Abstract
Excitation of multi-component materials by femtosecond laser pulses reveals interesting transient states.Using layer and element sensitive time-resolved magneto-optical Kerr effect in the pump-probe configuration,we evaluate the effect of fundamental parameters such as exchange interaction and spin currents on subpicosecond dynamics of magnetisation in exemplary systems: (i) Copper-doped ferromagnetic alloys and,(ii)Ni films deposited on gold underlayers.
In Copper-doped NiFe,we observe an anomalous speed-up of dynamics as the copper concentration is increased beyond 20%,contrary to expectations.Our analysis shows that this is due to the suppression of Nimoments stronger than Femoments in the alloy. We also show experimentally, the sudden reduction of the demagnetisation time constantat highpump fluences that was only theoretically predicted.In case of Ni films deposited on gold,we show that laser excitation of the ferromagnetic film causes a transient magnetic moment in the non-magnetic layer. We quantify the so far elusive amount of spin injection and thus the spin injection efficiency at the interface.
