Raman scattering from optical phonons and magnetic excitations in ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Se and ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$S

The Raman spectra of ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Mn}}_{\mathit{x}}$Se and ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Mn}}_{\mathit{x}}$S are investigated for various ${\mathrm{Mn}}^{2+}$ concentrations x. Both ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Mn}}_{\mathit{x}}$Se and ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Mn}}_{\mathit{x}}$S have the wurtzite structure and have point-group symmetry ${\mathit{C}}_{6\mathit{v}}$. ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Mn}}_{\mathit{x}}$Se shows a two-mode behavior, whereas ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Mn}}_{\mathit{x}}$S, in which the modes associated with ${\mathrm{Mn}}^{2+}$ appear in between the LO and TO phonons, shows an intermediate behavior. The frequencies of the TO modes and nonpolar ${\mathit{E}}_2$ modes are found not to depend significantly on the composition. We believe that this is due to the absence of polarization fields associated with this mode. The modified random-element-isodisplacement model gives a good description of optical phonons in ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Mn}}_{\mathit{x}}$Se. In an external magnetic field, a Raman line associated with a spin-flip excitation of ${\mathrm{Mn}}^{2+}$ and its combination with LO phonons are observed.