Spatial Resolution and Sensitivity of GMR Sensors with Magnetic Flux Concentrators used for Magnetic Field Microscopes

Spatial resolution and sensitivity of GMR sensors used in magnetic field microscopes are investigated by estimating the sensitivity distribution function. Sensors are used together with magnetic flux concentrators (MFCs), and detects local magnetic field with the typical sample-sensor distance of 5 mm. For the full-bridge type sensor unit, the spatial resolution was roughly determined by the distance of the GMR elements. Sharing the central MFCs is effective for improving the spatial resolution without losing sensitivity. It is found that the MFC loses its gain with decreasing sample-sensor distance because the MFC size is comparable with or larger than that distance. The half-bridge arrangement is found to be effective for obtaining small spatial resolution with high sensitivity.