Bound magnetic polarons belowT=1 K

Large bound magnetic polarons are observed at temperatures down to T=0.13 K (dilution re- frigerator) for donor electrons in Cd_1-x{Mn}ₓ$Se, using spin-flip Raman scattering. Variations of the electron Zeeman energy with temperature, in zero magnetic field, clearly demonstrate the cooperative s-d exchange of the polaron, quantitatively confirming the theoretical model. The increase in polaron energy below 2 K arises from a dramatic increase in the magnetic susceptibility (eightfold), which we model by considering higher-neighbor Mn²⁺-Mn²⁺ interactions.