Data storage device detecting write pole degradation for magnetic write head

1. A data storage device comprising:

a magnetic media;

a head actuatable over the magnetic media, wherein the head comprises a write coil and a write pole; and

control circuitry configured to:

write a test pattern to the magnetic media by applying a first current to the write coil;

apply a second current to the write coil while the head passes over the test pattern, wherein the second current has a polarity opposite the first current;

after applying the second current to the write coil while the head passes over the test pattern, read the test pattern from the magnetic media using the head to generate a first read signal;

measure a first noise power of the first read signal; and

detect degradation of the write pole based on the first noise power.

2. The data storage device as recited in claim 1 , wherein the control circuitry is further configured to:

apply a third current to the write coil while the head passes over the test pattern wherein the third current has a polarity the same as the second current;

after applying the third current to the write coil while the head passes over the test pattern, read the test pattern from the magnetic media using the head to generate a second read signal;

measure a second noise power of the second read signal; and

detect degradation of the write pole based on the first and second noise powers.

3. The data storage device as recited in claim 2 , wherein the control circuitry is further configured to:

estimate a target current applied to the write coil that achieves a target noise power measurement based on the first and second noise powers; and

detect the degradation of the write pole based on the target current.

4. The data storage device as recited in claim 3 , wherein the control circuitry is further configured to detect degradation of the write pole when a change in the target current exceeds a threshold.

5. The data storage device as recited in claim 3 , wherein the control circuitry is further configured to detect degradation of the write pole when a rate of change of the target current exceeds a threshold.

6. The data storage device as recited in claim 2 , wherein the control circuitry is further configured to:

estimate a target current applied to the write coil that achieves at least partial saturation of the magnetic media; and

detect the degradation of the write pole based on a noise power measurement at the target current.

7. The data storage device as recited in claim 1 , wherein the head further comprises a write assist element and the control circuitry is further configured to apply a first bias to the write assist element while writing the test pattern to the magnetic media.

8. The data storage device as recited in claim 7 , wherein the control circuitry is further configured to apply a second bias to the write assist element while the head passes over the test pattern.

9. The data storage device as recited in claim 8 , wherein the control circuitry is further configured to calibrate the second bias to achieve a target capacity of the magnetic media.

10. A data storage device comprising:

a magnetic media;

a head actuatable over the magnetic media, wherein the head comprises a write coil and a write pole; and

control circuitry configured to:

apply a current to the write coil while the head passes over a test area of the magnetic media;

after applying the current to the write coil while the head passes over the test area, read the test area using the head to generate a first read signal;

measure a first noise power of the first read signal;

estimate a target current applied to the write coil that achieves a target noise power measurement based on the first noise power; and

detect degradation of the write pole based on the first noise power and the target current.

11. The data storage device as recited in claim 10 , wherein prior to reading the test area, the control circuitry is further configured to:

write a test pattern to the test area of the magnetic media by applying a first current to the write coil; and

apply a second current to the write coil while the head passes over the test area, wherein the second current has a polarity opposite the first current.

12. The data storage device as recited in claim 11 , wherein:

the target current achieves at least partial saturation of the magnetic media; and

the control circuitry is further configured to detect the degradation of the write pole based on the target noise power measurement at the target current.

13. The data storage device as recited in claim 10 , wherein the control circuitry is further configured to detect degradation of the write pole when a change in the target current exceeds a threshold.

14. The data storage device as recited in claim 10 , wherein the control circuitry is further configured to detect degradation of the write pole when a rate of change of the target current exceeds a threshold.

15. The data storage device as recited in claim 10 , wherein the head further comprises a write assist element and the control circuitry is further configured to apply a first bias to the write assist element while applying the current to the write coil while the head passes over the test area of the magnetic media.

16. The data storage device as recited in claim 15 , wherein the control circuitry is further configured to apply a second bias to the write assist element while the head passes over the test area.

17. The data storage device as recited in claim 16 , wherein the control circuitry is further configured to calibrate the second bias to achieve a target capacity of the magnetic media.

18. A data storage device comprising:

a magnetic media;

a head actuatable over the magnetic media, wherein the head comprises a write coil and a write pole;

a means for writing a test pattern to a test area of the magnetic media by applying a first current to the write coil;

a means for applying a second current to the write coil while the head passes over the test area, wherein the second current has a polarity opposite the first current;

a means for reading the test area from the magnetic media using the head, after writing the test pattern to the test area and after applying the second current to the write coil while the head passes over the test area, to generate a first read signal;

a means for measuring a first noise power of the first read signal; and

a means for detecting degradation of the write pole based on the first noise power.

19. A data storage device comprising:

a magnetic media;

a head actuatable over the magnetic media, wherein the head comprises a write coil and a write pole; and

control circuitry configured to:

write a test pattern to a test area of the magnetic media by applying a first current to the write coil;

apply a second current to the write coil while the head passes over the test area, wherein the second current has a polarity opposite the first current;

after writing the test pattern to the test area and after applying the second current to the write coil while the head passes over the test area, read the test area using the head to generate a first read signal;

measure a first noise power of the first read signal; and

detect degradation of the write pole based on the first noise power.

20. The data storage device as recited in claim 19 , wherein the control circuitry is further configured to:

estimate a target current that achieves at least partial saturation of the magnetic media; and

detect the degradation of the write pole based on a noise power measurement at the target current.

21. A data storage device comprising:

a magnetic media;

a head actuatable over the magnetic media, wherein the head comprises a write coil, a write pole, and a write assist element; and

control circuitry configured to:

apply a current to the write coil while the head passes over a test area of the magnetic media;

apply a first bias to the write assist element while applying the current to the write coil while the head passes over the test area of the magnetic media;

after applying the current to the write coil while the head passes over the test area, read the test area using the head to generate a first read signal;

measure a first noise power of the first read signal; and

detect degradation of the write pole based on the first noise power.

22. The data storage device as recited in claim 21 , wherein the control circuitry is further configured to apply a second bias to the write assist element while the head passes over the test area.

23. The data storage device as recited in claim 22 , wherein the control circuitry is further configured to calibrate the second bias to achieve a target capacity of the magnetic media.