Heat transport of the spin-ice materials Ho${}_2$Ti${}_2$O${}_7$ and Dy${}_2$Ti${}_2$O${}_7$

Abstract

The elementary excitations of the spin-ice materials Ho${}_2$Ti${}_2$O${}_7$ and Dy${}_2$Ti${}_2$O${}_7$ in zero field can be described as independent magnetic monopoles. We investigate the influence of these exotic excitations on the heat transport by measuring the magnetic-field dependent thermal conductivity $\kappa$. Additional measurements on the highly dilute reference compounds HoYTi${}_2$O${}_7$ and DyYTi${}_2$O${}_7$ enable us to separate $\kappa$ into a sum of phononic (${\kappa }_{ph}$) and magnetic (${\kappa }_{mag}$) contributions. For both spin-ice materials, we derive significant zero-field contributions ${\kappa }_{mag}$, which are rapidly suppressed in finite magnetic fields. Moreover, ${\kappa }_{mag}$ sensitively depends on the scattering of phonons by magnetic excitations, which is rather different for the Ho- and the Dy-based materials and, as a further consequence, the respective magnetic-field dependent changes ${\kappa }_{ph}(B)$ are even of opposite signs.

5 pages, 4 figures