Abstract:
The present invention is a perpendicular writer having an air-bearing surface, a main pole with an extension, and return pole, and a back gap closure intermediate the main pole extension and the return pole. The main pole includes a top magnetic layer and a soft magnetic underlayer separated by a nonmagnetic spacer. The main pole extension is in direct contact with the main pole and recessed from the air-bearing surface. The top magnetic layer forms a trailing edge of the main pole at the ABS and has a magnetic moment greater than that of the soft magnetic underlayer. Further, the top magnetic layer and the soft magnetic underlayer are anti ferromagnetically coupled through the thin nonmagnetic spacer. The nonmagnetic spacer has predominantly 111-crystalline texture and promotes reduction of coercivity and grain size along with an increase of anistropy of the top magnetic layer material.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims priority from provisional U.S. Patent Application Serial No. 60/385,568, filed on May 28, 2002 for “Perpendicular Writer with Magnetically Soft and Stable High Magnetic Moment Main Pole” by Alexander Mikhailovich Shukh, Vladyslav Alexandrovich Vas&#39;ko, and Declan Macken. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to the field of electronic data storage and retrieval, and more particularly to a perpendicular magnetic writer with a magnetically soft and stable high magnetic moment main pole.  
         BACKGROUND OF THE INVENTION  
         [0003]    Perpendicular recording potentially can support much higher linear density than longitudinal recording due to lower demagnetizing fields in recorded bits, which diminish with linear density increase. To provide decent writeability, double layer media are used. The double layer perpendicular media consist of a high coercivity, thin storage layer with perpendicular to-plane anisotropy and a soft magnetic keeper (underlayer) having in-plane anisotropy and relatively high permeability.  
           [0004]    A magnetic head for perpendicular recording generally consists of two portions, a writer portion for storing magnetically-encoded information on a magnetic media (disc) and a reader portion for retrieving that magnetically-encoded information from the media. The reader portion typically consists of a bottom shield, a top shield, and a sensor, often composed of a magnetoresistive (MR) material, positioned between the bottom and top shields. Magnetic flux from the surface of the disc (media) causes rotation of the magnetization vector of a sensing layer of the MR sensor, which in turn causes a change in electrical resistivity of the MR sensor. The change in resistivity of the MR sensor can be detected by passing a current through the MR sensor and measuring a voltage across the MR sensor. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary to recover the data that was encoded on the disc.  
           [0005]    The writer portion of the magnetic head for perpendicular recording typically consists of a main pole and a return pole which are magnetically separated from each other at an air bearing surface (ABS) of the writer by a nonmagnetic gap layer, and which are magnetically connected to each other at a region distal from the ABS by a back gap closure. Positioned at least partially between the main and return poles are one or more layers of conductive coils encapsulated by insulating layers. The ABS is the surface of the magnetic head immediately adjacent to the perpendicular medium. The writer portion and the reader portion are often arranged in a merged configuration in which a shared pole serves as both the top or bottom shield of the reader portion and the return pole of the writer portion.  
           [0006]    To write data to the magnetic medium, an electrical current is caused to flow through the conductive coil, thereby inducing a magnetic field across the write gap between the main and return poles. By reversing the polarity of the current through the coil, the polarity of the data written to the magnetic media is also reversed. Data on double layer perpendicular media are recorded by a trailing edge of the main pole. Accordingly, it is the main pole that defines the track width of the written data. More specifically, the track width is defined by the width of the main pole at the ABS.  
           [0007]    The main and return poles are made of a soft magnetic material. Both of them generate magnetic field in the media during recording when the write current is applied to the coil. However, the main pole produces much stronger write field than the return pole by having a much smaller sectional area the ABS and being made of magnetic material with higher magnetic moment. A magnetic moment of the main pole should be oriented along an easy axis parallel to the ABS when the main pole is in a quiescent state, namely without a write current field from the write coil. When the magnetic moment does not return to an orientation parallel to the ABS after being subjected to multiple instances of the write current field, the main pole is not stable. In an unstable pole, the orientation of the magnetic moment might remain nonparallel to the ABS position even after current to the write coil is turned off. Thus, the main pole may form a magnetic flux and may deteriorate or even erase data from the disc. Further, an unstable pole results in increased switching time when a current is applied. In a perpendicular head for ultra-high track density recording, the main pole is a predominant source of instability due to a strong demagnetizing field across the pole width at the ABS and the necessity of using magnetic materials with the highest possible values of magnetic moment saturation, even though these materials have poor anisotropy and relatively high coercivity.  
           [0008]    A factor bearing upon the magnetic stability of the main pole and the return of its magnetic moment to an orientation parallel to the ABS is its uniaxial anisotropy. Uniaxial anisotropy is a measure of an amount of applied magnetic field required to rotate the magnetic moment of the main pole from the orientation parallel to the ABS to an orientation perpendicular to the ABS. If the uniaxial anisotropy is too low and the coercivity is high enough, the magnetic moment in the main pole may not always return to a position parallel to the ABS after a write current is removed. Thus, the erasure of recorded data on perpendicular media is likely.  
           [0009]    Strength of the write field in the media is proportional to the magnetic moment of the main pole material. It is desirable to use a material with a high magnetic moment saturation (or high flux density saturation) for construction of the main pole in heads for ultra high track density recording. Accordingly, when the magnetic moment saturation of the main pole material is increased, a track width of the main pole tip can be reduced for increasing the storage capability of the disc drive. An example of a material with a high magnetic moment is an alloy of iron and cobalt (FeCo). The CoFe-alloy will conduct a large amount of flux and thereby permit the use of a very narrow pole tip, resulting in a very narrow track width, thereby allowing for ultra-high recording densities. Unfortunately, while CoFe films have the highest magnetic moment saturation, they do not have good magnetic stability due to poor anisotropy and relatively high coercivity. This means that the magnetic moment might not return to the parallel position to the ABS after being subjected to multiple instances of the write current field in the main pole tip of submicron width.  
           [0010]    Accordingly, there is a strong-felt need to provide a writer which is magnetically stable and is made of material with high magnetic moment saturation. Such a stable writer will reduce switching time, increase a drive&#39;s data rate, and prevent unintentional erasing on perpendicular media after the write current is turned off.  
         BRIEF SUMMARY OF THE INVENTION  
         [0011]    The present invention is a perpendicular writer having an air-bearing surface, a main pole with a main pole extension, and return pole, and a back gap closure intermediate the main pole extension and the return pole. The main pole extension is in direct contact with the main pole and recessed from the air-bearing surface to prevent erasure of recorded data on adjacent tracks. The main pole includes a top magnetic layer, a soft magnetic underlayer and a nonmagnetic spacer placed in-between. The top magnetic layer forms a trailing edge of the main pole at the ABS and has a magnetic moment greater than that of the soft magnetic underlayer. The soft magnetic underlayer is in direct contact with the main pole extension made of magnetic material with low coercivity, high anisotropy, and high permeability. Further, the top magnetic layer and soft magnetic underlayer are antiferromagnetically coupled through the thin nonmagnetic spacer. The nonmagnetic spacer has predominantly 111-crystalline texture and promotes reduction of coercivity and grain size along with an increase of anisotropy of the top magnetic layer material. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 shows a top perspective view of a disc drive.  
         [0013]    [0013]FIG. 2 is a cross-sectional view of a first embodiment of the perpendicular writer of the present invention.  
         [0014]    [0014]FIG. 3 is a cross-sectional view of a second embodiment of the perpendicular writer of the present invention.  
         [0015]    [0015]FIG. 4 is a cross-sectional view of a third embodiment of the perpendicular writer of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    [0016]FIG. 1 shows a top perspective view of a disc drive  12 , which includes a voice coil motor (VCM)  13 , actuator arm  14 , suspension  16 , flexure  18 , slider  20 , head mounting block  22 , and disc or media  24 . Slider  20  is connected to the distal end of suspension  16  by flexure  18 . Suspension  16  is connected to actuator arm  14  at head mounting block  22 . Actuator arm  14  is coupled to VCM  13 . As shown on the right side of FIG. 1, disc  24  has a multiplicity of tracks  26  and rotates about axis  28 .  
         [0017]    During operation of disc drive  12 , rotation of disc  24  generates air movement which is encountered by slider  20 . This air movement acts to keep slider  20  aloft a small distance above the surface of disc  24 , allowing slider  20  to fly above the surface of disc  24 . VCM  13  is selectively operated to move actuator arm  14  around axis  30 , thereby moving suspension  16  and positioning the transducing head (not shown) carried by slider  20  over tracks  26  of disc  24 . Proper positioning of the transducing head is necessary for reading and writing data on concentric tracks  26  of disc  24 .  
         [0018]    [0018]FIG. 2 is a cross-sectional view of a first embodiment of perpendicular writer  36  of the present invention. Medium  24  for perpendicular recording comprises thin storage layer  32  having high coercivity and perpendicular anisotropy (the magnetization is held in a direction substantially normal to the surface of medium  24 ) and soft magnetic underlayer or keeper  34  having high permeability and in-plane orientation of the easy axis. Writer  36  comprises main pole  38 , main pole extension  48  and return pole  40 , connected to each other by back gap closure  42  at a distal end and separated from each other by write gap  46  at the ABS and write coil  44  positioned between main pole extension  48  and return pole  40 . Main pole  38  serves as a trailing pole for the given direction of motion  47  of medium  24 . Magnetization transitions on medium  24  are recorded by trailing edge  49  of main pole  38 . To provide decent write field strength in medium  24 , magnetic layer  50 , shown here as the top layer, of main pole  38  containing trailing edge  49  is made of a high magnetic moment material. Main pole  38  has a submicron width at the ABS, to provide recording of ultra-narrow tracks on medium  24 . Moreover, the proposed structure of main pole  38  increases the uniaxial anisotropy of top magnetic layer  50 , thereby rendering it more magnetically stable.  
         [0019]    To write data to perpendicular magnetic medium  24 , a time-varying write current is caused to flow through coil  44 , which in turn produces a time-varying magnetic field through main pole  38  and return pole  40 . Medium  24  is then passed by the ABS of writer  36  at a predetermined distance such that medium  24  is exposed to the magnetic field. With perpendicular writer  36 , the soft magnetic keeper  34  of magnetic medium  24  in essence acts as a third pole of the writer.  
         [0020]    A closed magnetic path for flux from writer  36  to medium  24  travels from main pole  38  through storage layer  32  of medium  24  to soft magnetic keeper  34  and returns to writer  36  through return pole  40 , again passing through storage layer  32 . To ensure that the magnetic field does not write data on this return path, the surface area of return pole  40  at the ABS is preferably substantially larger than the surface area of main pole  38  at the ABS. Thus, the strength of the magnetic field affecting storage layer  32  under return pole  40  will not be sufficient to overcome a nucleation field of storage layer  32 . In a preferred embodiment, the thickness of main pole  38  is between about 0.05 and about 1 micrometer.  
         [0021]    Main pole  38  preferably has a multilayer structure and is preferably formed on main pole extension  48 . Multilayer main pole  38  preferably comprises magnetic layer  50 , shown here as top magnetic layer  50 , made of high magnetic moment material; thin nonmagnetic spacer layer  52 ; and magnetic layer  54 , shown here as underlayer  54 , made of a soft magnetic material with well-defined anisotropy. This multilayer pole structure induces anisotropy in top magnetic layer  50  parallel to the ABS direction, thereby enhancing the magnetic stability of main pole  38  while retaining the high writeability and high data rate advantages of the high magnetic moment material use. When top magnetic layer  50  is coupled with soft magnetic underlayer  54  across nonmagnetic layer  52  according to the present invention, the properties of the coupled multilayer system improve the performance of main pole  38  compared with a main pole made of a single layer of high magnetic moment material. While the layers of writer  36  are illustrated as planar layers, it is contemplated that they may follow other contours. Additionally, the illustrations are not rendered to scale.  
         [0022]    Any suitable material with a high magnetic moment may be used for top magnetic layer  50 . In a preferred embodiment, an Fe-Co alloy with Co content in the range of about 30 to about 50 percent is used. This alloy possesses a saturation moment of about 2.4 Tesla. Top magnetic layer  50  can be of any suitable thickness for use in writer  36 ; it is preferably about 0.05 to about 1 micrometer thick, and more preferably about 0.1 to about 0.5 micrometer thick.  
         [0023]    Any suitable material with a magnetic moment lower than the magnetic moment of the material of top magnetic layer  50  may be used for magnetic underlayer  54 . This material is also preferably magnetically soft, with a preferred coercivity less than about 5 Oersted and more preferably less than about 1 Oersted. The material used for magnetic underlayer  54  preferably has a lower coercivity than the material used for top magnetic layer  50 . The chosen material preferably has well defined magnetic anisotropy, meaning that it has a stable orientation of the easy axis of magnetization parallel to the ABS. In a preferred embodiment, magnetic underlayer  54  is made of CoNiFe, FeCoN, CoNiFeN, FeAlN, FeTaN, FeN, NiFe (e.g. Ni 80 Fe 20 , Ni 45 Fe 55 , etc.), NiFeCr, NiFeN, CoZr, CoZrNb, FeAlSi, or another suitable material. Magnetic underlayer  54  preferably has a saturation moment less than about 2 Tesla, more preferably less than about 1.5 Tesla and most preferably less than about 1.0 Tesla. It is noted that while the material of magnetic underlayer  54  has a lower magnetic moment relative to that of top magnetic layer  50 , the material of magnetic underlayer  54  may still be what is considered a high magnetic moment material in absolute terms. Magnetic underlayer  54  can be of any suitable thickness but is preferably less than about 0.2 micrometer thick and more preferably less than about 0.05 micrometer thick.  
         [0024]    Nonmagnetic spacer  52  may be composed of any nonmagnetic material which is mechanically and chemically compatible with the magnetic materials used for top magnetic layer  50  and magnetic underlayer  54 . Copper (Cu) or Ruthenium (Ru) are used for nonmagnetic spacer  52  in a preferred embodiment in which top magnetic layer  50  is made of FeCo and magnetic underlayer  54  is made of Ni 80 Fe 20 . The use of nonmagnetic spacer  52  between top magnetic layer  50  and magnetic underlayer  54  results in formation of an antiferromagnetic (AFM) exchange coupling between top magnetic layer  50  and magnetic underlayer  54 . This coupling induces anisotropy in top magnetic layer  50  oriented parallel to the ABS, resulting in a more magnetically stable domain structure of top magnetic layer  50 , and as a result, a more stable main pole  38  due to a reduction in magnetic energy.  
         [0025]    According to the RKKY (Ruderman-Kittel-Kasuya-Yosida) interaction, nonmagnetic spacer  52  induces a periodic coupling between top magnetic layer  50  and magnetic underlayer  54 . The coupling alternates in quality between antiferromagnetic and ferromagnetic as a function of the thickness of nonmagnetic spacer  52  and depends upon the crystallographic orientation of the material of nonmagnetic spacer  52 . In a preferred embodiment with top magnetic layer  50  made of Fe 60 Co 40  and magnetic underlayer  54  made of Ni 80 Fe 20 , it is preferable that the material of nonmagetic spacer  52  has a 111-crystalline orientation. Suitable nonmagnetic materials include, for example, copper, ruthenium, gold, copper-silver alloys, and various oxides, including aluminum oxide and silicon dioxide. Preferred nonmagnetic materials are those which provide for antiferromagnetic exchange coupling between the adjacent magnet layers, such as copper, ruthenium, gold, and copper-silver alloys. It is contemplated that nonmagnetic materials of other crystalline orientations may be chosen to correspond with other choices in magnetic materials for top magnetic layer  50  and magnetic underlayer  54 .  
         [0026]    In a preferred embodiment, the thickness of nonmagnetic spacer  52  is chosen to maximize the antiferromagnetic quality of the coupling between top magnetic layer  50  and magnetic underlayer  54 . If the thickness corresponding to the first antiferromagnetic peak results in a nonmagnetic spacer which is too thin to be practical, then the thickness of nonmagnetic spacer  52  corresponding to the next antiferromagnetic peak can be used, and so on. In one embodiment, Cu or Ru spacer  52  has a thickness of about 5 to about 200 Angstroms (Å), more preferably a thickness of about 6 to about 30 Å, and most preferably a thickness of about 18 to about 25 Å.  
         [0027]    In the present invention, nonmagnetic spacer  52  serves not only to antiferromagnetically couple top magnetic layer  50  and magnetic underlayer  54 , but also to magnetically soften top magnetic layer  50  made of CoFe-alloy. The quantum interactions between the atoms at the interfacing surfaces of top magnetic layer  50  and nonmagnetic spacer  52  change the crystalline texture of top magnetic layer  50 , resulting in reduced grain size, decreased coercivity, increased anisotropy, and greater magnetic stability.  
         [0028]    Any suitable material may be used for main pole extension  48 , which is used in one embodiment to increase efficiency of writer  36 , as well as enhance the anisotropy and structural and magnetic integrity of multilayer main pole  38 . Extension  48  is preferably recessed from the ABS by a distance of about 0.2 to about 2 micrometers so that extension  48  does not contribute to an increased track width of main pole  38  at the ABS. A narrow track width of main pole  38  at the ABS allows for high track density recording and prevents skew-related side writing effects.  
         [0029]    In one embodiment, main pole extension  48  is made of a magnetic material such as CoNiFe, FeCoN, CoNiFeN, FeAlN, FeTaN, FeN, NiFe (e.g. Ni 80 Fe 20 , Ni 45 Fe 55 , etc.), NiFeCr, NiFeN, CoZr, CoZrNb, CoZrTa, FeAlSi, or other suitable materials. The chosen material preferably has well defined magnetic anisotropy, meaning that it has well defined easy and hard magnetic axes. The material is preferably magnetically soft, with a preferred coercivity less than about 5 Oersted and more preferably less than about 1 Oersted. Extension  48  preferably has a relative magnetic permeability more than about 500, and more preferably more than about 1000. In such an embodiment, main pole extension  48  also serves as an extension of magnetic underlayer  54  due to strong ferromagnetic coupling between them, thereby contributing to the antiferromagnetic coupling with top magnetic layer  50 . However, because extension  48  is preferably shorter than magnetic underlayer  54 , it is not exposed at the ABS and thus reduces skew-related effects on medium  24 . Thus, extension  48  can be as thick as necessary to effectively contribute to the magnetic stability of top magnetic layer  50  and magnetic underlayer  54 . Thickness of main pole extension  48  is preferably in a range from about 0.1 to about 2 micrometers. In a preferred embodiment, extension  48  is made of the same material as magnetic underlayer  54 . In an alternate embodiment, extension  48  is omitted.  
         [0030]    Any suitable magnetic material may be used for back gap closure  42 . In a preferred embodiment, back gap closure  42  is constructed of a soft magnetic material such as CoNiFe, NiFe, Ni 80 Fe 20 , Ni 45 Fe 55 , NiFeCr, CoZr, FeN, FeAlSi, or other suitable materials.  
         [0031]    [0031]FIG. 3 is a cross-sectional view of a second embodiment of the perpendicular writer  64  of the present invention. Compared to the embodiment of FIG. 2, the embodiment of FIG. 3 has a laminated top magnetic layer  50 . In one embodiment, top magnetic layer  50  is composed of two magnetic sublayers  66  and  68 , spaced from each other by nonmagnetic layer  70 . Magnetic sublayers  66  and  68  are made of FeCo, magnetic underlayer  54  is made of NiFe or CoNiFe, and nonmagnetic spacer  52  and nonmagnetic layer  70  are composed of Cu. Other suitable materials may also be used, as described with reference to FIG. 2 above. Magnetic sublayer  66  maybe composed of the same material as sublayer  68 , or they may be composed of different materials. Similarly, nonmagnetic spacer  52  may be composed of the same material as nonmagnetic layer  70 , or they may be composed of different materials.  
         [0032]    As in the embodiment illustrated in FIG. 2, top magnetic multilayer  50  is antiferromagnetically coupled with magnetic underlayer  54  through nonmagnetic spacer  52 . Moreover, magnetic sublayers  66  and  68  are antiferromagnetically coupled to each other through nonmagnetic layer  70 . Thus, the magnetization of each ferromagnetic layer is antiparallel with respect to an adjacent ferromagnetic layer, resulting in a more magnetically stable domain configuration due to a reduction in magnetic energy. It is contemplated that additional magnetic layers alternated with nonmagnetic layers may be used to form laminated top magnetic layer  50 .  
         [0033]    [0033]FIG. 4 is a cross-sectional view of a third embodiment of the perpendicular writer  72  of the present invention. In this embodiment, return pole  40  comprises (n) magnetic layers  74  and (n−1) nonmagnetic layers  76  in alternating relationship, where n is an integer equal to or greater than 1. Each magnetic layer  74  is antiferromagnetically coupled to each adjacent magnetic layer  74  through nonmagnetic layer  76 . As with main pole  38 , this configuration allows return pole  40  to have a high flux carrying capacity while remaining magnetically stable by suppressing the formation of domain walls. This prevents erasure of information of medium  24  by return pole  40 .  
         [0034]    Any suitable magnetic and nonmagnetic materials may be used for the alternating layers. For magnetic layers  76 , a material such as CoNiFe, FeCoN, CoNiFeN, FeAlN, FeTaN, NiFe (e.g. Ni 80 Fe 20 , Ni 45 Fe 55 , etc.), NiFeCr, NiFeN, CoZr, CoZrNb, FeAlSi, or similar material may be used, for example. The material is preferably magnetically soft, with a preferred coercivity less than about 5 Oersted and more preferably less than about 1 Oersted. The chosen material preferably has well defined magnetic anisotropic properties, meaning that it has well defined easy and hard magnetic axes. The most preferred materials for magnetic layers  74  are Ni 80 Fe 20 , CoNiFe, FeCoN, FeAlN, FeAlSi, and FeTaN. In a preferred embodiment, each magnetic layer  74  is made of the same material; however, in an alternate embodiment, magnetic layers  74  may be composed of varying materials.  
         [0035]    Nonmagnetic layers  76  may be composed of any nonmagnetic material which is mechanically and chemically compatible with the magnetic materials used for magnetic layers  74 . Suitable nonmagnetic materials include, for example, copper, ruthenium, gold, copper-silver alloys, and various oxides, including aluminum oxide and silicon dioxide, for example. In a preferred embodiment, each nonmagnetic layer  76  is made of the same material; however, in an alternate embodiment, nonmagnetic layers  76  may be composed of varying materials.  
         [0036]    Because it is not critical for return pole  40  to be thin, greater thicknesses of magnetic materials may be used in return pole  40  compared to main pole  38 . The total cross-sectional area at the ABS of all the magnetic layers of return pole  40  is preferably greater than 10 times and more preferably greater than 100 times the total cross-sectional area of all the magnetic layers of main pole  38 . It is contemplated that this layered configuration of return pole  40  may be used with a main pole  38  of any configuration.  
         [0037]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.