ge contacts in the present LSV devices can be estimated to be ∼0.018 at room temperature. We experimentally propose that it is important for enhancing the local MR ratio in n-Ge based LSV devices to improve the interface spin polarization of the Heusler-alloy/Ge contacts

Controlling the half-metallicity of Heusler/Si(1 1 1) interfaces by a monolayer of Si–Co–Si

By using first-principles calculations we show that the spin-polarization reverses its sign at atomically abrupt interfaces between the half-metallic Co₂ (Fe,Mn)(Al,Si) and Si(1 1 1). This unfavourable spin-electronic configuration at the Fermi-level can be completely removed by introducing a Si–Co–Si monolayer at the interface. In addition, this interfacial monolayer shifts the Fermi-level from the valence band edge close to the conduction band edge of Si. We show that such a layer is energetically favourable to exist at the interface. This was further confirmed by direct observations of CoSi₂ nano-islands at the interface, by employing atomic resolution scanning transmission electron microscopy

Growth of all-epitaxial Co2MnSi/Ge/Co2MnSi vertical spin-valve structures on Si

We explore epitaxial growth of Co2MnSi/Ge/Co2MnSi vertical spin-valve structures on Si, where the Co2MnSi (CMS) is expected to be a half-metallic material for spintronics. By combining solid phase epitaxy, low-temperature molecular beam epitaxy, and atomic layer termination techniques, we can grow an epitaxial Ge layer on CMS at 250 °C, where the atomic interdiffusion between Ge and CMS is suppressed. After further optimization of the growth condition of the Ge intermediate layer, all-epitaxial CMS/Ge/CMS vertically stacked structures with spin-valve like magnetization reversal processes are demonstrated. This vertically stacked structures can be utilized for vertical spin-valve devices with a Ge channel on Si