Semiconducting and Optical Properties of Ferromagnetic CdCr2S4 and CdCr2Se4

Electrical conductivity, Hall effect, magnetoresistance and thermoelectric properties have been studied on a number of undoped and doped polycrystalline CdCr2S4 and CdCr2Se4 samples. Undoped CdCr2S4 and CdCr2Se4 are n‐type and p‐type, respectively. With suitable doping, the conductivity of CdCr2Se4 can be changed by about six orders of magnitude [10−5 to 10 (Ω·cm)−1] without changing the magnetic properties. In Ag‐doped p‐type CdCr2Se4 the mobility at room temperature is 32 cm2/V·sec and rises with decreasing temperature. By doping with In, CdCr2Se4 can be made n‐type. The mobility of electrons is found to be two orders of magnitude lower than the mobility of holes. The conductivity of p‐type CdCr2Se4 decreases monotonically with decreasing temperature without any anomaly around the Curie temperature (Tc=130°K1). However, the conductivity of n‐type CdCr2Se4 has a minimum at 146°K and rises sharply with further decreasing temperature. This n‐type material also exhibits a large negative transverse magnetore...