The concept of a single-domain particle

Abstract

An attempt to calculate exchange and magnetostatic energies for several discrete atoms, which can only be done for larger interatomic distances, is discussed. All estimations of the single-domain particle size are based on certain approximations which apply to a continuous material, but break down in the limit of discrete atoms. It is shown that when these approximations are eliminated, a very small magnetic particle can never be completely saturated, even though such a state can be a very good approximation to the physical reality. The previous micromagnetic calculations are only approximately valid, which resolves the Brown paradox