Novel dynamical magnetic properties in the spin ice compound Dy2Ti2O7

Abstract

We found two distinct maxima in the ac magnetic susceptibility χ_ac of dysprosium titanate pyrochlore Dy₂Ti₂O₇. Their different frequency dependence of χ_ac 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 χ_ac, 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, τ_c, in the slow relaxations. The magnetic relaxation of the spin ice compound Dy₂Ti₂O₇ is uniquely in contrast with known slow dynamics.