  The observation of the spin Hall effect triggered intense research on pure
spin current transport. With the spin Hall effect, the spin Seebeck effect, and
the spin Peltier effect already observed, our picture of pure spin current
transport is almost complete. The only missing piece is the spin Nernst
(-Ettingshausen) effect, that so far has only been discussed on theoretical
grounds. Here, we report the observation of the spin Nernst effect. By applying
a longitudinal temperature gradient, we generate a pure transverse spin current
in a Pt thin film. For readout, we exploit the
magnetization-orientation-dependent spin transfer to an adjacent Yttrium Iron
Garnet layer, converting the spin Nernst current in Pt into a controlled change
of the longitudinal thermopower voltage. Our experiments show that the spin
Nernst and the spin Hall effect in Pt are of comparable magnitude, but differ
in sign, as corroborated by first-principles calculations.
