In-plane magnetic anisotropy of Fe atoms on Bi$_2$Se$_3$(111)

TL;DR

This study investigates the magnetic anisotropy of Fe atoms on Bi$_2$Se$_3$, revealing an in-plane magnetic easy axis due to crystal field and hybridization effects, challenging previous assumptions about magnetic gap opening.

Contribution

It provides a comprehensive experimental and theoretical analysis showing Fe adatoms have an in-plane magnetic easy axis on Bi$_2$Se$_3$, contrary to prior expectations.

Findings

Fe adatoms exhibit an in-plane magnetic easy axis

Surface relaxation influences magnetic anisotropy

Ab initio calculations explain the in-plane easy axis

Abstract

The robustness of the gapless topological surface state hosted by a 3D topological insulator against perturbations of magnetic origin has been the focus of recent investigations. We present a comprehensive study of the magnetic properties of Fe impurities on a prototypical 3D topological insulator Bi$_2$Se$_3$ using local low temperature scanning tunneling microscopy and integral x-ray magnetic circular dichroism techniques. Single Fe adatoms on the Bi$_2$Se$_3$ surface, in the coverage range $\approx 1%$ are heavily relaxed into the surface and exhibit a magnetic easy axis within the surface-plane, contrary to what was assumed in recent investigations on the opening of a gap. Using \textit{ab initio} approaches, we demonstrate that an in-plane easy axis arises from the combination of the crystal field and dynamic hybridization effects.