Figure 1

(a)–(d) Selected LEEM images from a sequence acquired during the growth of the magnetite crystals. Panels (a)–(c) show the completion of the FeO layer, while the last frame shows the final film with magnetite crystals with well-defined edges. The field of view is 10 $\mu$m and the electron beam energy is 19 eV.Reuse & Permissions

Figure 2

(a) LEEM image of a magnetite crystal (the field of view is 4 $\mu$m and the electron energy is 8 eV), with insets showing the low-energy electron diffraction patterns (acquired using an electron beam of 28 eV) of the crystal and its surrounding wetting layer. (b) Fe $2p$ core-level x-ray photoelectron spectra acquired from the crystal (orange, lower curve) and the wetting layer (green, upper curve). The solid lines are the sum of the different individual contributions (not shown) that are expected to be present in the XPS spectra of FeO and magnetite. The inset shows reference spectra for FeO (top, green), a Langmuir-Blodgett film containing Fe${}^{2+}$ and Fe${}^{3+}$ (middle, purple), and hematite (bottom, gray). A nonlinear background has been substracted from the spectra.Reuse & Permissions

Figure 3

(a) XAS and (b) XMCD image at 705.8 eV. The field of view is 30 $\mu$m. (c) XMCD image recorded in remanence showing the magnetization pattern of the same crystal presented in Fig. 2a. The field of view is 4 $\mu$m. The inset shows the experimental geometry. (d) (Top) XAS spectrum from the magnetite crystal. (Bottom) XMCD difference spectrum. The inset shows a typical XMCD spectra from stoichiometric magnetite (reprinted with permission from Ref. 45).Reuse & Permissions

Figure 4

Determination of the magnetite crystal thickness. (a) (Left) Electron reflectivity curves recorded from two regions of a continuous FeO film, in blue for the majority area (which appears light gray in the LEEM image on the right side and corresponds to a FeO bilayer) and in red for the minority regions (which appear in dark gray in the LEEM image and correspond to a FeO single layer). (Right) LEEM image of a complete FeO layer before growth of the magnetite crystals. (The electron energy is 16.75 eV and the field of view is 4 $\mu$m.) (b) Ru 3$d$ XPS spectra recorded from clean Ru through a FeO monolayer and bilayer respectively. (c) Ru 3$d$ XPS spectra recorded from clean Ru through the wetting layer around the magnetite crystals and through the magnetite crystals, respectively. (d) Semilogarithmic plot of the relative Ru XPS 3$d_{5/2}$ peak area recorded from the different films versus coverage in FeO layers. The black squares correspond to the spectra in (b), which give a mean free path of $1.25\pm 0.03$ ML${}_{\mathrm{FeO}}$ (line in the semilogarithmic plot). The green and blue squares correspond to the wetting layer and the magnetite crystal, respectively, from (c) (error bars from the wetting layer are within the symbol size). The additional thickness of the magnetite crystal does not depend on the particular wetting layer thickness.Reuse & Permissions