Ferrite head instability

Polycrystalline MIG (metal-in-gap) ferrite heads were investigated for unstable isolated transition responses. Some of the heads exhibited a severe left-right pulse asymmetry in the form of a foot on the leading edge of the transition response. The foot could be attributed to crystallites, magnetically defining the leading gap edge, having an unfavorable magnetization direction. Another phenomenon observed was perturbations (wiggles) in the readback signal around and during the isolated impulses. This was attributed to illumination, by passing transitions, of the micromagnetic granularity of the ferrite at the air-bearing surface directly adjoining the gap, as well as to hysteretic domain wall motion and delayed relaxation. The wiggle patterns changed upon write excitation; they gave rise to head instability. Pulsewidth distribution measurements in the presence of write excitation of the heads were found to give a good criterion for the degree of instability: the coefficient of variation of the distributions was found to closely track error rates.<
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