Ferromagnetism and metallicity in the CaMn1−xRuxO3 perovskites: a highly inhomogeneous system

The study of the magnetic and transport properties of the perovskites CaMn1−xRuxO3 shows that ferromagnetism and metallicity are developed for a large compositional range, with a much higher TC than for SrRuO3, reaching a maximum value of 210 K for x=0.40. The greatly inhomogeneous character of this system, showing phase separation between ferromagnetic (FM) and antiferromagnetic (AFM) domains, is inferred from ac-susceptibility measurements, explaining the magneto-transport properties of these oxides. This unique ability of ruthenium to induce FM and metallicity in the AFM CaMnO3 matrix is explained by the combination of valency effect (Ru5+ species creating Mn3+ species), which allows double exchange, and of FM interactions between Ru and Mn species through super-exchange, the hybridization between Ru and Mn eg orbitals favoring conduction paths in the matrix.