The³He nuclear magnetic relaxation in nematically ordered Al<inf>2</inf>O<inf>3</inf>aerogels: Effects of ⁴He and nitrogen pre-plating

Abstract

The results of 3He gas pulsed NMR spin-lattice relaxation study in high-porosity (84.9%-97.9%) nematically ordered Al2O3 aerogels at 1.5 and 4.2 K are presented. The linear dependence of T 1 on gas pressure is observed in aerogels that are pre-plated by helium-4. Nitrogen pre-plating prior to helium-4 pre-plating weakly decreases the 3He gas spin-lattice relaxation rate. A few possible mechanisms plausibly involved in 3He nuclear magnetic relaxation in aerogels are considered. The suggested nuclear spin-lattice relaxation model due to some magnetically 'dirty' aerogel fibers allows to estimate the effective mean free path of 3He atoms in aerogel.