Magnetic and Flow Relaxation in Superfluid Helium -3-A(1) Phase
Abstract
Magnetically driven supercurrents in the spin polarized superfluid ^3He-A _1 phase have been studied as function of temperature, pressure (3 to 28 bars) and static magnetic field (0.75 to 14 Koe) by a sensitive mechanical device. The most striking result was the observation of discontinuity of relaxation time as function of temperature at T _{c} which is the transition temperature at zero magnetic field. The effects of moving magnets relative to the device and coating cell surfaces with ^ {4}He on the driven superflow also were studied at static magnetic field 7.5 Koe. A "sign reversal" effect was unexpectedly observed. In the lower temperature range where a A_1 and A _2 interface is present, the observed relaxation time was not affected by shifting magnets and ^4He coating. In the higher range, where the normal phase is attached to the A_1 , the relaxation time increased when magnets moved and also increased with ^4He coverages. A theoretical model based on Liu's hydrodynamics was derived. It shows that the induced spin-density below the device plays a very important role in determining the relaxation time and the response amplitude. The model gives a mechanism of the relaxation. In the higher temperature range, the measured relaxation time was the relaxation time of this induced spin-density, while in lower range it was the normal-flow damping time. It also gives an explanation to the observation of discontinuity of relaxation time at T_{c}, pressure dependence, magnetic field dependence and the "sign reversal" effect. The observations with magnets in the shifted position give a concrete support to the model and the results of ^4He coverage experiments are in very good agreements with the model. By ^4 He coating the cell surfaces, T_1 , the longitudinal magnetic relaxation time in ^3He-A_1 were measured by the mechanical device, other than the NMR method. The frequency dependence of in-phase and quadrature response in AC measurements is also expected with the model. From the observed results, it is concluded that the magnetic moment of the super-fluid component in the ^3He-A_1 is aligned in the direction antiparallel to the applied magnetic field. This is contrary to the previous determinations.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1991
- Bibcode:
- 1991PhDT........25J
- Keywords:
-
- MAGNETIC RELAXATION;
- HELIUM 3 A(1)PHASE;
- Physics: Condensed Matter