Stable surface structures and magnetic properties of L1(0)-ordered CoPt thin films according to thin film layer thickness.

Magnetic thin films are expected to be a promising substitute for existing semiconductor materials in the memory device industry due to their stable non-volatility, fast reading/writing speed, and durability. Because of the potential of thin film magnetic materials, Co-Pt alloys have attracted attention for application in magnetic memory devices due to their great magnetic anisotropy energy. In this paper, the stable surface structures of L1(0)-ordered CoPt alloys on a Pt (001) surface according to the thickness of the CoPt thin films was investigated using density functional calculations. The surface phase diagram of the Co-Pt alloys was first obtained to find the most stable surface phases of Co-Pt, and finally the perpendicular A, Pt-rich, perpendicular C and Co-rich B phases were found to be the most stable Co-Pt surface phases considering a thin film thickness from 1 to 4 MLs. Through calculation of the magnetic properties and the analysis of the spin-polarized 3d-electron density of the states of these stable surface phases, the changes in the magnetic properties were found to originate from the change in the relative electron filling in the 3d(x2-y2) and 3d(z2) orbitals of the Co atoms.