Muon spin rotation studies of spin dynamics at avoided level crossings in LiY0.998Ho0.002F4

Abstract

We have studied the Ho3+ spin dynamics for LiY0.998Ho0.002F4 via the positive muon (μ+) transverse field depolarization rate λTF as a function of temperature and magnetic field. We find sharp minima in λTF(H) at fields for which the Ho3+ ion system has field-induced (avoided) level crossings. The reduction scales with calculated level repulsions, suggesting that μ+ depolarization by slow fluctuations of nonresonant Ho3+ spin states is partly suppressed when resonant tunneling opens new fluctuation channels at frequencies much greater than the muon precession frequency. © 2007 The American Physical Society.