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Measurements of both A?B and B?A transitions have been made as a function of magnetic field up to ~100 G at temperatures and pressures close to the polycritical point (PCP). Forms for the specific heat differenceCA-CB=C0(P)-a(P)(Tc-T)/Tc and for the magnetization differenceMA-MB=ßH(Tc-T)/Tc fit the data satisfactorily except very nearTc, where some other mechanism, thought to be a free energy difference due to residual heat flows, tends to stabilize the A phase. The pressure of the PCP, taken to be that at whichC0=0, is found to be 21.22±0.02 bar.

The propagation of 5-, 15-, and 25-MHz sound in superfluid 3He has been studied in zero magnetic field over a wide pressure range. Measurements of the structure and location of the attenuation peaks, velocity changes, and the low-temperature attenuation are described. The degree of strong coupling in the B phase is discussed. Observations of superheating and supercooling near the polycritical point have been extended and comparison is made with theory.

Experimental measurements of the cooling (A?B) and warming (B?A) transitions between3He-A and3He-B are presented for fields of 378 and 5 G. The relationship of these measurements to the existence in zero field of a polycritical point on the line of second-order transitions is then discussed.

Superfluid density of3He has been measured using fourth sound in two superleaks: “confined,” packed powder and “open,” parallel channels. The superleak pore size has little effect on the superfluid density near the melting pressure, but it has surprisingly large effects at lower pressures. The open, parallel channel superleak results show an unexpected pressure dependence of “strong coupling” effects and an unexpectedly small superfluid density change at the B?A transition.

Systematic measurements of the change a – ac of the absorption coefficient for zero sound in3He-A from its value atTc are presented for both 24.08 and 33.53 bar and several frequencies. The3He-A is oriented by means of a magnetic field, so only the case where field and sound directions are parallel give results which can be reliably compared with theory. We find that for 5-MHz zero sound at temperatures well below the collective modes peak there is a substantial anisotropy of the attenuation. We also find at high enough frequency a linear relationship between the sonic frequency and the location on a(1-T/Tc)1/2 scale of the collective modes peak forl·q=0. Comparison of theory and experiment for these data is excellent and suggests that the method may be an accurate one for measuring the temperature dependence of the energy gap in3He-A.

The results of a number of experiments on the dynamic and static magnetic properties of superfluids3He-A and3He-B are presented as well as a description of the 160-MHz rf-biased SQUID system used to make the magnetic flux measurements. Properties of both A and B phases were studied in both a rectangular cavity, a quasiideal geometry for3He-A, and in a stack of parallel plates, a quasiideal geometry for3He-B. The following results are presented: (1) Systematic studies of the properties of the “wall-pinned” magnetization ringing mode in3He-B, including the zero time frequency, which shows a discrepancy with theory, and the relaxation, which tends to confirm the essence of the theoretical ideas; also included are a variety of data on the effect of the finite size of the magnetic field change and the “biasing” field. (2) A complicated propagating magnetic disturbance has been observed using a novel method and systematics of its properties are studied. (3) The linear ringing frequencies of the B and A phases at a pressure of 27.0 bar in the parallel plate geometry have been studied with a result consistent with the assignment of the ABM state to3He-A and the BW state to3He-B. (4) Nonlinear ringing has been studied in both A and B phases in both geometries for both the oscillatory and driven modes. In the limit 1-T/Tc? 0 we find 2pfR/??H ? 2 for both phases in both geometries. Although the general character of ringing frequencyfRas a function of?H follows the theory, there are substantial quantitative discrepancies which cannot be explained by relaxation. Relaxation has been observed and our results have been discussed by Ambegaokar and Levy. (5) New measurements of static magnetism in the parallel plate geometry show agreement with all earlier work, indicating that the discrepancy between static and dynamic measurements cannot be explained by a geometrical effect. An experimental manifestation of the AB interfacial energy enabled an estimate of the coherence length to be made which is in qualitative agreement with theory.

Convective instabilities in a rectangular, unity-aspect-ratio Rayleigh-Bénard cell with a solution of 1.46%3He in superfluid4He have been studied in the temperature range 0.70–1.05 K, with a corresponding Prandtl number range of 0.045

The melting curve of3He was measured below 25 mK and in magnetic fields of 2.12, 6.36, 31.8, and 63.6 kG. The compressional cooling technique was used with a capacitive pressure gauge and a54Mn-in-iron ?-ray anisotropy thermometer. A depression was observed in the melting curve, indicating nuclear spin ordering in the solid3He. The effect is larger in magnitude and develops more rapidly with field than the theoretically expected results.

Measurements are given on the bulk nuclear spin polarization in a liquid-solid3He mixture cooled by compressional cooling to below 5 mK in a magnetic field of 54.5 kG. Owing to the low Pauli spin susceptibility of liquid3He, the observed polarization is primarily due to solid3He. A maximum average nuclear polarization of 47% was observed, although the corresponding solid3He polarization is believed to be higher. Our novel detection system, using a dual directional coupler for cw NMR, is a simple and versatile means of working in the awkward frequency range around 180 MHz. We also report transient heating measurements in the3He system which indicate that the internal thermal equilibrium time in bulk solid3He on the3He melting curve appears to be quite short (less than 5 min) at these temperatures. One type of transient measurement is complicated by the dramatic effect of the contribution of the3He nuclear magnetization to the total local magnetic field. This contribution is considered via a simple model.

An additional analysis of our low-temperature and high magnetic field measurements of the3He melting curve is presented, based on the assumption that the highest field (63.6 kG) theoretical melting curve is correct rather than the lowest field curve as assumed in the original paper. Between31.8 and63.6 kG there is reasonable agreement between experiment and theory, although a discrepancy remains at low fields that we assume is to be attributed to inaccuracies in the reduction of ?-ray anisotropies to temperatures. It is also shown that the measurements are not sufficiently precise to observe the effect seen in the(?P/?T)V,H measurements on solid3He by Kirk and Adams.

A study of adiabatic compressional cooling of a two-phase mixture of solid and liquid He3 has been made. Details of the experimental arrangement are given. Using a flexible elastic low temperature He3 cell that is compressed by liquid He4 and precooled by a continuously operating dilution refrigerator, cooling to below 2 m°K was obtained from starting temperatures near 20 m°K. Frictional heating is remarkably low. Calculations are presented which investigate the fraction of solid formed and which suggest rather long thermal equilibrium times in the solid He3 nuclear spin system. Application of the method to the production of bulk polarized He3 nuclei is discussed.

A new experimental arrangement has been used to measure the times for equilibrium between cerium magnesium nitrate (CMN) and liquid3He. Measurements have been made on a single crystal of CMN from temperatures of 5.5–15 mK and on a powdered specimen from temperatures of 2.5–35 mK. The thermal resistance deduced from the single-crystal data is proportional toT-2. The thermal resistance obtained from the powder data may be separated into three contributions: a resistance which is proportional toT-2in series with a parallel combination of a phonon resistance (with resistivity ?P=3×10-4T-3sec·cm2·K4·erg-1) and a magnetic resistance (with resistivity ?M=9×102T sec·cm2·erg-1 in zero applied magnetic field). A reduction in the magnetic resistance was observed when the powdered CMN was placed in a magnetic field, the magnitude of this reduction being comparable to that expected from a Redfield-like theory. TheT-2resistance is discussed in terms of two-dimensional energy transport within the CMN. The 17-Hz susceptibility of the powdered CMN was measured in magnetic fields of 0, 18.9, 30.2, and 37.8 G. The magnetic temperatureT* (H=37.8 G) was found to differ by +0.5 mK from the magnetic temperature in zero field whenT* (H=0)=3 mK.