Imaging of magnetic structures by photoemission electron microscopy

Photoemission electron microscopy (PEEM) has proven to be a powerful analytical tool in surface science. In this contribution, a status report is given on the application of the PEEM technique in the investigation of surface and interface magnetism. Owing to its fast parallel image acquisition and its wide zoom range, allowing fields of view from almost 1 mm down to a few micrometres, combined with a high base resolution of the order of 20 nm, the method offers a unique access to many aspects in surface and thin-film magnetism on the mesoscopic length scale. There are three basically different modes of magnetic imaging using PEEM. The first one exploits the magnetic x-ray circular dichroism (MXCD) for contrast formation. It offers the important advantage of selecting the magnetic contrast of a certain element via the corresponding x-ray absorption edges using a tuneable x-ray source such as synchrotron radiation. This mode gives access to magnetic structures and coupling phenomena with a sensitivity in the submonolayer range and the capability to image the signal of buried layers with an information depth up to more than 5 nm. The two other modes work with simple UV light sources and are therefore highly attractive for standard laboratory applications. The magnetic stray-field-induced changes of the electron trajectories close to the sample surface lead to a Lorentz-type contrast. A third type of contrast arises as a consequence of the Kerr rotation of the dielectric vector inside a magnetic material, a phenomenon which is also responsible for the well known magneto-optical Kerr effect. Examples and typical applications of magnetic imaging using PEEM are discussed.