Magnonic bandgap openings and in-gap propagating states in domain-wall waveguides induced by periodic modulations

Magnonic waveguides based on magnetic domain walls surpass conventional magnonic waveguides, which typically feature single magnetic domains, in nearly all critical aspects. Consequently, they are considered pivotal for the development of future nanomagnonic circuits. A distinctive feature of these waveguides is the complete absence of a bandgap, known as the vanishing magnon barrier. This feature is of great theoretical importance and has practical relevance for several applications, but it has received limited attention thus far. In our research, we employ micromagnetic simulations to investigate the spin-wave propagation in a domain-wall based magnonic waveguide, which includes reconfigurable periodic modulations. The magnonic band structure within the domain-wall waveguide can be significantly altered based on the magnetization configuration of the modulating magnets, resulting in the creation of bandgaps or leaving the structure unchanged, as though no modulation were applied. The bandgaps arise from the Bragg reflection of spin waves due to an induced periodic potential. A resonance-enhanced propagation state of the waveguide and modulation magnets, indicative of mode matching, results in the emergence of an allowed band within each bandgap under specific conditions. This study may open an effective route to control the band structure of domain-wall waveguides.