Influence of Se-deficiencies on the properties of In-doped CdCr2Se4 single crystals

Lattice constant, Curie temperature, and electrical conductivity of CdCr₂Se₄:In single crystals have been measured after heat treatments of the crystals in Se atmosphere and under streaming hydrogen. By these treatments, the concentration of the Se vacancies and of the charge carrier concentration is altered drastically. The lattice constant as well as the magnetic ordering temperature have been found not to be affected by these heat treatments.Since the Se vacancies act as doubly changed donors, the electrical conductivity is strongly dependent on the concentration of the Se vacancies. A resistivity anomaly and large magnetoresistance are observed only in crystals with considerable Se deficiency. From these results it is concluded that the magnetoresistance is caused by hopping conduction between donor sites partly emptied by compensating A-site vacancy acceptors. Large magnetoresistance is found in samples with considerable Se deficit because only in this case the conduction at lower temperatures is dominated by the impurity band.