Analogous Faraday effect of spin waves propagating in ferromagnetic nanotubes

We present a micromagnetic study of magnetization dynamics in ferromagnetic nanotubes. The sample is radially magnetized in equilibrium with the presence of a strong anisotropy. Micromagnetic simulations reveal that spin waves (SWs) propagating in the tube exhibit a novel effect, analogous to the well-known Faraday magneto-optic effect. Specifically, the location of the nodes/antinodes of the standing waves formed in the azimuthal direction undergoes a continuous rotation during the wave propagation under the influence of an external magnetic field. The physical mechanism is essentially the same as the Faraday effect, i.e., the breaking of the chiral symmetry by the external field. A qualitative explanation is presented by analytically solving the equation of motion of magnetization taking into account the exchange interaction. Our results may bear potential applications in the development of future spintronic devices based on SW propagation.