Ivan V. Kosarev

Nonlinear NMR in a superfluid B phase of 3He in aerogel

The properties of liquid 3He in a low-density aerogel preliminarily covered with a few monolayers of 4He were studied by pulsed and nonlinear CW NMR techniques. It was found that an NMR frequency shift from the Larmor value exhibits a sharp increase at a magnetization tilting angle exceeding 104°. Nonlinear CW NMR signals related to the formation of a macroscopic region featuring homogeneous precession of the magnetization (homogeneous precession domain) were observed. The experimental results confirm that the low-temperature superfluid 3He phase in the aerogel is analogous to the B-phase in bulk 3He and indicate that the spin supercurrents play an important role in the spin dynamics of superfluid 3He in aerogel.

Experiments on A-like to B phase transitions of 3He confined to aerogel

Abstract We have done pulsed and CW NMR studies of A-like to B phase transition in superfluid 3 He confined within aerogel with 98% porosity. The experiments were performed at pressure of 25.5 bar and in magnetic field of 284 Oe and 1 kOe . A kinetics of the transition is found to be different for pure 3 He in aerogel and for the cell preplated with 4 He .

Pulsed NMR experiments in superfluid 3He confined in aerogel

Abstract Pulsed NMR experiments have been performed in both B and supercooled A phases of superfluid 3 He in aerogel. Dependencies of spin precession frequency on tipping angle in B-phase of superfluid 3 He in aerogel are found to be different for pure 3 He and for the cell preplated with 4 He . A sharp increase of the frequency for tipping angles greater than 104° was observed in low temperature superfluid phase of 3 He in 4 He preplated aerogel as it is expected for the B-phase structure of the order parameter. Dependencies of the frequency on the tipping angle in supercooled A-phase are similar for both pure 3 He and 4 He preplated aerogel.

Simple Nuclear Demagnetization Stage

A nuclear demagnetization stage for an ultralow temperature cryostat has been made using the diffusion welding technique. The advantages of the stage are its simple design and large filling factor.

Homogeneous spin precession in superfluid 3He confined to aerogel

Abstract We report on systematic studies of creation and relaxation of a macroscopic region of homogeneous spin precession (homogeneously precessing domain—HPD) in B-like phase of 3 He in aerogel. Long lived free induction decay signal has been observed after filling up the whole cell with the HPD and switching off the CW radiofrequency field. Characteristics of CW NMR and free induction decay signal were found to be similar to those known for bulk 3 He -B.

Measurements of longitudinal and transverse magnetic relaxation in superfluid confined to aerogel

Abstract We present results of pulsed NMR measurements of magnetic relaxation in liquid 3 He in aerogel. It was found that both longitudinal and transverse relaxation starts to change below the temperature of the superfluid transition of 3 He in aerogel. Below Tca the longitudinal relaxation depends on the initial tipping angle.

Observation of fractional harmonics in the NMR signal from superfluid 3He-B

Unusual spin-precession states of 3He-B in which the magnetization is half the equilibrium value are investigated by continuous-wave NMR methods. Signals at frequencies equal to 1/2 and 3/2 of the magnetization precession frequency are observed in two such states. Such signals exist because the order parameter of superfluid 3He in these states precesses with frequency equal to half the magnetization precession frequency.

Low-frequency oscillations of Fermi-liquid domain wall in normal 3He

Abstract We studied low-frequency oscillations of a coherently precessing two-domain spin state in normal 3 He. Three modes of oscillations were observed and the dependence of their frequencies on external field gradient were measured. It was found that two of these modes correspond to oscillation modes predicted earlier theoretically. The origin of the third mode is not yet clear.