Synthesis, structural characterization and magnetic properties of RCrO₄ oxides, R = Nd, Sm, Eu and Lu

This paper reports the specific conditions used in the preparation of RCrO₄ oxides, R = Nd, Sm, Eu and Lu, the structural determination, and the study of their magnetic behaviour. The structure of these compounds has been refined from X-ray powder diffraction by the Rietveld method, assigning the zircon type, space group I4₁/amd. A linear decrease has been observed in the lattice parameters from NdCrO₄ to LuCrO₄, according to the lanthanide contraction. Magnetic susceptibility measurements reveal the existence of an antiferromagnetic ordering in which both Cr⁵⁺ and R³⁺ sublattices are involved. In the case of NdCrO₄, the estimated Neel temperature appears to be lower than 2 K; for the remaining oxides, it is 14.9 K, 15.9 K and 9.9 K for Sm, Eu and Lu, respectively. A superexchange mechanism has been proposed to explain such a magnetic behaviour. The pathways through which these interactions take place have also been analyzed, taking into account the structural features that these oxides present. The Cr⁵⁺ plays an important role as a promoter of these interactions in the R³⁺ sublattice.