Comparison of Sensitivity and Low Frequency Noise Contributions in GMR and TMR Spin Valve Sensors with a Vortex State Free Layer

Magnetoresistive spin-valve sensors based on the giant-magnetoresisitive (GMR) and tunneling-magnetoresisitive (TMR) effect with a flux-closed vortex-state free-layer design are compared by means of sensitivity and low-frequency noise. The vortex-state free layer allows high saturation fields up to 80 mT with negligible hysteresis, making it attractive for applications with a high dynamic range. The measured GMR devices comprise pink noise lower by a factor of 300 and better linearity in resistance but are less sensitive to external magnetic fields than TMR sensors. The results show comparable detectivity at low frequencies of about 2 mu T/root Hz for 1-mu m-diameter devices and 0.8 mu T/root Hz for 2-mu m-diameter devices at 1 Hz with ten active elements connected in series. The performance of the TMR minimum detectable field at frequencies in the white-noise limit is better by a factor of about 20 than that of the GMR devices.