Ultrafast control of spin order by linearly polarized light in noncollinear antiferromagnetic metals

TL;DR

This paper demonstrates ultrafast, non-thermal control of spin order in noncollinear antiferromagnetic metals using linearly polarized femtosecond laser pulses, revealing a novel polarization-dependent magnetic response.

Contribution

It introduces a new method for controlling magnetic order in metals via laser polarization, showing effects beyond heat-driven or helicity-dependent mechanisms.

Findings

Sub-picosecond changes in magnetic order observed

Magneto-optical response depends on pump-probe polarization orientation

Effect persists across various materials, wavelengths, fluences, and temperatures

Abstract

The non-thermal optical control of magnetic order offers a promising route to ultrafast, energy-efficient information technologies. Although optical manipulation of magnetism in metals has been extensively studied, experimentally demonstrated effects have so far been limited to heat-driven dynamics or helicity-dependent mechanisms. Here, we report ultrafast non-thermal control of spin order in noncollinear antiferromagnetic Mn-based antiperovskite nitrides Mn3NiN and Mn3GaN, driven solely by the polarization orientation of linearly polarized femtosecond laser pulses. Using time-resolved magneto-optical pump-probe experiments based on the Voigt effect, we observe sub-picosecond changes in magnetic order followed by picosecond relaxation. The magneto-optical response depends on the relative orientation of the pump and probe polarization planes, with linear-polarization dependence reaching up to 95%, a value unprecedented in metallic magnets. This phenomenon is observed in two different materials and persists over a wide range of excitation wavelengths, fluences, and temperatures, demonstrating its robustness. Symmetry analysis and microscopic modeling indicate that optically induced torques alone cannot fully explain the observed dynamics. We therefore propose laser-induced formation of transient spin-spiral states as a possible excitation mechanism.