Perpendicular magnetic anisotropy of Co₂Fe_xMn_1-xSi Heusler alloy ultra-thin films

Film thickness, composition, and buffer layer dependences of perpendicular magnetic anisotropy (PMA) were investigated for ultrathin Co₂Fe_xMn_1-xSi Heusler alloy films. The perpendicular magnetization was achieved when the thickness of the Co₂MnSi on the Pd buffer layer was 0.6 and 0.8 nm. For Co₂FeSi, only a 0.6 nm thick film exhibited perpendicular magnetization. Effective uniaxial magnetic anisotropy energy (K \(-{\rm u}^{\rm eff}\) ) was 1- \(2\,\times \, 10^{6}\) erg/cm \(^{3}\). From the buffer layer dependence, it was revealed that perpendicular magnetization of Co₂FeSi films was not achieved for a MgO or Cr buffer layer. These results imply that contributions from the Pd/Heusler alloy interface plays an important role in the PMA of ultrathin Co₂Fe_xMn_1-xSi Heusler alloy films.