Photoinduced giant magnetic polarons in EuTe

Photoinduced magnetic polarons in EuTe, with a magnetic moment of several hundred Bohr magnetons, were investigated as a function of pump intensity and temperature by pump-probe Faraday rotation. The quantum efficiency for optical generation of magnetic polarons is found to be 0.09. The pump-intensity dependence of the photoinduced Faraday rotation shows a sublinear increase, from which we deduce that the population of photoexcited polarons is limited by a maximum value of $4.5\ifmmode\times\else\texttimes\fi{}{10}^{15}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. This is four orders of magnitude less than the concentration of polarons that would completely fill the crystal, which suggests that the photoexcited polarons are anchored by defects. In addition to the generation of polarons, at high pump densities the modulated pump light also causes a small alternating heating of the illuminated region. The temperature dependence of the polaron magnetic moment is well described by the Curie--Weiss law. Above 100 K, polarons are thermally quenched with an activation energy of 11 meV.