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Abstract: Neutron diffraction studies were performed on the spinel oxide system Mg x Co1−x Cr x Fe2−x O4 (x =0.0, 0.25, 0.50, 0.75 and 1.0) as a function of temperature. Presence of magnetic long-range order at low temperatures was confirmed from the evolution of Bragg reflections with the decrease of temperature. Magnetic structural properties were determined from the Rietveld analysis of neutron diffraction data recorded in the temperature range 10–810K. Sublattice and net magnetic moments for various compositions at various temperatures were found out from the analysis. The transition temperatures were also determined for all the compositions. A decreasing ferrimagnetic order with increasing substitution was revealed from the decreasing ordered sublattice moments. Huge diffuse signals around the 111 Bragg diffraction line were observed in the neutron patterns of the composition x =1.0 below the Curie temperature indicating the existence of magnetic spin clusters. Hysteresis and low field dc magnetization measurements were done on the compositions x =0.75 and 1.0. Thermo-magnetic irreversibility in the zero-field cooled and field cooled magnetization together with a shallow transition below Curie temperature was also observed. The various observations suggest a canted ferrimagnetic ordering in the composition range x ≤0.75 and a semi-spin glass like behavior at x =1.0. A super-paramagnetic behavior below the paramagnetic state is also suggestive from the observed features. [Copyright &y& Elsevier]

Abstract: Quaternary spinel compound Mg x Co1−x Cr x Fe2−x O4 (x =0.0, 0.25, 0.50, 0.75 and 1.0) was synthesized in the solid state sintering method. Neutron powder diffraction measurements at room temperature were performed on the materials. Rietveld refinement of the neutron powder diffraction data was done for determining the cation distribution and crystallographic characterization of the system. The refinement yielded a mixed cationic distribution with Co, Fe and Mg being distributed over tetrahedral and octahedral sites in varying proportions while Cr was found to uniquely occupy the octahedral interstices. Increase of tetrahedral bond distance and decrease of octahedral bond distance with x was also revealed from the refinement. Sublattice and net magnetic moments at room temperature were also deduced from the refinement of room temperature neutron diffraction data. [Copyright &y& Elsevier]