Magnon-drag thermopile

Abstract

Spin related effects have been intensively studied using electrical transport methods, by measuring the spin diffusing length in metals and semiconductors. In addition to electrical transport, the thermoelectric properties of magnetic materials are increasingly gathering more attention. There, thermal magnons are expecting to play an major role. However, despite intensive studies on the spin transport, the coupling between electrons and magnons in ferromagnetic metals remains poorly known. Here, we demonstrate a conceptually new device that enables 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. These results demonstrate the feasibility of directly converting magnon dynamics of nanomagnets into an electrical signal and could pave the way to novel thermoelectric devices for energy harvesting.