First-principles study of MnAl for its application in MgO-based perpendicular magnetic tunnel junctions

Abstract

MnAl, as a prospective candidate of magnetic electrode materials for MgO-based magnetic tunnel junctions, possesses several advantages including the spin polarized Δ1 band, relatively low Gilbert damping factor, and large perpendicular magnetic anisotropy. Here, we report a thorough first-principles investigation on MnAl/MgO/MnAl-magnetic tunnel junctions (MTJs). It is found that the bulk anisotropy density is 17.39 Merg/cm3, while the interfacial anisotropy contribution is evaluated to be 0.12 erg/cm2 and 0.44 erg/cm2 for Mn- and Al-terminated structures, respectively. The large anisotropy can be attributed to dyz and dz2 orbits. Furthermore, the formation of a Mn-O bond on the interface of MnAl/MgO is shown to be detrimental for the improvement of perpendicular anisotropy. On the other hand, a giant zero-bias tunneling magnetoresistance ratio is predicted and can be maintained over 2000% even for a bias up to 0.6 V for Mn-terminated MTJs. The in-plane spin transfer torque for Mn-terminated MTJs increases linearly with a bias up to 0.6 V due to the large net spin-polarized current. This work paves the way for the further application of MnAl-based perpendicular magnetic tunnel junctions.