Revisiting static and dynamic spin-ice correlations inHo2Ti2O7with neutron scattering

Abstract

Elastic and inelastic neutron-scattering studies have been carried out on the pyrochlore magnet ${\text{Ho}}_{2}{\text{Ti}}_{2}{\text{O}}_{7}$. Measurements in zero applied magnetic field show that the disordered spin-ice ground state of ${\text{Ho}}_{2}{\text{Ti}}_{2}{\text{O}}_{7}$ is characterized by a pattern of rectangular diffuse elastic scattering within the [HHL] plane of reciprocal space, which closely resembles the zone-boundary scattering seen in its sister compound ${\text{Dy}}_{2}{\text{Ti}}_{2}{\text{O}}_{7}$. Well-defined peaks in the zone-boundary scattering develop only within the spin-ice ground state below $\ensuremath{\sim}2\text{ }\text{K}$. In contrast, the overall diffuse-scattering pattern evolves on a much higher-temperature scale of $\ensuremath{\sim}17\text{ }\text{K}$. The diffuse scattering at small wave vectors below [001] is found to vanish on going to $\mathbf{Q}=0$, an explicit signature of expectations for dipolar spin ice. Very high energy-resolution inelastic measurements reveal that the spin-ice ground state below $\ensuremath{\sim}2\text{ }\text{K}$ is also characterized by a transition from dynamic to static spin correlations on the time scale of ${10}^{\ensuremath{-}9}\text{ }\text{s}$. Measurements in a magnetic field applied along the $[1\overline{1}0]$ direction in zero-field-cooled conditions show that the system can be broken up into orthogonal sets of polarized $\ensuremath{\alpha}$ chains along $[1\overline{1}0]$ and quasi-one-dimensional $\ensuremath{\beta}$ chains along [110]. Three-dimensional correlations between $\ensuremath{\beta}$ chains are shown to be very sensitive to the precise alignment of the $[1\overline{1}0]$ externally applied magnetic field.