Magnetic-field-dependent Raman scattering in EuSe

Abstract

A new type of symmetry-forbidden resonant Raman scattering has been observed in the magnetic semiconductor EuSe at low temperatures and in an applied magnetic field. The most striking difference between this phenomenon and previously observed resonant Raman scattering is the observed dependence of the scattering intensity in EuSe on the magnitude and direction of the applied magnetic field. The intensity of the symmetry-forbidden scattering is observed to increase monotonically with increasing magnetic field strength for fields as high as 100 kG, increasing most rapidly in the low-field regime below the saturation magnetization. The scattering intensity is found to depend on the angle between the polarization of the incident light and the magnetic field, with the maximum scattering intensity observed when the incident beam is polarized normal to the applied magnetic field. This symmetry-forbidden scattering is observed only for temperatures below the magnetic critical temperature, T<TC. The observed scattering in EuSe exhibits a resonant-type behavior similar to that observed in symmetry-forbidden resonant Raman scattering in nonmagnetic materials in terms of (1) a strong dependence of the scattering intensity on the laser excitation energy, (2) the peak intensity occurring at the zone-center LO-phonon frequency LO, (3) observation of harmonic structure at multiples of LO, (4) relatively large scattering intensity and narrow linewidth, and (5) occurrence only in the diagonal scattering geometry where the incident and scattered light are similarly polarized. To interpret the results of this new type of symmetry-forbidden resonant Raman scattering, we have considered various models for resonant Raman scattering in which the effects of an external magnetic field on the electronic structure of EuSe are treated explicitly. We have found all existing models to be inadequate for the explanation of the experimental data. © 1974 The American Physical Society.