MAGNETIC POLARON OF GD2S3 STUDIED BY INFRARED-SPECTROSCOPY UNDER MAGNETIC-FIELD

Reflectivity spectra of a magnetic semiconductor Gd2S3 (=Gd(3-x)square (x)S(4), where square denotes vacancy and x congruent to 1/3) have bee n measured in the photon energy range from 2 meV to 0.5 eV at 14 K und er magnetic field up to 5 tesla. The energy gap of about 7 meV at 0 te sla was observed to become narrow as the magnetic field increases and to collapse at 3.3 tesla. The origin of the energy gap is attributed t o the trapped magnetic polaron. Another absorption band around 0.1 eV of which origin has been unclear is concluded to be the deep state of the magnetic polaron because it was shifted by the magnetic field.