Methods and apparatus for controlling the lapping of a slider based on an amplitude of a readback signal produced from an externally applied magnetic field

1. A method of lapping a slider which includes at least one magnetic head having a read sensor comprising:

lapping a slider which includes at least one magnetic head;

during the lapping of the slider:

producing a magnetic field around the magnetic head;

monitoring a readback signal amplitude of a read sensor of the magnetic head which varies during the lapping of the slider; and

terminating the lapping of the slider based at least in part on the monitoring of the readback signal amplitude.

2. The method of claim 1 , wherein the lapping of the slider is terminated when the readback signal amplitude is above a predetermined minimum threshold or reaches its peak value.

3. The method of claim 1 , further comprising:

during the lapping of the slider: monitoring a resistance of the read sensor which varies during the lapping; and

terminating the lapping of the slider based on the monitoring of the readback signal amplitude and the resistance.

4. The method of claim 1 , further comprising:

during the lapping of the slider: monitoring a resistance of the read sensor which varies during the lapping; and

terminating the lapping of the slider when the readback signal amplitude is above a predetermined amplitude threshold or reaches its peak value, and the resistance is within a predetermined resistance range.

5. The method of claim 1 , wherein the act of producing the magnetic field comprises producing the magnetic field with a direct current (DC).

6. The method of claim 1 , wherein the act of producing the magnetic field comprises producing the magnetic field at a predetermined frequency.

7. The method of claim 1 , further comprising:

wherein the act of producing the magnetic field comprises producing the magnetic field at a predetermined frequency; and

wherein the act of monitoring the readback signal amplitude comprises monitoring the readback signal amplitude at the predetermined frequency.

8. The method of claim 1 , further comprising:

wherein the act of producing the magnetic field comprises producing the magnetic field at a predetermined frequency; and

performing a Fast Fourier Transform (FFT) or a Phase-Locked-Loop (PLL) at the predetermined frequency in monitoring the readback signal amplitude.

9. The method of claim 1 , further comprising:

during the lapping of the slider: calculating an asymmetry measurement of the read sensor; and

terminating the lapping of the slider based on the calculated asymmetry measurement.

10. A method of lapping a slider which includes at least one magnetic head having a read sensor comprising:

lapping a slider which includes at least one magnetic head;

during the lapping of the slider:

producing a magnetic field around the magnetic head;

monitoring a readback signal amplitude of a read sensor of the magnetic head which varies during the lapping of the slider;

generating an asymmetry measurement based on the monitored readback signal amplitude; and

terminating the lapping of the slider based at least in part on the monitoring of the asymmetry measurement.

11. The method of claim 10 , wherein the lapping of the slider is terminated when the asymmetry measurement is within a predetermined range.

12. The method of claim 10 , wherein the act of producing the magnetic field comprises producing the magnetic field with a direct current (DC).

13. The method of claim 10 , wherein the act of producing the magnetic field comprises producing the magnetic field at a predetermined frequency.

14. The method of claim 10 , wherein the asymmetry measurement is based on (A−B)/(A+B)=−3π/4 Peak(2f 0 )/Peak(f 0 ), where A is a peak positive readback signal amplitude, B is a peak negative readback signal amplitude, and f 0 is frequency.