EFFECT OF NEXT-NEAREST-NEIGHBOR INTERACTIONS ON SPIN-WAVES IN MAGNETIC SUPERLATTICES

Results are presented for 3D magnetic superlattices consisting of alternating films of cubic Heisenberg ferromagnets. Taking into account the next-nearest-neighbour (NNN) interactions, an explicit equation for the spin-wave dispersion relation is obtained by means of a transfer matrix method. Numerical results am presented for FOC ferromagnetic films with different values of the exchange constant ratio eta = J(NNN)/J(NN). If eta not-equal 0, for every frequency omega, there are two pairs of allowed values of wavenumbers k and in some frequency range both can be real if eta greater-than-or-equal-to 1. For the superlattice, a comparison with the dispersion relation obtained considering only NN interaction is made and the main physical features are discussed.