Reciprocal space measurements of spin diffusion in a single crystal of calcium fluoride (CaF2) have been extended to dipolar ordered states. The experimental results for the component of the spin diffusion rate parallel to the external field are D∥D=29±3×10-12 cm2/s for the  direction and D∥D=33±4×10-12 cm2/s for the  direction. The measured diffusion rates for dipolar order are faster than those for Zeeman order and are considerably faster than predicted by simple theoretical models. It is suggested that constructive interference in the transport of the two-spin states is responsible for this enhancement. As expected, the anisotropy in the diffusion rates is observed to be significantly less for dipolar order compared to the Zeeman case.
Physical Review Letters
- Pub Date:
- March 2004
- Macroscopic quantum phenomena in magnetic systems;
- Nuclear magnetic resonance and relaxation;
- Condensed Matter
- 4 pages, 2 figures. Resubmitted to PRL - new figure added / discussion expanded