Signature of electron-magnon Umklapp scattering in L10 FePt probed by thermoelectric measurements

We report unconventional thermoelectric power (Seebeck coefficient, S) in L10 structured FePt films. The temperature dependence of S can be well fitted by a phenomenological expression consisting of electron diffusion and magnon-drag contributions. Interestingly, the magnon drag coefficient carries an opposite sign to that of electron diffusion, revealing a dominant contribution from the elusive electron-magnon Umklapp scattering. Density-functional theory calculations identify several bands crossing the Brillouin zone boundaries, facilitating the Umklapp process. The large spin–orbit coupling in FePt results in strong mixing of majority and minority spins among some of those bands, greatly enhancing the electron-magnon scattering.