DIRECT OBSERVATION OF MAGNETIZATION REVERSAL PROCESSES IN MICRON-SIZED ELEMENTS OF SPIN-VALVE MATERIAL

Simple calculations suggest that when continuous films of spin-valve m aterial are patterned into micron-sized elements the magnetic properti es should change markedly, depending on the element shape and size. We have used the differential phase contrast imaging mode of transmissio n electron microscopy to study directly the magnetization distribution s supported by such elements in zero field and when subjected to an ap plied field in the pinning direction. For elements whose long axis is parallel to the pinning direction a parallel alignment of the free and pinned layers is favored. When subjected to a held a complex domain s tructure evolves and different irreversible paths are followed as the element is taken from negative to positive saturation and back again. By contrast, when the pinning direction is parallel to the short axis an antiparallel arrangement, where the magnetostatic contribution to t he energy is effectively suppressed, can be preferred and simpler reve rsal mechanisms, with a higher degree of reversibility, are frequently seen. (C) 1998 American Institute of Physics.