Spin Fluid Dynamics Observed by Magnetic Fountain Effect and Mechano-Spin Effect in the Ferromagnetic Superfluid $^3$He A$_1$ Phase

TL;DR

This study investigates spin fluid dynamics in superfluid $^3$He A$_1$ phase through magnetic fountain and mechano-spin effects, revealing increased spin relaxation near phase boundaries and supporting theoretical predictions of minority spin condensates.

Contribution

First systematic measurement of fountain pressure and mechano-spin effects in superfluid $^3$He A$_1$, demonstrating spin relaxation behavior consistent with minority spin condensate theories.

Findings

Measured decay of induced pressure in A$_1$ phase across various temperatures and fields.

Observed increased spin relaxation rate approaching the A$_2$ phase boundary.

Results support the presence of a minority spin condensate as predicted by theory.

Abstract

Systematic observations of the magnetically generated fountain pressure in the superfluid $^3$He A$_1$ have been carried out in a newly built apparatus designed to reduce the effect of thermal gradients. In the same apparatus, mechanical pumping and filtering of polarized nuclear spins were realized by the pneumatic pumping action of an electrostatically actuated membrane. In both experiments, the measured induced pressure was observed to decay at all temperatures where the A$_1$ phase appeared in magnetic fields up to 13 T and liquid pressures between 1 and 29 bar. The inferred spin relaxation rate tended to increase as the low temperature phase boundary with the A$_2$ phase (T$_{C2}$) was approached. The increase in spin relaxation rate near T$_{C2}$ can be explained by the presence of a minority spin condensate in the A$_1$ phase as predicted by Monien and Tewordt and by the application of the Leggett-Takagi theory of spin relaxation in superfluid $^3$He.