Methods and systems for magnetic media servo writing

1. A method comprising:

generating a first magnetic field component in a magnetic medium;

generating a second magnetic field component in the magnetic medium, substantially opposite the first magnetic field component;

writing a pattern onto the magnetic medium;

generating a signal by reading the pattern from the magnetic medium;

determining an asymmetry in the signal; and

controlling a magnitude of the second magnetic field component based on the asymmetry.

2. The method of claim 1 , wherein determining an asymmetry in the signal comprises comparing a positive peak amplitude in a servo signal to a negative peak amplitude in the servo signal.

3. The method of claim 2 , wherein controlling a magnitude of the second field component comprises controlling the magnitude to reduce the asymmetry.

4. The method of claim 1 , wherein generating the first field component comprises generating a fixed field component with a fixed-field magnetic head.

5. The method of claim 4 , wherein generating the second field component comprises generating a variable field component with an electromagnetic head.

6. The method of claim 5 , wherein controlling a magnitude of the second field component comprises adjusting a current supply to the electromagnetic head.

7. A magnetic tape formatted according to the method of claim 1 .

8. The magnetic tape of claim 7 , further comprising a recording layer configured for perpendicular recording.

9. The magnetic tape of claim 8 , wherein the recording layer comprises barium ferrite.

10. The magnetic tape of claim 8 , wherein the first and second field components are oriented substantially perpendicular to the recording layer.

11. The magnetic tape of claim 10 , wherein controlling a magnitude of the second field component comprises controlling the magnitude to reduce or minimize perpendicular bias in the recording layer.

12. A system comprising:

first and second magnetic heads positioned along a magnetic medium, the first and second magnetic heads configured to generate first and second substantially opposite magnetic field components in the magnetic medium;

a write head positioned along the magnetic medium, the write head configured to write a pattern onto the magnetic medium;

a read head positioned along the magnetic medium, the read head configured to generate a signal by reading the pattern; and

a controller connected to the read head and the second magnetic head, the controller configured to control a magnitude of the second magnetic field component based on an asymmetry of the signal.

13. The system of claim 12 , wherein the magnetic medium comprises a perpendicular recording layer.

14. The system of claim 13 , wherein the first and second magnetic field components are oriented substantially perpendicular to the recording layer.

15. The system of claim 13 , wherein the perpendicular recording layer comprises barium ferrite.

16. The system of claim 12 , wherein the first and second magnetic heads are spaced apart from one another along the magnetic medium.

17. The system of claim 12 , wherein the second magnetic head comprises an electromagnet.

18. The system of claim 17 , wherein the controller is configured to control the magnitude of the second magnetic field component by adjusting a coil current to the electromagnet.

19. The system of claim 17 , wherein the controller is configured to reduce or minimize the asymmetry of a servo signal by increasing or decreasing the coil current.

20. The system of claim 17 , wherein the controller is configured to reduce or minimize perpendicular bias in the magnetic medium by increasing or decreasing the coil current.