Order and disorder in the local and long-range structure of the spin-glass pyrochlore,Tb2Mo2O7

Abstract

To understand the origin of the spin-glass state in molybdate pyrochlores, the structure ofTb2Mo2O7 is investigated using two techniques: the long-range lattice structure was measured usingneutron powder diffraction, and local structure information was obtained from theextended x-ray absorption fine structure technique. While the long-range structureappears generally well ordered, enhanced mean-squared site displacements on theO(1) site and the lack of temperature dependence of the strongly anisotropicdisplacement parameters for both the Mo and O(1) sites indicate some disorder exists.Likewise, the local structure measurements indicate some Mo–Mo and Tb–O(1)nearest-neighbor disorder exists, similar to that found in the related spin-glass pyrochlore,Y2Mo2O7. Although the freezingtemperature in Tb2Mo2O7, 25 K, isslightly higher than in Y2Mo2O7, 22 K, the degree of local pair distance disorder is actually less inTb2Mo2O7. This apparent contradiction is considered in light of the interactions involved in thefreezing process.