Magnetic phase-dependent Raman scattering in EuS and EuSe

Abstract

Detailed evidence is presented linking the Raman spectra in the magnetic semiconductors EuSe and EuS to their respective magnetic phase diagrams. In particular, spectra for EuSe are presented for the paramagnetic, ferromagnetic, antiferromagnetic (\ensuremath{\uparrow}\ensuremath{\uparrow}\ensuremath{\downarrow}\ensuremath{\downarrow}), and ferrimagnetic (\ensuremath{\uparrow}\ensuremath{\uparrow}\ensuremath{\downarrow}) spin arrangements and are related to a Brillouin-zone-folding scheme for each magnetic sublattice structure. Based on our spectra, a set of phonon dispersion relations for EuSe in the $\ensuremath{\Gamma}\ensuremath{-}L$ direction is constructed. We have also obtained for the first time right-angle Raman scattering spectra in EuSe. These results are compared with those obtained in the back-scattering geometry. Of significance is our observation that the broad spectral line extending from ${\ensuremath{\omega}}_{\mathrm{TO}}$ to ${\ensuremath{\omega}}_{\mathrm{LO}}$ in the paramagnetic phase persists for laser excitation energies below the fundamental absorption edge, thereby ruling out a hot luminescence mechanism for this feature. Instead our results are consistent with a spin-disorder model. Resonant Raman enhancement results are given for scattering in ferromagnetically ordered EuS and EuSe, and are related to magnetic-field-modulated magnetoreflectivity spectra. Particular attention has been given to the magnetic-phase dependence of the EuSe modulated spectra in going from the ferrimagnetic to the ferromagnetic spin arrangements.