Abstract:
A magnetic recording head with an overall planar design and tight dimensional control of throat height and notch width is achieved below the gap. Writer poles include very high magnetic moment material on both sides of the writer gap. Additionally the pole tips are shaped to provide high field with good spatial gradient for optimal writing conditions, thereby extending the capability of longitudinal recording heads for high density and high frequency applications.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority from U.S. Provisional Application No. 60/409,917, filed on Sep. 11, 2002 for Recording Head Writer With High Magnetic Moment Material At The Writer Gap And Associated Process of Vladyslav Alexandrovich Vas&#39;ko, Frank Edgar Stageberg, Feng Wang, Vee Sochivy Kong, Daniel Joseph Dummer, and Martin Louis Plumer, which application is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to the storage and retrieval of data within magnetic media. In particular, the present invention relates to the placement of high magnetic moment material at the writer pole tip, a novel writer head design incorporating high magnetic moment material of the pole tip, and the process for manufacturing the novel writer head. 
     A typical magnetic head consists of two portions: a writer portion for storing magnetically encoded information on a magnetic media, for example a disc, and a reader portion for retrieving the magnetically encoded information from the disc. The reader portion typically consists of two shields with a magnetoresistive (MR) sensor positioned between the shields. Magnetic flux from the surface of the disc 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. This change in resistivity of the MR sensor can be detected by passing a current through the MR sensor and measuring the voltage across the MR sensor. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary. 
     The disc or other magnetic media is typically organized into tracks which are further organized into bit fields. The MR sensor is held in close proximity to the surface of the disc so that the sensor can be affected by the magnetic flux from each bit field within the disc. As the MR sensor travels along a track of the disc, any change in directionality of the magnetic flux between bit fields is detected by the MR sensor. The rotation of the magnetization vector with the change from one bit field to another results in the corresponding resistivity change and consequent voltage output from the MR sensor. Since it is the change from one bit field to another that is detected and results in the data output, it is critical that those transitions be sharp, that is, as narrow as possible. In other words, the domain wall between bit fields with opposite magnetization vectors will be as small in area as possible. Sharp transitions, as well as other characteristics for successful reading, are not controlled by the reader, but instead by the writer and the process used to encode the data within the magnetic media. 
     The writer typically consists of two magnetic poles separated from each other at an air bearing surface of the write head by a write gap. Additionally, the two magnetic poles are connected to each other at a region away from the air bearing surface by a back via. The magnetic flux path created by the two magnetic poles and back via is commonly called the magnetic core. Positioned between the two poles are one or more layers of conductive coils encapsulated by electrically insulating layers. To write data to the magnetic media, a time varying electrical current, or write current is caused to flow through the conductive coils. The write current produces a time varying magnetic field in the magnetic poles and across the write gap. A magnetic media is passed over the air bearing surface of the writer at a predetermined distance such that the magnetic surface of the media passes through the gap field. As the write current changes, the write gap field changes in intensity and direction. 
     The magnetic fringe field created by the writer gap causes and controls the write process. The cross sectional area of this writer gap is critical and determines the magnetic field strength. The cross-sectional area of the writer gap is defined by two parameters, the throat height and notch width. A very short throat height decreases the gap area and effectively increases the fringe field. A larger field allows the writer to activate the higher coercivity media that is necessary for high linear density recording. Control of the throat height is important for magnetic field control. Excessively short throat height can cause excessive magnetic flux density in the gap and create fringe field distortion. Dimensional control of the notch width is also important for reasons similar to those described for throat height control. 
     Recent years have seen a considerable increase in data storage densities. Generally, the storage capacity of a magnetic data storage and retrieval device is increased through use of magnetic media having an increased areal density. Areal density is the number of units of data stored in a unit area of the media. Areal density is determined by two components of the magnetic media: the track density (the number of data tracks per unit width of the magnetic media) and the linear density (the number of units of data stored per unit of length of the data track). To increase the areal density of a magnetic media one must increase the linear density and/or the track density of the magnetic media. 
     Increases in areal density have been achieved by: increasing the strength of the write gap field, decreasing the thickness of the gap between the magnetic poles at the air bearing surface, decreasing the width of the writer poles at the air bearing surface and increasing the coercivity of the magnetic media. These improvements require the material(s) of the magnetic core to conduct relatively high flux densities. Magnetic softness and well-defined anisotropy are properties of materials related to the ability to readily conduct magnetic flux. 
     Materials have a magnetic saturation level beyond which they will conduct no additional flux. Therefore each material has an intrinsic limit to the flux density that can be conducted. Consequently, it is desirable to incorporate high magnetic moment (HMM) materials because these materials can conduct a larger quantity of flux before reaching the point of magnetic saturation. The ability to conduct relatively high flux densities is especially desirable at those portions of the magnetic core or poles which are adjacent to the gap. Those portions, commonly called the pole tips, are critical for controlled and effective direction of the magnetic flux into the media. 
     In addition to the ability to conduct high flux densities, writer poles also need to avoid the formation of eddy currents. Eddy currents are induced through the magnetic core each time the write gap field changes directions. These eddy currents, which are counteracting to the flow of current from the change in direction of the write gap field, have a negative effect on the performance of the transducing head. First, the eddy currents act as a shield to prevent external fields from penetrating the magnetic core, thereby reducing the efficiency of the transducing head. Second, the increased eddy currents increase the time required to reverse the direction of magnetic flux through the magnetic core, thereby negatively impacting the data rate of the writer. Typically, eddy current effects can be minimized by increasing the resistivity of the material forming the magnetic core. Higher resistivity materials, however, generally have lower saturation moments and the high magnetic moment materials commonly have low resistivity. 
     Since it is difficult to find a material having the combined properties of a high magnetic moment, high permeability/low coercivity and a high resistivity, more recent prior art writers have used multiple materials to lend the combination of these properties to the writer. Frequently, prior art designs would focus on improving a single aspect of writer performance, for example reducing eddy currents. One such prior art approach is to form the magnetic core of two layers. One layer is formed of a high magnetic moment material and the other layer is formed of a material with a greater resistivity. But, the use of a multi-layer core will necessarily reduce the overall magnetic moment over that possible with a writer formed of solely high magnetic moment material. 
     A second prior art approach is to form a top pole of the magnetic core of two pieces: one piece of a high magnetic moment material and a second piece of a high resistivity material. This “two piece pole” (TPP) design originated from the need to build the pole tip separately from the pole yoke due to photo-processing concerns. Additionally, a bottom (or shared) pole of the magnetic core may be a recessed pole similarly formed of two pieces. In the case in which both the top and bottom pole are formed of two pieces, the build process of the writer would progress as follows: A planar second bottom pole piece would be deposited; a planar first bottom pole piece would be deposited on a portion of the second bottom pole piece; a write gap layer would be deposited over an exposed portion of the second bottom pole piece and the first bottom pole piece, a planar first top pole piece would be deposited over the write gap layer; a tri-layer stack formed of the first bottom pole piece, the write gap layer, and the first top pole piece would be shaped to define a pole tip region; insulating layers and coils would be deposited; and finally, a second top pole piece would be deposited over the first top pole piece, as well as over the insulating layers and coils. This build process is necessary because the first bottom pole piece and the second bottom pole piece need to be built on a flat surface to allow for proper shaping of the pole tips. Thus, the existing TPP structures all require stacking the first pole piece on the second pole piece, which is inefficient for flux transportation in addition to increasing the cost and complexity of the manufacturing process. 
     Accordingly, there is need for a high efficiency writer incorporating very high magnetic moment materials for use with high density magnetic data storage media. 
     BRIEF SUMMARY OF THE INVENTION 
     A magnetic transducing head including a magnetic write element with an overall planar design, including a substantially planar top pole and writer poles including very high magnetic moment material on both sides of the writer gap. The very high magnetic moment materials are additionally coupled to softer magnetic materials with medium to high magnetic moments. Additionally, tight dimensional control of throat height and notch width is achieved below the gap with shaping to provide high field with good spatial gradient for optimal writing conditions, thereby extending the capability of longitudinal recording heads for high density and high frequency applications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a prior art transducing head taken along a plane normal to the air bearing surface of the transducing head. 
         FIG. 2  is a layered diagram that illustrates the location of a plurality of magnetically significant elements of the transducing head of  FIG. 1  as they appear along the ABS of the transducing head. 
         FIG. 3  is a cross-sectional view of a transducing head in accord with the present invention, the cross-sectional view being taken along a plane parallel to the air bearing surface of the transducing head. 
         FIG. 4  is a cross-sectional view of a transducing head having a composite core in accord with the present invention, the cross-sectional view being taken along a plane normal to the air bearing surface of the transducing head. 
         FIG. 5  is a perspective view of transducing head in accord with the present intention. 
         FIGS. 6-17  are cross-sectional views illustrating a method of forming the writer portion of a transducing head of the present invention. 
         FIGS. 18-19  are cross-sectional views of the writer portion of a transducing head in accord with the present invention, the cross-sectional views being taken along a plane parallel to the air bearing surface of the transducing head, showing definition of the top pole. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a cross-sectional view of prior art transducing head  20  taken along a plane normal to air bearing surface (ABS) of transducing head  20 . The ABS of transducing head  20  faces disc surface  23  of magnetic disc  21 . Magnetic disc  21  travels or rotates in a direction relative to transducing head  20  as indicated by arrow A. Spacing between the ABS of the transducing head  20  and disc surface  23  is preferably minimized while avoiding contact between transducing head  20  and magnetic disc  21 . Transducing head  20  includes reader portion  22  and writer portion  24 .  FIG. 2  is a layered diagram that illustrates the location of a plurality of magnetically significant elements of transducing head  20  as they appear along the ABS of the transducing head. For clarity, the spacing and insulating layers have been omitted. 
     Reader portion  22  of transducing head  20  includes bottom shield  26 , first gap layer  28 , magnetoresistive (MR) read element  30 , second gap layer  33 , contact layer  32 , and shared pole  34 . A read gap is defined on the ABS between terminating ends of bottom shield  26  and shared pole  34 . MR read element  30  is positioned between terminating ends of first gap layer  28  and second gap layer  33 . First and second gap layers  28  and  33  are positioned between bottom shield  26  and shared pole  34 . Bottom shield  26  and shared pole  34  may be layered upon separate seed layers (not shown). The seed layers are selected to promote the desired magnetic properties of respective bottom shield  26  and shared pole  34 . 
     Writer portion  24  of transducing head  20  includes shared pole  34 , write gap layer  36 , conductive coils  38 , insulator layer  39 , top pole seed layer  40  and top pole  42 . A write gap is defined at the ABS by write gap layer  36  between terminating ends of shared pole  34  and top pole  42 . Conductive coils  38  are positioned in insulator layer  39  between shared pole  34  and top pole  42 , such that the flow of electrical current through conductive coils  38  generates a magnetic field across the write gap. 
     The performance of writer portion  24  of transducing head  20  is strongly tied to the magnetic characteristics of top pole  42  and shared pole  34 , which in turn are a function of the materials and processes used in the construction of top pole  42  and shared pole  34 . In particular, the prior art taught that the top pole  42  and shared pole  34  each have soft magnetic properties, such as a high permeability to increase the efficiency of writer  24 , a high saturation magnetization to increase the strength of the write gap field, a high corrosion resistance to increase the life of writer  24 , and a high resistivity to minimize eddy currents in shared and top poles  34  and  42 . 
     In prior art transducing heads, top pole  42  and shared pole  34  are commonly formed of materials such as Permalloy (Ni 81 Fe 19 ), which has a relative permeability of approximately 2500 at 10 MHz and a saturation magnetization of approximately 1 Tesla; Sendust (FeSiAl), which has a permeability of approximately 1000 at 10 MHz and a saturation magnetization of approximately 1.1 Tesla; or Ni 45 Fe 55 , which has a permeability of approximately 1500 at 10 MHz and a saturation magnetization of approximately 1.6 Tesla. Although these materials proved useful in prior art transducing heads, recent demand for increased data storage densities require magnetic poles in writers to have a saturation magnetization in excess of those achieved in poles formed of purely Permalloy or Sendust. Prior attempts of using higher magnetic moment materials in forming the poles to increase the saturation magnetization of the writer poles have negatively impacted several of the other necessary properties of the writer, such as decreasing the permeability and/or the corrosion resistance of the poles, or resulting in less robust manufacturing processes necessary to build the transducing head. 
       FIG. 3  is a cross-sectional view of transducing head  100  having composite poles and planar structure in accord with the present invention. The cross-sectional view of  FIG. 3  is taken along a plane normal to an air bearing surface ABS of transducing head  100 .  FIG. 4  is a cross-sectional view taken in the plane of the air bearing surface. For clarity, all spacing and insulating layers are omitted from  FIG. 4 .  FIG. 5  is perspective view of transducing head  100 , including writer and reader portions, in which all spacing and insulating layers have been omitted for clarity. 
     The ABS of transducing head  100  faces disc surface  103  of magnetic disc  101 . Magnetic disc  101  travels or rotates in a direction relative to transducing head  100  as indicated by arrow A. Spacing between the ABS of transducing head  100  and disc surface  103  is preferably minimized while avoiding contact between transducing head  100  and magnetic disc  101 . 
       FIG. 3  shows a cross-section of transducing head  100  including a reader portion  105  and a writer portion  113 . The reader portion  105  includes bottom shield  102 , first half gap  104 , read element  106 , metal contact layer  108 , second half gap  110  and top shield  112 . Read element  106  is positioned adjacent the ABS between bottom shield  102  and top shield  112 . More specifically, read element  106  is positioned between terminating ends of first half gap  104  and metal contact layer  108 . Metal contact layer  108  is positioned between first half gap  104  and second half gap  110 . Read element  106  has two passive regions defined as the portions of read element  106  positioned adjacent to metal contacts  108 . An active region of read element  106  is defined as the portion of read element  106  located between the two passive regions of read element  106 . The active region of read element  106  defines a read sensor width. 
     Typically, read element  106  is a magnetoresistive (MR) sensor. In operation of transducing head  100 , magnetic flux from disc surface  103  of disc  101  causes rotation of the magnetization vector of a sensing layer of MR sensor  106 , which in turn causes a change in electrical resistivity of MR sensor  106 . Passing a current through MR sensor  106  via metal contact layer  108  and measuring a voltage across MR sensor  106  can detect the change in resistivity within MR sensor  106 . External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary. 
     The writer portion  113  and reader portion  105  of transducing head  100  are often arranged in a merged configuration, as shown in  FIGS. 3 and 5 , in which shared pole  112  functions as both a top shield for the reader portion  105  and as a bottom pole for the writer portion  113 . The writer and reader portions of transducing head  100  may also be arranged in a piggyback configuration in which the top shield and bottom pole would be two separate layers separated by an insulating layer. Alternatively, the writer portion could be formed without the reader portion. 
     The writer portion  113  of transducing head  100  includes bottom pole  115 , write gap layer  118 , insulating layers  119  and  120 , conductive coils  122 , back via  124 , and composite top pole  128 . Bottom pole  115  includes shared pole  112 , shared pole extension  114 , and frosting layer  116 . Composite top pole  128  includes top pole seed layer  126  and top pole layer  130 . Composite top pole  128  and bottom pole  115  are separated from each other at the ABS of transducing head  100  by write gap layer  118 , and are connected to each other at a region away from the ABS by back via  124  and a second portion  117  of the back via. Frosting layer  116 , shared pole extension  114 , shared pole  112  of bottom pole  115 , back via  124 , second portion  117 , and top pole seed layer  126  and top pole layer  130  of composite top pole  128  form a path for conduction of magnetic flux, collectively called the magnetic core. Electrically conductive coils  122  are held in place between composite top pole  128  and bottom pole  115  by use of write gap layer  118  and insulating layers  119  and  120 . Electrically conductive coils  122  are provided to generate magnetic fields across the write gap. Conductive coils  122  are shown in  FIGS. 3 and 5  as one layer of coils, but may also be formed of more layers of coils as is known in the field of magnetic read/write head design. 
     To write data to a magnetic medium, such as magnetic disc  101 , a time-varying electrical current, or write current, is caused to flow through conductive coils  122 . The write current induces magnetic flux that is conducted within the core and focused at the write gap. The magnetic field bridges the write gap forming a write gap field. The magnetic disc is passed over the ABS of magnetic recording head  100  at a predetermined distance such that the to magnetic surface  103  of disc  101  passes through the gap field. As the write current changes, the write gap field changes in intensity and direction. 
     Magnetic softness and well-defined magnetic anisotropy of the pole material are important properties for improving writer performance. These properties are in conflict with the desire to include materials with very high magnetic moments in high areal density write heads. Materials with very high magnetic moments are generally hard ferromagnetic materials with the properties of low permeability and high coercivity. However, when composite structures are formed with very high magnetic moment materials in combination with other magnetic materials, the coercivity and permeability of very high magnetic moment materials depend on the properties of the coupled system. 
     In the present invention, the frosting layer  116  and top pole seed layer  126  are each formed of a material with a very high magnetic moment. The very high magnetic moment material (subsequently referred to as VHMM material) should have a saturation moment of 2.4 T or greater. These materials also have properties of high coercivity and low permeability that were previously considered poor magnetic properties for use in writer pole structures. The VHMM material chosen for the top pole seed layer may be the same material or a different material from that chosen for the frosting layer  116 . Suitable materials include FeCo alloys. The atomic percentage of Co in suitable FeCo alloys is approximately in the range of 30 to 50 and preferably in the range of 37 to 50 with about 40 being most preferable. Fe 60 Co 40  has a very high saturation moment of approximately 2.45 Tesla (T). By coupling the VHMM material with a magnetically soft film with a lower saturation magnetic moment, for example 1.8 T CoNiFe, the coercivity can be modified downward to 1-3 Oe from 50-80 Oe. Initial permeability of the VHMM layer is affected in a similar way, increasing substantially to about 1400-1600 firom values of 10-100 as an individual layer. 
     The VHMM material in the frosting layer  116  is coupled to the material used to form the shared pole extension  114 . Generally, shared pole extension  114  and back via  124  are formed of a magnetic material, (subsequently referred to as second magnetic material), with a lower saturation magnetic moment relative to the VHMM material. This second magnetic material will have a medium to high saturation magnetic moment compared to magnetic materials generally, with values generally in the range of 1.6-2.2 T. The second material will also generally have a higher resistivity, higher permeability and lower coercivity than the VHMM material. Ni 78 Fe 22 , Ni 45 Fe 55 , and Co 65 Ni 20 Fe 15  are examples of suitable materials for the shared pole extension and back via. 
     The top pole seed layer  126  is likewise coupled to the material(s) used to form the top pole layer  130 . Similarly, the shared pole  112  is coupled to the shared pole extension  114  and back via  124 . Top pole layer  130  and shared pole  112  are each formed of a layer of soft magnetic material or several layers of soft magnetic materials separated by layers of non-magnetic materials. The top pole layer  130  may be formed of the same or different materials and/or layer configurations from the shared pole  112 . The saturation magnetic moment of the top pole layer  130  and the saturation magnetic moment of the shared pole  112  are relatively lower than the saturation magnetic moment of the top pole seed layer  126  and frosting layer  116 . An example material suitable for shared pole  112  and top pole  130  is Permalloy (Ni 78 Fe 22  and other similar compositions). 
     The writer portion  113  of the present invention can be built using several conventional processing steps.  FIGS. 6-17  are cross-sectional views taken normal to the ABS, illustrating a method of forming the writer portion  113  of transducing head  100 .  FIGS. 18-19  are cross-sectional views from the ABS further illustrating the method of formation. The method is described according to the following steps: 
       FIG. 6  shows a partially formed writer portion  113 . The planarized structure shown in  FIG. 6  includes the shared pole  112 , the shared pole extension  114 , the back via  124 , the writer coil  122 , and the writer coil insulator  119 . The structure of  FIG. 6  may be formed using known methods of masking and electroplating. Subsequent deposition of insulator  119  with optional chemical-mechanical polishing results in the planar structure as shown in  FIG. 6 . The conductive coils are typically composed of electrically conductive but nonmagnetic materials such as copper or gold. Insulator  119  must be electrically nonconductive to prevent shorting of the coils. 
     VHMM material for frosting layer  116  is deposited onto the planar structure of  FIG. 6  to produce the structure shown in  FIG. 7 . Next, liftoff patterning is performed. An example of this process would be the deposition of a bi-layer photoresist  132 , for example PMGI-Novolac onto the VHMM layer  116 , followed by exposure and development to achieve the pattern shown in  FIG. 8 . A subtractive process is applied, for example ion milling to remove a portion the VHMM layer and thereby expose the insulator  119  around electrical coils  122 . Through action of the subtractive process, the VHMM layer becomes two separate areas, the frosting layer  116  adjacent to the ABS and a second portion  117  which functions with the back via  124 . The lift-off patterning displayed in  FIGS. 8 and 9  controls the throat height, h, of the writer portion  113  by dimensional control during formation of the frosting layer  116 . 
     Another layer  120  of insulating material is applied over the remaining photoresist and the exposed insulator  119  as shown in  FIG. 10 . The insulator  120  may be a different material or the same material as used for insulator  119 . The thickness of the insulating layer  120  should be equal to the thickness of the frosting layer  116 . 
     In  FIG. 11 , the partially formed writer portion  113  is shown following the removal of the resist  132  together with any insulator layer  120  deposited upon the resist  132 . Removal of the resist  132  and portions of insulator layer  120  results in a planar structure. In the following step shown in  FIG. 12 , a layer of insulator corresponding to the writer gap layer  118  is deposited across the structure. This layer of material may be electrically conductive but should be magnetically inactive. Suitable examples include alumina and copper. 
     In  FIG. 13 , the writer gap layer  118  is patterned by a subtractive process wherein a protective layer of resist  121  is applied across the structure and subsequently exposed and developed to remove that portion of the writer gap layer  118  over the back via  124  using etching or milling before removing the photoresist. Subtractive processing is performed thereby removing the excess material. The resulting structure is shown in  FIG. 14  where the VHMM over the region of the back via  124  is exposed. Subsequently the resist material  121  is removed leaving the structure as shown in  FIG. 15 . 
     Next, the VHMM material forming the top pole seed layer  126  is deposited across the structure resulting as shown in  FIG. 16 . The top pole seed layer  126  contacts the VHMM material previously deposited onto the back via  124  thereby connecting the magnetic core. The top pole seed layer  126  is substantially planar thereby assisting accurate masking for deposition of the top pole layer  130 . A photolithography process is used to create a mask defining the notch width. The top pole layer  130  is subsequently plated through the opening in the mask, followed by removal of the resist, resulting in the structure as shown in  FIG. 17 . 
     The same structure of  FIG. 17  is shown as viewed from the ABS in  FIG. 18 . Subsequently, the notch milling is performed into the top pole seed layer  126 , the write gap layer  118  and into the frosting layer  116 . It is desired that the milling stop within the frosting layer  116  resulting in the structure of  FIG. 19 . The planarity of the top pole layer  130  assists in accurate milling of the notch width, w, of the writer shown in  FIG. 19 . 
     The composite core writer of transducing head  100  offers significant improvements in writer efficiency over the prior art writers. The substantially planar design of the writer portion  113  is readily manufactured by current techniques. Additionally, the planar shape of composite top pole  128  allows for a reduction in core height and length, thereby increasing the efficiency of the writer due to a shortened flux path. Another advantage of planarity of composite top pole  128  is greater control over the notch width of the pole tip at the ABS, thereby allowing for greater control of a track width of the data written to the magnetic media. 
     Another advantage of the present design is the separation of throat height dimensional control from the dimensional control of composite top pole  128  and shared pole extension  114 . The size and shape of the frosting layer  116  below the writer gap, positioned on top of the shared pole extension, defines the magnetic throat height. When the frosting layer  116  is deposited in the form of a sheet film, then liftoff patterning is used to define the throat height, followed with planarization of the throat height edge using a deposition of a nonmagnetic material. A very short throat height decreases the gap area and effectively increases the fringe field allowing the writer to activate higher coercivity media for high linear density recording. However, control of the throat height is important for magnetic field control because excessively short throat height can cause excessive magnetic flux density in the gap and create fringe field distortion. 
     Additionally, separate definition of the frosting layer  116  from the shared pole  112  and shared pole extension  114  allows the portions to have different cross-sectional areas (volumes). Magnetic materials with lower saturation moments require a larger volume (cross-sectional area) of material to conduct the same amount of flux as a smaller volume of higher moment material. Therefore, separate definition of the bottom pole structures allows for effective channeling of magnetic flux to the frosting layer  116  by individually controlling the cross-sectional area (volume) of each structure in relation to the flux density capacity of the material used for that structure. This avoids problems such as excessive flux density leakage and other inefficiencies in the transmission of magnetic flux. 
     In summary, the transducing head of the present invention incorporates the use of VHMM materials on both sides of the writer gap in a composite magnetic core formed of a high magnetic moment material with one or more lower magnetic moment material to achieve a higher magnetic saturation than is possible with the softer materials alone and a higher permeability than is possible with the VHMM material alone. The inventive structure and use of VHMM materials increases the write gap field strength of the transducing head with a high field gradient for writing of sharp media transitions with minimum cross-track curvature. This leads to increased over-write (OVW) on high-coercivity media and a narrower pulse width of the detected signal. Thus the transducing head of the present invention will have an increased potential areal density and improved potential frequency response over prior art transducing heads. 
     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.