Local lattice disorder in the geometrically-frustrated spin glass   pyrochlore Y2Mo2O7
  The geometrically-frustrated spin glass Y2Mo2O7 has been considered widely to be crystallographically ordered with a unique nearest neighbor magnetic exchange interaction, J. To test this assertion, we present x-ray-absorption fine-structure results for the Mo and Y K edges as a function of temperature and compare them to results from a well-ordered pyrochlore, Tl2Mn2O7. We find that the Mo-Mo pair distances are significantly disordered at approximately right angles to the Y-Mo pairs. These results strongly suggest that lattice disorder nucleates the spin-glass phase in this material. 
C. H. Booth, J. S. Gardner, G. H. Kwei, R. H. Heffner, F. Bridges and   M. A. Subramanian