Delocalizing effect of polarons in colossal magnetoresistance material FeCr2S4

The electrical transport and magnetic properties of the colossal magnetoresistance material FeCr2S4 are studied. The temperature dependence of resistivity p and thermoelectric power S are investigated from 5 to 300K and from 77 to 300K, respectively The activation energy E-rho obtained from rho - T is larger than the activation energy E-S, obtained from S - T. This indicates that magnetic polarons dominate the conduction behaviour at temperatures above T-c. The M - T curve and electron spin resonance spectra show that the paramagnetic-ferromagnetic transition is incomplete, and that a paramagnetic phase coexists with a ferromagnetic phase in a certain temperature range below T-c. It is proposed that the insulator-metal transition near T-c could be attributed to the gradual delocalizing effect from magnetic polarons to naked carriers. The resistivity in the presented temperature range can be described by considering the coexistence of magnetic polarons and naked carriers.