Effect of nanometric grain size on electronic-transport, magneto-transport and magnetic properties of La(0.7)Ba(0.3)MnO(3) nanoparticles.

We have investigated the effect of nanometric grain size on electronic-transport, magneto-transport and magnetic properties of single-phase La(0.7)Ba(0.3)MnO(3) (LBMO) nanoparticles having an average grain size in the nanometric regime (21-35 nm). We have observed that both the metal-insulator transition temperature (T(P)) and para-ferromagnetic transition temperature (T(C)) shift to lower temperature with a decrease in average grain size. For the entire series of samples, a distinct minima in resistivity at a temperature (T(min)) followed by an upturn at a very low temperature (≤47 K) is observed. We have attributed the steeper low temperature (∼47 K) resistivity upturn in the smaller grain size sample than that in the larger grain size sample below T(min) to the increased value of charging energy (E(C)). E(C) has been estimated to be 1.3, 0.56 and 0.04 K for an average grain size of 21, 25 and 30 nm, respectively. Magneto-transport measurements show that the magnitude of low field MR (LFMR) varies with average grain size. In order to investigate the MR behavior of LBMO nanoparticles, we have analyzed our data in the light of a phenomenological model, based on spin-polarized transport of conduction electrons at the grain boundaries. Magneto-transport measurements show that the magnitude of low field MR (LFMR), as well as of high field MR (HFMR), remains constant up to sufficiently high temperature (∼50 K) and then drops sharply with temperature. We found that this strange temperature dependence of MR is decided predominantly by the nature of the temperature response of the surface magnetization (M(S)) of nanosized magnetic particles.