First-principles study on magnetocrystalline anisotropy of cobalt films: hcp vs fcc

Abstract

In this study, density functional calculations are performed on magnetocrystalline anisotropy (MCA) of hcp and fcc Co films to reveal influence of symmetry, thickness, and surface. First, MCA of bulk is revisited. MCA energy (EMCA) of hcp is 15.61 μeV/atom, two orders of magnitude larger than 0.53 μeV/atom of fcc Co. Smaller EMCA of fcc Co originates from the negative contributions from the highly peaked unoccupied minority |m|=1 states at Fermi level (EF). In Co films, EMCA is significantly enhanced to 175.90 and 211.48 μeV/atom at both hcp and fcc surfaces, resulting in the same order of magnitude for both the films. Substantial EMCA enhancement stems from the increased occupied and unoccupied minority |m|=2 states located very close to EF. Strong EMCA oscillation with thickness is observed for less than 10 monolayers, whose origin comes from the quantum well |m|=1 states at EF.