Theory of spin-disorder Raman scattering in magnetic semiconductors

Inelastic light scattering from non-zone-center phonons in the magnetic phases of the europium chalcogenides is interpreted in terms of two-spin correlation functions. Calculations of the Raman line shape in paramagnetic EuS are presented in addition to predictions of the temperature dependence of the centroid and integrated intensities of the first-order Raman spectra of all four europium chalcogenides. In the critical region, analytical expressions which relate the temperature dependence of the integrated intensity to the correlation length $\kappa$ are derived. The calculations make use of a formalism which relates the Raman and conductivity tensors. The symmetry operations of time reversal and spatial inversion are used to show that the scattering tensor arising from a one-phonon-one-spin mechanism is symmetric under the interchange of the incident and scattered photons. The results are compared with existing experiments and the temperature dependence of the characteristic spin frequency in paramagnetic EuS is inferred.