Noise Characterization of Vortex-State GMR Sensors with Different Free Layer Thicknesses

The spin valve principle is the most prominent sensor design among giant- (GMR) and tunneling (TMR) magnetoresistive sensors. A new sensor concept with a disk shaped free layer enables the formation of a flux-closed vortex magnetization state if a certain relation of thickness to diameter is given. The low frequency noise of current-in-plane GMR sensing elements with different free layer thicknesses at different external field strengths has been measured. The measurements of the 1/f noise in external fields enabled a separation of magnetic and electric noise contributions. It has been shown that while the sensitivity is increasing with a decreasing element thickness, the pink noise contribution is increasing too. Still the detection limit at low frequencies is better in thinner free layer elements due to the higher sensitivity.