Abstract:
Provided is a patterned magnetic recording medium including a plurality of magnetic recording layers arranged at predetermined regular intervals on a substrate, wherein the magnetic recording layers are multi-layered and comprise a means of suppressing magnetic interaction between the magnetic recording layers. The magnetic recording layer includes a first ferromagnetic layer, the means of suppressing magnetic interaction, and a second ferromagnetic layer sequentially stacked, wherein the means of suppressing magnetic interaction is a soft magnetic layer.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2006-0108391, filed on Nov. 3, 2006 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to recording medium, and more particularly, to a patterned magnetic recording medium having reduced interaction between neighboring magnetic recording layers. 
         [0004]    2. Description of the Related Art 
         [0005]    In continuous magnetic recording media (hereinafter referred to as ‘continuous media’) in which a continuous magnetic film is used as a recording layer, the size of magnetic grains consisting the magnetic film should be small in order to increase the recording density of the continuous media. However, when the magnetic grain size is smaller than a critical value, a superparamagnetic effect occurs, and thus thermal stability of the magnetic grains is decreased, such that the data storage characteristics of the continuous media are deteriorated. Thus it is difficult to increase the recording density of the continuous media. 
         [0006]    In order to overcome the limit of the recording density of the continuous media, patterned magnetic recording media (hereinafter referred to as ‘patterned media’) in which magnetic domains corresponding to bit regions are separated from each other have been suggested. The patterned media are disclosed in U.S, Patent Application No. US 2002/0068195 A1 and No. 2002/0154440 A1, and in Korean Patent Laid-Open Gazette No. 2005-0010338. The recording density of the patterned media is known to be 1000 Gbit/in 2  or greater, which is significantly greater than that of the continuous media. 
         [0007]    However, since magnetic interaction between neighboring magnetic domains is large in conventional patterned media, the switching field distribution is increased. Hereinafter, the above problem will be described in detail with reference to  FIGS. 1A and 1B . 
         [0008]      FIG. 1A  is a cross-sectional view of a conventional patterned medium. 
         [0009]    Referring to  FIG. 1A , the conventional patterned medium includes a plurality of magnetic recording layers  100   a  through  100   g  ( 100 ) on a substrate  10 . The magnetic recording layers  100   a  through  100   g  are disposed at a regular interval and are formed of a ferromagnetic material. Each magnetic recording layer is in the form of a pillar, and a non-magnetic boundary layer  150  is formed between the magnetic recording layers  100   a  through  100   g.    
         [0010]    Each magnetic recording layer is a bit region in which data is recorded. Each magnetic recording layer is magnetized in a first direction D 1  by a magnetic field generated by a recording head, or is magnetized in a second direction D 2 , which is opposite to the first direction D 1 . The magnetic recording layer magnetized in the first direction D 1  and the magnetic recording layer magnetized in the second direction D 2  may correspond respectively to a bit value of 0 (hereinafter, ‘0’) and a bit value of 1 (hereinafter, ‘1’). To record new data to the magnetic recording layer  100  which contains pre-recorded data, the magnetization direction of the magnetic recording layer  100  may need to be reversed. A magnetic field needed to reverse the magnetization direction is called a switching magnetic field. 
         [0011]    Ideally, the absolute value of the switching magnetic field to record ‘0’ and absolute value of the switching magnetic field to record ‘1’ are equal, and the switching field distribution should be zero. However, in a conventional patterned medium, the switching magnetization distribution is greater than zero due to magnetic interaction between neighboring magnetic domains. 
         [0012]    For example, in  FIG. 1A  where the magnetic recording layers  100   a  through  100   g  are all magnetized in the first direction D 1 , the absolute value of the switching magnetic field to reverse the magnetization direction of the magnetic recording layer  100   d  is smaller than the absolute value of the switching magnetic field needed to return the magnetization direction of the magnetic recording layer  100   d  to the first direction D 1  again. The reason is that a magnetic field H i , which is generated from magnetic recording layers  100   a  through  100   c  and  100   e  through  100   g,  which are located at the sides of the magnetic recording layer  100   d,  affects the magnetic recording layer  100   d.  In detail, when the magnetic recording layers  100   a  through  100   c  and  100   e  through  100   g  have the same magnetization direction (here, it is the first direction D 1 ) as the magnetic recording layer  100   d,  the magnetic field H i  generated from the magnetic recording layers  100   a  through  100   c  and  100   e  through  100   g  and passing through the magnetic recording layer  100   d  has the second direction D 2 , which is opposite to the first direction D 1 . Thus the absolute value of the switching magnetic field to change the magnetization direction of the magnetic recording layer  100   d  from the first direction D 1  to the second direction D 2  is smaller than the absolute value of the switching magnetic field to change the magnetization direction of the magnetic recording layer  100   d  from the second direction D 2  to the first direction D 1 . 
         [0013]      FIG. 1B  illustrates the hysteresis characteristic caused by a magnetic field H applied to the magnetic recording layer  100   d.  In  FIG. 1B , M denotes the magnetization of the magnetic recording layer  100   d.    
         [0014]    Referring to  FIG. 1B , the hysteresis loop of the magnetic recording layer  100   d  is largely off-set to the right. Thus the difference between the absolute value of a switching magnetic field H 1  for recording ‘0’ and the absolute value of a switching magnetic field H 2  for recording ‘1’ is large. 
         [0015]    The magnetization direction of the magnetic recording layers  100   a  through  100   c  and  100   e  through  100   g  may vary at different areas of a recording medium. Thus the difference between the absolute value of a switching magnetic field H 1  for recording ‘0’ and the absolute value of a switching magnetic field H 2  for recording ‘1’ also may vary at various areas of the recording medium. 
         [0016]    The switching field distribution (%) is calculated by (ΔH/H min )×100, where ΔH denotes ∥H 1 |−|H 2 ∥, and H min  is the smaller value of |H 1 | and |H 2 |. When the magnetic anisotropic energy of the magnetic recording layer  100  is 2×10 6  erg/cm 3 , and 4 πMs is 1.0 Tesla, where Ms denotes saturation magnetization and one bit is switched by one time of application of a magnetic field, the switching magnetic distribution of a conventional patterned medium is 70%, which is significantly high. 
         [0017]    Accordingly, it is difficult to secure recording reliability and data stability in conventional patterned media. 
       SUMMARY OF THE INVENTION 
       [0018]    The present invention provides a patterned magnetic recording medium having reduced magnetic interaction between neighboring magnetic domains. 
         [0019]    According to an aspect of the present invention, there is provided a patterned magnetic recording medium comprising a plurality of magnetic recording layers arranged at an interval on a substrate, wherein the magnetic recording layers are a multi-layer laminate which is disposed vertically with respect to the substrate and comprise a means which suppresses magnetic interaction between the respective magnetic recording layers. 
         [0020]    The magnetic recording layers each may comprise two or more ferromagnetic layers and the means which suppresses magnetic interaction is interposed between the respective ferromagnetic layers, the means being a soft magnetic layer. 
         [0021]    Each magnetic recording layer may comprise a first ferromagnetic layer, the soft magnetic layer, and a second ferromagnetic layer sequentially stacked. 
         [0022]    A non-magnetic layer may be formed between the first ferromagnetic layer and the soft magnetic layer and between the soft magnetic layer and the second ferromagnetic layer. 
         [0023]    The magnetic anisotropic energy of the ferromagnetic layers maybe 10 6 -10 7  erg/cm 3 . 
         [0024]    The thickness of the ferromagnetic layers may be 2-10 nm. 
         [0025]    The ferromagnetic layers may be each one of a CoCrPt layer, a CoPtP layer, a multi-layer comprising a Co layer and a Pt layer, and another multi-layer comprising a Fe layer and a Pt layer. 
         [0026]    The magnetic anisotropic energy of the soft magnetic layer may be 50-10000 erg/cm 3 . 
         [0027]    The thickness of soft magnetic layer may be 2-10 nm. 
         [0028]    The soft magnetic layer may be one of a CoFe layer, a NiFe layer, a CoNiFe layer, and a Co layer. 
         [0029]    47 πMs may be 0.3-1.5 Tesla, where Ms is the saturation magnetization of the soft magnetic layer. 
         [0030]    The thickness of the non-magnetic layer may be 1-5 nm. 
         [0031]    The non-magnetic layer may be one of a Cu layer, a Pt layer, a Ru layer, a Ta layer, an NiFeCr layer, and a Cr layer. 
         [0032]    According to the present invention, the magnetic interaction between neighboring magnetic recording layers can be reduced, thereby reducing the switching field distribution of the patterned magnetic recording medium. Thus the recording reliability and the data stability can be increased. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    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: 
           [0034]      FIG. 1A  is a cross-sectional view illustrating a structure of a conventional patterned magnetic recording medium and the problem thereof; 
           [0035]      FIG. 1B  is a graph illustrating the hysteresis characteristic of a magnetic recording layer included in the patterned magnetic recording medium of  FIG. 1A ; 
           [0036]      FIG. 2  is a cross-sectional view of patterned magnetic recording medium according to an embodiment of the present invention; 
           [0037]      FIGS. 3A and 3B  are cross-sectional views respectively illustrating the magnetic field caused in the magnetic recording layer included in a conventional patterned magnetic recording medium and a magnetic recording medium according to an embodiment of the present invention; and 
           [0038]      FIG. 4  is a graph illustrating the simulation result of switching field distribution of the patterned magnetic recording medium of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]    The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. In the drawings, the widths or the thicknesses of layers and regions are exaggerated for clarity. 
         [0040]      FIG. 2  is a cross-sectional view of a patterned magnetic recording medium according to an embodiment of the present invention. 
         [0041]    Referring to  FIG. 2 , the patterned magnetic recording medium according to the current embodiment of the present invention includes a plurality of magnetic recording layers  200  arranged on a substrate  20  at an interval. In one embodiment, the magnetic recording layers  200  are disposed at a regular interval. Each of the magnetic recording layers  200  is a multi-layer laminate comprising. It has a sandwich structure in which a soft magnetic layer  6  is interposed between a first ferromagnetic layer  2   a  and a second ferromagnetic layer  2   b.  A first non-magnetic layer  4   a  and a second non-magnetic layer  4   b  may be formed between the first ferromagnetic layer  2   a  and the soft magnetic layer and between the soft magnetic layer  6  and the second ferromagnetic layer  2   b,  respectively. A non-magnetic boundary layer  250  is provided between each of the magnetic recording layers  200 . The magnetic anisotropic energy of the first and second ferromagnetic layers  2   a  and  2   b  may be 10 6 -10 7  erg/cm 3 . The magnetic anisotropic energy of the soft magnetic layer  6  may be 50-10000 erg/cm 3 , and preferably 80-1000 erg/cm 3 . 
         [0042]    The first and second ferromagnetic layers  2   a  and  2   b  may be formed of a same material or different material, and each may be one of a CoCrPt layer, a CoPtP layer, a multi-layer comprising a Co layer and a Pt layer, and another multi-layer comprising a Fe layer and a Pt layer. The soft magnetic layer  6  may be one of a CoFe layer, a NiFe layer, a CoNiFe layer, and a Co layer. The first and second non-magnetic layers  4   a  and  4   b  may be formed of a same material or different material, and each may be one of a Cu layer, a Pt layer, a Ru layer, a Ta layer, a NiFeCr layer, and a Cr layer. 
         [0043]    The thickness of the first and second ferromagnetic layers  2   a  and  2   b  may be 2-10 nm, and the thickness of the soft magnetic layer  6  may be 2-10 nm. The thickness of the first and second non-magnetic layers  4   a  and  4   b  may be 1-5 nm. 
         [0044]    The non-magnetic boundary layer  250  may be formed of a material such as a resin, silicon oxide (SiO 2 ), or silicon nitride (Si x N y ) using a nano patterning method such as nano imprinting. The non-magnetic boundary layer  250  may be a vacant layer, that is, an air layer. When the non-magnetic boundary layer  250  is formed of a material such as a resin, the first ferromagnetic layer  2   a,  the first non-magnetic layer  4   a,  the soft magnetic layer  6 , the second non-magnetic layer  4   b,  and the second ferromagnetic layer  2   b  are sequentially filled between the non-magnetic boundary layers  250  to form the magnetic recording layers  200 . The various methods and sequences of forming the magnetic recording layers  200  and the non-magnetic boundary layers  250  are known in the art and proper methods and sequences may de determined by the one skilled. 
         [0045]    The patterned magnetic recording medium according to the current embodiment of the present invention has reduced magnetic interaction between the neighboring magnetic recording layers  200  due to the characteristics of the structure of the magnetic recording layers  200 . The reason for the reduction in the magnetic interaction between the magnetic recording layers  200  will be described in detail with reference to  FIGS. 3A and 3B . 
         [0046]      FIGS. 3A and 3B  are cross-sectional views respectively illustrating the magnetic field caused in a magnetic recording layer (hereinafter ‘conventional magnetic recording layer 100’) included in a conventional patterned magnetic recording medium, and in the magnetic recording layer of the present invention (hereinafter ‘magnetic recording layer 200’) included in a magnetic recording medium according to an embodiment of the present invention. 
         [0047]    In  FIGS. 3A and 3B , the conventional magnetic recording layer  100  and the magnetic recording layer  200  according to the present invention are magnetized in a first direction D 1 . The directions of magnetization correspond to the directions shown in  FIG. 1A . 
         [0048]    Referring to  FIGS. 3A and 3B , the magnetic field of the conventional magnetic recording layer  100  formed of a ferromagnetic layer is broadly distributed at a wide range of area around the conventional magnetic recording layer  100 . On the other hand, the magnetic field of the magnetic recording layer  200  according to the present invention is distributed only near the magnetic recording layer  200  because the soft magnetic layer  6  interposed between the first and second ferromagnetic layers  2   a  and  2   b  absorbs the magnetic field in the middle of the magnetic recording layer  200 . Accordingly, since the magnetic field generated by the first and second ferromagnetic layers  2   a  and  2   b  of the magnetic recording layer  200  mostly passes through the magnetic recording layer  200 , the magnetic interaction between neighboring magnetic recording layers  200  in the patterned magnetic recording medium according to the present invention is significantly reduced. 
         [0049]    Also, as the magnetization reversion speed of the soft magnetic layer  6  during switching is higher than the magnetization reversion speed of the first and second ferromagnetic layers  2   a  and  2   b,  the soft magnetic layer  6  functions as an initiator for magnetic reversion of the magnetic recording layer  200 . Thus the switching speed of the magnetic recording layer  200  is increased. 
         [0050]    Meanwhile, the first and second non-magnetic layers  4   a  and  4   b  prevent a formation of a magnetic domain wall between the first ferromagnetic layer  2   a  and the soft magnetic layer  6  and between the ferromagnetic layer  2   b  and the soft magnetic layer  6 , respectively, so that the magnetic recording layer  200  acts like a single magnetic domain. When the magnetic recording layer  200  acts like a single magnetic domain, excessive decrease in the magnetic field required for reversing the magnetic recording layer  200 , that is, the switching magnetic field, is prevented. 
         [0051]      FIG. 4  is a graph illustrating the results of a simulated switching field distribution of the patterned magnetic recording medium according to the present invention illustrated in  FIG. 2 , showing the variation of the switching field distribution of the magnetic recording layer  200  according to the change of magnetic characteristics of the soft magnetic layer  6 . In  FIG. 4 , Ms denotes saturation magnetization, and K denotes the magnetic anisotropic energy of the soft magnetic layer  6  (erg/cm 3 ). 
         [0052]    It shows the switching field distribution of the magnetic recording layer  200  calculated by varying 4 πMs of the soft magnetic layer  6  from 0.5 to 1.4 Tesla when K is each 80, 800, and 16000 erg/cm 3 . 
         [0053]    For the purpose of tests, all the magnetic recording layers  200  in a patterned magnetic recording medium were magnetized in a first direction D 1  and a predetermined magnetic recording layer was subject to a reverse magnetization to a second direction D 2 . In the simulation, one bit is switched by one time of application of a magnetic field. 
         [0054]    Referring to  FIG. 4 , the maximum switching field distribution of the magnetic recording layer  200  is less than 38%, and the switching field distribution of the magnetic recording layer  200  may be decreased to less than 20% in a region where 4 πMs is smaller than 0.6 Tesla. As can be seen from  FIG. 4 , 4 πMs of the soft magnetic layer  6  of the patterned magnetic recording medium according to the present invention is 0.3-1.5 Tesla, preferably 0.3-0.7 Tesla. 
         [0055]    Comparing  FIG. 4  with the calculation result shown in ‘Description of the Related Art’ of the switching field distribution of the conventional patterned magnetic recording medium, the switching field distribution of the patterned magnetic recording medium according to an embodiment of the present invention is significantly smaller than that of the conventional patterned magnetic recording medium. 
         [0056]    A particular embodiment of a magnetic recording layer having two ferromagnetic layers and a soft magnetic layer interposed between the two ferromagnetic layers has been explained above. However, the magnetic recording layer according to embodiments of the present invention may have three ferromagnetic layers or more, which are provided with a soft magnetic layer interposed between respective ferromagnetic layers. 
         [0057]    As described above, the patterned medium according to the present invention includes the soft magnetic layer  6  suppressing magnetic interaction between neighboring magnetic recording layers  200 , thereby greatly reducing the switching field distribution of the patterned medium. Accordingly, according to the present invention, the recording reliability and the data stability of the patterned magnetic recording medium can be increased. 
         [0058]    While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, the exemplary embodiments are for the illustrative purpose only and not to limit the scope of the present invention. For example, a non-magnetic interlayer and/or soft magnetic underlayer may be provided under the magnetic recording layer  200  and the magnetic boundary layer  250  or the stacking number of the ferromagnetic layers, the non-magnetic layers, and the soft magnetic layer included in the magnetic recording layer  200  may be varied by one of ordinary skill in the art. Thus the scope of the present invention is not defined by the exemplary embodiments but by the technical scope of the following claims.