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

TL;DR

This paper refines the theoretical understanding of the spin-wave spectrum in ferromagnetic films with in-plane magnetization, providing a more accurate analytical solution that corrects previous approximations especially for thicker films.

Contribution

It introduces an improved analytical approach by applying boundary conditions directly to bulk solutions, correcting inaccuracies in the widely used diagonal approximation for thicker films.

Findings

The new spectrum differs quantitatively from the diagonal approximation.

The refined theory is more accurate for relatively thick films.

Provides an analytical solution to the boundary problem.

Abstract

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