Magnetic anisotropy of vicinal (001) fcc Co films: role of crystal splitting and structure relaxation in step-decoration effect

TL;DR

This study investigates how step decoration and atomic relaxation influence magnetic anisotropy in ultrathin Co films, revealing that local electronic structure and atomic relaxation significantly affect magnetic properties, aligning well with experimental observations.

Contribution

It demonstrates that step decoration impacts magnetic anisotropy primarily through local electronic structure changes and atomic relaxation effects, providing a detailed theoretical explanation.

Findings

Step decoration reduces UIP-MA constant significantly when orbital splitting is considered.

Atomic relaxation around the step causes notable shifts in magnetic anisotropy.

Charge transfer effects between Cu and Co are minimal in influencing UIP-MA.

Abstract

The uniaxial in-plane magnetic anisotropy (UIP-MA) constant is calculated for a single step on the (001) surface of fcc Co($N$) films. The calculations are done for both an undecorated step and the step decorated with one or more, up to 7, Cu wires. Our objective is to explain the mechanisms by which the decoration decreases the UIP-MA constant, which is the effect observed experimentally for ultrathin Co films deposited on vicinal (001) Cu surfaces and can lead to reorientation of magnetization within the film plane. Theoretical calculations performed with a realistic tight-binding model show that the step decoration changes the UIP-MA constant significantly only if the splitting between the on-site energies of various $d$-orbitals is included for atoms located near the step edge. The local relaxation of atomic structure around the step is also shown to have a significant effect on the shift of the UIP-MA constant. The influence of these two relevant factors is analyzed further by examining individual contributions to the UIP-MA constant from atoms around the step. The magnitude of the obtained UIP-MA shift agrees well with experimental data. It is also found that an additional shift due to possible charge transfer between Cu and Co atoms is very small.