Hopping conduction behavior with the Coulomb effects in colossal magnetoresistance materials

We report on the temperature dependence of resistivity in La _0.7-xPr_xMnO₃ (x=0, 0.5, 0.7) bulk samples in order to explore the hopping transport behavior with the Coulomb effects for the colossal magnetoresistance materials. The experimental observations in La _0.7-xPr_xPb_0.3MnO₃ (x=0.5, 0.7) bulk samples reveal the exponential temperature dependence of resistivity ρ(T)∞ [T₁/T)ⁿ] with n = 1/2, when system was the paramagnetic (PM) insulator at the high temperature range (T>T_p). Evidence for the hopping conduction with Coulomb effects is presented By using the approximate method of the VRH conduction in the localization regime base on Efros and Shklovskii model [A. L. Efros and B. I. Shklovskii, J. Phys. C, Solid State Phys. 8, L49 (1975)], the localization length of e_g electrons can be estimated with the relationship, ξ=2.8e²/ (4πε₀κk_BT₁). The reasonable results of localization length can be evaluated to explain the possibility of the presence of the Coulomb interactions in these CMR materials.