Temperature-induced spin reversal in n-GaAs.

Free and bound electrons in bulk GaAs are investigated by cyclotron resonance in the freeze out regime at temperatures below 40 K. A temperature-induced reversal of the relative intensities of the spin split free electron transition 0 to 1 is observed, providing strong evidence for a spin reversal at a temperature of about 25 K. In contrast, no spin reversal is found for the single electron transition 1s to 2psubplus1 of the shallow donors.