Metal-to-insulator transition and magnetic ordering in CaRu_1-xCu_xO₃

CaRuO₃ is a perovskite with an orthorhombic distortion, and is believed to be close to magnetic ordering. Magnetic studies of single-crystal and polycrystalline CaRu_1-xCu_xO₃ (0≤x≤15 at. %Cu) reveal that a spinglass-like transition develops for x≤7 at. % Cu. The obtained value for the effective magnetic moment p_eff =3.55/μ_B for an x=5 at. % Cu single crystal, indicates the presence of Ru⁵⁺. At higher Cu concentrations more complex magnetic behaviors are observed. Electrical resistivity measured on polycrystalline samples shows a metal-to-insulator transition at 51 K for only 2-at. % Cu. Charge compensation, which is assumed to be present upon Cu^2+/3+ substitution, induces the appearance of Ru⁵⁺ and/or the creation of oxygen vacancies in a crystal structure. Since the observed changes in physical properties are completely attributable to the charge compensation, they cannot be related to behaviors of a pure compound where no such mechanism is present. This study provides the criterion for "good" chemical probes for studying Ru-based perovskites.