Slow dynamics of Dy pyrochlore oxides Dy2Sn2O7 and Dy2Ir2O7

We report the magnetic properties of Dy pyrochlore oxides, Dy2Sn2O7 and Dy2Ir2O7. We show that the temperature dependence of the relaxation time τ(T) in the case of Dy2Sn2O7 is very similar to that in the case of a typical spin ice, Dy2Ti2O7. However, the time scale of Dy2Sn2O7 is 10-100 times slower than that of Dy2Ti2O7 over the entire temperature range. Dy2Ir2O7 exhibits a metal-insulator transition at 134 K; it has a broad peak at 4.5 K in the DC magnetic susceptibility, indicating an antiferromagnetic correlation. However, the specific heat has no sharp anomaly at 4.5 K. We show that the Dy moments in Dy2Ir2O7 have no long-range ordering down to 100 mK. We elucidate the anomalous slow dynamics that τ(T) decreases and becomes inhomogeneous below 12 K.