Transient electronic and magnetic structures of nickel heated by ultrafast laser pulses

We investigate the evolution of the Ni electronic and magnetic structure on fs to ps time scales following fs-laser excitation. Within 200 fs after excitation the $\text{Ni}3d$ ferromagnetic moment is reduced as probed by x-ray magnetic circular dichroism. At the same time the $\text{Ni}3d$ electronic structure undergoes pronounced changes as demonstrated by x-ray absorption spectroscopy. We show that the latter persists also into thermal equilibrium which is reached on the ps time scale. Cluster calculations identify a reduction in $3d-4sp$ hybridization possibly associated with phonon-driven spin-flip excitations.