Frequency in Middle of Magnon Band Gap in a Layered Ferromagnetic Superlattice

Abstract

The frequency in middle of magnon energy hand in a five-layer ferromagnetic superlattice is studied by using the linear spin-wave approach and Green's function technique. It is found that four energy gaps and corresponding four frequencie in middle of energy gaps exist in the magnon band along Kx direction perpendicular to the superlattice plane. The spin quantum numbers and the interlayer exchange couplings all affect the four frequencies in middle of the energy gaps. When all interlayer exchange couplings are same, the effect of spin quantum numbers on the frequency ωg1 in middle of the energy gap Δω12 is complicated, and the frequency ωg1 depends on the match of spin quantum numbers in each layer. Meanwhile, the frequencies ωg2, ωg3, and ωg4 in middle of other energy gaps increase monotonously with increasing spin quantum numbers. When the spin quantum numbers in each layer are same, the frequencies ωg1, ωg2, ωg3, and ωg4, all increase monotonously with increasing interlayer exchange couplings.