Spin-Spin Relaxation in Phase-Separated 3He-4He Solid Mixtures

Abstract

The spin-spin relaxation time T 2 in a 3 He- 4 He solid mixture with an initial concentration of 3.18 % 3 He is measured during its phose separation in a temperature runge of 1-250 mK. Cooling down to the region of separation was carried out by small sleps (∼ 10 mK) followed by temperature stabilization for many hours. The time T 2 was measured by using the pulsed NMR technique at a frequency of 250 kHz. The spin echo method makes it possible to distinguish the contributions to magnetic relaxation from both the concentrated and the dilate separated phases. The relaxation time T 2 in the concentrated phase is found to be practically independent of temperature down to ∼ 50 mK and is determined by the same 3 He - 3 He exchange interaction as in pure bulk solid 3 He. It is found that the behavior of the spin echo signal at ultralow temperatures exhibits an anomaly, which may be connected with quasi-onc-dimensional spin diffusion. In the dilute daughter phase the spin-spin relaxation time is inversely proportional to concentration and is described correctly by the Torrey model taking into account 3 He - 4 He tunnel exchange. The values of T 2 in this phase coincide with those for a homogeneous (non-separated) mixture of the same concentration.