Magnetic Skyrmion Tubes as Nonplanar Magnonic Waveguides

Various recent experiments have proven the theoretical prediction that domain walls in planar magnetic structures can channel spin waves as magnonic waveguides, establishing a platform for building magnonic devices. Recently, three-dimensional nanomagnetism has been boosted and become a significant branch of magnetism, because three-dimensional magnetic structures expose much emerging physics hidden behind planar ones and will provide broader room for device engineering. Skyrmions and anti-skyrmions, as natural three-dimensional magnetic configurations, are not considered yet in the context of spin-wave channeling and steering. Here, we show that skyrmion tubes can act as nonplanar magnonic waveguides, if excited suitably. An isolated skyrmion tube in a magnetic nanoprism induces spatially separate internal and edge channels of spin waves; the internal channel has a narrower energy gap, compared with that of the edge channel and, accordingly, can transmit signals at lower frequencies. Additionally, we verify that those spin-wave beams along the magnetic nanoprism are restricted to the regions of potential wells. Transmission of spin-wave signals in such waveguides results from the coherent propagation of locally driven eigenmodes of skyrmions, i.e., the breathing and rotational modes. Finally, we find that spin waves along the internal channels are less susceptible to the magnetic field than those along the edge channels. Our work will open up an arena for spin-wave manipulation and help to bridge between skyrmionics and magnonics.