Abstract:
A magnetoresistive read head having a corrugated magnetoresistive layer wherein the corrugated section does not encroach on magnetic elements on either end of the magnetoresistive layer. The corrugations in the magnetoresistive layer stabilize the magnetization in the center region of the read head, while the magnetic elements stabilize the magnetization at the ends. By separating the two stabilization methods, unfavorable interactions between them is reduced.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to data storage technology, and particularly to devices implementing magnetoresistive read heads. 
   2. Background of the Invention 
   In the data storage field, information is stored in many ways. One way includes writing data onto a magnetic tape by selectively magnetizing regions of the tape. The magnetized tape regions produce a magnetic stray field which can be read by a read head located above the tape surface and converted into an electrical signal. A common type of read head for this task is the magnetoresistive (MR) read head. 
   A common goal in the information storage industry is to magnetically stabilize a magnetoresistive read head such that the generated electric signal is well behaved. This is frequently accomplished by controlling the boundary or end magnetic domains in a MR element. The control is via magnetic exchange tabs or permanent magnets (PM) deposited at the ends of the element. However, the wider the track width is made, the less effective boundary magnetic control is for the center of the element. A recent technique to overcome this limitation is to introduce a periodic perturbation (gratings) of the element shape in the middle of the device which creates a periodic magnetic charge that stabilizes the middle of the MR element. However, the periodic perturbation can interfere with the magnetic field of the PM and bias current flow direction into MR element. This problem is exacerbated by the fact that read elements must continue to decrease in size to keep up with the scaling of other related technologies. As the read heads are made smaller, the relative sizes of regions of magnetization instability in the MR element grow. 
   The technology of MR read heads would therefore benefit from a way to stabilize magnetization patterns in the read head. 
   SUMMARY OF THE INVENTION 
   The present application teaches an improvement to magnetic stabilization of MR read heads. In a preferred sample embodiment, this is done by limiting the undulations of the periodic structure in the MR element to areas not immediately next to or including the PMs at either end of the element. 
   A known way to take care of the problem of stabilizing the magnetic field is to install permanent magnets (PMs) on opposite sides of the MR element. This stabilizes the magnetization near the ends of the element. 
   Later, corrugated or periodic structure in the MR element itself was introduced, in order to stabilize the magnetic field in the regions between the PMs. This was best used in wide structures, because where the grating nears the PMs, large perturbations in the magnetization from the preferred configuration may result. 
   As MR heads shrink in size, the technique of putting a periodic structure in the MR element is less useful, because the relative sizes of the regions of interaction between the demagnetization magnetic fields of the grating and the PMs is increased. 
   In the present invention, the periodic structure of the MR element is used but limited to regions that are not directly adjacent to the PMs at either end of the element. This allows for the PMs to stabilize the magnetization near the ends of the MR element, and allows the periodic structure to stabilize the magnetic field in the middle region of the MR element without perturbing the magnetic field origination from the PMs. 
   In an example embodiment, by terminating the periodic structure before it encroaches in the MR boundary or end region where the PMs have been deposited, simultaneous stabilization of both the ends and the center of the MR element can be accomplished. 
   In preferred embodiments, the magnets formed on the read head are not contiguous with the section of the magnetoresistive layer having the grating or periodic structure. The permanent magnet layers preferably do not cover any of the gratings in the structure of the magnetoresistive layer. The edges of the magnets preferably begin just past the last lines of the grating structure. Of course, this distance can vary, from the permanent magnets beginning very close to the end of the grating, or a small distance can separate the grating from the magnet. 
   The present innovation offers the advantage of allowing control of unwanted domain activity over a wide range of MR track widths. 
   Though the detailed description depicts embodiments having permanent magnets at the ends of the magnetoresistive layer, magnetic exchange tabs or other types of magnetic elements can be used consistent with the present innovations. The type of magnetic element used is not intended to be a limiting factor; rather the relative placement of the magnetic elements and the grating of the magnetoresistive structure more clearly depicts the present innovations. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
       FIG. 1  shows a magnetic read head and a recording medium consistent with implementation in a preferred embodiment. 
       FIG. 2  shows a sectional view of an innovative read head structure according to a preferred embodiment. 
       FIG. 3  shows a planar view of the innovative read head structure according to a preferred embodiment as in  FIG. 2  but with the magnetic field shielding components not drawn for clarity. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The present innovations are described with reference to the several figures. The described embodiments and implementations teach the present innovations by way of example only, and are not intended to limit the scope of the invention to the exact embodiments, dimensions, or methods described. 
     FIG. 1  shows a general setup for a read head and magnetic media. The read head  102  uses the magnetoresistance effect to read data from the recording medium  104  by detecting changes in the resistance between two electrodes (or conductor leads)  106 ,  108  caused by changes in the recording medium magnetization. As the magnetized material passes near the read head, the magnetic field arising from the recording medium changes the magnetization of the magnetoresistive material in the read head, causing the resistance between the electrodes to change. This change is typically measured as a voltage change. 
   A way to increase the amount of information recorded in an area of recording medium is to increase the number of side by side tracks containing recorded information, by decreasing the width of each of them. To detect the data in a track, the read head therefore should preferably be narrow (i.e., be short along the “H” dimension in  FIG. 1 ) so as to experience the magnetic field from the recorded data in a single track. 
   To ensure proper and consistent operation of MR heads, unwanted domain activity must be suppressed. This must be accomplished for a wide range of track widths or Tracks per Inch (TPI). This means that the MR track width could vary from product to product while the need to maintain stable head operation remains. The current technique allows control of unwanted domain activity to be attempted over a wide range of MR track widths. 
   A preferred embodiment of the present invention is shown in  FIG. 2 . This figure shows a cutaway view of the magnetoresistive read head consistent with a preferred embodiment. Though the following structure is recited with particular dimensions and materials, this description is intended as an example only. Other dimension and materials can of course be used within the contemplation of the present innovations. 
   At the bottom of the shown structure  200  is one of two magnetic shields  202 . These are typically highly permeable magnetic shields that help focus the magnetic fields from the disk and help eliminate stray fields. In a preferred embodiment, the magnetic shield is made from a cobalt-zirconium tantalium alloy (CZT) and is about 2.5 micron thick. 
   Above the bottom magnetic shield  202  is a first gap layer  204 , made of aluminum oxide and about 1100 angstroms thick in a preferred embodiment. This layer forms the substrate upon which the magnetoresistive element is formed, and upon which the permanent magnets  206  are placed. The permanent magnets  206  are shown at either end of the structure. 
   Within the MR element itself are shown three layers  210 ,  212 ,  214 . The first layer  210  is formed from a cobalt zirconium molybdenum alloy (CZM) and is typically about 250 angstroms thick. This layer serves to create a magnetic field in the MR or NiFe layer and thus allows quasi-linear magnetic field (from the medium) to voltage device operation to occur. 
   Above this layer is a spacer layer. This layer is preferably made from tantalum and is about 80 angstroms thick. This layer serves to prevent direct contact between the magnetic first layer and the magnetic third layer or the magnetoresistive layer. 
   Above the spacer layer  212  is formed the third layer  214  of the MR element. This layer  214  is preferably comprised of a nickel iron alloy and is about 320 angstroms thick. This layer serves to create the magnetoresistive response which converts detected magnetic field changes to resistance or voltage changes. 
   Above the MR element is formed a final gap layer  216 . This layer is preferably comprised of alumina as was the first gap layer. Gap layer  216  is preferably formed at about 1500 angstroms thickness. The gap layer  216  covers both the MR element and the PMs at either end of the MR element. 
   Above the second gap layer is the top magnetic shield  218 . This shield  218  is preferably comprised of CZT, as is the bottom magnetic shield, and is about 2.5 micron thick. Top shield  218  works with bottom shield  202  to block stray magnetic fields. 
     FIG. 2  shows that the MR element is not planar shaped, but has undulations  208  built into it, forming a periodic structure on the surface of the element. These periodic perturbations  208  to the surface structure help to stabilize the magnetization in the interior region of the MR read head. 
   Forming the periodic structure in the whole length of the MR element, as has been done heretofore, causes boundary irregularity problems on the ends of the MR element. The combined magnetic fields of the PMs and the periodic structure interfere, causing non-optimum magnetic fields in direction and magnitude near the PM to MR element boundary and possibly causing undesirable structural and magnetic property changes in the PM material near the boundary. 
   The present innovations teach that these problems are alleviated by limiting the region of the periodic structure in the MR element to areas that are not directly adjacent to the PMs. This allows simultaneous stabilization of both the end regions and the center region of the MR element. 
   The periodic topography of the MR element shown in  FIG. 2  are preferably formed by photolithographic and iron milling means. 
     FIG. 3  shows a planar view of a preferred embodiment, with the magnetic shields removed for clarity. In this example embodiment, the non-penetration of the periodic grating structure into the PM region is clearly seen. 
   In this example embodiment, the tape bearing surface  302  is part of the SAL/MR region  304 . Permanent magnets  306  abut the SAL/MR region at junctions. The stabilizer grating  308  is located in the SAL/MR region  304  as well, between the PMs  306  and not encroaching beneath them. High conductivity leads  310  are also shown to provide power to the device.