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.
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