Effect of Al2O3 on conductive behavior of (1 - x) La0.7 Ca0.3 MnO3 + x Al2O3 composites

We report the resistivity (ρ) - temperature (T) patterns in (1 - x) La0.7 Ca0.3 MnO3 + x Al2O3 composites (0 ≤ x ≤ 0.05) over a temperature range of 5 K - 300 K. Based phenomenological equation for the conductivity under a mean field magnetization, we proposed a simple twochannel conduction model and fitted experimental data (σ - T) from 50 K to 300 K. We found that activation barrier increases as increasing of Al2O3 content. The unusual low - temperature resistivity upturn is closely related to Coulomb blockade (CB) of all samples, which is much sleeper for the large Al2O3 content sample than that with the smaller Al2O3 content. It mean that the Al2O3 content plays a vital role in this unusual behavior. (author)