Percolation conductivity model in A site-deficient La 0.8−x o x Na 0.2−x o x MnO 3 manganites and universal model of magnetic field-dependent resistivity and magnetoresistance behavior

The electrical and magnetoresistance behaviors of La0.8−xoxNa0.2−xoxMnO3 [with x = 0 (N0) and 0.1 (N0.1)] polycristalline samples were investigated. Resistance measurements versus temperature under different magnetic applied fields were performed to investigate the electronic transport as well as the magnetoresistance properties. The metal/insulator transition temperature decreases from 280 K for x = 0 to 275 K for x = 0.1. The electrical conduction in these compounds has been well described in the context of the percolation model based on the phase separation of ferromagnetic metallic regions with paramagnetic insulating ones. The temperature-dependent resistance shows the existence of a minimum at low temperature. This behavior is due to the existence of a competition between inelastic and elastic interactions expressed by Kondo-like spin-dependent scattering. An empirical model was used to describe the variation of the magetoresistance and normalized resistance as a function of the magnetic applied field. The model was successfully widely tested on several magnetic specimens and the evolution of the fitting parameters was discussed in detail.