Preparation of Co ₂FeSn Heusler alloy films and magnetoresistance of Fe/MgO/Co ₂FeSn magnetic tunnel junctions

To obtain magnetic tunnel junctions (MTJs) composed of non-equilibrium alloy, Co ₂FeSn films were prepared by atomically controlled alternate deposition at various substrate temperatures. X-ray diffraction patterns and Mössbauer spectra clarify that Co ₂FeSn films in the Heusler alloy phase can be realized by growing at a substrate temperature of 250°C or below. Phase separation into cubic CoSn, hexagonal CoSn and cubic CoFe phases occurs in films grown at substrate temperatures 300°C or greater. Fe/MgO/Co ₂FeSn MTJs were prepared with the Co ₂FeSn layer grown at various substrate temperatures. The MTJs with the ferromagnetic Co ₂FeSn layer grown at a substrate temperature of 250 C showed tunnel magnetoresistance ratios of 72.2 and 43.5 at 2 K and 300 K, respectively.