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 dc voltage versus field curve, because of hysteretic effects. Noise statistics are used to estimate 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 the ac response curve. For ac fields of about 0.3 mOe rms, sharp spikes appear in the field-dependent response, giving rise to large harmonic distortion, varying in an irregular way with the ac amplitude. Domain sizes are estimated for the regions, giving these nonlinear response spikes, and for the domains, giving the magnetic noise, and a comparison based on a fluctuation-dissipation relation of the noise, and the response shows the importance of hysteresis.