  Thermoelectric effects in spintronics are gathering increasing attention as a
means of managing heat in nanoscale structures and of controlling spin
information by using heat flow. Thermal magnons (spin-wave quanta) are expected
to play a major role, however, little is known about the underlying physical
mechanisms involved. The reason is the lack of information about magnon
interactions and of reliable methods to obtain it, in particular for electrical
conductors because of the intricate influence of electrons. Here, we
demonstrate a conceptually new device that allows us to gather information on
magnon-electron scattering and magnon-drag effects. The device resembles a
thermopile formed by a large number of pairs of ferromagnetic wires placed
between a hot and a cold source and connected thermally in parallel and
electrically in series. By controlling the relative orientation of the
magnetization in pairs of wires, the magnon-drag can be studied independently
of the electron and phonon-drag thermoelectric effects. Measurements as a
function of temperature reveal the effect on magnon drag following a variation
of magnon and phonon populations. This information is crucial to understand the
physics of electron-magnon interactions, magnon dynamics and thermal spin
transport.
