Le. Hueso et al., INFLUENCE OF THE GRAIN-SIZE AND OXYGEN STOICHIOMETRY ON MAGNETIC AND TRANSPORT-PROPERTIES OF POLYCRYSTALLINE LA0.67CA0.33MNO3+ -DELTA PEROVSKITES/, Journal of magnetism and magnetic materials, 189(3), 1998, pp. 321-328
Effects of grain size and oxygen stoichiometry in sol-gel and ceramics
samples of La0.67Ca0.33MnO3+/-delta have been studied. Grain size (90
nm versus > 10 mu m) does not change either the Curie temperature (T-
c) or the metal-insulator transition temperature (TM-I), but great dif
ferences in low-field magnetoresistance are observed. These difference
s have been explained by a spin polarized tunneling model for conducti
on between grains. Oxygen content (delta) could be changed in La defic
ient samples via an electrochemical method at room temperature (i.e.,
without changing grain size). We observe great differences in TM-I whe
n decreasing delta, while T-c remains unchanged. Broken ways between M
n ions leads to zones with ferromagnetic behavior, but inhibits conduc
tivity. (C) 1998 Elsevier Science B.V. All rights reserved.