Z. Q. Qiu

Magnetic and structural instabilities of ferromagnetic and antiferromagnetic Fe/Cu(100)

Fe wedges epitaxially grown on Cu(100) have been employed to investigate the interplay between magnetic and structural instabilities. 2–4 monolayer (ML) clean Fe films grown at room temperature are ferromagnetic with perpendicular easy axes. bcc Fe films≳11 ML thick are ferromagnetic with in‐plane easy axes. Most importantly, 6–11 ML fcc Fe films are antiferromagnetic and have a ferromagnetic surface. Films grown below 200 K and annealed to room temperature do not exhibit the antiferromagnetic phase, but remain ferromagnetic and undergo a spin‐reorientation transition from perpendicular to in plane at ∼6 ML. A new phase diagram for Fe/Cu(100) is proposed as a function of thickness and growth temperature. In addition, an impurity‐stabilized layer‐by‐layer growth that persists to 30–40 ML Fe is also reported.

Magnetic and structural instabilities of ultrathin Fe(100) wedges (invited)

An overview is provided of recent efforts to explore magnetic and related structural issues for ultrathin Fe films grown epitaxially as wedge structures onto Ag(100) and Cu(100). Experiments were carried out utilizing the surface magneto‐optic Kerr effect. Ordinary bcc Fe is lattice matched to the primitive unit cell of the Ag(100) surface. Fe wedges on Ag(100) can be fabricated whose thick end has in‐plane magnetic easy axes due to the shape anisotropy, and whose thin end has perpendicular easy axes due to the surface magnetic anisotropy. A spin‐reorientation transition can thus be studied in the center of the wedge where the competing anisotropies cancel. The goal is to test the Mermin–Wagner theorem which states that long‐range order is lost at finite temperatures in an isotropic two‐dimensional Heisenberg system. Fe wedges on Cu(100) can be studied in like manner, but the lattice matching permits fcc and tetragonally distorted fcc phases to provide structural complexity in addition to the interplay of...

Magnetic coupling of Fe/Mo/Fe and Co/Cu/Co sandwiches across wedged spacer layers (invited)

Fe/Mo/Fe and Co/Cu/Co sandwiches were grown by molecular beam epitaxy onto Mo(100) and Cu(100) single crystals, respectively, and characterized by high‐ and low‐energy electron diffraction and in situ surface magneto‐optic Kerr‐effect measurements. The spacer layer in both case was fabricated to have a wedged shape in order to create a continuous change of the spacer‐layer thickness. Oscillatory behavior between ferromagnetic and antiferromagnetic coupling was found; and is shown to originate at the interface between the magnetic layer and the spacer layer. For Fe/Mo/Fe, short‐period oscillations are observed with a periodicity of ∼3 ML of Mo. Hysteresis loops for antiferromagnetically coupled cases are calculated from a simple model, and the results reproduce the general characteristics observed experimentally.