Low field magnetoresistance effects in fine particles of La0.67Ca0.33MnO3 perovskites

In this work magnetic and magnetotransport experimental data in well-characterized small particles of La0.67Ca0.33MnO3 are presented. Grain size reduction leads to a larger resistivity and a decrease in metal-insulator transition temperature, intrinsic colossal magnetoresistance (CMR) is destroyed while intergranular one is promoted to larger values. This low field MR can be explained taking into account magnetization data through spin-polarized tunneling model, which ensures an acceptable first-order fit between both magnitudes. Finally, low-temperature resistivity upturn present in small particle size samples can be understood in terms of an electrostatic barrier between grains. (C) 2000 Elsevier Science B.V. All rights reserved.