Soft-adjacent-layer self-biased magnetoresistive heads in high-density recording

Various biasing techniques have been proposed for vertical magnetoresistive stripe detectors to improve their linearity. In the soft-adjacent- layer design, a high-permeability film (SAL) is located close to a magnetoresistive stripe (MR). The sense current in the MR magnetizes the SAL, which in turn generates a magnetostatic bias field at the MR. Thin-film heads based on the SAL concept have been fabricated on sapphire, using conventional methods, and tested. A theoretical description in which the SAL and the MR are treated as coupled Stoner-Wohlfarth particles has been generalized to include misorientation of the anisotropy axes and to include all applied field directions in the plane of the device. This provides a convenient description of the magnetic characteristics in uniform fields. For track widths of 39 μm, the 3.1 kHz slot RMS-signal-to-RMS-noise ratio at 80 KFCI and 19.1 cm/sec is 45 dB and is tape-noise limited. Barkhausen instability is evident at lower bit densities where the fields from the transitions are large, but is not a limiting factor at 80 KFCI. A comparison of the signal spectra with that of an externally biased head demonstrates that the bias angle across the element height is more uniform with SAL biasing.