Speed limits of the laser-induced phase transition in FeRh

Abstract

We use ultrafast x-ray diffraction (UXRD) and the polar time-resolved magneto-optical Kerr effect (tr-MOKE) to study the laser-induced metamagnetic phase transition in two FeRh films with thicknesses below and above the optical penetration depth. In the thin film, we identify an intrinsic timescale for the light-induced nucleation of ferromagnetic (FM) domains in the antiferromagnetic material of $8\text{ps}$ that is substantially slower than the speed of sound. For the inhomogeneously excited thicker film, only the optically excited near-surface part transforms within $8\text{ps}$. For strong excitations we observe an additional slow rise of the FM phase, which we experimentally relate to a growth of the FM phase into the depth of the layer by comparing the transient magnetization in front- and backside excitation geometry. In the lower lying parts of the film, which are only excited via near-equilibrium heat transport, the FM phase emerges significantly slower than $8\text{ps}$ after heating above the transition temperature.

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Cited by in corpus (3)

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• Non-thermal electrons open the non-equilibrium pathway of the phase transition in FeRh
• Dislocation-Driven Nucleation Type Switching Across Repeated Ultrafast Magnetostructural Phase Transition