Quasi-nonlocal harmonic detection of magnon-mediated spin-current generation in metallic Py/Pt bilayers

Magnons play a central role in spin transport and magnetoresistive phenomena in magnetic heterostructures. In ferromagnet(FM)/nonmagnet(NM) bilayers, unidirectional magnetoresistance (UMR) arises from both spin accumulation and magnon-mediated processes, yet their individual contributions remain unclear. In this work, we employ a non-local harmonic measurement geometry to understand the magnon contribution to UMR in the FM/NM bilayer. By analyzing the non-local harmonic voltages, we demonstrate that high-energy magnons are more efficient in driving spin pumping and spin-current generation than low-energy modes. These results establish high-energy magnons as a key factor in spin conversion and provide a perspective for designing efficient magnon-based devices