Abstract:
A magnetic head structure is disclosed which can avoid the problem of side erasing regardless of whether the skew angle is assigned to the positive side or negative side while ensuring write magnetic field intensity. The magnetic head includes at least two main magnetic poles having a single taper shape as a plane shape of a tip thereof opposite to a recording medium and axially symmetrically disposed with respect to a longitudinal direction of a slider, a return yoke for returning a write magnetic field generated by the main magnetic poles, and thin-film coils assigned to each of the main magnetic poles.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a magnetic head for perpendicular magnetic recording that can control side erasing without causing write magnetic field intensity to decrease and a magnetic disk apparatus using thereof. 
         [0003]    2. Description of the Related Art 
         [0004]    As storage technology makes progress in recent years, magnetic disk apparatuses including HDDs (hard disk drives) have been used, in addition to the conventional use of external recording apparatuses of personal computers, servers, and the like, for various application uses such as video recorders, portable music players, car navigation systems, game machines, and mobile phones. Thus, still higher recording densities will be demanded. Under such circumstances, adoption of the perpendicular magnetic recording has begun as a technology to meet the needs for higher recording density. 
         [0005]    Here, features of a recording medium and a magnetic head in the longitudinal magnetic recording and the perpendicular magnetic recording of conventionally used magnetic disk apparatuses will be described by comparing them. 
         [0006]    First, recording media will be described by comparing them. In the longitudinal magnetic recording, recorded bits are magnetized in a direction in which they are opposite each other with respect to adjacent recorded bits. Thus, there is a concern about degradation of thermal stability accompanying a reduced recorded bit volume caused by higher recording densities. In the perpendicular magnetic recording, on the other hand, recorded bits are magnetized in a direction in which they are stabilized with adjacent recorded bits. Thus, this is a recording mode effective in ensuring thermal stability. 
         [0007]    Also in the perpendicular magnetic recording, it becomes possible to abruptly draw a write magnetic field generated by a magnetic head to the recording medium side by forming a soft magnetic layer called a soft magnetic underlayer on the lower layer side of the recording layer. Thus, compared with a magnetic head of the longitudinal magnetic recording, effective write magnetic field intensity can be increased up to 1.5 to 2 times. Therefore, it becomes possible to have high coercivity imparted to the recording layer of recording medium, and low noise and thermal stability of the recording layer ensured. 
         [0008]    Next, magnetic heads will be described by comparing them. The magnetic head is a generic name for two mechanisms: a write head element part to record a read signal by applying a write magnetic field to a recording medium and a read head element part to detect a read signal from a recording medium. The read head element part detects a read signal using a magneto-resistive effect by arranging a GMR (Giant Magneto Resistance) or TuMR (Tunneling Magneto Resistance) element between upper and lower magnetic shield layers playing a role of absorbing unnecessary signals (magnetic fields) excluding the read signal. Meanwhile, there is no major difference between a mechanism of the longitudinal magnetic recording and that of the perpendicular magnetic recording of the read head element part. 
         [0009]    The write head element part, on the other hand, has a major difference between the mechanism of the longitudinal magnetic recording and that of the perpendicular magnetic recording. In the longitudinal magnetic recording, a ring write magnetic element having a gap is used to apply a write magnetic field in an in-plane (longitudinal) direction from the gap for recording. In the perpendicular magnetic recording, on the other hand, a single pole type write magnetic element comprising a main magnetic pole disposed perpendicular to a recording medium and a return yoke (return pole) used for forming a magnetic circuit by refluxing a write magnetic field applied in a vertical direction from the main magnetic pole via a soft magnetic underlayer of the recording medium is used for recording. 
         [0010]    In order to improve performance of the write head element part of the perpendicular magnetic recording, proposals such as a trailing shield type write magnetic element, which has a modified return yoke form, and a cusp coil type write magnetic element, which has a modified coil form, have been made and such proposals will be described below. 
         [0011]    The trailing shield type write magnetic element shown in FUJITSU, vol. 56, no. 4, pp. 286-291, 2005, for example, is characterized in that a soft magnetic material made of, for example, Ni—Fe group alloy is formed in such a manner that the soft magnetic material stretches to the return yoke toward the main magnetic pole side. By absorbing unnecessary write magnetic fields generated by the main magnetic pole toward the recording medium, the trailing shield type write magnetic element plays a role of making a write magnetic field gradient steeper. 
         [0012]    The cusp coil type write magnetic element shown in IEEE Trans. Magn., vol. 36, no. 5, pp. 2520-2523, 2000, for example, is characterized in that a thin film coil and a return yoke are disposed both on the trailing side and leading side with respect to the main magnetic pole in such a way that the main magnetic pole is sandwiched. By adopting such a head structure, the main magnetic pole can efficiently be magnetized and write magnetic field intensity of the main magnetic pole can be increased. 
         [0013]    Compared with the longitudinal magnetic recording system for both the recording medium and magnetic head, as described above, the perpendicular magnetic recording system has an advantage of higher recording densities of magnetic disk apparatus. However, the write head element part of a magnetic head of the perpendicular magnetic recording has a geometric problem in the plane shape of a tip of the main magnetic pole viewed from an air bearing surface side of the magnetic head and the problem will be described below. 
         [0014]      FIG. 1  shows a general internal outline structure of an HDD, which is a type of magnetic disk apparatus.  FIG. 2  is a diagram showing how a skew angle by a rotary actuator system is assigned. The HDD generally uses a rotary actuator  21  shown in  FIG. 2  as a way of causing the magnetic head to move to a desired recorded track position on a recording medium. Thus, about 15° on both the positive side and negative side will usually be assigned as a skew angle  24  of a magnetic head  23  mounted on a suspension  22  together with a slider. The skew angle is defined as a positive side when an air stream generated between the recording medium and magnetic head enters an outer circumferential leading edge of the magnetic head and gets out of an innermost circumferential trailing edge. That is, when the magnetic head is positioned at a recorded track  25  on the inner circumferential side of the recording medium, the skew angle is assigned to the positive side. When the magnetic head is positioned at a recorded track  26  on the outer circumferential side of the recording medium, the skew angle is assigned to the negative side. 
         [0015]      FIG. 3  is a perspective view of a tip portion of a main magnetic pole of a conventional write head element part. The plane shape of the main magnetic pole is rectangular.  FIG. 4  shows how the main magnetic pole in  FIG. 3  follows a recorded track on a recording medium. In  FIG. 4 , a plane shape  32  of the tip of a main magnetic pole  31  of the write head element part is rectangular with a long side in the longitudinal direction of the slider. If here a skew angle is assigned, the main magnetic pole  31  will be at some angle with a traveling direction  34  of the recorded track  25  on the inner circumferential side and the recorded track  26  on the outer circumferential side. Accordingly, a portion of the plane of the main magnetic pole tip geometrically protrudes from the recorded track and therefore, a problem arises that an area, that is, a side erase occurrence area  33  in which recorded signals and servo signals on adjacent tracks are deleted occurs. 
         [0016]    To address this problem, a method by which adjacent tracks are geometrically made less susceptible when a skew angle is assigned by changing the plane shape of the tip of the main magnetic pole to a trapezoidal double taper shape or single taper shape using (FIB Focused Ion Beam) processing or plating has been proposed (See, for example, Japanese Patent Application Laid-Open No. 2004-94997). 
         [0017]    However, since write magnetic field intensity is generally proportional to a plane area of the tip of the main magnetic pole viewed from the air bearing surface side, a problem arises that processing of the tip to a taper shape makes the area smaller and thus reduces write magnetic field intensity. In this case, the recording layer of the recording medium cannot be sufficiently magnetized, creating a new problem of causing degradation of signal quality. 
         [0018]      FIG. 5  is a perspective view of the tip portion of a main magnetic pole having a conventional single taper shape.  FIG. 6  is a diagram showing how the main magnetic pole in  FIG. 5  follows a recorded track on the recording medium. If the single taper shape is adopted for a plane shape  41  of the tip of the main magnetic pole to have write magnetic field intensity maintained, as shown in  FIG. 6 , the problem of side erasing can be controlled only for one polarity of the positive side or negative side of the skew angle.  FIG. 7  is a perspective view of the tip portion of a main magnetic pole having a double taper shape.  FIG. 8  is a diagram showing how the main magnetic pole in  FIG. 7  follows a recorded track on the recording medium. If the double taper shape is adopted for a plane shape  51 , as shown in  FIG. 8 , the problem of side erasing can be avoided for the skew angle of both the positive side and negative side, but the plane area of the tip of the main magnetic pole viewed from the air bearing surface side becomes too small. Thus, a problem of extremely reduced write magnetic field intensity arises. 
         [0019]    As has been described above, controlling side erasing when the skew angle of the magnetic head is assigned and ensuring write magnetic field intensity are in a trade-off relationship and it is difficult to realize both at the same time. This problem becomes more serious as the track density increases, that is, the magnetic disk apparatus has higher-density recording. 
         [0020]    It is an object of the present invention to realize a magnetic head structure which can avoid the problem of side erasing regardless of whether the skew angle is assigned to the positive side or negative side while ensuring write magnetic field intensity. 
       SUMMARY 
       [0021]    In accordance with an aspect of an embodiment, a magnetic head that includes at least two main magnetic poles having a single taper shape as a plane shape of a tip thereof opposite to a recording medium and axially symmetrically disposed with respect to a longitudinal direction of a slider, a return yoke for returning a write magnetic field generated by the main magnetic poles, and thin-film coils assigned to each of the main magnetic poles. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a general internal outline structure of an HDD, which is one of magnetic disk apparatuses; 
           [0023]      FIG. 2  is a diagram showing how a skew angle by a rotary actuator system is assigned; 
           [0024]      FIG. 3  is a perspective view of a tip portion of a main magnetic pole of a conventional write head element part; 
           [0025]      FIG. 4  shows how the main magnetic pole in  FIG. 3  follows a recorded track on a recording medium; 
           [0026]      FIG. 5  is a perspective view of the tip portion of a main magnetic pole having a conventional single taper shape; 
           [0027]      FIG. 6  is a diagram showing how the main magnetic pole in  FIG. 5  follows a recorded track on the recording medium; 
           [0028]      FIG. 7  is a perspective view of the tip portion of a main magnetic pole having a conventional double taper shape; 
           [0029]      FIG. 8  is a diagram showing how the main magnetic pole in  FIG. 7  follows a recorded track on the recording medium; 
           [0030]      FIG. 9  is a sectional view of a magnetic head in a first embodiment of the present invention; 
           [0031]      FIG. 10  is a top view from an air bearing surface side of the magnetic head in the first embodiment; 
           [0032]      FIG. 11  is a perspective view clarifying physical relationships among a main magnetic pole brace layer, a joint part, thin-film coils, a first main magnetic pole and a second main magnetic pole, and an inter-main magnetic pole magnetic shield of the magnetic head in the first embodiment; 
           [0033]      FIG. 12  is a diagram showing how a main magnetic pole having the shape of the main magnetic pole in  FIG. 11  follows a recorded track on the recording medium; 
           [0034]      FIG. 13  is a sectional view of a magnetic head having a cusp coil type write head element part that can be applied to the magnetic head in the first embodiment; 
           [0035]      FIG. 14  is a block diagram of a magnetic head switching control circuit, which is to be a second embodiment of the present invention, for controlling the magnetic head in the first embodiment; and 
           [0036]      FIG. 15  is a diagram from which the magnetic head switching control circuit in the second embodiment selects a write driver to be used based on head address information and cylinder address information. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0037]    Embodiments of the present invention will be described below with reference to  FIG. 9  or  FIG. 15 . The general sputtering process, plating process or the like is used as the formation process of each layer described below. Moreover, each layer can be processed to a desired shape using a patterning process using a resist film and lithography or the like. Thus, details of the formation process of each layer are omitted. 
         [0038]      FIG. 9  is a sectional view of a magnetic head in a first embodiment of the present invention. Though not shown in  FIG. 9 , the sputtering process is used to form an alumina layer made of Al 2 O 3  with a thickness of about 2 μm as an insulating layer on an alumina/titanium carbide layer made of Al 2 O 3 —Ti—C with the thickness of about 2 mm. Next, a lower magnetic shield  71 ( a ) made of soft magnetic material such as Ni—Fe is formed on the insulating layer using the plating process. Next, though not shown, the sputtering process is used to form an alumina layer to be a first read gap on the lower magnetic shield  71 ( a ) side with the thickness of about 0.6 μm. Next, a read element  72  of GMR or TuMR with a general structure is formed so that the read element  72  is disposed near a recording medium  70 . Also, though not shown, a pair of electrode layers electrically connected to the read element  72  is formed. Next, though not shown, the sputtering process is used to form an alumina layer to be a second read gap on an upper magnetic shield  71 ( b ) side with the thickness of about 0.6 μm. Next, like the lower magnetic shield  71 ( a ), the upper magnetic shield  71 ( b ) made of soft magnetic material is formed. 
         [0039]      FIG. 10  is a top view of the magnetic head in the first embodiment viewed from the air bearing surface side. Here, the read element  72  may be mounted at any position because the position of the magnetic head with respect to the recorded track can be determined by correcting an amount of offset of the read head element part and write head element part when reading a recorded signal. Here, the read element  72  was mounted in a center position of the upper and lower magnetic shields  71 ( a ) and  71 ( b ). A read head element part has been prepared by the above steps with the read element  72  of GMR or TuMR sandwiched by the upper and lower magnetic shields  71 ( a ) and  71 ( b ) via an insulating layer. 
         [0040]    A method of forming a write head element part will be described below. First, an alumina layer (not shown) is formed with the thickness of 0.3 μm on the upper magnetic shield  71 ( b ) in  FIG. 9 . Next, a magnetic shield  73  of the write head element made of soft magnetic material such as Hi-Fe is formed using the plating process. Next, a main magnetic pole brace layer  74 , a joint part  76 , thin-film coils  77 , and a return yoke  78  that play a role of supporting first and second main magnetic poles  64  and  65  are formed using the plating process. Here, a Ni—Fe, Co—Fe, or Co—Fe—B group alloy can be selected as a material of the main magnetic pole. Though not shown, a blank portion among the main magnetic pole, joint part  76 , thin-film coils  77 , and return yoke  78  is filled with an alumina layer using the sputtering process or plating process. Meanwhile, in the embodiments of the present invention, a soft magnetic material layer  75  made of Ni—Fe or the like is formed to make a trailing shield type head in order to make the magnetic field gradient steep. Here, since the present invention has two main magnetic poles, each layer of the write head element part is formed symmetrically with respect to an inter-main magnetic pole magnetic shield  66  made of soft magnetic material such as Ni—Fe in  FIG. 10 . Meanwhile, the sputtering process or plating process is used to have a space between the first main magnetic pole  64  and second main magnetic pole  65  filled with an alumina layer. 
         [0041]    In  FIG. 10 , the distance between centers of two main magnetic pole planes  61  and  67  was set to 100 nm. If the distance is longer than this, the two main magnetic poles will hardly interact magnetically even if the inter-main magnetic pole magnetic shield  66  is not formed. Thus, no problem will be caused if the inter-main magnetic pole magnetic shield  66  is not formed. However, the read element  72  and the main magnetic pole parts being too far apart is not preferred from the standpoint of design of a magnetic disk apparatus because the amount of offset for determining the position of the magnetic head with respect to a recorded track will be too large. 
         [0042]      FIG. 11  is a perspective view clarifying physical relationships among the main magnetic pole brace layer  74 , joint part  76 , thin-film coils  77 , first main magnetic pole  64  and second main magnetic pole  65 , and inter-main magnetic pole magnetic shield  66  of the magnetic head in the first embodiment. Here, the first main magnetic pole  64  and second main magnetic pole  65  are axially symmetric with respect to a longitudinal direction  95  of the slider. The single taper shape in the plane of the tip of the main magnetic pole is processed into a shape in which the main magnetic pole becomes wider from a leading side  62  to a trailing side  63 , which is a traveling direction of the magnetic head relative to the recording medium. Meanwhile, dimensions and the taper angle of the tip of the main magnetic pole should suitably be designed based on the degree of skew angle assigned to the magnetic disk and the track density. Here, an upper side  91  was set to 160 nm, a taper angle  92  to 60°, a height  93  to 190 nm, and a lower side  94  to 130 nm. 
         [0043]      FIG. 12  is a diagram showing how a main magnetic pole of the main magnetic pole in  FIG. 11  follows a recorded track on the recording medium. As shown in  FIG. 12 , in a positive skew angle area on the inner circumferential side of the recording medium, recording is performed on a predetermined recorded track by causing the first main magnetic pole  64  to generate a write magnetic field disposed in such a way that the plane of the tip of the main magnetic pole is like a taper shape toward an inner circumferential direction  68  of the recording medium. In this case, the plane  61  of the first main magnetic pole is within the recorded track  25  on the inner circumferential side. Thus, the side erase occurrence area can be eliminated. In a negative skew angle area on the outer circumferential side of the recording medium, recording is performed by the second main magnetic pole  65  disposed in such a way that the plane of the tip of the main magnetic pole is like a taper shape toward an outer circumferential direction  69  of the recording medium. The plane  67  of the second main magnetic pole is within the recorded track  26  on the outer circumferential side. Thus, the side erase occurrence area can be eliminated. Furthermore, for an area where the skew angle is 0°, recording can be performed using any of the main magnetic poles. 
         [0044]    As an application of the embodiments of the present invention, various magnetic poles can be used for different purposes depending on the skew angle by forming a plurality of main magnetic poles with different skew angles in consideration of side erasing when the track density increases due to higher recording densities of the magnetic disk apparatus. Also in this case, the taper angle may be designed in accordance with the degree of assigned skew angle. That is, the taper angle may be increased for a zone to which a large skew angle is assigned.  FIG. 13  shows a sectional view of a magnetic head having a cusp coil type write head element part that can be applied to the magnetic head in the first embodiment. In the embodiments of the present invention, as shown in  FIG. 11 , the application is easy because it is sufficient to form two main magnetic poles symmetrically with respect to a recorded track method. 
         [0045]    According to the present embodiment, an occurrence of side erasing can be controlled without lowering write magnetic field intensity by using the first main magnetic pole  64  and second main magnetic pole  65  for different purposes in accordance with the polarity of the skew angle. 
         [0046]    Next, when using a magnetic head of the present invention in a magnetic disk apparatus, it is necessary to selectively use two main magnetic poles depending on the polarity of assigned skew angle. A control method thereof will be described below. 
         [0047]      FIG. 14  is a block diagram of a magnetic head switching control circuit, which is to be a second embodiment of the present invention, for controlling the magnetic head in the first embodiment. This block diagram is a block diagram for controlling a plurality of magnetic heads in order to actually use the magnetic heads in a magnetic disk apparatus. Here, a method of using two magnetic heads, a first magnetic head  132  and a second magnetic head  133 , will be described. In each of the first magnetic head  132  and second magnetic head  133 , the read element  72 , first main magnetic pole  64 , and second main magnetic pole  65  are mounted. Though not shown, a bias current source applied to the read head element part and a write current source applied to the write head element part are disposed in a head amplifier IC part  131 . Here, a normal read method by which the read element  72  of the first magnetic head  132  or second magnetic head  133  amplifies a read signal from a recording medium using read amplifier parts  127  and  130  and sends data to a read/write channel LSI part  121  via a read data buffer part  124  is used. 
         [0048]    Though not shown, the read/write channel LSI part  121  has functions to code write data before sending the write data to a write data buffer part  123  disposed in the head amplifier IC part  131  and to decode read data received from the read data buffer part  124 . The read/write channel LSI part  121  also has a head address control part for selecting a magnetic head to be used for a recording medium with a plurality of surfaces disposed in a magnetic disk apparatus. Meanwhile, the read/write channel LSI part  121  also has a signal processing circuit part of the PRML (Partial Response Maximum Likelihood). Though not shown, a microcomputer part  120  has a cylinder address control part of recording tracks of a recording medium. The microcomputer part  120  also has control parts of interfaces and LSI parts. 
         [0049]    Here, a magnetic head switching control circuit  122  disposed in the head amplifier IC part  131  acquires cylinder address information of recording tracks from the microcomputer part  120 . The magnetic head switching control circuit  122  acquires head address information from the read/write channel LSI part  121 . The magnetic head switching control circuit  122  selects either of the first magnetic head  132  and second magnetic head  133  to be used based on the head address information. The selected magnetic head has two main magnetic poles. Thus, the magnetic head switching control circuit  122  determines the polarity of the skew angle of the recording track where a record should be made based on the cylinder address information to select write drivers  125  and  128  for the positive skew angle area of the first main magnetic pole  64  or write drivers  126  and  129  for the negative skew angle area of the second main magnetic pole  65  to be used. With this operation, a recording operation to the recording medium is performed. 
         [0050]      FIG. 15  shows a diagram from which the magnetic head switching control circuit  122  in the second embodiment selects a write driver to be used based on head address information and cylinder address information. As shown in  FIG. 15 , a plurality of magnetic heads having two or more main magnetic poles in the present invention can be controlled by entering head address information and cylinder address information in the magnetic head switching control circuit  122 .