Nanoscale Spatial Dependence of Photoinduced Structural Phase Transition in FeRh

Simultaneous temporal and spatial characterization of materials with high resolution provides multidimensional data essential for a deeper understanding of nanoscale heterogeneities that arise from complex interactions during solid-solid phase transitions.Time-resolved hard x-ray microscopy has unique capabilities to provide a direct structural probe. Here, using newly developed x-ray diffraction microscopy with unprecedented 100 ps and 30 nm resolution at the Advanced Photon Source, we have observed the nanoscale dependence of the structural relaxation dynamics following ultrafast laser excitation of an FeRh thin film. The spatial dependence is linked to variations in spatially inhomogeneous strain, resulting in different thresholds for driving the antiferromagnetic-ferromagnetic phase transition. In addition, we have found the spatially different degree of the broadening of transition in temperature near nano-island regions. The observed relationship between lattice parameter and transition threshold gives new insight on the photoinduced phase transition at the nanoscale and has important implications in heat-assisted magnetic recording.