Invited Paper IE-MoM3
Dynamic Studies of Magnetization Reversal Processes and Future Prospects for In-Situ TEM

Monday, October 15, 2007, 8:40 am, Room 618

The rapid increase in information storage density, memory density and speed have been brought about in part by the development of new materials, often consisting of layered structures, with properties that are engineered by controlling the microstructure and chemical profile. The layer thicknesses are of the order of a few nanometers, and the deposition techniques used tend to give polycrystalline films, resulting in variations in properties across the structures. One of the most spectacular examples is the development of devices based on the giant magnetoresistance (GMR) phenomenon, such as the spin-valve and the spin-dependent tunneling junction used for read heads or magnetoresistive random access memories. In addition, patterned single layer structures are of importance for both media and memory applications. The behavior of these materials relies on the local magnetic domain structure and magnetization reversal mechanism, and one of the techniques enabling micromagnetic studies at the sub-micron scale is Lorentz transmission electron microscopy (LTEM) which allows the magnetic domain structure and magnetization reversal mechanism of a FM material to be investigated dynamically in real-time with a resolution of a few nm. We have used LTEM and in-situ magnetizing experiments to study magnetization reversal in a range of materials including spin-tunnel junctions and patterned thin film elements. Quantitative analysis of the Lorentz TEM data has been carried out using the transport of intensity equation (TIE) approach. Studies of active spin valves have shown the way in which the magnetization reversal process depends on applied current. In addition to the local variations in the magnetic properties induced by the microstructure of the films, further variations arise when the films are patterned to form small elements and results will be presented for a range of structures patterned both from single layers and from device structures. Results of further in situ experiments to measure the local tunneling properties of magnetic tunnel junctions will also be presented. Recent progress in electron beam instrumentation is expected to have a strong impact on in-situ TEM, especially LTEM. E.g., correction of chromatic aberration is at present under development within the frame work of the TEAM project. The benefits of this novel corrector for in-situ experiments will be discussed.