  Muon spin relaxation measurements on some quantum spin ice candidate
materials, the insulating pyrochlores Pr2B2O7 (B = Sn, Zr, Hf), have been
performed for temperatures in the range 0.05-280 K. The results are indicative
of a static distribution of magnetic moments which appears to grow on cooling
and whose size at low temperatures is significantly larger than that expected
for Pr nuclear moments. Using density functional theory we show how this effect
can be explained via a hyperfine enhancement arising from a splitting of the
non-Kramers doublet ground states on Pr ions close to the muon which itself
causes a highly anisotropic distortion field. We provide a quantitative
relationship between this effect and the measured temperature dependence of the
muon relaxation and discuss the relevance of these observations to muon
experiments in other frustrated magnetic materials.
