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.
@article{arxiv.2507.20701,
title = {Femtosecond Engineering of magnetic Domain Walls via Nonequilibrium Spin Textures},
author = {Yuzhu Fan and Gaolong Cao and Junlin Wang and Sheng Jiang and Jing Wu and Johan Åkerman and Jonas Weissenrieder},
journal= {arXiv preprint arXiv:2507.20701},
year = {2025}
}