Influence of the grain-size and oxygen stoichiometry on magnetic and transport properties of polycrystalline La0.67Ca0.33MnO3±δ perovskites

HUESO, L.E; RIVADULLA, F; SÁNCHEZ, R.D; CAEIRO, D; JARDÓN, C; VÁZQUEZ-VÁZQUEZ, C; RIVAS, J; LÓPEZ-QUINTELA, M.A

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS

ELSEVIER SCIENCE BV

Año: 1998 vol. 189 p. 321 - 328

0304-8853

Effects of grain size and oxygen stoichiometry in sol?gel and ceramics samples of La0.67Ca0.33MnO3±δ have been studied. Grain size (90 nm versus >10 μm) does not change either the Curie temperature (TC) or the metal?insulator transition temperature (TM?I), but great differences in low-field magnetoresistance are observed. These differences have been explained by a spin polarized tunneling model for conduction between grains. Oxygen content (δ) could be changed in La deficient samples via an electrochemical method at room temperature (i.e., without changing grain size). We observe great differences in TM?I when decreasing δ, while TC remains unchanged. Broken ways between Mn ions leads to zones with ferromagnetic behavior, but inhibits conductivity.