Magnetic-Field Dependence of the Noise in a Magnetoresistive Sensor Having MEMS Flux Concentrators

We report the dc and ac magnetic field dependence of the low-frequency noise in a microelectromechanical system (MEMS) flux concentrator device containing a giant magnetoresistance spin valve (SV). The noise is dominated by resistance fluctuations having a magnetic origin. Under nominally zero magnetic-field biasing conditions, the noise power is large and varies rapidly with small changes in magnetic field. Metastability between distinct resistive states is observed and can be suppressed with the application of a moderate longitudinal field. Stationary flux concentrators do not contribute excess noise, rather the dominant source of noise is the SVs themselves. This result indicates that the device is likely to increase the sensitivity of many magnetic sensors at low frequencies by orders of magnitude