Perpendicular Magnetocrystalline Anisotropy on 3d Transition-Metals Multilayers – A First-principles Study

Magnetic tunnel junctions (MTJ) with perpendicular magnetocrystalline anisotropy (MCA) have much attention for applications to high-density, high-thermal stability, nonvolatile memories. Strong perpendicular MCA appears in transition-metal films such as Co/Pt, Co/Pd and CoFeB/Pd due to the strong hybridization between the 3d and 5d orbitals at the interfaces. The remaining challenge in these systems is to understand the role of the hcp-fcc phase transition that occurs in cobalt, which leads to the change of the easy magnetization direction. To address this challenge, the mechanisms of MCA in hcp-like and fcc-like stacking of Co-based 3d transition-metal multilayers are systematically investigated by using full-potential linearized augmented plane wave calculations. The MCA energy of possible atomic-layer alignments of Co-based films including Mn, Fe, and Ni layers is presented. The results predict that large perpendicular MCA can be achieved in Co/Ni multilayers for both hcp-like and fcc-like stackings. The large perpendicular MCA arises from a second-order effect of spin-orbit coupling between occupied and unoccupied Ni d_yz,xz states near the Fermi level. A promising transition-metal film for MTJ with giant perpendicular MCA and the preferred stacking stability is demonstrated.