Semiconducting Properties of Ferromagnetic CdCr2Se4

Measurements of the electrical conductivity, the Seebeck effect, and the Hall effect were performed on hot-pressed Cd${\mathrm{Cr}}_2$ ${\mathrm{Se}}_4$ between 77 and 300°K. The conductivity of $n$-type Cd${\mathrm{Cr}}_2$ ${\mathrm{Se}}_4$ (In-doped) shows a sharp minimum at 150°K. The increase of the conductivity at lower temperatures is due to an increasing mobility and an increasing carrier concentration. This increasing carrier concentration is explained in terms of a strong red shift of the absorption edge due to magnetic ordering. The conductivity of $p$-type Cd${\mathrm{Cr}}_2$ ${\mathrm{Se}}_4$ (Ag-doped) shows a change of the slope of $log\sigma$-versus-$\frac{1}{T}$ curve and a maximum of the normal Hall coefficient at 150°K. This fact is interpreted as being due to the onset of impurity conduction.