Ultrathin epitaxial Fe films grown on W(001) surfaces prepared to yield uniform 25-Å-wide terraces are shown to exhibit layer-dependent in-plane uniaxial magnetic anisotropy having an easy axis perpendicular to the steps. Hysteresis loops measured by magneto-optical techniques when steps are aligned parallel to the applied field H manifest the flip of magnetization that occurs near H=0. The absence of magneto-optic effects for films less than or equal to one monolayer thick is consistent with recent Iab initioR calculations that predict significant moment reduction resulting from strong film-substrate hybridization.

• Received 25 November 1991

DOI:https://doi.org/10.1103/PhysRevLett.68.1212