Structure, magnetism, and transport have been investigated for $L_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{Co}}_{1-x}{\mathrm{Ru}}_x{\mathrm{O}}_3$ $(L=\mathrm{La},$ Pr, Nd, Sm, and Eu, $x=0,$ 0.1, and 0.2), in which Ru is doped at the Co site in perovskites $L_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{CoO}}_3.$ The structures of most of the compounds were refined to orthorhombic Pnma. The compounds $L_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{CoO}}_3$ $\mathrm{}(x=0\mathrm{})\mathrm{}$ are metallic ferromagnets below Curie temperatures between ∼250 and ∼150 K. We found that Ru doping brings about the suppression of ferromagnetic order as well as the loss of metallicity. The Curie-Weiss analysis showed that the order (except for $L=\mathrm{La})$ commonly changes into an antiferromagnetic type with the doping. For $L=\mathrm{Sm}$ and Eu with $x=0.2,$ sharp cusps at around 50–60 K in the magnetization-temperature curves were ascribed to a spin-glass transition, a finding which was supported by measurements of ac magnetic susceptibility and magnetization relaxation. An origin of these phenomena is proposed by considering several factors such as the change of the spin states of Co induced by Ru doping.

• Received 7 May 2002

DOI:https://doi.org/10.1103/PhysRevB.67.094408