Dynamics of dilute spin ice: ghost spins and topological spin glass

Ho2Ti2O7 has attracted much attention as host to spin-ice behaviour, a magnetic phase that gives rise to intriguing topological properties, including the stabilisation of emergent magnetic monopoles, fractional excitations in three dimensions. Our work has shown that structural disorder in pyrochlore materials allows control of the magnetic state and the magnetic relaxation. Here we propose to study this by substituting magnetic Ho for non-magnetic Y in Ho2Ti2O7, where in the high Ho limit ghost spins at the Y sites lead to a topological spin glass, whereas at low Ho limit the system is dominated
by dipolar interactions. Our work to date reveals a number of changes in the dynamic behaviour of these materials below 2 K as a function of substitution. The proposed longitudinal-field muon-spin relaxation measurements allow a unique insight into the magnetic behaviour, where we are directly sensitive to the magnetism in the samples, rather than the stray field as has been previously measured.