López-Flores, V.; Arabski, J.; Stamm, C.; Halté, V.; Pontius, N.; Beaurepaire, E.; Boeglin, C.: Time-resolved x-ray magnetic circular dichroism study of ultrafast demagnetization in a CoPd ferromagnetic film excited by circularly polarized laser pulse. Physical Review B 86 (2012), p. 014424/1-6

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-L3 edge is strongly sensitive to the orbitalmagnetic moment Lz. The amount of angular momentum transferred by the circularly polarized ultrashort laser pulses to the ferromagnetic films is evaluated to ±0.1 ¯h/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 ∼100 fs. This experiment sets the methodology as well as an upper time limit for determination of angular momentum relaxation processes.