Spin-dependent interfacial tunnelling and tunnel-type GMR in granular perovskite family La1-xSrxMnO3 (0.05 <= x <= 0.45)

The granular perovskites La1-xSrxMnO3, with the concentration x from 0.05 t o 0.5, have been fabricated by the sol-gel method. The concentration-depend ent transport properties in the granular perovskites;have been investigated . Spin-dependent interfacial tunnelling and the corresponding tunnel-type m agnetoresistance have been observed in the samples sintered at lower temper atures in the doping range from x = 0.05 to 0.45 for the temperatures below the Curie point. The magnetization, the heat capacity and the oxygen stoic hiometry for the sample family have been measured to show that the interfac ial tunnelling stems from the magnetic difference between the surfaces and the cores of the grains, and that the tunnel-type GMR originates from the f ield-induced change of the surface magnetic configuration.