Nonlinear AC response and noise of a giant magnetoresistive sensor

We compare bridge voltage response measurements to ac magnetic fields from a giant magnetoresistive sensor with noise measurements on the same sensor. The small-signal response (for applied ac magnetic fields between 0.1 mOe rms and 30 mOe) is much less than is the slope of a de voltage versus field curve, because of hysteretic effects. Noise statistics are used to estimat e the size and number of the sites at which domain realignments occur near the response peak, Similar estimates are made by using fine-structure on th e ac response curve. For ac fields of about 0.3 mOe rms, sharp spikes appea r in the field-dependent response, giving rise to Large harmonic distortion , varying in an irregular way with the ac amplitude. Domain sizes are estim ated for the regions, giving these nonlinear response spikes, and for the d omains, giving the magnetic noise, and a comparison based on a fluctuation- dissipation relation of the noise, and the response shows the importance of hysteresis.