The spin-lattice relaxation in superfluid inclusions formed in the solid helium matrix

Abstract

Processes of spin-lattice relaxation in superfluid inclusions, formed during growth and rapid cooling of helium crystals, are studied by the pulse nuclear magnetic resonance method. Measurements of spin-lattice relaxation times were carried out using the two spin-echoes method. This allows to obtain reliable data for each of the coexisting phases of a two-phase system HCP matrix—superfluid inclusions. The samples of the solid solution 1% 3He in 4He with molar volume 20.2 cm3/mol are investigated in the temperature range 1.4–1.9 K. It is found that the time of spin-lattice relaxation in superfluid drops differs significantly from that in bulk superfluid. It is shown that in both cases the dominant relaxation mechanism is the wall relaxation, which is a few orders of magnitude faster than the bulk relaxation. However, in the bulk fluid, the velocity of wall relaxation is determined by the time of diffusion of atoms to the walls, while the spin relaxation processes directly on the wall play a major role in the superfluid inclusions. In the case of superfluid droplets, 3He atoms are the only magnetic impurities on the walls of the inclusions. They are much less efficient magnetic centers than the strong magnetic particles on the walls of the cell. Moreover, a spontaneous dramatic change is observed in the amplitude of one of the echo-signals, which is associated with the solidification of superfluid droplets and the formation of long-lived metastable disordered (glass) state.