Elementary excitations in the spin-ice compound ${\mathrm{Dy}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ can be described as magnetic monopoles propagating independently within the pyrochlore lattice formed by magnetic Dy ions. We studied the magnetic-field dependence of the thermal conductivity $\kappa \left(B\right)$ for $B\left|\right|\left[001\right]$ and observe clear evidence for magnetic heat transport originating from the monopole excitations. The magnetic contribution ${\kappa }_{\mathrm{mag}}$ is strongly field dependent and correlates with the magnetization $M\left(B\right)$. The diffusion coefficient obtained from the ratio of ${\kappa }_{\mathrm{mag}}$ and the magnetic specific heat is strongly enhanced below 1 K, indicating a high mobility of the monopole excitations in the spin-ice state.

• Received 25 May 2012

DOI:https://doi.org/10.1103/PhysRevB.86.060402