Effects of external white noise on spin valve sensors

Noise peaks have been observed in spin valve micro-sensors when they were biased in the region near saturation. These have been explained using a simple double well potential model. Such a system should also exhibit stochastic resonance. In this paper, we investigated the signal and noise responses of micro-fabricated anti-parallel biased NiFe/Cu spin valve sensors in this region. The free layer and the pinned layer are in a cross-configuration. White magnetic field noise was applied to check its effect on the signal response of the sensors. The variations of signal-to-noise ratio (SNR) and signal power spectral density were measured under different conditions at low frequency (below 1 kHz). Non-linear behaviour consistent with stochastic resonance has been observed. The SNR shows a peak as the input noise is increased, which means that power from wide band background noise can be transferred into the signal component. The results fit well to the theory of stochasitic resonance for a double well potential system as developed by McNamara and Wiesenfeld [6].