Ultrafast electron and magnetization dynamics of thin Ni and Co films on Cu(001) observed by time-resolved SHG

Utilizing pump-probe second-harmonic generation (SHG) with 150-fs, 800-nm l aser pulses, we investigated electron and magnetization dynamics of thin Ni and Co films on Cu(001) following optical excitation. A much longer electr onic relaxation time was found for Ni films than for Ni bulk. Various degre es of magnetic breakdown were induced in Ni and Co films of different thick ness, applying the variation of Curie temperature with film thickness. For Ni films systematic changes of pump fluence and substrate temperature are f ully consistent with the magnetization curve valid for thermal equilibrium.