Correlation between Exchange Anisotropy and Crystal Structure of Ferromagnetic Layer in γ-Mn-Ir/Fe-Co-Ni Bilayers

Abstract

The unidirectional anisotropy constant, JK, of γ-Mn-Ir / FM (FM = Fe-Co-Ni) bilayers was investigated by systematically changing the composition of the Fe-Co-Ni layers. The FM layers were grown in the crystal structures corresponding to their composition on the (111)-oriented face centered cubic (fcc) Mn-Ir layer. JK was significantly changed around the phase boundary of the FM layer between the body-centered cubic (bcc) phase and fcc-phase. The experimental results revealed a general feature where bcc-structured FM layers were more likely to induce stronger exchange anisotropy than fcc-structured FM layers. The JK values and the lattice mismatch between the Mn-Ir layer and the FM layer were increased with increasing Co concentration in the bcc-FM region. The dependence of JK on FM composition have been explained qualitatively with lattice distortion at the interface between the Mn-Ir and FM layers.