The(3)He Nuclear Magnetic Relaxation In Nematically Ordered Al2o3 Aerogels: Effects Of He-4 And Nitrogen Pre-Plating

The results of He-3 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 He-3 gas spin-lattice relaxation rate. A few possible mechanisms plausibly involved in He-3 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 He-3 atoms in aerogel.