Magnetic and electrical transport of the cation-deficient LaMnO33: Common origin for both Sr-doping and self-doping effects

We have investigated the effect of cation deficiency on the electric and magnetic properties of LaMnO3 in terms of both substitution of La by a divalent ion (Sr2+) and creating La-deficiency. The temperature and magnetic field dependence of electrical resistivity (p) and dc magnetization were studied. All the compounds are to be found in rhombohedral structure. The excess oxygen in all compounds was detected through iodometric titration. The metal to semiconducting transition and the paramagnetic to ferromagnetic transition is found to decrease with Mn4+ for all samples. The occurrence of magnetoresistance (MR) at low temperature and low field for La-deficient compounds is suggested due to the tunneling of electron through the grain boundary (GB). The nonlinear current-voltage (I-V) characteristic for La-deficient compounds indicates inelastic tunneling via localized states dominate the transport mechanism.