Analyses of field distributions and undershoots in GMR-type differential readers

Abstract A finite element method (FEM) model, with refinements for the free layers, is proposed for GMR-type differential readers (GDRs). Our purpose is to explore the underlying reasons for the effects of the gap length and bit length on the GDR responses and for the origin of the undershoots in the GDR pulses. Our major findings are that the maximum field within the free layers of GDRs increases with decreasing gap length due to flux concentration; and that the GDR pulse and the associated undershoot effect obtained from the FEM model proposed are consistent with those obtained from our micromagnetic modeling. It has been revealed, for the first time, that the undershoot effect in differential readers are related to that the downtrack profile of the mean field near a transition is non-monotonic.