A structural, electronic and magnetic study of ultrathin iron oxides

Iron oxides continue to fascinate us after nearly a century of ``modern'' science devoted to their growth, properties and structure. Recently, a revival of research has been spurred by the multiferroic character of magnetite, and by its predicted half-metal character, both interesting for spintronic applications. Maghemite is, on the other hand, an interesting counterpart to magnetite. They both present the same inverse spinel structure but maghemite is a ferrimagnetic insulator. In this work we individually characterize flat triangular islands, less than 10 atomic layers thick, of magnetite and maghemite on Ru(0001) by means of selected-area X-ray photoemission and absorption, X-ray circular dichroism and low-energy electron diffraction and reflectivity. We grow magnetite islands in-situ, with well-defined magnetic domains inside, surrounded by a w\"{u}stite wetting layer by depositing iron in a molecular oxygen background pressure. Further exposure to NO$_{2}$ transforms the magnetite islands into maghemite, while changing the w\"{u}stite wetting layer into hematite.