  We have studied the Ho3+ spin dynamics for LiY0.998Ho0.002F4 through the
positive muon (mu+) transverse field depolarization rate lambda_TF as a
function of temperature and magnetic field. We find sharp reductions in
lambda_TF(H) at fields of 23, 46 and 69 mT, for which the Ho3+ ion system has
field-induced (avoided) level crossings. The reduction scales with calculated
level repulsions, suggesting that mu+ depolarization by slow fluctuations of
non-resonant Ho3+ spin states is partially suppressed when resonant tunneling
opens new fluctuation channels at frequencies much greater than the muon
precession frequency.
