Method and system for measuring spacing in a perpendicular magnetic recording
View Patent ↗PMR spacing is measured by writing a pattern on a magnetic storage layer in non-return-to-zero notation, reading the pattern from the magnetic storage layer, analyzing a first harmonic component of the pattern that has a first amplitude, analyzing a second harmonic component of the pattern that has a second amplitude, measuring a ratio between the first and the second amplitudes of the first and second harmonic components, and determining a first spacing based on the ratio. In another embodiment, spacing is measured by analyzing a third harmonic component on the magnetic storage layer that has a third amplitude, measuring a difference in the amplitudes of the second and the third harmonic components while varying the first spacing and taking the ratio of the difference of the two each harmonic components.
1. A method for measuring a spacing in a perpendicular magnetic recording comprising:
writing a pattern on a magnetic storage layer in non-return-to-zero notation;
reading the pattern from the magnetic storage layer;
analyzing a first harmonic component that has a first amplitude using the pattern;
analyzing a second harmonic component that has a second amplitude using the pattern;
measuring a ratio between the first and the second amplitudes of the first and second harmonic components; and
determining a first spacing based on the ratio,
wherein the first harmonic component has a frequency that is two times a frequency of the second harmonic component and the ratio between the first amplitude and the second amplitude is less than 12 decibels.
2. The method of claim 1 wherein the pattern is fourteen bits.
3. The method of claim 1 wherein the first spacing is a head media spacing (HMS).
4. The method of claim 1 wherein the steps of analyzing further comprises using a digitizing scope or a spectrum analyzer.
5. The method of claim 1 further comprising:
analyzing a third harmonic component that has a third amplitude using the pattern;
measuring a difference in the amplitudes of the second and the third harmonic components while varying the first spacing;
calculating a ratio of the difference of the second and the third harmonic components; and
determining a second spacing based on the ratio,
wherein the second harmonic component has a frequency that is two times a frequency of the third harmonic component and the third amplitude is between the first amplitude and the second amplitude and the ratio between the second amplitude and the third amplitude is less than 12 decibels.
6. The method of claim 5 wherein the second spacing is a head keeper spacing (HKS).
7. The method of claim 5 wherein the step of analyzing a third harmonic component further comprises using a digitizing scope or a spectrum analyzer.
8. The method of claim 5 , wherein the pattern is written to a single portion of the magnetic storage layer.
9. The method of claim 1 wherein the first amplitude is 1.75T, the second amplitude is 3.5T, and the third amplitude is 7T.
10. The method of claim 1 wherein the pattern is 11100010110010.
11. A measuring system for a perpendicular magnetic recording comprising:
a pattern written in non-return-to-zero notation on a magnetic storage layer, which is read back from the magnetic storage layer;
a first harmonic component that has a first amplitude configured to be analyzed in the read back pattern;
a second harmonic component that has a second amplitude configured to be analyzed in the read back pattern; and
a measurement instrument configured to determine a ratio between the first and the second amplitudes of the first and second harmonic components and determine a first spacing based on the ratio,
wherein the first harmonic component has a frequency that is two times a frequency of the second harmonic component and the ratio between the first amplitude and the second amplitude is less than 12 decibels.
12. The system of claim 11 wherein the pattern is fourteen bits.
13. The system of claim 11 wherein the first spacing is a head media spacing (HMS).
14. The system of claim 11 wherein the measuring instrument comprises a digitizing scope or a spectrum analyzer.
15. The system of claim 11 further comprising:
a varying module;
a third harmonic component that has a third amplitude configured to be analyzed in the read back pattern; and
the measurement instrument further configured to measure a difference in the amplitudes of the second and the third harmonic components while the varying module varies the first spacing,
the measurement instrument further configured to calculate a ratio of the difference of the second and the third harmonic components and determine a second spacing based on the ratio,
wherein the second harmonic component has a frequency that is two times a frequency of the third harmonic component and the third amplitude is between the first amplitude and the second amplitude and the ratio between the second amplitude and the third amplitude is less than 12 decibels.
16. The system of claim 15 wherein the second spacing is a head keeper spacing (HKS).
17. The system of claim 15 , wherein the pattern is written to a single portion of the magnetic storage layer.
18. The system of claim 11 wherein the first amplitude is 1.75T, the second amplitude is 3.5T, and the third amplitude is 7T.
19. The system of claim 11 wherein the pattern is 11100010110010.
20. A hard disk drive apparatus comprising:
a magnetic storage layer having a relatively high coercivity;
an underlayer having a relatively low coercivity;
an interlayer between the magnetic storage layer and the underlayer configured to magnetically isolate the magnetic storage layer from the underlayer by a physical separation having a first spacing;
a read and write head positioned near the magnetic storage layer but not touching the magnetic storage layer, wherein there is a second spacing between the read and write head and the magnetic storage layer, the read and write head configured to write a fourteen bit pattern on a single portion of the magnetic storage layer and to read back the fourteen bit pattern;
an analysis module configured to analyze a first, a second, and a third harmonic component in the read back pattern, wherein the first harmonic component has a frequency that is two times a frequency of the second harmonic component and four times the frequency of the third harmonic component; and
a processing module configured to compute the second spacing using the analyzed first and second harmonic components and to compute the first spacing using the second and third harmonic components.
21. The hard disk drive apparatus of claim 20 wherein the second spacing is a head media spacing (HMS).
22. The hard disk drive apparatus of claim 20 wherein the first spacing is a head keeper spacing (HKS).
23. The hard disk drive apparatus of claim 20 wherein the first harmonic component has a first amplitude and the second harmonic component has a second amplitude, and
wherein a first ratio between the first amplitude and the second amplitude is less than 12 decibels.
24. The hard disk drive apparatus of claim 23 wherein the third harmonic component has a third amplitude and the third amplitude is between the first amplitude and the second amplitude and a second ratio of a difference between the second amplitude and the third amplitude is less than 12 decibels.
25. The hard disk drive apparatus of claim 24 wherein the first amplitude is 1.75T, the second amplitude is 3.5T, and the third amplitude is 7T.
26. The hard disk drive apparatus of claim 23 wherein the first ratio is determined using the Wallace equation.
27. The hard disk drive apparatus of claim 20 wherein the fourteen bit pattern is 11100010110010.
28. The hard disk drive apparatus of claim 20 wherein the fourteen bit pattern comprises a plurality of individual bits, wherein each of the individual bits is written to the magnetic storage layer with a spacing of between 50 nanometers and 100 nanometers.
29. The hard disk drive apparatus of claim 20 further comprising a synchronization module including a clock signal, the clock signal configured to provide a reference for the read and write head to read back the pattern.
30. The hard disk drive apparatus of claim 20 wherein the magnetic storage layer comprises an alloy including one or more of cobalt, chromium, platinum, silicon, or oxygen.
31. The hard disk drive apparatus of claim 20 wherein the underlayer comprises an alloy including one or more of cobalt, tantalum, or chromium.