Theoretical study of FeCo/W(1Â 1Â 0) surface alloys

Using first-principles band-structure theory we have calculated structural and magnetic properties of two-dimensional FeCo-ordered alloys deposited on W(1 1 0) substrate. For pseudomorphic overlayers a decrease of the total magnetic moment with increasing Co content has been found to be in agreement with experimental observation of decreasing Curie temperature. In a homogeneous Co/W(1 1 0) overlayer, the ferromagnetic, antiferromagnetic and nonmagnetic solutions are virtually degenerated. In addition, an experimentally observed non-pseudomorphic close-packed overlayer with 10 Co atoms placed over every 8 W atoms along the [0 0 1] direction has been explored. The surface structure with an incomplete misfit dislocation is found to be favoured over the structure containing a complete misfit dislocation. The close-packed Co overlayers are ferromagnetic.