Exchange Coupling in Magnetic Multilayers

In magnetic multilayers, the magnetizations of two ferromagnetic layers separated by a non-magnetic spacer layer are coupled by the electrons in the spacer layer. This coupling oscillates in sign as a function of the thickness of the spacer layer. Extensive research done on these systems has led to a simple model for this coupling and remarkable agreement between predictions of the model and measurements of the coupling. The model predicts that the periods of the coupling are determined by geometrical properties of the Fermi surface belonging to the spacer layer material. The oscillatory coupling is an instance of oscillations in metals caused by the existence of a Fermi surface.