Terahertz spin-orbit torque as a drive of spin dynamics in the insulating antiferromagnet Cr$_{2}$O$_{3}$

TL;DR

This paper predicts that terahertz electric fields can induce spin-orbit torque in insulating antiferromagnet Cr₂O₃, enabling ultrafast control of its magnetic order through displacement currents.

Contribution

It introduces a novel mechanism for spin dynamics in insulators via displacement current-driven N{é}el spin-orbit torque, expanding spintronics to magnetic insulators.

Findings

Displacement current in Cr₂O₃ generates N{é}el spin-orbit torque.

The effect enables ultrafast control of antiferromagnetic order.

The mechanism competes with the linear magnetoelectric response.

Abstract

Contrary to conventional wisdom that spin dynamics induced by current are exclusive to metallic magnets, we theoretically predict that such phenomena can also be realized in magnetic insulators, specifically in the magnetoelectric antiferromagnet $\mathrm{Cr}_{2}\mathrm{O}_{3}$. We reveal that the displacement current driven by the THz electric field is able to generate a N{\'e}el spin-orbit torque in this insulating system. By introducing an alternative electric dipole order parameter arising from the dipole moment at $\mathrm{Cr}^{3+}$ sites, we combine symmetry analysis with a Lagrangian approach and uncover that the displacement current couples to the antiferromagnetic spins and enables ultrafast control of antiferromagnetic order. The derived equations of motion show that this effect competes with the linear magnetoelectric response, offering a novel pathway for manipulating antiferromagnetic order in insulators. Our findings establish insulator antiferromagnets as a viable platform for electric field driven antiferromagnetic spintronics and provide general design principles for non-metallic spin-orbit torque materials.