  In thin film ferromagnets with perfect easy-plane anisotropy, the component
of total spin perpendicular to the easy plane is a good quantum number and the
corresponding spin supercurrent can flow without dissipation. In this Letter we
explain how spin supercurrents couple spatially remote spin-mixing vertical
transport channels, even when easy-plane anisotropy is imperfect, and discuss
the possibility that this effect can be used to fabricate new types of
electronic devices.
