Physics and Engineering of Nanodevices Group

a, The magnon population in ferromagnetic wires is represented schematically by an arrow with a given precession angle. A magnetic field, B>0, applied parallel to the magnetization, leads to a reduction/damping of the magnon population (represented by a reduction in the precession angle). In contrast, a magnetic field B<0, antiparallel to the magnetization, results in an increase of the magnon population (increase in the precession angle). b,c, Magnon-drag measurements. The wires are connected thermally in parallel and electrically in series. For parallel magnetization orientation (b), the thermoelectric voltage is zero because the contribution from each wire is the same and has opposite sign. For the antiparallel configuration (c), in the presence of B, a non-zero thermoelectric voltage is measured owing to the difference in magnon-drag effect, directly related to the difference in magnon populations induced by B. d, Scanning electron microscope image (SEM) of a typical device. A large number of pairs of NiFe wires (blue) are connected in series with Ag wires (red). A wide Pt wire (yellow) serves as a heater to generate a thermal gradient, .