Surface magnetism of L10 CoPt alloy: first principles predictions

Abstract

We used the first-principles density functional theory (DFT) to predict the magnetic properties of (1 0 0), (0 0 1), (1 0 1), (1 1 0), and (1 1 1) surfaces of L10 ordered CoPt alloy. Our results indicate that bulk-terminated CoPt surfaces exhibit magnetic moment higher than that of bulk CoPt crystal and surface magnetic anisotropy favoring in-plane magnetization. Moreover, our DFT calculations predict that Pt prefers to segregate to the outermost layer of all these five CoPt surfaces with energy gain in the range of 0.05–0.47 eV for each segregated Pt atom. Comparing the structural and magnetic properties of the bulk-terminated and Pt-segregated CoPt surfaces, we found that Pt surface segregation led to larger contraction relaxation, reduced magnetic moments (with the exception of (1 1 0) surface), smaller spin canting angles, and an out-of-plane contribution to the surface magnetic anisotropy energy of the CoPt surfaces. Furthermore, our electronic structure analysis suggests that the change in the density of minority spin states of surface Co atoms mainly underlies the observed phenomena related to the surface magnetism of L10 CoPt alloy.