Exchange-Biased AMR Bridges for Magnetic Field Sensing and Biosensing

We introduce magnetic field sensor bridges that are formed by combinations of stripes of an exchange-pinned magnetic stack displaying anisotropic magnetoresistance. We present a systematic overview on how the stripe geometries can be combined to form sensor bridges with a scalable signal and how these can be tailored toward detection of external magnetic fields and of magnetic beads over or tethered to the sensor surface. Particular attention is given to the case where the beads are magnetized by the sensor self-field due to the bias current passed through the sensor, which is interesting for magnetic bead sensing and where the static and dynamic magnetic bead response can be monitored in the second harmonic sensor response to an oscillating bias current. The recent literature on applications of these sensors for the detection of magnetic fields and of the dynamic and static response of magnetic beads in suspension and attached to the sensor surface is reviewed as well as the use of the sensors for magnetic biosensing in volume- and surface-based formats. We illustrate that the sensors can be flexibly designed and applied for a number of sensing applications with sensitive detection of magnetic fields down to the nanotesla range.