Abstract:
A magnetic storage medium is formed of magnetic nanoparticles that are encapsulated within nanotubes, which are arranged in a substrate to facilitate the reading and writing of information by a read/write head. The substrate may be flexible or rigid. Information is stored on the magnetic nanoparticles via the read/write head of a storage device. These magnetic nanoparticles are arranged into data tracks to store information through encapsulation within the carbon nanotubes. As carbon nanotubes are bendable, the carbon nanotubes may be arranged on flexible or rigid substrates, such as a polymer tape or disk for flexible media, or a glass substrate for rigid disk. A polymer may assist holding the nanoparticle-filled carbon tubes to the substrate.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 14/171,699, filed Feb. 3, 2014, which is a continuation of U.S. patent application Ser. No. 12/700,738, filed Feb. 5, 2010, now U.S. Pat. No. 8,647,757, which is a continuation of U.S. patent application Ser. No. 11/278,879, filed Apr. 6, 2006, now U.S. Pat. No. 7,687,160, the disclosures of which are hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    The pursuit of higher performance computing systems is driving the reduction in scale of magnetic storage media. Higher storage densities allow for the reduction of device sizes, an enhancement of device capabilities, and a reduction in data storage costs. To facilitate this increase in magnetic data storage density, the industry is constantly searching for structures and processes to reduce the size of information storage sectors and tracks on magnetic tape and magnetic disks. 
         [0003]    Current magnetic media technology is based upon the ability to polarize cells of magnetic materials that are deposited directly on a substrate material. These substrate materials are flexible, in the case of magnetic tape of floppy disks, or rigid, in the case of hard disks. Physics places an eventual limit on the ability to increase the storage density of media that is formed of magnetic particles deposited directly on such a storage tape or disk. In the near future, the magnetic storage media industry will reach this storage density limit. It is therefore essential to find new technologies to replace direct deposition of magnetic materials to facilitate further increases in magnetic storage media density. 
       SUMMARY 
       [0004]    The present disclosure is a magnetic storage medium formed of magnetic nanoparticles that are encapsulated within carbon nanotubes, which are arranged on a substrate to facilitate the reading and writing of information by a read/write head. The substrate may be flexible or rigid. Information is stored on the magnetic nanoparticles via the read/write head of a storage device. These magnetic nanoparticles are arranged into data tracks to store information through encapsulation within the carbon nanotubes. As carbon nanotubes are bendable, the carbon nanotubes may be arranged on flexible or rigid substrates, such as a polymer tape or disk for flexible media, or a glass substrate for rigid disk. A polymer matrix may assist holding the nanoparticle-filled carbon tubes to the substrate. 
         [0005]    The use of magnetic nanoparticles to store information facilitates a vast increase in the storage density capability of magnetic storage media. Encapsulation of these magnetic nanoparticles within carbon nanotubes allows for the organization of the magnetic nanoparticles into tracks and sectors of information storage media that a read/write head of a storage device can store information. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0006]    The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
           [0007]      FIG. 1  depicts an isometric view of magnetic nanoparticles encapsulated within a carbon nanotube; 
           [0008]      FIG. 2  depicts an isometric view of shunt nanoparticles encapsulated within a shunt carbon nanotube; 
           [0009]      FIG. 3  depicts a cross section of a nano-scale magnetic medium having magnetic and shunt nanoparticles encapsulated within respective carbon nanotubes that are on a substrate; 
           [0010]      FIG. 4  depicts a view of an arrangement of carbon nanotube data storage tracks on a magnetic tape; and 
           [0011]      FIG. 5  depicts a view of an arrangement of carbon nanotube data storage tracks on a disk. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]      FIG. 1  shows a magnetic carbon nanotube assembly  100  comprising a carbon nanotube  101 . Carbon nanotube  101  is illustrated as a single-wall hollow tube formed of a single layer of carbon atoms in either hexagonal lattice pattern  102  or  112  ( FIG. 2 ). Since carbon nanotube  101  is hollow, it can contain nanoparticles  103  and  104 . Carbon nanoparticle  103  has a high magnetic coercivity so that it can permanently retain a first magnetic field until that field is changed to a second magnetic field. Also, nanoparticle  103  is a particle that does not oxidize or rust in ambient air, such as CrO 2  (chromium dioxide). 
         [0013]    Such oxidation would cause the loss of the stored magnetic field. Nanoparticle  104  also has a high magnetic coercivity, so that it can permanently retain a first magnetic field until that field is changed to a second magnetic field. Nanoparticle  104  contains high coercivity core  105  that holds the permanent magnetic field. To prevent oxidation, core  105  is encapsulated in shell  106 . An example of core  105  is pure Fe (iron) and shell  106  is iron oxide, such as Fe 2 O 3 . 
         [0014]      FIG. 2  shows shunt carbon nanotube assembly  110  comprising carbon nanotube  111 . Like carbon nanotube  101 , carbon nanotube  111  is illustrated as a single-wall hollow tube preferably formed of a single layer of carbon atoms in either hexagonal lattice pattern  112  or  102  ( FIG. 1 ). Hexagonal lattice  112  is rotated 90° from hexagonal lattice  102  and suitable nanotubes comprising either lattice can be used. Since carbon nanotube  111  is hollow, it can contain nanoparticles  113  and  114 . Carbon nanoparticle  113  has a low or zero magnetic coercivity so that it does not permanently retain a first magnetic field, which allows nanoparticle  113  to act as a magnetic shunt. Also, nanoparticle  113  is a particle that does not oxide or rust in ambient air, such as a soft-ferrite. Nanoparticle  114  also has low or zero coercivity, so that it does not permanently retain a first magnetic field. Nanoparticle  114  contains low or zero coercivity core  115  that provides the desired magnetic shunt. To prevent oxidation, core  115  is encapsulated in shell  116 . An exemplary material for nanoparticle  114  is a soft-ferrite. Soft-ferrites, like other shunt materials, duct magnetic flux without retaining any “after field.” 
         [0015]      FIGS. 1 and 2  show the Z axis along the length of nanotubes  101  and  111 . Nanotubes  101  and  111  can either be single-walled carbon nanotubes (SWNT) or multi-walled carbon nanotubes (MWNT). MWNTs may be formed with two, three, or more layers. The diameter D of nanotubes  101  and  111  is measured in nanometers. The diameter of the nanotubes, up to 12 nm, limits the size of nanoparticles  103 ,  104 ,  113 , and  114 . In addition to those materials already mentioned, exemplary materials for magnetic nanoparticles  103  and  104  or  113  and  114  include Cobalt (Co) and its alloys, Cobalt-ferrite, Cobalt-nitride, Cobalt-oxide (Co—O), Cobalt-palladium (Co—Pd), Cobalt-platinum (Co—Pt), Iron (Fe) and its alloys, Iron-gold (Fe—Au), Iron-chromium (Fe—Cr), Iron-nitride (Fe—N), Iron-oxide (Fe 3  O 4 ), Iron-palladium (Fe—Pd), Iron-platinum (Fe—Pt), Fe—Zr—Nb—B, Manganese-nitride (Mn—N), Nd—Fe—B, Nd—Fe—B—Nb—Cu, Nickel (Ni) and its alloys, and soft-ferrites. These magnetic nanoparticles can be manufactured with sizes of 10 nm or less, such that these nanoparticles can fit within nanotubes  101  and  111 . Examples of soft-ferrites include Mn—Zn, single crystal Mn—Zn, and Ni—Zn. 
         [0016]      FIG. 3  shows magnetic storage medium  200 . The T axis is along the thickness direction of magnetic storage medium  200 . If magnetic medium  200  is magnetic tape, then the L axis is along the length of the tape and the W axis is along the width of the tape. Magnetic storage medium  200  comprises substrate  201 , data recording layer  202 , and optional shunt layer  203  in between substrate  210  and data recording layer  202 . For magnetic tape and floppy disks, substrate  210  is typically polytetrafluoroethelyne (PTFE), which is commonly known by the trade name MYLAR™. For hard disks, substrate  201  can be aluminum, glass, or a stiff plastic, such as polycarbonate. Data recording layer  202  comprises a plurality of magnetic carbon nanotube assemblies  100  that are embedded in a polymer matrix, such as HDPE  230  (High Density Polyethylene). Alternately, nanotube assemblies  100  are first encapsulated in HDPE and then embedded in a second polymeric matrix. Nanotubes  100  provide a home for nanoparticles  103  and  104 , so they do not clump into large masses within the data recording layer. 
         [0017]    Shunt layer  203  comprises a plurality of magnetic carbon nanotube assemblies  110  that are embedded in a matrix comprising HDPE  231 . Alternately, nanotube assemblies  110  are first encapsulated in HDPE and then embedded in a second polymeric matrix. Nanotubes  110  provide a home for the shunt nanoparticles  113  and  114 , so they do not clump into large masses within the shunt layer. Use of shunt layer  203  is optional, but it yields improved data recording when included in magnetic storage medium  200 . 
         [0018]    Magnetic recording head  210  comprises write element  212  mounted on a soft ferrite matrix  211 . Write element  212  is essentially a U-shaped piece of low coercivity material and a wire coil, which forms an electro-magnet. That portion of write element  212  adjacent to magnetic storage medium  200  is open, to allow magnetic flux  213  to leave recording head  210  and penetrate magnetic storage medium  200  and imprint data in the form of ones and zeros based on the magnetic polarity of flux  213 . Shunt layer  203  completes the magnetic circuit (analogous to completing an electrical circuit) and keeps flux  213  from “fringing” excessively. Shunt layer  203  permits more crisp edge transitions, thus permitting higher data densities on magnetic storage medium  200 . Thus, data is stored in layer  202  with the assistance of shunt layer  203 . Similarly, shunt layer  203  can assist in the reading of data. Write element  212  may further comprise a Metal-InGap (MIG) write head. 
         [0019]    Data is read from magnetic storage medium  200 , by means of a non-limiting example, via a magnetoresistive head or a spin-valve head that is alternately knows as a giant magnetoresistive “GMR” head. 
         [0020]    The process for forming magnetic storage medium  200  is to first apply shunt layer  203  onto substrate  201 . This may be done as a thin monolayer of nanotubes by running magnetic tape through a solution of HDPE  231  containing nanotubes  110 . This may also be done as a thin monolayer of nanotubes  100  by spin coating a solution of HDPE  231  containing nanotubes  100  onto a magnetic disk. Multiple shunt mono layers can be layered on top of the first monolayer forming shunt layer  203  through repeating this process. To maximize dispersal of nanotubes  100  and  110 , ethylene or another material that disperses carbon nanotubes may be used. 
         [0021]    Once shunt layer  203  is cured, which may include supplemental heating or compression by rollers, data recording layer  202  is then added. This may be done as a thin monolayer of nanotubes by running magnetic tape through a solution of HDPE  230  containing nanotubes  100 , and then curing the data layer  202 . This may also be done as a thin monolayer of nanotubes  100  by spin coating a solution of HDPE  230  containing nanotubes  100  onto a disk, and then curing the data layer. Multiple data recording monolayers can be layered on top of the first monolayer forming data layer  202  through repeating this process. To maximize dispersal of nanotubes  100  and  110 , ethylene, another material that disperses carbon nanotubes, may be used. Nanotubes  100  and  110  may be coated with an initial shell of HDPE before being added to HDPE  230  and  231 . 
         [0022]      FIG. 4  shows magnetic tape media  300  comprising substrate  301 , magnetic datarecording layer  202 , and shunt layer  203 . The L axis is along the length of tape  300 , the 
         [0023]    W axis is along the width of the tape, and the T axis is along the thickness of the tape. Tape media  300  has substrate  301  typically formed of polytetrafluoroethelyne (PTFE), which is commonly known by the trade name MYLAR™. Shunt layer  203  is formed on substrate  301 . Shunt layer  203  is formed of a monolayer of shunt carbon nanotube assemblies  110 . Assemblies  110  include carbon nanotubes  111  containing nanoparticles  113  and  114 . Carbon nanoparticle  113  has a low or zero magnetic coercivity so that it does not permanently retain a first magnetic field, which allows nanoparticles  103  to act as a magnetic shunt. Data recording layer  202  is formed of a monolayer of carbon nanotube assemblies  100 . Assemblies  100  include carbon nanotubes  101  that contain nanoparticles  103  and  104 . Carbon nanoparticle  103  has a high magnetic coercivity so that it can permanently retain a first magnetic field until that field is changed to a second magnetic field, allowing for data storage. Carbon nanotubes  101  and  111  are oriented such that they are generally parallel to the lengthwise direction of tape media  300 . Data tracks  303  are shown, from magnetic flux transitions recorded by magnetic head  210  in magnetic datarecording layer  202 . 
         [0024]      FIG. 5  shows magnetic disk  400  with monolayer rings  404  of layers  202  and  203  formed in layers about the center of disk  400 . These layers may be further masked into individual rings  404 . Rings  404  may be formed as distinct rings on disk  400  to form independent tracks. If disk  400  is a hard disk, substrate  402  can be aluminum, glass, or a stiff plastic, such as polycarbonate. If disk  400  is a floppy disk, substrate  402  is typically polytetrafluoroethelyne (PTFE), which is commonly known by the trade name MYLAR™ Z is the direction perpendicular to the disk and the R axis is the radial direction. Shunt layer  203  is formed of a monolayer of shunt carbon nanotube assemblies  110 . Assemblies  110  include carbon nanotubes  111  containing nanoparticles  113  and  114 . Carbon nanoparticle  113  has a low or zero magnetic coercivity so that it does not permanently retain a first magnetic field, which allows nanoparticle  113  to act as a magnetic shunt. Data recording layer  202  is formed of a monolayer of carbon nanotube assemblies  100 . Assemblies  100  include carbon nanotubes  101  that contain nanoparticles  103  and  104 . Carbon nanoparticle  103  has a high magnetic coercivity so that it can permanently retain a first magnetic field until that field is changed to a second magnetic field, allowing for data storage. Carbon nanotubes  101  and  111  may be oriented such that they extend radially from the center of disk  400 . Alternatively, carbon nanotubes  101  and  111  may be oriented such that they extend in a spiral pattern from the center of the disk  400 . One method of forming rings  404  is through a photo-etching process. Layers  202  and  203  are first deposited onto disk  400  preferably through a spin coating process. A layer of photoresist material is then deposited on top of layers  202  and  203 . This layer of photoresist is exposed through a mask, thereby patterning layers  202  and  203 . A removal process leaves the patterned layers  202  and  203 . While shown as rings  404 , layers  202  and  203  may be patterned into any desirable track or sector pattern for data storage. 
         [0025]    Alternatively, when disk  400  is made of polycarbonate, rings  404  could be formed through a molding process. Recording layer  202  may further comprise buckyballs  299 , which would act to reduce friction between the recording layer  202  and the magnetic head  210 . 
         [0026]    While the present disclosure has been shown and described with reference to a particular embodiment thereof, it will be understood to those skilled in the art, that various changes in form and details may be made therein without departing from the spirit and scope of the invention.