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Ferromagnetic semiconductors (FMSs), which show both ferromagnetic and semiconducting characteristics, are promising materials for future low-power spintronics devices. Among various FMSs, Fe-doped III-V FMSs are promising, because both p-type and n-type materials are available and the highest Curie temperature ( $T_{\mathrm{C}}$ ) exceeds room temperature. In this work, we demonstrate clear magnetoresistance due to the spin valve effect in ferromagnetic heterostructures containing high- $T_{\mathrm{C}}$ (Ga, Fe)Sb. The samples examined here consist of (Ga 0.75 , Fe 0.25 )Sb ( $40\ \text{nm},\ T_{\mathrm{C}} > 320\ \mathrm{K}$ ) / InAs (thickness $t=0,\ 3,\ 6,\ 9\ \text{nm}$ ) / (Ga 0.8 , Fe 0.2 )Sb ( $40\ \text{nm},\ T_{\mathrm{C}} > 320\ \mathrm{K}$ ) grown by low-temperature molecular-beam epitaxy. Clear MR of ∼2% with an open minor loop is observed at 3.7 K when $t =3\ \text{nm}$ , whose peaks (⋍ ±0.1 T) are consistent with the coercive forces of the (Ga, Fe)Sb layers obtained with superconducting quantum interference device (SQUID) magnetometry. We found that the GMR ratio increases (from 0.03 to 1.28%) with decreasing $t$ (from 9 to 3 nm), which is caused by the enhancement of spin-dependent scattering at the InAs/(Ga, Fe)Sb interfaces. This is the first demonstration of the spin-valve effect in Fe-doped FMS heterostructures, paving the way for device applications of high- $T_{\mathrm{C}}$ FMSs.

Ferromagnetic semiconductor (FMSs), which exhibits both magnetic and semiconducting properties, are promising for semiconductor-based spintronics devices. Magnetic anisotropy (MA) plays an important role in determining the magnetization direction of ferromagnetic materials. Here, we present the thickness-dependence control of MA in (Ga 0.7 , Fe 0.3 )Sb by growing samples with different thicknesses $d=20-55\ \text{nm}$ grown on AlSb by low-temperature molecular beam epitaxy. We used ferromagnetic resonance (FMR) to estimate the MA constants of the (Ga 0.7 , Fe 0.3 )Sb. We systematically measured the dependence of the FMR resonance field on the external magnetic-field direction and fitted a theoretical curve to obtain the MA fields of the (Ga, Fe)Sb thin films, and obtained the effective MA constants ( $K_{\text{eff}}$ ) of (Ga, Fe)Sb. From the sign of $K_{\text{eff}}$ , we found that MA changes from in-plane magnetic anisotropy (IMA) to perpendicular magnetic anisotropy (PMA) with increasing $d$ . To understand this, we separated the $K_{\text{eff}}$ into the volume contribution ( $K_{\mathrm{V}}$ ) and the interface contribution ( $K_{\mathrm{I}}$ ). We show that the IMA originates from the film interface due to the tensile strain when the films are thin, whereas $K_{\mathrm{V}}$ causes PMA in (Ga, Fe)Sb. The observation of FMR at room temperature and control of MA are important steps towards device applications of (Ga, Fe)Sb.

The evolution of information technology has been driven by the discovery of new forms of large magnetoresistance (MR), such as giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) in magnetic multilayers. Recently, new types of MR have been observed in much simpler bilayers consisting of ferromagnetic (FM)/nonmagnetic (NM) thin films; however, the magnitude of MR in these materials is very small (0.01 ~ 1%). Here, we demonstrate that NM/FM bilayers consisting of a NM InAs quantum well conductive channel and an insulating FM (Ga,Fe)Sb layer exhibit giant proximity magnetoresistance (PMR) (~80% at 14 T). This PMR is two orders of magnitude larger than the MR observed in NM/FM bilayers reported to date, and its magnitude can be controlled by a gate voltage. These results are explained by the penetration of the InAs two-dimensional-electron wavefunction into (Ga,Fe)Sb. The ability to strongly modulate the NM channel current by both electrical and magnetic gating represents a new concept of magnetic-gating spin transistors.

A spin metal-oxide-semiconductor field-effect transistor (MOSFET) is one of the most promising devices for future electronics because of the compatibility with the conventional semiconductor technologies and its variety of potential applications such as reconfigurable circuits; however, there are some problems to be solved to realize spin MOSFET. In particular, realizing and controlling the spin dependent transport in a MOSFET are fundamental ones. Here, we demonstrated the basic operations of the spin MOSFET in a vertical spin electric double layer transistor (EDLT).We obtained large spin dependent transport signal 50–1000 times as large as the values obtained in previous studies by adopting the vertical structure. Furthermore, we modulated the spin dependent transport signal by modulating magnetic anisotropy fields of ferromagnetic source/drain, applying gate electric field.

We show high-temperature ferromagnetism in heavily Fe-doped ferromagnetic semiconductor (Ga 1−x ,Fe x )Sb (x = 23% and 25%) thin films grown by low-temperature molecular beam epitaxy (LT-MBE). Our crystal structure analysis by scanning transmission electron microscopy (STEM) indicates that the (Ga 1−x ,Fe x )Sb thin films maintain the zinc-blende crystal structure at x = 25%. The intrinsic ferromagnetism was confirmed by magnetic circular dichroism (MCD) spectroscopy and anomalous Hall effect (AHE) measurements. The Curie temperature reaches 300 K and 340 K for x = 23% and 25%, respectively, which are the highest values reported so far in intrinsic III–V ferromagnetic semiconductors.