Investigation of the magnetic spin correlations in the layered molybdenates, Mn2Mo3O8 and MnAMo3O8 (A = Fe, Co, Zn)

Abstract

An exotic range of magnetic (and other) properties have been observed in A₂Mo₃O₈ materials (where A is a single or mix of transition metals) making understanding their chemistry and physics timely. We have investigated the structural–property relationships in Mn₂Mo₃O₈ and the related materials, MnFeMo₃O₈, MnCoMo₃O₈ and MnZnMo₃O₈. We report a detailed powder diffraction analysis confirming ferrimagnetic structures for Mn₂Mo₃O₈ and MnFeMo₃O₈. Differing rates of spin ordering on crystallographically distinct sites (tetrahedral or octahedral) gives rise to magnetic hysteresis, which abruptly disappears in 2 K data. This appears to be correlated with ion displacement and/or electrostriction effects, which also relax at 2 K. We confirm an antiferromagnetic structure type for MnCoMo₃O₈ and no discernible magnetic ordering within the temperature range studied for MnZnMo₃O₈. For MnZnMo₃O₈ we suggest a small amount of site disorder acts to suppress magnetic ordering. This suggests that magnetic properties can be tuned both through A-site cation order and choice of A-site cations.