# Patent

## Title
TbFeCo in PMR media for SNR improvement

## Abstract

The present disclosure generally relates to a PMR media for use in a HDD. The PMR media has an amorphous ferri-magnetic material layer disposed within the capping structure. The amorphous ferri-magnetic material layer reduces the noise. The amorphous ferri-magnetic material layer may be disposed between capping layer or on top of the capping layers. Additionally, the amorphous ferri-magnetic material layer may contain Tb.

## Background
BACKGROUND
1. Field of the Disclosure
Embodiments of the present disclosure generally relate to perpendicular magnetic recording (PMR) media in a hard disk drive (HDD).
2. Description of the Related Art
In HDDs, a magnetic head is disposed over a magnetic media. The magnetic head reads from, and writes data to, the magnetic media. The magnetic head has a surface, referred to as an air bearing surface (ABS), facing the magnetic media. As the magnetic media moves, air exerts a pressure on the ABS and pushes the magnetic head away from the magnetic media. The magnetic head is formed on a slider, which is coupled to a suspension. The suspension exerts a counter force that, when considered in concert with the moving media, ensures the magnetic head is disposed a predetermined distance from the magnetic media during operation.
PMR has been used to increase the areal recording density of magnetic storage media. A PMR media stack generally includes a substrate, several magnetic layers, one or more exchange control layers, a capping structure and a carbon overcoat layer. The signal-to-noise ratio (SNR) of a PMR media stack can be quite high.
Therefore, there is a need in the art for an improved PMR media with reduced noise.



BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.
FIG. 1 is a schematic illustration of a HDD according to one embodiment.
FIG. 2 is a schematic illustration PMR media stack.
FIGS. 3A-3C are schematic illustrations of PMR stacks according to one embodiment.
FIG. 4A is a graph illustrating how noise decreases with the presence of an amorphous ferri-magnetic material layer in the PMR media stack.
FIG. 4B is a graph illustrating how the amorphous ferri-magnetic material layer has little to no effect on the signal.



To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. It is to be understood that all drawings are not to scale.
DETAILED DESCRIPTION
The present disclosure generally relates to a PMR media for use in a HDD. The PMR media has an amorphous ferri-magnetic material layer disposed within the capping structure. The amorphous ferri-magnetic material layer reduces the noise. The amorphous ferri-magnetic material layer may be disposed between capping layer or on top of the capping layers. Additionally, the amorphous ferri-magnetic material layer may contain Tb.
FIG. 1 is a schematic illustration of a magnetic recording device, such as a hard disk drive (HDD) 100 according to one embodiment. 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. A magnetic head that is mounted on a slider 108 moves over the disk 102 to read and write information from/to the disk 102. The head rides on an air bearing above the disk 102 during read/write operations. The slider 108 is coupled to an actuator 110 by a suspension 112 and arm 114. The suspension 112, which may comprise stainless steel, provides a slight spring force, which biases the slider 108 towards the disk surface. Each actuator 110 is attached to an actuator means that controls the movement of the head 106 relative to the disk 102.
FIG. 2 is a schematic illustration PMR media stack 200. The PMR stack 200 includes a SUL layer 202 and a seed layer 204. In one embodiment, the SUL layer 202 may comprise an antiferromagnetic material. In another embodiment, the seed layer 204 may contain nickel, iron, or combinations thereof. One or more intermediate under layers 206 may be present on the seed layer 204. In one embodiment, the intermediate under layer 206 may comprise ruthenium. A grain isolation initiation layer (GIIL) 208 may be disposed on the intermediate under layer 206. In one embodiment, the GIIL layer 208 may comprise a cobalt-chromium oxide.
One or more first magnetic layers 210 may be present on the GIIL layer 208. A first exchange break layer (EBL) 212 may be disposed on the one or more first magnetic layers 210. One or more second magnetic layers 214 may be disposed on the first exchange break layer 212, and a second exchange break layer (EBL) 216, may be disposed on the one or more second magnetic layers 214. One or more third magnetic layers 218 may be present on the second EBL 216, and a third EBL 220 may be present on the one or more third magnetic layers 218. A capping structure 223 may be present on the third EBL 220. The capping structure 223 includes a first capping layer 222 and a second capping layer 224. A carbon overcoat layer 226 is disposed on the capping structure 223. The one or more first magnetic layers 210, the one or more second magnetic layers 214 and the one or more third magnetic layers 218 may include a CoPtX-oxide alloy, wherein X is selected from the group consisting of Cr, Ru, and B, and the oxide is selected from the group consisting of TiO2, SiO2, Cr2O3, and B2O3. In one embodiment, the first, second, and third EBLs 212, 216, 220 may include a CoCrRu-oxide. In one embodiment, the GIIL 208 may include a material selected from the group consisting of a CoCrRu-oxide and a CoCr-oxide. In one embodiment, the first, second and third EBLs 212, 216, 220 may include a number of EBLs, and two of the EBLs may include different materials. The GIIL can enhance magnetic decoupling of the magnetic layers, and the EBLs help to reduce the coercivity (Hc) and saturation field (Hs) of the PMR media stack as a whole.
As noted above, PMR media may have an undesirably high noise. Amorphous ferri-magnetic material may be used in the capping structure to reduce the noise. TbFeCo is a well-known ferri-magnetic material. TbFeCo is amorphous and has a very high magnetic anisotropy (Ku) while possessing low saturation magnetization (Ms). By appropriate choice of composition (RE Tb vs. TM Co/Fe), it is possible to tailor the magnetic properties such as Ms, Ku, Tc (curie temperature) and Tcomp (compensation temperature).
As discussed herein, Applicants have discovered that using an amorphous ferri-magnetic material layer in the capping structure of a PMR media will reduce noise, yet have minimal to no effect on the signal. In one embodiment, the amorphous ferromagnetic material layer may be TbFeCo. It is to be understood that amorphous ferri-magnetic material layers other than TbFeCo are contemplated.
FIGS. 3A-3C are schematic illustrations of PMR stacks according to one embodiment. In the PMR stacks of FIGS. 3A-3C, an amorphous ferri-magnetic material layer is disposed within the capping structure 223. In one embodiment, the thickness of the amorphous ferri-magnetic material layer greater than zero and less than 1 nm. In another embodiment, the amorphous ferri-magnetic material layer is between about 0.4 nm and 2 nm. In one embodiment, the amorphous ferri-magnetic material layer includes Tb. In another embodiment, the amorphous ferri-magnetic material layer includes TbFeCo. In one embodiment, the Tb may be present in an amount of greater than zero and up to 30 percent by weight. The composition of the amorphous ferri-magnetic material layer may be chosen such that the Ms is low relative to rest of the media stack. TbFeCo is amorphous (2-5 nm nano-crystallites), has low Ms, and is expected to have low lateral exchange coupling relative to a CoPt based cap while possessing high Ku. It is believed that the unique property of amorphous ferri-magnetic material, and in particular TbFeCo, helps to reduce the high frequency noise while maintaining the signal.
In the embodiment shown in FIG. 3A, the PMR 300 includes an amorphous ferri-magnetic material layer 302 is disposed within the capping structure 223 and on the third EBL 220 and is used in place of the first capping layer 222. The second capping layer 224 is still present in the capping structure 223.
In the embodiment shown in FIG. 3B, the PMR 310 includes an amorphous ferri-magnetic material layer 312 used within the capping structure 223 in addition to the first capping layer 222 and the second capping layer 224. The first capping layer 222 is disposed on the third EBL 220. The amorphous ferri-magnetic material layer 312 is disposed on the first capping layer 222. The second capping layer 224 is disposed on the amorphous ferri-magnetic material layer 312.
In the embodiment shown in FIG. 3C, the PMR 320 includes an amorphous ferri-magnetic material layer 322 that is disposed within the capping structure 223. The amorphous ferri-magnetic material layer 322 is disposed on top of the second capping layer 224. The second capping layer 224 is disposed on the first capping layer 220.
Table I shows a comparison of results when no amorphous ferri-magnetic material layer is present in the capping structure and when an amorphous ferri-magnetic material layer is not present.












TABLE I








Trackwidth
Overwrite
SNR



Disk
Uin
dB
dB









Relative to
0
0
0



Reference






Disk






Disk w/TFC
3.6%
−3.0%
0.8%










FIG. 4A is a graph illustrating how noise decreases with the presence of an amorphous ferri-magnetic material layer in the PMR media stack. As shown in FIG. 4A, the noise is lower in the PMR media having an amorphous ferri-magnetic material layer (line with no dots) in the capping structure when compared to a capping structure without an amorphous ferri-magnetic material layer (line with dots). At higher frequencies, such as 1T and 2T, there is a significant noise reduction. In other words, the amorphous ferri-magnetic material layer reduces the noise. The noise reduction may be between about 10% and about 15% at the higher frequencies.
FIG. 4B is a graph illustrating how the amorphous ferri-magnetic material layer has little to no effect on the signal. As shown in FIG. 4B, the signal is minimally reduced in the PMR media when an amorphous ferri-magnetic material layer is present in the capping structure (line with no dots). In other words, the amorphous ferri-magnetic material layer has little to no effect on the signal of the PMR media.
When considered together, FIGS. 4A and 4B show that the presence of an amorphous ferri-magnetic material layer in the capping structure reduces noise and has little to no effect on signal. Thus, the amorphous ferri-magnetic material layer in the capping structure increases the SNR.
The benefit of using an amorphous ferri-magnetic material layer is the noise is reduced. Specifically, the amorphous ferri-magnetic material layer reduces the noise while having little to no effect on the signal from the PMR.
While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

## Claims

1. A magnetic recording medium, comprising:
a substrate;
a plurality of magnetic layers disposed over the substrate;
a capping layer structure disposed over the plurality of magnetic layers, the capping layer structure comprising at least one capping layer and an amorphous ferri-magnetic material layer; and
a carbon overcoat layer disposed on the capping layer structure.

2. The magnetic recording medium of claim 1, wherein the amorphous ferri-magnetic material layer comprises Tb.

3. The magnetic recording medium of claim 2, wherein the amorphous ferri-magnetic material layer comprises TbFeCo.

4. The magnetic recording medium of claim 3, wherein the amorphous ferri-magnetic material layer has a thickness of greater than 0 and less than 1 nm.

5. The magnetic recording medium of claim 4, wherein the at least one capping layer comprises a single capping layer.

6. The magnetic recording medium of claim 5, wherein the single capping layer is disposed on the amorphous ferri-magnetic material layer.

7. The magnetic recording medium of claim 1, wherein the at least one capping layer comprises a first capping layer and a second capping layer.

8. The magnetic recording medium of claim 1, wherein the amorphous ferri-magnetic material layer comprises TbFeCo and the Tb is present in an amount of up to 30 percent by weight.

9. A magnetic recording medium, comprising:
a substrate;
a plurality of magnetic layers disposed over the substrate;
a capping layer structure disposed over the plurality of magnetic layers, the capping layer structure comprising at least one capping layer and an amorphous ferri-magnetic material layer, wherein the at least one capping layer comprises a first capping layer and a second capping layer, wherein the first capping layer is disposed on the amorphous ferri-magnetic material layer and the second capping layer is disposed on the first capping layer; and
a carbon overcoat layer disposed on the capping layer structure.

10. A magnetic recording medium, comprising:
a substrate;
a plurality of magnetic layers disposed over the substrate;
a capping layer structure disposed over the plurality of magnetic layers, the capping layer structure comprising at least one capping layer and an amorphous ferri-magnetic material layer, wherein the at least one capping layer comprises a first capping layer and a second capping layer, wherein the amorphous ferri-magnetic material layer is disposed on the first capping layer and the second capping layer is disposed on the amorphous ferri-magnetic material layer; and
a carbon overcoat layer disposed on the capping layer structure.

11. A magnetic recording device, comprising:
a magnetic recording head disposed on a slider; and
a magnetic recording medium disposed opposite the magnetic recording head, the magnetic recording medium comprising:
a substrate;
a plurality of magnetic layers disposed over the substrate;
a capping layer structure disposed over the plurality of magnetic layers, the capping layer structure comprising at least one capping layer and an amorphous ferri-magnetic material layer; and
a carbon overcoat layer disposed on the capping layer structure.

12. The magnetic recording device of claim 11, wherein the amorphous ferri-magnetic material layer comprises Tb.

13. The magnetic recording device of claim 12, wherein the amorphous ferri-magnetic material layer comprises TbFeCo.

14. The magnetic recording device of claim 13, wherein the amorphous ferri-magnetic material layer has a thickness of greater than 0 and less than 2 nm.

15. The magnetic recording device of claim 14, wherein the at least one capping layer comprises a single capping layer.

16. The magnetic recording device of claim 15, wherein the single capping layer is disposed on the amorphous ferri-magnetic material layer.

17. The magnetic recording device of claim 11, wherein the at least one capping layer comprises a first capping layer and a second capping layer.

18. The magnetic recording device of claim 17, wherein the amorphous ferri-magnetic material layer comprises TbFeCo.

19. A magnetic recording device, comprising:
a magnetic recording head disposed on a slider; and
a magnetic recording medium disposed opposite the magnetic recording head, the magnetic recording medium comprising:
a substrate;
a plurality of magnetic layers disposed over the substrate;
a capping layer structure disposed over the plurality of magnetic layers, the capping layer structure comprising at least one capping layer and an amorphous ferri-magnetic material layer, wherein the at least one capping layer comprises a first capping layer and a second capping layer, wherein the first capping layer is disposed on the amorphous ferri-magnetic material layer and the second capping layer is disposed on the first capping layer; and

a carbon overcoat layer disposed on the capping layer structure.

20. A magnetic recording device, comprising:
a magnetic recording head disposed on a slider; and
a magnetic recording medium disposed opposite the magnetic recording head, the magnetic recording medium comprising:
a substrate;
a plurality of magnetic layers disposed over the substrate;
a capping layer structure disposed over the plurality of magnetic layers, the capping layer structure comprising at least one capping layer and an amorphous ferri-magnetic material layer, wherein the at least one capping layer comprises a first capping layer and a second capping layer, wherein the amorphous ferri-magnetic material layer is disposed on the first capping layer and the second capping layer is disposed on the amorphous ferri-magnetic material layer; and
a carbon overcoat layer disposed on the capping layer structure.