Magnetic properties of thin films of Co and of (CoPt) superstructures on Pt(100) and Pt(111)

Abstract

The magnetic properties of ${\mathrm{Co}}_{n}/\mathrm{Pt}(100),$ ${\mathrm{Co}}_{n}/\mathrm{Pt}(111),$ $({\mathrm{Co}}_{0.5}{\mathrm{Pt}}_{0.5}{)}_{n}/\mathrm{Pt}(100),$ $(\mathrm{CoPt}{)}_{n}/\mathrm{Pt}(100)$, and $(\mathrm{CoPt}{)}_{n}/\mathrm{Pt}(111),$ $n<~15$, are investigated using the relativistic spin-polarized screened Korringa-Kohn-Rostoker method. It is found that only the artificial superstructures $(\mathrm{CoPt}{)}_{n}/\mathrm{Pt}(100)$ and $(\mathrm{CoPt}{)}_{n}/\mathrm{Pt}(111)$ show a perpendicular magnetic anisotropy beyond $n=10$. For the free surfaces of Co on Pt in the case of the (100) orientation, a multiple reorientation transition below $n=7$ is found, while along (111) such a transition is predicted at about four layers of Co. For the homogeneous, statistically disordered alloy ${\mathrm{Co}}_{0.5}{\mathrm{Pt}}_{0.5}$ on Pt(100) the orientation of the magnetization remains in-plane for all n investigated. A comparison to experiment yields interesting insight into aspects of order and disorder, surface segregation, and phase separation frequently encountered in experimental studies of perpendicular magnetism in the Co/Pt system.