Pattern evolution and fluctuations in a magnetic model system

In pattern forming systems, such as out-of-plane magnetized ferromagnetic samples, magnetic patterns occur in a variety of shapes and sizes. The mechanism of pattern transformation is, however, not well understood due to the lack of experiments featuring sufficient spatial as well as temporal resolution. Since thermal fluctuations can be regarded as the main driving force for domain pattern transformations, a non-stroboscopic measurement technique is necessary. For this purpose, a photoemission electron microscope was equipped to obtain magnetic contrast by the effect of threshold photoemission magnetic circular dichroism. This measurement setup offers a high spatial (<100nm) as well as temporal (<450µs) resolution and was used to investigate the magnetic domain pattern of the ferromagnetic model system of ultrathin Fe and Ni films on Cu(001). Moreover, the transformation of domain patterns triggered by changes of external stimuli could be recorded and investigated. In addition, the fingerprint of different, local domain patterns (topological defects) have been analyzed with respect to thermal fluctuations. The threshold photoemission magnetic circular dichroism is explained in detail by a one-step as well as a three-step photoemission model calculation within the framework of LSDA+DMFT band structure calculations.