Phonons and magnetic order in ferromagnetic CdCr2Se4 and CdCr2S4

TLDR: In this paper, measurements of the Raman effect on single crystal ferromagnetic CdCr2Se4 and CcCr2S4 as a function of temperature were reported.

Abstract: Measurements are reported of the Raman effect on single crystal ferromagnetic CdCr2Se4 and CdCr2S4 as a function of temperature. The lines observed at 158 cm−1, 172 cm−1 and 241 cm−1 for CdCr2Se4 and 257 cm−1, 281 cm−1 and 396 cm−1 for CdCr2S4 have been identified as due toГ12+,Г25+ andГ1+ phonons, respectively. Certain lines ofГ1+ orГ25+ symmetry, observed in both materials, show a temperature dependence of the intensity which resembles the behaviour of the spin correlation function. Some of these lines also exhibit a symmetry change at the Curie point. A group theoretical analysis of the eigenvectors of the Raman active modes is given. The results are interpreted in terms of a model proposed by Baltensperger which involves the ion position dependence of the magnetic exchange interaction in order to couple spin system and phonons. The weak frequency shift of the lines, which occurs predominantly in the ordered state, is interpreted in terms of the same model.