Coherent terahertz control of antiferromagnetic order in the intercalated transition metal dichalcogenide.*

Antiferromagnetic (AFM) materials have been widely discussed as potential replacements for conventional ferromagnetic memory devices because of their stability in external magnetic fields and fast terahertz (THz) switching timescales. Recent work has shown that the AFM metal Fe_1/3NbS₂ can be electrically switched using remarkably low current densities. However, optical switching of Fe_1/3NbS₂ using a THz electrical field has not yet been demonstrated. Here, we perform static polar Kerr and THz-induced dynamic Kerr rotation measurements, combined with neutron scattering experiments and density-functional theory (DFT) calculations to investigate the AFM switching mechanisms in Fe_1/3NbS₂. We confirm the non-collinear nature of the AFM ordering below the Néel temperature and observe a THz-induced Kerr ellipticity that persists at temperatures three times higher than the Néel temperature. These findings underscore the presence of glassy dynamics in Fe_1/3NbS₂ and highlight the possibility of manipulating antiferromagnetic ordering in metals using THz electric fields.