Perfect and imperfect particles

The theory of magnetization reversal process in an isolated, ellipsoidal particle is rigorous, and its results are unambiguous. There is no approximation in this theory, except for the assumption of a perfect single crystal, with a perfectly smooth spheroidal surface, and nothing new can be found, as long as this assumption is maintained. In order to advance towards a theory of realistic particles, one must look for ways to take into account the effect of nonellipsoidal shape and of crystalline defects, as well as the effect of magnetic interactions between the particles.