Optical Observation of Magnetic-Field-Induced Spin Alignment in Antiferromagnetic EuTe

The effects of spin alignment induced by a large external magnetic field have been observed in the optical reflectivity spectra of antiferromagnetic EuTe at 1.5 K. By comparison with the reflectivity spectra of ferromagnetic EuO, EuS, and EuSe, we conclude that we have observed the transition from an antiferromagnetic superlattice band splitting to the ferromagnetic exchange splitting that occurs with complete spin alignment at $H\sim 80$ kOe.