Experimental investigation of polaron effects inGa1−xMnxAsby time-resolved and continuous-wave midinfrared spectroscopy

Abstract

The magneto-optical properties of a $1\text{\ensuremath{-}}\ensuremath{\mu}\mathrm{m}$-thick ${\mathrm{Ga}}_{0.94}{\mathrm{Mn}}_{0.06}\mathrm{As}$ sample having a $110\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ Curie temperature are investigated by time-resolved pump-probe and continuous-wave (cw) midinfrared transmittance spectroscopies. The pump pulses are linearly polarized and have a $3.1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ energy, a $130\phantom{\rule{0.3em}{0ex}}\mathrm{fs}$ width, and a $660\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{J}∕{\mathrm{cm}}^{2}$ fluence. They produce a thermally driven demagnetization process in the hundreds of picosecond time scale. A three-temperature model based on one-dimensional diffusion equations was developed to compute the carrier, lattice, and spin temperatures in the material. We observed that an average photoinduced spin temperature increase near $3\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ leads to an augmentation of the Mn acceptor impurity binding energy in the range of $1\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$. cw absorption measurements were performed at temperatures ranging from $4\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, and a nonmonotonic temperature dependence of the position of the midinfrared absorption peak is found that is consistent with the increased binding energy observed by time-resolved measurements. The variation of the sample resistivity with temperature is phenomenologically related to the optical measurements. Results are compatible with a polaron percolation model of ferromagnetism.