Stuart McKernan

Molecular beam epitaxy growth of ferromagnetic single crystal (001) Ni2MnGa on (001) GaAs

The ferromagnetic shape memory alloy Ni2MnGa has been grown on GaAs by molecular beam epitaxy. In situ reflection high energy electron diffraction, ex situ x-ray diffraction, and transmission electron microscopy selective area electron diffraction indicate the single crystal growth of a pseudomorphic tetragonal phase of Ni2MnGa on (001) GaAs. Both vibrating sample magnetometry and superconducting quantum interference device magnetometry measurements show that the Ni2MnGa film is ferromagnetic with in-plane magnetization and has a Curie temperature of ∼320 K.

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.

Spin injection from perpendicular magnetized ferromagnetic δ-MnGa into (Al,Ga)As heterostructures

Electrical spin injection from ferromagnetic δ-MnGa into an (Al,Ga)As p-i-n light-emitting diode (LED) is demonstrated. The δ-MnGa layers show strong perpendicular magnetocrystalline anisotropy, enabling detection of spin injection at remanence, without an applied magnetic field. The bias and temperature dependence of the spin injection are found to be qualitatively similar to Fe-based spin LED devices. A Hanle effect is observed and demonstrates complete depolarization of spins in the semiconductor in a transverse magnetic field.

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.

Interfacial reactions of Mn/GaAs thin films

Mn thin films were deposited in situ on molecular beam epitaxy grown GaAs(001) surfaces at 0 °C. Postgrowth anneals of the Mn/GaAs samples were done at 200, 300, and 400 °C for times ranging from 0.5 to 30 h. Rutherford backscattering spectrometry, x-ray diffraction, and transmission electron microscopy show that for samples annealed at 300 °C the interfacial reactions initially result in the formation of an epitaxial two phase region (Mn2As and MnGa) with an average composition of Mn0.6Ga0.2As0.2. The rate of reaction between the Mn and GaAs shows a square root of time dependence, indicating that the reactions are diffusion limited.

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.

Characterization of the Absolute Crystal Polarity across Twin Boundaries in Gallium Phosphide Using Convergent-Beam Electron Diffraction.

: The measurement of absolute crystal polarity is crucial to understanding the structural properties of many planar defects in compound semiconductors. Grain boundaries, including twin boundaries, in the sphalerite lattice are uniquely characterized by the crystallographic misorientation of individual grains and the direction of the crystal polarity in domains adjoining the grain boundary. To evaluate crystal polarity in gallium phosphide (GaP), asymmetrical interference contrast in convergent-beam electron-diffraction (CBED) patterns was used to ascertain the nature and direction of polar bonds. The direction of the asymmetry in the electron diffraction reflections was correlated with the crystal polarity of a sample with known polarity. The CBED technique was applied to determine the polar orientation of grains adjoining Sigma = 3 coherent and lateral twin boundaries in polycrystalline GaP.

Phase formation in the thin film Fe∕GaAs system

Interfacial reactions between epitaxial films of Fe and GaAs were examined using Rutherford backscattering spectrometry, x-ray diffraction, and transmission electron microscopy as a function of postgrowth annealing conditions. At 450°C, two stable binary phases were observed at the Fe∕GaAs(001) interface with DO3Fe3Ga forming near the Fe interface and Fe2As forming near the GaAs interface. The diffusion rate of Fe in the reacted interface was found to be of similar magnitude to that of Ga and As resulting in a rough and intermixed interfacial region.

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.