Exchange energies, bound magnetic polarons, and magnetization in CdSe:Co and CdS:Co

The sp-d exchange energies, bound magnetic polarons, and magnetization have been studied in ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Co}}_{\mathit{x}}$Se and ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Co}}_{\mathit{x}}$S. For x=0.02–0.05, magnetization measurements of the ${\mathrm{Co}}^{2+}$ ions at liquid-helium temperatures are adequately described by a modified Brillouin function for pure spin S=3/2 ions. In spin-flip Raman-scattering (SFRS) measurements from donor-bound electrons we observe a large Zeeman splitting of ∼4–10 meV at high magnetic fields, and bound magnetic polaron energies of 0.2–0.4 meV at B=0. The s-d exchange energy between conduction electrons and ${\mathrm{Co}}^{2+}$ ions, obtained by combining the SFRS and magnetization results, is found to be α${\mathit{N}}_0$=274±6 meV for CdSe, and α${\mathit{N}}_0$=179±4 meV for CdS. For ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Co}}_{\mathit{x}}$Se, from reflectivity measurements and the α${\mathit{N}}_0$ value we obtain β${\mathit{N}}_0$=-2120±50 meV.