Surface resonance on the NiFe(001) alloy surface

First principles calculations based on density-functional theory are used to investigate the geometrical and electronic structure of a NiFe(001) invar surface. We use different ordered as well as alloy fcc-like structures to simulate the system. Ab initio atomic force minimizations show that the (001) invar surface is rumpled; Fe atoms are shifted outwards, Ni atoms inwards. A surface resonance is observed at (0.1–1.0) eV below the Fermi level, depending on the chemical ordering at and below the surface. Our calculations show that this resonance is pronounced in iron-rich surface regions.