Effect of 4d and 5d Transition-Metal Insertions to Spin-Dependent Transports in Fe/MgO Superlattices

We systematically investigated the effect of the spin–orbit coupling (SOC) to the tunneling magnetoresistance (TMR) ratio of the Fe/MgO (001) superlattices with inserted 4d (Ru, Rh, Pd) and 5d (Os, Ir, Pt) transition-metal (TM) monolayers by the first-principles full-potential linearized augmented plane wave method. We find that the TMR ratios for both 4d and 5d TM insertions decrease due to the introduction of the SOC. We observe that in all systems, the TMR values are mainly determined by the electric conductivities in the parallel magnetic configuration, as they are two orders of magnitude larger than the conductivities in the antiparallel magnetic configuration. When the SOC is introduced, we find that the TMR values are reduced depending on the SOC strength, and the largest TMR reduction occurs for the Pt monolayer insertion. In-plane wave vector (k∥) dependence of the electric conductivity shows that the reduction of TMR is indeed related to the decrease of electric conductivity in the parallel magnetic configuration.