Magnetic and Thermal Relaxation in Phase-Separated Solid 3He-4He Mixtures

Relaxation processes in phase-separated solid mixtures of3He in4He with the initial concentration about 3.18 % under the pressure about 3.7 MPa are investigated in the temperature range 1-250 mK. The system was subjected to the action of various sequences of NMR pulses and the character of relaxation was determined from restoration of the longitudinal magnetization to its equilibrium value. Above 100 mK two exponential curves corresponding to the daughter phases - concentrated and diluted - were distinctly observed, which permitted the spin-lattice relaxation time to be determined in these phases. Below 100 mK the NMR signal from the dilute phase practically disappears because of a very small amount of3He in the phase; in this case the Zeeman subsystem and the lattice are related both through magnetic and through thermal relaxation. The measurements using NMR pulses of different length and power demonstrate appreciable overheating of Zeeman subsystem. This shows up as nonmonotonic multi-exponential restoration of equilibrium magnetization whose parameters depend on the power of tipping NMR pulses. The results obtained are described within the proposed physical model.