Tsuneo Fukuda

Search for superfluidity of3He in3He-4He solution

We have tried to cool a3He-4He solution down to the microkelvin temperature region to search for a superfluid transition of the3He component in the solution. The contact surface area between the solution and a sintered powder has been increased enormously by the use of a fine platinum powder, to reduce the effect of the residual heat leak directly entering into the solution. Although the heat leak was found to be time dependent, the ultimate ratio of the heat leak to the surface area is about 0.046 pW/m2, improved very much from those by the other groups. But the lowest temperature of the solution is still around 0.2 mK, and no evidence of the transition has been observed yet.

MAGNETIC PHASE DIAGRAM OF BCC 3HE

Abstract A complete magnetic phase diagram of bcc solid 3He at a molar volume of 22.7 cm3/mol has been determined by pressure measurements at temperatures down to 250 μK in magnetic fields up to 7 T. The transition temperature between the paramagnetic phase and the high-field antiferromagnetic ordered phase increases with field and reaches a maximum (=0.96 mK) at 3 T. Above this field, it turns to decrease and seems to be zero at 5.4 T, i.e., the upper critical field Bc2(0). The transition is not the first-order one from 1 T to Bc2(0). The observed reentrant phase diagram strongly supports the multiple spin exchange model, but reveals a severe quantitative inaccuracy of the mean field approximation even at high fields near Bc2(0).

Nuclear magnetism of BCC solid 3He in a high magnetic field

Isochoric pressure measurements have been made for bcc solid 3He with a high density in a magnetic field up to 7 Tesla. The sample has successfully been cooled down to 0.4 mK at 7 T. Temperature dependence of the pressure suggests that the upper critical field for the molar volume of 22.53 cm3/mol is below 7 T.

Melting pressure of solid 3He near the magnetic tricritical point

Abstract We have performed precise measurements of the melting pressure of solid 3He near the magnetic tricritical point. The line which surrounds the low-field ordered phase on a melting pressure vs magnetic field phase diagram has a sharp turn at 3.92kG over a field interval no more than 0.03kG. This means that the entropy and the magnetization of the solid rapidly change across the transition from the paramagnetic phase to the high-field ordered phase in a narrow temperature range.

Magnetic interaction at oxygen sites of YBa2Cu3O6.25 studied by TDPAD with 19F isomer

Abstract We measured the internal field at oxygen sites in a single crystal of the magnetic compound YBa2Cu3O6.25 with the time differential perturbed angular distribution method using 19F isomer. The asymmetry of the rotation pattern in 1.37 T decreases to about half at low temperature from the value at 300 K. At the same time, the rotation amplitude decays considerably while the frequency is uncharged. The present results suggest that the magnetic interaction between Cu ions in the plane layers is the exchange via oxygen while the oxygens in the barium and chain layers feel the weak dipole field.

Magnetization of bcc solid 3He in a high magnetic field

Abstract A bulk bcc solid 3He with a molar volume of Vm=23.06 cm3/mol was cooled down to 0.5 mK in a magnetic field of 5.729 T. Magnetization was measured across the nuclear ordering transition to the high field phase by use of NMR method. The magnetization as large as 90 % of the saturation magnetization was observed at the lowest temperature.

Spin waves in − 4 3 He solutions

Standing spin-wave modes in /sup 3/He-/sup 4/He dilute solutions with /sup 3/He atomic concentrations between 1.3% and 8.6%, and at pressures of 0, 7, or 8 bars have been studied with cw NMR at Larmor frequencies of 1 and 2 MHz. The spin waves, which produce peaks in the NMR absorption lines, are visible at temperatures below a few millikelvins. At the lowest temperatures, an additional field gradient along the static field causes a new side peak at the outermost frequency. These spin-wave peaks shift with the field gradient. The field-gradient dependence of the spin-wave peaks is fitted to the theory of Leggett, leading to the determination of the Fermi-liquid interaction parameter (lambda). The sign of lambda is found to change at /sup 3/He atomic concentration between 3% and 5% at pressures of both 0 and 7 bars. Its concentration and pressure dependence are discussed on the basis of the quasiparticle interaction potential.

Spin waves in /sup 3/He-/sup 4/He solutions

Standing spin-wave modes in /sup 3/He-/sup 4/He dilute solutions with /sup 3/He atomic concentrations between 1.3% and 8.6%, and at pressures of 0, 7, or 8 bars have been studied with cw NMR at Larmor frequencies of 1 and 2 MHz. The spin waves, which produce peaks in the NMR absorption lines, are visible at temperatures below a few millikelvins. At the lowest temperatures, an additional field gradient along the static field causes a new side peak at the outermost frequency. These spin-wave peaks shift with the field gradient. The field-gradient dependence of the spin-wave peaks is fitted to the theory of Leggett, leading to the determination of the Fermi-liquid interaction parameter (lambda). The sign of lambda is found to change at /sup 3/He atomic concentration between 3% and 5% at pressures of both 0 and 7 bars. Its concentration and pressure dependence are discussed on the basis of the quasiparticle interaction potential.

Spin waves in−43He solutions

Standing spin-wave modes in /sup 3/He-/sup 4/He dilute solutions with /sup 3/He atomic concentrations between 1.3% and 8.6%, and at pressures of 0, 7, or 8 bars have been studied with cw NMR at Larmor frequencies of 1 and 2 MHz. The spin waves, which produce peaks in the NMR absorption lines, are visible at temperatures below a few millikelvins. At the lowest temperatures, an additional field gradient along the static field causes a new side peak at the outermost frequency. These spin-wave peaks shift with the field gradient. The field-gradient dependence of the spin-wave peaks is fitted to the theory of Leggett, leading to the determination of the Fermi-liquid interaction parameter (lambda). The sign of lambda is found to change at /sup 3/He atomic concentration between 3% and 5% at pressures of both 0 and 7 bars. Its concentration and pressure dependence are discussed on the basis of the quasiparticle interaction potential.