Time-resolved x-ray magnetic circular dichroism study of ultrafast demagnetization in a CoPd ferromagnetic film excited by circularly polarized laser pulse

The magnetization dynamics of CoPd films excited by circularly polarized ultrashort laser pulses is studied by time-resolved x-ray magnetic circular dichroism. In those films the ultrafast dynamics measured at the Co-L-3 edge is strongly sensitive to the orbitalmagnetic moment L-z. The amount of angular momentum transferred by the circularly polarized ultrashort laser pulses to the ferromagnetic films is evaluated to +/- 0.1 (h) over bar /atom, which is above the detection limit of the experiment. Despite this, no polarization-dependent difference on the magnetization dynamics could be evidenced. These results are explained by ultrafast electronic relaxation mechanisms of the transferred angular momentum, faster than similar to 100 fs. This experiment sets the methodology as well as an upper time limit for determination of angular momentum relaxation processes.