Femtosecond x-ray absorption spectroscopy of spin and orbital angular momentum in photoexcited Ni films during ultrafast demagnetization

摘要

We follow the evolution of the spin and orbital angular momentum of a thin Ni film during ultrafast demagnetization, by means of x-ray magnetic circular dichroism. Both components decrease with a 130 ±40 fs time constant upon excitation with a femtosecond laser pulse. Additional x-ray absorption measurements reveal an increase in the spin-orbit interaction by 6 ± 2% during this process. This experimental observation of a transient change in spin-orbit interaction provides input for the theoretical modeling of the ultrafast demagnetization mechanism.