Shinobu Ohya

We present a systematic study of the properties of room temperature deposited TiN films by varying the deposition conditions in an ultra-high-vacuum reactive magnetron sputtering chamber. By increasing the deposition pressure from 2 to 9 mTorr while keeping a nearly stoichiometric composition of Ti1−xNx (x = 0.5) without substrate heating, the film resistivity increases, the dominant crystal orientation changes from (100) to (111), grain boundaries become clearer, and the strong compressive in-p

We report on the resonant tunneling effect and the increase of tunneling magnetoresistance induced by it in ferromagnetic-semiconductor $\mathrm{GaMnAs}$ quantum-well (QW) heterostructures. The resonant tunneling effect was observed when the $\mathrm{GaMnAs}$ QW thickness was from 3.8 to $20\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, which indicates that highly coherent tunneling occurs in these heterostructures. The observed quantum levels of the $\mathrm{GaMnAs}$ QW were successfully explained by

The authors have studied the magneto-optical and magnetotrasnport properties of Ga1−xMnxAs thin films with high Mn concentrations (x=12.2%–21.3%) grown by molecular-beam epitaxy. These heavily Mn-doped GaMnAs films were formed by decreasing the growth temperature to as low as 150–190°C and by reducing the film thickness to 10nm in order to prevent precipitation of hexagonal MnAs clusters. Magnetic circular dichroism and anomalous Hall effect measurements indicate that these GaMnAs films have the

The valence-band structure and the Fermi level (E(F)) position of ferromagnetic-semiconductor GaMnAs are quantitatively investigated by electrically detecting the resonant tunneling levels of a GaMnAs quantum well (QW) in double-barrier heterostructures. The resonant level from the heavy-hole first state is clearly observed in the metallic GaMnAs QW, indicating that holes have a high coherency and that E(F) exists in the band gap. Clear enhancement of tunnel magnetoresistance induced by resonant

We have studied magnetic properties of heavily Mn-doped [(In0.44Ga0.56)0.79Mn0.21]As thin films grown by low-temperature molecular-beam epitaxy on InP substrates. (InGaMn)As with high Mn content (21%) was obtained by decreasing the growth temperature to 190 °C. When the thickness of the [(In0.44Ga0.56)0.79Mn0.21]As layer is equal or thinner than 10 nm, the reflection high-energy electron diffraction pattern and transmission electron microscopy show no MnAs clustering, indicating that a homogeneo

We have studied the tunneling magnetoresistance (TMR) of Ga0.94Mn0.06As∕AlAs(dnm)∕In0.4Ga0.6As(0.42nm)∕AlAs(dnm)∕Ga0.94Mn0.06As double-barrier magnetic tunnel junctions with various AlAs thicknesses (d=0.8–2.7nm) grown on p+GaAs (001) substrates by low-temperature molecular-beam epitaxy. In some junctions, unusual inverse TMR, in which the tunnel resistance in antiparallel magnetization is lower than that in parallel magnetization, was observed. The TMR ratio oscillated between positive and nega

Strontium titanate (SrTiO₃ or STO) is important for oxide-based electronics as it serves as a standard substrate for a wide range of high-temperature superconducting cuprates, colossal magnetoresistive manganites, and multiferroics. Moreover, in its heterostructures with different materials, STO exhibits a broad spectrum of important physics such as superconductivity, magnetism, the quantum Hall effect, giant thermoelectric effect, and colossal ionic conductivity, most of which emerge

We have studied the growth and properties of quaternary alloy magnetic semiconductor (InGaMn)As grown on both GaAs substrates and InP substrates by low-temperature molecular-beam epitaxy (LT-MBE). (InGaMn)As thin films were ferromagnetic below ∼ 30 K, exhibiting a strong magneto-optical effect. The lattice constant of [(InyGa1-y)1-xMnx]As, whose Mn concentration x is below 4%, is slightly smaller than that of InyGa1-yAs with the same In/Ga content ratio. We have also obtained very smooth surface

To clarify the whole picture of the valence-band structures of prototype ferromagnetic semiconductors (III,Mn)As (III: In and Ga), we perform systematic experiments of the resonant tunneling spectroscopy on [(In${}_{0.53}$Ga${}_{0.47}$)${}_{1\ensuremath{-}x}$Mn${}_{x}$]As ($x$ $=$ 0.06--0.15) and In${}_{0.87}$Mn${}_{0.13}$As grown on AlAs/In${}_{0.53}$Ga${}_{0.47}$As:Be/${p}^{+}$InP(001). We show that the valence band of [(In${}_{0.53}$Ga${}_{0.47}$)${}_{1\ensuremath{-}x}$Mn${}_{x}$]As almost re

We investigate the spin-dependent tunneling properties in a three-terminal III–V-based ferromagnetic-semiconductor heterostructure with a 2.5 nm thick GaMnAs quantum well (QW) and double barriers. We successfully control the quantum levels and modulate the spin-dependent current with varying the voltage of the electrode connected to the GaMnAs QW. Our results will open up a new possibility for realizing three-terminal spin resonant-tunneling devices.

Topological crystalline insulator SnTe is a promising material for future spintronics applications because of the strong spin-orbit coupling and surface states protected by the mirror symmetry of the crystal. In this paper, using a high-quality epitaxial (001)-oriented Fe/SnTe/CdTe/ZnTe heterostructure grown on GaAs, we successfully observe the inverse spin Hall effect in SnTe induced by spin pumping, which is confirmed by detailed analyses of the dependence of the electromotive force on the mic

Developing technology to realize oxide-based nanoscale planar integrated circuits is in high demand for next-generation multifunctional electronics. Oxide circuits can have a variety of unique functions, including ferromagnetism, ferroelectricity, multiferroicity, superconductivity, and mechanical flexibility. In particular, for spin-transistor applications, the wide tunability of the physical properties due to the presence of multiple oxide phases is valuable for precise conductivity matching b

To achieve a desirable magnitude of spin-orbit torque (SOT) for magnetization switching and realize multifunctional spin logic and memory devices utilizing SOT, controlling the SOT manipulation is vitally important. In conventional SOT bilayer systems, researchers have tried to control the magnetization switching behavior via interfacial oxidization, modulation of spin-orbit effective field, and effective spin Hall angle; however, the switching efficiency is limited by the interface quality. A c