Low-temperature magnetotransport in nanometric half-metallic ferromagnetic perovskites

We have conducted a systematic study of the temperature and magnetic field dependence of the electrical resistivity of granular nanometric La2/3Sr1/3MnO3 ceramics. The results can be analysed within the framework of a model involving the existence of a Coulomb gap, E-C, superimposed on a tunnelling barrier between individual grains, which produces a significant blockade at temperatures below similar to 100 K. Detailed data analysis allow us to separate the contributions from tunnelling and Coulomb gap and to determine their value and the grain size and magnetic field dependence. It is found that the Coulomb gap increases as 1/empty set where empty set is the mean grain size and the interface surface barrier also becomes more prominent as empty set is reduced.