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 {k) of Dy_2 Ti_2O_7 along and perpendicular to the (111) plane and under the magnetic field along the [111] direction. Besides the steplike decreases of k at the field-induced transitions from the spin-ice state to the kagome-ice state and then to the polarized state, an abnormal phenomenon is that the k{H) isotherms show a clear irreversibility at very low temperatures upon sweeping the magnetic field up and down. This phenomenon surprisingly has no correspondence with the well-known magnetization hysteresis. Possible origins for this irreversibility are discussed; in particular, a pinning effect of magnetic monopoles in a spin-ice compound by the weak disorders is proposed.