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 I4(1)/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 analysed, 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. (C) 2000 Elsevier Science B.V. All rights reserved.