Rationally phase-locked magnon frequency combs from the pinned domain wall

Abstract

Frequency combs, composed of equally spaced spectral lines, have revolutionized precision metrology and the generation of coherent waveforms. Extending this concept to magnetism, spin waves (SWs) offer a nonlinear and phase-coherent platform for frequency synthesis. In this work, we demonstrate that a magnetic domain wall (DW) can itself act as an active source of frequency combs through rational synchronization between its internal modes and an external AC magnetic field. When a pinned Bloch-type DW, confined by a notch-induced potential well, is simultaneously driven by a propagating SW and a tunable AC field, multiple harmonic modes (high-order harmonics, HHGs) naturally emerge within the DW. The nonlinear coupling among these HHG modes and the external drive leads to rational synchronization satisfying fAC−fseed≈fAC/m*≈fseed/n*, where m* and n* are integers. This interaction produces subharmonic combs with tunable spacing Δf, which become imprinted onto the SW channel, forming a dual-seeded cascade of coherent spectral lines. The emergence of evenly spaced harmonics reflects a self-organized and energetically favorable state rooted in confined DW dynamics. These findings elucidate a nonlinear regime, positioning magnetic domain walls as reconfigurable sources of tunable magnonic combs for next-generation spintronic and magnonic devices.