Various sensor and storage technologies rely on magnetic thin-film components with a unidirectional anisotropy. To obtain it, exchange bias (EB) in adjacent antiferromagnet (AF) / ferromagnet (F) structures is used. EB is not fully understood. It is generally believed that EB implies the presence of pinned uncompensated spins pinUCS in the AF layer that are coupled to the F layer. An obstacle to understanding the EB effect is that only a subset of the UCS (those pinned, and coupled to the F) are responsible for the EB. The experimental method and preparation may affect these subsets in distinct ways and an interpretation of UCS measurements must take this into account. In our previous work we have advantageously combined MFM with magnetometry to demonstrate the co-existence of pinned UCS that are parallel and antiparallel to the cooling field in metallic (IrMn) and oxidic (CoO) EB systems. We further conclude that the EB effect is mainly a result of pinned interfacial UCS, which are antiparallel to the FM spins. In addition we have studied the evolution of ferromagnetic domains over a pattern of pinned UCS and have substantially enhanced the exchange bias effect by decoupling the grains of the AF layer. Within this project various thin film magnetic heterostructures will be sputter-deposited onto flat and microstructured substrates. A first workpackage is devoted to the study of the switching field distribution of particulate media. New exchange-bias systems exhibiting an exchange-bias field above 1T will be developed. A second workpackage is devoted to the development of MFM measurement methods for exchange-biased samples with in-plane magnetic anisotropy, to independently map the rotating and pinned UCS, to study the role of the UCS pinned in the bulk of the AF, and to map the blocking temperature of single AF grains. The results are expected to contribute to a better microscopic understanding of the exchange bias effect and the role of the different subsets of UCS. New materials with a considerably larger exchange bias effects will be developed on the basis of the microscopic undestanding.