SPIN-LATTICE RELAXATION IN FERROMAGNETS STUDIED BY TIME-RESOLVED SPIN-POLARIZED PHOTOEMISSION

The spin-lattice relaxation time tau(sl) is the characteristic time needed for the energy transfer between the lattice and the spin system. It is demonstrated that tau(sl) can be determined with laser-induced spin-polarized photoemission. Upper and lower limits are derived from a single-pulse experiment using pulses of various time durations. It is found that tau(sl) of iron is shorter than 20 ns but longer than 30 ps. A direct measurement of tau(sl) is possible with a pump-probe experiment. One laser pulse heats the sample and a second time-delayed pulse is used to probe the magnetic state. Tau(sl) is found to be 100+/-80 ps for ferromagnetic gadolinium.