Relaxation of the nuclear magnetism of liquid {sup 3}He at the surface of paramagnetic crystals

We present the results of experimental studies of the nuclear magnetic relaxation of {sup 3}He atoms located in a narrow gap (100 {mu}m) between the pairs of crystals LiYF{sub 4}-LiYF{sub 4} and LiYF{sub 4}-LiTmF{sub 4}. We propose a theoretical model to describe how the bounded geometry affects the relaxation rate of helium nuclei. The model allows us to qualitatively understand features in the relaxation process observed in experiments both with crystals and with powders. We show that an important role in the magnetic relaxation of helium is played by local nonuniformities in the magnetic field caused by defect paramagnetic ions of Tm{sup 3+} located at the walls of microcracks at the crystal surface. The experimental data show no evidence that resonant magnetic coupling between {sup 3}He and {sup 169}Tm influences the relaxation rate of magnetization of liquid helium-3. 31 refs., 6 figs., 1 tab.