Hideyuki Kojima

Development of a 3He-hydraulic actuator for spin pump in superfluid 3He-A1

The superfluid 3He A1 phase contains a spin-polarized condensate. This property allows novel superfluid spin current experiments. In the mechano-spin effect of the A1 phase a mechanically applied pressure gradient and a superleak-spin filter enable to directly boost spin polarization of 3He in a small chamber. Using a flexible membrane as an electrostatically actuated pump, we carried out such experiments and observed 50% enhancement of spin density. Here we report on a new 3He-hydraulic actuator for achieving greater enhancement of spin density. The actuator consists of two liquid 3He chambers located at a 4.2 K plate and in the interior of the cell. The pressure in the 4.2 K chamber is heater-controlled and it transmits a force onto a membrane in the cell. The motion of the membrane induces spin-polarized current into an accumulation chamber.

Dynamics of Magnetically Induced Superflow in Spin‐Polarized 3He A1

The spin relaxation time (τ) in superfluid 3He A1 phase is measured by observing the magnetic fountain pressure induced across a superleak. Preliminary data are reported on the dependence of τ on applied magnetic field (H), pressure and 4He coverage. When 0.5 < H <1 tesla, τ increases linearly with H in accordance with Hammel‐Richardson model. However, τ varies little with field when 2 < H < 8 tesla. As pressure is decreased, τ increases. When the interior wall surfaces (including those of heat exchanger) are covered with five layers of 4He, τ does not change significantly. Conflicting observations show that the driven spin flow phenomena are not well understood. A new oscillatory behavior in magnetic fountain effect at 29 bars is also described.

Magnetically induced spin flow and relaxation in superfuid 3He A1

The magnetic fountain effect occurring in superfluid 3He A1 phase is a unique phenomenon in which the pressure and magnetic field gradients in the chemical potential are balanced. The effect has been applied extensively to investigate the intrinsic spin relaxation. We constructed a new improved sample cell. The new cell includes an inner detector and an outer reservoir chamber made of Macor which was helpful to reduce the heat release possibly arising from proton nuclei under high magnetic fields. The measured temperature difference between the two chambers was cut to less than 5 μK. The measured relaxation time τ of the fountain pressure decreases monotonically and smoothly as the temperature is decreased from Tc1 (normal- A1 boundary) towards Tc2 (A1- A2 boundary). As the temperature approaches Tc2, τ tends to vanish smoothly.