Effect of interlayer exchange coupling on spin-wave spectra in magnetic double layers: Theory and experiment

Abstract

The spin-wave spectra of dipolar and exchange coupled double-layer systems are investigated both theoretically and experimentally. The theoretical formalism is based on a macroscopic description using the Landau-Lifshitz equation of motion and Rado-Weertman and Hoffmann boundary conditions. The experimental spin-wave spectra were obtained for ${\mathrm{Ni}}_{0.8}$ ${\mathrm{Fe}}_{0.2}$/Pd/${\mathrm{Ni}}_{0.8}$ ${\mathrm{Fe}}_{0.2}$ and ${\mathrm{Ni}}_{0.8}$ ${\mathrm{Fe}}_{0.2}$/Cr/Co systems by means of Brillouin light scattering. From comparison of the theoretical calculations and experimental data, the dependence of the interlayer exchange constant on the interlayer thickness is determined. In addition, we analyzed recent microwave absorption data for ${\mathrm{Ni}}_{0.8}$ ${\mathrm{Fe}}_{0.2}$/Cu/${\mathrm{Ni}}_{0.8}$ ${\mathrm{e}}_{0.2}$ taken from the literature. In all systems the interlayer exchange coupling was found to be ferromagnetic. It vanishes for interlayer thicknesses of the order of 10 Å for Cr and 20–30 Å for Cu and Pd. The full coupling limit is also treated in detail.