J. W. Dong

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.

SELF-ASSEMBLED ERAS ISLANDS IN GAAS: GROWTH AND SUBPICOSECOND CARRIER DYNAMICS

We report the growth of self-assembled ErAs islands embedded in GaAs by molecular beam epitaxy. The nucleation of ErAs on GaAs occurs in an island growth mode leading to spontaneous formation of nanometer-sized islands. Several layers of ErAs islands separated by GaAs can be stacked on top of each other to form a superlattice. X-ray diffraction shows superlattice fringes from such samples. Pump–probe measurements indicate carrier capture times as short as 120 fs. These capture times are strongly correlated with the period of the superlattice.

Anomalous magnetotransport properties of epitaxial full Heusler alloys

We report the magnetotransport properties of epitaxial films of the full Heusler alloys Ni2MnGa, Ni2MnGe, and Ni2MnAl, grown by molecular beam epitaxy on (001) GaAs. The ferromagnetic alloys (Ni2MnGa,Ni2MnGe) exhibit an anomalous temperature dependence of the resistivity and a negative magnetoresistance peaking near the Curie temperature due to spin disorder scattering. Considering the absolute values of the resistivity, the anomalous high temperature behavior and an upturn in the resistivity below 20 K, we suggest that these Heusler alloys rather than being conventional metals are in fact strongly disordered electronic systems.

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.

Magnetic domain observations of freestanding single crystal patterned Ni2MnGa films

Ni2MnGa thin films have been grown pseudomorphically on a 6-monolayer thick Sc0.3Er0.7As interlayer on GaAs(001) by molecular-beam epitaxy. They have a tetragonal structure (a=b=5.65 A and c=6.18 A) which is different from any of the known bulk phases. Magnetic measurements reveal Ni2MnGa to have an in-plane easy axis and a Curie temperature around 350 K. The magnetic properties of these films are given and compared to the corresponding measurements in bulk material. In contrast to bulk material, single crystal films have been predicted to exhibit exact austenite–martensite interfaces (without fine twinning of the martensite). Films have been patterned along the predicted interfaces using the conventional photolithography and reactive ion etching. The patterns are then released from the substrate by backside photolithography and selective wet chemical etching, to yield freestanding films. The martensitic transformation of the freestanding films has been observed slightly above the room temperature. Magnet...

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.