Studies of R2Ti2O7 (R = Gd and Yb) : new results

Specific heat and muon spin rotation and relaxation data are presented for two geometrically frustrated systems: Gd2Ti2O7 which antiferromagnetically orders and Yb2Ti2O7 which presents dynamical short range correlations at low temperature. The muon data help to characterize the spin dynamics of these two compounds.Comment: 6 pages, 5 figures. To be published in the proceedings of the 10th International Conference on Muon Spin Rotation, Relaxation and Resonance, Physica

First order transition in the spin dynamics of geometrically frustrated Yb₂Ti₂O₇

Using neutron diffraction, 170Yb Mossbauer and muSR spectroscopies, we have examined the pyrochlore Yb2Ti2O7 where the Yb3+ S'=1/2 ground state has planar anisotropy. Below ~0.24K, the temperature of the known specific heat lambda transition, there is no long range magnetic order. We show that the transition corresponds to a first order change in the fluctuation rate of the Yb3+ spins. Above the transition temperature, the rate, in the GHz range, follows a thermal excitation law, whereas below, the rate, in the MHz range, is essentially temperature independent indicative of a quantum fluctuation regime.Comment: 4 pages, 4 postscript figures (one double with 2 ps files