Magneto-transport properties of nano-crystalline and poly-crystalline La0.6Pb0.4MnO3 thin films

We have investigated the magneto-transport properties of nano-crystalline (NC) and polycrystalline (PC) La0.6Pb0.4MnO3 (LPMO) thin films, which have different grain-boundary properties. Above metal-insulator transition temperature (T IM), the magnetic coupling between the grains governs the transport. In the low-temperature (T<T IM) metallic state, T 4.5 dependences of normalized resistance for both types of films suggest the importance of scattering of spin polarized electron by the electron-magnon interaction. In contrast to the field dependence of magneto-resistance (MR) for PC LPMO films, NC films show the absence of low-field MR, which is a characteristic feature of granular CMR samples. Using current-voltage characteristic we demonstrate that the spin flip scattering (inelastic process) of carriers in NC films contributes to enhancement of MR, but does not contribute to the low-field MR