Electronic Raman scattering inCd1−xCoxSe

Abstract

The Raman spectrum of the diluted magnetic semiconductor ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Co}}_{\mathrm{x}}$Se (x=0.035 and 0.082) exhibits a line (${\omega }_{\mathrm{PM}}$) associated with the transition between the Zeeman-split orbital ${\Gamma }_2$ ground-state levels of ${\mathrm{Co}}^{2+}$ and is characterized by g=2.32. Below 20 K, this Raman peak shifts to higher frequencies, signaling the onset of magnetic ordering. At low temperatures, spin-flip Raman scattering from electrons bound to shallow donors (${\omega }_{\mathrm{SF}}$) is observed. The Raman shift as a function of magnetic field and temperature shows a large s-d exchange interaction (α$N_0$=320 meV) and clear evidence of a bound magnetic polaron. Evidence of magnetic ordering at low temperatures, indicated by the temperature dependence of ${\omega }_{\mathrm{PM}}$, and the large antiferromagnetic temperature ($T_{\mathrm{AF}}$) required to fit the temperature and magnetic-field dependence of ${\omega }_{\mathrm{SF}}$, indicate a significantly larger ${\mathrm{Co}}^{2+}$-${\mathrm{Co}}^{2+}$ antiferromagnetic coupling than is the case for ${\mathrm{Mn}}^{2+}$-${\mathrm{Mn}}^{2+}$ in, for example, ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Mn}}_{\mathrm{x}}$Se.