Annealing time dependence of electrical resistivity and magneto-resistance of La0.6Y0.07Ca0.33MnO3 pellets prepared by 'pyrophoric' method

We present the electrical transport behavior of nanocrystalline La0.6Y0.07Ca0.33MnO3 prepared by using a novel soft chemical synthesis route called the 'pyrophoric method'. The process is based on the thermolysis of an aqueous, polymeric-based precursor solution prepared from water-soluble coordinated complexes of the composing metal ions. The temperature dependence of the electrical resistivity of the pellets shows metal-insulator transition that is followed by a ferromagnetic-paramagnetic transition. The transition temperature (TMI) is found to be strongly dependent on the annealing time and hence on the grain size. Temperature dependence of the electrical resistivity of our samples between TMI and 300 K confirms activated conduction compatible with adiabatic small polaron hopping and, in the metallic region (T<TMI), electron-electron and electron-magnon scattering governs the temperature variation of electrical resistivity. The observed low field magnetoresistance (MR) that is very much sensitive to the grain size and the intrinsic behavior is prominent around the TMI gives rise to a negative MR as large as 40%. The MR behavior is discussed in the light of magnetic clusters model and spin polarized tunneling of conduction electrons across the grain boundaries