New mode of growth of ^{3}B in hypercooled ^{3}A: Evidence of a spin supercurrent

We report results of an investigation of the growth of the ${}_{}{}^3{}_{}{}^{}\mathit{B}$ phase into the hypercooled ${}_{}{}^3{}_{}{}^{}\mathit{A}$ phase. The form of the magnetization signal associated with the interface evolved radically with increased hypercooling, suggesting a transition to a new mode of growth. We propose a model based on magnetization transport by a spin supercurrent which accounts for many features of the data.