Abstract:
A perpendicular magnetic recording head includes a main write pole and multiple return poles. The size of each return pole is controlled in order to provide substantially the same magnetic reluctance through each return pole. The return poles effectively reduce or eliminate the flux antenna effect caused by stray magnetic fields.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Serial No. 60/192,053 filed Mar. 24, 2000. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to perpendicular magnetic recording heads, and more particularly relates to a perpendicular recording head having a main write pole and multiple return poles which reduce or eliminate the flux antenna effect caused by stray magnetic fields. 
     BACKGROUND INFORMATION 
     Perpendicular magnetic recording systems have been developed for use in computer hard disk drives. A typical perpendicular recording head includes a trailing main pole, a leading return pole magnetically coupled to the main pole, and an electrically conductive magnetizing coil surrounding the main pole. The bottom of the return pole has a surface area greatly exceeding the surface area of the tip of the main pole. Conventional perpendicular recording media typically include a hard magnetic recording upperlayer and a soft magnetic underlayer which provide a flux path from the trailing write pole to the leading return pole of the writer. 
     To write to the magnetic recording media, the recording head is separated from the magnetic recording media by a distance known as the flying height. The magnetic recording media is moved past the recording head so that the recording head follows the tracks of the magnetic recording media, with the magnetic recording media first passing under the return pole and then passing under the main pole. Current is passed through the coil to create magnetic flux within the main pole. The magnetic flux passes from the main pole tip, through the hard magnetic recording track, into the soft underlayer, and across to the return pole. 
     The closed magnetic flux path provided by the trailing pole, soft underlayer and return pole increases efficiency of such conventional systems. The soft underlayer also effectively doubles the recording layer thickness through the effect of magnetic imaging. Furthermore, the soft underlayer advantageously increases vertical field gradients in the recording media through the magnetic imaging effect. 
     However, a problem associated with the use of soft underlayers is that such layers cause extreme sensitivity of the perpendicular recording system to stray magnetic fields. For example, stray fields of approximately 5 œ, e.g., from a voice coil motor, may be sufficient to cause data instability and to initiate random erasing of previously written information. This problem resulting from stray magnetic fields is known as the flux antenna effect. 
     The present invention has been developed in view of the foregoing. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is to provide a perpendicular magnetic recording head comprising a main write pole and multiple return poles. The return poles substantially eliminate the flux antenna effect during operation of the recording head. 
     Another aspect of the present invention is to provide a perpendicular magnetic recording system comprising a perpendicular magnetic recording medium including a hard magnetic recording layer and a soft magnetic underlayer, and a perpendicular magnetic recording head positionable over the medium. The recording head comprises a main write pole, and multiple return poles. 
     A further aspect of the present invention is to provide a method of making poles of a perpendicular magnetic recording head. The method includes the steps of depositing a first return pole layer, depositing a main write pole layer over at least a portion of the first return pole layer, and depositing a second return pole layer over at least a portion of at least one of the first return pole layer and main write pole layer. 
     These and other aspects of the present invention will be more apparent from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partially schematic sectional side view of a conventional perpendicular magnetic recording system including a writer having a trailing main pole and a leading return pole, illustrating the problem caused by a stray magnetic field which travels through the soft underlayer of the recording media, and which is amplified as it travels through the head from the return pole to the main pole. 
     FIG. 2 is a partially schematic sectional side view of a perpendicular magnetic recording head having a main write pole and two return poles in accordance with an embodiment of the present invention. 
     FIG. 3 is a partially schematic bottom view of the recording head of FIG. 2, illustrating the relatively small cross sectional area of the main write pole and the relatively large cross sectional areas of the return poles at the air bearing surface of the recording head. 
     FIG. 4 is an isometric view illustrating deposited layers of a perpendicular magnetic recording head having a main write pole and two return poles in accordance with an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 schematically illustrates a perpendicular recording head  10  which includes a trailing main write pole  12  and a leading return pole  14  connected by a yoke  15 . A magnetizing coil  16  surrounds the main pole  12 . The perpendicular recording head  10  is positioned above a magnetic recording disk  18 . The disk  18  includes a substrate  20 , a soft magnetic underlayer  22 , a hard magnetic recording layer  24  and a protective layer  26 . The disk  18  may also include a magnetic decouple layer (not shown) between the soft underlayer  22  and recording layer  24 . 
     As shown in FIG. 1, when current is passed through the coil  16 , a closed magnetic flux path is generated which travels along a path M from the tip of the main pole  12  perpendicularly through the recording layer  24 , across the soft underlayer  22  to the return pole  14 . A problem associated with the design shown in FIG. 1 is that stray magnetic fields S 1  enter the soft underlayer  22  of the disk  18  and, due to the closed magnetic path between the opposing pole  14  and the main pole  12 , are drawn into the recording head  10  through the opposing pole  14 . The stray magnetic fields S 1  may be produced by such sources as voice coil motors (up to 50 œ fields), and some bit patterns under the leading pole which can generate fields up to 50 œ and higher due to the soft underlayer. 
     As shown in FIG. 1, stray fields S 1  under the return pole  14  get amplified approximately by the ratio of the area of the return pole  14  to the area of the main pole  12 . This causes a deleterious flux antenna effect. With this ratio being approximately 50 for typical designs, the fields S 2  can be amplified, e.g., up to 2,500 œ, under the main pole. This can be sufficient to cause data instability or even erase previously written information. 
     FIG. 2 schematically illustrates a perpendicular recording head  30  in accordance with an embodiment of the present invention. Similar to the embodiment shown in FIG. 1, the recording head  30  of FIG. 2 includes a main write pole  32 , a leading return pole  34 , and an interconnecting yoke  35 . A magnetizing coil  36  surrounds the main pole  32 . The recording head  30  includes a second return pole  40  connected to the main pole  30  by an interconnecting yoke  42 . 
     As shown in FIG. 2, the second return pole  40  reduces or eliminates the flux antenna effect by providing a flux path for stray magnetic fields which essentially circumvents the main pole  32 . The stray magnetic field S 1  which enters the return pole  34  travels through the yokes  35  and  42  and exits the head via the return pole  40 . In the embodiment shown in FIG. 2, the stray magnetic field S 2  exiting the return pole  40  is approximately the same order of magnitude as the incoming stray magnetic field S 1 . The ratio of S 1 :S 2  is about equal, and the flux antenna effect is substantially eliminated, thereby avoiding data instability and possible unwanted erasure of the magnetic recording layer  24 . 
     FIG. 3 illustrates the air bearing surface of the recording head  30 . The main pole  32  has a relatively small cross sectional area, while the first and second return poles  34  and  40  each have relatively large areas at the air bearing surface. The ratio of the air bearing surface area of the first return pole  34  to the second return pole  40  may range from about 1:2 to about 2:1, typically from about 1:1.5 to about 1.5:1. In a particular embodiment, the air bearing surface area ratio of the first and second return poles  34  and  40  is about 1:1. The relative cross sectional areas of the yokes  35  and  42  may be similar to the relative cross sectional areas of the first and second return poles  34  and  40 . The air bearing surface area of the main pole  32  is typically at least  10  times smaller than either of the air bearing surface areas of the first and second return poles  34  and  40 , for example, at least 20 times smaller. 
     In accordance with the present invention, the magnetic reluctance of the first return pole  34  should be approximately equal to the magnetic reluctance of the second return pole  40 . Similarly, the magnetic reluctance of the yokes  35  and  42  should be approximately equal. When the first and second return poles  34  and  40  are made of the same or similar materials, the relative magnetic reluctance is equalized by controlling the relative cross sectional areas of the return poles, as shown in FIGS. 2 and 3. Alternatively, the magnetic reluctance of the return poles may be substantially equalized by using different types of materials having different magnetic properties for each pole. For example, if the material of the second return pole  40  has a permeability that is higher than the permeability of the material of the first return pole  34 , the cross sectional area of the second return pole  40  may be smaller than the cross sectional area of the first return pole  34 . 
     In the embodiment shown in FIGS. 2 and 3, the first and second return poles  34  and  40  are provided on opposite sides of the main pole  32 , and are spaced substantially equal distances therefrom. However, other return pole configurations may be used in accordance with the present invention. For example, more than two return poles may be provided. Instead of two separate return poles as shown in FIG. 3, the return poles may be connected at or near the air bearing surface to provide a configuration which at least partially surrounds the main pole  32  at the air bearing surface. Although the first and second return poles  34  and  40  shown in FIGS. 2 and 3 are aligned with the main pole  32  in a direction parallel with the track direction of the recording media  18 , different alignments may be used. For example, the return poles and the main pole may be aligned in a direction perpendicular to the track direction of the recording media. Furthermore, although the main pole  32  is centrally aligned with respect to the return poles  34  and  40  in the embodiments shown in FIGS. 2 and 3, the main pole  32  could be positioned closer to one return pole than the other return pole, or could be positioned at a location which does not lie directly between the return poles. 
     FIG. 4 illustrates various deposited layers of a perpendicular recording head  50  in accordance with an embodiment of the present invention. The magnetically permeable components of the recording head  50  include a first return pole  52  upon which a first pedestal  54  has been deposited. The main write pole  56  is deposited over the first pedestal  54 . The tip of the main pole  56  at the air bearing surface of the recording head  50  defines a track width TW of the recording head  50 . A second magnetically permeable pedestal  58  is deposited on the main pole  56 . A seed layer  59  comprising NiFe is deposited on the second pedestal  58 , followed by deposition of the second return pole  60 . The first return pole  52 , first pedestal  54 , main write pole  56 , second pedestal  58  and second return pole  60  may be made of any suitable magnetically permeable material(s) such as NiFe or NiFeCo. 
     The thickness of the main pole  56  typically ranges from about 100 to about 3,000 nm. The track width TW of the main pole  56  typically ranges from about 25 to about 1,000 nm. The thicknesses of the first and second return poles  52  and  60  typically range from about 250 to about 3,000 nm. The thicknesses of the first and second pedestals  54  and  58  typically range from about 1 to about 3 micron. However, the thicknesses of the various magnetically permeable components may be controlled as desired. 
     As shown in FIG. 4, a magnetization coil is provided which comprises first and second conductive lines  62  and  64  deposited on opposite sides of the main pole  56 . The conductive lines  62  and  64  may be made of any suitable electrically conductive material such as Cu, Au or Ag. The recording head  50  also includes several deposited layers of insulating material  66 ,  67 ,  68  and  69  such as alumina, silicon nitride or the like. 
     The various layers shown in FIG. 4 may be formed by standard deposition techniques. For example, the poles  52 ,  56  and  60 , as well as the pedestals  54  and  58 , may be deposited by plating or vacuum deposition techniques. The conductive lines  62  and  64  may be deposited by plating. The insulating layers  66 ,  67 ,  68  and  69 , and the seed layer  59 , may be deposited by vacuum deposition. 
     Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.