The3He nuclear magnetic relaxation in nematically ordered Al2O3aerogels: effects of4He and nitrogen pre-plating.

The results of3He gas pulsed NMR spin-lattice relaxation study in high-porosity (84.9%-97.9%) nematically ordered Al2O3aerogels at 1.5 and 4.2 K are presented. The linear dependence ofT1on gas pressure is observed in aerogels that are pre-plated by helium-4. Nitrogen pre-plating prior to helium-4 pre-plating weakly decreases the3He gas spin-lattice relaxation rate. A few possible mechanisms plausibly involved in3He 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 of3He atoms in aerogel.