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 2.49B. 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 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.