Femtosecond electron and spin dynamics in Ni/W(110) films

The collapse of the magnetic exchange splitting in 7 monolayer thick epitaxial Ni/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+/-70 fs. At longer times the electronic system cools down and the magnetization is finally reestablished with a time constant of 3.2+/-0.2 ps.