MAGNONIC SPECTRA OF FERROMAGNETIC COMPOSITES VERSUS MAGNETIZATION CONTRAST

It had been shown recently that the calculated magnonic spectra of two -dimensional periodic ferromagnetic composites can present frequency r anges forbidden for the propagation of magnon excitations throughout t he composite. However, those forbidden energy gaps were found to be hi ghly sensitive to the exchange contrast between the component ferromag netic materials but were very weakly sensitive to the contrast in spon taneous magnetizations of the two materials. Accordingly, in this pape r we introduce a new mathematical definition of the exchange field act ing in inhomogeneous medium. With this new definition the present theo ry gives magnonic spectra reasonably sensitive to magnetization contra st, as they should be from the physical view point; moreover, the magn etization contrast now becomes a gap-creating factor as well.