Patent ID: 8664950

Claim:
A method for measuring longitudinal bias magnetic field in a tunnel magnetoresistive sensor of a magnetic head, the method comprising: (a) applying an external longitudinal time-changing magnetic field onto the tunnel magnetoresistive sensor, with a direction opposite to that of the longitudinal bias magnetic field; (b) determining a shield saturation value of the tunnel magnetoresistive sensor under the application of the external longitudinal time-changing magnetic field; (c) applying an external transverse time-changing magnetic field onto the tunnel magnetoresistive sensor, with a direction perpendicular to that of the longitudinal bias magnetic field; (d) applying an external longitudinal DC magnetic field, with a direction opposite to that of the longitudinal bias magnetic field; (e) determining a plurality of different output amplitudes under the application of the external transverse time-changing magnetic field and the application of different field strength values of the external longitudinal DC magnetic field; (f) plotting a graph according to the different output amplitudes and the different field strength values; and (g) determining the strength of the longitudinal bias magnetic field according to the graph and the shield saturation value, wherein (g) further comprises: (g1) determining the final field strength value corresponding to the maximum output amplitude in the graph; and (g2) determining the strength of the longitudinal bias magnetic field by subtracting the shield saturation value from the final field strength value.