Magnetic imaging of static and dynamic states in systems of reduced dimensions

Within this thesis, static and dynamic states in magnetic systems of reduced dimensions are investigated by means of the advanced magnetic imaging technique ``scanning electron microscopy with polarization analysis'' (SEMPA). After a short introductory overview of the historical development of storage media, its current status is described with a focus on random-access memory (RAM). The basic concepts of modern non-volatile storage devices based on magnetism are introduced and the physical mechanisms behind the phenomena that are used to manipulate and access the data are discussed.

Magnetic imaging is a powerful, yet illustrative tool to further explore the physics behind these mechanisms. Throughout this book SEMPA imaging is used to determine the parameters of spin-transfer torque from the current-induced vortex displacement in a permalloy square. A concept for the extension of the SEMPA technique into the nanosecond regime is discussed. Using this time-resolved SEMPA, the gyrotropic motion of a vortex core is observed as a first proof of concept.

In another project of this thesis, the interplay between ferromagnetic and ferroelectric domain walls is investigated. Two different types of walls are observed: charged walls and uncharged walls. The book concludes with a theoretical chapter in which the uniaxial anisotropy is derived that emerges when a magnetic film is prepared on top of a rippled substrate. The results are compared to experimental studies.