Surface ferromagnetism of Cr(001)

Results of self-consistent all-electron local- (spin-) density-functional studies of the electronic and magnetic properties of a seven-layer Cr(001) film are reported using our full-potential linearized augmented-plane-wave method. In agreement with earlier theoretical studies and recent photoemission experiments, a ferromagnetic Cr(001) surface is confirmed but with an associated surface magnetic moment of 2.49μB. The origin of the surface ferromagnetism is related to the sharp surface density-of-states peak near the Fermi level for the paramagnetic state. The calculated work function for the ferromagnetic state is found to be 4.05 eV---some 0.4 eV lower than that for the paramagnetic state; the difference indicates the importance of the magnetic order on this electrostatic quantity. In agreement with photoemission experiments, we find a prominent majority-spin surface state with a binding energy of 1 eV at the {Γ}{} point. Layer-by-layer contact hyperfine fields are evaluated: The core contributions are proportional to the magnetic moment of the corresponding atom, and the conduction-electron contribution shows a Friedel oscillation near the center layer. The contact hyperfine field for the surface atoms is also enhanced in magnitude, and a value of -73 kG is predicted.