Magnetoreflectance and magnetization of the Co-based wurtzite-structure diluted magnetic semiconductor ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Co}}_{\mathit{x}}$Se

Magnetoreflectance measurements of excitonic interband transitions in the wurtzite-structure compound ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Co}}_{\mathit{x}}$Se with various directions of applied magnetic field combined with magnetization measurements, allowed us to determine the ion-carrier exchange parameters for the conduction and valence bands (${\mathit{N}}_0$α=258±10 meV, ${\mathit{N}}_0$β=-1883±30 meV), without making any assumption concerning the band parameters. The magnitude of these exchange parameters, compared with the values previously obtained for ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Fe}}_{\mathit{x}}$Se and ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Mn}}_{\mathit{x}}$Se, indicates a small variation of the conduction-band exchange parameter, but an important enhancement of the valence-band exchange parameter. This large variation of the hybridization-induced exchange is explained within a generalized Schrieffer-Wolff formula.