Structural and magnetic properties of ultrathin bcc Fe films on Ge(001)

We have performed first-principles electronic structure calculations to investigate the structural and magnetic properties of Ge(001)-Fe film systems with up to three Fe layers. In the calculations full interlayer distance optimizations of the surface systems are carried out allowing both Fe and Ge surface layers to relax. The supported Fe films are found to be ferromagnetic in the ground state, where the layer-resolved magnetic moments are increased with respect to bulk Fe values. The increase is always largest for the topmost layer and becomes smaller for the sublayers. In addition, geometry optimizations of Ge(001)-Fe with different spin orientation between the Fe layers show that parallel spin directions of neighbouring layers lead to an expanded interlayer distance, whereas antiparallel spin results in contracted interlayer spacing. The induced magnetic moments and modified density of states near interfaces are also discussed.