Band engineering for large perpendicular magnetocrystalline anisotropy and low magnetic Gilbert damping constant by anion substitution at Fe/MgO interface

Abstract

Large interfacial perpendicular magnetocrystalline anisotropy (iPMA) and low Gilbert magnetic damping constant (α) in magnetic tunnel junctions (MTJs) are desired to achieve higher storage density and lower standby power operations in magnetic random-access memory. This work theoretically investigates effects of nitrogen and fluoride anions (N-anion and F-anion) substitution on the MgO barrier interface of Fe/MgO/Fe MTJ for iPMA and α using first-principles calculations. We find that the N-anion substitution significantly enhances iPMA by four times and reduces α by 65% compared to the pristine Fe/MgO/Fe, indicating a guideline toward an MTJ with large iPMA and low α simultaneously. The mechanism is explained by a band realignment at the Fermi level (EF) where Fe d±1 (dxz,dyz) orbitals at the interface are pushed above and below EF but Fe d±2 (dxy, dx2−y2) orbitals remain at EF by the N-anion substitution.