Finite-size effects on spin configurations in antiferromagnetically coupled multilayers

Nonuniform canting states are found for multilayers of a finite size that are constructed from ferromagnetic films which are antiferromagnetically coupled. Our results are applicable to a wide variety of experimentally realizable systems such as Fe/Cr and Co/Ru. We find that at low fields, a twist in the ground-state configuration of the spins reduces the net Zeeman energy and is energetically favorable to the uniform canted state which has previously been assumed by most authors. At higher fields, the character of this twist changes and eventually leads to a state that is fully aligned along the direction of the applied magnetic field. A numerical self-consistent mean-field model is used to examine the properties of these states and a variational method is developed in order to obtain analytic expressions for the lengths and magnitudes of these twists. The deviations from the uniform spin-flop state at both high and low fields can be quite large and involve the entire sample.