Magnetic write head characterization with nano-meter resolution using nitrogen vacancy color centers

• US 8,885,301 B1
• Filed: 02/19/2014
• Issued: 11/11/2014
• Est. Priority Date: 02/19/2014
• Status: Active Grant

• Current Assignee: Infinitum Solutions, Inc.
• Original Assignee: Infinitum Solutions, Inc.
• Inventors: Heidmann, Juergen
• Primary Examiner(s): HINDI, NABIL Z
• Application Number:
  US14/184,610
• Time in Patent Office: 265 Days
• Field of Search: 360/59, 360/323, 360/324.12, 360/324.22, 360/114.01, 360/97.12, 360/31, 369/13.33, 369/130.02, 356/345, 324/304
• US Class Current: 360/323
• CPC Class Codes: G01N 21/6489 Photoluminescence of semiconductors
• CPC Class Codes: G11B 2005/0021 Thermally assisted recording using an auxiliary energy source for heating the recording layer locally to assist the magnetization reversal
• CPC Class Codes: G11B 5/012 Recording on, or reproducing or erasing from, magnetic disks G11B17/00, G11B19/00 take precedence
• CPC Class Codes: G11B 5/455 Arrangements for functional testing of heads; Measuring arrangements for heads

Abstract

A crystal film with one or more nitrogen vacancy centers is placed in a magnetic field produced by a recording head and excitation illumination and a varying excitation field is applied. A confocal microscope or wide-field microscope optically detects a decrease in a spin dependent photoluminescence in response to the excitation illumination caused by electron spin resonance (ESR) of the at least one nitrogen vacancy center at varying excitation frequencies of the excitation field to measure Optically Detected Spin Resonance (ODMR). A characteristic of the recording head is determined using the ODMR.

Claims

1. A method comprising:

providing a bias signal to a recording head that includes a write pole to produce a magnetic field from the recording head, wherein a crystal film with nitrogen vacancy centers is positioned in the magnetic field;

providing an excitation field to the crystal film;

producing excitation illumination that is incident on the crystal film;

measuring Optically Detected Spin Resonance (ODMR) by detecting a decrease in a spin dependent photoluminescence in response to the excitation illumination caused by electron spin resonance (ESR) of the nitrogen vacancy centers at varying excitation frequencies of the excitation field; and

determining a characteristic of the recording head using the ODMR detected at the one or more excitation frequencies of the excitation field.

2. The method of claim 1, further comprising providing a plurality of bias signals with different levels to the recording head.

3. The method of claim 1, wherein the nitrogen vacancy centers have a known density and wherein determining the characteristic of the recording head uses the known density of the nitrogen vacancy centers.

4. The method of claim 3, wherein the characteristic of the recording head comprises a spatial extent of the write pole.

5. The method of claim 4, wherein the spatial extent of the write pole is determined based on a spatial extent of a write field produced by the recording head.

6. The method of claim 4, further comprising:

determining a number of nitrogen vacancy centers contributing to an ODMR signal measured at one or more excitation frequencies based on a contrast of the ODMR signal at the one or more excitation frequencies and a known contrast of the ODMR signal for a single nitrogen vacancy center;

wherein the spatial extent of the write pole is determined based on the number of nitrogen vacancy centers contributing to the ODMR signal emitting at the one or more excitation frequencies and the known density of the nitrogen vacancy centers.

7. The method of claim 4, further comprising determining a width of the write pole near a write gap based on the spatial extent of the write pole.

8. The method of claim 4, wherein measuring ODMR at varying excitation frequencies produces an ESR spectrum, the method further comprising:

determining a maximum excitation frequency in the ESR spectrum at which an ODMR signal is produced by one or more nitrogen vacancy centers;

determining a number of spectral lines in the ESR spectrum associated with an edge of the write pole; and

using the maximum excitation frequency, the number of spectral lines, and the known density of the nitrogen vacancy centers which determines the spatial relation of the spectral lines to determine the spatial extent of the write pole.

9. The method of claim 3, wherein the characteristic of the recording head is the magnetic write width, the method further comprising:

determining a maximum excitation frequency at which an ODMR signal is produced by one or more nitrogen vacancy centers;

determining a number of nitrogen vacancy centers contributing to the ODMR signal at the maximum excitation frequency; and

determining the magnetic write-width of the write pole using the number of nitrogen vacancy centers contributing to the ODMR signal at the maximum excitation frequency and the known density of the nitrogen vacancy centers.

10. The method of claim 9, further comprising determining the magnetic write width as a function of bias level.

11. The method of claim 3, wherein the characteristic of the recording head is the magnetic write width, the method further comprising:

determining an integrated spectral intensity using the ODMR from a minimum write field to a maximum write field and an exponential constant based on the density of the nitrogen vacancy centers; and

determining the magnetic write width based on the integrated spectral intensity.

12. The method of claim 11, further comprising determining the magnetic write width as a function of bias level.

13. The method of claim 3, further comprising:

determining a maximum excitation frequency at which an ODMR signal is produced by one or more nitrogen vacancy centers; and

using the maximum excitation frequency to determine a maximum write field produced by the write pole.

14. The method of claim 1, wherein adjacent nitrogen vacancy centers are separated by a distance greater than a width of the write pole, further comprising producing relative movement between the recording head and the crystal film thereby scanning a nitrogen vacancy center over the recording head in two dimensions.

15. The method of claim 14, wherein the nitrogen vacancy center is scanned over the write pole and wherein the determined characteristic of the recording head is magnetic field values.

16. The method of claim 14, wherein the nitrogen vacancy center is scanned over the write pole and wherein the determined characteristic of the recording head is a surface area of the write pole.

17. The method of claim 14, wherein the nitrogen vacancy center is scanned over a near-field aperture area of the recording head for thermally assisted recording and wherein the determined characteristic of the recording head is temperature values of the near-field aperture area of the recording head.

18. The method of claim 1, wherein adjacent nitrogen vacancy centers are separated by a distance less than a width of the write pole, further comprising:

producing a depletion illumination that is coincident on the crystal film with the excitation illumination;

scanning the coincident excitation illumination and the depletion illumination in two dimensions over the crystal film over a portion of the recording head;

wherein measuring ODMR uses the coincident excitation illumination and depletion illumination.

19. The method of claim 18, wherein the depletion illumination is one of a group consisting essentially of:

Stimulated Emission Depletion (STED) illumination and Ground State Depletion (GSD) illumination.

20. The method of claim 18, wherein the excitation illumination and the depletion illumination are scanned over the write pole and wherein the determined characteristic of the recording head is magnetic field values.

21. The method of claim 18, wherein the excitation illumination and the depletion illumination are scanned over the write pole and wherein the determined characteristic of the recording head is a surface area of the write pole.

22. The method of claim 18, wherein the excitation illumination and the depletion illumination are scanned over a near-field aperture area of the recording head for thermally assisted recording and wherein the determined characteristic of the recording head is temperature values of the near-field aperture area of the recording head.

23. The method of claim 18, wherein the crystal film is attached to an air bearing surface of the recording head.

24. An apparatus comprising:

a biasing source configured to provide a bias signal;

a probe card coupled to the biasing source and configured to be connected to a recording head that includes a write pole to provide the bias signal to the recording head that causes the recording head to produce a magnetic field;

a light source that produces excitation illumination that is incident on a crystal film with nitrogen vacancy centers that is in the magnetic field produced by the recording head;

a radio frequency antenna that provides an excitation field to the crystal film;

a microscope configured to detect photoluminescence produced by the nitrogen vacancies in response to the excitation illumination; and

a processor coupled to the microscope and configured to measure Optically Detected Spin Resonance (ODMR) by detecting a decrease in a spin dependent photoluminescence in response to the excitation illumination caused by electron spin resonance (ESR) of the nitrogen vacancy centers at varying excitation frequencies of the excitation field, and determine a characteristic of the recording head using the ODMR detected at the one or more excitation frequencies of the excitation field.

25. The apparatus of claim 24, wherein the biasing source is configured to provide a plurality of bias signals with different levels, which the probe card provides to the recording head.

26. The apparatus of claim 24, wherein the nitrogen vacancy centers have a known density and wherein the processor is configured to further use the known density of the nitrogen vacancy centers to determine the characteristic of the recording head.

27. The apparatus of claim 26, wherein the characteristic of the recording head comprises a spatial extent of the write pole.

28. The apparatus of claim 27, wherein the spatial extent of the write pole is determined based on a spatial extent of a write field produced by the recording head.

29. The apparatus of claim 27, wherein the processor is configured to:

determine a number of nitrogen vacancy centers contributing to an ODMR signal measured at one or more excitation frequencies based on a contrast of the ODMR signal at the one or more excitation frequencies and a known contrast of the ODMR signal for a single nitrogen vacancy center;

wherein the spatial extent of the write pole is determined based on the number of nitrogen vacancy centers contributing to the ODMR signal emitting at the one or more excitation frequencies and the known density of the nitrogen vacancy centers.

30. The apparatus of claim 27, wherein the processor is further configured to determine a width of the write pole near a write gap based on the spatial extent of the write field.

31. The apparatus of claim 27, wherein the processor is configured to measure ODMR at varying excitation frequencies to produce an ESR spectrum, the processor is further configured to:

determine a maximum excitation frequency in the ESR spectrum at which an ODMR signal is produced by one or more nitrogen vacancy centers;

determine a number of spectral lines in the ESR spectrum associated with an edge of the write pole; and

use the maximum excitation frequency, the number of spectral lines, and the known density of the nitrogen vacancy centers which determines the spatial relation of the spectral lines to determine the spatial extent of the write pole.

32. The apparatus of claim 26, wherein the characteristic of the recording head is the magnetic write width, and wherein the processor is further configured to:

determine a maximum excitation frequency at which an ODMR signal is produced by one or more nitrogen vacancy centers;

determine a number of nitrogen vacancy centers contributing to the ODMR signal at the maximum excitation frequency; and

determine the magnetic write-width of the write pole using the number of nitrogen vacancy centers contributing to the ODMR signal at the maximum excitation frequency and the known density of the nitrogen vacancy centers.

33. The apparatus of claim 32, wherein the magnetic write width is determined as a function of bias level.

34. The apparatus of claim 26, wherein the characteristic of the recording head is the magnetic write width, and wherein the processor is configured to:

determine an integrated spectral intensity using the ODMR from a minimum write field to a maximum write field and an exponential constant based on the density of the nitrogen vacancy centers; and

determine the magnetic write width based on the integrated spectral intensity.

35. The apparatus of claim 34, wherein the magnetic write width is determined as a function of bias level.

36. The apparatus of claim 26, wherein the processor is further configured to:

determine a maximum excitation frequency at which an ODMR signal is produced by one or more nitrogen vacancy centers; and

use the maximum excitation frequency to determine a maximum write field produced by the write pole.

37. The apparatus of claim 24, wherein adjacent nitrogen vacancy centers are separated by a distance greater than a width of the write pole, the apparatus comprising at least one actuator to produce relative movement between the recording head and the crystal film thereby scanning a nitrogen vacancy center over the recording head in two dimensions.

38. The apparatus of claim 37, wherein the nitrogen vacancy center is scanned over the write pole and wherein the determined characteristic of the recording head is magnetic field values.

39. The apparatus of claim 37, wherein the nitrogen vacancy center is scanned over the write pole and wherein the determined characteristic of the recording head is a surface area of the write pole.

40. The apparatus of claim 37, wherein the nitrogen vacancy center is scanned over a near-field aperture area of the recording head for thermally assisted recording and wherein the determined characteristic of the recording head is temperature values of the near-field aperture area of the recording head.

41. The apparatus of claim 24, wherein adjacent nitrogen vacancy centers are separated by a distance less than a width of the write pole, the apparatus further comprising:

a second light source that produces depletion illumination that is coincident on the crystal film with the excitation illumination;

at least one mirror to scan the coincident excitation illumination and the depletion illumination in two dimensions over the crystal film over a portion of the recording head;

wherein the processor is configured to use the coincident excitation illumination and depletion illumination to measure the ODMR.

42. The apparatus of claim 41, wherein the depletion illumination is one of a group consisting essentially of:

Stimulated Emission Depletion (STED) illumination and Ground State Depletion (GSD) illumination.

43. The apparatus of claim 41, wherein the excitation illumination and the depletion illumination are scanned over the write pole and wherein the determined characteristic of the recording head is magnetic field values.

44. The apparatus of claim 41, wherein the excitation illumination and the depletion illumination are scanned over the write pole and wherein the determined characteristic of the recording head is a surface area of the write pole.

45. The apparatus of claim 41, wherein the excitation illumination and the depletion illumination are scanned over a near-field aperture area of the recording head for thermally assisted recording and wherein the determined characteristic of the recording head is temperature values of the near-field aperture area of the recording head.

46. The apparatus of claim 41, wherein the crystal film is attached to an air bearing surface of the recording head.

47. A method comprising:

providing a bias signal to a recording head that includes a thermal device and a near-field aperture and includes a write pole to produce a magnetic field from the recording head, wherein a crystal film with nitrogen vacancy centers having a known density is positioned in the magnetic field;

providing a bias signal to the thermal device to heat the crystal film using the near-field aperture;

providing an excitation field to the crystal film;

producing excitation illumination that is incident on the crystal film;

measuring Optically Detected Spin Resonance (ODMR) by detecting a decrease in a spin dependent photoluminescence in response to the excitation illumination caused by electron spin resonance (ESR) of the nitrogen vacancy centers at varying excitation frequencies of the excitation field; and

determining a temperature characteristic of the near-field aperture of the recording head using the ODMR and the known density of the nitrogen vacancy centers.

48. An apparatus comprising:

a biasing source configured to provide bias signals;

a probe card coupled to the biasing source and configured to be connected to a recording head that includes a thermal device and a near-field aperture and includes a write pole, the probe card provides a bias signal to the recording head that causes the recording head to produce a magnetic field and a second bias signal to the thermal device to heat a crystal film using the near-field aperture, the crystal film includes nitrogen vacancy centers having a known density and is in the magnetic field produced by the recording head;

a light source that produces excitation illumination that is incident on the crystal film;

a radio frequency antenna that provides an excitation field to the crystal film;

a microscope configured to detect photoluminescence produced by the nitrogen vacancies in response to the excitation illumination; and

a processor coupled to the microscope and configured to measure Optically Detected Spin Resonance (ODMR) by detecting a decrease in a spin dependent photoluminescence in response to the excitation illumination caused by electron spin resonance (ESR) of the nitrogen vacancy centers at varying excitation frequencies of the excitation field; and

determine a temperature characteristic of the near-field aperture of the recording head using the ODMR and the known density of the nitrogen vacancy centers.

49. A method comprising:

providing a bias signal to a recording head that includes a write pole to produce a magnetic field from the recording head;

scanning a probe having a probe tip comprising a crystal particle with at least one nitrogen vacancy center through the magnetic field produced by the recording head;

providing an excitation field to the crystal particle;

producing excitation illumination that is incident on the crystal particle;

measuring Optically Detected Spin Resonance (ODMR) by detecting a decrease in a spin dependent photoluminescence in response to the excitation illumination caused by electron spin resonance (ESR) of the at least one nitrogen vacancy center at varying excitation frequencies of the excitation field; and

determining a characteristic of the recording head using the ODMR measured at the one or more excitation frequencies of the excitation field.

50. The method of claim 49, wherein the probe is scanned over a write pole of the recording head and wherein the determined characteristic of the recording head is magnetic field values.

51. The method of claim 49, wherein the probe is scanned over a write pole of the recording head and wherein the determined characteristic of the recording head is a surface area of the write pole.

52. The method of claim 49, wherein the probe is scanned over a near-field aperture area of the recording head for thermally assisted recording and wherein the determined characteristic of the recording head is temperature values of the near-field aperture area of the recording head.

53. An apparatus comprising:

a biasing source configured to provide a bias signal;

a probe card coupled to the biasing source and configured to be connected to a recording head that includes a write pole to provide the bias signal to the recording head that causes the recording head to produce a magnetic field;

a probe having a probe tip comprising a crystal particle with at least one nitrogen vacancy center, the probe configured to be scanned through the magnetic field produced by the recording head;

a light source that produces excitation illumination that is incident on the crystal particle;

a radio frequency antenna that provides an excitation field to the crystal particle;

a microscope configured to detect photoluminescence produced by the at least one nitrogen vacancy in the crystal particle;

a processor coupled to the microscope and configured to measure Optically Detected Spin Resonance (ODMR) by detecting a decrease in a spin dependent photoluminescence in response to the excitation illumination caused by electron spin resonance (ESR) of the at least one nitrogen vacancy center at varying excitation frequencies of the excitation field; and

determine a characteristic of the recording head using the ODMR measured at the one or more excitation frequencies of the excitation field.

54. The apparatus of claim 53, wherein the probe is scanned over a write pole of the recording head and wherein the determined characteristic of the recording head is magnetic field values.

55. The apparatus of claim 53, wherein the probe is scanned over a write pole of the recording head and wherein the determined characteristic of the recording head is a surface area of the write pole.

56. The apparatus of claim 53, wherein the probe is scanned over a near-field aperture area of the recording head for thermally assisted recording and wherein the determined characteristic of the recording head is temperature values of the near-field aperture area of the recording head.