Intergrain tunneling in granular Sr2FeMoO6 studied by pulsed high currents -: art. no. 134420

The zero-field intergrain tunneling conductivity sigma of sintered and granular Sr2FeMoO6 increases linearly with temperature over the range similar to20-300 K, at least. The residual conductivity of the investigated samples ranges over more than four orders of magnitude and the total change of sigma up to room temperature ranges from similar to20% in the sintered samples to a factor of 3 in granular samples. sigma(T) is hysteretic upon cycling through the Curie temperature T-c and becomes slightly superlinear above T-c. In order to identify the parameter responsible for the unusual linear T dependence, the nonlinear (electric-field dependent) conductivity of granular samples was investigated at various temperatures up to 300 K using pulsed high currents. The results indicate that the effective height and width of the potential barrier in the exponent of the current density are temperature independent, while the preexponent exhibits a linear T dependence. The significance of this result is discussed in view of the crucial role played by the preexponent in intergrain magnetoresistance.