Complex electrical transport behavior in low temperature sintered M-type hexaferrites

Temperature dependence of resistivity from room temperature to 750 °C at different frequency for the low temperature sintered Sr1−xLaxFe12−xCoxO19 (x=0-0.3) ferrites was investigated, and a theory model based on a hybrid grain structure was established to explain the observed complex electrical transport behavior. It indicates that the formation of surface phase associated with non-uniform La3+-Co2+ substitution is crucial to the hybrid grain structure, which consists of body phase, surface phase, and interface. The abnormal double metal-semiconductor (M-S) transitions in La3+-Co2+ substituted ferrites are suggested to arise from the competition of lattice vibration scattering effect and thermal excitation of different conduction electrons strongly correlated with the hopping of electrons between Fe2+ and Fe3+ at octahedral sites in body phase and surface phase.