Abstract

The substitution of molybdenum for manganese has been studied in the CaMn_1−xMo_xO₃ series for 0 ≤ x ≤ 0.15. We establish a structural and magnetic diagram combining electron microscopy, neutron diffraction and magnetic susceptibility measurements. Four regions have been evidenced versus composition (x) and temperature. The transport properties and thermoelectric power have been analyzed on the basis of this diagram. The structural transition temperature, linked either to a monoclinic deformation characteristic for antiferromagnetism (AFM) with a C-type orbital polarization (0.07 ≤ x ≤ 0.12) or associated with ordered stripes (x > 0.12), significantly increases with x. The fact that these orders develop at high temperatures (exceeding 300 K) is determined by two favourable parameters: the A-site cationic mismatch is zero and the magnetic order, linked with the orbital one, is not confronted with the magnetic sub-lattice of rare-earth ion. The great analogy of these materials with the Mn⁴⁺-rich manganites Sm_1−xCa_xMnO₃ is discussed, referring to the injection of electrons in the CaMn^IVO₃ matrix.