Ferromagnetic Layered Composites. Transfer Matrix Approach

A theoretical analysis of spin-wave excitations in a ferromagnetic layered composite (ABAB... ABA; A and B are different homogeneous ferromagnetic materials) is performed by means of the transfer matrix approach. We focus our attention on two features not yet well studied in the present literature, namely, the existence of forbidden energy gaps in the spin-wave mode spectrum, as well as the properties of multilayer spin-wave mode profiles. These features are discussed in relation to several multilayer characteristics, such as the filling fraction, and the exchange or magnetization contrast; surface pinning conditions and dipolar interactions are also taken into account. The existence of forbidden gaps as well as properties of mode profiles are successfully explained by having recourse to an approximate model of independent constituent sublayers. Finally, as a byproduct of our investigation, we ascertain that the conventional test for computational convergence within the finite difference method demands to be completed by symmetry mode profile verification, in addition to standard verification of the frequency convergence alone.