Exchange coupling in magnetic heterostructures

TLDR

Magnetic multilayers separated by nonmagnetic spacers exhibit oscillatory exchange coupling. The study calculates extremal spanning vectors and Fermi‑surface geometrical factors for many spacer materials and interface orientations to test these models. A simple model attributes the oscillatory coupling to the spacer’s Fermi surface, with periods set by its extremal spanning vectors and strength governed by Fermi‑surface geometry and interface reflection amplitudes. The calculated periods agree with all measured oscillations, and the models are consistent with experimental data, though transition metals show more calculated than observed periods.

Abstract

Many structures consisting of magnetic layers separated by a nonmagnetic spacer layer show an oscillatory exchange coupling. This behavior is explained in terms of a simple model that shows that the Fermi surface of the spacer-layer material is responsible for the oscillatory coupling. The periods of the oscillatory coupling are set by extremal spanning vectors of the Fermi surface of the spacer-layer material. The strength of the coupling depends both on the geometry of the Fermi surface and on the reflection amplitudes for electrons scattering from the interfaces between the spacer layers and the magnetic layers. To test this and related models, the extremal spanning vectors and the associated Fermi-surface geometrical factors have been calculated for a large set of spacer-layer materials and interface orientations. These models are at least consistent with the experimental data. All measured oscillation periods are consistent with the calculated periods, but particularly for transition metals there are many more periods calculated than are seen experimentally.