What determines the sizes and shapes magnetic domains can have at finite temperature ? And what can be the minimum size of thermally stable magnetic domains in a material ? Answers to these questions are interesting, both to understand basic magnetic phenomena and to guide the development of materials for spin-electronics applications. Using spin-polarized low-energy electron microscopy (SPLEEM) to study magnetization in epitaxial layered structures, we found that magnetic domains and domain walls in the top Fe layer of Fe/NiO/Fe(100) trilayers are dramatically smaller than the corresponding domain structures observed in Fe(100) substrates. In fact, the widths of some domains in the top Fe layer are smaller than the widths of just the walls of domains we observe in our Fe(100) substrates ! Our structures were build on top of clean Fe(100) single crystals, using in-situ preparation techniques. Freshly fabricated NiO/Fe(100) samples (thickness : Fe = bulk, NiO ≈ 5 nm) were UHV-transferred into the specimen chamber of our microscope, where we grew the top Fe layer (thickness ≈ 3 nm) under conditions of very good vacuum and very low stray-magnetic field.

Magnetic thin films with perpendicular magnetic anisotropy (PMA) have special attributes for explorations and perpendicular magnetic recording. We have observed three hitherto unknown new features in materials with PMA: Asymmetrical domain nucleation centers that produce domains for only one magnetization direction (Fig. 1). The backward domain wall motion of the asymmetrical nucleation centers is much faster than that of the forward motion. Magnetic domains with a fixed boundary but fading contrast. These results have been accounted for by a theory that we have developed. Magnetic domain alignment in sputtered magnetic films results in narrower transitions and faster rise times. Dexter has designed and produced a wide variety of devices for this purpose, and has developed proprietary and patented technology for this application. Bulk erase tools, permanent magnet magnetizers, plating dipoles and dipoles for furnace annealing typically require large structures and highly uniform flux densities with low skew, or divergence over the working volume. We have extensive experience in meeting exacting requirements for these applications.