The crystallographic and magnetic properties of CaRu 1−x Mn x O 3 ͑0 Յ x Յ 1.0͒ were investigated in detail by x-ray powder diffraction, magnetization, and magnetic Compton scattering measurements. The lattice parameters show considerable deviation from Vegard's law. Ferromagnetism appears at a relatively large Mn concentration ͑x Ն 0.2͒, and the magnetization and the Curie temperature have a maximum at a Mn content near x = 0.7. The magnetic Compton scattering measurement revealed that Mn makes a dominant contribution to the magnetization and the Mn moment is antiparallel to the Ru moment, which is induced by Mn doping. The anomalous change in the unit cell volume and the occurrence of ferromagnetism were discussed on the basis of the mixed-valence model of Mn 3+ , Mn 4+ , Ru 4+ , and Ru 5+ ions. The Mn-composition dependence of the spontaneous magnetization was explained semiquantitatively assuming ͑1͒ ferromagnetic coupling between Mn 3+ and Mn 4+ ions, ͑2͒ antiferromagnetic coupling between Ru 5+ and Mn ions, and ͑3͒ the theoretical spin moments of Mn 3+ , Mn 4+ , and Ru 5+ . The ferromagnetic interaction between Mn 3+ and Mn 4+ ions seems to make a dominant contribution to the Curie temperature. The CaRu 1−x Mn x O 3 system is considered to be a ferrimagnet induced through competition between the ferromagnetic interaction between Mn ions and the antiferromagnetic interaction between Ru 5+ and Mn ions.

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