Low Temperature Physics: 42, 729 (2016); https://doi.org/10.1063/1.4963324
Fizika Nizkikh Temperatur: Volume 42, Number 9 (September 2016), p. 929-935    ( to contents , go back )

Influence of the intermediate bcc phase on the evolution of superfluid inclusions in hcp matrix 3He–4He

A.P. Birchenko, N.P. Mihin, A.S. Neoneta, E.Ya. Rudavskii, and Ya.Yu. Fysun

B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine 47 Pr. Nauky, Kharkiv 61103, Ukraine
E-mail: mikhin@ilt.kharkov.ua

Received March 29, 2016

Abstract

The evolution of liquid inclusions which are formed in the hcp matrix by rapid cooling of the 3He–4He solution containing 1.05% 3He was studied by pulse NMR. The diffusion coefficient of 3He in the liquid was measured by two-pulses spin-echo method during evolution of the inclusions. Measurements were carried out at 1.67 K which corresponds to the bcc phase existence in the phase diagram, as well as at 1.38 K, where the bcc phase is absent. It is found that in the process of the evolution, in both cases the size of the liquid inclusions is less than diffusion length and so the diffusion is restricted. The measured restricted diffusion coefficient allowed to find the characteristic size of the inclusions. In the first case, during the evolution of liquid inclusions, dendrites of intermediate bcc phase is forming and the inclusions are separating into a lot of smaller droplets. Due to the rapid growth of the bcc dendrites, the droplet size decreases rapidly, and the process comes to disappearance of bcc phase and an amorphous state appearance. The results obtained by measuring the diffusion coefficient, correlated with the behavior of the spin-lattice relaxation time in such a system. In the second case at a lower temperature bcc phase is not formed, and the size of the liquid inclusions decreases very slow until the completion of their solidification.

PACS: 64.70.K– Solid–solid transitions;
PACS: 67.80.dj Defects, impurities, and diffusion;
PACS: 67.80.dk Magnetic properties, phases, and NMR;
PACS: 67.60.–g Mixtures of 3He and 4He.

Key words: superfluid inclusions, solid helium, NMR, restricted diffusion.

Published online: July 25, 2016

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