Quantum well states and oscillatory magnetic interlayer coupling

Some interesting magnetic properties of artificially layered metallic materials are strongly connected with the existence of electron standing waves, or quantum well (QW) states. One such property is the oscillation in exchange coupling between two ferromagnetic materials separated by a nonmagnetic spacer layer of varying thicknesses. This article summarizes the findings of an extended investigation of QW states and their relation to oscillatory magnetic interlayer coupling carried out using angle-resolved photoemission with synchrotron radiation and auxiliary techniques such as magnetic x-ray linear dichroism and surface magnetic optical Kerr effect. A key feature of the measurements was the use of wedge-shaped samples, which, in combination with the small spot size of the synchrotron source, permitted investigation of the entire layer thickness range in a single experiment. Single-wedge samples were used as well as double-wedge samples tapered in orthogonal directions. The systematics of QW formation are well understood in terms of the elementary quantum mechanics of a particle in a box. We treat a single well, a double well and a corrugated well. The work on single wells focused on the elucidation of the long and short magnetic oscillatory periods for a Cu spacer layer, and their relation to the belly and neck regions of the Cu Fermi surface. The effects of interfacial roughness and interfacial mixing were investigated. The studies on double wells focused on the controllable degree of tunnelling between the wells and the avoided crossings that occur when the QW energies in one well are swept through those of the other. Finally, we consider the QW wavefunctions and their envelope modulation. The latter can be understood in terms of Bragg diffraction within a corrugated well. With use of a double-wedge-shaped sample it has proved possible to pass a thin probe across the well and to detect experimentally the envelope modulation. (author)