Origin of magnetic freezing in the pyrochlore Y2Mo2O7

We investigated the nature of the spin glass-like phase transition in the geometrically frustrated pyrochlore lattices Y$_{2}$Mo$_{2}$O$_{7}$ using the local probes nuclear and muon magnetic resonances, and the field-dependent long range probes x-ray and neutron scattering. The long range probes indicated that Y$_{2}$Mo$_{2}$O$_{7}$ does not undergo any global symmetry changes, even in a field of $6$~T. In contrast, the local signal indicates a lattice distortion close to the critical temperature. The nuclei show at least two inequivalent Y sites, and the muons show sub-linear line broadening as a function of moment size, over a wide temperature range. The conclusion from all the measurements is that even in high field, the distortion of Y$_{2}$Mo$_{2}$O$%_{7}$ takes place within the unit-cell, while its global cubic symmetry is preserved. Moreover, the muon result clearly indicates the presence of magneto-elastic coupling.