Theory of the dipole-exchange spin wave spectrum in ferromagnetic films with in-plane magnetization revisited

We present a refinement of the widely accepted spin-wave spectrum that Kalinikos and Slavin (Kalinikos, 1981; Kalinikos and Slavin, 1986) computed for magnetic films with an in-plane magnetization. The spin wave spectrum that follows from the diagonal approximation in this theor y becomes inaccurate for relatively thick films, as has already been noted by Kreisel et al. (2009). Rather than solving an integrodifferential equation which follow s from the magnetostatic Green's function, as done by Kalinikos and Slavin (Kalinikos, 1981; Kalinikos and Slavin, 1986), we impose the exchange and magnetostatic boundar y conditions on b u l k spin-wave solutions. This boundary problem has an accurate analytical solution which is quantitatively different from the commonly used diagonal theor y (Kalinikos, 1981; Kalinikos and Slavin, 1986) for magnetic films.