MAGNETIC AND STRUCTURAL INSTABILITIES OF ULTRATHIN FE(100) WEDGES (INVITED)

An overview is provided of recent efforts to explore magnetic and rela ted structural issues for ultrathin Fe films grown epitaxially as wedg e structures onto Ag(100) and Cu(100). Experiments were carried out ut ilizing the surface magneto-optic Ken effect. Ordinary bcc Fe is latti ce matched to the primitive unit cell of the Ag(100) surface. Fe wedge s on Ag(100) can be fabricated whose thick end has in-plane magnetic e asy axes due to the shape anisotropy, and whose thin end has perpendic ular easy axes due to the surface magnetic anisotropy. A spin-reorient ation transition can thus be studied in the center of the wedge where the competing anisotropies cancel. The goal is to test the Mermin-Wagn er theorem which states that long-range order is lost at finite temper atures in an isotropic two-dimensional Heisenberg system. Fe wedges on Cu(100) can be studied in like manner, but the lattice matching permi ts fee and tetragonally distorted fee phases to provide structural com plexity in addition to the interplay of competing magnetic anisotropie s. The results of these studies are new phase identifications that hel p both to put previous work into perspective and to define issues to p ursue in the future.