A neutron diffraction study of the spin-glass-like system Y2Mo2O7 (abstract)

It has been reported recently that the crystalline, magnetically concentrated material Y2Mo2O7 displays behavior normally associated with spin-glass or cluster glass systems.1 This compound is widely reported to have the cubic pyrochlore structure, space group Fd3m, but no detailed structure determination had been reported. We have determined the crystal structure of Y2Mo2O7 from a powder profile analysis of neutron diffraction data and confirm the space group and structural assignment. That is, all of the 88 atoms in the cubic unit cell fully occupy the Wyckoff positions normally associated with the fully ordered cubic pyrochlore structure: Y in 16d, Mo in 16c, O1 in 48 f, and O2 in 8b. Alternative models with disorder between Y and Mo or with O2 randomly occupying 1/4 of the 32c sites gave poorer agreement indices than the fully ordered model. Thus, to within the limits of accuracy of this study, Y2Mo2O7 is a spin-glass-like material with negligible atomic scale disorder. To date, this situation is unique among all known concentrated, crystalline spin-glass systems.