Frequency Dependent Susceptibiltiy Measurements of Dilute Spin Ice.*

We have recently demonstrated in the classical spin ice materials Dy2Ti2O7 and Ho2Ti2O7 that the magnetic relaxation below the spin freezing transition is dominated by nuclear assisted tunnelling. Indeed, this is likely a mechanism for monopole separation and dynamics under an applied potential at temperature below ~0.65K. Given this surprising result, we have simplified the system further to isolate possible dynamical processes driven by the nuclear moments. We have considered samples with non-magnetic ion dilution, namely HoxY2-xTiO7 at the 1 and 0.25 % level. We have investigated the samples as a function of frequency up 5 MHz and see clear evidence of evolving single ion dynamics within distinct frequency response time windows strongly suggesting other mechanisms of spin dynamics in the dilute spin ice system. The properties of these dynamics will be explained in detail.