Nuclear magnetic resonance of adsorbed3He films on Grafoil and argon-coated grafoil. II. Intermediate and near-monolayer coverages

✍ Scribed by S. G. Hegde; J. G. Daunt

• Publisher: Springer US
• Year: 1979
• Tongue: English
• Weight: 845 KB
• Volume: 34
• Category: Article
• ISSN: 0022-2291
• DOI: 10.1007/bf00117152

✦ Synopsis

Continuous wave (CW) nuclear magnetic resonance measurements have been made at 5.5MHz of 3He adsorbed on Grafoil and on argon (monolayer)-coated Grafoil at coverages 0.55 ~ x <~ 1.35 (x = 1 corresponds to one monolayer ), in the temperature range 0.35-4.21 K. The results indicate that the near-monolayer coverages (0.9<~ x <<-1.0) behave as 219 solids with dipole-dipole coupling modulated by quantum exchange between nearest neighbors. The exchange frequency for this solid phase is evaluated and is seen to be comparable to that observed in bulk, solid SHe for similar atomic spacing. The intermediate coverages, 0.55<~x ~ 0.80, showed no evidence of line broadening in the entire temperature range investigated, while the relative magnetic susceptibilities indicated no deviation from Curie's law. No evidence f3or the registered phase was found at x = 0.60 either for 3He on Grafoil or for He on argon-coated GrafoiL A sharp decrease was observed in linewidth after completion of the monolayer, making NMR an excellent probe for the determination of monolayer completion. We have also made linewidth measurements for a coverage x = 0.95 of 3He on graphitized carbon black (Sterling FT grade) at 4.2 and 1.2 K. The results are consistent, as in the case 3 of He on Grafoil, with a 2D solid with significant quantum tunneling between nearest neighbors. This result, however, is in disagreement with the measurements of Rollefson, also for ~ on graphitized carbon black of the same grade, who observed a rigid lattice behavior withnegligible tunneling between neighbors, for a coverage x = 0.90. This discrepancy is not yet understood.