Electrical properties of Ag–La0.7Ca0.3MnO3

The temperature dependence of the electrical resistivity in (1 − x ) La 0.7 Ca 0.3 MnO 3 + x Ag composites has been investigated between 5 and 300 K for H = 0 and 3 T . Ag addition has increased the conductivity of this system. Curie temperature ( T C ) is almost independent of Ag content and is ~ 260 K for all the samples, while the metal–insulator transition temperature ( T MI ) increases with increasing content of Ag. The ρ–T of all samples fit well with the phenomenological percolation approach, which is based on the phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions. In addition, all the samples clearly reveal the unusual low temperature resistivity minimum. Analysis of our results in terms of the model based on charge carrier tunneling between the anti-ferromagnetically coupled grains shows excellent agreement with the experiment data for both H = 0 and 3 T .