Magnetic frustration in the disordered pyrochlore Yb2GaSbO7

In the pyrochlore Yb2GaSbO7, the Yb3+ sublattice forms a network of corner sharing tetrahedra and the second sublattice is made up of disordered, non-magnetic Ga3+ and Sb5+ ions. We have examined this compound using magnetic susceptibility, 170Yb Moessbauer spectroscopy (down to 0.03 K) and muon spin relaxation (μSR) (down to 0.02 K) measurements. We establish the size of the Yb3+ magnetic moments and that of the Yb3+-Yb3+ coupling. At low temperatures, the correlated moments fluctuate between directions that are well tilted relative to the local [111] axis. The lattice disorder does not quench the frustration induced low temperature spin fluctuations but it does remove the first order dynamic transition that is present in the crystallographically ordered counterpart Yb2Ti2O7. Below 1.0 K, the fluctuation rate of the correlated moments decreases progressively as the temperature is reduced and the moments remain dynamic down to 0.02 K where the rate is 7 x 107 s-1. Magnetic frustration is operative in Yb2GaSbO7 where the Yb3+-Yb3+ interaction is antiferromagnetic as it is in Yb2Ti2O7 where the interaction is ferromagnetic.