Ferromagnetism and electronic structures of nonstoichiometric Heusler-alloy Fe3-xMnxSi epilayers grown on Ge(111)

For the study of ferromagnetic materials which are compatible with group-IV semiconductor spintronics, we demonstrate control of the ferromagnetic properties of Heusler-alloy Fe3-xMnxSi epitaxially grown on Ge(111) by tuning the Mn composition x. Interestingly, we obtain L21-ordered structures even for nonstoichiometric atomic compositions. The Curie temperature of the epilayers with x 0.6 exceeds 300 K. Theoretical calculations indicate that the electronic structures of the nonstoichiometric Fe3-xMnxSi alloys become half-metallic for 0.75≤x≤1.5. We discuss the possibility of room-temperature ferromagnetic Fe3-xMnxSi/Ge epilayers with high spin polarization.