Patent Publication Number: US-8116031-B2

Title: Perpendicular magnetic recording system with helical write coil and auxiliary coil for fast switching of write pole magnetization

Description:
RELATED APPLICATION 
     This application is related to concurrently filed application Ser. No. 12/419,281 titled “PERPENDICULAR MAGNETIC RECORDING SYSTEM WITH AUXILIARY COIL AND CIRCUITRY FOR FAST SWITCHING OF WRITE POLE MAGNETIZATION”. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to perpendicular magnetic recording systems, and more particularly to a system with fast switching of the magnetization direction of the perpendicular write head. 
     2. Description of the Related Art 
     Perpendicular magnetic recording, wherein the recorded bits are stored in a perpendicular or out-of-plane orientation in the recording layer, allows for ultra-high recording densities in magnetic recording hard disk drives. The write head must be able to write data not only at high bit-density but also at high data-rates. The write speed is particularly important in enterprise disk drives. However, the switching time for the main pole of the write head to switch from one magnetization direction to the other is a limiting factor as the data rate is increased. At high data-rates, the available magnetic flux from the write head, as seen by the recording layer on the disk, is dominated by the low-frequency flux output of the write head. The reason for such loss of write flux includes a slow intrinsic time-constant of the magnetization reversal in the main pole of the write head. Also, lower data-rate systems still require additional overshoot of the write current from the disk drive&#39;s write driver circuitry to aid in the magnetization reversal. This additional overshoot requires additional power from the write driver circuitry. 
     Perpendicular magnetic recording systems with high-frequency assisted writing have been proposed, as described in U.S. Pat. Nos. 6,816,339 B1 and 7,256,955 B2. In these proposed systems, the write coil generates the main perpendicular write field as well as a high-frequency auxiliary field. The auxiliary field has a frequency close to the resonance frequency of the magnetic grains in the recording layer to facilitate the switching of the magnetization of the grains. US 2007/0253106 A1 describes a high-frequency assisted writing system where an auxiliary coil is used to apply the high-frequency auxiliary field to the magnetic grains of the recording layer. 
     Thus for both high data-rate and lower data-rate perpendicular magnetic recording, what is needed is a write head and system that reduces the magnetization reversal time of the main pole and overshoot for the main pole without the application of a high-frequency auxiliary field to the recording layer. 
     SUMMARY OF THE INVENTION 
     The invention relates to a perpendicular magnetic recording system with a write head having a main helical coil (the write coil) and main pole (the write pole) that directs write flux in a direction perpendicular to the recording layer in the magnetic recording medium, and an auxiliary coil and auxiliary pole that injects magnetic flux into the write pole at an angle to the primary or perpendicular axis of the write pole. The auxiliary coil is preferably a helical coil wrapped around the auxiliary pole. The additional flux from the auxiliary pole, which is injected non-parallel to the primary magnetization of the write pole, exerts a relatively large torque on the magnetization of the write pole, thereby facilitating magnetization reversal of the write pole. The auxiliary pole has its longitudinal axis oriented at an angle (greater than 15 degrees) and preferably substantially orthogonal (70 to 90 degrees) to the primary or perpendicular axis of the write pole. 
     Electrical circuitry is connected to the main coil and the auxiliary coil to generate the auxiliary flux simultaneous with the switching of the magnetization of the write pole. The current to the auxiliary coil preferably has a magnitude at least about 20% of the magnitude of the write current. The frequency of the signal to the auxiliary coil is preferably greater than the maximum write frequency, and preferably close to the ferromagnetic resonance frequency of the magnetic material of the write pole. Ferromagnetic resonance arises from the precessional motion of the magnetic material of the write pole in the presence of the auxiliary magnetic field from the auxiliary coil. The auxiliary magnetic field puts a torque on the magnetization of the magnetic material of the write pole which causes the magnetic moment to precess. However, auxiliary fields with frequencies lower than the ferromagnetic resonance frequency will also contribute to the switching of the magnetization of the write pole when applied at appreciable angles relative to the main direction of the magnetic anisotropy of the write pole. If the auxiliary field is at a frequency less than the ferromagnetic resonance frequency, the beneficial effect of the auxiliary field on the switching of the magnetization of the write pole will be dominated by the increase of the magnetic reversal torque in proportion to sin(θ), where θ is the angle between the local direction of the total field from the main and auxiliary coils and the local direction of the magnetization of the write pole. 
     For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken together with the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a top plan view of a head/disk assembly of a hard disk drive. 
         FIG. 2  is an enlarged end view of the slider and a section of the disk taken in the direction  2 - 2  in  FIG. 1 . 
         FIG. 3  is a view in the direction  3 - 3  of  FIG. 2  and shows the ends of the read/write head as viewed from the disk. 
         FIG. 4A  is a sectional view of a portion of a slider showing a prior art perpendicular write head with a pancake coil according and a portion of a perpendicular magnetic recording disk. 
         FIG. 4B  is a view in the direction  4 B- 4 B of  FIG. 4A  and illustrates the flare region of the flared write pole for the perpendicular write head. 
         FIG. 5  is a side sectional view of a portion of a slider showing a read head, a prior art perpendicular write head with a helical coil, and a perpendicular magnetic recording disk. 
         FIG. 6A  is a side sectional view of a portion of a slider with a planar perpendicular write head with a helical coil taken through a plane parallel to a data track. 
         FIG. 6B  is a view in the direction  6 B- 6 B of  FIG. 6A  and illustrates the coplanar main pole and return poles of the perpendicular write head of  FIG. 6A . 
         FIG. 7A  is a schematic illustrating the basic concept of the invention showing a main coil (MC) with main pole and auxiliary coil (AC) with auxiliary pole oriented substantially orthogonal to the main pole. 
         FIG. 7B  is a graph of a computer-generated micromagnetic simulation of the magnetization reversal of a cylindrical magnetic nanostructure representing the write pole with (Curve B) and without (Curve A) an auxiliary orthogonal field. 
         FIG. 8A  shows an embodiment of the electrical circuitry connected to the main coil (MC) and the auxiliary coil (AC) with a separate oscillator signal source and separate interconnect lines. 
         FIG. 8B  is a graph of the write current (I w ) to the MC and the auxiliary current to the AC as a function of time for the circuitry embodiment of  FIG. 8A . 
         FIG. 9A  shows an embodiment of the electrical circuitry connected to the MC and the AC that does not require an oscillator as a separate signal source and separate interconnect lines. 
         FIG. 9B  is a graph of the write current (I w ) to the MC and the auxiliary current to the AC as a function of time for the circuitry embodiment of  FIG. 9A . 
         FIGS. 10A-10B  show an embodiment of the write head according to the invention as a modification of the planar write head with helical coil shown in corresponding  FIGS. 6A-6B . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a top plan view of a head/disk assembly of a hard disk drive  10  with the cover removed. The disk drive  10  includes a rigid base  12  supporting a spindle  14  that supports a stack of disks, including top disk  16 . The spindle  14  is rotated by a spindle motor (not shown) for rotating the disks in the direction shown by curved arrow  17 . The hard disk drive  10  has at least one load beam assembly  20  having an integrated lead suspension (ILS) or flexure  30  with an array  32  of electrically conductive interconnect traces or lines. The load beam assemblies  20  are attached to rigid arms  22  connected to an E-shaped support structure, sometimes called an E-block  24 . Each flexure  30  is attached to an air-bearing slider  28 . A magnetic recording read/write head  29  is located at the end or trailing surface  25  of slider  28 . The flexure  30  enables the slider  28  to “pitch” and “roll” on an air-bearing generated by the rotating disk  16 . Disk drive  10  also includes a rotary actuator assembly  40  rotationally mounted to the rigid base  12  at a pivot point  41 . The actuator assembly  40  is a voice coil motor (VCM) actuator that includes a magnet assembly  42  fixed to base  12  and a voice coil  43 . When energized by control circuitry (not shown) the voice coil  43  moves and thereby rotates E-block  24  with attached arms  22  and load beam assemblies  20  to position the read/write heads  29  to the data tracks on the disks. The trace interconnect array  32  connects at one end to the read/write head  29  and at its other end to read/write circuitry contained in an electrical module or chip  50  secured to a side of the E-block  24 . The chip  50  includes a read preamplifier and a write driver circuit. 
       FIG. 2  is an enlarged end view of the slider  28  and a section of the disk  16  taken in the direction  2 - 2  in  FIG. 1 . The slider  28  is attached to flexure  30  and has an air-bearing surface (ABS)  27  facing the disk  16  and an end or trailing surface  25  generally perpendicular to the ABS  27 . The ABS  27  causes the airflow from the rotating disk  16  to generate a bearing of air that supports the slider  28  in very close proximity to or near contact with the surface of disk  16 . The read/write head  29  is formed as a series of thin films deposited on the slider  28  on its trailing surface  25 . Typically a layer of insulating material, like alumina, is deposited over the read/write head  29  and serves as the outer surface of slider  28 . The read/write head  29  is connected to terminal pads  31 . The terminal pads  31  connect to the trace array  32  on flexure  30  for electrical connection to the read preamplifier and write driver in chip  50  ( FIG. 1 ). 
       FIG. 3  is a view in the direction  3 - 3  of  FIG. 2  and shows the ends of read/write head  29  as viewed from the disk  16 . The read/write head  29  includes a read head  96  and a write head  33  that are formed as a series of thin films deposited and lithographically patterned on the trailing surface  25  of slider  28 , with the films of the read head being deposited first and the films of the write head being deposited over the read head. The magnetoresistive read sensor or head  96  is located between two magnetic shields S 1  and S 2 , with first shield SI being located on trailing surface  25 . The write head  33  has a perpendicular write head and includes magnetic write pole (WP) with WP tip  72  and flux return pole  76 . The WP tip  72  may be generally surrounded at the ABS by optional side shields  84  and trailing shield  80 . The trailing shield  80  and side shields  84  may be connected to form a wraparound shield (WAS). The WAS is described in detail as a shield for a conventional perpendicular recording head in U.S. Pat. No. 7,002,775 B2 assigned to the same assignee as this application. The WAS, which is separated from the WP tip  72  by nonmagnetic gap material, alters the angle of the write field and improves the write field gradient at the point of writing, and also shields the writing field at regions of the disk away from the track being written. The shields S 1 , S 2  for the read head  96  and the shields  80 ,  84  for the WP tip  72  are formed of magnetically permeable material. A layer of insulating material, like alumina, is deposited over the write head  33 , resulting in an outer surface  26 . The width of the WP tip  72  and the read head  96  in the cross-track direction correspond generally to the trackwidth (TW) of the data tracks on the disk  16 . 
       FIG. 4A  is a sectional view of a portion of slider  28  showing the perpendicular write head  33  and a portion of a perpendicular magnetic recording disk  16 . The disk  16  includes a perpendicular magnetic data recording layer (RL) on a “soft” or relatively low-coercivity magnetically permeable underlayer (SUL) formed on the disk substrate. The write head  33  includes a yoke made up of the main pole  74 , flux return pole  76 , and yoke stud  78  connecting the main pole  74  and flux return pole  76 ; and a thin film “pancake” coil  79  shown as sections wrapped around yoke stud  78 . The return pole  76  and yoke stud  78  are formed of soft ferromagnetic material, such as alloys of NiFe, CoFe and NiFeCo that are typically formed by electroplating. The write head  33  in  FIG. 4A  is depicted without the optional WAS ( FIG. 3 ). The coil  79  is connected to terminals, such as terminal  31 , on the outer surface  26  of slider  28 . A flared write pole (WP)  70  is part of the main pole  74  and has a flared portion  71  and a pole tip  72  that faces the surface of disk  16 . The WP  70  is formed of a high-moment material, such as a high-moment CoFe alloy, that is typically formed by sputter deposition, and may be a laminated structure. Write current through the thin film coil  79  induces a magnetic field (shown by dashed line  90 ) from the flared WP  70  that passes through the data RL (to magnetize the region of the RL beneath the WP  70 ), through the flux return path provided by the SUL, and back to the return pole  76 . The slider  28  has its air-bearing surface (ABS)  27  supported above the surface of disk  16  as the disk  16  moves past the write head  33  in the direction indicated by arrow  100 . The RL is illustrated with a perpendicularly recorded or magnetized region representing data adjacent to the pole tip  72 . Preceding regions are shown having random prerecorded magnetization directions, as represented by the arrows. The magnetic transitions are detectable by the read head (not shown in  FIG. 4A ) as the recorded bits. The write coil  79  is called a “pancake” coil because it is deposited and patterned on the trailing end of the slider as essentially a single layer and thus all of the coil turns lie in substantially the same plane. When write current from the write driver in chip  50  ( FIG. 1 ) is directed to coil  79  in one direction, for example in  FIG. 4A  out of the paper in the upper coil sections  79  with dots and into the paper in the lower coil sections  79  with the Xs, the region of the RL beneath the WP tip  72  is magnetized in one direction, down or into the disk in  FIG. 4A . When the write driver switches the direction of the write current to coil  79 , the region of the RL beneath the WP tip  72  is magnetized in the opposite direction, i.e., up or out of the disk in  FIG. 4A . 
       FIG. 4B  is a view in the direction  4 B- 4 B of  FIG. 4A  and illustrates the flare region  71  of the flared WP  70 . The region between the WP tip  72  and the flare portion  71  is called the flare point  75 . The flare point  75  of the WP  70  is sometimes referred to as the “choke” point because it is the point where the flux density is highest and where the WP  70  saturates. The WP tip  72  has its primary or perpendicular axis oriented perpendicular to the ABS and has a “height” or distance from the ABS to flare point  75  called the throat height (TH). As shown in  FIG. 4B , the two side walls of WP tip  72  define its width in the cross-track direction, which substantially defines the trackwidth (TW) of the data recorded in the RL of disk  16 . 
     The perpendicular write head of  FIG. 4A  has a “pancake” coil  79 .  FIG. 5  shows slider  28  with trailing surface  25 , outer surface  26  and a read head  96  between shields S 1 , S 2  like that in  FIGS. 4A-4B , but wherein the perpendicular write head  133  has a thin film “helical” coil (shown with coil sections  139   a ,  139   b ) wrapped around the main pole  74 . A perpendicular write head with a helical coil is described in US 2008/0186628 A1 assigned to the same assignee as this application. The write head  133  is formed on slider  28  having an outer surface  26  and also includes a yoke made up of the main pole  74 , a shield layer  135 , and connection stud  137  to the main pole  74 . Pole  136  is the return path for the magnetic flux  90  and is connected to trailing shield  150 , which may be part of a WAS. Return pole  136  has a yoke stud  138  that connects the return pole  136  to the main pole  74 . A flared WP  70  is part of the main pole  74  and has a flared portion  71  and a WP tip  72  like that shown in  FIGS. 4A-4B . Write current through coil  139   a ,  139   b  induces a magnetic field (shown by dashed line  90 ) from the WP  70  that passes through the RL (to magnetize the region of the RL beneath the WP tip  72 ), through the flux return path provided by the SUL, and back to the return pole  136 . The end of WP tip  72  is located substantially at the ABS, and the return pole  136  has an end  136 a that is located substantially at the ABS and thus generally coplanar with end WP tip  72 . 
       FIG. 6A  is a side sectional view showing slider  28  with trailing surface  25 , outer surface  26  and a read head  96  between shields S 1 , S 2  like that in  FIG. 5 , but wherein the perpendicular write head  233  is a “planar” write head with a thin film “helical” coil (shown with coil sections  239   a ,  239   b ) wrapped around the main pole  274 .  FIG. 6A  shows a first set of coil segments  239   a , the main pole  274  and connected WP  270 , and a second set of coil segments  239   b . In  FIG. 6A  the flux return path is not visible, unlike item  90  in  FIG. 5 , because the return poles are substantially coplanar with main pole  274 . 
       FIG. 6B  is a view in the direction  6 B- 6 B of  FIG. 6A . The main pole  274 , first return pole  235 , second return pole  236  and connecting stud  237  are all formed as a single continuous layer. The return poles  235 ,  236  are spaced on opposite sides of main pole  274  in the cross-track direction.  FIG. 6B  also illustrates the two sets of coil segments  239   a ,  239   b.  The first coil segments  239   a  are formed before the main pole and return poles and the second coil segments  239   b  are formed after the main pole and return poles. The two sets of coil segments  239   a ,  239   b  are then connected at their ends to form the helical coil that is wrapped around the main pole  274 . Write current to and from leads  239   c ,  239   d  travels in a helical path around the main pole  274 . Depending on the direction of current, a magnetic field is induced in one of two directions from WP  270  generally perpendicular to the RL. For example, in  FIG. 6B  the coil is wrapped in a direction such that write current in from lead  239   c  and out through lead  239   d  would induce a magnetic field perpendicularly toward the RL, as shown by the direction of the arrow in RL just beneath the end of WP tip  272 . The return poles  235 ,  236  may optionally have ends  235   a ,  236   a , respectively, that are tapered toward the end of WP tip  272 . This results in the return pole end faces  235   a ,  236   a  being located closer to the main pole  274  than the return pole regions recessed from the ABS and facilitates the flux return path  290  while still providing space for formation of the coil segments  239   a ,  239   b.  The planar perpendicular write head with helical coil shown in  FIGS. 6A-6B  is described in pending application Ser. No. 11/743,150 filed May 2, 2007, published as US 2008/0273268 A1, and assigned to the same assignee as this application. 
     In this invention an auxiliary pole with auxiliary coil is used to inject magnetic flux into the main pole at an angle, preferably substantially orthogonal, to the primary axis of the main pole. The write flux from the main pole flows in a direction perpendicular to the ABS, either toward or away from the RL, depending on the direction of write current in the main coil. The additional flux from the auxiliary pole, which is injected non-parallel to the primary magnetization of the main pole, exerts a relatively large torque on the magnetization of the main pole, thereby facilitating magnetization reversal of the main pole. The basic concept of the invention is shown in  FIG. 7A , which illustrates the main coil (MC) and main pole with write flux directed perpendicular to the RL of the disk and the auxiliary coil (AC) and auxiliary pole with auxiliary flux directed at an angle (greater than 15 degrees) and preferably substantially orthogonal (70 to 90 degrees) to the main pole. 
     A computer simulation has established that the time required for flux reversal in the main pole, which directly relates to data rate performance, is significantly reduced with this invention. This reduced switching time, or increased write head switching speed, thus allows for a disk drive with an increased data rate.  FIG. 7B  shows the computer-generated micromagnetic simulation of the magnetization reversal of a cylindrical magnetic nanostructure representing the write pole. The nanostructure has a diameter D=8 nm and a height h=10 nm. At time t=0, the nanostructure has a normalized magnetization of +1. Curve A shows the attempt to reverse the magnetization to −1 by applying a field parallel to the height of the nanostructure at a frequency of 0.5 GHz. As shown by Curve A, the magnetization is not switched but only reduced to about +0.3 after about 1 ns. Curve B shows the result when the same parallel field is applied together with an auxiliary field orthogonal to the height of the nanostructure. The orthogonal auxiliary field had an amplitude equal to 20% of the amplitude of the parallel field and was applied at a frequency of 1.0 GHz, twice the frequency of the parallel field. As shown by Curve B the magnetization is completely switched to −1 after about 0.8 ns. Additional simulations at different frequencies for the auxiliary orthogonal field show that higher frequencies improve the switching time even further. For example at a frequency of 6.5 GHz for the auxiliary orthogonal field, the magnetization is switched to −1 in about 0.5 ns. 
     Thus it has been determined that switching of the write pole magnetization benefits from the application of an orthogonal auxiliary magnetic field with the improvement depending on the frequency of the auxiliary field. As is well known in the art, ferromagnetic materials absorb applied magnetic fields more efficiently at or near their ferromagnetic resonance frequency [Kittel C., “On the Theory of Ferromagnetic Resonance Absorption”, Phys. Rev. 73, p. 155-161 (1948)]. Accordingly, the frequency of the auxiliary magnetic field from the auxiliary coil can be selected to be preferably within a range near the ferromagnetic resonance of the magnetic material making up the write pole, which generally implies a frequency higher than the frequency of the main write field. Ferromagnetic resonance arises from the precessional motion of the magnetic material of the write pole in the presence of the auxiliary magnetic field from the auxiliary coil. The auxiliary magnetic field puts a torque on the magnetization of the magnetic material of the write pole which causes the magnetic moment to precess. The resonant frequency of the ferromagnetic precession depends on the material properties, including magnetic anisotropy and moment density and the shape of the magnetic structure. For example, for material used as write poles in conventional disk drive write heads, the ferromagnetic resonance frequency is typically in the range of 1-4 GHz. However, auxiliary fields with frequencies lower than the ferromagnetic resonance frequency will also contribute to the switching of the magnetization of the write pole when applied at appreciable angles relative to the main direction of the magnetic anisotropy of the write pole. If the auxiliary field is at a frequency less than the ferromagnetic resonance frequency, the beneficial effect of the auxiliary field on the switching of the magnetization of the write pole will be dominated by the increase of the magnetic reversal torque in proportion to sin(θ), where θ is the angle between the local direction of the total field from the main and auxiliary coils and the local direction of the magnetization of the write pole. The proportionality of the magnetic torque to sin(θ) also explains why the auxiliary field is useful not only at angles of 90 degrees but at lesser angles, preferably in the range of 15 to 90 degrees, relative to the write pole. 
       FIG. 8A  shows an embodiment of the electrical circuitry connected to the main coil (MC) and the auxiliary coil (AC) to generate the auxiliary flux simultaneous with the switching of the magnetization of the main pole. The write driver circuitry is in the read/write integrated circuit of chip  50  ( FIG. 1 ) that is located away from the slider, typically on the E-block  24  ( FIG. 1 ). The write driver is connected via interconnect lines on the integrated lead suspension (ILS) to the MC at terminals T 1 , T 2 . The write head has a resistance R w , the MC has an inductance L MC , and the term C MC  represents the parasitic capacitance. In the embodiment of  FIG. 8A , an oscillator is also located in the circuitry of chip  50  as an independent signal source for the auxiliary coil (AC) with inductance L AC . The oscillator is connected to the AC via interconnect lines separate from the interconnect lines between the write driver and the MC, but also located on the ILS. The oscillator provides the high-frequency signal (higher than the frequency of the write signal from the write driver) to the AC. The frequency of the oscillator is controlled by the voltage (V fentl ). The phase (θ) of the oscillator is controlled with respect to the phase of the write signal so that the AC generates the auxiliary flux in phase with the switching of the write current from the MC. The independent signal source for the auxiliary current with phase matched to the phase of the write signal can be accomplished with use of a conventional phase-locked-loop (PLL) and voltage-controlled oscillator (VCO). 
       FIG. 8B  is a graph of the write current (I w ) to the MC and the auxiliary current to the AC as a function of time. In this example, the write current is depicted as switching from +50 mA to −50 mA at a frequency of 250 MHz, which corresponds to a maximum data rate of 500 Mb/sec. The auxiliary current should have a frequency greater than the maximum write frequency, preferably close to the ferromagnetic resonance frequency of the magnetic material of the write pole. The auxiliary current should have a magnitude at least about 20% of the magnitude of the write current. For example, in  FIG. 8B  the auxiliary signal is at a frequency about 12 times the frequency of the write signal with a signal amplitude of about 20% the amplitude of the write signal and thus switches the current in the AC from +10 mA to −10 mA. 
       FIG. 9A  shows an embodiment of the electrical circuitry connected to the MC and the AC that does not require the oscillator as a separate signal source and separate interconnect lines. In this embodiment the high-pass filtered signal of the write signal is used to energize the AC and create the auxiliary flux. A pair of matched capacitors C AC  are in series with the AC and serve as a high-pass filter (HPF) for the write signal from the write driver to the MC. The HPF is in parallel with the MC. In  FIG. 9B  I w  is the write current to the MC and is shown with the current to the AC that is generated from the HPF. When the write signal switches the direction of write current, for example from positive to negative at 2 ns, the HPF passes high-frequency components which are directed to the AC to create the auxiliary flux. The high-frequency components are generated by the high-pass transitions of the write current. The following equation shows a calculation of the natural resonance frequency (f HP ) of the write signal, which is the high-pass of the HPF: 
     
       
         
           
             
               f 
               HP 
             
             ≈ 
             
               
                 1 
                 
                   2 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   π 
                 
               
               ⁢ 
               
                 
                   2 
                   
                     
                       C 
                       
                         A 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         C 
                       
                     
                     ⁡ 
                     
                       ( 
                       
                         
                           L 
                           MC 
                         
                         + 
                         
                           L 
                           
                             A 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             C 
                           
                         
                       
                       ) 
                     
                   
                 
               
             
           
         
       
     
     Passive components can be formed on the slider to create the HPF and fabricated using the same materials and thin film processes as used to fabricate the read/write head on the slider. Resistors on the order of several Ohms to tens of kOhms can be fabricated from existing films with resistivity ranging from 0.01 Ohm/sq to 20 Ohms/sq. Capacitors ranging from a few femtoF to tens of picoF can be fabricated from alumina gaps ranging from 10 nm to several microns. Inductors up to tens of nanoH can be made from shield and pole material required for the read/write head. In addition, resistive passive components may be added in series with L AC  and or L MC  to aid in dampening the resonance of the HPF. 
       FIGS. 10A-10B  show one embodiment of the write head of the invention as a modification of the planar write head with helical coil shown in  FIGS. 6A-6B . In the side sectional view of  FIG. 10A , an auxiliary pole  280  is formed with its longitudinal axis oriented preferably substantially orthogonal (70 to 90 degrees) to the primary axis of both main pole  274  and its attached WP  270 . A single-turn auxiliary coil  282  is shown in section wrapped around auxiliary pole  280 . The auxiliary coil  282  may also be a multi-turn coil. The auxiliary pole  280  may have an attached flux guide  281  that faces the WP  270  and assists in directing flux to WP  270 . The auxiliary pole  280  and flux guide  281  may be formed of the same high-moment material used in conventional write poles, like WP  270 .  FIG. 10B  is a view of the outer surface of slider  28  with protective alumina overcoat removed to show the underlying features of the write head of the invention. The auxiliary coil  282  is connected to terminals T 3 , T 4  on slider  28 . The main coil  239   a ,  239   b  is connected to terminals T 1 , T 2  on slider  28 . In  FIG. 10B , the write head is depicted as connected to the embodiment of electrical circuitry wherein the auxiliary coil is energized by the high-pass filtered write signal, like that shown in  FIG. 9A . Thus the two matched capacitors C AC  that form the HPF are shown as being fabricated on the slider  28  and connected between T 1  and T 4 , and T 2  and T 3 , respectively. 
     Other embodiments of a write head with helical coil and auxiliary coil are also possible. For example, referring to the helical write coil depicted in  FIG. 5 , this structure can be modified by the addition of an auxiliary coil and auxiliary pole (like coil  282  and pole  280  with flux guide  281  in  FIGS. 10A ,  10 B) between WP  70  and return pole  136 . 
     While the present invention has been particularly shown and described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the invention. Accordingly, the disclosed invention is to be considered merely as illustrative and limited in scope only as specified in the appended claims.