# Impact of single atomic defects and vacancies on the magnetic anisotropy energy of CoPt thin films

## TL;DR

This study uses first-principles calculations to show how surface vacancies and adatoms significantly alter the magnetic anisotropy energy of CoPt thin films, potentially switching their magnetic orientation.

## Contribution

It reveals how atomic-scale defects can change the magnetic anisotropy in CoPt thin films, providing insights for magnetic material engineering.

## Key findings

- Defects induce in-plane magnetic anisotropy in CoPt films.
- Pt vacancies have the largest impact on MAE.
- Fe adatoms and Pt vacancies can switch MAE from out-of-plane to in-plane.

## Abstract

The impact of surface vacancies and single adatoms on the magnetic properties of tetragonal {\bf{L1}$_{0}$} CoPt thin films is investigated from first principles. We consider Co and Fe single adatoms deposited on a Pt-terminated thin film while a Pt adatom is assumed to be supported by a Co-terminated film. The vacancy is injected in the top-surface layer of the films with both types of termination. After finding the most stable location of the defects, we discuss their magnetic properties tight to those of the substrate and investigate the magnetic crystalline anisotropy energy (MAE). Previous simulations [Brahimi et al. J. Phys.: Condens. Matter. \textbf{28}, 496002 (2016)] predicted a large out-of-plane surface MAE for the Pt-terminated CoPt films (4 meV per f.u.) in contrast to in-plane surface MAE for Co-terminated films (-1 meV per f.u.). Here, we find that the surface MAE is significantly modified upon the presence of the atomic defects. All investigated defects induce an in-plane MAE, which is large enough for Fe adatom and Pt vacancy to switch the surface MAE from out-of-plane to in-plane for the Pt-terminated films. Interestingly, among the investigated defects Pt vacancy has the largest effect on the MAE in contrast to Co vacancy, which induced the smallest but still significant effect. This behavior is explained in terms of the orbital moment anisotropy of the thin films.