An irreversible magnetic-field dependence of low-temperature heat transport of spin-ice compound Dy_2Ti_2O_7 in a [111] field

摘要

We study the low-temperature thermal conductivity (\kappa) of Dy_2Ti_2O_7along and perpendicular to the (111) plane and under the magnetic field alongthe [111] direction. Besides the step-like decreases of \kappa at thefield-induced transitions from the spin-ice state to the kagom\'e-ice state andthen to the polarized state, an abnormal phenomenon is that the \kappa(H)isotherms show a clear irreversibility at very low temperatures upon sweepingmagnetic field up and down. This phenomenon surprisingly has no correspondencewith the well-known magnetization hysteresis. Possible origins for thisirreversibility are discussed; in particular, a pinning effect of magneticmonopoles in spin ice compound by the weak disorders is proposed.