Resonance Raman scattering in CdCr_{2}S_{4}: Magnetic-circular-polarization properties

Abstract

Spin-dependent (SD) phonon Raman scattering of Cd${\mathrm{Cr}}_{2}$${\mathrm{S}}_{4}$ is studied using a circularly polarized beam of a He-Ne (632.8-nm) laser in the Faraday configuration. It is found that magnetic-circular-polarization effects on the SD scattering are due to resonance with the "red-shifting" transitions in this ferromagnetic spinel. Anomalous temperature dependences of the Raman intensity for specific phonon lines $E$ (351 ${\mathrm{cm}}^{\ensuremath{-}1}$) and $F$ (394 ${\mathrm{cm}}^{\ensuremath{-}1}$) are explained by a phenomenological model which takes account of both resonance and magnetic-ordering effects for the scattering process. The mechanism for SD resonance scattering is shown to be closely connected to the absorption process which depends on magnetic ordering. Various models for the red-shifting transitions are discussed in the light of the present resonance Raman-scattering results for this ferromagnetic semiconductor.