  Spin transport via electrons is typically plagued by Joule heating and short
decay lengths due to spin-flip scattering. It is known that dissipationless
spin currents can arise when using conventional superconducting contacts, yet
this has only been experimentally demonstrated when using intricate
magnetically inhomogeneous multilayers, or in extreme cases such as half-metals
with interfacial magnetic disorder. Moreover, it is unknown how such spin
supercurrents decay in the presence of spin-flip scattering. Here, we present a
method for generating a spin supercurrent by using only a single homogeneous
magnetic element. Remarkably, the spin supercurrent generated in this way does
not decay spatially, in stark contrast to normal spin currents that remain
polarized only up to the spin relaxation length. We also expose the existence
of a superconductivity-mediated torque even without magnetic inhomogeneities,
showing that the different components of the spin supercurrent polarization
respond fundamentally differently to a change in the superconducting phase
difference. This establishes a mechanism for tuning dissipationless spin and
charge flow separately, and confirms the advantage that superconductors can
offer in spintronics.
