Abstract:
An apparatus having a recording layer of a magnetic material with a concentration of implanted ions that increases in relation to a thickness direction of the recording layer to provide the recording layer with a continuously varied perpendicular magnetic anisotropy constant.

Description:
RELATED APPLICATION 
     The present application is a continuation of copending U.S. patent application Ser. No. 12/018,270 filed on Jan. 23, 2008, which issues on Jan. 29, 2013 as U.S. Pat. No. 8,361,641 and which claims the benefit of Korean Patent Application No. 10-2007-0052915 filed May 30, 2007. 
    
    
     BACKGROUND 
     1. Field of the Disclosure 
     Various embodiments disclosed herein are generally directed to a perpendicular magnetic recording medium including a recording layer having a plurality of regions with different magnetic anisotropy constants and a method of manufacturing the perpendicular magnetic recording medium. 
     2. Description of the Related Art 
     Magnetic recording methods may be classified into perpendicular and longitudinal magnetic recording methods. In the longitudinal magnetic recording method, information is recorded by using a characteristic that a magnetization direction of a magnetic layer is aligned in parallel with a surface of the magnetic layer. In the perpendicular magnetic recording method, information is recorded by using a characteristic that a magnetization direction of a magnetic layer is aligned perpendicularly to the surface of the magnetic layer. Regarding the recording density, the perpendicular magnetic recording method is more advantageous than the longitudinal magnetic recording method. Accordingly, in order to obtain high density in magnetic recording, the perpendicular magnetic recording medium has been continuously researched. 
       FIG. 1  illustrates a general structure of a conventional perpendicular magnetic recording medium. Referring to  FIG. 1 , the perpendicular magnetic recording medium includes a substrate  10 , a soft-magnetic underlayer  12 , an intermediate layer  14 , and a recording layer  16 . A magnetic field generated from a recording head (not shown) passes through the soft-magnetic underlayer  12  and returns to the recording head, thereby forming a magnetic path H. At this time, a perpendicular component of the magnetic field magnetizes magnetic domains of the recording layer  16  and records information. 
     On the other hand, in magnetic recording, the recording density is limited due to a superparamagnetic effect. That is, as the recording density increases, a grain size of the recording medium decreases. Accordingly, thermal stability decreases. When the thermal stability decreases below a predetermined threshold, magnetic moments may not be aligned in one direction due to thermal agitation. The threshold is represented as follows: 
                         K   U     ⁢   V         K   B     ⁢   T       &gt;   40           [     Inequality   ⁢           ⁢   1     ]               
where, K U  is a magnetic anisotropy constant, V is a grain volume, K B  is the Boltzmann constant, and T is an absolute temperature.
 
     Accordingly, in order to manage the increase of the recording density, the thermal stability that satisfies inequality 1 has to be maintained. In order to maintain the thermal stability, a magnetic recording medium with a large magnetic anisotropy constant K U  has to be manufactured so as to have a high anisotropic energy even in a small grain size. When the anisotropic energy of the recording medium increases, the coercivity Hc of the recording medium necessarily increases. Accordingly, it is difficult that magnetization reversal occurs. Thus, writability becomes low. For example, in order to secure the stability of recorded data for ten years in recording of 1000 Gb/in 2 , the required magnetic anisotropy constant K U  is 1.997E7 erg/cc. However, it is difficult for a current recording head to record data in a magnetic recording medium having a large magnetic anisotropy constant K U . In order to solve this problem, a method of depositing a magnetic thin film having a large magnetic anisotropy constant K U , a magnetic thin film having a small magnetic anisotropy constant K U , and an intermediate layer therebetween by changing the thickness of the intermediate layer has been tried. However, in this case, materials selectable for a recording layer are limited, and thus it is difficult to manufacture a magnetic recording medium by using the aforementioned method. That is, since it is impossible to form the same isolation regions in two different magnetic layers, transition noise increases. Accordingly, the signal to noise ratio (SNR) increases. 
     SUMMARY 
     Various embodiments disclosed herein are generally directed to an apparatus comprising a recording layer of a magnetic material with a concentration of implanted ions that increases in relation to a thickness direction of the recording layer to provide the recording layer with a continuously varied perpendicular magnetic anisotropy constant. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present disclosure will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  illustrates a general structure of a conventional perpendicular magnetic recording medium; 
         FIG. 2  illustrates a structure of a perpendicular magnetic recording medium according to an embodiment of the present disclosure; 
         FIG. 3  is a graph illustrating examples of distribution of ion concentration for various ion irradiation conditions; 
         FIG. 4A to 4C  are schematic diagrams illustrating a recording layer with magnetic anisotropy constants K U  according ion irradiation conditions; and 
         FIG. 5  is a graph illustrating a switching field according to an angle between an external magnetic field and an magnetization easy axis of grain in the perpendicular magnetic recording medium having the structures of  FIGS. 4A to 4C . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, a perpendicular magnetic recording medium and a method of manufacturing the same according to an exemplary embodiment of the present disclosure will be described in detail by explaining exemplary embodiments of the disclosure with reference to the attached drawings. 
       FIG. 2  schematically illustrates a structure of a perpendicular magnetic recording medium  100  according to an embodiment of the present disclosure. Referring to  FIG. 2 , the perpendicular magnetic recording medium  100  includes a recording layer  170  having perpendicular magnetic anisotropy. The perpendicular magnetic recording medium  100  has a structure such that a soft-magnetic underlayer  130 , an intermediate layer  150  and recording layer are sequentially formed on a substrate  110 . A protection layer (not shown) protecting the recording layer  170  from the outside may be formed on the recording layer  170 . A lubrication layer may be formed on the protection layer so as to reduce abrasion of the protection layer. 
     The substrate  110  may be made of glass, an Al—Mg alloy, magnesium oxide (MgO), silicon (Si), and the like. 
     The soft-magnetic underlayer  130  may be made of a soft magnetic material containing one or more materials selected from the group consisting of cobalt (Co), iron (Fe), and nickel (Ni). 
     The intermediate layer  150  is disposed between the recording layer  170  and the soft-magnetic underlayer  130  in order to improve the crystal orientation and magnetic properties of the recording layer  170 . The intermediate layer  150  may be made of an alloy containing one or more materials selected from the group consisting of ruthenium (Ru), magnesium oxide (Mg), and nickel (Ni). 
     Information is recorded in the recording layer  170  through perpendicular magnetization. The recording layer  170  is constructed with a magnetic thin film or magnetic multi-layered thin films containing one or more materials selected from the group with high perpendicular magnetic anisotropy consisting of cobalt (Co), iron (Fe), platinum (Pt), and palladium (Pd). For example, the recording layer  170  may be made of a CoCrPtX-based material. For example, the recording layer  170  includes a first region  171  with a magnetic anisotropy constant K U1 , a second region  172  with a magnetic anisotropy constant K U2 , and a third region  173  with a magnetic anisotropy constant K U3 . A magnetic anisotropy constant of a relatively deeper region among the first to third regions  171  to  173  is greater than that of another region. That is, the magnetic anisotropy constants satisfies the condition K U1 &gt;K U2 &gt;K U3 . Here, the recording layer  170  constructed with the three regions is exemplified. However, the recording layer  170  may be constructed with one or more number (n) of regions that satisfy the condition that the magnetic anisotropy constant of the relatively deeper region is greater than that of another region. The size of each region is also exemplified. The size of each region can vary based on ion irradiation conditions. In addition, when N is sufficiently large, the magnetic anisotropy constant of the recording layer  170  has an increasing gradient with respect to the depth in the recording layer  170 . The magnetic anisotropy constant K U1  of the first region  171  that is the deepest region in the recording layer  170  has a value that secures thermal stability sufficient to obtain desirable recording density. Similarly, when the recording layer  170  has a gradient characteristic that the magnetic anisotropy constant increases as the depth in the recording layer  170  increases, the maximum value of the magnetic anisotropy constant has a value that secures thermal stability sufficient to obtain desirable recording density. 
     Table 1 shows magnetic anisotropy constants required to secure the stored data for ten years as the recording density increases. 
     
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Areal density (Gb/in 2 ) 
                 Grain volume (nm 3 ) 
                 Required K U  (10 7  erg/cc) 
               
               
                   
               
             
             
               
                 100 
                 855 
                 0.19 
               
               
                 130 
                 900 
                 0.18 
               
               
                 180 
                 704 
                 0.24 
               
               
                 250 
                 484 
                 0.34 
               
               
                 300 
                 387 
                 0.43 
               
               
                 450 
                 256 
                 0.65 
               
               
                 600 
                 196 
                 0.85 
               
               
                 800 
                 116 
                 1.43 
               
               
                 1000  
                  83 
                 1.99 
               
               
                   
               
             
          
         
       
     
     A method of forming the recording layer  170  having the aforementioned magnetic anisotropy constant is described hereinafter. The recording layer is made of a material with a sufficiently large magnetic anisotropy constant. For example, the recording layer  170  is formed so as to have a magnetic anisotropy constant K U  corresponding to the desirable recording density. Then, the recording layer  170  is irradiated with ions. The ion irradiation is performed by using focused ion beam (FIB) equipment. The ions may be nitrogen (N) ions, helium (He) ions, and gallium (Ga) ions. The selection of ions, a dose of ions, energy, a scan method, and the like are controlled so as to obtain a desirable magnetic anisotropy constant K U .  FIG. 3  is a graph illustrating examples of distribution of ion concentration for various ion irradiation conditions. The magnetic anisotropy constant K U  is largely decreased at a region with a high ion concentration. Therefore, the ion irradiation condition can be controlled so that the ion concentration is the highest in the surface side of the recording layer  170 , for example, so as to satisfy the aforementioned condition K U1 &gt;K U2 &gt;K U3 . The ion irradiation condition can be controlled so that the value of the magnetic anisotropy constant K U  may be continuously varied or so that two or more regions have different magnetic anisotropy constants K U . For this, when irradiating the recording layer  170  with ions, the ion energy or dosed of ions may be constant or continuously varied, if necessary. In addition, an ion penetration depth is controlled by forming a stopping layer on the recording layer  170 . The aforementioned processes may be simulated or performed experimentally. The ion irradiation condition is controlled so as to maintain the magnetic anisotropy direction and reduce the coercivity. 
     When irradiating the recording layer  170  with ions, the ions influence locations of atoms constituting the recording layer  170 . Accordingly, a magnetic property of a ferromagnetic material, specifically, anisotropy or bonding strength is sensitively changed due to the rearrangement of the atoms. For example, when irradiating cobalt/platinum (Co/Pt) multi-layered films with gallium (Ga) ions, the magnetic property of the multi-layered films is changed. Specifically, when the ion energy is 30 keV and when the dose of ions is 5E12 ions/cc, the ion penetration depth ranges 6.8 nm to 9.2 nm. The magnetic anisotropy direction of the multi-layered films is maintained, and the coercivity is reduced. 
       FIGS. 4A to 4C  are schematic diagrams illustrating a recording layer with magnetic anisotropy constants K U  according ion irradiation conditions.  FIG. 4A  shows a recording layer  170 ′ constructed with a single region having a magnetic anisotropy constant K U  of 1E7 erg/cc. The recording layer  170 ′ has a conventional structure that is not irradiated with ions and a comparative example to compare with the present disclosure.  FIGS. 4B and 4C  respectively show recording layers constructed with two and five regions with different magnetic anisotropy constants K U  which range from 1 E6 erg/cc to 1E7 erg/cc. 
       FIG. 5  is a graph illustrating a switching field according to an angle between an external magnetic field and a magnetization easy axis of grain of the perpendicular magnetic recording medium having the structures of  FIGS. 4A to 4C . Referring to  FIG. 5 , the recording layer according to the present embodiment has a lower switching field than the conventional structure of  FIG. 4A . Accordingly, writability is improved. In addition, the recording layer having five regions with different magnetic anisotropy constants has a lower switching field than the recording layer having two regions with different magnetic anisotropy constants. 
     As described above, in the perpendicular magnetic recording medium and the method of manufacturing the same, the recording layer includes a plurality of regions with different magnetic anisotropy constants or has a gradient in magnetic anisotropy constants by irradiating a recording layer having a high magnetic anisotropy constant with ions. Since the perpendicular magnetic recording medium including the recording layer has high thermal stability and writability, the perpendicular magnetic recording medium may be used as a high density perpendicular magnetic recording medium. 
     In addition, in the case of manufacturing the perpendicular magnetic recording medium with the aforementioned features by using the ion irradiation method, it is possible to solve a problem in that a recording characteristic is deteriorated when an interface is not neatly formed in a case where a recording layer is formed by using two different materials, that is, a material with a high magnetic anisotropy constant K U  and a material with a low magnetic anisotropy constant K U . 
     While the perpendicular magnetic recording medium and the method of manufacturing the same according to an exemplary embodiment of the present disclosure has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by 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 present disclosure as defined by the appended claims.