19F NMR and longitudinal field μSR studies of the spin dynamics in LiY0.998Ho0.002F4

It has recently been demonstrated that quantum tunneling of magnetization occurs between the low-lying electro-nuclear energy levels of Ho3+ ions doped into LiYF4. Here, we report 19F NMR and longitudinal field μSR measurements on single crystal LiY0.998Ho0.002F4. We observe that the 19F spin-lattice relaxation rate 1/T1 is controlled by the fluctuating field of the Ho ion and, consequently, 1/T1 increases sharply at resonant magnetic field values where the energy levels are predicted to have level crossings/avoided level crossings, in agreement with the magnetization measurements. Complementary to these ongoing NMR studies we have undertaken longitudinal field μSR measurements. At low magnetic fields, the muon depolarization rate is dominated by strong depolarization due to the formation of F–muon–F bonds, while at higher fields the longitudinal field dominates, and any enhancement of the depolarization rate due to the energy level crossings is very weak.