Photo-induced antiferromagnetic-ferromagnetic and spin-state transition in a double-perovskite cobalt oxide thin film

Abstract Investigation of ultrafast dynamic behaviors can provide novel insights about the coupling mechanisms among multiple degrees of freedom in condensed matters, such as lattice, magnetism and electronic structure. Here we investigate both the ferromagnetic (FM) and antiferromagnetic (AFM) dynamics of a strongly correlated oxide system, GdBaCo 2 O 5.5 thin film by time-resolved x-ray magnetic circular dichroism in reflectivity (XMCDR) and resonant magnetic x-ray diffraction (RMXD). A photo-induced AFM-FM transition characterized by an increase of the transient XMCDR (sensitive to FM order) beyond the unpumped value and a decay of RMXD (sensitive to AFM order) was observed. The photon-energy dependence of the transient XMCDR and reflectivity could be interpreted as a concomitant photo-induced spin-state transition (SST). The AFM-FM transition and SST couple with each other in the time domain, resulting in unusual dynamic behaviors of the magnetism.