Giant perpendicular magnetic anisotropy energies in CoPt thin films: Impact of reduced dimensionality and imperfections

TL;DR

This study investigates how reduced dimensionality and surface imperfections affect the magnetic anisotropy energy in CoPt thin films, revealing that surface chemistry and defects significantly influence magnetic properties.

Contribution

It provides new insights into the role of surface termination and defects on magnetic anisotropy in CoPt thin films through ab-initio calculations.

Findings

Pt-terminated films exhibit up to 1000% larger MAE than Co-terminated films.

Surface defects such as stacking faults reduce the MAE significantly.

Electronic structure analysis links MAE behavior to virtual bound states.

Abstract

The impact of reduced dimensionality on the magnetic properties of the tetragonal L1$_{0}$ CoPt alloy is investigated from ab-initio considering several kinds of surface defects. By exploring the dependence of the magnetocrystalline anisotropy energy (MAE) on the thickness of CoPt thin films, we demonstrate the crucial role of the chemical nature of the surface. For instance, Pt-terminated thin films exhibit huge MAEs which can be 1000% larger than those of Co-terminated films. Besides the perfect thin films, we scrutinize the effect of defective surfaces such as stacking faults or anti-sites on the surface layers. Both types of defects reduce considerably the MAE with respect to the one obtained for Pt-terminated thin films. A detailed analysis of the electronic structure of the thin films is provided with a careful comparison to the CoPt bulk case. The behavior of the MAEs is then related to the location of the different virtual bound states utilising second order perturbation theory.