Nuclear Magnetic Resonance in Adsorbed Helium

Abstract

There is at present comparatively little information available on the nuclear magnetic properties of adsorbed He³. Most of the experiments have been done on heterogeneous adsorbing surfaces such as Zeolite⁽¹⁾ or Vycor porous glass⁽²⁾, but recent work has been initiated with other adsorbents, including the more regular surface of Grafoil⁽³⁾, as described elsewhere in this conference. Here, we shall report mainly work carried out in Sussex on Vycor. Its aim has been to determine the disposition and motion of the adsorbed atoms and the nature of their magnetic interactions as a function of coverage, through observations of the nuclear magnetic susceptibility X, and the spin-lattice (T₁) and spin-spin (T₂) relaxation times. Both continuous wave and pulsed techniques have been used, at frequencies varying from 0.65 to 7.1 MHz. For coverages of a monolayer and below, the temperature range studied has been 0. 3K to 2.5K. With higher coverages, measurements have been taken down to 45mK, and provide some interesting results on the nature of the interactions within these thicker films, and on the spin diffusion coefficient of Landau quasiparticles in limited geometries. These will not be discussed in detail here since they are outside the main scope of the conference.