MAGNETIC WRITE HEAD CHARACTERIZATION WITH NANO-METER RESOLUTION USING NITROGEN VACANCY COLOR CENTERS

• US 20160071532A9
• Filed: 11/04/2014
• Published: 03/10/2016
• Est. Priority Date: 02/19/2014
• Status: Active Grant

• Current Assignee: Infinitum Solutions, Inc.
• Original Assignee: Infinitum Solutions, Inc.
• Inventors: Heidmann, Juergen
• Granted Patent: US 9,472,217 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01N 24/08 by using nuclear magnetic resonance G01N24/12 takes precedence
• 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 5/455 Arrangements for functional testing of heads; Measuring arrangements for heads

Abstract

A crystal film with one or more nitrogen vacancy centers is placed in close proximity to a recording head. A magnetic field or heat produced by the recording head as well as excitation illumination and an excitation field is applied to the crystal film. The magnetic field produced by the recording head, the heat produced by a thermal device on the recording head, and/or the excitation field may be varied. A confocal microscope or wide-field microscope optically detects a decrease in a spin dependent photoluminescence in response to the magnetic field or heat, excitation field and excitation illumination caused by electron spin resonance (ESR) of the at least one nitrogen vacancy center 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 magnetic field, the excitation field and the excitation illumination caused by electron spin resonance (ESR) of the nitrogen vacancy centers; and

determining a characteristic of the recording head using the ODMR.

2. The method of claim 1, wherein the ODMR is measured at varying excitation frequencies of the excitation field.

3. The method of claim 1, wherein the characteristic of the recording head is efficiency of the recording head as a function of bias signal level.

4. The method of claim 1, wherein the crystal film is attached to an air bearing surface of the recording head.

5. The method of claim 1, wherein the recording head further comprises a thermal device and a near-field aperture, the method further comprising:

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

determining a second characteristic of the recording head using measured ODMR based on heating of the crystal film by the thermal device and the near-field aperture.

6. The method of claim 5, wherein the second characteristic of the recording head is a near-field power of the near-field aperture.

7. The method of claim 5, wherein the second characteristic of the recording head is a spatial extent of the near-field aperture.

8. The method of claim 5, further comprising providing a plurality of bias signals with different levels to the thermal device and wherein the second characteristic of the recording head is a function of the heat produced at different levels of bias signals.

9. The method of claim 5, wherein the bias signal provided to the recording head and the second bias signal provided to the thermal device are provided sequentially or serially.

10. 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 magnetic field, the excitation field, and the excitation illumination caused by electron spin resonance (ESR) of the nitrogen vacancy centers, and determine a characteristic of the recording head using the ODMR.

11. The apparatus of claim 10, wherein the ODMR is measured at varying excitation frequencies of the excitation field.

12. The apparatus of claim 10, wherein the characteristic of the recording head is efficiency of the recording head as a function of bias signal level.

13. The apparatus of claim 10, wherein the crystal film is attached to an air bearing surface of the recording head.

14. The apparatus of claim 10, wherein the recording head further comprises a thermal device and a near-field aperture, the apparatus further comprising:

a second biasing source configured to provide a second bias signal to the thermal device to heat the crystal film using the near-field aperture;

wherein the processor is further configured to determine a second characteristic of the recording head using measured ODMR based on heating of the crystal film by the thermal device and the near-field aperture.

15. The apparatus of claim 14, wherein the second characteristic of the recording head is a near-field power of the near-field aperture.

16. The apparatus of claim 14, wherein the second characteristic of the recording head is a spatial extent of the near-field aperture.

17. The apparatus of claim 14, wherein the second biasing source provides a plurality of bias signals with different levels to the thermal device and wherein the second characteristic of the recording head is a function of the heat produced at different levels of bias signals.

18. The apparatus of claim 14, wherein the bias signal provided to the recording head and the second bias signal provided to the thermal device are provided sequentially or serially.

19. A method comprising:

providing a bias signal to a device that includes a thermal device that is controlled by the bias signal to produce heat, wherein a crystal film with nitrogen vacancy centers is positioned to be heated by the thermal device;

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 heat, the excitation field and the excitation illumination caused by electron spin resonance (ESR) of the nitrogen vacancy centers; and

determining a characteristic of the device using the ODMR.

20. The method of claim 19, wherein a heat absorption layer is disposed between the thermal device and the crystal film.

21. The method of claim 19, wherein the ODMR is measured at varying excitation frequencies of the excitation field.

22. The method of claim 19, further comprising providing a plurality of bias signals with different levels to the device and wherein the characteristic of the device is a function of the heat produced at different levels of bias signals.

23. The method of claim 19, wherein the device is a recording head that includes the thermal device and a near-field aperture.

24. The method of claim 23, wherein the characteristic of the device is a near-field power of the near-field aperture.

25. The method of claim 23, wherein the nitrogen vacancy centers have a known density and wherein determining the characteristic of the head uses the known density of the nitrogen vacancy centers.

26. The method of claim 25, wherein the characteristic of the device comprises a spatial extent of the near-field aperture.

27. The method of claim 26, wherein the spatial extent of the near-field aperture is determined based on a spatial extent of the heat produced by the recording head.

28. The method of claim 26, 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 near-field aperture 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.

29. The method of claim 26, further comprising determining a width of the near-field aperture based on the spatial extent of the near-field aperture.

30. The method of claim 26, wherein the ODMR is measured at varying excitation frequencies of the excitation field to produce an ESR spectrum, the method further comprising:

determining a minimum 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 a center of the near-field aperture; and

using the minimum 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 near-field aperture.

31. The method of claim 25, wherein the characteristic of the recording head is a heating width, the method further comprising:

determining a minimum 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 minimum excitation frequency; and

determining the heating width using the number of nitrogen vacancy centers contributing to the ODMR signal at the minimum excitation frequency and the known density of the nitrogen vacancy centers.

32. The method of claim 31, further comprising determining the heating width as a function of bias level.

33. The method of claim 25, wherein the characteristic of the recording head is a heating width, the method further comprising:

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

determining the heating width based on the integrated spectral intensity.

34. The method of claim 33, further comprising determining the heating width as a function of bias level.

35. The method of claim 25, further comprising:

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

using the minimum excitation frequency to determine a maximum heating produced by the thermal device.

36. The method of claim 23, wherein adjacent nitrogen vacancy centers are separated by a distance greater than a width of the near-field aperture, 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.

37. The method of claim 36, wherein the nitrogen vacancy center is scanned over the near-field aperture and wherein the determined characteristic of the recording head is heating values.

38. The method of claim 36, wherein the nitrogen vacancy center is scanned over the near-field aperture and wherein the determined characteristic of the recording head is a surface area of the near-field aperture.

39. The method of claim 23, wherein adjacent nitrogen vacancy centers are separated by a distance less than a width of the near-field aperture, 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.

40. The method of claim 39, wherein the depletion illumination is one of a group consisting essentially of:

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

41. The method of claim 39, wherein the excitation illumination and the depletion illumination are scanned over the near-field aperture and wherein the determined characteristic of the recording head is heating values.

42. The method of claim 39, wherein the excitation illumination and the depletion illumination are scanned over the near-field aperture and wherein the determined characteristic of the recording head is a surface area of the near-field aperture.

43. The method of claim 39, wherein the crystal film is attached to an air bearing surface of the recording head.

44. 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 device that includes a thermal device, the probe card provides a bias signal to the device that causes the thermal device to heat a crystal film, the crystal film includes nitrogen vacancy centers;

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 heat, the excitation field, and the excitation illumination caused by electron spin resonance (ESR) of the nitrogen vacancy centers;

and determine a characteristic of the device using the ODMR.

45. The apparatus of claim 44, wherein a heat absorption layer is disposed between the thermal device and the crystal film.

46. The apparatus of claim 44, wherein the ODMR is measured at varying excitation frequencies of the excitation field.

47. The apparatus of claim 44, wherein the biasing source is configured to provide a plurality of bias signals with different levels to the device and wherein the characteristic of the device is a function of the heat produced at different levels of bias signals.

48. The apparatus of claim 44, wherein the device is a recording head that includes the thermal device and a near-field aperture.

49. The apparatus of claim 48, wherein the characteristic of the device is a near-field power of the near-field aperture.

50. The apparatus of claim 48, wherein the nitrogen vacancy centers have a known density and wherein the processor is configured to determine the characteristic of the head using the known density of the nitrogen vacancy centers.

51. The apparatus of claim 50, wherein the characteristic of the device comprises a spatial extent of the near-field aperture.

52. The apparatus of claim 51, wherein the processor is configured to determine the spatial extent of the near-field aperture based on a spatial extent of the heat produced by the recording head.

53. The apparatus of claim 51, 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 near-field aperture 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.

54. The apparatus of claim 51, wherein the processor is further configured to determine a width of the near-field aperture based on the spatial extent of the near-field aperture.

55. The apparatus of claim 51, 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 minimum 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 a center of the near-field aperture; and

use the minimum 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 near-field aperture.

56. The apparatus of claim 50, wherein the characteristic of the recording head is a heating width, and wherein the processor is further configured to:

determine a minimum 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 minimum excitation frequency; and

determine the heating width using the number of nitrogen vacancy centers contributing to the ODMR signal at the minimum excitation frequency and the known density of the nitrogen vacancy centers.

57. The apparatus of claim 56, wherein the heating width is determined as a function of bias level.

58. The apparatus of claim 50, wherein the characteristic of the recording head is a heating width, and wherein the processor is configured to:

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

determine the heating width based on the integrated spectral intensity.

59. The apparatus of claim 58, wherein the heating width is determined as a function of bias level.

60. The apparatus of claim 50, wherein the processor is further configured to:

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

use the minimum excitation frequency to determine a maximum heating produced by the thermal device.

61. The apparatus of claim 48, wherein adjacent nitrogen vacancy centers are separated by a distance greater than a width of the near-field aperture, the apparatus further 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

62. The apparatus of claim 61, wherein the nitrogen vacancy center is scanned over the near-field aperture and wherein the determined characteristic of the recording head is heating values.

63. The apparatus of claim 61, wherein the nitrogen vacancy center is scanned over the near-field aperture and wherein the determined characteristic of the recording head is a surface area of the near-field aperture.

64. The apparatus of claim 48, wherein adjacent nitrogen vacancy centers are separated by a distance less than a width of the near-field aperture, 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.

65. The apparatus of claim 64, wherein the depletion illumination is one of a group consisting essentially of:

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

66. The apparatus of claim 64, wherein the excitation illumination and the depletion illumination are scanned over the near-field aperture and wherein the determined characteristic of the recording head is heating values.

67. The apparatus of claim 64, wherein the excitation illumination and the depletion illumination are scanned over the near-field aperture and wherein the determined characteristic of the recording head is a surface area of the near-field aperture.

68. The apparatus of claim 64, wherein the crystal film is attached to an air bearing surface of the recording head.

69. 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; and

determining a characteristic of the recording head using the ODMR.

70. The method of claim 69, wherein the ODMR is measured at varying excitation frequencies of the excitation field.

71. The method of claim 69, further comprising providing a plurality of bias signals with different levels to the recording head.

72. The method of claim 69, wherein the recording head further comprises a thermal device and a near-field aperture, the method further comprising:

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

determining a second characteristic of the recording head using measured ODMR based on heating of the crystal film by the thermal device and the near-field aperture.

73. The method of claim 72, wherein the second characteristic of the recording head is a near-field power of the near-field aperture.

74. The method of claim 72, wherein the second characteristic of the recording head is a spatial extent of the near-field aperture.

75. The method of claim 72, further comprising providing a plurality of bias signals with different levels to the thermal device and wherein the second characteristic of the recording head is a function of the heat produced at different levels of bias signals.

76. The method of claim 72, wherein the bias signal provided to the recording head and the second bias signal provided to the thermal device are provided sequentially or serially.

77. 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; and

determine a characteristic of the recording head using the ODMR.

78. The apparatus of claim 77, wherein the ODMR is measured at varying excitation frequencies of the excitation field.

79. The apparatus of claim 77, further comprising providing a plurality of bias signals with different levels to the recording head.

80. The apparatus of claim 77, 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.

81. The apparatus of claim 77, wherein the recording head further comprises a thermal device and a near-field aperture, the apparatus further comprising:

a second biasing source configured to provide a second bias signal to the thermal device to heat the crystal film using the near-field aperture;

wherein the processor is further configured to determine a second characteristic of the recording head using measured ODMR based on heating of the crystal film by the thermal device and the near-field aperture.

82. The apparatus of claim 81, wherein the second characteristic of the recording head is a near-field power of the near-field aperture.

83. The apparatus of claim 81, wherein the second characteristic of the recording head is a spatial extent of the near-field aperture.

84. The apparatus of claim 81, wherein the second biasing source provides a plurality of bias signals with different levels to the thermal device and wherein the second characteristic of the recording head is a function of the heat produced at different levels of bias signals.

85. The apparatus of claim 81, wherein the bias signal provided to the recording head and the second bias signal provided to the thermal device are provided sequentially or serially.