In all-optical pump-probe experiments on ferromagnetic layers, the determination of the temperature under the pump laser spot is crucial for a quantitative modeling of the magnetization dynamics. We present here a method to quantify this thermal gradient, exemplified on a (Ga, Mn)(As, P) ferromagnetic semiconductor layer on a GaAs substrate. To estimate the local steady-state temperature, we use the coercive field as a thermometer. The probe records the hysteresis cycle spatially across the hot spot, using the magnetic linear birefringence/dichroism of the sample. Our results are analyzed using the heat diffusion equation with two fitting parameters, the thermal conductivity of the layer/substrate sample and the thermal resistance between the substrate and the thermostat. This opens the way to a quantitative modeling of laser pulse-triggered magnetization dynamics in the presence of transient temperature effects.
Steady-state thermal gradient induced by pulsed laser excitation in a ferromagnetic layer
S. Shihab, L. Thevenard, A. Lemaître, J.-Y. Duquesne, C. Gourdon; Steady-state thermal gradient induced by pulsed laser excitation in a ferromagnetic layer. J. Appl. Phys. 21 April 2016; 119 (15): 153904. https://doi.org/10.1063/1.4947226
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