Baseline popping noise (BLPN) is characterized by the spurious popping of baseline between readback pulses from magnetoresistive/giant MR (MR/GMR) heads. This article focuses on experimental investigation of BLPN from hard-magnet-biased GMR head. It is found that BLPN is sensitive to read bias current in both magnitude and polarity. Also, we found that BLPN is very sensitive to head offset across a written track as a result of interaction between localized BLPN active slice and written track edge. Full-track and microtrack profiling of BLPN is used to substantiate these behaviors. A close-fit model is proposed to further explain the BLPN mechanism. With this model, GMR BLPN is explained by longitudinal hard bias insufficiency on a free layer. When hard bias is not strong enough, due to the demagnetization field, magnetization around edge area rotates either up or down. This skewed magnetization is not stable, a small field will make it flip up and down, which results in jumps in transfer curve and eventually instability in track average amplitude.

Absrruci--We systematically studied the micro-track profiles of ESD damaged AMR and spin valve GMR heads, and correlated with the dynamic electric performances of each head. Spin valve GMR heads and two types of AMR heads made by different structure and material are ESD (HBM) stressed and studied. We observed double peak in micro-track profile after more than 10 % change of MR resistance. This means that the centers of AMR and GMR sensors become less sensitive before the total melting of MR element during ESD zapping. We also observed double peak micro-track profile after pin reversal of SV head. We attribute this to changes in the domain configuration caused by partial reversal of pinned layer moment along MR (GMR) stripe.

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The effect of track-edge amplitude asymmetry on position-error signal, PES, of spin-valve GMR heads was investigated. Cross-track profiles of both amplitude and amplitude asymmetry are showed along with the PES line of the head. The results indicated that amplitude-asymmetry effect from servo burst is finite but not significant enough to alter PES sensitivity, or the slope of PES line. However, it is shown experimentally that the PES linearity is functionally correlated with asymmetry of the servo bursts, which substantiates the track-edge effect of spin-valve heads.Index Terms-Amplitude asymmetry, position error signal, servo, spin-valve GMR head.