Exchange-Coupling Between Ferromagnets Across Non-Metallic Amorphous Spacer-Layers: Si and SiO

Abstract

The discovery of exchange coupling between ferromagnetic films separated by a nonmagnetic spacer layer over distances of a few nanometers has provoked a renaissance in the research of magnetism. So far only metals have been studied and long as well as short period oscillations have been observed.¹The theoretical descriptions all share in common that this phenomenon essentially is a consequence of two properties of the spacer material: the existence and topology of a Fermi surface and the discreteness of the layer thickness. In addition, a certain roughness of the interfaces is made responsible for smearing out short-wavelength oscillations. It remains quite surprising, however, that many studies have revealed similar periods of the coupling for a wide variety of materials and structures. Starting from this situation we set out, in the present investigation, to question the very role of the Fermi surface or, more generally, to investigate the response of the exchange coupling to variations in geometrical structure and electrical conduction properties of the spacer. Thus we extend the investigations to a group of completely different spacer materials: non-metallic and non-crystalline solids. We choose as a first model material amorphous Si, 2 which is a semiconductor, and then amorphous SiO, which is an insulator.