Stability and biasing characteristics of a permanent magnet biased SAL/MR device

A longitudinal bias field can be produced by exchange-coupling a soft ferromagnetic MR layer, such as NiFe with a permanent magnetic (PM) thin film. This exchange bias field creates a single domain state in the MR layer and thereby suppresses the Barkhausen noise. The center active region of an MR sensor could remain magnetically soft if only the end regions of the MR stripe are exchange coupled. A CoNiCr hard magnetic thin film is deposited on top of a Cr underlayer to achieve a high coercivity of 750 Oe. The exchange coupling effect between the CoNiCr and the NiFe is significantly enhanced after a 290°C 3-hour annealing cycle. Unshielded devices fabricated with the patterned hard bias scheme were found very stable and the biasing characteristics are quite different from those coupled with FeMn. The PM materials are generally less prone to corrosion as compared to FeMn and are more compatible with wafer and slider fabrication processes