Neutron-Diffraction Data on Ti2O3 and V2O3

Abstract

Without considerable care one might conclude from neutron-diffraction studies of Ti2O3 and V2O3 that these materials are antiferromagnetic. The problem is that multiple-Bragg scattering can masquerade as small superlattice reflections. We have noted a large and rapid change in the intensities at the superlattice positions when the crystal is tilted about the scattering vector, indicating multiple scattering. The intensities of these reflections relative to the nuclear reflections decrease with increased collimation. In order to reduce this source of scattering, we have used a 2.09 Å beam instead of the usual 1.07 Å neutrons. Energy analysis of the beam reflected from the superlattice positions gives the result that there is essentially no real magnetic scattering at either the (111) or the (100) in Ti2O3. We can put an upper limit of 0.01 μB to Néel-type antiferromagnetism. Investigations of a single crystal of V2O3 above the phase transition (∼150°K) were subject to the same problems. However, below the transition, the mosaic structure of the crystal increased (indicating that the crystal was broken up) and there remained no detectable intensity at the superlattice positions.