Magnetic domain structure and spin-reorientation transition in ultrathin Fe-Co alloy films

The evolution of the magnetic domain structure with the thickness of Fe1-xCox alloy films deposited at room temperature on epitaxial Au(111) films is studied for xless than or equal to0.3 by spin-polarized low-energy electron microscopy. In contrast to pure Fe films that show no out-of-plane magnetization small amounts of Co are sufficient to induce strong perpendicular magnetization below three monolayers with a pronounced striped domain structure. A reorientation transition to in-plane magnetization is found.