Indication of Stochastic Photothermal Dynamics around a Topological Defect in a Chiral Magnet

TL;DR

This study explores the ultrafast stochastic recovery dynamics of magnetic order around topological defects in a chiral magnet following laser-induced phase transition, revealing defect-specific relaxation pathways.

Contribution

It provides the first experimental evidence of stochastic, defect-mediated recovery processes in topological magnetic textures using ultrafast microscopy.

Findings

Magnetic contrast recovery is anisotropic and delayed near dislocations.

Recovery dynamics involve multiple relaxation paths, indicating stochastic behavior.

Topological defects enhance stochasticity during magnetic phase transition recovery.

Abstract

Chiral magnets host topologically protected spin textures whose nonequilibrium dynamics are crucial in phase transitions and domain evolution, yet ultrafast defect-mediated processes remain poorly understood. Here, we investigate photothermally induced helical-to-paramagnetic phase transition in Co$_9$Zn$_9$Mn$_2$ using pump-probe Lorentz transmission electron microscopy (LTEM). Following the suppression of the magnetic stripe contrast induced by femtosecond pulsed laser, we observe a directional recovery process of magnetic order driven by the anisotropic thermal diffusion, toward the thick region that effectively acts as a heat sink. Remarkably, around a magnetic edge dislocation, the magnetic contrast recovery exhibits a pronounced delay accompanied by a transient blurring of LTEM contrast. These findings suggest that the recovery dynamics around the magnetic edge dislocation proceed through multiple relaxation paths that are selected stochastically. Our results indicate a possible enhancement of stochasticity around topological defects during the recovery dynamics of magnetic phase transitions.