Magnetic structure of the manganites heavily doped by Fe and Cr ions

Powder neutron diffraction and magnetic studies have been performed for NdMn0.5Fe0.5O3 and NdMn0.5Cr0.5O3 manganites. In NdMn0.5Cr0.5O3, magnetic structure has been revealed consisting of ferromagnetic and G-type antiferromagnetic components as result of a 3d-ions magnetic moments ordering. Magnetic moments of Nd-ions are parallel to the ferromagnetic component. In NdMn0.5Fe0.5O3 only the antiferromagnetic G-type structure has been found whereas Nd-sublattice was not ordered. In the both compounds, magnetic moments of 3d-ions are significantly less than one can expect, what is interpreted in terms of intrinsic chemical inhomogeneity. Magnetic phase diagrams have been constructed for the Nd(Mn1−xMx)O3 (M=Fe, Cr) systems, interpreted assuming superexchange interactions Mn3+–O–Cr3+ to be positive, Mn3+–O–Fe3+ negative and taking into account a disordered arrangement of Mn and Cr ions in the crystal structure sublattice as well as interplay between Jahn–Teller effect and superexchange interactions.