Femtosecond Engineering of magnetic Domain Walls via Nonequilibrium Spin Textures

TL;DR

This study demonstrates ultrafast optical control of magnetic domain walls in ferrimagnetic films, revealing rapid formation, transient states, and a nonlinear nucleation mechanism on femtosecond timescales, advancing spintronic device potential.

Contribution

It introduces a real-time imaging approach combined with simulations to uncover the nonequilibrium formation dynamics of magnetic domain walls under ultrafast excitation.

Findings

Rapid formation of ordered DW arrays within 10 ps

Transient, asymmetric DW states observed

A nonlinear nucleation pathway involving hybrid transition states

Abstract

Ultrafast optical control of magnetic textures offers new opportunities for energy-efficient, high-speed spintronic devices. While uniform magnetization reversal via all-optical switching is well established, the formation dynamics of non-uniform domain walls (DWs) under ultrafast excitation remain poorly understood. Here, we use Lorentz ultrafast electron microscopy combined with transient optical grating excitation to directly image the real-time formation of DWs in a ferrimagnetic GdFeCo film. We observe a rapid evolution from disordered spin contrast to ordered DW arrays within 10 ps, including a transient, strongly asymmetric DW state. In a narrow fluence window, short-lived DWs form and spontaneously vanish within picoseconds. Multiscale simulations combining atomistic spin dynamics and micromagnetics reveal a nonlinear nucleation pathway involving a hybrid transition state where localized, unstable spin textures coalesce into metastable DWs. This nonequilibrium mechanism explains the observed asymmetry and spatial ordering, and establishes a framework for controlling spin textures in magnetic materials on femtosecond timescales.