Novel dynamical magnetic properties in the spin ice compound Dy₂Ti₂O₇

Abstract

We found two distinct maxima in the ac magnetic susceptibility χac of dysprosium titanate pyrochlore Dy2Ti2O7. Their different frequency dependence of χac suggest the existence of two different types of dynamical behaviour. One of them, observed below 2 K is the relaxation becoming very slow at lower temperature T, possibly related to a highly degenerate ground state (`spin ice' state). Another slowing down phenomenon is evident above ~10 K. Surprisingly, however, there is no anomaly in the dc magnetic susceptibility at this temperature range. Analysing the frequency dependence of χac, we found that in spite of a structurally ordered system the magnetic relaxation is well expressed by a Davidson-Cole formula, which is characterized by a wide distribution of the relaxation time τ to the short-τ region and a temperature dependent cut-off, τc, in the slow relaxations. The magnetic relaxation of the spin ice compound Dy2Ti2O7 is uniquely in contrast with known slow dynamics.