Phenomenological theory of Raman scattering in europium chalcogenides

First-order Raman scattering from phonons in the magnetic phases of the europium chalcogenides is analyzed in terms of symmetry for both electric-dipole and electric-quadrupole virtual electronic transitions. The magnetic ordering increases the size of the unit cell and lowers the point group symmetry of the various phases. The magnetic symmetry is used to derive the allowed Raman transitions and polarization selection rules. A phonon dispersion curve for EuSe along the 111] axis is inferred from recent experimental data by applying the selection rules derived on the basis of the magnetic symmetry.