Anisotropy changes in magnetoresistive heads due to lapping and annealing

The elimination of Barkhausen noise in order to attain stable read performance is of primary interest in magnetoresistive (MR) read heads. One approach to making MR elements stable is to make the effective uniaxial anisotropy field large with respect to the hard axis fields experienced during operation and storage. In addition to providing a stabilizing effect, the anisotropy field determines the sensitivity of the element. A simple measurement of sensitivity at the component level is used to evaluate the effects of lapping and annealing. Analysis of sensitivity data, measured transfer functions, and calculated transfer functions shows that the stress-induced anisotropy can be reduced by magnetic annealing. Recording tests with unshielded, annealed, read-only heads reading a track recorded by a separate head show that the read signal is stable and free of Barkhausen noise for externally applied hard axis fields of up to 100 Oe. However, this stability comes at the cost of lower sensitivity hence lower readback signal level. A balance of stability and output can be achieved by adjusting the magnetocrystalline anisotropy, the magnetostriction, or the thermally induced stress and by the use of annealing after final lapping.<>