U.S. patent application number 13/049124 was filed with the patent office on 2012-09-20 for patterned perpendicular magnetic recording medium with ultrathin oxide film and reduced switching field distribution.
Invention is credited to Olav Hellwig, Ernesto E. Marinero, Dieter K. Weller.
Application Number | 20120236694 13/049124 |
Document ID | / |
Family ID | 46800678 |
Filed Date | 2012-09-20 |
United States Patent
Application |
20120236694 |
Kind Code |
A1 |
Hellwig; Olav ; et
al. |
September 20, 2012 |
PATTERNED PERPENDICULAR MAGNETIC RECORDING MEDIUM WITH ULTRATHIN
OXIDE FILM AND REDUCED SWITCHING FIELD DISTRIBUTION
Abstract
A patterned perpendicular magnetic recording disk has a Co-alloy
recording layer patterned into discrete data islands arranged in
concentric tracks and exhibits a narrow switching field
distribution (SFD). The disk includes a substrate, a NiTa alloy
planarizing layer on the substrate, a nonmagnetic Ru-containing
underlayer on the planarizing layer, an oxide-free Co alloy
magnetic recording layer, and an ultrathin oxide film between the
Ru-containing layer and the Co-alloy magnetic recording layer. The
oxide film may be an oxide selected from a Ta-oxide, a Co-oxide and
a Ti-oxide, and is ultrathin so that it may be considered a
discontinuous film. The planarizing layer and ultrathin oxide film
improve the growth homogeneity of the Co-alloy recording layer, so
that the patterned disk with data islands shows significantly
reduced SFD.
Inventors: |
Hellwig; Olav; (San Jose,
CA) ; Marinero; Ernesto E.; (Saratoga, CA) ;
Weller; Dieter K.; (San Jose, CA) |
Family ID: |
46800678 |
Appl. No.: |
13/049124 |
Filed: |
March 16, 2011 |
Current U.S.
Class: |
369/13.33 ;
360/110; 428/831; 428/831.2; G9B/11; G9B/5.04; G9B/5.241;
G9B/5.283; G9B/5.293 |
Current CPC
Class: |
G11B 5/7325 20130101;
G11B 5/855 20130101; G11B 5/746 20130101 |
Class at
Publication: |
369/13.33 ;
428/831; 428/831.2; 360/110; G9B/11; G9B/5.04; G9B/5.283;
G9B/5.241; G9B/5.293 |
International
Class: |
G11B 11/00 20060101
G11B011/00; G11B 5/127 20060101 G11B005/127; G11B 5/82 20060101
G11B005/82; G11B 5/667 20060101 G11B005/667; G11B 5/73 20060101
G11B005/73 |
Claims
1. A patterned perpendicular magnetic recording medium comprising:
a substrate; a planarizing layer on the substrate; a nonmagnetic
Ru-containing underlayer on the planarizing layer; a perpendicular
magnetic recording layer of an alloy comprising cobalt and
platinum; and an oxide film between the Ru-containing layer and the
magnetic recording layer and having a thickness less than 1.5 nm;
and wherein the magnetic recording layer is patterned into a
plurality of discrete islands.
2. The medium of claim 1 wherein the oxide film comprises an oxide
selected from a Ta-oxide, a Co-oxide and a Ti-oxide.
3. (canceled)
4. The medium of claim 3 wherein the oxide film is a discontinuous
film of oxide clusters on the Ru-containing layer, whereby the
magnetic recording layer is in contact with the Ru-containing layer
and the oxide clusters.
5. The medium of claim 1 wherein the planarizing layer comprises an
alloy comprising Ni and Ta.
6. The medium of claim 5 wherein the NiTa alloy planarizing layer
has a thickness greater than 20 nm.
7. The medium of claim 1 further comprising a NiW alloy seed layer
on the planarizing layer below and in contact with the
Ru-containing underlayer.
8. The medium of claim 1 wherein the magnetic recording layer alloy
is an oxide-free alloy.
9. The medium of claim 1 wherein the magnetic recording layer alloy
further comprises Cr.
10. The medium of claim 1 further comprising a soft underlayer
(SUL) of soft magnetically permeable material on the substrate
below the planarizing layer.
11. The medium of claim 10 wherein the planarizing layer comprises
an alloy comprising Ni and Ta having a thickness greater than or
equal to 2 nm and less than or equal to 10 nm.
12. The medium of claim 10 wherein the SUL is formed of a material
selected from the group consisting of alloys of CoFe, CoNiFe, NiFe,
FeCoB, CoCuFe, FeAlSi, FeTaN, FeN, FeTaC, CoTaZr and CoZrNb.
13. The medium of claim 10 wherein the SUL is a lamination of
multiple magnetically permeable films separated by nonmagnetic
films.
14. The medium of claim 13 wherein the nonmagnetic films in the
lamination provide antiferromagnetic coupling of the magnetically
permeable films in the lamination.
15. The medium of claim 1 wherein the medium is a magnetic
recording disk and wherein the islands are arranged on the
substrate in a plurality of generally concentric circular
tracks.
16. A magnetic recording disk drive comprising: the disk of claim
15; a write head for magnetizing the perpendicular magnetic
recording layer in the islands; and a read head for reading the
magnetized recording layer in the islands.
17. A thermally-assisted recording (TAR) magnetic recording disk
drive comprising: the disk of claim 15 further comprising a heat
sink layer between the substrate and the islands; a write head for
applying a magnetic field to the perpendicular magnetic recording
layer in the islands; an optical data channel and near-field
transducer for directing radiation to the islands to heat the
perpendicular magnetic recording layer in the islands; and a read
head for reading the magnetized recording layer in the islands.
18. A patterned perpendicular magnetic recording disk comprising: a
substrate; a planarizing layer comprising an alloy comprising Ni
and Ta on the substrate; a nonmagnetic Ru-containing underlayer on
the planarizing layer; a perpendicular magnetic recording layer of
an oxide-free alloy comprising cobalt and platinum; and an oxide
film between the Ru-containing layer and the magnetic recording
layer, the oxide film comprising an oxide selected from a Ta-oxide,
a Co-oxide and a Ti-oxide and having a thickness less than or equal
to 1.5 nm; and wherein the perpendicular magnetic recording layer
is patterned into a plurality of discrete islands arranged in a
plurality of concentric tracks.
19. The disk of claim 18 wherein the oxide film is a discontinuous
film of oxide clusters on the Ru-containing layer, whereby the
magnetic recording layer is in contact with the Ru-containing layer
and the oxide clusters.
20. The disk of claim 18 further comprising a NiW alloy seed layer
on the planarizing layer below and in contact with the
Ru-containing underlayer.
21. The disk of claim 18 wherein the NiTa alloy planarizing layer
has a thickness greater than 20 nm.
22. The disk of claim 18 further comprising a soft underlayer (SUL)
of soft magnetically permeable material on the substrate below the
planarizing layer, and wherein the NiTa alloy planarizing layer has
a thickness greater than or equal to 2 nm and less than or equal to
10 nm.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates generally to patterned perpendicular
magnetic recording media, such as disks for use in magnetic
recording hard disk drives, and more particularly to patterned
disks with data islands having improved magnetic recording
properties.
[0003] 2. Description of the Related Art
[0004] Magnetic recording hard disk drives with patterned magnetic
recording media have been proposed to increase data density. In
conventional continuous magnetic recording media, the magnetic
recording layer is a continuous layer over the entire surface of
the disk. In patterned media, also called bit-patterned media
(BPM), the magnetic recording layer on the disk is patterned into
small isolated data islands arranged in concentric data tracks.
While BPM disks may be longitudinal magnetic recording disks,
wherein the magnetization directions are parallel to or in the
plane of the recording layer, perpendicular magnetic recording
disks, wherein the magnetization directions are perpendicular to or
out-of-the-plane of the recording layer, will likely be the choice
for BPM because of the increased data density potential of
perpendicular media. To produce the magnetic isolation of the
patterned data islands, the magnetic moment of the spaces between
the islands is destroyed or substantially reduced to render these
spaces essentially nonmagnetic. Alternatively, the media may be
fabricated so that there is no magnetic material in the spaces
between the islands.
[0005] Nanoimprint lithography (NIL) has been proposed to form the
desired pattern of islands on BPM disks. NIL is based on deforming
an imprint resist layer by a master template or mold having the
desired nano-scale pattern. The master template is made by a
high-resolution lithography tool, such as an electron-beam tool.
The substrate to be patterned may be a disk blank with the magnetic
recording layer, and any required underlayers, formed on it as
continuous layers. Then the substrate is spin-coated with the
imprint resist, such as a thermoplastic polymer, like
poly-methylmethacrylate (PMMA). The polymer is then heated above
its glass transition temperature. At that temperature, the
thermoplastic resist becomes viscous and the nano-scale pattern is
reproduced on the imprint resist by imprinting from the template at
a relatively high pressure. Once the polymer is cooled, the
template is removed from the imprint resist leaving an inverse
nano-scale pattern of recesses and spaces on the imprint resist. As
an alternative to thermal curing of a thermoplastic polymer, a
polymer curable by ultraviolet (UV) light, such as MonoMat
available from Molecular Imprints, Inc., can be used as the imprint
resist. The patterned imprint resist layer is then used as an etch
mask to form the desired pattern of islands in the underlying
magnetic recording layer.
[0006] A critical issue for the development of BPM is that the
switching field distribution (SFD), i.e., the island-to-island
variation of the coercive field, needs to be narrow enough to
insure exact addressability of individual islands without
overwriting adjacent islands. Ideally the SFD width would be zero,
meaning that all the bits would switch at the same write field
strength. There are extrinsic contributions to the SFD, including
variations in the size, shape and spacing of the islands, and
dipolar interactions between adjacent islands, as well as intrinsic
contributions, including variations in the composition and
crystallographic orientation of the magnetic material, which result
in variations in the magnetic anisotropy of the islands.
Additionally, it has been found that the SFD broadens (that is, the
bit-to-bit variation in the coercive field increases) as the size
of the magnetic islands is reduced, which limits the achievable bit
areal density of BPM.
[0007] What is needed is a patterned perpendicular magnetic
recording medium that has a narrow SFD.
SUMMARY OF THE INVENTION
[0008] The invention relates to a patterned perpendicular magnetic
recording disk with a Co-alloy recording layer and a narrow SFD,
and a disk drive incorporating the disk. The disk includes a
substrate, an optional soft underlayer (SUL) of soft magnetically
permeable material on the substrate, a planarizing layer on the
substrate or optional SUL, a nonmagnetic Ru-containing underlayer
on the planarizing layer, a perpendicular magnetic recording layer
of a Co alloy that preferably contains no oxides, and an ultrathin
oxide film between the Ru-containing layer and the Co-alloy
magnetic recording layer. The recording layer is patterned into
discrete islands arranged in concentric tracks. An optional NiW
alloy seed layer may be located on the planarizing layer below and
in contact with the Ru-containing underlayer. The planarizing layer
is preferably a NiTa alloy with a thickness preferably greater than
20 nm, but if the optional SUL is present between the substrate and
the planarizing layer, the planarizing layer can have a thickness
between about 2 to 10 nm. The oxide film may be an oxide selected
from a Ta-oxide, a Co-oxide and a Ti-oxide and having a thickness
less than or equal to 1.5 nm. In this thickness regime, the oxide
film thickness may be considered an "average" thickness of a
discontinuous film, so that the surface onto which the Co-alloy
magnetic recording layer is deposited may be both the Ru-containing
layer and clusters or regions of the oxide film. The planarizing
layer and ultrathin oxide film improve the growth homogeneity of
the Co-alloy recording layer, so that a BPM with data islands
according to the invention shows significantly reduced SFD.
[0009] For a fuller understanding of the nature and advantages of
the present invention, reference should be made to the following
detailed description taken together with the accompanying
figures.
BRIEF DESCRIPTION OF THE DRAWING
[0010] FIG. 1 is a top view of a perpendicular magnetic recording
disk drive with bit-patterned media (BPM) and shows the patterned
data islands arranged in concentric circular data tracks according
to the prior art.
[0011] FIG. 2 is a top view of an enlarged portion of a prior art
BPM disk showing the detailed arrangement of the data islands.
[0012] FIGS. 3A-3C are sectional views of a BPM disk at various
stages of etching and planarizing the disk according to the prior
art.
[0013] FIG. 4 is a sectional view of a portion of a disk substrate
showing a data island with the structure according to the
invention.
[0014] FIGS. 5A-5B show the comparison in magnetic switching for
data islands according to the prior art and data islands according
to the invention.
[0015] FIG. 6 is a graph of anisotropy (K.sub.u) as a function of
recording layer thickness for different data islands with a
Co.sub.80Pt.sub.10Cr.sub.10 recording layer, and shows the
improvement in film growth homogeneity for the data islands
according to the invention.
[0016] FIG. 7 is a sectional view of an air-bearing slider for use
in a thermally-assisted recording (TAR) system and a portion of a
TAR disk with data islands according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] FIG. 1 is a top view of a patterned-media magnetic recording
disk drive 100 with a patterned-media magnetic recording disk 200.
The drive 100 has a housing or base 112 that supports an actuator
130 and a drive motor for rotating the magnetic recording disk 200.
The actuator 130 may be a voice coil motor (VCM) rotary actuator
that has a rigid arm 131 and rotates about pivot 132 as shown by
arrow 133. A head-suspension assembly includes a suspension 135
that has one end attached to the end of actuator arm 131 and a head
carrier, such as an air-bearing slider 120, attached to the other
end of suspension 135. The suspension 135 permits the slider 120 to
be maintained very close to the surface of disk 200 and enables it
to "pitch" and "roll" on the air-bearing generated by the disk 200
as it rotates in the direction of arrow 20. A magnetoresistive read
head (not shown) and an inductive write head (not shown) are
typically formed as an integrated read/write head patterned as a
series of thin films and structures on the trailing end of the
slider 120, as is well known in the art. The slider 120 is
typically formed of a composite material, such as a composite of
alumina/titanium-carbide (Al.sub.2O.sub.3/TiC). Only one disk
surface with associated slider and read/write head is shown in FIG.
1, but there are typically multiple disks stacked on a hub that is
rotated by a spindle motor, with a separate slider and read/write
head associated with each surface of each disk.
[0018] The patterned-media magnetic recording disk 200 includes a
hard or rigid disk substrate and discrete data islands 30 of
magnetizable material on the substrate. The data islands 30 are
arranged in radially-spaced circular tracks 118, with only a few
islands 30 and representative tracks 118 near the inner and outer
diameters of disk 200 being shown in FIG. 1. The islands 30 are
depicted as having a circular shape but the islands may have other
shapes, for example generally rectangular, oval or elliptical. As
the disk 200 rotates in the direction of arrow 20, the movement of
actuator 130 allows the read/write head on the trailing end of
slider 120 to access different data tracks 118 on disk 200.
[0019] FIG. 2 is a top view of an enlarged portion of disk 200
showing the detailed arrangement of the data islands 30 on the
surface of the disk substrate in one type of pattern according to
the prior art. The islands 30 contain magnetizable recording
material and are arranged in circular tracks spaced-apart in the
radial or cross-track direction, as shown by tracks 118a-118e. The
tracks are typically equally spaced apart by a fixed track spacing
TS. The spacing between data islands in a track is shown by
distance IS between data islands 30a and 30b in track 118a, with
adjacent tracks being shifted from one another by a distance IS/2,
as shown by tracks 118a and 118b. Each island has a lateral
dimension W parallel to the plane of the disk 200, with W being the
diameter if the islands have a circular shape. The islands may have
other shapes, for example generally rectangular, oval or
elliptical, in which case the dimension W may be considered to be
the smallest dimension of the non-circular island, such as the
smaller side of a rectangular island. The adjacent islands are
separated by nonmagnetic regions or spaces, with the spaces having
a lateral dimension D. The value of D may be greater than the value
of W.
[0020] BPM disks like that shown in FIG. 2 may be perpendicular
magnetic recording disks, wherein the magnetization directions are
perpendicular to or out-of-the-plane of the recording layer in the
islands. To produce the required magnetic isolation of the
patterned data islands 30, the magnetic moment of the regions or
spaces between the islands 30 must be destroyed or substantially
reduced to render these spaces essentially nonmagnetic. The term
"nonmagnetic" means that the spaces between the islands 30 are
formed of a nonferromagnetic material, such as a dielectric, or a
material that has no substantial remanent moment in the absence of
an applied magnetic field, or a magnetic material in a trench
recessed far enough below the islands 30 to not adversely affect
reading or writing. The nonmagnetic spaces may also be the absence
of magnetic material, such as trenches or recesses in the magnetic
recording layer or disk substrate.
[0021] FIG. 3A is a sectional view showing the disk 200 according
to the prior art before lithographic patterning and etching to form
the BPM disk. The disk 200 is a substrate 201 having a generally
planar surface 202 on which the representative layers are
deposited, typically by sputtering. The disk 200 is depicted as a
perpendicular magnetic recording disk with a recording layer (RL)
having perpendicular (i.e., generally perpendicular to substrate
surface 201) magnetic anisotropy and an optional soft magnetic
underlayer (SUL) below the RL. The optional SUL serves as a flux
return path for the magnetic write field from the disk drive write
head.
[0022] The hard disk substrate 201 may be any commercially
available glass substrate, but may also be a conventional aluminum
alloy with a NiP surface coating, or an alternative substrate, such
as silicon, canasite or silicon-carbide. An adhesion layer or onset
layer (OL) for the growth of the SUL may be an AlTi alloy or a
similar material with a thickness of about 2-10 nm that is
deposited on the substrate surface 202.
[0023] The SUL may be formed of magnetically permeable materials
such as alloys of CoNiFe, FeCoB, CoCuFe, NiFe, FeAlSi, FeTaN, FeN,
FeTaC, CoTaZr, CoFeTaZr, CoFeB, and CoZrNb. The SUL may also be a
laminated or multilayered SUL formed of multiple soft magnetic
films separated by nonmagnetic films, such as electrically
conductive films of Al or CoCr. The SUL may also be a laminated or
multilayered SUL formed of multiple soft magnetic films separated
by interlayer films that mediate an antiferromagnetic coupling,
such as Ru, Ir, or Cr or alloys thereof. The SUL may have a
thickness in the range of about 5 to 50 nm.
[0024] The RL in the discrete magnetic islands may be a cobalt (Co)
alloy, like a cobalt-platinum (CoPt) or cobalt-platinum-chromium
(CoPtCr) alloy. The Co alloy RL is grown on a growth-enhancing
underlayer (UL) that induces the crystalline C-axis of the Co alloy
to be perpendicular to the plane of the RL, so that the RL has
strong perpendicular magnetocrystalline anisotropy. The UL may be a
Ru or Ru alloy layer. A seed layer (SL), like a NiW or NiWCr alloy
layer, may be deposited on the SUL to enhance the growth of the
Ru-containing UL. If the optional SUL is present, then the UL and
SL also function as an exchange-break layer (EBL) that breaks the
magnetic exchange coupling between the magnetically permeable films
of the SUL and the RL.
[0025] A protective overcoat (OC) is deposited on the RL. The OC
may be sputter-deposited amorphous carbon, like DLC, which may also
be hydrogenated and/or nitrogenated. Other materials that may be
used for the OC include carbides such as silicon carbides and boron
carbides; nitrides such as silicon nitrides (SiN.sub.x), titanium
nitrides, and boron nitrides; metal oxides, such as TiO.sub.2,
ZrO.sub.2, Al.sub.2O.sub.3, Cr.sub.2O.sub.3, Ta.sub.2O.sub.5 and
ZrO.sub.2--Y.sub.2O.sub.3; and mixtures of these materials.
[0026] The disk of FIG. 3A is lithographically patterned, for
example by a nanoimprinting process. In nanoimprinting, a master
template is fabricated, for example by direct e-beam writing, to
have the desired pattern of data islands and nonmagnetic regions. A
thin film of imprint resist (i.e., a thermoplastic polymer) is spin
coated onto the disk. Then the master template with its predefined
pattern is brought into contact with the imprint resist film and
the template and disk are pressed together and heat is applied.
When the imprint resist polymer is heated above its glass
transition temperature, the pattern on the template is pressed into
the resist film. After cooling, the master template is separated
from the disk and the patterned resist is left on the RL. The
patterned imprint resist is then used as an etch mask.
Reactive-ion-etching (RIE) or ion milling can be used to transfer
the pattern in the imprint resist to the underlying disk to form
the data islands and nonmagnetic regions.
[0027] FIG. 3B is a sectional view of the disk 200 after
lithographic patterning and etching. After etching, elevated lands
30 with RL material and grooves or recesses 32 are formed above the
substrate surface 202. The typical depth of the recesses 32, which
is also essentially the height of the lands 30, is in the range of
about 4 to 50 nm and the typical width of the recesses is in the
range of about 4 to 50 nm. As shown in FIG. 3B, the etching is
preferably performed to a depth that removes all of the RL material
so that there is no RL material in the recesses 32. The etching may
remove a small amount of the EBL material. Typically there would be
a layer of EBL material below the lower surface of the recesses
32.
[0028] FIG. 3C is a sectional view of the etched disk 200 of FIG.
3B after deposition of a second optional protective overcoat 34
into the recesses 32 and over the tops of lands 30 and after
deposition and chemical-mechanical-polishing (CMP) of fill material
36 in the recesses 32. The optional second protective overcoat 34
may be formed of one of the materials like that used for the OC
directly on top of the RL. The fill material 36 may be SiO.sub.2 or
a polymeric material, or a nonmagnetic metal, like Cu. The CMP
results in essentially a planarized disk surface. A layer of
conventional liquid lubricant (not shown) may be deposited, for
example by spin coating, on the surface of the disk 200.
[0029] In the patterned perpendicular media of this invention, the
data islands have a planarizing layer (PL) on the substrate and an
ultrathin oxide film below the Co-alloy RL. This results in
substantially improved homogeneity in the growth of the Co-alloy
RL, and a significant reduction in SFD. FIG. 4 is a sectional view
of a portion of a disk showing a portion of the SUL with a single
data island. The PL is preferably a NiTa alloy, preferably a
Ni.sub.xTa.sub.100-x, where x is in the range of about 50 to 70
atomic percent, with a thickness in the range of about 5 to 40 nm.
The seed layer (SL) for the Ru-containing underlayer (UL) is
deposited on the PL. The SL is preferably a NiW alloy, preferably
Ni.sub.xW.sub.100-x, where x is in the range of about 80 to 95
atomic percent, with a thickness in the range of about 2 to 20 nm.
The UL is deposited on the SL. The UL is preferably Ru, but may be
a Ru alloy like RuCr or Ru-doped with oxides such as
Ta.sub.2O.sub.5, SiO.sub.2 or TiO.sub.2, with a thickness in the
range of about 5 to 30 nm. The RL is a Co alloy, preferably a
CoPtCr alloy, with a thickness in the range of about 4 to 15 nm.
While granular Co-alloy magnetic layers for conventional continuous
magnetic recording disks typically include an oxide, like
SiO.sub.2, to decrease the grain size, in this invention it is
preferable that the Co-alloy RL be oxide-free and has a grain size
as large as possible.
[0030] In this invention an ultrathin oxide film is deposited on
the UL below the RL prior to deposition of the RL. The oxide film
is preferably a Ta-oxide, like Ta.sub.2O.sub.5, but may also be a
Ti-oxide or a Co-oxide, with a thickness in the range of about 0.1
to 1.5 nm. The oxide film is ultrathin, less than or equal to 1.5
nm, and preferably less than or equal to 1.0 nm. In this thickness
regime, the thickness may be considered an "average" thickness of a
discontinuous film, so that the surface onto which the Co-alloy RL
is deposited may be both, the Ru or Ru alloy material of the UL and
clusters or regions of the oxide film. The Ta-oxide film may be
deposited by sputter deposition from a Ta.sub.2O.sub.5 target. If
the target is conducting, DC sputtering can be readily employed. On
the other hand if the target is an insulator or a high resistance
target, RF sputtering is the preferred mode. Alternatively, the
Ta.sub.2O.sub.5 can be grown in situ by reactive sputtering of Ta
with a sputter gas mixture containing the appropriate amount of
oxygen.
[0031] FIGS. 5A-5B show the improvement in magnetic nucleation
field for a non-patterned full magnetic film. FIG. 5A shows a Kerr
angle hysteresis loop with the circled region expanded to show the
full film nucleation field with a structure of [NiTa-5 nm/NiW-8
nm/Ru-10 nm/Co.sub.80Pt.sub.10Cr.sub.10-10 nm] on a glass
substrate. In the expanded region of FIG. 5B a much sharper
nucleation field is shown for the same structure as for FIG. 5A but
with a 0.3 nm Ta.sub.2O.sub.5 film between the Ru UL and CoPtCr RL.
The sharper transition in FIG. 5B is indicative of a narrower range
of applied fields needed to nucleate film reversal. In other words,
there are less pinning sites such as structural defects in these
films that normally hinder reversal and thereby require a wider
range of applied fields. This is a result of the growth
improvements in the quality of the crystallinity of the CoPtCr
alloy when the ultrathin Ta.sub.2O.sub.5 film is employed below the
RL. The improvement shown in FIG. 5 B means that the RL layers,
when formed as individual data islands in a BPM, will have better
switching properties on account of fewer defects/pinning sites
present in the RL alloy. FIG. 5B shows media with sharper
transitions compared with FIG. 5A.
[0032] FIG. 6 is a graph of the magnetic anisotropy (K.sub.u) as a
function of RL thickness for different continuous thin film systems
with a Co.sub.80Pt.sub.10Cr.sub.10 RL, and shows the improvement in
film growth homogeneity according to the invention. Curve A is for
a thin film with a structure of [Ta-2 nm/NiW-9 nm/Ru-7
nm/Co.sub.80Pt.sub.10Cr.sub.10-10 nm] and shows a variation in
K.sub.u of about 20% over a RL thickness range of about 2-16 nm.
Curve B is for a thin film according to the invention with a
structure of [NiTa-5 nm/NiW-8 nm/Ru-10 nm/Ta.sub.2O.sub.5-0.3
nm/Co.sub.80Pt.sub.10Cr.sub.10-10 nm] and shows a variation in
K.sub.u of only about 8% over the same RL thickness range. The
oxide film and the replacement of a Ta layer with the NiTa
planarizing layer (PL) result in significantly improved homogeneity
in the growth of the CoPtCr layer. Curve C is for a thin film
according to the invention identical to the structure for Curve B,
but wherein the thickness of the NiTa PL is increased from 5 nm to
30 nm. The variation in K.sub.u is reduced from about 8% to about
6% over the same RL thickness range. Thus the film growth
homogeneity can be improved with a thicker NiTa PL, preferably a
thickness greater than 20 nm for the case where no SUL is employed.
When the SUL is present, the thickness of this PL can be
significantly reduced to a range of 2 to 10 nm.
[0033] As a result of the improved switching quality and film
growth homogeneity, a BPM with data islands according to the
invention shows significantly reduced SFD. For a BPM with islands
having a structure like that for Curve A in FIG. 6, the intrinsic
SFD was measured at 630 Oe. For a BPM with islands having a
structure according to the invention (like that for Curve B in FIG.
6, the intrinsic SFD was measured at 450 Oe. The intrinsic SFD is
measured via the method described by Tagawa et al., "Relationships
between high density recording performance and particle coercivity
distribution," IEEE TRANSACTIONS ON MAGNETICS, VOL. 27, NO. 6,
NOVEMBER 1991, 4975-4977.
[0034] Perpendicular magnetic recording disks with BPM have been
proposed primarily for use in conventional magnetic recording,
wherein an inductive write head alone writes data to the islands.
However, perpendicular BPM disks have also been proposed for use in
heat-assisted recording, also called thermally-assisted recording
(TAR). In a TAR system, an optical waveguide with a near-field
transducer (NFT) directs heat from a radiation source, such as a
laser, to heat localized regions of the magnetic recording layer on
the disk. The radiation heats the magnetic material locally to near
or above its Curie temperature to lower the coercivity enough for
writing to occur by the inductive write head. The improved BPM of
this invention is also applicable to perpendicular BPM disks for
TAR disk drives.
[0035] FIG. 1 thus depicts a conventional magnetic recording system
with a perpendicular BPM disk 200 and an air-bearing slider 120
that supports the write head and read head. FIG. 7 depicts a
sectional view, not drawn to scale because of the difficulty in
showing the very small features, of an air-bearing slider 120' for
use in a TAR system and a portion of a TAR disk 200'. The
air-bearing slider 120' supports the write head 50 (with yoke 54
and write pole 52), read head 60, and shields S1 and S2. In the TAR
disk 200', a heat sink layer 21 is located below the islands 30 and
nonmagnetic regions 32. The islands 30 may be islands according to
this invention, like the island in FIG. 4. Heat sink layer 21 is
formed of a material that is a good thermal conductor, like Cu, Au,
Ag or other suitable metals or metal alloys. Layer 19 may be a
thermal resist layer, such as a layer of MgO or SiO.sub.2, between
the heat sink layer 21 and the islands 30 to help control the heat
flow so that heat is not distributed too rapidly into the heat sink
layer 21. The TAR disk 200' may also include an optional SUL, which
if present would be located below the heat sink layer 21. If there
is no SUL, then there is no need for an EBL. The slider 120' has an
air-bearing surface (ABS) that faces the disk 200'. The slider 120'
also supports a laser 70, mirror 71, optical waveguide or channel
72 and NFT 74, which has its output at the ABS.
[0036] When write-current is directed through coil 56, the write
pole 52 directs magnetic flux to the data islands 30, as
represented by arrow 80 directed to one of the data islands 30. The
dashed line 17 with arrows shows the flux return path back to the
return pole 54. The NFT 74 directs near-field radiation, as
represented by wavy arrow 82, to the data islands 31 as the TAR
disk 10' moves in the direction 23 relative to the slider. The
electric charge oscillations in the NFT heat the data islands 30 at
the same time the data islands are exposed to the write field from
the write pole 52. This raises the temperature of the magnetic
recording material in the data islands to near or above its Curie
temperature to thereby lower the coercivity of the material and
enable the magnetization of the data island to be switched by the
write field. When the data islands according to this invention are
used in a TAR disk drive, the anisotropy field of the Co-alloy may
be between about 15 and 100 kOe, which is considerably higher than
the write field from a conventional write head. For example, a
high-anisotropy Co-alloy like Co.sub.50Pt.sub.50 with an anisotropy
field of 50 kOe may be used. The composition of the Co-alloy layer
may be varied to allow tuning of the Curie temperature.
[0037] While the present invention has been particularly shown and
described with reference to the preferred embodiments, it will be
understood by those skilled in the art that various changes in form
and detail may be made without departing from the spirit and scope
of the invention. Accordingly, the disclosed invention is to be
considered merely as illustrative and limited in scope only as
specified in the appended claims.
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