Effect of annealing temperature on electrical transport in La2/3Ca1/3MnO3

The electrical conductivity of La2/3Ca1/3MnO3 samples prepared using a sol–gel method is shown to be strongly dependent on the annealing temperature (hence the grain size). This is studied using a random resistor-network model in which ferromagnetic metallic particles with the number density p randomly fill the space of sample. The Monte Carlo simulation for the temperature dependence of resistivity shows results in excellent agreement with the experimental data measured in the larger and smaller grain size samples. From this simulation, we find that p is largely decreased for the whole temperature range below the Curie temperature as the grain size decreases. On the basis of temperature dependence of p obtained in the larger and smaller grain size samples, the effect of grain-size on the electrical transport is discussed and a possible explanation is also presented for the grain-size-dependent magnetoresistance behavior.