Systematic Study for Magnetization Dependence of Exchange Anisotropy Strength in Mn-Ir/FM (FM${=}$Ni-Co, Co-Fe, Fe-Ni) Bilayer System

Abstract

The unidirectional anisotropy constant, JK, of the Mn76Ir24/FM (FM =Ni-Co, Co-Fe, Fe-Ni) bilayers was investigated, systematically changing the FM layer composition. On the (111)-oriented face centered cubic (fcc) Mn-Ir layer, the FM layers were grown in the respective crystal structure, corresponding to their composition. The phase boundaries between fcc and body centered cubic (bcc) structures existed around Co80Fe20 and Fe70Ni30, roughly corresponding to those in the bulk binary alloy systems. The saturation magnetization, Ms, of the FM layer showed a broad peak around Fe60Co40 and a shallow dip at Fe70Ni30 , corresponding well with the Slater-Pauling curve of bulk alloys. On the other hand, the JK reached a maximum around Co70Fe30 and showed different variation from that of the Ms against the FM layer composition. Therefore, the correlation plot between JK and Ms did not provide any clear relationship. From the experimental results, we found a general feature that bcc structured FM layers are more likely to induce strong exchange anisotropy than fcc structured FM layers.