Abstract:
A perpendicular magnetic recording medium of the embodiments of the invention comprises a substrate, a hcp soft underlayer (SUL), and a magnetic layer, wherein the hcp SUL is adapted to create a [0002] growth orientation in the magnetic layer and to enhance a magnetic head field during writing of data to the magnetic layer; further wherein the perpendicular magnetic recording medium does not contain an interlayer (IL) that is different from the hcp SUL and provides a [0002] growth orientation in the magnetic layer.

Description:
RELATED APPLICATIONS 
       [0001]    None. 
       FIELD OF INVENTION 
       [0002]    The present invention relates to improved, high recording performance magnetic recording media comprising an hexagonal closed packed (hcp) soft underlayer (SUL) that can perform the roles of an interlayer, which typically sets the [0002] growth orientation, and that of SUL. 
       BACKGROUND 
       [0003]    Thin film magnetic recording media, wherein a fine-grained polycrystalline magnetic alloy layer serves as the magnetic recording layer, are generally classified as “longitudinal” or “perpendicular,” depending on the orientation of the magnetic domains (bits) of the grains in the magnetic recording layer.  FIG. 1 , obtained from  Magnetic Disk Drive Technology  by Kanu G. Ashar, 322 (1997), shows magnetic bits and transitions in longitudinal and perpendicular recording. 
         [0004]    Besides magnetic recording layer/s (ML), perpendicular magnetic media also includes an interlayer (IL) and soft magnetic underlayer (SUL). The role of IL is to provide the [0002] growth orientation, and to establish a surface roughness and a physical grain separation required for an oxide segregation to the grain boundaries. For this reason IL consists of two layers, one layer is used to establish the [0002] growth orientation and the role of the other layer is to provide required surface morphology. The SUL is used to enhance the magnetic head field during the writing process. 
       SUMMARY OF THE INVENTION 
       [0005]    The embodiments of the invention are directed to a perpendicular magnetic recording medium comprising a substrate, a hcp soft underlayer (SUL), and a magnetic layer, wherein the hcp SUL is adapted to create a [0002] growth orientation in the magnetic layer and to enhance a magnetic head field during writing of data to the magnetic layer; further wherein the perpendicular magnetic recording medium does not contain an interlayer (IL) that is different from the hcp SUL and provides a [0002] growth orientation in the magnetic layer. Preferably, a shape anisotropy, (2πM s ) is larger than a magnetocrysalline anisotropy (K 1 ), orienting a magnetic moment along a film plane of the magnetic layer. Preferably, the hcp SUL comprises CoFe and one or more elements selected from the group consisting of Ni, Al, Si, Ti, V, Cr, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Ir, Pt, and Au. Preferably, the hcp SUL comprises CoFe and one or more elements selected from the group consisting of Cr, Ru, and Re. Preferably, the hcp SUL comprises Co 100-x Fe x  (x≦30) and one or more elements selected from the group consisting of Ni, Al, Si, Ti, V, Cr, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Ir, Pt, and Au. Preferably, the hcp SUL comprises Co 100-x Fe x  (x≦30) and one or more elements selected from the group consisting of Cr, Ru, and Re. 
         [0006]    Another embodiment relates to a perpendicular magnetic recording medium comprising a substrate, a hcp soft underlayer (SUL), and a magnetic layer, wherein the hcp SUL has the following properties: 1) has a hcp crystal structure, 2) is ferromagnetic, 3) has a saturation magnetization (M s ) of greater than 100 emu/cm 3 , 4) has a shape anisotropy (2πM s ) larger than a magnetocrysalline anisotropy (K 1 ), orienting the magnetic moment along a film plane of the magnetic layer, 5) has an in-plane coercivity (H c ) of less than 10 Oe, and 6) does not have stripe domains. 
         [0007]    Another embodiment of the invention relates to a method of manufacturing a perpendicular magnetic recording medium comprising obtaining a substrate, depositing a hcp soft underlayer (SUL), and depositing a magnetic layer, wherein the hcp SUL is adapted to create a [0002] growth orientation in the magnetic layer and to enhance a magnetic head field during writing of data to the magnetic layer; further wherein the perpendicular magnetic recording medium does not contain an interlayer (IL) that is different from the hcp SUL and provides a [0002] growth orientation in the magnetic layer. 
         [0008]    As will be realized, this invention is capable of other and different embodiments, and its details are capable of modifications in various obvious respects, all without departing from this invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  shows (a) longitudinal and (b) perpendicular recording bits. 
           [0010]      FIG. 2  shows a design of a perpendicular recording medium having a single hcp soft underlayer of the embodiments of the invention. 
           [0011]      FIGS. 3 and 4  show that in the embodiments of the invention, the shape anisotropy is greater than the magnetocrystalline anisotropy. 
           [0012]      FIG. 5  shows that the in-plane coercivity of the hcp underlayer of the embodiments of the invention. 
           [0013]      FIG. 6  shows that polarization resistance of the Co-containing hcp soft underlayer increases with the addition Ru and Fe, while the polarization resistance decreases with the addition of Re. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The embodiments of the invention provide magnetic recording media suitable for high areal recording density exhibiting high SMNR. The embodiments of the invention achieve such technological advantages by forming a soft underlayer. A “soft magnetic material” is a material that is easily magnetized and demagnetized. As compared to a soft magnetic material, a “hard magnetic” material is one that neither magnetizes nor demagnetizes easily. 
         [0015]    The underlayer is “soft” because it is made up of a soft magnetic material, which is defined above, and it is called an “underlayer” because it resides under a recording layer. In a preferred embodiment, the soft layer is amorphous. The term “amorphous” means that the material of the underlayer exhibits no predominant sharp peak in an X-ray diffraction pattern as compared to background noise. The “amorphous soft underlayer” of the embodiments of the invention encompasses nanocrystallites in amorphous phase or any other form of a material so long the material exhibits no predominant sharp peak in an X-ray diffraction pattern as compared to background noise. 
         [0016]    When soft underlayers are fabricated by magnetron sputtering on disk substrates, there are several components competing to determine the net anisotropy of the underlayers: effect of magnetron field, magnetostriction of film and stress originated from substrate shape, etc. The soft magnetic underlayer can be fabricated as single layers or a multilayer. 
         [0017]    A seedlayer could be optionally included in the embodiments of this invention. A seedlayer is a layer lying in between the substrate and the underlayer. Proper seedlayer can also control anisotropy of the soft underlayer by promoting microstructure that exhibit either short-range ordering under the influence of magnetron field or different magnetostriction. A seedlayer could also alter local stresses in the soft underlayer. 
         [0018]    Preferably, in the underlayer of the perpendicular recording medium of the embodiments of the invention, an easy axis of magnetization is directed in a direction substantially transverse to a traveling direction of the magnetic head. This means that the easy axis of magnetization is directed more toward a direction transverse to the traveling direction of the read-write head than toward the traveling direction. Also, preferably, the underlayer of the perpendicular recording medium has a substantially radial or transverse anisotropy, which means that the domains of the soft magnetic material of the underlayer are directed more toward a direction transverse to the traveling direction of the read-write head than toward the traveling direction. In one embodiment, the direction transverse to the traveling direction of the read-write head is the direction perpendicular to the plane of the substrate of the recording medium. 
         [0019]    In accordance with embodiments of this invention, the substrates that may be used in the embodiments of the invention include glass, glass-ceramic, NiP/aluminum, metal alloys, plastic/polymer material, ceramic, glass-polymer, composite materials or other non-magnetic materials. Glass-ceramic materials do not normally exhibit a crystalline surface. Glasses and glass-ceramics generally exhibit high resistance to shocks. 
         [0020]    A preferred embodiment of this invention is a perpendicular recording medium comprising at least two amorphous soft underlayers with a spacer layer between the underlayers and a recording layer. The amorphous soft underlayer should preferably be made of soft magnetic materials and the recording layer should preferably be made of hard magnetic materials. The amorphous soft underlayer is relatively thick compared to other layers. The interlayer can be made of more than one layer of non-magnetic materials. The purpose of the interlayer is to prevent an interaction between the amorphous soft magnetic underlayer and recording layer. The interlayer could also promote the desired properties of the recording layer. 
         [0021]    The underlayer and magnetic recording layer could be sequentially sputter deposited on the substrate, typically by magnetron sputtering, in an inert gas atmosphere. A carbon overcoat could be typically deposited in argon with nitrogen, hydrogen or ethylene. Conventional lubricant topcoats are typically less than about 20 Å thick. 
         [0022]    The magnetic recording medium of the embodiments of the invention contains a layer that can resume both roles, that of an interlayer, setting the [0002] growth orientation, and that of SUL. This layer is called hcp SUL. The preferred requirements for hcp SUL are: 1) to have hcp crystal structure, 2) to be ferromagnetic, 3) to have a large saturation magnetization, 4) to have the shape anisotropy, 2πM s , larger than its magnetocrysalline anisotropy, orienting the magnetic moment along the film plane, 5) to have small in-plane coercivity, 6) not to have stripe domains, and 7) to be corrosion resistant. This layer may consists of combination of Fe, Co, Ni, Al, Si, Ti, V, Cr, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Ir, Pt, Au. 
         [0023]    Another advantage of amorphous materials as soft underlayer materials is the lack of long-range order in the amorphous material. Without a long-range order, amorphous alloys have substantially no magnetocrystalline anisotropy. The use of amorphous soft underlayer could be one way of reducing noise caused by ripple domains and surface roughness. The surface roughness of the amorphous soft underlayer is preferably below 1 nm, more preferably below 0.5 nm, and most preferably below 0.2 nm. 
         [0024]    In accordance with the embodiments of the invention, the test methods for determining different parameters are as follows. If a particular test method has not been explicitly stated below to determine a parameter, then a conventional method used by persons of ordinary skill in this art could be used to determine that parameter. 
         [0025]    The advantageous characteristics attainable by the embodiments of the invention are illustrated in the following examples. 
       EXAMPLES 
       [0026]    All samples described in this disclosure were fabricated with DC magnetron sputtering except carbon films were made with AC magnetron sputtering. 
         [0027]    Applicants investigated a recording medium having the structure shown in  FIG. 2  including a hcp SUL. The advantages of the hcp SUL layer are: 1) the hcp SUL can have up to 1.5 times larger saturation magnetization, M S , in comparison to currently used amorphous SUL&#39;s (from 1000 to 1500 emu/cm 3 ); 2) media design with hcp SUL would be 2 layers less, resulting in a simpler design as shown in  FIG. 2 ; 3) the distance from the head to SUL in the media with hcp SUL is reduced, resulting in better writing performance for cusp heads. 
         [0028]      FIGS. 3 and 4  show that even in the case of Co magnetic the shape anisotropy, 2πM s , is larger than the magnetocrysalline anisotropy, orienting the magnetic moment along the film plane. Anisotropy perpendicular to the film plane is equal 4πM s −2K 1 /M s  as shown in  FIG. 4 . 
         [0029]      FIG. 5  shows that in-plane coercivity is small, less than 10 Oe. This is due to the six fold in-plane symmetry that leads to a small in-plane anisotropy. Applicants investigated Co 100-x Fe x  (x≦30) with addition of Ru, Re, Cr. Both Ru and Cr were used to improve corrosion resistance of CoFe and Re to increase melting point of CoFe and therefore surface energy. Results on FeCo (Ru, Re) are summarized in Table 1. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 M slong  [emu/cm 3 ] 
                 4πMs [Oe] 
                 Ha [Oe] 
                 Hk [Oe] 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 CoRu10 
                 982 
                 12334 
                 9500 
                 2834 
               
               
                 CoRu20 
                 624 
                 7837 
                 5500 
                 2337 
               
               
                 CoRu30 
                 280 
                 3517 
                 1100 
                 2417 
               
               
                 CoRe10 
                 754 
                 9470 
                 5250 
                 4220 
               
               
                 CoRe20 
                 367 
                 4610 
                 2000 
                 2610 
               
               
                 CoRe30 
                 15 
                 188 
                   
                 188 
               
               
                 CoRu5Re5 
                 908 
                 11404 
                 7500 
                 3904 
               
               
                 CoRu10Re10 
                 487 
                 6117 
                 2750 
                 3367 
               
               
                 CoFe20 
                 1481 
                 18601 
                 17000 
                 1601 
               
               
                 CoFe30 
                 1546 
                 19418 
                 18500 
                 918 
               
               
                 CoFe20Ru10 
                 1030 
                 12937 
                 12500 
                 437 
               
               
                 CoFe20Ru20 
                 305 
                 3831 
                 3750 
                 81 
               
               
                 CoFe20Re10 
                 808 
                 10148 
                 10000 
                 148 
               
               
                 CoFe20Re20 
                 131 
                 1645 
                 1500 
                 145 
               
               
                 CoFe20Ru5Re5 
                 888 
                 11153 
                 11000 
                 153 
               
               
                 CoFe20Ru10Re10 
                 240 
                 3014 
                 3000 
                 14 
               
               
                   
               
             
          
         
       
     
         [0030]      FIG. 6  shows that the polarization resistance of Co increases with an addition of Ru, and Fe. Ru increases electro potential of Co and FeCo oxide presumably passivates Co alloy surface increasing corrosion resistance. On the other hand, Re decreases the polarization resistance of Co as shown in  FIG. 6 . An addition of Cr can be also used to passivates surface of Co alloy and increase the polarization resistance. 
         [0031]    This application discloses several numerical range limitations that support any range within the disclosed numerical ranges even though a precise range limitation is not stated verbatim in the specification because this invention can be practiced throughout the disclosed numerical ranges. Finally, the entire disclosure of the patents and publications referred in this application are hereby incorporated herein in entirety by reference.