Advances in materials growth and characterization have, over the past ten years, made possible the investigation of basic physical processes in new "artificial" materials. These materials are artificial in the sense that the geometry and composition are controlled during growth on micrometer and nanometer length scales. This results in macroscopic behaviour that can be dramatically different from that of a material in its bulk form. Magnetic order and reversal processes, which have been extensively studied since the turn of the century, are now being reexamined for nanostructured materials.

During the last decade, much attention has been devoted to artificial layered magnetic materials which revealed a large variety of fascinating new phenomena such as the oscillatory interlayer exchange coupling in magnetic/non-magnetic multilayers, surface and interface anisotropy the giant magnetoresistance effect and quantum size effect in electronic properties as well as in magneto-optical properties of magnetic and metallic ultrathin films and related layered structures. Those fundamental developments made such systems also of great interest from a technological point of view in the area of communication devices and storage media. Stimulated by this physics resulting from the layering and reduction of the system size in the vertical direction, a natural extension was the venture into a further reduction of the lateral sizes and quite general into low dimensional systems of nanometer extend. Great interest has been developed for these mesoscopic magnetic structures. The term "mesoscopic" is used here to emphasize that the material dimensions are comparable to fundamental length scales associated with the transport and magnetic properties such as the conduction electron mean free path, the exchange lengths or the domain wall width.

The control of the unique micromagnetic properties at nanometer lengthscales through a variation of the system dimensions made these lowdimensional magnetic structures interesting not only from a fundamental, but also from a technological point of view. Examples for applications of high quality artificial low dimensional materials are well known for some time from the world of semiconductors, such as quantum wires and quantum dots. In contrast a variety of tantalizing new possibilities for devices, structured from magnetic low dimensional systems have only been reported in the literature over the last years. Research and development of new magnetic structures has largely profited from these potential applications, in particular in high density data storage materials.

For the study of the static and dynamic properties of very small particles, say a few 10 nm to a few 100 nm, two approaches are possible. The first one consists in performing an ensemble average measurement on an assembly of many presumably identical (monodisperse, likely shaped) particles. Due to the small particle volume however, magnetization measurements are then limited to the study of a large number (millions) of small particles. The disadvantage of such an ensemble average is that it masks the intrinsic magnetic property of the individual particle by the inevitable distribution of size or shape.
This can be overcome by state of the art deep UV, X-ray and e-beam lithography techniques, making it possible to study one single particle at the time with a very local technique such as local near field probes, electrical measurements or SQUID loop surrounding the particle to be studied.

Studies of the magnetic properties of individual particles have become possible with the development of the Magnetic Force microscopy (MFM) scanning probe technique. MFM has proven to be a well suited tool for imaging the stray fields of individual laterally confined elements for which studies can be performed for example in the as-grown state, after applying different magnetic field histories or even as a function of an applied field following the hysteresis loop.