RECORDING HEAD WITH NEAR-FIELD ANTENNA AND COMPOSITE POLE
A near field transducer antenna has a first end proximate a media writing surface and a second end proximate a waveguide that delivers light to the antenna. The antenna includes an aperture disposed along a propagation axis that extends from the first end to the second end. A notch protrudes within the aperture. The notch is facing an opening of the aperture that extends along the propagation axis. A magnetic pole is proximate the antenna, and includes a first portion of magnetic material and a second portion of antenna material. The second portion is disposed over the opening of the aperture and facing the notch of the antenna.
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The present disclosure is generally directed to an optical near-field antenna usable in heat assisted magnetic recording. In one embodiment, an apparatus includes a near field transducer antenna with a first end proximate a media writing surface and a second end proximate a waveguide that delivers light to the antenna. The antenna includes an aperture disposed along a propagation axis that extends from the first end to the second end. A notch protrudes within the aperture. The notch is facing an opening of the aperture that extends along the propagation axis. A magnetic pole is proximate the antenna, and includes a first portion of magnetic material and a second portion of antenna material. The second portion is disposed over the opening of the aperture and facing the notch of the antenna.
These and other features and aspects of various embodiments may be understood in view of the following detailed discussion and accompanying drawings.
The discussion below makes reference to the following figures, wherein the same reference number may be used to identify the similar/same component in multiple figures.
Heat assisted magnetic recording (HAMR) generally refers to the concept of locally heating recording media to reduce the coercivity of the media so that the applied magnetic writing field can more easily direct the magnetization of the media during the temporary magnetic softening of the media caused by the heat source. A tightly confined, high power laser light spot is used to heat a portion of the recording media to substantially reduce the coercivity of the heated portion. Then the heated portion is subjected to a magnetic field that sets the direction of magnetization of the heated portion. In this manner the coercivity of the media at ambient temperature can be much higher than the coercivity during recording, thereby enabling stability of the recorded bits at much higher storage densities and with much smaller bit cells.
One approach for directing light onto recording media uses a planar solid immersion mirror (PSIM) or lens. The PSIM/lens may be fabricated on/with a planar waveguide and may generally include a near-field transducer (NFT). For example, the NFT may be in the form of an isolated metallic nanostructure, placed near the PSIM focus. The NFT is designed to reach a local surface plasmon (LSP) condition at a designated light wavelength. At LSP, a high field surrounding the NFT appears, due to collective oscillation of electrons in the metal. Part of the field will tunnel into an adjacent media and get absorbed, raising the temperature of the media locally for recording.
The power absorption in the HAMR recording media may be dependent, among other things, on head to media spacing (HMS) and power output from NFT or laser. In such a system, the power output requirements may be exponentially inverse to HMS due to the evanescent decay of optical near-field. Such variation may lead to variation of the thermal spot size. As the areal density increases, there is a need to more tightly control the size of the heated portion of the media.
In reference now to
The top pole 38 is a two-piece pole that includes a first portion, or pole body 52, having a first end 54 that is spaced from the air bearing surface 56, and a second portion, or sloped pole piece 58, extending from the first portion and tilted in a direction toward the bottom pole. The second portion 58 may be structured to include an end adjacent to the air bearing surface (ABS) 56 of the recording head, with the end being closer to the waveguide than the first portion of the top pole. A top layer of insulating material 63 can be formed on the top pole 38. A heat sink 64 is positioned adjacent to the sloped pole piece 58. The heat sink 64 can be comprised of a non-magnetic material, such as Au, Ag, Cu, etc.
A planar coil 60 also extends between the top and bottom poles and around the pedestal. While this example includes a planar coil, other types of coils, such as a helical coil, could be used. A helical coil would wrap around the bottom/return pole. In this example, the top pole serves as a write pole and the bottom pole serves as a return pole. An insulating material 62 separates the coil turns.
As illustrated in
The data storage media 16 is positioned adjacent to or under the recording head 30. The waveguide 42 conducts light from a source 78 of electromagnetic radiation, which may be, for example, ultraviolet, infrared, or visible light. The source 78 may be, for example, a laser diode, or other suitable laser light source for directing a light beam 80 toward the waveguide 42. The waveguide 42 may be configured as a rectangular dielectric waveguide. The waveguide 42 includes core layer 44, which can be for example Ta2O5. Cladding layer 46, which can be for example SiO2, is shown disposed on opposite sides of the core layer 44.
Various techniques that are known for coupling the light beam 80 into the waveguide 42 may be used. For example, the light source 78 may work in combination with an optical fiber and external optics for collimating the light beam 80 from the optical fiber toward a diffraction grating on the waveguide 42. Alternatively, a laser may be mounted on the waveguide 42 and the light beam 80 may be directly coupled into the waveguide 42 without the need for external optical configurations.
Once the light beam 80 is coupled into the waveguide 42, the light propagates through the waveguide 42 toward an end of the waveguide 42 that is formed adjacent the ABS 56 of the recording head 30. Light exits the end of the waveguide and heats a portion of the media, as the media moves relative to the recording head as shown by arrow 82. A near-field transducer 91 is positioned in or adjacent to the waveguide to further concentrate the light in the vicinity of the air bearing surface. Although the example of
In various embodiments discussed below, the NFT 91 may include an antenna 92 having a first end 93 proximate the media reading/writing surface (e.g., ABS 56) and a second end 95 proximate the waveguide 42, which delivers light to the antenna 92. In
Light is delivered to the NFT 91 via the waveguide 42 via focal point 106 adjacent to the NFT antenna 92. The core layer 44 of the waveguide 42 can be shaped to deliver light to the focal point 106. The antenna 92 is positioned adjacent to data storage medium 108, and may be separated from the storage medium by a gap 110. In hard drive implementations, this gap 110 may correspond to an air bearing gap that separates a media surface from and air bearing surface 56 of a read/write head.
In
Numerical simulations of performance were performed on the antenna geometry as seen in
In this case, the method of lines revealed an effective index of 1.77842 and full width at half maximum (FWHM) spot size for the waveguide 42 of 340 nm by 407 nm. The field intensity within the air gap was found to be between 2300 and 2900 and the spot size in the air gap was 34 nm by 29 nm. However, the field intensity within the air gap 110 may not always be a reliable measure of NFT performance, and so the field intensity within the center of the recording medium was also computed. In this case, field intensity within a plane of the medium 108 located 6 nm below the surface is estimated as ranging between 0.72 and 1.2. The spot size at this media depth increased to 99 nm×57 nm, and total power dissipation within a 48 nm×48 nm square was a relatively low 2.3% of the incident power in the waveguide.
In some embodiments, it may be possible to insert a cobalt recording pole alongside the NFT waveguide with minimal loss in coupling efficiency. This arrangement is shown in
In the embodiments described below, the homogenous magnetic pole 100 is replaced by a composite magnetic pole to improve coupling efficiency of the NFT. For example, a composite magnetic pole may include a first portion of magnetic material and a second portion of antenna material. The second portion is disposed over the aperture opening facing the notch of the antenna (e.g., notch 106 of antenna 102). The magnetic material may include, for example, FeCo, FeCoNi, NiFe, etc. The antenna material used for the second portion may include the same, non-magnetic, plasmonic materials used for the NFT, such as Au, Ag, Al, and alloys thereof.
In reference now to
The antenna material portion 130 is part of a composite recording pole 133 disposed proximate the NFT 122. The pole 133 includes a magnetic portion 134 that may be formed from a ferrite material (e.g., FeCo, FeCoNi, NiFe, etc.). The recording pole 133 includes a tip 132 that is positioned closely to the aperture 129 of the NFT antenna 122 at the air bearing surface 124. As indicated by the diagonal line 131, the magnetic portion 134 is separated from the aperture 129 by an increasingly wider antenna portion 130 at distances farther away from the air bearing surface 124. This combination of the magnetic material 134 with the antenna material 130 provides a balance of good magnetic performance (e.g., due to the pole tip 132 being closely proximate the hot spot created by the NFT) and optical efficiency (e.g., the surrounding material 130 improves coupling efficiency of the NFT).
Shown in
In a write operation, data is stored in tracks on the media 140. An approximate location of a data track is illustrated as item 142 in
Shown in
Curve 150 in
The data for
In reference now to
Numerical modeling of the embodiment of
In reference now to
A dielectric material 186 fills the aperture, and also forms a dielectric layer between the recording pole 184 and the antenna 182. This design may be simpler to fabricate than a previous E-antenna design, because the spacing between the notch 180 and the recording pole 184 is more easily controlled by means of a thin film deposition process rather than a chemical-mechanical polishing/planarization (CMP) lapping process as might be used in other arrangements.
The wavelength dependence of the coupling efficiency for the head of
In
The slider 22 may include a composite write pole and NFT as described above. The composite write pole and NFT may interface with other integrated optical and electrical components of the slider 22. Those other components may include, but are not limited to, read heads, laser light sources (e.g., laser diode), waveguides, mirrors, prisms, gratings, mode converters, and electrical signal/power conductors.
While the several example embodiments have been described hereinabove, it will be apparent to those skilled in the art that various changes can be made to the described examples without departing from the scope of the invention as set forth in the following claims. The implementation described above and other implementations are within the scope of the following claims.
Claims
1. An apparatus comprising:
- a near field transducer antenna having a first end proximate a media writing surface and a second end proximate a waveguide that delivers light to the antenna, wherein the antenna comprises: an aperture disposed along a propagation axis that extends from the first end to the second end; and a notch protruding within the aperture, wherein the notch is facing an opening of the aperture that extends along the propagation axis;
- a magnetic pole proximate the antenna, wherein the magnetic pole comprises a first portion of magnetic material and a second portion of non-magnetic antenna material, wherein the second portion is disposed over the opening of the aperture and facing the notch of the antenna.
2. The apparatus of claim 1, wherein cross sectional areas of the first and second portions of the magnetic pole vary relative to each other_along the propagation axis.
3. The apparatus of claim 2, wherein the first portion of the magnetic pole comprises a tip that is proximate the opening of the aperture at a cross section near the media-reading surface, and wherein the second portion is disposed between the first portion and the opening of the aperture at cross sections away from the media reading surface.
4. The apparatus of claim 2, wherein the first and second portions of the magnetic pole vary linearly relative to each other along the propagation axis.
5. The apparatus of claim 1, wherein the second portion of the magnetic pole comprises a plug of the antenna material disposed at least partly along the propagation axis.
6. The apparatus of claim 5, wherein the plug covers a portion of the opening of the aperture, and wherein the first portion of magnetic material covers the remainder of the opening of the aperture.
7. The apparatus of claim 5, further comprising a dielectric layer between the magnetic pole and the antenna.
8. The apparatus of claim 1, further comprising a dielectric layer between the magnetic pole and the antenna.
9. The apparatus of claim 8, wherein the dielectric fills the aperture of the antenna.
10. (canceled)
11. An apparatus comprising:
- a waveguide having an end adjacent to an air bearing surface;
- a near-field transducer positioned adjacent to a focal point of the waveguide, wherein the near-field transducer includes an E-shaped cross sectional shape along cross sections parallel to the air bearing surface, wherein a propagation direction of the near-field transducer is normal to the air bearing surface; and
- a write pole magnetically proximate one side of the near-field transducer along the propagation direction, wherein the write pole includes a non-magnetic portion and a magnetic portion, wherein the non-magnetic portion covers at least part of the E-shaped cross-sectional shape of the near-field transducer along at least part of the propagation direction.
12. The apparatus of claim 11, wherein cross sectional areas of the magnetic and non-magnetic portions of the write pole vary relative to each other along the propagation axis.
13. The apparatus of claim 12, wherein the magnetic portion of the write pole comprises a tip that is proximate the near-field transducer near the air bearing surface, and wherein the non-magnetic portion is disposed between the magnetic portion and the near-field transducer at cross sections away from the air bearing surface.
14. The apparatus of claim 12, wherein the magnetic and non-magnetic portions of the write pole of the write pole vary linearly relative to each other along the propagation direction.
15. The apparatus of claim 11, wherein the non-magnetic portion of the write pole comprises a plug of an antenna material disposed at least partly along the propagation direction.
16. The apparatus of claim 15, wherein the plug covers a portion of an opening of the E-shaped cross-sectional shape, and wherein the magnetic material covers the remainder of the opening.
17. The apparatus of claim 15, further comprising a dielectric layer between the write pole and the near-field antenna.
18. The apparatus of claim 11, further comprising a dielectric layer between the magnetic pole and the antenna.
19. The apparatus of claim 18, wherein the dielectric fills a aperture of the near-field transducer.
20. An apparatus comprising:
- means for producing a focused electric field at a media writing surface in response to local surface plasmon conditions being excited by optical energy, wherein the means for producing the focused electric field comprises an aperture disposed along a propagation axis that extends from the media writing surface to a second end, and a notch protruding within the aperture, wherein the notch face an opening of the aperture that extends along the propagation axis;
- means for generating a variable magnetic field that comprises a first portion of magnetic material and a second portion of antenna material, wherein the second portion is disposed over the opening of the aperture and facing the notch.
Type: Application
Filed: Jul 16, 2012
Publication Date: Jan 16, 2014
Applicant: SEAGATE TECHNOLOGY LLC (Cupertino, CA)
Inventors: William Albert Challener (Schenectady, NY), Michael Allen Seigler (Eden Prairie, MN)
Application Number: 13/550,280
International Classification: G11B 11/105 (20060101);