Magnetic and intergranular transport properties in manganite/alumina composites

We report the magnetic and transport properties of La2/3Ca1/3MnO3/Al2O3 cry stal composites at low insulator component ratio. Phase purity and microstr ucture are guaranteed by X-ray and microanalysis studies. DC electric condu ction is progressive blocked by scattering in alumina regions. With an insu lator percentage around 10% in volume, percolation occurs. Merging the spin polarization of the manganite and the extra disorder contribution to elect ric transport induced by alumina we have been able to increase the low temp erature magnetoresistance (MR) nearly three times with respect to the undop ed manganese perovskite. Experimental results are analyzed on the basis of an earlier theory developed for a granular ferromagnetic material in an ins ulator matrix. (C) 2001 Elsevier Science B.V. All rights reserved.