Electric field control of magnetization and anisotropy in ultrathin Fe und FePt/Fe films

The control of magnetic properties by an electric field is exciting both from the point of view of applications and fundamental research. Low-power electrical switching of magnetic properties is e.g. discussed as promising alternative to temperature control as in heat assisted magnetic recording. Magnetoelectric coupling is known for one- or two-phase multiferroic materials and magnetic semiconductors but is, in these cases, restricted to low temperatures or a fixed substrate. More and more studies report on an influence of electric field on the magnetism also of nanostructured metals [1-6]. The advantage here is that an effect can be exploited at room temperature and may be very large due to the strong ferromagnetism. The electric field can be applied either by using solid dielectric layers or by liquid electrolytes. Many magnetic properties as e.g. coercivity, saturation magnetization, anisotropy and Curie temperature have been shown to be electric field dependent and large effects have been achieved already. Materials studied include Fe, Co, FePt, FePt, CoPt ultrathin films or nanoporous structures. In almost all cases, however, the simple picture of an increase/decrease of DOS at the metal surface is not sufficient to explain the dependencies. Enlightening the underlying mechanism requires a detailed interface analysis to understand the influence of interface chemistry, stress and strain for the distinct sample and gating architecture. The role of oxygen at the interface has been found to be crucial. Reversible potential dependent oxidation and reduction reactions as well as oxygen hybridization have been discussed as origin for magnetic property changes [2-6]. Our concept follows this argumentation and seeks to by intention exploit reversible electrochemical surface reactions involving magnetic species. This allows addressing surface magnetism by an external voltage, opening the way to controlled electrical switching of magnetic properties.