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We have used full-field optical Kerr microscopy to study the double-vortex interaction in epitaxially grown micron-sized elliptical ferromagnetic thin films by observing magnetization-switching behavior. Both micromagnetic simulation and experimental measurements were carried out to determine the origin of the observed magnetization reversal process. It was found that the direction in which each vortex core rotates largely depends on the edge spins that are not saturated by an externally applied magnetic field. It was also found that the switching fields depend significantly on the relative direction in which the vortex cores rotate. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated a remote encoding/decoding method of micrometer-sized multibit magnetic tags and demonstrated the operation of magnetic digital tags to discuss the practical issues which arise. The tags are formed from micron scale patterned ferromagnetic Co thin films, which are engineered to have different switching fields by tailoring the geometric shape of the elements. This enables the tags to be encoded and read by a sequence of globally applied magnetic fields. Full-field magneto-optical microscopy was used to achieve the remote writing and reading for magnetic digital tags. Cur results demonstrate that the elements in the multibit tags are well separated in switching field and can be encoded/decoded independently by using globally applied magnetic fields and magneto-optical microscopy. We will discuss practical issues for high-information multibit magnetic tags including switching field distribution and repeatability with implications for the field of bioassays. [ABSTRACT FROM AUTHOR]