Origin of biquadratic interlayer exchange coupling in Co2MnSi-based current-perpendicular-to-plane pseudo spin valves

We fabricated current-perpendicular-to-plane pseudo spin valves (CPP PSVs) having Co2Mn alpha Si0.82 electrodes with various Mn compositions, alpha, and an Ag spacer and investigated the strength of biquadratic interlayer exchange coupling (90 degrees coupling) in the CPP PSVs by comparing magnetoresistance characteristics and spin-transfer-torque induced magnetization switching characteristics. We experimentally found that (a) the strength of the 90 degrees coupling increased as alpha increased, (b) it was weakened by insertion of an ultrathin CoFe layer between Co2MnSi (CMS) and the Ag spacer, resulting in the suppression of the 90 degrees coupling at 290 K, and (c) it strongly depended on temperature. These results clarify that the Mn atoms diffused into an Ag spacer with paramagnetic character are the origin of the 90 degrees coupling in CMS-based CPP PSVs. Published under license by AIP Publishing.