Abstract:
A perpendicular magnetic recording head which moves in a track direction of a recording layer of a perpendicular magnetic recording medium to write information on the recording layer or read information from the recording layer. The perpendicular magnetic recording head includes: the perpendicular magnetic recording medium including a soft magnetic underlayer and the recording layer; a write head including a main pole that applies a magnetic field to, and writes information to, the recording layer and a return pole having a first end which is connected to the main pole and having a second end which is spaced apart from the main pole over an air bearing surface (ABS) of the perpendicular magnetic recording head which is adjacent to the recording layer; and a permanent magnet formed on at least one side of the write head.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
   This application claims priority from Korean Patent Application No. 10-2005-0074571, filed on Aug. 13, 2005, 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 
   Apparatuses consistent with the present invention relate to a perpendicular magnetic recording head, and more particularly, to a perpendicular magnetic recording head in which a magnetic material is formed to control the magnetization direction of a soft magnetic underlayer of a perpendicular magnetic recording medium. 
   2. Description of the Related Art 
   With the advent of the Information Age, the amount of digital information that a person or organization deals with has significantly increased. For example, many people use computers that have high data processing speeds and large information storage capacities to access the Internet and obtain various pieces of information. Central processing unit (CPU) chips and computer peripheral units have been improved to enhance the speed of data processing in computers, and various types of high density information storage media like hard disks are being developed to enhance data storage capabilities of computers. 
   Recently, various types of recording media have been introduced. Most of the recording media use a magnetic layer as a data recording layer. Data recording types for magnetic recording media can be classified into longitudinal magnetic recording and perpendicular magnetic recording. 
   In longitudinal magnetic recording, data is recorded using the parallel alignment of the magnetization of the magnetic layer on a surface of the magnetic layer. In perpendicular magnetic recording, data is recorded using the perpendicular alignment of the magnetization of the magnetic layer on a surface of the magnetic layer. From the perspective of data recording density, the perpendicular magnetic recording is more advantageous than the longitudinal magnetic recording. 
     FIG. 1A  is a cross-sectional view of a conventional perpendicular magnetic recording head. Referring to  FIG. 1A , the conventional magnetic recording head includes a perpendicular magnetic recording medium  10 , a write head  100  writing data on the recording medium  10 , and a read head  110  reading data from the perpendicular magnetic recording medium  10 . 
   The write head  100  includes a main pole P 1 , a return pole P 2 , and a coil C. The main pole P 1  and the return pole P 2  may be formed of a magnetic material, e.g., NiFe, and may have different coercivities due to different compositions. The main pole P 1  and the return pole P 2  are directly used to write data on a recording layer  13  of the perpendicular magnetic recording medium  10 . An auxiliary pole  101  may be formed on a side of the main pole P 1  to concentrate the magnetic field generated in the main pole P 1  while data is recorded in a selected region of the perpendicular magnetic recording medium  10 . The coil C surrounds the main pole P 1  and generates a magnetic field. 
   The read head  110  includes first and second magnetic shield layers S 1  and S 2  and a data reading magnetoresistance device  111  positioned between the first and second magnetic shield layers S 1  and S 2 . While data is read from a predetermined area of a selected track, the first and second shield layers S 1  and S 2  shield the magnetic field generated by magnetic elements near the magnetoresistance device  111  from affecting the predetermined area. The data reading magnetoresistance device  111  may be a giant magnetoresistance (GMR) device or a tunneling magnetoresistance (TMR) device. 
     FIG. 1B  is an enlarged view of portion A of  FIG. 1A . A method of recording information on the perpendicular magnetic recording medium  10  will now be explained with reference to  FIG. 1B . The magnetic field applied from the main pole P 1  due to the coil C magnetizes the recording layer  13  in a perpendicular Z-axis direction to record data. The magnetic field passes through an intermediate layer  12  and a soft magnetic underlayer  11  and returns to the return pole P 2 . The perpendicular magnetic recording medium  10  travels in an X-axis direction continuously having information recorded on a predetermined track. Magnetic domains with independent magnetization directions are formed in the soft magnetic underlayer  11  made of a magnetic material. The magnetic field applied from the main pole P 1  and passing through the soft magnetic underlayer  11  affects the magnetic domains of the soft magnetic underlayer  11  thereby changing the magnetization directions thereof. After data is recorded on the recording layer  13 , the magnetic domains with the changed magnetization directions in the soft magnetic underlayer  11  may change the magnetization directions of magnetic domains in the recording layer  13 . In this case, the data retention characteristics of the recording layer  13  are degraded. Furthermore, the changed magnetization direction of the domains in the soft magnetic underlayer  11  leads to formation of magnetic domain walls. And such kind of domain walls formation is highly undesirable since it generate magnetic noise signal during the reading process. 
   Accordingly, there is an attempt to fix the magnetization direction of the soft magnetic underlayer  11  by forming an antiferromagnetic layer made of IrMn, a ferromagnetic layer made of NiFe, and a spacer layer made of Ru under the soft magnetic underlayer  11 . However, such an attempt increases the thickness of the perpendicular magnetic recording medium  10 , thereby increasing the thickness of a storage medium using multi-layered disks and complicating manufacturing processes. This also increases the manufacturing cost and complexity. Also, since the coupling constant between the ferromagnetic layer and the soft magnetic underlayer  11  is small, it is difficult to fix the magnetization direction of the soft magnetic underlayer  11 . 
   SUMMARY OF THE INVENTION 
   The present invention provides a perpendicular magnetic recording head configured such that the influence of a soft magnetic underlayer on a recording layer of a magnetic recording medium can be minimized. 
   According to an aspect of the present invention, there is provided a perpendicular magnetic recording head that moves in a track direction of a recording layer of a perpendicular magnetic recording medium. Here, the perpendicular magnetic recording head comprises: the perpendicular magnetic recording medium including a soft magnetic underlayer and the recording layer; a write head including a main pole that applies a magnetic field and writes information on the recording layer and a return pole having a first end which is connected to the main pole and a second end which is spaced apart from the main pole over an air bearing surface (ABS) of the perpendicular magnetic recording head which is adjacent to the recording layer; and at least one permanent magnet formed on at least one side of the write head. 
   The permanent magnet may be formed in the track direction of the write head. 
   The permanent magnet may be formed on both sides of the write head in the track direction. 
   A remnant magnetization of the permanent magnet may be less than 0.4 T. 
   The permanent magnet may include at least one of NbFeB, AlNiCo, Ferrite, and a rare-earth magnetic material. 
   The perpendicular magnetic recording head may further comprise at least one side shield formed on both sides of the permanent magnet in the track direction. 
   A magnetic field applied from the permanent magnet to the soft magnetic underlayer may be greater than 0.01 T. 
   A magnetic field applied from the permanent magnet to the recording layer may be less than 0.05 T. 
   A height of the permanent magnet from the ABS of the perpendicular magnetic recording head may be greater than 0.2 nm. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other aspects of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings, in which: 
       FIG. 1A  is a cross-sectional view of a conventional perpendicular magnetic recording head; 
       FIG. 1B  is an enlarged view of portion A of  FIG. 1A ; 
       FIG. 2A  is a cross-sectional view of a perpendicular magnetic recording head according to an exemplary embodiment of the present invention; 
       FIG. 2B  is a cross-sectional view illustrating an air bearing surface of the perpendicular magnetic recording head of  FIG. 2A ; 
       FIG. 3A  is a cross-sectional view illustrating a permanent magnet and side shields of the perpendicular magnetic recording head of  FIG. 2A  in a track direction of a recording medium; 
       FIG. 3B  is a cross-sectional view illustrating a magnetic field that is generated by the permanent magnet of the perpendicular magnetic recording head of  FIG. 2A  and that magnetically affects the recording medium; 
       FIG. 4  is a graph illustrating a relation between the strength Hy in tesla (T) of a magnetic field and the proportion My of magnetic domains magnetized in a cross-track direction (Y-axis) when the magnetic field is applied to magnetic domains of a soft magnetic underlayer which are magnetized by a magnetic field of 100 Oe according to an exemplary embodiment of the present invention; 
       FIG. 5  is a graph illustrating the strength of a magnetic field flowing through magnetic domains of a recording layer due to the magnetic field applied by the permanent magnet of the perpendicular magnetic recording head of  FIG. 2A  according to an exemplary embodiment of the present invention; and 
       FIG. 6  is a graph illustrating the strength of a magnetic field flowing through the soft magnetic underlayer due to the magnetic field applied by the permanent magnet of the perpendicular magnetic recording head of  FIG. 2A  according to an exemplary embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The thicknesses of layers or regions in the drawings are exaggerated for clarity. 
     FIG. 2A  is a cross-sectional view of a perpendicular magnetic recording head according to an exemplary embodiment of the present invention. Referring to  FIG. 2A , the perpendicular magnetic recording head includes a perpendicular magnetic recording medium  20  (referred to as recording medium hereinafter), a write head  200  for writing data on the recording medium  20 , and a read head  210  for reading data from the recording medium  20 . The recording medium  20  includes a soft magnetic underlayer  21 , an intermediate layer  22 , and a recording layer  23 . In  FIG. 2A , an X-axis denotes a track direction of the recording layer  23  of the recording medium  20 , and a Y-axis denotes a cross-track direction. 
   The write head  200  includes a main pole P 1 , a return pole P 2 , and a coil C. The main pole P 1  and the return pole P 2  write data on the recording layer  23  of the recording medium  20 . An auxiliary pole  201  may be formed on a side of the main pole P 1 . The coil C surrounds the main pole P 1 , and generates a magnetic field in the main pole P 1  to magnetize the recording layer  23  of the recording medium  20 . The read head  210  includes first and second magnetic shield layers SI and S 2  and a data reading magnetoresistance device  211  positioned between the first and second magnetic shield layers S 1  and S 2 . While data is read from a predetermined area of a selected track, the first and second magnetic shield layers SI and S 2  block a magnetic field generated by magnetic elements near the data reading magnetoresistance device  211  from reaching the predetermined area. The data reading magnetoresistance device  211  may be a giant magnetoresistance (GMR) or tunneling magnetoresistance (TMR) device. 
   The perpendicular magnetic recording head of the present exemplary embodiment is characterized in that permanent magnets  202   a  and  202   b  are formed on one or more sides in the track direction (X-axis) of the write head  200 . Referring to  FIG. 2A , the permanent magnets  202   a  and  202   b  are disposed on a left (should be the back side) side of the read head  210  and on a right (should be the front side) side of the write head  200  in the track direction, respectively. However, if the first permanent magnet  202   a  is disposed on a front side of the main pole P 1  in the track direction, the first permanent magnet  202   a  may be formed in any place irrespective of the position of the magnetoresistance device  211 . However, the first permanent magnet  202   a  should be disposed so that the magnetic field of the first permanent magnet  202   a  does not affect other magnetic elements. The first and second permanent magnets  202   a  and  202   b  may include at least one of NbFeB, AlNiCo, Ferrite, and a rare-earth material such as SmCo. The magnetization directions of the first and second permanent magnets  202   a  and  202   b  may be equal to the cross-track direction of the recording layer  23  of the recording medium  20 . 
     FIG. 2B  is a cross-sectional view illustrating an air bearing surface (ABS) of the magnetic head of  FIG. 2A . Referring to  FIG. 2B , the first and second permanent magnets  202   a  and  202   b  are formed on both sides of the read head  210  and write head  200  in the track direction (X-axis). An insulating material surrounds each of the first and second permanent magnets  202   a  and  202   b . The write head  200  and the read head  210  may be commonly used magnetic heads, and the perpendicular magnetic recording head of the present exemplary embodiment may be manufactured using a conventional manufacturing method by simply adding the first permanent magnet  202   a  before forming the magnetic heads and adding the second permanent magnet  202   b  after forming the return pole P 2 . 
   When the first and second permanent magnets  202   a  and  202   b  are formed, an external magnetic field may be applied to cause magnetization in the cross-track direction of the recording layer  23  of the recording medium  20 . Also, after the first and second permanent magnets  202   a  and  202   b  are formed, an external magnetic field may be applied to fix the magnetization directions of the first and second permanent magnets  202   a  and  202   b . In detail, if an external magnetic field is applied into a process chamber in which at least one of NbFeB, AlNiCo, Ferrite, and a rare-earth material such as SmCo is formed on a substrate by sputtering, the magnetic materials are magnetized in a direction in which the external magnetic field is applied. 
     FIG. 3A  is a cross-sectional view illustrating the first permanent magnet  202   a  or the second permanent magnet  202   b  of the perpendicular magnetic recording head of  FIG. 2A  in the track direction (X-axis). Here, the first and second permanent magnets  202   a  and  202   b  are collectively indicated by reference numeral  202 . Referring to  FIG. 3A , side shields  231  and  232  are formed on both sides of the permanent magnet  202 . 
   The side shields  231  and  232  optimize the influence of the permanent magnet  202  on the recording medium  20 . The side shields  231  and  232  may be formed of a soft magnetic material and may be formed on both sides of the permanent magnet  202  in the track direction. The second magnetic shield layer  52  may be used as the side shield  232 . The distance between each of the side shields  231  and  232  and the permanent magnet  202  (Sg) may range from 100 to 500 nm. The height of the permanent magnet  202  above the ABS of the side shields  231  and  232  (h) that face the recording layer  23  of the recording medium  20  may be greater than 25 nm. 
     FIG. 3B  is a cross-sectional view illustrating the magnetic field that is generated by the permanent magnet  202  of the perpendicular magnetic recording head of  FIG. 2A  and that affects the recording medium  20 . Referring to  FIG. 3B , the permanent magnet  202  is magnetized in the cross-track direction (Y-axis) of the recording layer  23 . The magnetic field applied from the permanent magnet  202  does not affect a track area of the recording layer  23 , but magnetizes the soft magnetic underlayer  21  in the cross-track direction (Y-axis). When the soft magnetic underlayer  21  is magnetized in the cross-track direction, the influence of the soft magnetic underlayer  21  on the magnetic domains of the recording layer  23  which are magnetized in the perpendicular direction can be reduced. The magnetized soft magnetic underlayer also reduce the magnetic domain wall noise during the reading process. The magnetic domain wall is moved away by the magnetic field from the permanent magnet  202 . 
   Referring to  FIGS. 2A and 3B , the recording medium  20  travels in the X-axis, and the first permanent magnet  202   a  first fixes the magnetization direction of the soft magnetic underlayer  21  to the cross-track direction (Y-axis). When information is written on the recording layer  23  by the main pole P 1 , the magnetization direction of the soft magnetic underlayer  21  is forced to change to the track direction (X-axis), but the second permanent magnet  202   b  fixes again the magnetization direction of the soft magnetic underlayer  21  to the cross-track direction (Y-axis). At this time, the magnetic field flowing through the recording layer  23  exits between tracks outside a track width TW of the recording layer  23  such that the influence on the recording layer  23  can be minimized. 
     FIG. 4  is a graph illustrating a relation between the strength Hy in tesla (T) of a magnetic field and the proportion My of magnetic domains magnetized in the cross-track direction when the magnetic field is applied to the magnetic domains of the soft magnetic underlayer  21  which are magnetized by a magnetic field of 100 Oe. 
   Referring to  FIG. 4 , when a magnetic field of 0.01 T is applied, the magnetization directions of 40% or more of the magnetic domains of the soft magnetic underlayer  21  are changed to the Y-axis. When the magnetization directions of 40% or more of the magnetic domains of the soft magnetic underlayer  21  are fixed to the Y-axis, that is, to the cross-track direction of the recording medium  20 , the influence on the recording layer  23  can be reduced significantly. Accordingly, it is preferable, but not necessary, that the strength of the magnetic field applied from the permanent magnet  202  to the soft magnetic underlayer  21  be greater than 0.01 T. 
     FIG. 5  is a graph illustrating a relation between a shield gap Sg, between the permanent magnet  202  and each of the side shields  231  and  232  (see  FIG. 3A ), and a magnetic field Hz affecting the recording layer  23  to obtain the influence of the magnetic field applied from the permanent magnet  202  of the perpendicular magnetic recording head of  FIG. 2A  on the magnetic domains of the recording layer  23 . Here, the height h of the permanent magnet  202  from the ABS is set to 0, 25, and 50 nm and the remnant magnetization M of the permanent magnet  202  is set to 0.2 and 0.4 T. 
   Referring to  FIG. 5 , when the height h of the permanent magnet  202  from the ABS is 0 nm, the magnetic field affecting the recording layer  23  of the recording medium  20  is relatively high. Also, when the strength of the magnetic field of the permanent magnet  202  is 0.4 T, the magnetic field affecting the recording layer  23  is high. Accordingly, it is preferable, but not necessary, that the remnant magnetization M of the permanent magnet  202  be less than 0.4 T. When the height of the permanent magnet  202  from the ABS is 25 nm or greater and the remnant magnetization M is 0.4 T or less, then the strength of the magnetic field affecting the recording layer  23  is less than 0.05 T. 
     FIG. 6  is a graph illustrating the strength of a magnetic field flowing through the soft magnetic underlayer  21  due to the magnetic field applied from the permanent magnet  202  of the perpendicular magnetic recording head of  FIG. 2A . The X-axis denotes the distance, that is, the shield gap Sg, between the permanent magnet  202  and each of the side shields  231  and  232 , and the Y-axis denotes the strength T of the magnetic field flowing through the soft magnetic underlayer  21  in the cross-track direction (Y-axis). The remnant magnetization M of the permanent magnet  202  is set to 0.2 and 0.4 T. 
   Referring to  FIG. 6 , when the shield gap Sg ranges from 100 to 500 nm, a magnetic field of 0.01 T or more flows through the soft magnetic underlayer  21 . When the height of the permanent magnet  202  from the ABS is 0, 25, or 50 nm, a magnetic field of 0.01 T or more flows through the soft magnetic underlayer  21 . 
   As a result, when the remnant magnetization M of the permanent magnet  202  is less than 0.4 T, the influence on the magnetic domains of the recording layer  23  can be reduced and the soft magnetic underlayer  21  can be effectively magnetized in the cross-track direction. To minimize the influence on the recording layer  23 , the height of the permanent magnet  202  from the ABSs may be greater than 0, and preferably, but not necessarily, 20 nm. 
   As described above, the perpendicular magnetic recording head of the present invention can fix the magnetization directions of the magnetic domains of the soft magnetic underlayer  21  to the cross-track direction without affecting the recording characteristics of the magnetic domains of the recording layer  23 . Accordingly, the magnetic domains of the soft magnetic underlayer  21  can be prevented from corrupting the magnetization direction of the recording layer  23  and reduce the magnetic domain wall noise during the reading process, and thus the retention characteristics and signal reliability of the recording medium  20  can be greatly improved. 
   While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill 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 following claims.