We have fabricated micron-sized NiFe ring-shaped sensors that show localized detection of the radial component of the dipolar fringing field from a single, partially magnetized, micron-sized NiFe sphere. Specifically, the anisotropic magnetoresistance response to this fringing field is strongly peaked when the sphere is directly above the center of the ring and rapidly decreases to zero when the sphere is outside the ring. Such a device is a model system for a proposed biosensor array architecture that could operate similarly to high-density random access computer memory.

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These particles were manufactured by Novamet, Wycoff, NJ. The composition of these particles is nominally Ni70Fe30. However, any soft ferromagnet would function identically for the magnetizing fields utilized in this work.
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