J. Q. Xie

Spin injection from the Heusler alloy Co2MnGe into Al0.1Ga0.9As∕GaAs heterostructures

Electrical spin injection from the Heusler alloy Co2MnGe into a p-i-nAl0.1Ga0.9As∕GaAs light emitting diode is demonstrated. A maximum steady-state spin polarization of approximately 13% at 2 K is measured in two types of heterostructures. The injected spin polarization at 2 K is calculated to be 27% based on a calibration of the spin detector using Hanle effect measurements. Although the dependence on electrical bias conditions is qualitatively similar to Fe-based spin injection devices of the same design, the spin polarization injected from Co2MnGe decays more rapidly with increasing temperature.

Shape memory and ferromagnetic shape memory effects in single-crystal Ni2mnGa thin films

Epitaxial Ni2MnGa and Ni2Mn1.2Ga0.8 thin films have been grown by molecular beam epitaxy on GaAs (001) substrates with Sc0.3Er0.7As interlayers. Structural characterization of as-grown films confirms the epitaxially stabilized single crystal structure of the films and indicates that the films grow pseudomorphically on GaAs (001) substrates in a tetragonal structure (a=b=5.65 A, c=6.18 A). The films are ferromagnetic at room temperature with coercivity of ∼50 Oe, saturation magnetization of ∼250 emu/cm3, and weak in-plane magnetic anisotropy. The Curie temperature of the films is found to be ∼340 K. However, while the films were attached to the substrate martensitic phase transformations were not observed. In order to observe martensitic phase transformations, free-standing Ni2MnGa bridges and cantilevers were fabricated using front and back side photolithography together with a combination of dry and wet etching. After removal of the substrate, the free-standing bridges and cantilevers showed a unique tem...

Epitaxial growth of ferromagnetic Ni2MnIn on (001) InAs

The ferromagnetic Heusler alloy Ni2MnIn has been grown on InAs (001) by molecular-beam epitaxy. In situ reflection high-energy electron diffraction, ex situ x-ray diffraction, Rutherford backscattering spectrometry, and transmission electron microscopy indicate the high-quality epitaxial growth of Ni2MnIn with the B2 crystal structure on InAs (001). Superconducting quantum interference device magnetometry shows that the Ni2MnIn film is ferromagnetic with a Curie temperature ∼170 K.

Epitaxial growth of ferromagnetic Ni2MnGa on GaAs(001) using NiGa interlayers

Heusler alloy Ni2MnGa thin films have been grown pseudomorphically on a relaxed NiGa interlayer on GaAs(001) by molecular-beam epitaxy. In situ reflection high-energy electron diffraction patterns, ex situ x-ray diffraction, and cross-sectional view transmission electron microscopy electron diffraction patterns confirm the single-crystal growth of Ni2MnGa. The films grow pseudomorphically on the relaxed NiGa interlayer with a tetragonal structure (a=b=5.79 A and c=6.07 A). Magnetic measurements using vibrating sample and superconducting quantum interference device magnetometers reveal Ni2MnGa to have an in-plane easy axis and a Curie temperature ∼350 K.

Molecular-beam-epitaxy growth of ferromagnetic Ni2MnGe on GaAs(001)

Single-crystal Heusler alloy Ni2MnGe thin films have been grown on GaAs(001) by molecular-beam epitaxy. X-ray diffraction and transmission electron microscopy were used for postgrowth structural characterization. The Ni2MnGe grew in a tetragonally distorted L21-like structure (a=5.65 A, c=5.96 A) with the c axis perpendicular to the film surface. An in-plane ordering with 2× periodicity and an out-of-plane ordering with 3× periodicity was observed for the as-grown films. Magnetometry measurements performed at 50 K indicate that the films are ferromagnetic and have a weak in-plane anisotropy with a coercivity ∼5.5 Oe and saturation magnetization of ∼450 emu/cm3. The Curie temperature was measured to be ∼320 K.

Effects of doping profile and post-growth annealing on spin injection from Fe into (Al,Ga)As heterostructures

The influence of the Fe∕Ga0.9Al0.1As interface on spin injection into a spin light-emitting diode is studied. Spin injection is found to depend strongly on the interfacial doping profile demonstrating the importance of band bending in the semiconductor near the interface. The effect of post-growth annealing on spin injection from Fe contacts into GaAs-based spin light-emitting diodes is also examined. Post-growth annealing up to 250 °C is found to increase the spin injection efficiency. It is demonstrated that the annealing modifies electronic properties of the Fe∕Ga0.9Al0.1As interface, as evidenced by an increase of the Schottky barrier height.

Formation and characterization of single crystal Ni2MnGa thin films

In this paper, molecular beam epitaxial growth of Ni 2 MnGa single crystal layers on GaAs (001) using a NiGa interlayer is reported. X-ray diffraction and transmission electron microscopy confirmed an epitaxial relationship of Ni 2 MnGa [100]“010] // GaAs [100] [010] and a tetragonal structure of the film ( a = b = 5.79 A, c = 6.07 A). Magnetic measurements using vibrating sample and superconducting quantum interference device magnetometers revealed an in-plane magnetization of ∼200 emu/cm 3 at room temperature and a Curie temperature of ∼350 K. The martensitic phase transformation was observed to occur at ∼250 K

Effects of growth temperature on the structural and magnetic properties of epitaxial Ni2MnIn thin films on InAs (001)

Heusler alloy Ni2MnIn thin films have been grown on InAs (001) by molecular beam epitaxy at growth temperatures ranging from 120 to 300 °C. For growth at 120 °C, transmission electron diffraction confirms the epitaxial growth of Ni2MnIn in the B2 crystal structure on InAs (001) with an epitaxial relationship of Ni2MnIn(001)⟨100⟩‖InAs(001)⟨100⟩. Magnetic measurements show that the Ni2MnIn film is ferromagnetic with a Curie temperature ∼170K. However, for growth at 120 °C followed by a postgrowth anneal at 200 °C, a Curie temperature as high as 330 K was obtained. The increase in Curie temperature is attributed to the formation of partial L21 ordering in the Ni2MnIn film, as determined by convergent beam electron diffraction.

MBE growth and interfacial reaction control of ferromagnetic metal/GaAs heterostructures

Summary form only given. We have investigated the epitaxial growth of a number of Heusler alloys (Ni,Co)/sub 2/Mn(Al,Ga,ln,Ge) and Fe/sub l-x/Co/sub x/ on Ga/sub 1-x/In/sub x/As. X-ray diffraction and cross-sectional TEM indicated single crystal ferromagnetic film growth. The magnetic properties were measured by vibrating sample and superconducting quantum interference device magnetometers. The Heusler alloy heterostructures showed in-plane magnetization and Curie temperatures /spl sim/300K. The effects of growth conditions and the use of interfacial layers on the chemical ordering, interfacial reactions and the structural and magnetic properties will be discussed.