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

Abstract

The magnetic properties of ${\mathrm{Co}}_n/\mathrm{Pt}\mathrm{}\left(100\right),$ ${\mathrm{Co}}_n/\mathrm{Pt}\mathrm{}\left(111\right),$ $({\mathrm{Co}}_{0.5}{\mathrm{Pt}}_{0.5}{)}_n/\mathrm{Pt}\mathrm{}(100),$ $(\mathrm{CoPt}{)}_n/\mathrm{Pt}\mathrm{}(100)\mathrm{}$, and $(\mathrm{CoPt}{)}_n/\mathrm{Pt}\mathrm{}(111),$ $n<~15$, are investigated using the relativistic spin-polarized screened Korringa-Kohn-Rostoker method. It is found that only the artificial superstructures $(\mathrm{CoPt}{)}_n/\mathrm{Pt}\mathrm{}(100)\mathrm{}$ and $(\mathrm{CoPt}{)}_n/\mathrm{Pt}\mathrm{}(111)\mathrm{}$ show a perpendicular magnetic anisotropy beyond $n=10\mathrm{}$. For the free surfaces of Co on Pt in the case of the (100) orientation, a multiple reorientation transition below $n=7\mathrm{}$ 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.