Growth-induced magnetic anisotropy and clustering in vapor-deposited Co-Pt alloy films

Polycrystalline and epitaxial (100)-, (110)-, and (111)-oriented ${\mathrm{CoPt}}_{3}$ and ${\mathrm{Co}}_{0.35}{\mathrm{Pt}}_{0.65}$ films were deposited at various growth rates and over a range of growth temperatures from -50 to 800 \ifmmode^\circ\else\textdegree\fi{}C. Films grown at moderate temperatures (200--400 \ifmmode^\circ\else\textdegree\fi{}C) exhibit remarkable growth-induced properties: perpendicular magnetic anisotropy and large coercivity, as well as enhanced Curie temperature and low-temperature saturation magnetization. Magnetic measurements indicate significant Co clustering in these epitaxial fcc films. These properties are independent of crystallographic orientation, increase with increasing growth temperature, and vanish with annealing. We propose that the correlation between magnetic inhomogeneity, magnetic anisotropy, and enhanced moment is explained by clustering of Co into thin platelets in a Pt-rich lattice. This clustering occurs at the growth surface and is trapped into the growing film by low bulk atomic mobility.