Abstract:
A magnetic head, according to one embodiment, includes a main magnetic pole having a protruding portion such that a distance from a first side of a trailing edge of the main magnetic pole to a leading edge of the main magnetic pole is different from a distance from a second side of the trailing edge of the main magnetic pole to the leading edge of the main magnetic pole, an auxiliary magnetic pole, and a coil wound around a magnetic circuit, the magnetic circuit including the main magnetic pole and the auxiliary magnetic pole. In another embodiment, a disk drive system includes a magnetic storage medium, at least one magnetic head as described previously for writing to the magnetic medium, a slider for supporting the magnetic head, and a control unit coupled to the magnetic head for controlling operation of the magnetic head. Additional systems and heads are also presented.

Description:
FIELD OF THE INVENTION 
     The present invention relates to magnetic recording, and more particularly, to a magnetic head having an asymmetrical shape used in perpendicular shingled recording. 
     BACKGROUND OF THE INVENTION 
     High-density recording technology for magnetic disk devices has made significant progress in recent years, including remarkable advances in the miniaturization of the magnetic poles included with the magnetic recording heads. However, since a correlation between the strength of the recording magnetic field generated by the magnetic recording head and the volume of the magnetic pole exists, a problem arises in that increased miniaturization of the magnetic pole makes it more difficult to maintain the strength of the recording magnetic field. 
     Thermally-assisted recording has been developed as one way of dealing with this problem. Thermally-assisted recording works by heating the magnetic recording medium as recording takes place to reduce the coercive field strength, and is a method of recording which reduces the magnetic field strength required for writing. Moreover, more recently a microwave-assisted recording system has been proposed as another form of assisted recording which uses spin torque to enable recording densities greater than 1 Tb/in 2 . With this system, a high-speed magnetized rotor which rotates at high speed is positioned adjacent to the main magnetic pole of a perpendicular magnetic recording head, with microwaves being radiated onto the magnetic recording medium, recording data on a magnetic recording medium, which has large magnetic anisotropy. Application to the medium of microwaves generated by an oscillator means that the magnetic field required for magnetic reversal in the medium is reduced. This indicates that the strength of the recording magnetic field generated by the main magnetic pole of the magnetic recording head can be less than that required in other conventional devices not using microwaves. 
     Moreover, as cited both in U.S. Pat. No. 7,443,625 and Tagawa Kanai et al.,  SRC  27 th    Technical Report Materials,  May 2009, the shingled recording system has been proposed as another high-density recording system. With the shingled system, the tracks recorded in the magnetic recording medium by the magnetic head are partially overlapped. This enables a magnetic recording device to have a track pitch smaller than the tracks recorded. It is also considered possible to use a perpendicular magnetic recording device in which the width of the magnetic pole of the recording head is wider than in conventional devices. 
     In light of the above situation, it would be beneficial to have a magnetic head that can produce a sufficient recording magnetic field strength while being operated in recently developed systems, such as microwave-assisted recording systems and shingled recording systems. 
     SUMMARY OF THE INVENTION 
     In one embodiment, a magnetic head includes a main magnetic pole having a protruding portion such that a distance from a first side of a trailing edge of the main magnetic pole to a leading edge of the main magnetic pole is different from a distance from a second side of the trailing edge of the main magnetic pole to the leading edge of the main magnetic pole, an auxiliary magnetic pole, and a coil wound around a magnetic circuit, the magnetic circuit including the main magnetic pole and the auxiliary magnetic pole. 
     In another embodiment, a magnetic head includes a main magnetic pole having a protruding portion such that a distance from a first side of a trailing edge of the main magnetic pole to a leading edge of the main magnetic pole is different from a distance from a second side of the trailing edge of the main magnetic pole to the leading edge of the main magnetic pole, an auxiliary magnetic pole, and a coil wound around a magnetic circuit, the magnetic circuit including the main magnetic pole and the auxiliary magnetic pole. The protruding portion of the main magnetic pole is comprised of a magnetic material having a higher degree of saturated flux density than the remainder of the main magnetic pole. Also, the protruding portion of the main magnetic pole is comprised of a magnetic material having a higher iso-magnetic permeability than the remainder of the main magnetic pole, and a magnetic body is positioned towards the trailing side of the main magnetic pole and towards a track width side of the main magnetic pole. 
     Any of these embodiments may be implemented in a magnetic data storage system such as a disk drive system, which may include a magnetic head, a drive mechanism for passing a magnetic medium (e.g., hard disk) over the magnetic head, and a controller electrically coupled to the magnetic head. 
     Other aspects and advantages of the present invention will become apparent from the following detailed description, which, when taken in conjunction with the drawings, illustrate by way of example the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an oblique view of a magnetic disk device, according to one embodiment. 
         FIG. 2  is a diagram showing the front end of a head assembly, according to one embodiment. 
         FIGS. 3(   a )-( b ) show several views of a portion of a magnetic head, according to one embodiment. 
         FIG. 4  is a cross-sectional view of a magnetic head at the track center, according to one embodiment. 
         FIG. 5  shows iso-magnetic field curves illustrating an effect of using the magnetic head, according to one embodiment. 
         FIG. 6  shows iso-magnetic field curves illustrating an effect of using a magnetic head, according to a comparative example. 
         FIG. 7  shows magnetic gradients illustrating an effect of using the magnetic head, according to one embodiment. 
         FIG. 8  is a plan view of the magnetic head seen from the floating surface, according to one embodiment. 
         FIG. 9  shows iso-magnetic field curves illustrating an effect of using the magnetic head, according to one embodiment. 
         FIG. 10  is an oblique view of the tip of a main magnetic pole in a magnetic head, according to one embodiment. 
         FIG. 11  is a plan view of a magnetic head seen from the floating surface, according to one embodiment. 
         FIG. 12  is a plan view of the magnetic head seen from the floating surface, according to one embodiment. 
         FIGS. 13(   a )-( c ) show a diagram of a construction process of a magnetic head, according to one embodiment. 
         FIGS. 14(   a )-( c ) show a schematic diagram illustrating the overlapping of tracks in a shingled magnetic recording system. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is made for the purpose of illustrating the general principles of the present invention and is not meant to limit the inventive concepts claimed herein. Further, particular features described herein can be used in combination with other described features in each of the various possible combinations and permutations. 
     Unless otherwise specifically defined herein, all terms are to be given their broadest possible interpretation including meanings implied from the specification as well as meanings understood by those skilled in the art and/or as defined in dictionaries, treatises, etc. 
     It must also be noted that, as used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless otherwise specified. 
     In one general embodiment, a magnetic head includes a main magnetic pole having a protruding portion such that a distance from a first side of a trailing edge of the main magnetic pole to a leading edge of the main magnetic pole is different from a distance from a second side of the trailing edge of the main magnetic pole to the leading edge of the main magnetic pole, an auxiliary magnetic pole, and a coil wound around a magnetic circuit, the magnetic circuit including the main magnetic pole and the auxiliary magnetic pole. 
     In another general embodiment, a magnetic head includes a main magnetic pole having a protruding portion such that a distance from a first side of a trailing edge of the main magnetic pole to a leading edge of the main magnetic pole is different from a distance from a second side of the trailing edge of the main magnetic pole to the leading edge of the main magnetic pole, an auxiliary magnetic pole, and a coil wound around a magnetic circuit, the magnetic circuit including the main magnetic pole and the auxiliary magnetic pole. The protruding portion of the main magnetic pole is comprised of a magnetic material having a higher degree of saturated flux density than the remainder of the main magnetic pole. Also, the protruding portion of the main magnetic pole is comprised of a magnetic material having a higher iso-magnetic permeability than the remainder of the main magnetic pole, and a magnetic body is positioned towards the trailing side of the main magnetic pole and towards a track width side of the main magnetic pole. 
     A shingled recording system, according to one embodiment, is a device in which tracks are recorded onto a magnetic recording medium by a magnetic head with the tracks partially overlapping. A magnetic recording device can be created which has a track pitch smaller than the tracks being recorded. It is also possible to have a magnetic head with a magnetic pole wider than those used in conventional magnetic recording devices by designing the magnetic pole differently. However, as the tracks are recorded in an overlapped fashion, the quality of the recording magnetic field is more important at the edges of the tracks than in the middle. 
     With conventional perpendicular recording heads, the strength and gradient of the magnetic field is large at the center of the track. For this reason, if a perpendicular magnetic recording head having a conventional structure is used as a shingled recording head, a difficulty arises where the good characteristics of the recording head will not be utilized. To improve recording performance, it is desirable to concentrate the distribution of the magnetic field more to the edge portions of the main magnetic pole of the recording head. Japanese Patent Office Pub. No. 2006-323899 and Tagawa Kanai et al.;  SRC  27 th    Technical Report Materials , May 2009, cite devices where a side shield is fitted to one side only, but further improvements to the head are desirable. 
     Taking note of the above situation, it is desirable to have a magnetic pole design for a magnetic recording head suitable for a shingled magnetic recording system in which the quality of the magnetic field in the vicinity of the track edges is improved. A magnetic head, according to one embodiment, has a structure whereby the distances from the leading edge to the left and right ends of the trailing side of the main magnetic pole are different. 
     In another embodiment, the trailing side of the main magnetic pole is provided with a protrusion or a step on one side only. Furthermore, the saturated magnetic flux density of the protruding portion of the main magnetic pole is large. In another embodiment, the magnetic permeability of the protruding portion of the main magnetic pole is high. 
     According to one embodiment, it is possible to provide a magnetic recording head suitable for a shingled magnetic recording system in which the magnetic gradient in the vicinity of the track edges is improved. 
     An embodiment of the magnetic disk device, head assembly, and head slider on which the magnetic recording head is mounted is described with reference to the drawings. 
       FIG. 1  shows an oblique view of a magnetic disk device  1 . In  FIG. 1 , the top cover is not shown. Magnetic recording medium  2  and head assembly  4  are accommodated within the chassis of the magnetic disk device  1 . Magnetic recording medium  2  is attached to a spindle motor  3  which is provided on the bottom of the chassis. Head assembly  4  is supported on bearings so as to be rotatable adjacent to the magnetic recording head  2 . The front end of this head assembly  4  is provided with a suspension arm  5 , the tip of which supports a head slider  10 . At the same time, a coil motor  7  is provided at the rear end of head assembly  4 , such as a voice coil motor. The coil motor  7  is the drive source which rotates the head assembly  4 , and moves the head slider  10  across the magnetic recording medium  2  in an approximately radial direction. 
       FIG. 2  is a schematic diagram illustrating the front end of a head assembly  4 . In the diagram, directions X, Y, and Z, respectively, show the longitudinal, lateral, and depth directions for the head slider  10 . Of these, direction Z corresponds to the direction of float for the head slider  10 . Moreover, directions X and Y essentially correspond, respectively, to the rotational and diametric directions (in other words, the longitudinal and lateral directions of the track) of the magnetic recording head  2 . Furthermore, arrow DR shows the direction of rotation of the magnetic recording medium  2 , arrow LD shows the leading direction of the head slider  10 , and arrow TR shows the trailing direction of the head slider  10 . 
     Head slider  10  is supported at the tip of the suspension arm  5 . With this head slider  10 , surface  10   a , which faces disk-shaped medium  2 , is known as an Air Bearing Surface (ABS) and floats above the rotating disk-shaped medium  2  due to the wedge effect of a gas, such as air. This head slider  10  is provided with a slide base  12  of a flattened orthogonal shape comprised of sintered aluminum, titanium carbide, etc., and thin film section  14  is formed using a thin-film forming method on the end surface of the trailing side of the slide base  12 . 
       FIG. 4  is a schematic cross-sectional view showing the main parts of the thin film ( 14 ,  FIG. 2 ) provided on the trailing section of the head slider  10 . A recording head ( 32 ,  FIG. 4 ) is provided with a pillar  323  comprising a magnetic body between a main magnetic pole  321  and an auxiliary magnetic pole  325 . The main magnetic pole  321 , auxiliary magnetic pole  325  and pillar  323  are comprised of a soft magnetic material, such as permalloy, CoFe alloy, etc. The main magnetic pole  321  is attached to a tip section  327  via a yoke  326 . Tip section  327  extends as far as the medium-facing surface  10   a  of the head, its tip surface  327   a  appearing on the medium-facing surface  10   a . The trailing side and side edge of the tip section  327  are provided with a side shield  38  and a trailing shield  39  to enhance the magnetic gradient. Playback head  34  contains a playback element  341  comprising a magnetic resistance effect element and a pair of magnetic shields  343 ,  344  which surround the magnetic resistance effect element. Furthermore, shield  37  comprising a magnetic body is provided with the purpose of reducing influx of the recording magnetic field into the magnetic shield  344 . 
     The main magnetic pole  321  is magnetized by a coil  329  wound around the yoke  326 , with the recording magnetic field being generated from the tip surface  327   a  of the tip section  327 . The recording magnetic field generated from the tip section  327  penetrates magnetic recording layer  21  and intermediate layer  22  of the magnetic disk  2  perpendicularly, and is returned at the soft magnetic reversing layer  23 , being absorbed by the auxiliary magnetic pole  325 . The recording is magnetized and written into magnetic recording layer  21  by the recording magnetic field generated from the tip section  327 . 
       FIGS. 3(   a )-( b ) show several views of the magnetic recording head, in some embodiments.  FIG. 3(   a ) is an overall plan view of the main parts of the thin film  14  seen from the floating surface, and  FIG. 3(   b ) is an enlarged view showing the vicinity of the end section of the main magnetic pole. The end section of the main magnetic pole, according to one embodiment, has a structure whereby the distances from the leading edge to a first and second end of the trailing side of the main magnetic pole are different. In other words, the main magnetic pole has a structure such that L 1  shown in  FIG. 3(   b ) is larger than L 2 . For purposes of explanation, and not limiting in any way, the first and second ends will be described as the left and right ends of the trailing side of the main magnetic pole, as depicted in  FIG. 3(   b ), for use in shingled recording systems where the tracks are written from the right to left. However, the protruding portion of the main magnetic pole may be on either side of the main magnetic pole, and is not limited to a left or right side as described herein. Thus, if the tracks are written from the left to the right, the protruding portion  328  may be positioned on the left side of the main magnetic pole. 
     With continued reference to  FIG. 3(   b ), this type of structure is possible due to the projecting portion  328 . Moreover, the structure of the side shield is such that it is only provided on the L 1  side, according to one approach. Of course, a shield may be provided on other sides of the main magnetic pole as well. By arranging the magnetic head in this way, it is possible to provide a magnetic recording head suitable for shingled magnetic recording in which the magnetic field gradient is improved in the vicinity of the track edges. 
       FIG. 5  is a diagram showing results of three-dimensional magnetic field calculation of magnetic field strength applied to the magnetic recording medium device of the magnetic head, according to one embodiment. 
     The calculation is performed as follows, with reference to  FIG. 4 . The magnetic field generated from the main magnetic pole  321  including the tip section  327  is calculated in a three-dimensional magnetic field calculation which uses the limited element method. The gap between the tip section  327  of main magnetic pole  321  and the trailing shield  39  is about 25 nm. The gap between the tip section  327  of the main magnetic field  321  and the side shield  38  is about 40 nm. The width of the end section of the trailing side of the end surface  327   a  of the main magnetic pole  321  is about 80 nm. End surface  327   a  of the main magnetic pole  321  is bevelled to an angle α of about 9°, giving it a reverse trapezoidal shape in which the width of the leading edge end is narrower than the width of the trailing side end. The material of tip section  327  of the main magnetic pole  321  is assumed to be CoNiFe (but is not so limited), with a saturated magnetic flux density of 2.4 T, and relative magnetic permeability of 100. Yoke section  326  of the main magnetic pole  321  is assumed to be 80 at % Ni-20 at % Fe (but not so limited) with a saturated magnetic flux density of 1.0 T. For the auxiliary magnetic pole  325 , the saturated magnetic flux density of the material is assumed to be 1.0 T, with the width in the Y direction being about 30 μm, the length in the Z direction about 16 μm, and the length in the X direction about 2 μm. 
     Moreover, magnetic shields  343 ,  344  of the playback head, and shield  37  are assumed to be 80 at % Ni-20 at % Fe (but not so limited) with a saturated flux density of 1.0 T, the width in the Y direction being about 32 μm, the length in the Z direction about 16 μm, and the length in the X direction about 1.5 μm. The magnetic material for the magnetic body  38  is assumed to be 45 at % Ni-55 at % Fe (but not so limited), with a saturated flux density of 1.7 T and relative magnetic permeability of 1000. The thickness of the trailing shield  39  and the side shield  38  is about 200 nm. The number of windings on coil  329  is assumed to be 4 turns, with the recording current being about 35 mA. The soft magnetic under layer  23  of the magnetic disk  2  is made of a material with a saturated flux density of 1.1 T, and a thickness of about 40 nm is assumed. The thickness of the magnetic recording layer  21  is about 19 nm. The thickness of the intermediate layer  22  is about 22 nm. It is presumed that the head slider  10  will float by about 9 nm. Thus the distance between the surface of the under layer  23  and the slider  10  is about 50 nm. The recording magnetic field is calculated as the value at the position of the magnetic recording layer  21  at a depth of about 18.5 nm from the medium-facing surface  10   a.    
     The X-axis in  FIG. 5  shows the width direction and the Y-axis in the scanning direction. The interval between iso-magnetic curves is 1000 (×1000/4π[A/M]). It is clear that the magnetic field distribution is concentrated on the right side of the diagram. It will be seen that the magnetic field is greatest in the vicinity shown by the letter A in the diagram. 
       FIG. 6  shows iso-magnetic curves for a structure without a protruding portion  328 . The magnetic field has not increased in the position corresponding to letter A in  FIG. 5 . 
       FIG. 7  shows the profile for the magnetic gradient at the magnetic field position of 8×10 3 (×1000/4π[A/M]). The X-axis shows the position in the track width direction, the Y-axis the magnetic gradient standardized for the respective maximum magnetic gradients. Compared to the conventional structure without a projecting portion ( 328 ,  FIG. 4 ), it is clear that with the structure disclosed herein, the magnetic gradient is largest at the center on the right side of the graph, referring to  FIG. 7 . In the case of shingled recording, the edge of one side of the magnetic distribution is used to record the track. For this reason, the structure with a large magnetic gradient on one side is suitable for shingled magnetic recording. 
     To have a large variation in the magnetic distribution, it is desirable that the width in the track width direction of the protruding portion ( 328 ,  FIG. 4 ) be smaller than other track width directions for protruding portion  328 . Moreover, if the length of protruding portion  328  in the scan direction is greater than the width in the track width direction, it is possible to vary the magnetic distribution more. 
       FIG. 8  is a diagram showing the structure of another embodiment. It has a structure such that the trailing shield has a shape which follows the main magnetic pole.  FIG. 9  shows iso-magnetic curves for which the magnetic distribution was calculated with the three-dimensional magnetic method used for the structure in  FIG. 8 . The portions with a higher magnetic field density in the diagram have shifted to the right, meaning that the device is suitable for shingled magnetic recording. 
       FIG. 10  shows an oblique view of an example of the tip of the main magnetic pole, according to one embodiment. To vary the magnetic distribution so that it is suitable for shingled magnetic recording, it is desirable that protruding portion  328  be provided in the direction of height of the head element toward the first position (squeeze position) from the floating surface in which the width in the track width direction varies greatly. 
     Moreover, as shown in  FIG. 11 , the saturated magnetic flux density of the magnetic body used across the range of protruding portion  328  may be larger than the tip section  327  of the main magnetic pole. In this way, it is possible to concentrate the flux to make it suitable for shingled magnetic recording. Moreover, the saturated magnetic flux density of the magnetic body on one side of the leading edge of protruding portion  328  may be made greater than tip section  327  of the other main magnetic pole. In addition to the saturated magnetic flux density, the relative magnetic permeability may also be larger. 
     In the case where side shields are provided on both sides as shown in  FIG. 12 , it is desirable that gap W 1  between the main magnetic pole on the side of protruding portion  328  and the side shield be less than W 2 . In this way, it is possible to concentrate the magnetic distribution on one side of the track so that it is suitable for shingled magnetic recording. 
     The manufacture of the main magnetic pole, according to one embodiment, involves the formation of a non-magnetic layer after a magnetic film has been formed on the main magnetic pole, with a subsequent process in which the magnetic film of the main magnetic pole is cut away using this non-magnetic layer as a mask. 
       FIGS. 13(   a )-( c ) show an example of this portion of a manufacturing process for the main magnetic pole, according to one embodiment. The diagram shows the shape seen from the floating surface, with the trailing and leading directions shown at the top and bottom of the diagram, the track width being shown to left and right. 
     In  FIG. 13(   a ) a situation where an inorganic insulating layer  50  has been formed is shown, and after the formation of the tip section  327 , resist pattern  51  is formed above it. Methods of forming tip section  327  include a process which uses a magnetron sputter method using photo resist as a mask, and a process which employs plating using the resist pattern used to form the main magnetic pole. Resist pattern  51  is characterized in being formed asymmetrically. Next, as shown in  FIG. 13(   b ), this resist pattern  50  is used as a mask, and a tip section  327  and inorganic insulation film  50  are cut away using ion milling. Materials suitable for inorganic insulation film  50  include, but are not limited to, Al 2 O 3 , AlN, Ta 2 O 5 , TiC, TiC 2 , SiO 2 , SiO, etc. In  FIG. 13(   c ) the resist pattern  51  is shown removed after ion milling. The side shield and trailing shields are then formed. The side shield may be formed in advance of the process shown in  FIGS. 13(   a )-( c ). Moreover, after the process in  FIG. 13  and after forming the non-magnetic film for the trailing gap, a process may be carried out including chemical polishing, mechanical polishing, etc., to flatten the surface. Using this method, it is possible to manufacture the magnetic head described herein according to several embodiments. 
     In  FIGS. 14(   a )-( c ), an illustrative shingled recording system is shown. In  FIG. 14(   a ), a first track having a track width Tw 1  is recorded. The relative movement between the disc and the trapezoidal shaped head is such that the head scan moves in a direction pointing down. In  FIG. 14(   b ), a second track having a track width Tw 2  is recorded adjacent to the first track. As can be seen, the first and second track overlap slightly. In  FIG. 14(   c ), a third track having a track width Tw 3  is recorded adjacent to the second track. Once again, the third track overlaps slightly with the second track. Therefore, as previously described, the magnetic flux properties of the head at the track width edges is important in shingled recording systems. As shown here, tracks are written left to right, but may be written right to left. 
     While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of an embodiment of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.