Magnetic ordering in manganites substituted by chromium ions

NdMn_1?x Cr _x O₃ and Nd_0.6Ca_0.4Mn_1?x Cr _x O₃ solid solutions have been studied by neutron diffraction and magnetic measurements. NdMn_0.5Cr_0.5O₃ is found to have a magnetic structure consisting of an antiferromagnetic G-type component and a ferromagnetic component, which are caused by 3d ions. The magnetic moments of the neodymium ions are parallel to the ferromagnetic component. Nd_0.6Ca_0.4Mn_0.5Cr_0.5O₃ mainly has a G-type magnetic structure, and the magnetic moments of the neodymium ions are normal to the antiferromagnetism vector. Magnetic phase diagrams are plotted for both systems. They are interpreted on the assumption that the Mn³⁺-O-Cr³⁺ superexchange interactions are positive and the Mn⁴⁺-O-Cr³⁺ interactions are negative; the fact that manganese and chromium ions are not ordered in a crystal lattice is taken into account. Concentration magnetic phase transformations proceed through a two-phase state because of the internal chemical inhomogeneity of the solid solutions.