Low Temperature Physics: 39, 801 (2013); https://doi.org/10.1063/1.4821755
Fizika Nizkikh Temperatur: Volume 39, Number 9 (September 2013), p. 1031-1040 ( to contents , go back )
The spin-lattice relaxation in superfluid inclusions formed in the solid helium matrix
А.P. Birchenko, Ye.O. Vekhov, N.P. Mikhin, and E.Ya.Rudavskii
B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine 47 Lenin Ave., Kharkov 61103, Ukraine
Received March 29, 2013
The processes of spin-lattice relaxation in the superfluid inclusions, formed during growth and rapid cooling of helium crystals are studied by the pulse nuclear magnetic resonance method. The measurements of spin-lattice relaxation time were carried out using a two spin-echoes method. This allows us 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 the superfluid drops differs significantly from that in the bulk superfluid. It is shown that in both cases the dominant relaxation mechanism is the wall relaxation, which is some orders of magnitude faster than the bulk relaxation. However, in the bulk fluid, the velocity of wall relaxation is determined by the time of atoms diffusion 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 ob-served in the amplitude of one of the echo-signals, which associated with the solidification of superfluid droplets and the formation of long-lived metastable disordered (glass) state.
PACS: 64.70.K– Solid-solid transitions;
Key words: superfluid inclusions, solid helium, NMR, spin-lattice relaxation.