Quantum-well and tight-binding analyses of spin-polarized photoemission from Ag/Fe(001) overlayers

Spin-polarized photoemission experiments on expitaxial Ag overlayers on Fe(001) have shown that a minority-spin surface state of the bare substrate evolves into an interface state, moves to higher energies, and crosses the Fermi level ${\mathit{E}}_{\mathit{F}}$ between 3 and 4 Ag monolayers. Application of a phase accumulation model shows that this state is a quantum-well (QW) state characterized by the quantum number ν=1, where ν=m-n, and where n and m are the number of wave-function nodes and number of layers, respectively. Higher members of the QW series cross ${\mathit{E}}_{\mathit{F}}$ with a periodicity Δm=(1-${\mathit{k}}_{\mathit{F}}$/${\mathit{k}}_{\mathrm{BZ}}$${)}^{\mathrm{-}1}$ identical with that in recent theories for the alternation between ferromagnetic and antiferromagnetic coupling in magnetic multilayers. The QW model fails at low coverages. A tight-binding model captures the behavior at low coverages while reproducing QW behavior at high coverages.