We report on the origin and the influence of small variations in magnetic properties of magnetically soft Sendust films, used as a bottom shield in magnetoresistive heads, on instability parameters probed by quasi-static measurements. A strong correlation of the shield's magnetic characteristics with the average wafer asymmetry range is found. The variations in magnetic properties are directly connected with local anisotropy effects as revealed by Kerr microscopy. A direct correlation of the domain structures at the shield's surface with microstructure of the film is found. The magnetic domains display a change of magnetics with film growth. The deviations of magnetic properties are due to small structural Sendust changes.
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