We have been studying the magnetic switching behavior in NiFe/IrMn nanostructures in which only part of the ferromagnet is exchange biased. Examples of such structures are shown in the SEM images. What makes these partially patterned exchange bias structures interesting compared to their uniform counterparts is the more complicated switching behavior. Depending on the lengthscale of the structure, the ferromagnet may reverse in one step or the exchange-biased and unbiased regions may switch separately producing a domain wall. This behavior can be tailored according to the pattern dimensions, and the results can be applied to magnetic nanodevices, such as domain wall logic in which opposite exchange-bias at each end of a wire ensures the existence of a single domain wall within the wire. While the behavior in uniformly exchange biased systems is well-known, there has not yet been many studies about partially exchange biased systems. Our study focuses on the lower-dimensions (< 500 nm), including NiFe films with IrMn stripes, and NiFe stripes with IrMn rectangles, and developed a patterning method to obtain local exchange bias.

Left: Patterned antiferromagnet IrMn (10 nm) on top of continuous ferromagnet NiFe (10 nm). Right: Patterned antiferromagnet IrMn (10 nm) on top of patterned ferromagnet NiFe (10 nm)