AVS 46th International Symposium
    Magnetic Interfaces and Nanostructures Technical Group Monday Sessions
       Session MI-MoM

Paper MI-MoM7
Epitaxial Ferromagnetic Ni@sub 2@MnGa Film Grown on GaAs (001) by Molecular Beam Epitaxy

Monday, October 25, 1999, 10:20 am, Room 618/619

Session: New Magnetic Materials
Presenter: J.W. Dong, University of Minnesota
Authors: J.W. Dong, University of Minnesota
L.C. Chen, University of Minnesota
D.M. Carr, University of Minnesota
C.J. Palmstrom, University of Minnesota
Correspondent: Click to Email
In the bulk, stoichiometric Ni@sub 2@MnGa is ferromagnetic with a Curie temperature 376°K. Above 202°K, the stable austenitic phase has the cubic L2@sub 1@ Heusler structure with a lattice parameter 3% larger than GaAs. This structure can be considered as a NaCl crystal structure of Mn and Ga with Ni in the tetrahedral sites. It may also be considered as an 'ordered' CsCl structure with a simple cubic lattice of Ni with every other interstitial site filled with Mn and Ga, respectively. The similarity in crystal structures suggests that metallic compounds with either the NaCl or CsCl structures should act as excellent templates for Ni@sub 2@MnGa growth. The growth of Ni@sub 2@MnGa on GaAs with a 6 ML-thick Sc@sub 0.3@Er@sub 0.7@As (NaCl structure) lattice matched to GaAs interlayer resulted in single crystal growth. In-situ reflection high energy electron diffraction patterns were streaky, indicative of high crystalline quality. Ex-situ X-ray diffraction and plan-view TEM selected area electron diffraction patterns confirmed single crystal growth and showed that a 300Å thick Ni@sub 2@MnGa grew pseudomorphically on GaAs. Considering the lattice mismatch, this seems surprising. However, we speculate that the epitaxy is stabilizing a new tetragonal phase of Ni@sub 2@MnGa with a = b = 5.65 Å, c = 6.12 Å and will present a model to explain this. Magnetic measurements using vibrating sample and superconducting quantum interference device magnetometers revealed the Ni@sub 2@MnGa to have in-plane magnetization and a Curie temperature ~320°K. The growth and properties of Ni@sub 2@MnGa films grown with a NiGa (CsCl structure) interlayer and directly on GaAs will be compared with ones grown on Sc@sub 0.3@Er@sub 0.7@As interlayers. The effect of the interlayer on the interfacial properties will also be discussed.