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

The unidirectional anisotropy constant, J
_K
, of the Mn
₇₆
Ir
₂₄
/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 Co
₈₀
Fe
₂₀
and Fe
₇₀
Ni
₃₀
, roughly corresponding to those in the bulk binary alloy systems. The saturation magnetization, M
_s
, of the FM layer showed a broad peak around Fe
₆₀
Co
₄₀
and a shallow dip at Fe
₇₀
Ni
₃₀
, corresponding well with the Slater-Pauling curve of bulk alloys. On the other hand, the J
_K
reached a maximum around Co
₇₀
Fe
₃₀
and showed different variation from that of the M
_s
against the FM layer composition. Therefore, the correlation plot between J
_K
and M
_s
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.