Magnetic seed layer used with an unbalanced soft underlayer

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 & 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_xFe_y, NiW_xCo_y and NiW_xCo_yAl_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_aCo_b, NiW_xV_aCo_y, or NiW_xV_aFe_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_xV_aCo_y, or NiW_xV_aFe_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 & 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_xFe_y, NiW_xCo_y and NiW_xCo_yAl_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_aCo_b, NiV_aCo_bAl_c, NiW_xV_aCo_b, or NiW_xV_aFe_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_xV_aCo_y, or NiW_xV_aFe_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 & 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.