Magnonic bands in periodic arrays of vertically-stacked cylindrical magnetic nanoelements

Abstract

The spin-wave spectra are studied theoretically in periodic magnonic crystals (MCs) of vertically-stacked cylindrical nickel nanodisks or nanorings separated by nonmagnetic spacers, resulting in infinitely long segmented nanowire or nanotube MC arrays, respectively. A microscopic or Hamiltonian-based approach is employed for the magnetization dynamics, in which an external magnetic field is applied along the cylinder axis and the periodic length is varied by changing the length of the spacers. The results show a broadening and shift of the spin-wave frequency bands at smaller spacer length due to the strong dipolar inter-element coupling, which also modifies the spatially-inhomogeneous equilibrium magnetization in the finite-length cylindrical elements. The effects are found to be more pronounced in a nanotube MC than in a nanowire MC, mainly because the absence of the core in a nanotube favours vortex states.