Effects of silicon addition on the electrical and magnetic properties of copper-doped (La,Ca)MnO3 compounds

Abstract

In this paper we report about the electrical properties of La 0.7 Ca 0.3 MnO 3 compounds substituted by copper on the manganese site and/or deliberately contaminated by SiO 2 in the reactant mixture. Several phenomena have been observed and discussed. SiO 2 addition leads to the formation of an apatite-like secondary phase that affects the electrical conduction through the percolation of the charge carriers. On the other hand, depending on the relative amounts of copper and silicon, the temperature dependence of the electrical resistivity can be noticeably modified : our results enable us to compare the effects of crystallographic vacancies on the A and B sites of the perovskite with the influence of the copper ions substituted on the manganese site. The most original result occurs for the compounds with a small ratio Si/Cu, which display double-peaked resistivity vs. temperature curves.

Evidence for magnetic phase separation in La0.86Sr0.14Mn1−xCuxO3+δmanganites from NMR and magnetic measurements

“…The values of the saturation magnetization M S , obtained by extrapolating the linear part of the M × H −1 curves to H −1 = 0, are shown in table 2. For all samples M S is much smaller than M max S , the expected value calculated considering spin-only contributions from Mn 3+ , Mn 4+ , and Cu 2+ ions [17,34] and also taking into account the small contribution due to the oxygen non-stoichiometry. This discrepancy also suggests the presence of FM clusters embedded in a non-ferromagnetic matrix as responsible for the magnetization values attained in high magnetic field.…”