Baseline popping noise of giant magnetoresistive head

Abstract

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.

Drive-level instabilities correlated to quasi-static field testing

“…A LTHOUGH there is a desire to continually improve the sensitivity of giant magnetoresistive (GMR) readers for head applications, an equally challenging task is to produce stable sensors [1]- [3]. Head designers are to the point where head stability may be compromised for increased sensitivity, due to track width reductions, thinner free layers and reduced pinning fields.…”