Magnetic properties of ultrathin discontinuous Co/Pt multilayers: Comparison with short-range ordered and isotropicCoPt3films

Abstract

Magnetic properties of thin Co/Pt multilayers have been investigated in order to study the dependence of magnetization $M$, uniaxial anisotropy ${K}_{u}$, and Curie temperature ${T}_{\mathrm{C}}$ on the multilayer thickness, composition, and structure. A comparison between epitaxial submonolayer multilayers and epitaxial fcc ${\mathrm{CoPt}}_{3}$ alloy films with large perpendicular magnetic anisotropy (PMA) attributed to growth-induced Co clustering reveals significant differences in the temperature dependence of magnetization $M(T)$, despite the presence of thin planar Co platelets in both cases. Even the thinnest discontinuous multilayered structure shows a Langevin-like $M(T)$, while the alloy films with PMA show a broadened and enhanced $M(T)$ indicating a distribution of environments, including monolayer Co platelets separated by only 1--2 layers of Pt. These differences have been reproduced in Monte Carlo simulations, and are shown to be due to different distributions of Co-Co and Co-Pt nearest neighbors. The relatively uniform Co-Co coordination of even a discontinuous rough multilayer produces a Langevin-like $M(T)$, whereas the broader distribution associated with platelets in the PMA films results in a nearly linear $T$ dependence of $M$.