Neutron diffraction study of Pr1 - xCaxMnO3 perovskites

A thorough powder neutron diffraction study of Pr_{1 - x}Ca_x- Mn³⁺_{1 - x}Mn⁴⁺_xO₃ (0 < x < 1) was performed over a wide temperature range, completed by X-ray diffraction and electrical measurements. The existence of four composition regions with different orderings of Mn ³⁺ ions and their orbitals (0 ⩽ x ⪅ 0.3, 0.3 ⪅ x < 0.75, 0.75 ⪅ x ⪅ 0.9 and 0.9 ⪅ x ⩽ 1) was revealed. The corresponding prototypes are x = 0, 0.5, 0.75 and 1. The departures from these ideal compositions introduce substancial changes in magnetic interactions and, as a consequence, a variety of magnetic structures (including different noncollinear ones) are observed at low temperatures. The magnetic structures are interpreted by considering the role of superexchange and double exchange.