Probing spin dynamics and quantum relaxation in LiY0.998Ho0.002F4 via 19F NMR

TL;DR

This study uses 19F NMR to investigate spin dynamics and quantum relaxation in LiY0.998Ho0.002F4, revealing quantum effects, level crossing phenomena, and suppressed decoherence, with potential for direct measurement of level repulsions.

Contribution

It demonstrates the use of 19F NMR as a probe for rare-earth spin dynamics in a single-ion magnet, highlighting quantum effects and low-temperature level broadening.

Findings

19F 1/T1 depends on coupling with rare-earth moments.

Behavior similar to molecular nanomagnets due to energy level discreteness.

Level broadening at crossings becomes extremely small at low temperatures.

Abstract

We report measurements of 19F nuclear spin-lattice relaxation 1/T1 as a function of temperature and external magnetic field in LiY0.998Ho0.002F4 single crystal, a single-ion magnet exhibiting interesting quantum effects. The 19F 1/T1 is found to depend on the coupling with the diluted rare-earth (RE) moments. Depending on the temperature range, a fast spin diffusion regime or a diffusion limited regime is encountered. In both cases we find it possible to use the 19F nucleus as a probe of the rare-earth spin dynamics. The results for 1/T1 show a behavior similar to that observed in molecular nanomagnets, a result which we attribute to the discreteness of the energy levels in both cases. At intermediate temperatures the lifetime broadening of the crystal field split RE magnetic levels follows a T3 power law. At low temperature the field dependence of 1/T1 shows peaks in correspondence to the critical magnetic fields for energy level crossings (LC). The results can be explained by inelastic scattering between the fluorine nuclear spins and the RE magnetic levels. A key result of this study is that the broadening of the levels at LC is found to be become extremely small at low temperatures, about 1.7 mT, a value which is comparable to the weak dipolar fields at the RE lattice positions. Thus, unlike the molecular magnets, decoherence effects are strongly suppressed, and it may be possible to measure directly the level repulsions at avoided level crossings.