Abstract:
A magnetic recording medium of the perpendicular type, for a disc drive. The magnetic recording material includes a Cobalt alloy layer interspersed with a noble metal layer. The initial graded material is paramagnetic to increase to the magnetic properties of perpendicular recording media into increase the signal to noise ratio. The final recording layer has 8-20 alternating multilayer of the Cobalt alloy and a noble metal.

Description:
This application is based on provisional patent application Ser. No. 60/258,790, filed Dec. 29, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to magnetic recording media such as for a computer disc drive, and more particularly to an exchange decoupled Cobalt/noble metal perpendicular recording medium. 
     2. Background of the Invention 
     Most modern information storage systems depend on magnetic recording due to its reliability, low cost, and high storage capacity. The primary elements of a magnetic recording system are the recording medium and the read/write head. Magnetic discs with magnetizable media are used for data storage in almost all computer systems. Various modeling and simulations have suggested that perpendicular recording (in which the medium is magnetized with a direction perpendicular to the surface of the disc, that is, in the direction of thickness thereof) is superior to conventional longitudinal recording due to various reasons, including larger optimal medium thickness, better write field efficiency, less demagnetizing fields from the stored bit pattern, etc. As the longitudinal magnetic recording technology reaches its limit in the areal density due to the lower thermal stability, perpendicular magnetic recording possesses the potential to a higher recording density. The larger perpendicular anisotropy and high remanence squareness of the Co(X)/noble metal (X=B, Cr, and etc.) multilayers suggest that these thin films are promising candidates for perpendicular magnetic recording. Doping nonmagnetic materials such as Chromium (Cr) or Boron (B) into a Cobalt (Co) layer for the Co(X)/noble metal multilayers can reduce intergranular exchange coupling and result in lower medium noise. However, the earlier studies of CoB/Pd multilayers showed that the initial CoB layers were continuous. Therefore, it could provide a source for transition media noise, resulting in lower signal-to-noise recording. 
     It is therefore an object of the present invention to provide a magnetic recording material for a perpendicular recording medium having improved intergranular exchange decoupling. 
     It is a further object of the present invention to provide a perpendicular magnetic recording medium having lower medium noise and resultant higher signal to noise recording. 
     It is a still further object of the present invention to provide a graded Cobalt/noble metal bilayer perpendicular recording material having alternating layers of a Cobalt alloy and a noble metal. 
     SUMMARY OF INVENTION 
     The above and other objects, features and advantages of the present invention are attained by a magnetic recording medium having a substrate, a magnetic interlayer and a layer of magnetic recording material thereon, the magnetic recording material comprising a plurality of bilayers having a Cobalt alloy and a noble metal. 
     In an alternate embodiment, the magnetic recording medium comprises a substrate, a soft magnetic underlayer, a paramagnetic layer and a perpendicular recording material including alternating layers of a Cobalt alloy and a noble metal. 
     In a further embodiment, the magnetic recording medium comprises a substrate, a soft magnetic underlayer, and a graded magnetic recording material including alternating layers of a Cobalt alloy and a noble metal. 
     The initial growth region is graded, such that this initial film is paramagnetic at room temperature and does not exchange link neighboring grains. Ideally, the graded region has identical structure to the subsequent magnetic multilayer. This could be accomplished by changing the magnetic alloy CoX such that this alloy by itself becomes paramagnetic, e.g., CoCr 40 . Another implementation of this idea is to drop the thickness of the CoX layer low enough, so that the ferromagnetic Curie temperature of this (CoX/Pd)x N multilayer drops below room temperature, thereby also rendering this initial region paramagnetic. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various other objects, features and advantages of the present invention will become readily apparent by reading the following description in conjunction with the drawings, which are shown by way of example only, wherein: 
         FIG. 1  is a cross-sectional diagram of a perpendicular magnetic recording material manufactured according to the present invention; 
         FIG. 2  shows a schematic cross-sectional representation of the graded magnetic recording material layers according to the present invention; and 
         FIG. 3  is a graphical representation of a polar MOKE loop of the Cobalt alloy/noble metal multi-layer film produced according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings in detail there is shown in  FIG. 1  a cross-sectional representation of a magnetic recording medium  10  manufactured according to the present invention. A perpendicular magnetic recording medium such as a computer disc, comprises a substrate  13  upon which is deposited a soft magnetic underlayer  16  and then the graded Cobalt/noble metal perpendicular recording material  19  of the present invention. If desired, a 2-5 nm thick adhesion layer or magnetic interlayer  20  may be provided between the substrate  13  and the soft magnetic underlayer  16 , which adhesion layer may comprise tantalum. The soft magnetic underlayer  16  may comprise a laminated radially textured soft magnetic underlayer manufactured according to the teaching of applicant&#39;s co-pending application Ser. No. 10/003,363 filed on Nov. 15, 2001, which application is assigned to the present assignee herein, and is hereby incorporated by reference herein in its entirety. By way of brief explanation the soft magnetic underlayer  16  comprises an amorphous iron-Cobalt-boron alloy layer with tantalum layer applied to a total thickness of about 240 nm. The soft magnetic underlayers are applied by sputtering techniques, which are well known to those skilled in the art. 
     The perpendicular magnetic recording material preferably comprises a Cobalt alloy (Co(X))having alternate layers of a noble metal. The Cobalt is alloyed with one or more of the group comprising boron (B), chromium (Cr), Tantalum (Ta), Francium (Fr), Platinum (Pt), Tungsten (W), Manganese (Mn), Molybdenum (Mo), Ruthenium (Ru), Silicon (Si), Nickel (Ni), Copper (Cu), or Gold (Ag), whereas the noble metal preferably comprises palladium (Pd) or platinum (Pt). In an alternate embodiment, the perpendicular magnetic material comprises graded bilayers of the Co(X)/noble metal multi-layers. In the embodiment shown in  FIG. 2 , the perpendicular magnetic recording material  19  comprises an initial nonmagnetic or paramagnetic  22  layer and a final perpendicular recording layer  25 . 
     The initial paramagnetic material layer  22  preferably comprises a relatively very thin layer  28  of the Cobalt alloy, on the order of &lt;1.5 Å. In this embodiment there are three such layers of the Cobalt alloy  28  which alternate with a palladium layer  31  which has a thickness on the order of about 1 nm. By the use of the relatively thin Cobalt alloy, the thickness is low enough such that the magnetic Curie temperature of the Cobalt alloy drops below room temperature, which renders this initial region paramagnetic. In this manner magnetic coupling between the layers  28  is prevented so as to increase the magnetic properties of the perpendicular recording media and to increase signal to noise ratio. 
     The final Cobalt alloy/noble recording metal multi-layers  25  are applied such that the individual Cobalt alloy layers  34  are about 2-6 Å thick, generally about 3 Å, and the noble metal layers  37  are approximately 8-15 Å in thickness. In this embodiment the magnetic recording material  25  is applied in a range of 8-20 layers and generally 15 layers. That is, after the initial paramagnetic layers  22  are applied, about 15 bilayers of the Cobalt alloy/noble metal are applied, the Cobalt alloy having at thickness of about 3 Å and the noble metal being a thickness of about 1 nm. 
     Depending upon the desired magnetic recording properties, the magnetic material layers  25  number between 8-20. This produces a low noise perpendicular magnetic recording medium having the desired magnetic properties, such as those shown in the polar MOKE loop of FIG.  3 . 
     By providing the initial paramagnetic layers  22 , the layers are exchanged decoupled such that there is no magnetic coupling between neighboring grains of the Cobalt alloy. The grading of the initial growth region makes this initial film paramagnetic at room temperature. As shown in  FIG. 3  the coercivity of the multilayer deposited with initial graded bilayers is enhanced. Furthermore as shown in the MOKE loop, as coercivity increases also the coercivity slope increases, indicating a higher degree of exchange decoupling. 
     While specific embodiments of the invention have been shown in the drawings and described in detail, it will be appreciated by those skilled in the art that various modifications and alterations would be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and in any and all equivalents thereof.