Activation of anomalous Hall effect and orbital magnetization by domain walls in altermagnets

TL;DR

This paper shows that domain walls in pure altermagnets can activate the anomalous Hall effect and orbital magnetization, which are otherwise forbidden by symmetry, revealing new ways to control Hall transport and magnetism.

Contribution

It demonstrates that domain walls lift symmetry constraints in pure altermagnets, enabling the activation of AHE and orbital magnetization, a novel mechanism for magnetic control.

Findings

Domain walls induce anomalous Hall effect in pure altermagnets.

Orbital magnetization is closely related to domain wall effects.

External magnetic fields can control domain wall arrangements and net AHE.

Abstract

Altermagnets are an emerging class of unconventional antiferromagnets, characterized by a N\'eel ordering that does not break the translation symmetry of the underlying lattice. Depending on the orientation of the N\'eel vector, the anomalous Hall effect (AHE) may or may not exist. In the so-called pure altermagnets, AHE is forbidden by the magnetic symmetry. Here, we demonstrate that in pure altermagnets, the domain walls can lift the symmetry constraints, thereby activating the AHE and orbital magnetization. Taking a representative example of a rutile-lattice tight-binding minimal model in slab geometry, we use the linear response theory to demonstrate the emergence of the domain wall AHE, finding that it is closely related with the orbital magnetization, while the spin magnetization does not play a significant role. Using Landau theory, we argue that while for a random arrangement of $\pi$ domain walls, the contributions from the individual domain walls will cancel one another, an external magnetic field will favor domain-wall arrangements with specific chirality giving rise to a net AHE signal. Using group theory, we discuss how these findings can be generalized straightforwardly to certain other classes of altermagnets. Our work reveals a crucial role of the domain walls in the understanding of the Hall transport and orbital magnetism of altermagnets.