Abstract:
A perpendicular magnetic head suppresses pole erasing due to a remanent magnetization component of a main pole and is capable of higher density recording. The perpendicular magnetic head is equipped with a main pole that produces magnetic flux toward a medium surface of a recording medium. The main pole is formed by laminating a top thin magnetic layer and a bottom thin magnetic layer in the thickness direction. The top thin magnetic film is formed as a high Bs thin magnetic film with a first saturation flux density and the bottom thin magnetic film is formed as a low Bs thin magnetic film with a second saturation flux density that is lower than the first saturation flux density, and the high Bs thin magnetic film and the low Bs thin magnetic film satisfy the following equation 
 
(volume of the high Bs thin magnetic film)×(first saturation flux density) 
 
&lt;(volume of the low Bs thin magnetic film)×(second saturation flux density).

Description:
[0001]     This is a Continuation-in-part of application Ser. No. 11/485,494, filed Jul. 12, 2006. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a perpendicular magnetic head, and in more detail to a perpendicular magnetic head characterized by the construction of a main pole of a recording head.  
         [0004]     2. Related Art  
         [0005]      FIG. 7  shows one example of the construction of a perpendicular magnetic head used in a magnetic disk apparatus. This perpendicular magnetic head is made up of a read head  8  provided at a position where a reproduction MR element  6  is sandwiched between a lower shield layer  5  and an upper shield layer  7 , and a write head  10  equipped with a main pole  12  and a return yoke  15  disposed on opposite sides of a shield gap  13 . On an end portion of a return yoke  15 , a trailing shield  14  that prevents a magnetic field produced from the main pole  12  from spreading to the return yoke  15  is provided, and a recording coil  11  is disposed between the return yoke  15  and the main pole  12 .  
         [0006]     In a magnetic disk apparatus, as the recording density has increased, materials with higher coercive forces have come to be used for the recording medium. The write head of the magnetic head therefore needs to produce a strong magnetic field to write information on tracks that have become narrower. For this reason, a magnetic material with a high saturation flux density (a high Bs value) is used for the write head of a perpendicular magnetic head and in particular for the main pole of the write head.  
         [0007]     However, since materials with a high Bs value usually have poor soft magnetic characteristics and a large remanent magnetization component, a so-called “pole erasing” problem occurs whereby information recorded on the recording medium is deleted by a magnetic field produced from the main pole even when a current is not flowing in the recording coil.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention was conceived to solve the above problems with conventional perpendicular magnetic heads, and it is an object of the present invention to provide a perpendicular magnetic head where the construction of the main pole of the perpendicular magnetic head is improved so that the problem of pole erasing due to a remanent magnetization component of the main pole is solved and a magnetic material with a high saturation flux density can be used for the main pole, thereby making high density recording possible.  
         [0009]     To achieve the object stated above, a perpendicular magnetic head according to the present invention is equipped with a main pole that produces magnetic flux toward a medium surface of a recording medium, wherein the main pole is formed by laminating a top thin magnetic layer and a bottom thin magnetic layer in a thickness direction of the main pole, the top thin magnetic film is formed as a high Bs thin magnetic film with a first saturation flux density, the bottom thin magnetic film is formed as a low Bs thin magnetic film with a second saturation flux density that is lower than the first saturation flux density, and the high Bs thin magnetic film and the low Bs thin magnetic film satisfy the following equation 
 
(volume of the high Bs thin magnetic film)×(first saturation flux density)&lt;(volume of the low Bs thin magnetic film)×(second saturation flux density).
 
         [0010]     In addition, by forming the main pole so that an end surface of a pole end has an inverse trapezoidal form, it is possible to further suppress a pole erasing action caused by a remanent magnetization component of the main pole.  
         [0011]     The main pole may be formed when a length of a bottom edge of an end surface of a pole end of the main pole is expressed as “a”, a length of a top edge as “c”, a length of the bottom edge of the high Bs thin magnetic film as “b”, a height of the high Bs thin magnetic film as “T_h”, a saturation flux density of the high Bs thin magnetic film as “Bs_h”, a height of the low Bs thin magnetic film as “T_ 1 ”, and a saturation flux density of the low Bs thin magnetic film as “Bs_ 1 ”, the high Bs thin magnetic film and the low Bs thin magnetic film may satisfy the following equation 
 
T_h×(c+b)×Bs_h&lt;T — 1×(b+a)×Bs — 1.
 
         [0012]     In this way, when the main pole is formed with a trapezoidal cross-sectional form, it is possible to design the high Bs thin magnetic film and the low Bs thin magnetic film based on the end surface form of the pole end of the main pole.  
         [0013]     Also, by forming the low Bs thin magnetic film using a magnetic material with a coercive force (Hc) in the hard axis of 5 Oe or below, it is possible to effectively suppress the pole erasing effect due to the remanent magnetization component caused by the main pole including the high Bs thin magnetic film.  
         [0014]     By forming the main pole with a laminated construction composed of a high Bs thin magnetic film and a low Bs thin magnetic film that has superior soft magnetic characteristics, the perpendicular magnetic head according to the present invention is capable of recording information with a high density on a recording medium due to the action of the high Bs thin magnetic film. The action of the low Bs thin magnetic film also makes it possible to suppress the remanent magnetization component caused by the high Bs thin magnetic film. This means it is possible to realize the object of writing information at high density using the main pole and also the object of preventing pole erasing.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The aforementioned and other objects and advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying drawings.  
         [0016]     In the drawings:  
         [0017]      FIGS. 1A and 1B  are diagrams useful in explaining a construction of a main pole of a write head;  
         [0018]      FIG. 2  is a diagram useful in explaining an example design of a magnetic pole;  
         [0019]      FIG. 3  is a diagram showing a magnetic field that acts from the main pole onto a recording medium;  
         [0020]      FIGS. 4A  to  4 C are diagrams useful in explaining a method of manufacturing the main pole;  
         [0021]      FIG. 5  is a graph showing the relationship between the coercive force and the thickness ratio of laminated films of FeNi and FeCo;  
         [0022]      FIG. 6  is a diagram useful in explaining the end surface construction of a magnetic film with a two-layer construction composed of layers of FeCo and FeNi; and  
         [0023]      FIG. 7  is a cross-sectional view showing the construction of a perpendicular magnetic head. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0024]     A preferred embodiment of the present invention will now be described with reference to the attached drawings.  
         [0025]     A perpendicular magnetic head according to the present invention is characterized by the main pole of the write head having a two-layer construction composed of a high Bs material and a low Bs material.  FIG. 1A  shows the main pole of a perpendicular magnetic head according to the present invention when looking toward an end of the pole.  FIG. 1B  shows the main pole of a conventional perpendicular magnetic head as a comparative example.  
         [0026]     Although an example where the present invention has been adapted to the main pole  12  of the perpendicular magnetic head shown in  FIG. 7  will now be described, the perpendicular magnetic head may have various different constructions. The present invention can also be applied to such various perpendicular magnetic heads. Note that since the construction of the perpendicular magnetic head shown in  FIG. 7  has been described above, further description thereof has been omitted. The pole end  12   a  of the main pole shown in  FIG. 1A  is shown in a state when looking toward the pole end  12   a  of the main pole  12  in  FIG. 7 .  
         [0027]     As shown in  FIG. 1B , the main pole used in the write head of the conventional perpendicular magnetic head is formed so that the end surface form of the pole end  12   a  is produced in an inverted trapezoidal form where the side that faces the trailing shield  14  is wider than the read head side. This main pole is formed of a thin magnetic film with a high saturation flux density such as FeCo, and is formed as a single film.  
         [0028]     As shown in  FIG. 1A , although the end surface form of the pole end  12   a  is produced with an inverted trapezoidal form in the same way as the conventional example, the main pole  12  of the write head of the perpendicular magnetic head according to the present invention is characterized by being formed of two layers composed of different magnetic materials in the thickness direction of the main pole  12 . The side facing the trailing shield  14  (the top thin magnetic film) is formed as a high Bs thin magnetic film  121  composed of a high Bs material and a read head side (the bottom thin magnetic film) is formed as a low Bs thin magnetic film  122  composed of a low Bs material.  
         [0029]     To make it possible for the write head  10  to write with high precision, the high Bs thin magnetic film  121  provided on the side of the main pole  12  that faces the trailing shield  14  is formed using a magnetic material such as Fe 60 Co 40  with a sufficiently high saturation magnetic flux density. The magnetic material that forms the high Bs thin magnetic film  121  is selected with the production of a strong magnetic field having primary importance.  
         [0030]     On the other hand, the low Bs thin magnetic film  122  is provided to suppress the remanent magnetization component of the main pole  12 , and therefore a magnetic material is selected with soft magnetic characteristics having primary importance. As one example, nickel iron (NiFe) alloys are materials with superior soft magnetic characteristics. A magnetic material with such superior soft magnetic characteristics is used for the low Bs thin magnetic film  122 .  
         [0031]     According to the present invention, the high Bs thin magnetic film  121  is disposed on the side of the main pole  12  that faces the trailing shield  14  because the action whereby the main pole  12  writes on the recording medium is produced by a magnetic field from close to the surface of the main pole  12  that faces the trailing shield  14 .  
         [0032]      FIG. 3  is a diagram useful in explaining the positional relationship between the main pole  12 , the trailing shield  14 , and a recording medium  20 . When information is recorded on the recording medium  20  by the write head  10 , magnetic flux is directed from the main pole  12  toward the recording medium  20 , and as shown in  FIG. 3 , the intensity of the recording magnetic field produced by the main pole  12  is substantially localized in a region of the main pole  12  that faces the trailing shield  14  (shown by the curved lines in  FIG. 3 ). Accordingly, to cause a strong magnetic field to act upon the recording medium  20 , it is sufficient to use a high Bs material for the thin magnetic film at a part of the main pole  12  that faces the trailing shield  14 .  
         [0033]     On the other hand, if the entire main pole  12  were formed from only a high Bs material, there would be the problem of pole erasing due to the remanent magnetization component of the main pole  12  and therefore it is effective to use a magnetic material with superior soft magnetic characteristics in regions aside from the part of the main pole  12  that faces the trailing shield  14 . For this reason, according to the present invention, the low Bs thin magnetic film  122  is used as the read head side of the main pole  12 .  
         [0034]     To counteract the remanent magnetization component from the main pole  12  when a current is not flowing through the recording coil 11, the action of the low Bs thin magnetic film  122  needs to be predominant. To do so, since the magnetic characteristics of the high Bs thin magnetic film  121  and the low Bs thin magnetic film  122  are believed to be reflected by the products of the respective volumes of the films in the main pole  12  and the respective saturation flux densities showing the magnetic characteristics of the films, the thicknesses and the like of the high Bs thin magnetic film  121  and the low Bs thin magnetic film  122  are determined so as to satisfy the following equation 
 
(volume of the high Bs thin magnetic film)×(Bs value of the high Bs thin magnetic film)
 
&lt;(volume of the low Bs thin magnetic film)×(Bs value of the low Bs thin magnetic film).
 
         [0035]     In this way, if the magnetic component provided by the entire low Bs thin magnetic film  122  is made larger than the magnetic component provided by the entire high Bs thin magnetic film  121 , when a current is not flowing through the recording coil, the entire main pole  12  is expressed by the soft magnetic characteristics due to the low Bs thin magnetic film  122 .  
         [0036]     Note that the expressions “the volume of the high Bs thin magnetic film” and “the volume of the low Bs thin magnetic film” here refer to the volumes at positions that contribute to the writing of information by the main pole  12  on the recording medium. Accordingly, as shown in  FIG. 5B , when the main pole  12  is formed so as to project outward with an inverse trapezoidal cross-sectional form, the volumes of the films may be set by considering only the form of the end surface of the pole end  12   a  of the main pole  12 .  
         [0037]     Here, as shown in  FIG. 1A , when a length of a bottom edge of the main pole  12  is expressed as “a”, a length of a top edge as “c”, a length of the bottom edge of the high Bs thin magnetic film  121  as “b”, a height (in the thickness direction of the main pole  12 ) of the high Bs thin magnetic film  121  as “T_h”, the saturation flux density of the high Bs thin magnetic film  121  as “Bs_h”, a height of the low Bs thin magnetic film  122  as “T_ 1 ”, and the saturation flux density of the low Bs thin magnetic film  122  as “Bs_”, the thicknesses and the like of the high Bs thin magnetic film  121  and the low Bs thin magnetic film  122  should be decided so as to satisfy the following equation 
 
T_h×(c+b)×Bs_h&lt;T_ 1 ×(b+a)×Bs_ 1 .
 
         [0038]     The equation given above shows that the high Bs thin magnetic film  121  and the low Bs thin magnetic film  122  are decided according to only the end surface form of the main pole  12 .  
         [0039]     Note that actual experiments were carried out to find out the approximate level of coercive force of the thin magnetic films forming the main pole  12  at which pole erasing occurs. The relative merits of the soft magnetic characteristics were compared in general using the coercive force (Hc) in the hard axis. According to such experiments, pole erasing occurred when the main pole was formed as a single film of Fe 60 Co 40  where Hc is around 10 Oe, but pole erasing did not occur when the main pole was formed as a single film of Ni 10 Fe 90  where Hc is around 5 Oe. From this evidence, it is possible to regard magnetic materials where Hc is around 5 Oe or below as having superior soft magnetic characteristics and it is therefore effective to use a magnetic material where Hc is around 5 Oe or below as the low Bs thin magnetic film  122  according to the present invention.  
         [0040]      FIG. 2  shows an example design of a perpendicular magnetic head according to the present invention. Fe 60 Co 40  is used as the high Bs thin magnetic film  121  and Ni 80 Fe 20  is used as the low Bs thin magnetic film  122 . For Fe 60 Co 40 , the saturation flux density is 2.4T and Hc is 15 Oe, while for Ni80Fe20, the saturation flux density is 1.0T and Hc is 1 Oe. Also, as shown in  FIG. 2 , a=90 nm, b=140 nm, c=150 nm, T_h=100 nm, and T_ 1 =500 nm.  
         [0041]     Calculation for the high Bs thin magnetic film. 
 
Bs_h×T_h×(c+b)=2.4×100×(150+140)=69600(T·nm 2 )
 
         [0042]     Calculation for the low Bs thin magnetic film. 
 
Bs_ 1 ×T_ 1 ×(b+a)=1.0×500×(149+90)=115000(T·nm 2 )
 
         [0043]     These calculation results satisfy the equation T_h×(c+b)×Bs_h &lt;T_ 1 ×(b+a)×Bs_ 1  given above.  
         [0044]     That is, with the example construction of the main pole  12  shown in  FIG. 2 , by disposing the high Bs thin magnetic film  121  in a region of the main pole  12  that faces the trailing shield  14 , when a current is passed through the recording coil  11  to record information, it is possible to make use of the characteristics of the high Bs thin magnetic film  121  and carry out high density writes. Conversely, when a current is not passed through the recording coil  11 , the soft magnetic characteristics of the low Bs thin magnetic film  122  become predominant, making it possible to suppress the remanent magnetization component caused by the high Bs thin magnetic film  121 . By doing so, it is possible to eradicate pole erasing due to the remanent magnetization component caused by the high Bs thin magnetic film  121 .  
         [0045]     As a method of forming a main pole  12  such as that shown in  FIGS. 1A and 2  with a two-layer construction composed of the high Bs thin magnetic film  121  and the low Bs thin magnetic film  122 , as shown in  FIGS. 4A  to  4 C, after a base layer  30  of the main pole  12  has been formed on the surface of a workpiece (a wafer), the base layer  30  is coated with a resist  32 , and then exposing and developing are carried out in accordance with a formation pattern of the main pole  12  to form a concave channel  32   a  at a position where the main pole  12  is to be formed.  FIG. 4A  shows the state where the concave channel  32   a  is viewed in a direction where an end surface of the main pole  12  is visible. The concave channel  32   a  is formed in an inverse trapezoidal form where the bottom is narrow and the opening is wide so that the end surface of the main pole  12  has an inverse trapezoidal form.  
         [0046]      FIG. 4B  shows a state where the low Bs thin magnetic film  122  that composes the main pole  12  has been formed inside the concave channel  32   a . The low Bs thin magnetic film  122  can be formed by plating or sputtering on the bottom of the concave channel  32   a  with a predetermined thickness.  
         [0047]      FIG. 4C  shows a state where the high Bs thin magnetic film  121  has next been formed inside the concave channel  32   a  so as to be laminated on the low Bs thin magnetic film  122 . The high Bs thin magnetic film  121  can also be formed by plating or sputtering with a predetermined thickness.  
         [0048]     As shown in  FIG. 4C , after the high Bs thin magnetic film  121  has been laminated on the low Bs thin magnetic film  122 , by lifting off the resist  32 , the main pole  12  which is composed of the low Bs thin magnetic film  122  and the high Bs thin magnetic film  121  formed on top of each other and whose pole end  12   a  is formed in an inverse trapezoidal form is left in a pattern on the surface of the workpiece.  
         [0049]     In this way, the main pole  12  can be formed using a conventional process that forms a layer by patterning a resist. It is possible to decide the end surface form of the concave channel  32   a  in accordance with the end surface form of the main pole  12 , and the main pole  12  can be formed with a desired form by controlling the thicknesses of the low Bs thin magnetic film  122  and the high Bs thin magnetic film  121 .  
         [0050]     Next, the write head  10  is formed by successively forming the shield gap  13 , the coil  11 , and the return yoke  15 .  
         [0000]     Magnetic Characteristics of Main Pole and Example Test for Pole Erasing  
         [0051]     To investigate the magnetic characteristics of a magnetic pole with the two-layer construction composed of a high Bs thin magnetic film and a low Bs thin magnetic film described above and the pole erasing characteristics of such magnetic pole, samples were fabricated by forming an Fe 70 Co 30  film as the high Bs thin magnetic film and an Fe 90 Ni 10  film as the low Bs thin magnetic film on the surface of a 2 cm by 2 cm square substrate. When doing so, the overall thickness of the pole was kept constant at 200 nm but the ratio of the thicknesses of the respective films was varied. The coercive force Hc in the hard axis and the saturation flux density Bs value were then measured for each sample.  
         [0052]     Table 1 shows measured values for the coercive force Hc in the hard axis and the saturation flux density Bs of laminated films where the ratio (FeNi/FeCo) of the thicknesses of the Fe 90 Ni 10  and the Fe 70 Co 30  was varied and also shows the product of the Bs value and the film thickness for each sample.  FIG. 6  is a graph showing the relationship between the coercive force Hc and the ratio (FeNi/FeCo) of the thicknesses of the Fe 90 Ni 10  and the Fe 70 Co 30 .  
                                                                           TABLE 1                           t = 200 nm            FeNi/FeCo   Hc               tBs ratio           (thickness ratio)   (Oe)   Bs (T)   tBs_FeNi   tBs_FeCo   FeNi/FeCo   Hce (A/m)                    0   10.27   2.3   0   460   0   817.2866       27   7.743   2.246   113.4   335.8   0.337701013   616.18794       44   6.534   2.212   184.8   257.6   0.717391304   519.97572       68   3.27   2.164   285.6   147.2   1.940217391   260.2266       100   2.631   2.1   420   0   —   209.37498                  
 
         [0053]     Measurement was carried out for five different samples where the FeNi/FeCo ratio was 0% (i.e., a single layer of FeCo), 27%, 44%, 68%, and 100% (i.e., a single layer of FeNi).  
         [0054]     As shown in Table 1 and in  FIG. 6 , when the FeNi/FeCo ratio is low, that is, when the FeCo film is thick, the coercive force Hc and the saturation flux density Bs both increase, and when the FeNi/FeCo ratio is high, that is, when the FeCo film is thin, the coercive force Hc and the saturation flux density Bs both decrease.  
         [0055]     As described earlier, it is believed that the magnetic characteristics of a magnetic film with a two-layer construction composed of a high Bs thin magnetic film and a low Bs thin magnetic film are determined by the relative magnitudes of the products of the volume (in the present embodiment, thickness corresponds to the volume) and the Bs value for the respective thin magnetic films.  
         [0056]     In this example test, if the thickness ratio of the FeNi/FeCo is expressed as x%, since the Bs value of Fe 70 Co 30  is 2.3T and the Bs value of Fe 90 Ni 10  is 2.1 T, the value of x where the respective products of the volume and Bs value for each thin magnetic film become equal is calculated by 2.3x=2.1(100-x), which gives the result x=47.7%. That is, if the ratio of FeNi/FeCo is 47.7% or above, it is believed that the characteristics of the FeNi magnetic thin film will be more significant than the characteristics of the FeCo in the characteristics of the magnetic film. As shown in  FIG. 5 , the coercive force Hc of a laminated film of Fe 90 Ni 10  and Fe 70 Co 30  exhibits a tendency whereby the coercive force Hc falls suddenly when the FeNi/FeCo ratio is 47.7% or above. The results of this test back up the above assertion that the magnetic characteristics of a magnetic film with a two-layer construction composed of a high Bs thin magnetic film and a low Bs thin magnetic film change according to the products of the volume of a thin magnetic film and the Bs value of the thin magnetic film.  
         [0057]     To investigate whether pole erasing is caused by the main magnetic pole, as shown in  FIG. 6 , a magnetic film with a two-layer construction of Fe 70 Co 30  and Fe 90 Ni 10  was formed and compared to a single-layer film of Fe 70 Co 30  and a single-layer film of Fe 90 Ni 10 . Table 2 shows the overwrite characteristics together with whether pole erasing occurred.  
                                             TABLE 2                                   O/W (dB)   Pole Erasing                                        FeNi   −30   No           FeNi/FeCo   −35   No           FeCo   −38   Yes                      
 
         [0058]     As shown in Table 2, although pole erasing does not occur for an FeNi single-layer film, the overwrite value is high at −30 dB. On the other hand, with an FeCo single-layer film, although the overwrite value is extremely low at −38 dB, resulting in high recording performance, pole erasing occurs and therefore such pole cannot be used. On the other hand, with the two-layer construction of FeCo and FeNi shown in  FIG. 6 , it is possible to obtain overwrite characteristics that are close to those of an FeCo single film and to simultaneously prevent pole erasing from occurring.  
         [0059]     With the construction shown in  FIG. 6 , the end area of the FeCo thin magnetic film located on the trailing side is (110+100)×70/2=7350 nm 2 , the product of this area and the Bs value is 16905(T·nm 2 ), the end area of the FeNi thin magnetic film located on the read head side is (100+80)×140/2=12600 nm 2 , and the product of this area and the Bs value is 26460 (T·nm 2 ). The FeNi/FeCo ratio of the products of the respective areas and Bs values in this case is 61.0%.  
         [0060]     The results in Table 2 confirm that the product of the end area and the Bs value for FeNi exceeds the product of the end area and the Bs value for FeCo so that the soft magnetic characteristics of FeNi appear as the magnetic characteristics of the laminated film.  
         [0061]     Note that as described earlier, since the coercive force Hc of the laminated thin magnetic films should be set at around 5 Oe or below to prevent pole erasing from occurring, for the example test shown in  FIG. 5 , the ratio of the end surface areas of the FeNi and FeCo should be set at 55% or above so that the coercive force Hc becomes 5 Oe or below. When doing so, the FeNi/FeCo ratio of the products of the areas and the Bs values is actually 52.7% and the upper limit for the end area of the FeNi in the laminated film of FeNi and FeCo is determined in view of the recording characteristics of the main pole.