Susceptibility of solid 3He near the ordering temperature

The magnetic susceptibility of solid ³He at melting pressure has been measured down to 1.25 mK. Below about 4 mK, the susceptibility begins to rise significantly above the Curie-Weiss behavior followed at higher temperatures.     

Measurement of the susceptibility of solid 3He along the melting curve from 20 mK down to the nuclear ordering temperature

The susceptibility of solid ³He is deduced from multiple echoes observed in pulsed NMR experiments. It follows a Curie Weiss law at high temperature, increases faster than this law below 5 mK and drops abruptly around 1 mK.     

The concentration susceptibility in He3He4 mixtures near the superfluid transition

We report direct measurements of the concentration susceptibility in He³He⁴ mixtures by observing the gravity-induced concentration change δX₃ over a height of 2 mm in the mixture. The predicted peak at the superfluid transition is observed for the investigated mixtures, 0.60 ? X₃ ? 0.67.     

Observation of unusual mass transport in solid hcp (4)He

Solid (4)He has been created off the melting curve by growth at a nearly constant mass via the "blocked capillary" technique and growth from the (4)He superfluid at constant temperature. The experimental apparatus allows injection of (4)He atoms from superfluid directly into the solid. Evidence for the superfluidlike transport of mass through a sample cell filled with hcp solid (4)He off the melting curve is found. This mass flux depends on temperature and pressure.     

Magnetization studies of the nuclear spin ordered phases of solid <Superscript>3</Superscript>He in silver sinters

Solid ³He, in the bcc lattice between 34 and 100 bar, exhibits two nuclear magnetic ordered phases in the sub-mK temperature range, the so called U2D2 low (magnetic) field phase and the “high field phase” above 0.4 T. To determine the exact spin structure of these phases we started a project of neutron scattering from the ordered solid in collaboration with the Hahn-Meitner Institute, Berlin, and other European and US groups. For this experiment it is crucial to grow a single crystal within the sinter needed for cooling the solid to temperatures of the order of 500 μK (or even twenty times lower in the case of the hcp lattice which is formed above 100 bar) and to keep it there long enough to measure a magnetic neutron reflection. We studied the growth of crystals in Ag sinters of different pore size and with different growth speeds to find an optimal way to obtain single crystalline samples. As a first diagnostic step we performed pulsed NMR measurements in the ordered phases of solid ³He in a sinter of 2700 Å particle size down to temperatures of 450 μK at various molar volumes. We could keep the samples in the ordered state for as long as 140 h. The second method we used was SQUID magnetometry. For the low field phase T_N was indicated by a drop of the intensity, both in the NMR signal and in the dc magnetization, whereas in the high field phase an increase of about 30% was observed below the ordering temperature. For the fabrication of the sinters a packing fraction of 50% and subsequent annealing proved to be very favorable to obtain cold ordered solid. Furthermore, we find that a paramagnetic surface contribution from a few monolayers of ³He exists down to 500 μK in addition to the bulk magnetization.     

Lifetime of the Cs 6P1/2 state in bcc and hcp solid 4He

We present the first experimental study of time-resolved fluorescence from laser-excited Cs(6P_1/2) atoms isolated in a solid ⁴He matrix. The results are compared to the predictions of the bubble model including the interaction of the atomic dipole with its radiation reflected at the bubble interface. Our results show that in liquid He as well as in the body-centered cubic (bcc) crystalline phase of He the lifetime of excited Cs atoms does not depend on He pressure, in agreement with our theory. When going from the bcc to the hexagonally close-packed (hcp) phase of ⁴He the lifetime is reduced by ≈10% and decreases further with increasing He pressure. We assign this effect to the formation of Cs^*He_n exciplexes, and determine the pressure dependence of the probability that the 6P_1/2 state decays via this nonradiative channel.     

Simple and inexpensive3He insert for an ac susceptometer

The design of a simple and inexpensive³He insert for the existing ac susceptometer is described. The system uses a home built mutual inductance bridge for the ac susceptibility measurements from 0·4 K to 300 K. Simple and inexpensive design with the top loading facility are the main features of this set up. The insert can also be used as a continuously³He operating refrigerator down to 0·5 K.     

Global ac susceptibility of low pinning high-T c crystals near T c

We have studied the hysteretic loss and the shielding capability of Bi₂Sr₂CaCu₂O₈and YBa₂Cu₄O₈ crystals as a function of ac field (μ ₀ H ≤ 1mT), frequency, and temperature at small dc fields (μ₀ H _a < 1 mT) near the critical temperature T _c . We show that the global ac field dependence of the susceptibility can be described in terms of a geometrical barrier model in agreement with local permeability results. At temperatures very near T _c , however, we observe a crossover to diffusive behavior. The frequency dependence of the temperature of the dissipation maximum at finite dc fields shows a thermally activated behavior.     

Magnetization and magnetic susceptibility of GdH3

Magnetic susceptibility measurement in the range 1.4 to 4.2 K reveal a maximum in χ at 3.65 K, and two maxima in Δχ/ΔT, one at 3.32 K (assumed to be T_N), and another at 1.8 K. High field magnetization measurements indicate a saturation moment of 7 μ_B.