# Patent

## Title
Perpendicular magnetic recording layer with regions having different magnetic anisotropy constants

## Abstract

A perpendicular magnetic recording medium and a method of manufacturing the same are provided. The perpendicular magnetic recording medium comprises a recording layer including a plurality of regions formed in the depth direction of the recording layer and a magnetic anisotropy constant of a region relatively deeper than another region, among the plurality of regions, is greater than that of the another region. The method of manufacturing a perpendicular magnetic recording medium includes: forming a recording layer having perpendicular magnetic anisotropy; and irradiating the recording layer with ions.

## Background
CROSS-REFERENCE TO RELATED PATENT APPLICATION
This application claims the benefit of Korean Patent Application No. 10-2007-0052915, filed on May 30, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
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
            
          
          >
          40
        
        ,
      
    
    
      
        [
        
          Inequality
          ⁢
          
            
          
          ⁢
          1
        
        ]
      
    
  




where, KU is a magnetic anisotropy constant, V is a grain volume, KB 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 KU 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/in2, the required magnetic anisotropy constant KU is 1.99E7 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 KU. In order to solve this problem, a method of depositing a magnetic thin film having a large magnetic anisotropy constant KU, a magnetic thin film having a small magnetic anisotropy constant KU, 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 OF THE INVENTION
Various embodiments disclosed herein are generally directed to a perpendicular magnetic recording layer of selected ferro-magnetic material having a non-uniform concentration of ions diffused therein to provide a lower first region of the layer with a first agnetic anisotropy constant and an upper second region of the layer with a second magnetic anisotropy constant less than the first magnetic anisotropy constant.
According to another aspect of the present invention, a method of manufacturing a perpendicular magnetic recording medium comprises forming a recording layer having perpendicular magnetic anisotropy and irradiating the recording layer with ions.



BRIEF DESCRIPTION OF THE DRAWINGS
The above and other features and advantages of the present invention 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 invention;
FIG. 3 is a graph illustrating examples of distribution of ion concentration for various ion irradiation conditions;
FIGS. 4A to 4C are schematic diagrams illustrating a recording layer with magnetic anisotropy constants KU 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 OF THE INVENTION
Hereinafter, a perpendicular magnetic recording medium and a method of manufacturing the same according to an exemplary embodiment of the present invention will be described in detail by explaining exemplary embodiments of the invention 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 invention. 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 (MgO), 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 KU1, a second region 172 with a magnetic anisotropy constant KU2, and a third region 173 with a magnetic anisotropy constant KU3. 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 KU1>KU2>KU3. 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 KU1 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/in2)
Grain volume (nm3)
Required KU (107 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 KU 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 KU. FIG. 3 is a graph illustrating examples of distribution of ion concentration for various ion irradiation conditions. The magnetic anisotropy constant KU 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 KU1>KU2>KU3. The ion irradiation condition can be controlled so that the value of the magnetic anisotropy constant KU may be continuously varied or so that two or more regions have different magnetic anisotropy constants KU. For this, when irradiating the recording layer 170 with ions, the ion energy or dose 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 KU according ion irradiation conditions. FIG. 4A shows a recording layer 170′ constructed with a single region having a magnetic anisotropy constant KU 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 invention. FIGS. 4B and 4C respectively show recording layers constructed with two and five regions with different magnetic anisotropy constants KU which range from 1E6 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 KU and a material with a low magnetic anisotropy constant KU,
While the perpendicular magnetic recording medium and the method of manufacturing the same according to an exemplary embodiment of the present invention 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 invention as defined by the appended claims.

## Claims

1. An apparatus comprising a perpendicular magnetic recording layer of selected ferro-magnetic material having a concentration of implanted ions adjacent an upper surface of the recording layer higher than that deeper in a thickness direction of the recording layer to establish at least first and second regions with different respective magnetic anisotropy constants.

2. The apparatus of claim 1, wherein the first region has a first magnetic anisotropy constant Ku1, the second region is disposed between the first region and the upper surface, and the second region has a second magnetic anisotropy constant Ku2 less than Ku1.

3. The apparatus of claim 1, wherein the second region is disposed between the first region and the upper surface, and the first region maintains thermal stability of the perpendicular magnetic recording layer at a predetermined recording density.

4. The apparatus of claim 1, further comprising a substrate, a soft-magnetic underlayer and an intermediate layer, wherein the recording layer is formed on the intermediate layer.

5. The apparatus of claim 4, wherein the soft-magnetic underlayer is made of a magnetic material containing one or more materials selected from the group consisting of cobalt (Co), iron (Fe), and nickel (Ni).

6. The apparatus of claim 4, wherein the intermediate layer is made of an alloy containing one or more materials selected from the group consisting of ruthenium (Ru), magnesium oxide (MgO), and nickel (Ni).

7. The apparatus of claim 4, wherein the recording layer is constructed with a magnetic thin film or magnetic multi-layered thin films containing one or more materials selected from the group consisting of cobalt (Co), iron (Fe), platinum (Pt), and palladium (Pd).

8. An apparatus comprising a perpendicular magnetic recording layer of selected ferro-magnetic material having a non-uniform concentration in a thickness direction of ions diffused therein to provide a lower first region of the material with a first magnetic anisotropy constant and an upper second region of the material with a second magnetic anisotropy constant less than the first magnetic anisotropy constant.

9. The apparatus of claim 8, in which the non-uniform concentration of ions diffused in the layer of selected ferro-magnetic material further provides a third region of the material above the second region with a third magnetic anisotropy constant less than the second magnetic anisotropy constant.

10. The apparatus of claim 8, wherein a magnetic anisotropy constant of the first region has a value that maintains thermal stability of the perpendicular magnetic recording layer at a predetermined recording density.

11. The apparatus of claim 8, further comprising a substrate, a soft-magnetic underlayer and an intermediate layer, wherein the recording layer is formed on the intermediate layer.

12. The apparatus of claim 11, wherein the soft-magnetic underlayer is made of a magnetic material containing one or more materials selected from the group consisting of cobalt (Co), iron (Fe), and nickel (Ni).

13. The apparatus of claim 11, wherein the intermediate layer is made of an alloy containing one or more materials selected from the group consisting of ruthenium (Ru), magnesium oxide (MgO), and nickel (Ni).

14. The apparatus of claim 11, wherein the recording layer is constructed with a magnetic thin film or magnetic multi-layered thin films containing one or more materials selected from the group consisting of cobalt (Co), iron (Fe), platinum (Pt), and palladium (Pd).

15. The apparatus of claim 8, wherein the ions are nitrogen (N) ions or helium (He) ions.

16. The apparatus of claim 1, in which the ions are gallium (Ga) ions.