Magnetism of Fe on W(001) and the effects of oxygen adsorption

Structural, electronic and magnetic properties of monolayer and bilayer Fe on W(001), denoted by 1Fe/W(001), and 2Fe/W(001), and oxygen on 2Fe/W(001) have been calculated using the full potential linearized augmented plane wave method. The ferromagnetism of the Fe monolayer is found to be removed by the W(001) substrate (even as a metastable state) for the monolayer Fe/W(001) system; the AFM coupling becomes the ground state. Interestingly, an additional Fe overlayer can activate the ferromagnetism of the 'dead' Fe layer - which indicates the sensitivity of the magnetism to the overlayer thickness for Fe/W(001) especially around monolayer coverages. The bilayer Fe adopts a tetragonal (rather than bcc) structure on W(001), which keeps the interatomic distance between two Fe layers identical to that in bulk bcc Fe (4.69 a.u.). Oxygen adsorption induces a large change of the atomic structure and the Fe magnetic moment (an increase in the top layer and a reduction in the underlayer). Magnetic Fe overlayers induce a large magnetic moment of 0.19-0.22μ_B on the interfacial W atoms and a very large magnetic hyperfine interaction. The spin density at E_F, m(r,E_F), is negative in the surface-vacuum region for the bilayer Fe/W(001) system, but becomes positive on oxygen adsorption.