Growth and properties of CoO/Fe perpendicular exchange coupled ultra-thin films

We investigated the molecular beam epitaxy growth, the structure and the magnetic properties of the exchange coupled CoO/Fe bilayers on Ag(0 0 1). In situ X-ray scattering shows that Fe grows in registry with Ag(0 0 1) with an out-of-plane lattice parameter that varies with the Fe layer total thickness. The growth of CoO to build an exchange coupled CoO/Fe system impacts the Fe layer even at room temperature. Two different bilayers grown under close conditions are studied. They differ by the ratio of the oxidized Fe layers over the 7 initial Fe monolayers (30% and 40% respectively). Low temperature exchange magnetic coupling with a blocking temperature TB of about 180 K-150 K and similar thermal behavior are observed for the two samples. We studied one sample with synchrotron X-ray resonant magnetic scattering confirming that the magnetization was perpendicular to the surface below TB. Noteworthy, we found that the magnetic easy axis was lying in-plane at room temperature, above TB. These results point to another example of perpendicular ferromagnetism in an ultra-thin film due to an exchange mechanism with an antiferromagnetic layer that rotates the magnetic easy axis from in-plane to perpendicular below TB.