Double exchange-related interfacial tunneling and the corresponding giant magnetoresistance in granular La1-xSrxMnO3 perovskites

Fine grain manganese perovskites La1-xSrxMnO3 have been synthesized by usin g the inorganic sol-gel method. The grain size-dependent and the doping lev el-dependent magnetic transport properties in the fine grain system have be en studied. The interfacial tunneling associated with the double exchange i nteraction and the corresponding tunnel-type magnetoresistance have been ob served in the samples with an average grain size no greater than 0.12 mu m in the doping range 0.05 less than or equal to x less than or equal to 0.45 for temperatures below the Curie point. The magnetization, the heat capaci ty, and the oxygen stoichiometry for the sample system have been measured t o demonstrate that the interfacial tunneling originates from the difference in magnetic configuration between the surfaces and the cores of the grains , and the corresponding giant magnetoresistance results from the field-indu ced change of the surface magnetic ordering. (C) 1999 American Vacuum Socie ty.