Femtosecond Electron and Spin Dynamics inNi/W(110)Films

The collapse of the magnetic exchange splitting in 7 monolayer thick epitaxial $\mathrm{N}\mathrm{i}/\mathrm{W}(110)$ films following a femtosecond laser pulse was measured using time-resolved photoemission spectroscopy. Ultrafast demagnetization during the laser induced hot electron cascade proceeds via spin-flip excitations with a relaxation time constant of $300\pm 70\mathrm{f}\mathrm{s}$. At longer times the electronic system cools down and the magnetization is finally reestablished with a time constant of $3.2\pm 0.2\mathrm{p}\mathrm{s}$.