Structure and Magnetism of MnGa Ultra-Thin Films on GaAs(111)B

Abstract

MnGa alloys with compositions in the range of 52 to 60 at. % Mn were grown by molecular beam epitaxy (MBE) on GaAs(111)B substrates. High quality epilayers were obtained at growth temperatures between 25 and 250 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C. Epilayers are stabilized by post-growth annealing at 400 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C for 30 min. In situ reflection high energy electron diffraction (RHEED) and X-ray photoelectron spectroscopy (XPS) have been performed to probe surface structure and stoichiometry during growth and post-annealing process. Ex situ X-ray diffraction (XRD) measurements were also performed in order to access the bulk crystalline structure using synchrotron radiation source. MnGa epilayers are formed by stacking of (111) planes of tetragonal zinc-blende structure (ZB) which are rotated by approximately 11 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> with respect to the underlying (111) planes of the GaAs lattice. The tetragonal ZB structure of MnGa exhibits lattice parameters of a = 0.55 nm and c = 0.61 nm. Magnetic measurements performed using a vibrating sample magnetometer (VSM) reveal nearly isotropic in-plane magnetization with saturation magnetization varying between 650 and 300 emu/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> for different concentrations of Mn.