Electrical transport properties of sintered granular manganite/insulator systems

Magnetic, structural and transport measurements on granular [La0.7Sr0.3MnO3]1−x[Insulator]x pellets were carried out. The system displayed a conduction threshold at x>30%, i.e., for a La0.7Sr0.3MnO3 volume fraction XFM∼70%. Beyond this value, the resistivity increased steeply, setting up a rather insulating behavior. Nevertheless, the maximum enhancement in magnetoresistance was observed at a concentration x=xc∼10% at low temperatures and ∼20% at room temperature. This result was demonstrated to be independent of the applied magnetic field strength. The observed magnetoresistance enhancement seemed to be consistent with the disorder-driven amplification of spin-dependent transport at the structural boundaries of the mixture, due to the presence of the insulating material within the ferromagnetic matrix.