Effects of interfacial noncollinear magnetic structures on spin-dependent conductance in Co₂MnSi/MgO/Co₂MnSi magnetic tunnel junctions: A first-principles study

We investigate the effects of spin-flip scattering on tunneling magnetoresistance (TMR) in magnetic tunnel junctions (MTJs) with half-metallic Co₂MnSi (CMS) and MgO on the basis of the first-principles calculations. We found that noncollinear magnetic structures of interfacial Co spin moments resulting from the thermal fluctuations cause spin-flip scattering, leading to a significant reduction of the TMR. Interface states originating from a projection of the majority-spin Δ₁ states of CMS in the minority-spin half-metallic gap because of the interfacial noncollinear magnetic structures play an important role in the spin-flip process. From these results, together with an estimated interfacial exchange stiffness constant, we conclude that the TMR ratio at room temperature in MTJs with half-metallic Co-based full-Heusler alloys can be attributed to the spin-flip scattering by the interfacial noncollinear magnetic structures as a result of the thermal fluctuation.