Magnetic impurities in conducting oxides. II.(Sr1−xLax)(Ru1−xCox)O3system

Abstract

The perovskite solid solution between ferromagnetic ${\mathrm{SrRuO}}_{3}$ and antiferromagnetic ${\mathrm{LaCoO}}_{3}$ is studied and its structural, electronic,and magnetic properties are compared with $({\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{La}}_{x})({\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}){\mathrm{O}}_{3}$. The lower $3d$ energy levels of ${\mathrm{Co}}^{3+}$ cause a local charge transfer from $4d\phantom{\rule{0.3em}{0ex}}{\mathrm{Ru}}^{4+}$, a reaction that has the novel feature of being sensitive to the local atomic structure such as cation order. Despite such a complication, $\mathrm{Co}$, like $\mathrm{Fe}$, spin-polarizes the itinerant electrons in ${\mathrm{SrRuO}}_{3}$ to form a large local magnetic moment that is switchable at high fields. In the spin glass regime when Anderson localization dominates, a large negative magnetoresistance emerges as a result of spin polarization of mobile electronic carriers that occupy states beyond the mobility edge. A phenomenological model predicting an inverse relation between magnetoresistance and saturation magnetization is proposed to explain the composition dependence of magnetoresistance for both$({\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{La}}_{x})({\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{CO}}_{x}){\mathrm{O}}_{3}$ and $({\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{La}}_{x})({\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}){\mathrm{O}}_{3}$ systems.