Electrical transport in manganite granular systems

A systematic investigation of magnetic and transport properties is carried out for La2/3Ca1/3MnO3 granular system. Based on the magnetization measurement, it is argued that oscillatory indirect magnetic exchange coupling via the boundary material with thickness s sandwiched between the neighboring grains exists in polycrystalline manganites. By introducing a distribution function of s and averaging the conductivity deduced from the spin-polarized tunneling model for the neighboring grains, we obtain a general expression for the temperature dependence of resistance that can reproduce the experimental data observed in polycrystalline manganites. The present model provides information on the microscopic transport mechanism.