CMR effect and related properties of Mo-based oxides with double-perovskite structure

Abstract

In this thesis, firstly grain boundary modification studies of Sr2FeMoO6 polycrystals are presented. We reported our investigations on the effect of SrMoO4 impurities on the magnetoresistance of Sr2FeMoO6 polycrystals. They led to an improvement in the understanding on the intergrain tunneling magnetoresistance of the double perovskite materials, especially at a relatively low magnetic field and room temperature. Secondly, Sr2CoMoO6-I' film was investigated at high temperatures, especially around TC. It resulted in new direct evidence that a phase separation scenario also exists in the ordered double-perovskite structures materials. Thirdly, the substitution of Fe3+ ions by Cu2+ ions in Sr2FeMoO6 was found to facilitate the formation of the ordered structure, which also induces the occurrence of Fe3+I' ions and the double exchange (DE) interaction in Fe3+-O-Mo-O-Fe3+I'. Finally, for perovskite manganites La0.7Ca0.3Mn1-xCuxOy, the substitution of Mn by Cu was found to suppress the ferromagnetic ordering of the material.