Magnetism of ultrathin Fe films on MgO(001)

We grow ultrathin (<2-monolayer (ML)) Fe films on MgO(001) at 80 K, limiting oxide formation to the very early stages of Fe growth, and then investigate in situ the magnetism of the films using x-ray magnetic circular dichroism (XMCD). The 0.2-ML-thick Fe film exhibits superparamagnetism, disproving the existence of a magnetically dead layer. For all the films, the spin moments per Fe atom are far less than that of bulk Fe, while anomalously large orbital moments are observed. Those are attributed, respectively, to both the oxidation Fe film at the interface and the existence of some Fe nanoclusters in fcc phase and to the high population of low coordinated atoms, such as Fe at the edges of the nanoclusters.