# Patent

## Title
Systems and methods for controlling damping of magnetic media for heat assisted magnetic recording

## Abstract

Systems and methods for controlling the damping of magnetic media for heat assisted magnetic recording are provided. One such system includes a heat sink layer, a growth layer on the heat sink layer, a magnetic recording layer on the growth layer, where the growth layer is configured to facilitate a growth of a preselected crystalline structure of the magnetic recording layer, and a capping magnetic recording layer on the magnetic recording layer, the capping recording layer including a first material configured to increase a damping constant of the capping recording layer to a first preselected level.

## Background
FIELD
The present invention relates to magnetic media used in storage systems, and more specifically to systems and methods for controlling the damping of magnetic media for heat assisted magnetic recording.
BACKGROUND
Perpendicular magnetic recording (PMR) is approaching the maximum areal density (AD) that can be achieved with multi-layer media in which the magnetic anisotropy field (Hk) is graded from a low value in the top layer to a high value in the lowest layer. Therefore alternate recording technologies such as heat assisted magnetic recording (HAMR), which may encompass or be synonymous with additional technologies such as energy assisted magnetic recording (EAMR), are being investigated to achieve higher areal density.
HAMR technologies are intended to address the areal density problem. In these assisted recording systems, a laser beam is delivered through an optical waveguide and interacts with a near field transducer (NFT) that absorbs part of the optical energy and forms a very strong localized electromagnetic field in the near field region. When the localized electromagnetic field is close enough to the recording medium, the recording medium absorbs part of the localized electromagnetic field energy and is thereby heated up thermally, which helps to realize the magnetic recording process.
Recent atomistic calculations associated with HAMR media switching have revealed a relatively severe fast cooling rate problem for HAMR media. More specifically, for the fast cooling rates needed to support HAMR in high speed applications, theoretical results have revealed that conventional HAMR media experience fluctuations in magnetization and anisotropy during fast cooling which will cause grains to flip when they should not and to not flip when they should. This will lead to wide and noisy transitions with poor bit error rate performance. In addition, this will lead to DC-like noise proximate to the transitions but not at them, which is due to the associated magnetization and anisotropy fluctuations. As such, an improved magnetic media for use in HAMR applications that addresses these problems is desirable.
SUMMARY
Aspects of the invention relate to systems and methods for controlling the damping of magnetic media for heat assisted magnetic recording. In one embodiment, the invention relates to a magnetic media structure for heat assisted magnetic recording, the media structure including a heat sink layer, a growth layer on the heat sink layer, a magnetic recording layer on the growth layer, where the growth layer is configured to facilitate a growth of a preselected crystalline structure of the magnetic recording layer, and a capping magnetic recording layer on the magnetic recording layer, the capping recording layer including a first material configured to increase a damping constant of the capping recording layer to a first preselected level.
In another embodiment, the invention relates to a magnetic media structure for heat assisted magnetic recording, the media structure including a heat sink layer, a growth layer on the heat sink layer, a magnetic recording underlayer on the growth layer, the underlayer including a first material configured to increase a damping constant of the underlayer to a first preselected level, and a magnetic recording layer on the underlayer, where the growth layer and the underlayer are configured to facilitate a growth of a preselected crystalline structure of the magnetic recording layer.
In yet another embodiment, the invention relates to a method for increasing a damping constant of a magnetic media structure for heat assisted magnetic recording, the method including providing a heat sink layer, providing a growth layer on the heat sink layer, providing a magnetic recording layer on the growth layer, where the growth layer is configured to facilitate a growth of a preselected crystalline structure of the magnetic recording layer, and providing a capping magnetic recording layer on the magnetic recording layer, the capping recording layer including a first material configured to increase a damping constant of the capping recording layer to a first preselected level.
In still yet another embodiment, the invention relates to a method for increasing a damping constant of a magnetic media structure for heat assisted magnetic recording, the method including providing a heat sink layer, providing a growth layer on the heat sink layer, providing a magnetic recording underlayer on the growth layer, the underlayer including a first material configured to increase a damping constant of the underlayer to a first preselected level, and providing a magnetic recording layer on the underlayer, where the growth layer and the underlayer are configured to facilitate a growth of a preselected crystalline structure of the magnetic recording layer.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view of a heat assisted magnetic recording (HAMR) system including a read/write head positioned above a damped magnetic media in accordance with one embodiment of the invention.
FIG. 2a is a side view of a damped magnetic media with a continuous doped capping layer positioned on a magnetic recording layer that can be used in conjunction with the read/write head of FIG. 1 in accordance with one embodiment of the invention.
FIG. 2b is a side view of a damped magnetic media with a non-continuous doped capping layer positioned on a magnetic recording layer that can be used in conjunction with the read/write head of FIG. 1 in accordance with one embodiment of the invention.
FIG. 3a is a side view of a damped magnetic media with a continuous doped underlayer positioned beneath a magnetic recording layer that can be used in conjunction with the read/write head of FIG. 1 in accordance with one embodiment of the invention.
FIG. 3b is a side view of a damped magnetic media with a non-continuous doped underlayer positioned beneath a magnetic recording layer that can be used in conjunction with the read/write head of FIG. 1 in accordance with one embodiment of the invention.
FIG. 4 is a flowchart of a process for forming a damped magnetic media with a doped capping layer positioned on a magnetic recording layer in accordance with one embodiment of the invention.
FIG. 5 is a flowchart of a process for forming a damped magnetic media with a doped underlayer positioned beneath a magnetic recording layer in accordance with one embodiment of the invention.



DETAILED DESCRIPTION
Referring now to the drawings, embodiments of systems and methods for controlling the damping of magnetic media for heat assisted magnetic recording (HAMR) are illustrated. The systems can include a damped magnetic media with a continuous or non-continuous doped capping layer positioned on the recording layer, or a damped magnetic media with a continuous or non-continuous doped underlayer positioned beneath the recording layer, that can be used in conjunction with a HAMR read/write head. The methods can be used to form the various embodiments of the damped magnetic media. The doped capping layer or doped underlayer includes a first material (e.g., rare earth dopant) that is configured to increase a damping constant of the capping layer to a first preselected level. In many embodiments, a heat sink layer and growth layer are positioned beneath the recording layer and the doped capping layer or doped underlayer.
While not bound by any particular theory, the doped capping layer or doped underlayer can sharpen transitions and allow for faster cooling for higher data rates, higher thermal gradients, and higher linear density. It may also suppress certain types of noise. In effect, the doped capping layer or doped underlayer can be exchange coupled to the recording grains, and can thus absorb magnons (e.g., quantized magnetic fluctuations) that are generated at high temperatures and persist to low temperatures because the intrinsic damping of conventional HAMR media is low.
FIG. 1 is a side view of a heat assisted magnetic recording (HAMR) system 100 including a read/write head 102 positioned above a damped magnetic media 104 in accordance with one embodiment of the invention. The head 102 includes a write pole 106 consisting of a leading write pole 106a and a trailing write pole 106b, where a portion of the write pole 106 is enclosed by a pancake style write coil 108. The head 102 further includes a waveguide 110 consisting of a waveguide core 110a surrounded by a waveguide cladding 110b. The head 102 also includes a near field transducer (NFT) 112 positioned within the waveguide cladding 110b, and a NFT heat sink 114 to dissipate heat from the NFT 112. The operation of HAMR read/write heads and their components is well known in the art, and head 102 can be operated accordingly.
The damped magnetic media 104 includes a doped capping layer or doped underlayer made of a first material (e.g., rare earth dopant) that is configured to increase a damping constant of the capping layer to a first preselected level. In several embodiments, the first material is a rare earth dopant such as Ho. In one such case, the concentration of Ho is greater than about 0.5 percent. In other embodiments, the first material is a rare earth dopant that includes one or more materials from the group consisting of Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, or other suitable dopants.
FIG. 2a is a side view of a damped magnetic media 204 with a continuous doped capping layer 214 positioned on a magnetic recording layer 212 that can be used in conjunction with the read/write head of FIG. 1 in accordance with one embodiment of the invention. The damped magnetic media 204 has a stacked multi-layer structure with a bottom heat sink layer 206, a thermal resistor layer 208 on the heat sink layer 206, a growth layer 210 on the thermal resistor layer 208, the recording layer 212 on the growth layer 210, and the continuous doped capping layer 214 on the recording layer 212. In some embodiments, an additional layer, such as an exchange coupling layer, is positioned between the doped capping layer 214 (e.g., capping magnetic recording layer) and the magnetic recording layer 212. In some embodiments, the heat sink 206 is on another additional layer (e.g., a substrate or a soft magnetic underlayer on a substrate).
The recording layer 212 consists of a number of discrete grains oriented in a vertical direction and can be made of FePt, CoCrPt, CoPt, CoPtNi, and/or other suitable materials. In several embodiments, the recording layer 212 consists of one or more materials suitable to provide an L10 crystalline structure. The doped capping layer 214 is made of a first material (e.g., a magnetic alloy with a rare earth dopant) that is configured to increase a damping constant of the capping layer 214 to a first preselected level. In one embodiment, the first preselected level is about 20% and corresponds to an overall damping of the media 204 of about 5%. In several embodiments, the first material is a rare earth dopant such as Ho or Ho oxide. In one such case, the concentration of Ho in the capping layer 214 is greater than about 0.5 percent. In other embodiments, the first material is a rare earth dopant that includes one or more materials from the group consisting of Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, or other suitable dopants.
In several embodiments, the first material or doping material is deposited on the grains of the recording layer 212 such that portions of the doping material are disposed between the grains. In one such embodiment, the volume average of damping is segmented such that about one third is contributed by the doped capping layer 214 and about two thirds is contributed by the recording layer 212 (e.g., by the doping material positioned between the grains). In several embodiments, the rare earth dopant for the doped capping layer 214 is selected for its ability to increase intrinsic damping and its capability to avoid disturbing a desired crystalline structure of the recording layer 212 (e.g., L10 crystalline structure).
The heat sink layer 206 is configured to dissipate heat and is made of one or more high thermal conductivity materials (e.g., an alloy of Cu and/or other thermally conductive materials). The optional thermal resistor layer 208 is configured to resist thermal conduction and is made of one or more materials suited for such (e.g., SiOx, WSe, and/or other suitable materials).
The growth layer 210 is configured to facilitate a growth of a preselected structure (e.g., L10 crystalline structure or other suitable structure) of the recording layer 212. In several embodiments, the growth layer 210 is made of one or more materials conducive to growing the preselected structure of the recording layer 212, such as MgO and/or other suitable materials. The optional exchange coupling layer positioned between the recording layer 212 and the doped capping layer 214 can be made of Ru and/or other suitable materials as are known in the art.
In several embodiments, the doped capping layer 214 and/or recording layer 212 increase the damping of the magnetic media 204 and therefore sharpen transitions and allow for faster media cooling for higher data rates, higher thermal gradients, and higher linear density while suppressing certain types of undesirable noise.
FIG. 2b is a side view of a damped magnetic media 304 with a non-continuous doped capping layer 314 positioned on a recording layer 312 that can be used in conjunction with the read/write head of FIG. 1 in accordance with one embodiment of the invention. The damped magnetic media 304 has a stacked multi-layer structure with a bottom heat sink layer 306, a thermal resistor layer 308 on the heat sink layer 306, a growth layer 310 on the thermal resistor layer 308, the recording layer 312 on the growth layer 310, and the non-continuous (e.g., discrete) doped capping layer 314 on the recording layer 312. In some embodiments, an additional layer, such as an exchange coupling layer, is positioned between the doped capping layer 314 (e.g., capping magnetic recording layer) and the magnetic recording layer 312.
The recording layer 312 includes a number of discrete grains oriented in a vertical direction and can be made of FePt, CoCrPt, CoPt, CoPtNi, and/or other suitable materials. In several embodiments, the doped capping layer 314 includes a number of discrete grains in vertical correspondence with the grains of the recording layer 312. Similarly, the optional exchange coupling layer can include a number of discrete grains in vertical correspondence with the grains of the recording layer 312. The layers of the damped magnetic media 304 can otherwise function, and be made of the same materials, as described above for the damped magnetic media 204 of FIG. 2a. 
FIG. 3a is a side view of a damped magnetic media 404 with a continuous doped underlayer 414 positioned beneath a magnetic recording layer 412 that can be used in conjunction with the read/write head of FIG. 1 in accordance with one embodiment of the invention. The damped magnetic media 404 has a stacked multi-layer structure with a bottom heat sink layer 406, a thermal resistor layer 408 on the heat sink layer 406, a growth layer 410 on the thermal resistor layer 408, the continuous doped underlayer 414 on the growth layer 410, and the recording layer 412 on the continuous doped underlayer 414. In some embodiments, the stacked structure further includes a capping layer on the recording layer 412.
The recording layer 412 includes a number of discrete grains oriented in a vertical direction and can be made of FePt, CoCrPt, CoPt, CoPtNi, and/or other suitable materials. In several embodiments, the recording layer 412 is made of one or more materials providing for an L10 crystalline structure. The doped underlayer 414 is made of a first material (e.g., rare earth dopant) that is configured to increase a damping constant of the capping layer 414 to a first preselected level and to facilitate a growth of the recording layer 412 with a preselected crystalline structure. In one embodiment, the first preselected level is about 20% and corresponds to an overall damping of the media 404 of about 5%. In several embodiments, the first material is a rare earth dopant such as Ho or Ho oxide. In one such case, the concentration of Ho is about 0.5 percent or greater. In other embodiments, the first material is a rare earth dopant that includes one or more materials from the group consisting of Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, or other suitable dopants.
In several embodiments, the first material or doping material is deposited such that portions of the doping material are disposed between the grains of the recording layer 412. In one such embodiment, the volume average of damping is segmented such that about one third is contributed by the doped underlayer 414 and about two thirds is contributed by the recording layer 412 (e.g., by the doping material between the grains). In several embodiments, the rare earth dopant for the doped underlayer 414 is selected for its ability to increase intrinsic damping and its capability to avoid disturbing a desired crystalline structure of the recording layer 412.
The other layers of the damped magnetic media 404 can function, and be made of the same materials, as described above for the damped magnetic media 204 of FIG. 2a. 
FIG. 3b is a side view of a damped magnetic media 504 with a non-continuous doped underlayer 514 positioned beneath a magnetic recording layer 512 that can be used in conjunction with the read/write head of FIG. 1 in accordance with one embodiment of the invention. The damped magnetic media 504 has a stacked multi-layer structure with a bottom heat sink layer 506, a thermal resistor layer 508 on the heat sink layer 506, a growth layer 510 on the thermal resistor layer 508, the non-continuous (e.g., discrete) doped underlayer 514 on the growth layer 510, and the recording layer 512 on the continuous doped underlayer 514. In some embodiments, the stacked structure further includes a capping layer on the recording layer 512.
The recording layer 512 includes a number of discrete grains oriented in a vertical direction and can be made of FePt, CoCrPt, CoPt, CoPtNi, and/or other suitable materials. In several embodiments, the doped underlayer 514 includes a number of discrete grains in vertical correspondence with the grains of the recording layer 512.
The other layers of the damped magnetic media 504 can function, and be made of the same materials, as described above for the damped magnetic media 204 of FIG. 2a. 
FIG. 4 is a flowchart of a process 400 for forming a damped magnetic media with a doped capping layer positioned on the recording layer in accordance with one embodiment of the invention. In particular embodiments, the process 400 can be used to form the damped magnetic media of FIGS. 2a and 2b. The process first provides (402) a heat sink layer. In some embodiments, the heat sink layer is formed on a substrate (e.g., soft magnetic underlayer). The process then provides (404) a growth layer on the heat sink layer. In some embodiments, the process also provides a thermal resistor layer on the heat sink layer. In such case, the growth layer is formed on the thermal resistor layer.
The process then provides (406) a magnetic recording layer on the growth layer, where the growth layer is configured to facilitate a growth of a preselected crystalline structure of the magnetic recording layer. The process then provides (408) a capping magnetic recording layer on the magnetic recording layer, where the capping recording layer includes a first material configured to increase a damping constant of the capping recording layer to a first preselected level. In some embodiments, the process also provides an exchange coupling layer on the magnetic recording layer. In such case, the capping magnetic recording layer is formed on the exchange coupling layer.
In a number of embodiments, the process can use suitable deposition processes (e.g., sputtered deposition and/or other physical vapor deposition methods known in the art) known in the art to provide the various layers.
In one embodiment, the process can perform the sequence of actions in a different order. In another embodiment, the process can skip one or more of the actions. In other embodiments, one or more of the actions are performed simultaneously. In some embodiments, additional actions can be performed.
FIG. 5 is a flowchart of a process 500 for forming a damped magnetic media with a doped underlayer positioned beneath the recording layer in accordance with one embodiment of the invention. In particular embodiments, the process 500 can be used to form the damped magnetic media of FIGS. 3a and 3b. The process first provides (502) a heat sink layer. In some embodiments, the heat sink layer is formed on a substrate (e.g., soft magnetic underlayer). The process then provides (504) a growth layer on the heat sink layer. In some embodiments, the process also provides a thermal resistor layer on the heat sink layer. In such case, the growth layer is formed on the thermal resistor layer.
The process then provides (506) a magnetic recording underlayer on the growth layer, where the underlayer includes a first material configured to increase a damping constant of the underlayer to a first preselected level. The process then provides (508) a magnetic recording layer on the underlayer, where the growth layer and the underlayer are configured to facilitate a growth of a preselected crystalline structure of the magnetic recording layer. In some embodiments, the process also provides a capping layer on the magnetic recording layer. In some embodiments, the magnetic recording layer includes a number of discrete magnetic grains separated by gaps. In one such case, the process also deposits additional amounts of the first material in the gaps in the recording layer, thereby doping the recording layer in addition to the underlayer.
In a number of embodiments, the process can use suitable deposition processes (e.g., sputtered deposition and/or other physical vapor deposition methods known in the art) known in the art to provide the various layers.
In one embodiment, the process can perform the sequence of actions in a different order. In another embodiment, the process can skip one or more of the actions. In other embodiments, one or more of the actions are performed simultaneously. In some embodiments, additional actions can be performed.
While the above description contains many specific embodiments of the invention, these should not be construed as limitations on the scope of the invention, but rather as examples of specific embodiments thereof. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their equivalents.

## Claims

1. A magnetic media structure for heat assisted magnetic recording, the media structure comprising:
a heat sink layer;
a growth layer on the heat sink layer;
a magnetic recording layer on the growth layer, wherein the growth layer is configured to facilitate a growth of a preselected crystalline structure of the magnetic recording layer; and
a capping magnetic recording layer on the magnetic recording layer, the capping magnetic recording layer comprising a first material configured to increase a damping constant of the capping recording layer to a first preselected level,
wherein the magnetic recording layer comprises a plurality of discrete magnetic grains separated by a plurality of gaps; and
wherein the plurality of gaps are at least partially filled with the first material.

2. The media structure of claim 1, wherein the first material comprises a rare earth dopant.

3. The media structure of claim 2, wherein the rare earth dopant comprises Ho.

4. The media structure of claim 2, wherein the rare earth dopant comprises a material selected from the group consisting of Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Hf.

5. The media structure of claim 1, wherein the capping magnetic recording layer comprises a substantially continuous structure.

6. The media structure of claim 1:
wherein the magnetic recording layer comprises a plurality of discrete magnetic grains; and
wherein the capping magnetic recording layer comprises a plurality of grains in vertical correspondence with the plurality of discrete magnetic grains.

7. The media structure of claim 1, further comprising an exchange coupling layer positioned between the capping magnetic recording layer and the magnetic recording layer.

8. The media structure of claim 1, further comprising a thermal resistor layer positioned between the heat sink layer and the growth layer.

9. The media structure of claim 1:
wherein the magnetic recording layer comprises FePt;
wherein the growth layer comprises MgO; and
wherein the capping magnetic recording layer comprises a material selected from the group consisting of Fe, Pt, Co, Cr, Ni, and combinations thereof.

10. The media structure of claim 1, further comprising an underlayer comprising a soft magnetic material, wherein the heat sink layer is positioned on the soft underlayer.

11. The media structure of claim 1, wherein the first material increases a damping constant of the capping recording layer to a first preselected level.

12. A magnetic media structure for heat assisted magnetic recording, the media structure comprising:
a heat sink layer;
a growth layer on the heat sink layer;
a magnetic recording underlayer on the growth layer, the underlayer comprising a first material configured to increase a damping constant of the underlayer to a first preselected level; and
a magnetic recording layer on the underlayer, wherein the growth layer and the underlayer are configured to facilitate a growth of a preselected crystalline structure of the magnetic recording layer,
wherein the magnetic recording layer comprises a plurality of discrete magnetic grains separated by a plurality of gaps; and
wherein the plurality of gaps are at least partially filled with the first material.

13. The media structure of claim 12, wherein the first material comprises a rare earth dopant.

14. The media structure of claim 13, wherein the rare earth dopant comprises Ho.

15. The media structure of claim 13, wherein the rare earth dopant comprises a material selected from the group consisting of Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Hf.

16. The media structure of claim 12, wherein the underlayer comprises a substantially continuous structure.

17. The media structure of claim 12:
wherein the magnetic recording layer comprises a plurality of discrete magnetic grains; and
wherein the underlayer comprises a plurality of grains in vertical correspondence with the plurality of discrete magnetic grains.

18. The media structure of claim 12, further comprising a thermal resistor layer positioned between the heat sink layer and the growth layer.

19. The media structure of claim 12:
wherein the magnetic recording layer comprises FePt;
wherein the growth layer comprises MgO; and
wherein the underlayer comprises a material selected from the group consisting of Fe, Pt, Co, Cr, Ni, and combinations thereof.

20. The media structure of claim 12, further comprising a second underlayer comprising a soft magnetic material, wherein the heat sink layer is on the second underlayer.

21. The media structure of claim 12, wherein the first material increases a damping constant of the capping recording layer to a first preselected level.

22. A method for increasing a damping constant of a magnetic media structure for heat assisted magnetic recording, the method comprising:
providing a heat sink layer;
providing a growth layer on the heat sink layer;
providing a magnetic recording layer on the growth layer, wherein the growth layer is configured to facilitate a growth of a preselected crystalline structure of the magnetic recording layer; and
providing a capping magnetic recording layer on the magnetic recording layer, the capping recording layer comprising a first material configured to increase a damping constant of the capping recording layer to a first preselected level,
wherein the magnetic recording layer comprises a plurality of discrete magnetic grains separated by a plurality of gaps; and
wherein the plurality of gaps are at least partially filled with the first material.

23. The method of claim 22, wherein the first material comprises a rare earth dopant.

24. The method of claim 23, wherein the rare earth dopant comprises Ho.

25. The method of claim 23, wherein the rare earth dopant comprises a material selected from the group consisting of Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Hf.

26. The method of claim 22, wherein the capping magnetic recording layer comprises a substantially continuous structure.

27. The method of claim 22:
wherein the magnetic recording layer comprises a plurality of discrete magnetic grains; and
wherein the capping magnetic recording layer comprises a plurality of grains in vertical correspondence with the plurality of discrete magnetic grains.

28. The method of claim 22, further comprising an exchange coupling layer positioned between the capping magnetic recording layer and the magnetic recording layer.

29. The method of claim 22, further comprising a thermal resistor layer positioned between the heat sink layer and the growth layer.

30. The method of claim 22:
wherein the magnetic recording layer comprises FePt;
wherein the growth layer comprises MgO; and
wherein the capping magnetic recording layer comprises a material selected from the group consisting of Fe, Pt, Co, Cr, Ni, and combinations thereof.

31. The method of claim 22, further comprising an underlayer comprising a soft magnetic material, wherein the heat sink layer is positioned on the soft underlayer.

32. The method of claim 22, wherein the first material increases a damping constant of the capping recording layer to a first preselected level.

33. A method for increasing a damping constant of a magnetic media structure for heat assisted magnetic recording, the method comprising:
providing a heat sink layer;
providing a growth layer on the heat sink layer;
providing a magnetic recording underlayer on the growth layer, the underlayer comprising a first material configured to increase a damping constant of the underlayer to a first preselected level; and
providing a magnetic recording layer on the underlayer, wherein the growth layer and the underlayer are configured to facilitate a growth of a preselected crystalline structure of the magnetic recording layer,
wherein the magnetic recording layer comprises a plurality of discrete magnetic grains separated by a plurality of gaps; and
wherein the plurality of gaps are at least partially filled with the first material.

34. The method of claim 33, wherein the first material comprises a rare earth dopant.

35. The method of claim 34, wherein the rare earth dopant comprises Ho.

36. The method of claim 34, wherein the rare earth dopant comprises a material selected from the group consisting of Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Hf.

37. The method of claim 33, wherein the underlayer comprises a substantially continuous structure.

38. The method of claim 33:
wherein the magnetic recording layer comprises a plurality of discrete magnetic grains; and
wherein the underlayer comprises a plurality of grains in vertical correspondence with the plurality of discrete magnetic grains.

39. The method of claim 33, further comprising a thermal resistor layer positioned between the heat sink layer and the growth layer.

40. The method of claim 33:
wherein the magnetic recording layer comprises FePt;
wherein the growth layer comprises MgO; and
wherein the underlayer comprises a material selected from the group consisting of Fe, Pt, Co, Cr, Ni, and combinations thereof.

41. The method of claim 33, further comprising a second underlayer comprising a soft magnetic material, wherein the heat sink layer is on the second underlayer.

42. The method of claim 33, wherein the first material increases a damping constant of the capping recording layer to a first preselected level.