Small-polaron transport in the Zn-doped colossal-magnetoresistance materials Fe1-xZnxCr2S4

The electrical resistivity, magnetization, thermoelectric power, and specific heat have been studied on a series of Zn-doped polycrystalline samples Fe1-xZnxCr2S4 (0 less than or equal to x less than or equal to 0.75) with a spinel structure over a wide range of composition and temperature. The properties show a systematical change with substituting monovalent and nonmagnetic Zn for Fe. At high temperatures, a significant difference between the activation energy deduced from the electrical resistivity rho(T) and the thermopower S(T), a characteristic of small polarons, is observed. The conductivity is dominated by hopping of small polarons, All of the experimental data can be well explained on the basis of the polaron model. At the same time, we discuss the origin of the colossal magnetoresistance effect in these kinds of compounds.