Accelerating the Laser-Induced Phase Transition in Nanostructured FeRh via Plasmonic Absorption

Abstract

By ultrafast x-ray diffraction (UXRD), it is shown that the laser-induced magnetostructural phase transition in FeRh nanoislands proceeds faster and more complete than in continuous films. An intrinsic 8 ps timescale is observed for the nucleation of ferromagnetic (FM) domains in the optically excited fraction of both types of samples. For the continuous film, the substrate-near regions are not directly exposed to light and are only slowly transformed to the FM state after heating above the transition temperature via near-equilibrium heat transport. Numerical modeling of the absorption in the investigated nanoislands reveals a strong plasmonic contribution near the FeRh/MgO interface. The larger absorption and the optical excitation of the electrons in nearly the entire volume of the nanoislands enables a rapid phase transition throughout the entire volume at the intrinsic nucleation timescale. Nanostructuring FeRh thin films by solid state dewetting make the laser-induced antiferromagnetic to ferromagnetic phase transition more efficient and speed the switching up to the intrinsic timescale. Ultrafast x-ray diffraction experiments directly measure the structural order parameter averaged over the entire film. Finite element modeling reveals the enhanced plasmonic light absorption near the substrate as the crucial factor. imageBy ultrafast x-ray diffraction (UXRD), it is shown that the laser-induced magnetostructural phase transition in FeRh nanoislands proceeds faster and more complete than in continuous films. An intrinsic 8 ps timescale is observed for the nucleation of ferromagnetic (FM) domains in the optically excited fraction of both types of samples. For the continuous film, the substrate-near regions are not directly exposed to light and are only slowly transformed to the FM state after heating above the transition temperature via near-equilibrium heat transport. Numerical modeling of the absorption in the investigated nanoislands reveals a strong plasmonic contribution near the FeRh/MgO interface. The larger absorption and the optical excitation of the electrons in nearly the entire volume of the nanoislands enables a rapid phase transition throughout the entire volume at the intrinsic nucleation timescale. Nanostructuring FeRh thin films by solid state dewetting make the laser-induced antiferromagnetic to ferromagnetic phase transition more efficient and speed the switching up to the intrinsic timescale. Ultrafast x-ray diffraction experiments directly measure the structural order parameter averaged over the entire film. Finite element modeling reveals the enhanced plasmonic light absorption near the substrate as the crucial factor. image