Muon Spin Rotation Studies of Spin Dynamics at Avoided Level Crossings in LiY_(0.998)Ho_(0.002)F_4

摘要

We have studied the Ho~(3+) spin dynamics for LiY_(0.998)Ho_(0.002)F_4 via the positive muon (μ~+) transverse field depolarization rate λ_(TF) as a function of temperature and magnetic field. We find sharp minima in λ_(TF)(H) at fields for which the Ho~(3+) ion system has field-induced (avoided) level crossings. The reduction scales with calculated level repulsions, suggesting that μ~+ depolarization by slow fluctuations of nonresonant Ho~(3+) spin states is partly suppressed when resonant tunneling opens new fluctuation channels at frequencies much greater than the muon precession frequency.