Structural, electronic, and magnetic properties of the hcp Gd(0001) surface have been determined using the all-electron local-density full-potential linearized augmented-plane-wave method. A precise total-energy analysis reveals that (1) surface Gd atoms occupy the hcp sites; the outermost interlayer spacing expands by ∼6%; (2) the surface Gd layer couples antiferromagnetically with the underlying ferromagnetic bulk; and (3) the energy stability of the surface antiferromagnetic coupling arises from the enhancement of the second-neighbor interactions. A localized ${\mathit{d}}_{\mathit{z}}^2$ surface state is found near the Γ¯ point, which is occupied (empty) in the majority (minority)-spin band and results in an enhancement of the surface magnetic moment.

• Received 14 March 1991

DOI:https://doi.org/10.1103/PhysRevB.44.9400