Local lattice disorder in the geometrically frustrated spin-glass pyrochlore Y 2 Mo 2 O 7

The geometrically frustrated spin-glass Y{sub 2}Mo{sub 2}O{sub 7} has been widely considered 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, Tl{sub 2}Mn{sub 2}O{sub 7}. 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) 2000 The American Physical Society.