Role of Berry phase theory for describing orbital magnetism: From magnetic heterostructures to topological orbital ferromagnets

TL;DR

This paper emphasizes the importance of the modern theory of orbital magnetization in accurately describing magnetic properties in complex materials, especially in inhomogeneous and topologically non-trivial systems, beyond traditional atom-centered models.

Contribution

It demonstrates the necessity of the modern orbital magnetization theory for inhomogeneous and topological materials, highlighting its limitations over conventional atom-centered approaches.

Findings

Modern theory is essential for topological orbital ferromagnets.

Atom-centered approximation fails in inhomogeneous systems.

Modern theory improves predictions for magnetic thin films and topological insulators.

Abstract

We address the importance of the modern theory of orbital magnetization for spintronics. Based on an all-electron first-principles approach, we demonstrate that the predictive power of the routinely employed "atom-centered" approximation is limited to materials like elemental bulk ferromagnets, while the application of the modern theory of orbital magnetization is crucial in chemically or structurally inhomogeneous systems such as magnetic thin films, and materials exhibiting non-trivial topology in reciprocal and real space,~e.g.,~Chern insulators or non-collinear systems. We find that the modern theory is particularly crucial for describing magnetism in a class of materials that we suggest here $-$ topological orbital ferromagnets.