Structural and Magnetic Transitions in CaMn_1-xW_xO₃

The perovskite manganites CaMn 1 - x W x O 3 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 P 2 1 / 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 W 6+ ion creates two extra electron carriers in the Mn 4+ 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).