Handedness filter and Doppler shift of spin waves in ferrimagnetic domain walls

Abstract

Excitation and propagation of spin waves inside magnetic domain walls (DWs) have received attention because of their potentials in spintronic and communication applications. In addition to wave amplitude and frequency, spin waves have a third character: handedness, whose manipulation is certainly of interest. We propose in this paper that the handedness of low-energy spin-wave excitations can be controlled by tuning the net angular momentum ${\ensuremath{\delta}}_{s}$ in a ferrimagnetic (FiM) DW, attributing to the inequivalent magnetic sublattices. The results indicate that the spin-wave dispersion depends on both ${\ensuremath{\delta}}_{s}$ and wave handedness. For a positive (negative) ${\ensuremath{\delta}}_{s}$, a gapless dispersion is observed for left-handed (right-handed) spin waves, while a frequency gap appears for right-handed (left-handed) spin waves. Thus, a FiM wall could serve as a filter of low-energy spin waves in which only spin waves with a specific handedness can propagate. Furthermore, the energy consumption loss for spin-wave excitation in the wall is much lower than that inside the domain, while the group velocity is much faster too, demonstrating the advantages of DWs serving as spin waveguides. Moreover, the current-induced spin-wave Doppler shift in the FiM wall is also revealed and can be controlled by ${\ensuremath{\delta}}_{s}$. In this paper, we unveil the interesting spin-wave dynamics in FiM DWs, benefiting future spin-wave applications.