Spin polarised quantum-well states in layered magnetic nanostructures of Cu/Co/Cu(100)

Abstract

The unoccupied electronic structures of bilayer Co/Cu(100) and trilayer Cu/Co/Cu(100) structures have been investigated by spin-resolved inverse photoemission. For the first time, the spin-polarised unoccupied quantum-well states have been observed for both systems. The exchange splitting of the quantum-well states and the bulk-like sp band of Co (100) have been determined. A simple phase accumulation model simulated the electron confinement in the ultra-thin Co(100) film very well. The offset between the Co and Cu X4’ point provides the confinement potential for electrons in the Co film. For the sandwich structure of Cu/Co/Cu(100), in addition to the spin-polarised quantum-well states, surface states and a surface resonant state at the copper/vacuum interface, and bulk-like minority d contributions from the underlying ferromagnetic Co layer have also been identified. The quantum-well states are shown to develop into a surface resonant state as a function of the electron momentum, as evidenced by the loss of the exchange splitting. The quantum-well states in Cu/Co structure are formed by resonance due to high reflectivity, because there is no absolute confinement potential for this structure. The experiment has shown that the spin resolution provides a possible access to the penetration depth of the wave function of the surface state and surface resonant state.