Resolving the genuine laser-induced ultrafast dynamics of exchange interaction in ferromagnet/antiferromagnet bilayers

The response of exchange coupled ferromagnet/antiferromagnet metallic bilayers to laser excitation down to the femtosecond time scale is investigated. Differently from previous attempts, the ultrafast dynamics of exchange interaction is deduced by carefully analyzing precessional transients of the ferromagnetic magnetization, measured by means of time-resolved magneto-optical Kerr effect, rather than by monitoring changes in the hysteresis loop as a function of pump-probe delay. Thereby we are able to estimate the characteristic time scale of laser-induced exchange-bias quenching in a polycrystalline Co/IrMn bilayer, tEB,0 = (0.7±0.5) ps. The fast decrease in exchange coupling upon laser heating is attributed to a spin disorder at the interface created by laser heating.