Site preference of magnetic atoms in Ni–Mn–Ga–M (M = Co, Fe) ferromagnetic shape memory alloys

Site preference of cobalt and iron atoms substituted in Ni–Mn–Ga alloys is examined using the compositional dependence of saturation magnetization determined at 5 K. Variations in magnetization of Ni50Mn25+xGa25−x−yMy(M = Co, Fe) alloys are systematically compared with the values computed for different possible configurations of site occupancies. The study reveals that the dopant atoms occupy the regular Mn site, rather than the vacant Ga site, with ferromagnetic exchange relative to the moments on Ni and Mn sublattices. The excess and displaced Mn atoms occupy the vacant Ga site with antiferromagnetic exchange. Site preference appears to have a correlation to the atomic volume of the elements.