First-principles study of perpendicular magnetic anisotropy in CoFe/MgO and CoFe/Mg₃B₂O₆ interfaces

The CoFeB/MgO interface is important not only because of its ability to act as a good spin filter, but also because it exhibits significant magnetic interface anisotropy. However, there is experimental evidence that the mineral kotoite (Mg₃B₂O₆) forms at this interface, possibly as a result of B diffusion into the oxide. Recent calculations have demonstrated that kotoite is a surprisingly good spin filter material, despite the lack of cubic symmetry. It is not a priori clear how the perpendicular anisotropy is affected if kotoite forms at the interface. Hereby, we have performed first-principles density functional calculations to investigate the magnetic anisotropy of CoFe/kotoite interfaces. We find that the Co/Fe atoms bind strongly to O atoms of kotoite, and the CoFe/kotoite interfaces exhibit strong perpendicular magnetic anisotropy (PMA) comparable to that of CoFe/MgO interfaces. Analysis of the electronic structure shows that CoFe states having d_xz and d_yz character are strongly affected by the magnetization direction and play an important role in determining the magnetic anisotropy of both CoFe/kotoite and CoFe/MgO interfaces. Our observations are consistent with previous experimental observations of PMA. We demonstrate that the interface properties are only weakly affected by the formation of kotoite compared to MgO.