Delta-phase manganese gallium on gallium nitride: a magnetically tunable spintronic system
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1118-K06-06
Delta-phase manganese gallium on gallium nitride: a magnetically tunable spintronic system Kangkang Wang1, Abhijit Chinchore1, Wenzhi Lin1, Arthur Smith1 and Kai Sun2 1 Department of Physics and Astronomy, Ohio University, Athens, OH 45701, U.S.A. 2 Department of Materials Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109, U.S.A. ABSTRACT Ferromagnetic delta-phase manganese gallium with Mn:Ga ratio between 1:1 to 1.5:1 is grown on wurtzite gallium nitride and scandium nitride substrates, using molecular beam epitaxy. The dependencies of growth properties, e.g. interface formation, surface reconstruction and crystalline quality, on substrate crystallographic structure and polarity are investigated. Results suggest that for growth on wurtzite GaN, Ga-polar surface promotes quicker interface formation, and also results in better crystalline quality of the MnGa film, as compared to N-polar. The crystal orientation and magnetic anisotropy are found to be different than those grown on cubic scandium nitride substrates. INTRODUCTION Ferromagnetic metal/semiconductor layered structures are of great interest due to their potential for novel spintronics applications such as spin light-emitting diodes[1]. Delta phase manganese gallium, a ferromagnetic alloy with high magnetic moments (~2.51 μB/Mn atom[2]) and Curie temperature above room temperature, appears to be a promising candidate for such applications. There have been several reports[3,4] on epitaxial growth of δ-MnGa on zinc-blende GaAs(001) substrates, where perpendicular magnetization was found. Furthermore, it was recently reported[5] that ferromagnetic δ-MnGa can be grown epitaxially on top of wide band-gap Ga-polar wurtzite GaN(0001), with controllable magnetism by adjusting slightly the Mn:Ga atom concentration. While many important spintronics properties, such as spin injection efficiency and magnetic anisotropy, strongly depend on the interface abruptness and crystallographic structure of the film, further experiments targeting a better understanding of these issues, especially for MnGa/GaN system, appear to be still lacking. Here we further investigate the substrate and polarity dependencies of the growth and magnetic properties of the MnGa film, with a focus on the interface formation. We will show that, compared to N-polar wurtzite GaN substrates, Ga-polar appears to promote quicker formation of the new δ-MnGa lattices, hence resulting in a more well-defined, abrupt interface. This advantage also continues into thicker films, yields smoother surface as well as better crystallinity. These differences could be due to the different chemical environments on different polarities of GaN surfaces. A comparison to the growth on cubic-structured scandium nitride substrates reveals dramatically different magnetic anisotropies, resulting from the different orientation of the film. EXPERIMENT Experiments are carried out in a custom-designed, ultra-high-vacuum (UHV) molecular beam epitaxy (MBE) / scanning tunneling microscope (STM) system,
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