Structural and magnetic properties of SrMn$_{1-x}$Ru$_{x}$O$_{3}$ perovskites

Ferromagnetism of SrRuO$_{3}$ is unique among 4d transition metal based perovskite oxides. On substitution of Mn its T$_{C}$ decreases from 163 K to 0 for x$\sim $0.5-0.6 followed by a formation of an antiferromagnetic insulating state at a quantum critical point. The other end member of the SrMn$_{1-x}$Ru$_{x}$O$_{3}$ family, a cubic perovskite SrMnO$_{3}$ is a G-type antiferromagnet with T$_{N}$=233 K. We have synthesized the complete SrMn$_{1-x}$Ru$_{x}$O$_{3}$ solid solution. The polycrystalline samples were characterized by neutron difraction, magnetic, and transport experiments. The incorporation of Ru in the SrMnO$_{3}$ matrix (0.1$\le $x$\le $0.4) results in a phase transition to a C-type antiferromagnetic state accompanied by a cubic-tetragonal transition. The intermediate substitution level induces a spin-glass behavior, due to competing ferro- and antiferromagnetic interactions. Mixed valence Mn$^{3+}$/Mn$^{4+}$ and Ru$^{4+}$/Ru$^{5+}$ pairs introduce additional frustration to the magnetic states. The glassy behavior can be observed for x up to 0.7 in the tetragonal structure. Supported by NSF (DMR-0302617) and the U.S. Department of Education