Switchable Altermagnetism Induced by Polyhedral Rotation Distortion.

Abstract

Altermagnetism has emerged as a distinct class of unconventional magnetism, uniquely combining the nonrelativistic spin splitting of ferromagnets with the stray-field immunity of antiferromagnets. However, realizing altermagnetism driven by universal and strain-tunable structural geometry effects remains a critical challenge. Here, we introduce a mechanism for inducing altermagnetism via a polyhedral rotation distortion. We demonstrate that cooperative polyhedral rotations selectively break the symmetry operations enforcing spin degeneracy while preserving those required for altermagnetism. Crucially, the sign of the spin splitting is coupled to the direction of rotation distortion, providing a deterministic structural degree of freedom to switch the spin splitting. We validate this mechanism in two-dimensional MnX₂ (X = O, S, Se, Te) monolayers and reveal a significant strain-tuning effect, including a reversible phase transition between spin-degenerate antiferromagnetic and altermagnetic states. This work establishes polyhedral rotation as a design strategy for altermagnetism, offering a versatile platform for strain-controlled nanoscale spintronics.