Magnetic and electronic properties of binary alloy monolayers:FexMn1−xandCo1−xFexon W(110)

Pseudomorphic binary alloy monolayers Fe x Mn 1 - x and Co 1 - x Fe x were grown on W(110) by molecular-beam epitaxy in ultrahigh vacuum. Fe atoms are randomly replaced by Mn or Co atoms. The pseudomorphic monolayers form extended areas of monolayer coverages at elevated temperatures in the step flow growth mode. For Fe x Mn 1 - x /W(1100) monolayers the Kerr rotation decreases with decreasing Fe concentration, corresponding to a decrease of the magnetization of Δμ/Δx=-(8′2)μ B /atom. The Curie temperature decreases with a rate of [ΔT C (x)/Δx]T C (Fe)=-(1.8′0.2)×10 - 2 /at. %. Scanning tunneling spectroscopy reveals characteristic maxima in the unoccupied local density of states near the Fermi level, which shift towards E F with decreasing Fe concentration for both alloys investigated here. The reduction of magnetization with decreasing Fe concentration can be explained by a simple model of d-band filling, similar to the explanation of the Slater-Pauling curve for binary alloys. We observe a maximum value for T C and for the Kerr rotation for the pure Fe/W(110) monolayer, in contrast to the behavior of bulk alloys where maximum values are obtained for Co-Fe alloys.