Stray fields in thin magnetic films

From the second variation of the integral of all free energies in thin magnetic films, an effective field is deduced, which for real polycrystalline films is analogous to the Stoner-Wohlfarth field of ideal single-domain films. The effective field is composed of the single-domain field, two different stray fields, and a field caused by local anisotropies. The varies from point to point. As in the single-domain theory, means that the magnetization direction over the entire film is stable; in regions with , the local magnetization becomes unstable and turns by a very small angle to another stable state. After that, the domain structure is blocked by the intrinsic stray field. The blocking condition, which is the external single-domain field at which blocking occurs, is calculated as a function of film structure. The critical curve for stray-field blocking shows that the critical Stoner-Wohlfarth curve of the single-domain theory must not be used in discussing experiments on real polycrystalline films.