Effect of the oxygen deficiency in physical properties of La0.7Ca0.25Sr0.05MnO3-delta square(delta) oxides (0 <=delta <= 0.15)

The La0.7Ca0.25Sr0.05MnO3-delta square(delta) compounds were prepared by the solid-state reaction with 0.00 <= delta <= 0.15. X-ray diffraction, electrical and magnetic measurements were performed to examine the effect of the oxygen deficiency on the physical properties of these compounds. It was found that these samples crystallize in an orthorhombic structure and present a ferromagnetic behaviour for delta <= 0.1. For delta = 0.125 and 0.15, the structure becomes rhombohedral and the magnetization curves reveal the presence of an antiferromagnetic character. The electrical study indicates the existence of a transition from the metallic phase to the semiconductor one for delta = 0 and 0.05. When increasing delta, the measures of the resistivity show the presence of semiconductor behaviour only. Oxygen deficiency modifies also the electrical transport properties delineating an electronic phase boundary between metal and semiconducting phase. Finally, oxygen deficiency affects the coupling between magnetism and transport properties, i.e., the double exchange of electrons between ferromagnetically coupled Mn ions. (c) 2007 Elsevier B.V. All rights reserved.