Limitations of Coherent Precession Models

This paper uses the solutions of the linearized Landau–Lifshitz equation to establish the limitations of coherent precession models. Contrary to traditional argument, such models are valid only in the limit of vanishing surface anisotropy. The paper examines the theoretical basis for this conclusion in the context of an idealized magnetic surface. It considers several practical examples in which the response of bilayer composites is explained in terms of a unidirectional surface anisotropy.