Measurement of the Conduction Electron Spin Scattering Cross Sections of Argon, Krypton, and Xenon on Lithium

The conduction electron spin resonance technique was used to measure spin relaxation by rare gas adsorbates on lithium films that had been evaporated and maintained under ultra high vacuum conditions. The dependence of the spin resonance line width on gas coverage was measured. For fractional monolayer coverage the line width was found to be linear in the coverage allowing the determination of a spin scattering cross section which parameterizes the strength of spin scattering by an isolated adatom. The spin resonance signal was calculated by incorporating the effect of surface spin relaxation in a boundary condition on the transverse spin magnetization at the surface. A linear relationship between the transverse spin relaxation rate and the surface spin scattering cross section was derived and shown to be independent of sample geometry provided the adsorbate coverage is dilute and, the transverse spin magnetization uniform. The experiments were performed in an ultra high vacuum system which was specially designed around the requirements of measuring the spin resonance signal of a sample which was prepared in situ. A specially constructed continuous flow ultra high vacuum compatible liquid helium cryostat was used to maintain sample temperatures anywhere in the range 4-400(DEGREES)K. The spin scattering cross sections of the rare gases were found to be smaller than those of bulk metallic impurities of comparable atomic number, but not by many orders of magnitude. The size of the cross sections were interpreted as confirming a theoretically predicted transfer of conduction electron charge onto rare gas adsorbates.