Real-time temperature dynamics in exchange-biased bilayers upon laser excitation

A hot-spin and phonon gas in an exchange-biased metallic bilayer is induced by an 8.5-ps laser excitation. The spin-lattice temperature dynamics is sensed in real time by the time evolution of the exchange bias field on the picosecond time scale. A calibration with temperature-dependent quasi-static Kerr measurements yields a pump-pulse induced temperature increase of about 100°C at the interface. Upon photoexcitation, the exchange coupling across the interface between the ferromagnetic and antiferromagnetic layer is reduced within the first 10 ps, leading to a reduction of the bias field to about 50% of its initial value. The fast thermal unpinning of the exchange coupling is followed by a heat-diffusion dominated recovery with a relaxation time on the order of 160 ps. A heat transport analysis reveals the diffusivity of the bilayer system.