Structural and Magnetic Transitions in CaMn1-xWxO3

The perovskite manganites CaMn1-xWxO3 are studied up to the solubility limit by using transmission electron microscopy, X-ray powder diffraction, and magnetic and transport measurements. The phase diagram shows three compositional regions at low temperatures. As x increases, (i) regular Pnma perovskite structure and G-type antiferromagnetism (AFM) combined with a weak ferromagnetic (FM) component, (ii) strongly distorted monoclinic P21/m structure and C-type AFM associated with orbital ordering, and (iii) strongly distorted Pnma structure, associated with charge and orbital ordering and AFM arrangement, are observed. Our measurements demonstrate that each W6+ ion creates two extra electron carriers in the Mn4+ matrix and appears as a defect in the Mn sublattice. This B-site disorder, together with the lower itinerancy of the doped carriers, make favorable conditions for orbital and/or charge ordering at unusually high critical temperatures (up to 380 K).