Ab initio calculation of interlayer exchange coupling in Co-based synthetic antiferromagnet with alloy spacer

Synthetic antiferromagnets (SAF) are widely used in magnetic tunnel junctions in order to reduce the stray field of the pinned layer. In SAF, the antiparallel spin alignment is stabilized by interlayer exchange coupling (IEC) between two ferromagnetic layers that are separated by a spacer layer. The strength of IEC depends on the spacer material. It is known that strong IEC is required for stable operation of magnetic random access memory with a low error rate, and hence a spacer material that shows strong IEC has been highly sought after. In this study, we investigate the IEC of ordered alloy spacers in Co multilayers by ab initio calculations based on density functional theory. We find that the IEC of binary alloy spacers composed of group 8 and 9 elements, namely, RuIr, RuRh, and OsIr, are greater than that of Ru and Ir spacers, which have commonly been used in SAF pinned layers. We also present dependence of IEC strength on the composition ratio of these alloy spacers. The relation between the strength of IEC and the lattice length is discussed.