Flexocurrent-induced magnetization: Strain gradient-induced magnetization in time-reversal symmetric systems

TL;DR

This paper demonstrates that nonuniform strain can induce magnetization in time-reversal symmetric nonmagnetic materials, expanding the understanding of strain-induced magnetic responses beyond traditional symmetry-breaking mechanisms.

Contribution

The authors develop a theoretical framework showing that strain gradients can generate magnetization in time-reversal symmetric systems, supported by examples like MoS2 and Janus monolayers.

Findings

Finite magnetization response in nonmagnetic materials due to strain gradients.

Symmetry analysis confirms the response is allowed in time-reversal symmetric systems.

Theoretical predictions align with symmetry considerations and material examples.

Abstract

Symmetry constraints determine which physical responses are allowed in a given system. Magnetization induced by strain fields, such as in piezomagnetic and flexomagnetic effects, has typically been considered in materials that break time-reversal symmetry. Here, we propose that nonuniform strain can induce magnetization even in nonmagnetic metals and semiconductors that preserve time-reversal symmetry. This mechanism differs from the conventional flexomagnetic effect: the strain gradient acts as a driving force on the electrons, generating magnetization in a manner closely analogous to current-induced magnetization. Treating the strain field as an external field, we derive a general expression for the magnetization induced by a strain gradient and demonstrate that this response is symmetry-allowed even in time-reversal symmetric systems. We apply our formulation to nonmagnetic systems that lack spatial inversion symmetry while preserving time-reversal symmetry, using a decorated square lattice, monolayer MoS$_2$, and monolayer Janus MoSSe as representative examples. We find a finite magnetization response to strain gradients, which is consistent with symmetry arguments, supporting the validity of our theoretical framework. These results offer a pathway for controlling magnetization in nonmagnetic materials using strain fields.