J. H. Zhao

Low-temperature magnetotransport behaviors of heavily Mn-doped (Ga,Mn)As films with high ferromagnetic transition temperature

We report the low-temperature magnetotransport behaviors of (Ga,Mn)As films with the nominal Mn concentration x larger than 10%. The ferromagnetic transition temperature T-C can be enhanced to 191 K after postgrowth annealing (Ga,Mn)As with x=20%. The temperature T-m, corresponding to the resistivity minimum in the curve of resistivity versus temperature at temperature below T-C, depends on Mn concentration, annealing condition, and magnetic field. Moreover, we find that the variable-range hopping may be the main conductive mechanism when temperature is lower than T-m.

Growth of thicker zinc-blende CrSb layers by using (In,Ga)As buffer layers

Zinc-blende CrSb (zb-CrSb) layers with room-temperature ferromagnetism have been grown on (In,Ga)As buffer layers epitaxially prepared on (001) GaAs substrates by molecular-beam epitaxy. Compared with the typical thickness [2-3 ML (ML denotes monolayers)] of zb-CrSb grown directly on GaAs, the thickness of zb-CrSb grown on (In,Ga)As has been increased largely; the maximum can be up to similar to 9 ML. High-resolution cross sectional transmission electron microscopy images show that the zb-CrSb layer is combined with (In,Ga)As buffer layer without any dislocations at the interface

Microstructure and magnetic properties of Sm2(Fe, Si)17Cx/α-Fe nanocomposite magnets prepared under high pressure

We present microstructure and magnetic properties of Sm2(Fe, Si)17Cx/α-Fe nanocomposite magnets prepared under a pressure of 4 GPa at a temperature of 923 K. A high-pressure experiment was carried out in a belt-type pressure apparatus. Analyses of x-ray diffraction and transmission electron microscopy show that the nanocomposite magnets have a grain size of 6–8 nm, which provides a strong exchange coupling between hard and soft magnetic phases. As a result, the magnets have, compared with nanocomposite magnets prepared under normal pressure, a significant increase in both coercivity, from 132 to 500 kA/m, and remanent magnetization, from 0.68 to 0.83Ms.

Effects of buoyancy convection on phase morphology during solidification of Pd40Ni40P20 alloy

Samples of Pd40Ni40P20 alloy were solidified both on the ground and on board a Chinese Retrievable Satellite in order to study the effects of gravity-induced convection on the phase morphology. In comparison to the secondary dendritic spacing, the effective mass transport coefficient under normal gravity condition was estimated to be 1.95 times as high as that under microgravity conditions at the cooling rate of 0.056 K s(-1). The higher mass transport coefficient value due to the existence of buoyancy convection on the ground led to the formation of coarser dendrites of the primary phase Ni5P2 in the ground-based sample

Short-wavelength photoluminescence from silicon and nitrogen coimplanted SiO2 films

Intense short-wavelength photoluminescence (PL) observed at room temperature from thermal SiO2 films implanted with Si and N is reported. A flat Si profile was first created. N ions were subsequently implanted into the same depth region as the implanted Si ions. Two PL bands peaking at ∼330 and ∼430 nm were observed from the samples at room temperature with and without annealing. It is found that the PL has a strong dependence on the stabilized N in the Si- and N-coimplanted SiO2 films. The PL may originate from a complex of Si, N, and O.

Room-temperature ferromagnetism in zinc-blende and deformed CrAs thin films

We try to clarify the controversy about the origin of room-temperature ferromagnetism in a CrAs compound. Two kinds of CrAs thin films were grown on GaAs by molecular-beam epitaxy. Structural analyses confirm that the as-grown CrAs film is a pure zinc-blende phase. Magnetic measurements suggest that room-temperature ferromagnetism exists in zinc-blende CrAs. In contrast, the CrAs film turns into a mixture of zinc-blende and deformed CrAs after annealing. A ferromagnetic signal measured at room temperature demonstrates that zinc-blende CrAs remains room-temperature ferromagnetism even when it is partly deformed into a non-zinc-blende phase.

Anomalous Hall effect and spin-orbit torques in MnGa/IrMn films: Modification from strong spin Hall effect of the antiferromagnet

We report systematic measurements of anomalous Hall effect (AHE) and spin-orbit torques (SOTs) in MnGa/IrMn films, in which a single

Strain and magnetic anisotropy of as-grown and annealed Fe films on c(4x4) reconstructed GaAs (001) surface

L{1}_{0}\text{\ensuremath{-}}\mathrm{MnGa}

Memory effect in a system of zincblende Mn-rich Mn(Ga)As nanoclusters embedded in GaAs

epitaxial layer reveals obvious orbital two-channel Kondo (2CK) effect. As increasing the thickness of the antiferromagnet IrMn, the strong spin Hall effect (SHE) has gradually suppressed the orbital 2CK effect and modified the AHE of MnGa. A scaling involving multiple competing scattering mechanisms has been used to distinguish different contributions to the modified AHE. Finally, the sizeable SOT in the MnGa/IrMn films induced by the strong SHE of IrMn have been investigated. The IrMn layer also supplies an in-plane exchange bias field and enables nearly field-free magnetization reversal.

Interdiffusion in Ni80Fe20/Mo magnetic multilayers

Fe films with the different thicknesses were grown on c(4x4) reconstructed GaAs (001) surfaces at low temperature by molecular-beam epitaxy. Well-ordered bcc structural Fe epitaxial films are confirmed by x-ray diffraction patterns and high-resolution cross-sectional transmission electron microscopy images. A large lattice expansion perpendicular to the surface in Fe film is observed. In-plane uniaxial magnetic anisotropy is determined by the difference between magnetizing energy along [110] and [110] directions, and the constant of interfacial uniaxial magnetic anisotropy is calculated to be 1.02x10(-4) J m(-2). We also find that magnetic anisotropy is not obviously influenced after in situ annealing, but in-plane strain is completely changed.