Pulsed NMR study of submonolayer and multilayer 3He films adsorbed on Grafoil

Abstract

The nuclear spin relaxation times T 1 and T 2 of submonolayer and multilayer 3He films adsorbed on Grafoil have been measured at temperatures between 1.2 and 4.2 K by a pulsed NMR technique. The T 1 data for high-coverage films (solid and dense fluid phases) and the substrate registered phase are interpreted in terms of thermally activated vacancies. In solids the quantum exchange inherent in 3He is shown to be important at low temperatures. The data for multilayer films are discussed in the light of the particle exchange between layers and the relaxation time of each layer. The dynamical behavior of adatoms in the solid, fluid, and substrate registered phases as well as the nature of phase transitions between them are discussed on the basis of information obtained from the analysis of T 1 and T 2 data. The present results as a whole seem to support the phase diagram determined by specific heat measurements. In addition, the nuclear susceptibility in submonolayer films has been measured by the same technique. The effect of Fermi degeneracy was not seen in the temperature range between 1.2 and 4.2 K.