Magnetic Vortex Dynamics Probed by Time-Resolved Magnetic Helicoidal Dichroism

The laser excitation of magnetization dynamics without applying external fields is a topic of high interest for its potential applications (e.g., magnetic memories, oscillators, and THz emitters). We explore the use of an ultrashort infrared laser pulse for triggering transient changes in a magnetic vortex, probing the induced dynamics by time-resolved magnetic helicoidal dichroism (MHD) in resonant extreme ultraviolet scattering. MHD describes the optical response of a magnetic sample upon sign reversal of either the light orbital angular momentum or the magnetization and was demonstrated to be sensitive to the sample spin texture. Here, we show that, in addition to the well-known ultrafast demagnetization and remagnetization laser-induced processes, the analysis of the MHD signal, supported by micromagnetic simulations, provides direct evidence of important transient reorganizations of the spin texture. In particular, we find that an ultrafast laser pulse of sufficient intensity can induce a surface transient magnetic texture where the vortex curling direction is reversed with respect to the bulk. This result provides insight into the preparation of metastable complex spin states in magnetic films by optical methods without applying an external field, which is of relevance for novel applications in data storage and manipulation.