Study on lattice symmetry of sputtered Co–Cu–Pt metastable ordered thin films

Abstract

The lattice symmetry and atomic stacking sequence of Cu-doped metastable L11 Co50Pt50 (Co50−xCuxPt50) films with thicknesses varied from 5 to 50nm were examined by X-ray diffraction along the (10.1) diffraction rod. Replacement of Co with Cu significantly decreases the linewidth of the (111) superlattice diffraction peak, revealing reduced defect density. The crystal symmetry of CoPt L11 is identified as face-centered. After the addition of Cu (x≥23), it evolves into rhombohedral, which is the thermodynamically equilibrium structure of CuPt. Furthermore, the decrease in film thickness results in the modification of structure in CoPt binary films, forming pseudo-hexagonal phase. As the film thickness is decreased from 10 to 5nm, the component of pseudo-hexagonal phase increases from 7.1vol.% to 13.6vol.%. However, such a phase evolution disappears in the films with x=23. The stabilization of rhombohedral L11 promotes the alignment of magnetic easy-axis, yielding a high perpendicular remanence ratio and negligible in-plane magnetic component, even in the 5nm-thick sample. The presented results provide detailed information for the understanding of the relation between structure and magnetic properties of metastable CoPt-based L11 films.