Tunable magnetic anisotropy from higher-harmonics exchange scattering on the surface of a topological insulator

TL;DR

This paper demonstrates that higher-harmonics exchange scattering on topological insulator surfaces can induce tunable magnetic anisotropy, which varies with chemical potential and surface band structure, offering potential for magnetic control.

Contribution

It reveals a new mechanism for magnetic anisotropy arising from higher-harmonics exchange scattering, tunable via chemical potential and affected by surface warping.

Findings

Anisotropy magnitude and sign depend on chemical potential.

Hexagonal warping reduces and suppresses anisotropy.

The induced anisotropy can be comparable to intrinsic crystal field effects.

Abstract

We show that higher-harmonics exchange scattering from a magnetic adatom on the surface of a three dimensional topological insulator leads to a magnetic anisotropy whose magnitude and sign may be tuned by adjusting the chemical potential of the helical surface band. As chemical potential moves from the Dirac point towards the surface band edge, the surface normal is found to change from magnetic easy, to hard axis. Hexagonal warping is shown to diminish the region with easy axis anisotropy, and to suppress the anisotropy altogether. This indirect contribution can be comparable in magnitude to the intrinsic term arising from crystal field splitting and atomic spin-orbit coupling, and its tunability with chemical potential makes the two contributions experimentally discernible, and endows this source of anisotropy with potentially interesting magnetic functionality.