Abstract:
A magnetic media is described including a substrate, an unbalanced soft under layer (SUL), a magnetic seed layer, which may consist of one or more of NiWxCoy, NiWxCoyAlz, NiVaCob, NiVaCobAlc, NiWxVaCob, and NiWxVaFeb, and a magnetic recording layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/984,615, entitled “MAGNETIC SEED LAYER HAVING AN UNBALANCED SOFT UNDERLAYER” and filed on Apr. 25, 2014, which is expressly incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
       FIG. 1  is a schematic illustration of a magnetic recording device, such as an HDD  100 , according to one embodiment of the present disclosure. The HDD  100  includes at least one magnetic recording medium, such as a disk  102  that is supported on a spindle  104 . A motor causes the spindle  104 , and hence the disk  102 , to rotate. One or more magnetic heads  106  are mounted on a slider  108  and move over the disks  102  to read and write information from and to the disks  102 . The heads  106  ride on an air bearing in close proximity to the disks  102  during read and write operations. The slider  108  is coupled to an actuator  110  by a suspension  112 . The suspension  112  provides a slight spring force which biases the slider  108  towards the disk surface. Each actuator  110  is attached to an actuator means  114  that controls the movement of the head  106  relative to the disk  102 . A HDD ramp  116  is positioned such that when the actuator  110  rotates the slider  108  and head  106  away from the disk  102 , the heads and slider can “park” on the HDD ramp  116 . 
     The disk  102  is formed on either a glass or an aluminum alloy substrate depending on the particular design requirements of the device. The disk  102  (also referred to as the media) is configured to be usable at high recording densities, and in some embodiments, to be used in the Perpendicular Magnetic Recording (PMR). The media thus stores data in which the bits of magnetic moment orient in substantially perpendicular direction to the surface of the disk  102 . 
       FIG. 2  depicts a conventional magnetic recording media with a non-magnetic seed layer. As shown in  FIG. 2 , the magnetic media  102  may generally include some or all of the constituent layers shown in  FIG. 2 , including a substrate  202 , a bottom soft magnetic underlayer (SUL)  204  and a top SUL  208  separated by an AFC coupling layer  206 , a non-magnetic seed layer  210 , an intermediate layer  212 , a magnetic recording layer  214 , a cap layer  216  and an overcoat layer  218 . 
     The top SUL layer  208  and the bottom SUL layer  204  are magnetically coupled through the antiferromagnetic coupling layer (AFC)  206 . The bottom SUL  204 , AFC coupling layer  206  and top SUL  208  are also referred to as the SUL structure  220 . The recording layer  214  and the soft under layers  204  and  208  provide a magnetic circuit that allows magnetic flux to travel from the magnetic recording head  106  through the magnetic recording layer  214  and the soft underlayers  204  and  208 , back to the magnetic recording head, thus forming a loop. Additionally, the SUL layers  204  &amp;  208  allow for increasing conductance of magnetic flux through the magnetic media  102  and therefore improve writabilty of the magnetic media  102 . However, the writabilty of the magnetic media  102  further improves if the distance between the magnetic recording head  106  and the top SUL  208  is as small as possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts components of a hard disk drive. 
         FIG. 2  depicts the structure of a conventional magnetic media with an unbalanced SUL and a non-magnetic seed layer. 
         FIG. 3  depicts the structure of a magnetic media with an unbalanced SUL and a magnetic seed layer according to an exemplary embodiment. 
         FIG. 4  depicts another view of the magnetic media with an unbalanced SUL and a magnetic seed layer according to an exemplary embodiment. 
         FIG. 5  illustrates the SNR and Overwrite properties of a magnetic media according to an exemplary embodiment. 
         FIG. 6  illustrates a method of making a a magnetic media according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Aspects of the present invention provide magnetic seed layers in a magnetic recording media. Various aspects of the magnetic recording media according to the present invention will now be described. 
       FIG. 3  depicts the structure of magnetic media with an unbalanced SUL and a magnetic seed layer according an exemplary embodiment. The magnetic media  300  may be used in the disk drive depicted in  FIG. 1 . For clarity, figures are not to scale. For simplicity not all portions of the disk drive, recording head and the media are shown. In addition, although the disk drive is depicted in the context of particular components other and/or different components may be used. For example, circuitry used to drive and control various portions of the disk drive is not shown. For simplicity, only single components are shown. However, multiples of each component and/or its sub-component might be used. 
     A magnetic media  300  according to exemplary embodiments may be formed over a substrate made of aluminum alloy or glass  302 . The media  300  may include a bottom SUL layer  304  deposited on the substrate. In exemplary embodiments, a top SUL layer  308  located above the bottom SUL layer  304 , and separated by an antiferromagnetic coupling (AFC) layer  306  that couples the bottom  304  and top SUL  308  layers, forming the SUL structure  320 . In exemplary embodiments, the bottom SUL  304  thickness may be greater than the thickness of the top SUL  308  layer. In these embodiments, the SUL may be unbalanced with respect to the AFC layer  306 , meaning there is more magnetic material located below the AFC layer  306  than above the AFC layer. In some embodiments the AFC  306  layer may be Ruthenium. Stated differently, the thicknesses and/or magnetic moments of the bottom SUL  304  and top SUL  308  layers may not be the same. 
     In exemplary embodiments, the media  300  may include a magnetic seed layer  310  located on the top SUL  308 . The magnetic seed layer  310  may have a thickness of at least three nanometers and not more than seven nanometers. The magnetic seed layer  310  may have a crystalline structure configured to facilitate growth and orientation of the magnetic recording layer  314 . For example, the magnetic seed layer  310 , along with a nonmagnetic seed layer  312  (also referred to as an intermediate layer), may be used to promote the columnar grain growth along the easy axis, promote the grain size, and provide grain segregation in the magnetic recording layer  314 . In some embodiments, the intermediate layer  312  has a thickness of at least six and not more than fifteen nanometers. The magnetic seed layer  310  includes Nickel (Ni) alloyed with a nonmagnetic material and at least one other magnetic material, such as Fe and/or Co. For example, in one exemplary embodiment, Ni is alloyed with Tungsten (W) and/or Vanadium (V) in addition to Iron (Fe), Cobalt (Co) or Aluminum (Al). In some embodiments, the magnetic seed layer  310  may include at least one of NiW x Fe y , NiW x Co y  and NiW x Co y Al z , where x is between three to seven atomic percent, y and z may be between fifteen and to forty atomic percent, and the remainder of the composition consists of Nickel. In alternative embodiments, the magnetic seed layer  310  may include at least, NiV a Co b , NiW x V a Co y , or NiW x V a Fe b  alloys, where x and a may be at least three atomic percent but not more than seven atomic percent, y and b may be at least fifteen atomic percent and not more than forty atomic percent, c may be between 0.5 and 2 atomic percent, and the remainder of the composition would consist of Nickel. In alternative embodiments of NiW x V a Co y , or NiW x V a Fe b  alloys, the media performance may be optimized by having “x” and “a” equal percent, and/or y and b equal. 
     In some embodiments, the media  300  may include an intermediate layer  312 . As previously stated, the intermediate layer acts as a non-magnetic seed layer above the magnetic seed layer  310 , and may help promote the easy axis for the columnar grain growth as well as the grain size of the magnetic layer  314 . 
     A magnetic recording layer  314  (or magnetic layer)  314  includes magnetic bits that are used by the magnetic recording head to store data on the magnetic media. The recording layer has high coercivity to provide more magnetic and thermal stability for the recorded bits. In some embodiments, the magnetic recording layer  314  may include FePt alloys or FePtX alloys. 
     The magnetic media  300  may have improved performance. The magnetic seed layer  310  and nonmagnetic interlayer  312  may provide the desired growth template to control the grain size, variation in grain size, crystal orientation dispersion and easy axis of the magnetic layer  314 . Thus, the signal to noise ratio of the media  300  may be improved. Because the magnetic seed layer  310  is magnetic instead of nonmagnetic, coupling between the magnetic layer  314  and the soft underlayer structure  320  may be improved. Stated differently, the space between the magnetic layer  314  and a magnetic layer that is magnetically coupled with the soft underlayer structure  320  may be reduced over a media ( 102 ) in which a nonmagnetic seed layer  210  (see  FIG. 2 ) is used in lieu of the magnetic seed layer  310  (see  FIG. 3 ). The magnetic seed layer  310  may, therefore, function magnetically as part of the soft underlayer (bottom SUL  304  &amp; top SUL  308 ) because the magnetic seed layer  310  is magnetically coupled with the top SUL  308  which is coupled to the bottom SUL  304 . Thus, use of the magnetic seed layer  310  may improve writability. Furthermore, the use of a magnetic seed layer above the top SUL  308  allows for a thinner top SUL layer  308 . The top SUL  308  may be decreased in thickness because this layer is magnetically coupled with the magnetic seed layer  310 . Thus, the effective magnetic thickness of the soft underlayer structure  320  (bottom SUL  304  and top SUL  308 ) may be maintained or increased while decreasing/without increasing the physical thickness of the soft underlayer  320 . In some embodiments, the total (effective) magnetic thickness of the top SUL  308  and magnetic seed layer  312  match the magnetic thickness of the bottom SUL  304 . In some embodiments, the moments and/or permeability of the combination of the top SUL  308  and magnetic seed layer  312  match that of the bottom SUL  304 . Thus, writability may be improved without significantly sacrificing track width. The distance between the top of the top SUL  308  and the magnetic head  106  used in conjunction with the media  300  may be decreased. In some cases, the decrease may be equal to the thickness of the magnetic seed layer  312 . Performance of the magnetic recording media  300  at higher densities may be improved. 
     In exemplary embodiments the media  300  may include a capping layer  316  and a protective carbon overcoat layer  318 . The capping layer  316  may help improve the magnetic performance of the recording layer  314 . The carbon overcoat layer  318  is used to provide wear protection for the media  300 . In alternative embodiments, an optional lubrication layer  319  may be placed on the COO to help the recording head  106  glide more easily on the media  300 . 
       FIG. 4  depicts another view of the magnetic media with an unbalanced SUL and a magnetic seed layer according to an exemplary embodiment. The media depicted in  FIG. 4  may be used in the disk drive of  FIG. 1 . For simplicity not all portions of the magnetic media  300  are shown. In addition, although the magnetic media  300  is depicted in the context of particular components other and/or different components may be used. A magnetic media  300  according to exemplary embodiments may be formed over a substrate made of aluminum alloy or glass  402 . The media  300  may include a bottom SUL layer  404  deposited on the substrate. In exemplary embodiments, a top SUL layer  408  located above the bottom SUL layer  404 , and separated by an antiferromagnetic coupling (AFC) layer  406  that couples the bottom  404  and top SUL  408  layers. In exemplary embodiments, the bottom SUL  404  thickness is greater than the thickness of the top SUL  408 . In these embodiments, the SUL structure  410  is considered unbalanced because there is more magnetic material (bottom SUL  404 ) located below the AFC layer  406  than above the AFC layer (top SUL  408 ). Stated differently, the thicknesses and/or magnetic moments of the bottom SUL  404  and top SUL  408  layers may not be the same. In some embodiments the thickness of the top SUL  408  may be different than the thickness of the bottom SUL  404 . 
     In exemplary embodiments, the media  300  includes a magnetic seed layer  416  located above the top SUL  408 . The thickness of the magnetic seed layer  416  may be between 3 and 7 nanometers. The magnetic seed layer  410  has a crystal structure configured to facilitate growth of the magnetic recording layer  428 . For example, the magnetic seed layer  416 , along with nonmagnetic intermediate layer  422  may be used to promote the easy axis for the columnar grain growth as well as the grain size of the magnetic layer  428 . In some embodiments, the intermediate layer  422  has a thickness of at least six and not more than fifteen nanometers. The magnetic seed layer  416  includes Ni alloyed with a nonmagnetic material and with at least one other magnetic material, such as Fe and/or Co. For example, Ni alloyed with W or V and with Fe or Co may be used. In at least some embodiments, the magnetic seed layer  416  includes at least one of NiW x Fe y , NiW x Co y  and NiW x Co y Al z , where x may be at least three atomic percent and not more than seven atomic percent, y, and z may be at least fifteen atomic percent and not more than forty atomic percent. In alternative embodiments, NiV a Co b , NiV a Co b Al c , NiW x V a Co b , or NiW x V a Fe b  where x may be at least three atomic percent and not more than seven atomic percent, y may be at least fifteen atomic percent and not more than forty atomic percent, a may be between five to fifteen atomic percent, and b may be between fifteen to forty atomic percent, c may be between 0.5 and 2 atomic percent, and the remainder of the composition would consist of Nickel. In exemplary embodiments of NiW x V a Co y , or NiW x V a Fe b  alloys, when x and a atomic are equal, the media performance is optimized. 
     In some embodiments, the media  300  may include an intermediate layer  422 . As previously stated, the intermediate layer acts as a non-magnetic seed layer above the magnetic seed layer  416 , and it helps promote the easy axis for the columnar grain growth as well as the grain size of the magnetic layer  428 . 
     The magnetic recording layer  428  (also referred to as magnetic layer)  428  stores the magnetic bits used to store data on the magnetic media  300 . In some embodiments, the magnetic recording layer  428  may include FePt alloys or FePtX alloys. 
     The magnetic media  300  may have improved performance. As depicted in the  FIG. 4 , the magnetic seed layer  416  and nonmagnetic interlayer  422  (shown as the seed layer structure  418 ) may provide the desired growth template to control the grain size (magnetic layer grains  426 ), variation in grain size, crystal orientation dispersion and easy axis of the magnetic layer  428 . Thus, the signal to noise ratio of the media  300  may be improved. Because the magnetic seed layer  416  is magnetic instead of nonmagnetic, coupling between the magnetic layer  428  and the soft underlayer structure  410  may be improved. Stated differently, the space  418  between the magnetic layer  428  and the magnetic seed layer  416  that is magnetically coupled with the soft underlayer structure  410  may be reduced when compared to a conventional magnetic media structure ( 102 ) in which a nonmagnetic seed layer  210  (see  FIG. 1 ) may be used in lieu of the magnetic seed layer  416  (see  FIG. 4 ). The magnetic seed layer  410  may, therefore, function magnetically as part of the soft underlayer (bottom SUL  404  &amp; top SUL  408 ) because the magnetic seed layer  416  is magnetically coupled with the top SUL  408  which is coupled to the bottom SUL  404  through the AFC layer  406 . Thus, use of the magnetic seed layer  416  may improve writability. Furthermore, the use of a magnetic seed layer above the top SUL  408  allows for a thinner top SUL layer  408 . In some embodiments, the total (effective) magnetic thickness of the top SUL  408  and magnetic seed layer  416  match the magnetic thickness of the bottom SUL  404 . In some embodiments, the moments and/or permeability of the combination of the top SUL  408  and magnetic seed layer  416  match that of the bottom SUL  404 . The top SUL  408  may be decreased in thickness because this layer is magnetically coupled with the magnetic seed layer  416 . Thus, the effective magnetic thickness of the soft underlayer structure  410  may be maintained or increased without increasing or even decreasing the physical thickness of the soft underlayer structure  410 . Thus, writability of the magnetic media  300  may be improved without significantly sacrificing track width. The distance between the top of the top SUL  408  and the magnetic head  106  used in conjunction with the media  400  may be decreased. In some cases, the decrease may be equal to the thickness of the magnetic seed layer  416 . Performance of the magnetic recording media  300  at higher densities may also be improved. In exemplary embodiments the media  300  may include an optional capping layer (not shown), an optional overcoat layer  430 , and an optional lubrication layer  432  that may reside on the overcoat layer. 
       FIG. 5  illustrates the SNR and Overwrite properties of a magnetic media according to an exemplary embodiment. As depicted in  FIG. 5 , both the signal to noise ratio (SNR) and the overwrite property of the magnetic media  300  may improve with the use of a magnetic seed layer  416  above the soft underlayer structure  410 . This may be partially due to the fact that the use of a magnetic seed layer  416  allows for an underlayer structure  410  that is thinner than a conventional media where a non-magnetic seed layer was used, as shown in  FIG. 2 . The curve  502  shows the SNR vs. overwrite signal for a recording media with a non-magnetic seed layer as shown in  FIG. 2 . The curve  504  shows the SNR vs. overwrite signal for one embodiment of a recording media with a magnetic seed layer as depicted in  FIG. 3 . Other embodiments may have different curves. Additionally, a more uniform and columnar growth of the magnetic grains of the recording layer  428  promoted by the use of the magnetic seed layer  416  and intermediate layer  422  provides for a lower SNR value for the magnetic media  300 . Furthermore, the overwrite property of the magnetic media  300  may be improved over the conventional media  102  without a magnetic seed layer  416 . Overwrite for the magnetic media is determined by measuring multiple signal read backs from the recording media  300  after multiple writings and rewritings. In some embodiments, hundreds of writing, erasing, rewriting and reading operations are performed to calculate the overwrite value for the magnetic media  300 . In some embodiments, an overwrite (OW) of the 300 media is in the range of 25-45 db. 
       FIG. 6  illustrates a method of making a magnetic media according to an exemplary embodiment. In exemplary embodiments, in operation  602 , a media substrate is provided. In some embodiments, the substrate may be glass. In other embodiments the substrate may be made of aluminum alloys. 
     In operation  604 , a first unbalanced SUL is provided on the substrate. As previously described, the unbalanced SUL may comprise of a thicker bottom SUL layer antiferromagnetically coupled to a thinner top SUL layer though an AFC layer. 
     In operation  606 , a magnetic seed layer is provided on the SUL layer. The magnetic seed layer may couple to the unbalanced SUL. In some embodiments, the magnetic seed layer may be designed to magnetically balance the SUL. 
     In operation  608 , an interlayer or a non-magnetic seed layer may be provided. The magnetic seed layer and the non-magnetic interlayer may help promote a desired growth template to control the grain size, variation in grain size, crystal orientation dispersion and easy axis of a magnetic recording layer. Thus, the signal to noise ratio of the media  300  may be improved. 
     In operation  610 , a magnetic recording layer may be provided. The magnetic recording layer may include FePt alloys or FePtX alloys. 
     In operation  612 , an optional capping layer, carbon overcoat protective layer and lubrication layer may also be provided. 
     In the foregoing specification, the invention is described with reference to specific exemplary embodiments, but those skilled in the art will recognize that the invention is not limited to those. It is contemplated that various features and aspects of the invention may be used individually or jointly and possibly in a different environment or application. The specification and drawings are, accordingly, to be regarded as illustrative and exemplary rather than restrictive. For example, the word “preferably,” and the phrase “preferably but not necessarily,” are used synonymously herein to consistently include the meaning of “not necessarily” or optionally. The drawings are not necessarily to scale. “Comprising,” “including,” and “having,” are intended to be open-ended terms.