Abstract:
A recording head for use in conjunction with a magnetic storage medium, comprises a waveguide for providing a path for transmitting radiant energy, a near-field coupling structure positioned in the waveguide and including a plurality of arms, each having a planar section and a bent section, wherein the planar sections are substantially parallel to a surface of the magnetic storage medium, and the bent sections extend toward the magnetic storage medium and are separated to form a gap adjacent to an air bearing surface, and applying a magnetic write field to sections of the magnetic recording medium heated by the radiant energy. A disc drive including the recording head and a method of recording data using the recording head are also provided.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/346,432, filed Jan. 7, 2002. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the field of data storage, and more particularly to write heads and methods for recording information on data storage media using near-field optical coupling structures. 
     BACKGROUND OF THE INVENTION 
     Magnetic recording heads are used in magnetic disc drive storage systems. Most magnetic recording heads used in such systems today are “longitudinal” magnetic recording heads. Longitudinal magnetic recording in its conventional form has been projected to suffer from superparamagnetic instabilities at densities above approximately 40 Gbit/in 2 . It is believed that reducing or changing the bit cell aspect ratio will extend this limit up to approximately 100 Gbit/in 2 . However, for recording densities above 100 Gbit/in 2 , different approaches will likely be necessary to overcome the limitations of longitudinal magnetic recording. 
     An alternative to longitudinal recording that overcomes at least some of the problems associated with the superparamagnetic effect is “perpendicular” magnetic recording. Perpendicular magnetic recording is believed to have the capability of extending recording densities well beyond the limits of longitudinal magnetic recording. Perpendicular magnetic recording heads for use with perpendicular magnetic storage media may include a pair of magnetically coupled poles, including a write pole having a relatively small bottom surface area and a return pole having a larger bottom surface area. A coil having a plurality of turns is located adjacent to the write pole for inducing a magnetic field between the pole and a soft underlayer of the storage media. The soft underlayer is located below a hard magnetic recording layer of the storage media and enhances the amplitude of the field produced by the write pole. In the recording process, an electric current in the coil energizes the write pole, which produces a magnetic field. The image of this field is produced in the soft underlayer to enhance the field strength produced in the magnetic media. Magnetic flux that emerges from the write pole passes into the soft underlayer and returns through the return flux pole. The return pole is located sufficiently far apart from the main write pole such that the material of the return pole does not affect the magnetic flux of the write pole, which is directed vertically into the hard layer of the storage media. This allows the use of storage media with higher coercive force, consequently, more stable bits can be stored in the media. 
     As the magnetic media grain size is reduced for high areal density recording, superparamagnetic instabilities become an issue. The superparamagnetic effect is most evident when the grain volume V is sufficiently small that the inequality K U V/k B T &gt;40 can no longer be maintained. K u  is the material&#39;s magnetic crystalline anisotropy energy density, k B  is Boltzmann&#39;s constant, and T is absolute temperature. When this inequality is not satisfied, thermal energy demagnetizes the individual grains and the stored data bits will not be stable. Therefore, as the grain size is decreased in order to increase the areal density, a threshold is reached for a given material K u  and temperature T such that stable data storage is no longer feasible. 
     The thermal stability can be improved by employing a recording medium formed of a material with a very high K u . However, the available recording heads are not able to provide a sufficient or high enough magnetic writing field to write on such a medium. Heat assisted magnetic recording, sometimes referred to as optical or thermal assisted recording, has been proposed to overcome at least some of the problems associated with the superparamagnetic effect. Heat assisted magnetic recording generally refers to the concept of locally heating a recording medium to reduce the coercivity of the recording medium so that an applied magnetic writing field can more easily direct the magnetization of the recording medium during the temporary magnetic softening of the recording medium caused by the heat source. 
     By heating the medium, the K u  or the coercivity is reduced such that the magnetic write field is sufficient to write to the medium. Once the medium cools to ambient temperature, the medium has a sufficiently high value of coercivity to assure thermal stability of the recorded information. When applying a heat or light source to the medium, it is desirable to confine the heat or light to the track where writing is taking place and to generate the write field in close proximity to where the medium is heated to accomplish high areal density recording. The separation between the heated spot and the write field spot should be minimal or as small as possible so that writing may occur while the medium temperature is substantially above ambient temperature. This also provides for the efficient cooling of the medium once the writing is completed. 
     In order to increase areal density in an optically assisted write head, the spot size of the optical beam can be decreased by either decreasing the wavelength of the light or increasing the numerical aperture of the focusing elements. Other optical techniques which either directly or indirectly reduce the effective optical spot size are generally referred to as “superresolution” techniques. For example, it is well known that the resolving power of a microscope can be increased by placing an aperture with a pinhole (having a diameter smaller than the focused spot size) sufficiently close to the object being observed. As another example, tapered optical fibers have been used to achieve superresolution in near field scanning optical microscopy. 
     There is identified a need for an improved magnetic recording head that overcomes limitations, disadvantages, and/or shortcomings of known optically assisted magnetic recording heads. 
     SUMMARY OF THE INVENTION 
     This invention provides a recording head for use in conjunction with a magnetic storage medium, comprising a waveguide for providing a path for transmitting radiant energy; a near-field coupling structure positioned in the waveguide and including a plurality of arms, each having a planar section and a bent section, wherein the planar sections are substantially parallel to a surface of the magnetic storage medium, and the bent sections extend toward the magnetic storage medium and are separated to form a gap adjacent to an air bearing surface; and means for applying a magnetic write field to sections of the magnetic recording medium heated by the radiant energy. 
     The recording head can further comprise a semi-reflective layer positioned in the path to form a resonant cavity with a surface of the magnetic storage medium. The means for applying a magnetic write field to the magnetic recording medium can comprise a magnetic yoke having a write pole, a return pole, and a coil for producing magnetic flux in the yoke, wherein the near-field coupling structure is position adjacent to the write pole. 
     The waveguide can comprise a transparent layer mounted adjacent to the write pole, wherein the write pole is located down track from the near-field coupling structure. The near-field coupling structure can form a square opening adjacent to the air bearing surface of the recording head. 
     The invention also encompasses a magnetic disc drive storage system comprising a housing; means for supporting a magnetic storage medium positioned in the housing; and means for positioning a recording head adjacent to the rotatable magnetic storage medium, wherein the recording head includes a waveguide for providing a path for transmitting radiant energy; a near-field coupling structure positioned in the waveguide and including a plurality of arms, each having a planar section and a bent section, wherein the planar sections are substantially parallel to a surface of the magnetic storage medium, and the bent sections extend toward the magnetic storage medium and are separated to form a gap adjacent to an air bearing surface; and means for applying a magnetic write field to sections of the magnetic recording medium heated by the radiant energy. 
     The invention further encompasses a method of recording data on a data storage medium, comprising heating a section of the data storage medium by applying radiant energy to a waveguide including a transparent layer, a semi-reflective layer, and a near-field coupling structure at a frequency such that radiant energy resonates between the semi-reflective layer and a surface of the data storage medium; and applying a magnetic write field to the section of data storage medium. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a pictorial representation of a disc drive that can include a recording head constructed in accordance with this invention; 
     FIG. 2 is a side view of a recording head constructed in accordance with the invention; 
     FIG. 3 is a cross-sectional view of a portion of the waveguide of the recording head of FIG. 2; 
     FIG. 4 is a cross-sectional view of the portion of the waveguide of FIG. 3 taken in a plane perpendicular to the view shown in FIG. 3; 
     FIG. 5 is an isometric view of the near-filed coupling structure of the recording head of FIG. 2; 
     FIG. 6 is a side view of an alternative recording head constructed in accordance with the invention; and 
     FIG. 7 is a cross-sectional view of a portion of the waveguide of the recording head of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings, FIG. 1 is a pictorial representation of a disc drive  10  that can use a recording head constructed in accordance with this invention. The disc drive  10  includes a housing  12  (with the upper portion removed and the lower portion visible in this view) sized and configured to contain the various components of the disc drive. The disc drive  10  includes a spindle motor  14  for rotating at least one magnetic storage medium  16 . At least one arm  18  is contained within the housing  12 , with the arm  18  having a first end  20  for supporting a recording head or slider  22 , and a second end  24  pivotally mounted on a shaft by a bearing  26 . An actuator motor  28  is located at the arm&#39;s second end  24  for pivoting the arm  18  to position the recording head  22  over a desired sector or track of the disc  16 . The actuator motor  28  is controlled by a controller, which is not shown in this view and is well known in the art. 
     FIG. 2 is a partially schematic side view of a perpendicular magnetic recording head  30  constructed in accordance with the invention. The recording head includes a magnetic write head  32  that is constructed using known technology and includes a yoke  34  that forms a write pole  36  and a return pole  38 . The recording head  30  is positioned adjacent to a perpendicular magnetic storage medium  40  having a magnetically hard layer  42  and a magnetically soft layer  44  supported by a substrate  46 . An air bearing  48  separates the recording head from the storage medium by a distance D. A coil  50  is used to control the magnetization of the yoke to produce a write field at an end  52  of the write pole adjacent to an air bearing surface  54  of the write head. The recording head  30  can also include a read head, not shown, which may be any conventional type read head as is generally known in the art. 
     The perpendicular magnetic storage medium  40  is positioned adjacent to or under the recording head  30  and travels in the direction of arrow A. The recording medium  40  includes a substrate  46 , which may be made of any suitable material such as ceramic glass or amorphous glass. A soft magnetic underlayer  44  is deposited on the substrate  46 . The soft magnetic underlayer  44  may be made of any suitable material such as, for example, alloys or multilayers having Co, Fe, Ni, Pd, Pt or Ru. A hard magnetic recording layer  42  is deposited on the soft underlayer  44 , with the perpendicular oriented magnetic domains  56  contained in the hard layer  42 . Suitable hard magnetic materials for the hard magnetic recording layer  42  may include at least one material selected from, for example, FePt or CoCrPt alloys having a relatively high anisotropy at ambient temperature. 
     The recording head  30  also includes means for heating the magnetic storage medium  40  proximate to where the write pole  36  applies the magnetic write field H to the storage medium  40 . Specifically, the means for heating includes an optical waveguide  58  formed by a transparent layer  60 . The optical waveguide  58  acts in association with a source  62  of radiant energy which transmits radiant energy via an optical fiber  64  that is in optical communication with the optical waveguide  60 . The radiant energy can be, for example, visible light, infrared or ultra violet radiation. The source provides for the generation of surface plasmons or guided modes that travel through the optical waveguide  58  toward a heat emission surface  66  that is formed along the air-bearing surface thereof. The transmitted radiant energy, generally designated by reference number  68 , passes from the heat emission surface  66  of the optical waveguide  58  to the surface of the storage medium for heating a localized area of the storage medium  40 , and particularly for heating a localized area of the hard magnetic layer  42 . 
     The source  62  may be, for example, a laser diode, or other suitable laser light source. At the surface of the medium  40 , the surface plasmons convert a portion of their energy into heat in the medium  40 . The transparent layer may be formed, for example, from a silica based material, such as SiO 2 . The transparent layer should be a non-conductive dielectric, and have extremely low optical absorption (high transmissivity). It will be appreciated that in addition to the transparent layer, the waveguide  58  may include an optional cladding layer, such as aluminum, positioned adjacent the transparent layer or an optional overcoat layer, such as an alumina oxide, for protecting the waveguide  58 . 
     In addition, the waveguide  58  includes a near-field coupling structure  70  for confining the radiant energy to the recording spot. Specifically as shown in FIGS. 3,  4  and  5 , the near-field coupling structure includes a plurality of arms  72 ,  74 ,  76  and  78 . 
     FIG. 3 is an enlarged cross-sectional view of a portion of the optical waveguide  58 . The waveguide includes a transparent layer  60  and first and second arms  72  and  74 , which in this embodiment are embedded within the transparent layer  60 . Arm  72  includes a first section  80  that is positioned substantially parallel the surface of the storage medium, and a second section  82  that extends from the first section toward the air bearing surface at a first angle θ 1 . Arm  74  includes a first section  84  that is positioned substantially parallel the surface of the storage medium, and a second section  86  that extends from the first section toward the air bearing surface at a second angle θ 2 . The ends  88  and  90  of the second sections of arms  72  and  74  are separated to form a gap  92 . The gap has a width that can be, for example, less than 50 nm. The width of the gap determines the breadth of the near radiation field, and the resulting thermal field in the medium is desired to be no larger than 50 nm in the largest dimension. 
     FIG. 4 is an enlarged cross-sectional view of the portion of the optical waveguide  58  of FIG. 3 taken in a plane perpendicular to the plane of FIG.  3 . The waveguide is shown to further include third and fourth arms  76  and  78 , which are also embedded within the transparent layer. Arm  76  includes a first section  94  that is positioned substantially parallel the surface of the storage medium, and a second section  96  that extends from the first section toward the air bearing surface at a first angle θ 3 . Arm  78  includes a first section  98  that is positioned substantially parallel the surface of the storage medium, and a second section  100  that extends from the first section toward the air bearing surface at a second angle θ 4 . The ends  102  and  104  of the second sections of arms  76  and  78  are separated to form a gap  106 . 
     FIG. 5 is an isometric view of the arms  72 ,  74 ,  76  and  78 , which are positioned together to form the near-field coupling structure  70 . In this view, the bent sections of the arms are seen to have a trapezoidal shape. The ends of the arms form an opening  110  for passage of radiant energy from the light source. While the opening is illustrated as having a square shape, it will be appreciated that other shapes can be used. The arms should be made of excellent conductors in the optical frequency band, such as Au, Ag or Cu. The overall length of the arms, designated as L in FIGS. 3 and 4, can be determined by a resonant condition with the exciting radiation in the waveguide, so that the overall length of a pair of arms will be comparable to an integer multiple of half or full wavelengths of the radiation in the waveguide. This will achieve a resonant coupling condition. The overall length is the total span of the antenna formed by arms  72 ,  74 ,  76  and  78 . That is, for example, the distance from the outside edge of arm section  80  to the outside edge of arm section  84  in FIG.  3 . This distance is distinct from, and independent of, the gap length of the structure. The opening or gap between the arms is comparable to the desired near radiation field extent, as indicated above. 
     To most effectively heat the recording medium  40 , the heat emission surface  66  of the optical waveguide  58  is preferably spaced apart from the medium  40  and, more specifically, spaced apart from the hard magnetic layer  42 , by a distance of about 2 nm to about 50 nm. It will be appreciated that the separation distance is also dependent on the fly height required to maintain acceptable reading and writing (electromagnetic coupling for heating) by the recording head  30 . 
     The write head of FIG. 2 allows for heating of the recording medium  40  in close proximity to the write pole  36 , which applies a magnetic write field H to the recording medium  40 . It also provides for the ability to align the waveguide  58  with the write pole  36  to maintain the heating application in the same track of the medium  40  where the writing is taking place. Locating the optical waveguide  58  adjacent to the write pole  36 , provides for increased writing efficiency due to the write field H being applied immediately down track from where the recording medium  40  has been heated. The hot spot will ideally raise the temperature of the medium  40  to approximately 200° C. The recording takes place at the thermal profile, which can also be called the thermal field or the thermal distribution, in the medium  40  for which the coercivity is equal to the applied recording field. Ideally, this thermal profile should be near the edge of the write pole  36  where the magnetic field gradients are the largest. This will record the sharpest transition in the medium  40 . The optical waveguide  58  may be integrally formed with the write pole  36 . 
     In operation, the recording medium  40  passes under the recording head  30 , in the direction indicated by arrow A in FIG.  2 . The source  62  transmits radiant energy via the optical fiber  64  to the optical waveguide  58 . The optical waveguide  58  transmits the optical energy for heating the storage medium  40 . More specifically, a localized area of the recording layer  42  is heated to lower the coercivity thereof prior to the write pole  36  applying a magnetic write field H to the recording medium  40 . Advantageously, this allows for higher coercivity storage media to be used while limiting the superparamagnetic instabilities that may occur with such recording media used for high recording densities. 
     At a down track location from where the medium  40  is heated, the magnetic write pole  36  applies a magnetic write field to the medium  40  for storing magnetic data in the recording medium  40 . The write field H is applied while the recording medium  40  remains at a sufficiently high temperature for lowering the coercivity of the recording medium  40 . This ensures that the write pole  36  can provide a sufficient or high enough magnetic write field to perform a write operation on the recording medium  40 . As described herein, the recording head  30  advantageously allows for the point of writing to be in close proximity to where the recording medium  40  is heated. 
     FIG. 6 is a side view of a recording head  112  that can be constructed in accordance with an alternative embodiment of the invention. In the embodiment of FIG. 6, a semitransparent layer  114  is added within a transparent layer  60 . 
     FIG. 7 is a cross-sectional view of a portion of the waveguide of FIG.  6 . The semitransparent layer  114 , in combination with the surface of the data storage medium creates a resonant cavity  116 . The resonant cavity will enable “recycling” of the electromagnetic energy, and will thus enhance the throughput efficiency of the device. The height from the semitransparent layer to the reflecting surface can be comparable to an integer times half the wavelength of the radiation. 
     While particular embodiments of the invention have been described herein for the purpose of illustrating the invention and not for the purpose of limiting the same, it will be appreciated by those of ordinary skill in the art that numerous variations of the details, materials, and arrangements of parts may be made without departing from the scope of the invention as defined in the appended claims.