Modelling nonlocal nonlinear spin dynamics in antiferromagnetic orthoferrites.

Excitation with an ultrashort light pulse is arguably the only way to control spins in antiferromagnetic materials at both the nanoscale in space and ultrafast time scale. While recent experiments highlighted tantalising opportunities for spin switching and magnonics in antiferromagnets, the theoretical description of antiferromagnetic spin dynamics driven by strongly localised and ultrashort excitation is in its infancy. Here we report a theoretical model describing the nonlocal and nonlinear spin response to the excitation by light. We show that strongly localised ultrafast excitation can drive spin switching, which propagates in space and acts as a source of spin waves. Our theoretical formalism is readily available to describe current and future ultrafast spectroscopy experiments in antiferromagnets.