Laser-driven formation of transient local ferromagnetism in FeRh thin films

Highlights: • We present the first spatial-resolved laser-induced magnetization experiments on the equiatomic FeRh alloy. • Time-resolved optical pump and X-ray probe in a photoelectron emission microscope. • We demonstrate the existence of an intrinsic time limit for the magnetization phase transition in FeRh. - Abstract: The antiferromagnetic to ferromagnetic phase transition in FeRh can be induced globally by either heating the material above its phase transition temperature or applying a combination of external stimuli (such as mechanical strain, electric/magnetic fields) on the material preheated close to its transition temperature. On the other hand, to locally induce this phase transition is more desirable for applications and requires a confined source of energy such as a focused laser beam. Here we combine laser excitation with X-ray magnetic imaging to determine the effect of laser heating on the local and transient magnetization of FeRh using time-resolved photoelectron emission microscopy. Excitation by an ultrashort laser pulse generates a local ferromagnetic state within 0.6 ns which recovers its initial antiferromagnetic state after a further 2 ns. The form of the domains during the growth and diminution of ferromagnetic ordering suggests an intrinsic speed limit for magnetic and structural changes.