Extremely large spin-polarization in Co2MnSi based magnetic tunnel junctions

Abstract

We fabricated Co2MnSi/(Mg)/Al-O/CoFe MTJs using UHV magnetron sputtering. The interfacial chemical bond between Co2MnSi and Al-O was intensively optimized by changing plasma oxidation time for Al-O and by inserting a Mg layer. The Mg inserted layer between Co2MnSi and Al-O effectively suppressed the generation of interfacial magnetic impurities. Finally, we successfully observed a giant TMR ratio of 203% at 2 K in the MTJ with a 1.0 nm-Mg layer inserted. The spin-polarization for Co2MnSi estimated from this TMR ratio was 0.971.00, which indicated that an almost perfect spin-polarized state was achieved. We also investigated the relationship between the TMR ratio and the site-ordering level of Co2MnSi. As a result, we found that an L21-ordering state is not necessary to achieve high spin-polarization for Co2MnSi in MTJs.