U.S. patent application number 11/448770 was filed with the patent office on 2007-12-13 for thin sul perpendicular magnetic recording media and recording systems comprising same.
This patent application is currently assigned to SEAGATE TECHNOLOGY LLC. Invention is credited to Yong-Chang Feng, Samuel D. Harkness, Thomas P. Nolan, Hans J. Richter, Li Tang, Zhong (Stella) Wu, Youfeng Zheng.
Application Number | 20070287031 11/448770 |
Document ID | / |
Family ID | 38822360 |
Filed Date | 2007-12-13 |
United States Patent
Application |
20070287031 |
Kind Code |
A1 |
Nolan; Thomas P. ; et
al. |
December 13, 2007 |
Thin sul perpendicular magnetic recording media and recording
systems comprising same
Abstract
A perpendicular magnetic recording system, comprises: a
perpendicular magnetic recording medium including a non-magnetic
substrate having a surface and a stacked plurality of thin film
layers forming a layer stack overlying the substrate surface and
including a magnetically soft underlayer (SUL) beneath at least one
perpendicular magnetic recording layer, wherein the SUL has a
saturation magnetization (M.sub.s)--thickness (t) product
(M.sub.st) less than about 4 memu/cm.sup.2, and a ring-type
magnetic transducer head is positioned in spaced adjacency to an
upper surface of the layer stack.
Inventors: |
Nolan; Thomas P.; (Fremont,
CA) ; Tang; Li; (Fremont, CA) ; Feng;
Yong-Chang; (Fremont, CA) ; Wu; Zhong (Stella);
(Fremont, CA) ; Harkness; Samuel D.; (Berkeley,
CA) ; Richter; Hans J.; (Palo Alto, CA) ;
Zheng; Youfeng; (San Jose, CA) |
Correspondence
Address: |
SEAGATE TECHNOLOGY LLC;c/o MCDERMOTT WILL & EMERY LLP
600 13TH STREET, NW
WASHINGTON
DC
20005-3096
US
|
Assignee: |
SEAGATE TECHNOLOGY LLC
|
Family ID: |
38822360 |
Appl. No.: |
11/448770 |
Filed: |
June 8, 2006 |
Current U.S.
Class: |
428/827 ;
360/135; 428/828; 428/829; G9B/5.044; G9B/5.288 |
Current CPC
Class: |
G11B 5/667 20130101;
G11B 5/1278 20130101 |
Class at
Publication: |
428/827 ;
428/828; 428/829; 360/135 |
International
Class: |
G11B 5/66 20060101
G11B005/66; G11B 5/82 20060101 G11B005/82 |
Claims
1. A perpendicular magnetic recording medium, comprising: (a) a
non-magnetic substrate having a surface; and (b) a stacked
plurality of thin film layers forming a layer stack overlying said
substrate surface and including a magnetically soft underlayer
(SUL) beneath at least one perpendicular magnetic recording layer,
said SUL having a saturation magnetization (M.sub.s)--thickness (t)
product (M.sub.st) less than about 4 memu/cm.sup.2.
2. The medium as in claim 1, wherein: said SUL comprises a material
having a saturation magnetization (M.sub.s) of about 500 to about
2,000 emu/cc and a thickness from about 1 to about 40 nm.
3. The medium as in claim 1, wherein: said SUL and said at least
one perpendicular magnetic recording layer are spaced apart at a
spacing determined by an interlayer stack between said SUL and said
at least one perpendicular magnetic recording layer.
4. The medium as in claim 3, wherein: said SUL and said at least
one perpendicular magnetic recording layer are spaced apart from
about 5 to about 200 nm.
5. The medium as in claim 4, wherein: said SUL and said at least
one perpendicular magnetic recording layer are spaced apart from
about 30 to about 100 nm.
6. The medium as in claim 3, wherein: said interlayer stack
includes a spacer layer and an interlayer.
7. The medium as in claim 6, wherein: said spacer layer comprises
an amorphous material and said interlayer comprises an hcp material
with a preferred c-axis perpendicular growth orientation.
8. The medium as in claim 6, wherein: said interlayer stack further
includes a seed layer.
9. The medium as in claim 1, wherein: said SUL has a saturation
magnetization (M.sub.s)--thickness (t) product (M.sub.st) less than
about 1 memu/cm.sup.2.
10. The medium as in claim 1, wherein: said SUL comprises a
material having a magnetic permeability greater than about 10 and a
thickness less than about 10 nm.
11. The medium as in claim 1, wherein: said SUL comprises at least
one soft magnetic material selected from the group consisting of:
Ni, Co, Fe, NiFe (Permalloy), FeN, FeSiAl, FeSiAlN, CoZr, CoZrCr,
CoZrNb, CoFeZrNb, CoFe, FeCoB, and FeCoC.
12. The medium as in claim 1, wherein: said at least one
perpendicular magnetic recording layer comprises an hcp Co-based
alloy with a preferred c-axis perpendicular growth orientation.
13. The medium as in claim 12, wherein: said at least one
perpendicular magnetic recording layer comprises at least partially
isolated magnetic particles or grains with c-axis growth
orientation.
14. The medium as in claim 12, wherein: said at least one
perpendicular magnetic recording layer comprises a granular layer
with uniform grain size, composition, and crystallographic
orientation.
15. The medium as in claim 1, wherein: said layer stack comprises a
protective overcoat layer above said at least one perpendicular
magnetic recording layer and a lubricant topcoat layer over said
protective overcoat layer.
16. The medium as in claim 15, wherein: said protective overcoat
layer comprises a carbon-based material and said lubricant topcoat
layer comprises a fluoropolymer material.
17. The medium as in claim 1, wherein: said non-magnetic substrate
comprises a material selected from the group consisting of: Al,
Al--Mg alloys, other Al-based alloys, NiP-plated Al or Al-based
alloys, glass, ceramics, glass-ceramics, polymeric materials, and
composites or laminates of these materials.
18. A perpendicular magnetic recording system, comprising: (a) a
perpendicular magnetic recording medium including: (i) a
non-magnetic substrate having a surface; and (ii) a stacked
plurality of thin film layers forming a layer stack overlying said
substrate surface and including a magnetically soft underlayer
(SUL) beneath and spaced from at least one perpendicular magnetic
recording layer, said SUL having a saturation magnetization
(M.sub.s)--thickness (t) product (M.sub.st) less than about 4
memu/cm.sup.2; and (b) a ring-type magnetic transducer head
positioned in spaced adjacency to an upper surface of said layer
stack to form a head gap, said transducer head comprising leading
and trailing poles.
19. The system as in claim 18, wherein: said SUL has a saturation
magnetization (M.sub.s)--thickness (t) product (M.sub.st) less than
about 4 memu/cm.sup.2.
20. The system as in claim 18, wherein: the orientation ratio of
said medium of said system is greater than about 10.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to improved perpendicular
magnetic recording media with very thin magnetically soft
underlayers (SUL's) and magnetic recording systems utilizing the
improved media with ring-type magnetic transducer heads. The
invention has particular utility in the manufacture and use of very
high areal recording density media, such as hard disks, comprising
perpendicular magnetic recording layers.
BACKGROUND OF THE INVENTION
[0002] Magnetic media are widely used in various applications,
particularly in the computer industry for data/information storage
and retrieval applications, typically in disk form, and efforts are
continually made with the aim of increasing the areal recording
density, i.e., bit density of the magnetic media. Conventional
thin-film type magnetic media, wherein a fine-grained
polycrystalline magnetic alloy layer serves as the active recording
layer, are generally classified as "longitudinal" or
"perpendicular", depending upon the orientation of the magnetic
domains of the grains of magnetic material.
[0003] Perpendicular recording media have been found to be superior
to longitudinal media in achieving very high bit densities without
experiencing the thermal stability limit associated with the
latter. In perpendicular magnetic recording media, residual
magnetization is formed in a direction ("easy axis") perpendicular
to the surface of the magnetic medium, typically a layer of a
magnetic material on a suitable substrate. Very high to ultra-high
linear recording densities are obtainable by utilizing a
"single-pole" magnetic transducer or "head" with such perpendicular
magnetic media.
[0004] At present, efficient, high bit density recording utilizing
a perpendicular magnetic medium requires interposition of a
relatively thick (as compared with the magnetic recording layer),
magnetically "soft" underlayer ("SUL"), i.e., a magnetic layer
having a relatively low coercivity below about 1 kOe, such as of a
NiFe alloy (Permalloy), between a non-magnetic substrate, e.g., of
glass, aluminum (Al) or an Al-based alloy, and a magnetically
"hard" recording layer having relatively high coercivity, typically
about 3-8 kOe, e.g., of a cobalt-based alloy (e.g., a Co--Cr alloy
such as CoCrPtB) having perpendicular anisotropy. The magnetically
soft underlayer serves to guide magnetic flux emanating from the
head through the magnetically hard perpendicular recording
layer.
[0005] A typical conventional perpendicular recording system 10
with a perpendicularly oriented magnetic medium 1 and a magnetic
transducer head 9 is schematically illustrated in cross-section in
FIG. 1, wherein reference numeral 2 indicates a non-magnetic
substrate, reference numeral 3 indicates an optional adhesion
layer, reference numeral 4 indicates a relatively thick
magnetically soft underlayer (SUL), reference numeral 5 indicates
an interlayer stack comprising at least one non-magnetic
interlayer, sometimes referred to as an "intermediate" layer, and
reference numeral 6 indicates at least one relatively thin
magnetically hard perpendicular recording layer with its magnetic
easy axis perpendicular to the film plane. Interlayer stack 5
commonly includes at least one interlayer 5.sub.B of a hcp material
adjacent the magnetically hard perpendicular recording layer 6 and
an optional seed layer 5.sub.A adjacent the magnetically soft
underlayer (SUL) 4, typically comprising at least one of an
amorphous material and an fcc material.
[0006] Still referring to FIG. 1, reference numerals 9.sub.M and
9.sub.A, respectively, indicate the main (writing) and auxiliary
poles of the magnetic transducer head 9. The relatively thin
interlayer 5, comprised of one or more layers of non-magnetic
materials, serves to (1) prevent magnetic interaction between the
magnetically soft underlayer 4 and the at least one magnetically
hard recording layer 6; and (2) promote desired microstructural and
magnetic properties of the at least one magnetically hard recording
layer 6.
[0007] As shown by the arrows in the figure indicating the path of
the magnetic flux .phi., flux .phi. emanates from the main writing
pole 9.sub.M of magnetic transducer head 9, enters and passes
through the at least one vertically oriented, magnetically hard
recording layer 6 in the region below main pole 9.sub.M, enters and
travels within soft magnetic underlayer (SUL) 4 for a distance, and
then exits therefrom and passes through the at least one
perpendicular hard magnetic recording layer 6 in the region below
auxiliary pole 9.sub.A of transducer head 9. The direction of
movement of perpendicular magnetic medium 21 past transducer head 9
is indicated in the figure by the arrow in the figure.
[0008] Completing the layer stack of medium 1 is a protective
overcoat layer 7, such as of a diamond-like carbon (DLC), formed
over magnetically hard layer 6, and a lubricant topcoat layer 8,
such as of a perfluoropolyether (PFPE) material, formed over the
protective overcoat layer.
[0009] Substrate 2 is typically disk-shaped and comprised of a
non-magnetic metal or alloy, e.g., Al or an Al-based alloy, such as
Al--Mg having a Ni--P plating layer on the deposition surface
thereof, or alternatively, substrate 2 is comprised of a suitable
glass, ceramic, glass-ceramic, polymeric material, or a composite
or laminate of these materials. Optional adhesion layer 3, if
present on substrate surface 2, typically comprises a less than
about 200 .ANG. thick layer of a metal or a metal alloy material
such as Ti, a Ti-based alloy, Ta, a Ta-based alloy, Cr, or a
Cr-based alloy. The relatively thick soft magnetic underlayer 4 is
typically comprised of an about 50 to about 300 nm thick layer of a
soft magnetic material such as Ni, Co, Fe, an Fe-containing alloy
such as NiFe (Permalloy), FeN, FeSiAl, FeSiAlN, a Co-containing
alloy such as CoZr, CoZrCr, CoZrNb, or a Co--Fe-containing alloy
such as CoFeZrNb, CoFe, FeCoB, and FeCoC. Relatively thin
interlayer stack 5 typically comprises an about 50 to about 300
.ANG. thick layer or layers of non-magnetic material(s). Interlayer
stack 5 includes at least one interlayer 5.sub.A of a hcp material,
such as Ru, TiCr, Ru/CoCr.sub.37Pt.sub.6, RuCr/CoCrPt, etc.,
adjacent the magnetically hard perpendicular recording layer 6.
When present, seed layer 5.sub.B adjacent the magnetically soft
underlayer (SUL) 4 may typically include a less than about 100
.ANG. thick layer of an fcc material, such as an alloy of Cu, Ag,
Pt, or Au, or an amorphous or fine-grained material, such as Ta,
TaW, CrTa, Ti, TiN, TiW, or TiCr. The at least one magnetically
hard perpendicular recording layer 6 is typically comprised of an
about 10 to about 25 nm thick layer(s) of Co-based alloy(s)
including one or more elements selected from the group consisting
of Cr, Fe, Ta, Ni, Mo, Pt, W, Cr, Ru, Ti, Si, O, V, Nb, Ge, B, and
Pd.
[0010] Of the conventional media types described above,
longitudinal media are more developed than perpendicular media and
have been utilized for several decades in the computer industry.
During this interval, components and sub-systems, such as
transducer heads, channels, and media, have been repeatedly
optimized in order to operate efficiently within computer
environments. However, it is a common current belief that
longitudinal recording is reaching the end of its lifetime as an
industry standard in computer applications owing to physical limits
which effectively prevent further increases in areal recording
density.
[0011] Perpendicular media, on the other hand, are expected to
replace longitudinal media in computer-related recording
applications and continue the movement toward ever-increasing areal
recording densities far beyond the capability of longitudinal
media. However, perpendicular media and recording technology is
less well developed than all facets of longitudinal media and
recording technology. Specifically, each individual component of
perpendicular magnetic recording technology, including transducer
heads, media, and recording channels, is less completely developed
and optimized than the corresponding component of longitudinal
recording technology. As a consequence, the gains observed with
perpendicular media and systems vis-a-vis the prior art, i.e.,
longitudinal media and systems, are difficult to assess.
[0012] In view of the foregoing, there exists a clear need for
improved perpendicular media and system technology therefor which
are designed to function in optimal fashion and provide a full
range of benefits and performance enhancement vis-a-vis
conventional longitudinal media and systems, consistent with
expectation afforded by adoption of perpendicular media as an
industry standard in computer-related applications.
SUMMARY OF THE INVENTION
[0013] An advantage of the present invention is improved
perpendicular magnetic recording media.
[0014] Another advantage of the present invention is improved
perpendicular magnetic recording media capable of operation with
ring-type magnetic transducer heads.
[0015] Still another advantage of the present invention is improved
perpendicular magnetic recording systems comprising ring-type
magnetic transducer heads.
[0016] Additional advantages and other features of the present
invention will be set forth in the description which follows and in
part will become apparent to those having ordinary skill in the art
upon examination of the following or may be learned from the
practice of the present invention. The advantages of the present
invention may be realized and obtained as particularly pointed out
in the appended claims.
[0017] According to an aspect of the present invention, the
foregoing and other advantages are obtained in part by an improved
perpendicular magnetic recording medium, comprising:
[0018] (a) a non-magnetic substrate having a surface; and
[0019] (b) a stacked plurality of thin film layers forming a layer
stack overlying the substrate surface and including a magnetically
soft underlayer (SUL) beneath at least one perpendicular magnetic
recording layer, the SUL having a saturation magnetization
(M.sub.s)--thickness (t) product (M.sub.st) less than about 4
memu/cm.sup.2.
[0020] According to embodiments of the present invention, the SUL
comprises a material having a saturation magnetization (Ms) of
about 500 to about 2,000 emu/cc and a thickness from about 1 to
about 40 nm; and the SUL and the at least one perpendicular
magnetic recording layer are spaced apart at a spacing determined
by an interlayer stack between the SUL and the at least one
perpendicular magnetic recording layer.
[0021] In accordance with certain preferred embodiments of the
present invention, the SUL and the at least one perpendicular
magnetic recording layer are spaced apart from about 5 to about 200
nm; whereas, according to other preferred embodiments of the
invention, the SUL and the at least one perpendicular magnetic
recording layer are spaced apart from about 30 to about 100 nm.
[0022] Preferably, the interlayer stack includes a spacer layer and
an interlayer; the spacer layer comprises an amorphous material;
the interlayer comprises an hcp material with a preferred c-axis
perpendicular growth orientation; and the interlayer stack further
includes a seed layer.
[0023] According to further preferred embodiments of the present
invention, the SUL has a saturation magnetization
(M.sub.s)-thickness (t) product (M.sub.st) less than about 1
memu/cm.sup.2; the SUL comprises a material having a magnetic
permeability greater than about 10 and a thickness less than about
10 nm; and the SUL comprises at least one soft magnetic material
selected from the group consisting of: Ni, Co, Fe, NiFe
(Permalloy), FeN, FeSiAl, FeSiAlN, CoZr, CoZrCr, CoZrNb, CoFeZrNb,
CoFe, FeCoB, and FeCoC.
[0024] Preferred embodiments of the present invention include those
wherein the at least one perpendicular magnetic recording layer
comprises an hcp Co-based alloy with a preferred c-axis
perpendicular growth orientation; the at least one perpendicular
magnetic recording layer comprises at least partially isolated
magnetic particles or grains with c-axis growth orientation; and/or
the at least one perpendicular magnetic recording layer comprises a
granular layer with uniform grain size, composition, and
crystallographic orientation.
[0025] In accordance with embodiments of the present invention, the
layer stack comprises a protective overcoat layer above the at
least one perpendicular magnetic recording layer and a lubricant
topcoat layer over the protective overcoat layer, the protective
overcoat layer comprising a carbon-based material and the lubricant
topcoat layer comprising a fluoropolymer material; and the
non-magnetic substrate comprises a material selected from the group
consisting of: Al, Al--Mg alloys, other Al-based alloys, NiP-plated
Al or Al-based alloys, glass, ceramics, glass-ceramics, polymeric
materials, and composites or laminates of these materials.
[0026] Another aspect of the present invention is a perpendicular
magnetic recording system, comprising:
[0027] (a) a perpendicular magnetic recording medium including:
[0028] (i) a non-magnetic substrate having a surface; and [0029]
(ii) a stacked plurality of thin film layers forming a layer stack
overlying said substrate surface and including a magnetically soft
underlayer (SUL) beneath and spaced from at least one perpendicular
magnetic recording layer; and
[0030] (b) a ring-type magnetic transducer head positioned in
spaced adjacency to an upper surface of the layer stack to form a
head gap, the transducer head comprising leading and trailing
poles.
[0031] According to embodiments of the present invention, the SUL
has a saturation magnetization (M.sub.s)--thickness (t) product
(M.sub.st) less than about 4 memu/cm.sup.2 and the orientation
ratio of the medium of the system is greater than about 10.
[0032] Additional advantages and aspects of the present disclosure
will become readily apparent to those skilled in the art from the
following detailed description, wherein embodiments of the present
invention are shown and described, simply by way of illustration of
the best mode contemplated for practicing the present invention. As
will be described, the present invention is capable of other and
different embodiments, and its several details are susceptible of
modification in various obvious respects, all without departing
from the spirit of the present invention. Accordingly, the drawings
and description are to be regarded as illustrative in nature, and
not as limitative.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] The following detailed description of the embodiments of the
present invention can best be understood when read in conjunction
with the following drawings, in which the same reference numerals
are employed throughout for designating the same or similar
features, and wherein the various features are not necessarily
drawn to scale but rather are drawn as to best illustrate the
pertinent features, wherein:
[0034] FIG. 1 schematically illustrates, in simplified
cross-sectional view, a portion of a magnetic recording, storage,
and retrieval system 10 according to the conventional art,
comprised of a conventionally structured perpendicular magnetic
recording medium 1 and a single-pole magnetic transducer head
9;
[0035] FIG. 2 schematically illustrates, in simplified
cross-sectional view, a portion of a magnetic recording, storage,
and retrieval system 20 according to an illustrative, but
non-limitative, embodiment of the present invention, comprised of a
perpendicular magnetic recording medium 11 structured for use with
ring-type magnetic transducer head 19;
[0036] FIG. 3 is a graph for illustrating Bit Error Rate as a
function of SUL thickness for improved perpendicular magnetic
recording media fabricated according to the principles of the
present invention, and utilized in a data/information recording,
storage, and retrieval system according to the invention comprising
a ring-type transducer head such as conventionally utilized in
data/information recording, storage, and retrieval systems
comprising longitudinal magnetic recording media; and
[0037] FIG. 4 is a graph for illustrating Overwrite as a function
of SUL thickness for improved perpendicular magnetic recording
media according to the present invention, utilized in a
data/information recording, storage, and retrieval system according
to the invention utilizing a ring-type transducer head such as
conventionally utilized in data/information recording, storage, and
retrieval systems comprising longitudinal magnetic recording
media.
DETAILED DESCRIPTION OF THE INVENTION
[0038] The present invention is based upon recognition that
obtainment of optimized perpendicular magnetic recording media and
systems therefor is facilitated by design and utilization of
perpendicular media which are specifically designed and adapted for
functioning in combination with well-developed and optimized system
components of longitudinal magnetic recording systems. In
particular, the present invention is based upon utilization of
improved perpendicular magnetic recording media designed for use
with the "ring"-type transducer heads associated with longitudinal
magnetic recording media, rather than with the heretofore utilized
"single pole" type transducer heads such as have been described
supra.
[0039] According to the present invention, therefore, perpendicular
media of improved, optimal design operate in concert with ring-type
transducer heads according to a recording paradigm wherein the
magnetic recording process occurs within or proximate the head gap,
i.e., between the trailing edge of the trailing pole and the
leading edge of the leading pole. The invention provides a method
for altering the head field from a ring type transducer head so as
to optimize it for perpendicular recording. In addition, the
present invention enables the perpendicular media to maintain a
desirable microstructure and facilitates obtainment of significant
improvement in recording performance and reliability, compared to
conventional longitudinal and perpendicular magnetic recording
media.
[0040] As indicated supra, conventional thin film perpendicular
magnetic recording media typically comprise a relatively thick,
magnetically soft underlayer (SUL) of high saturation magnetization
(M.sub.s) beneath the perpendicular magnetic recording layer(s)
that serves to maximize the perpendicular component of the head
field for strong writing behind the trailing edge of the relatively
smaller, trailing edge of the main pole of the single-pole
transducer head, and then shunt or spread out and transmit the head
field horizontally toward the relatively larger, auxiliary (or
return) pole that minimally affects the recording process. Such
single-pole transducer heads produce a strong vertical field at the
recording layer in the "head gap" between the main pole and the SUL
of the medium. Recording generally occurs near the trailing edge of
the main pole.
[0041] On the other hand, ring-type transducer heads utilized with
longitudinal media have a high, horizontally oriented magnetic
field in the horizontal gap between each of the two magnetic poles,
and writing of the media is performed in front of the front edge of
the trailing pole, employing the fringing field beneath the poles
that includes large horizontal and vertical components. When
conventional perpendicular media of the prior art are utilized with
a ring-type transducer head, the SUL causes the magnetic flux at
both the leading and trailing poles to become vertical, and fairly
strong, at the trailing edge of the trailing pole and at the
leading edge of the leading pole. However, the shape of the
trailing pole is not optimized for the perpendicular field, and the
leading (front) pole is not sufficiently large as to avoid erasure.
As a consequence, the ability to write conventional perpendicular
media with ring-type transducer heads is very poor, and the
recording performance is correspondingly poor.
[0042] In this regard, perpendicular media can be fabricated
without the SUL and utilized with a ring-type transducer head. In
this instance, the ring-type head attempts to write the media at
the front edge of the trailing pole, but a significant portion of
the field lies in the horizontal direction, and correspondingly,
the write capability and recording performance are much lower than
desired.
[0043] The present invention is based upon recognition that, in
order to optimize writing of perpendicular media by means of a
ring-type transducer head such as is utilized with longitudinal
media, it is better to apply a magnetic field with a greater
perpendicular component, preferably with a very high total field at
an angle approaching 45.degree. away from the horizontal. It is
also desirable to increase the vertical component in order to
increase the size of the recording "write bubble", and thereby
reduce interaction between the high field regions at the leading
and trailing poles of the ring type magnetic transducer head.
According to the invention, the vertical component of the fringing
magnetic field at the leading edge of the trailing pole is
increased, without resorting to a trailing edge vertical field, by
fabricating the perpendicular media with a much thinner SUL than
utilized in conventional perpendicular media, or by positioning the
SUL at a much greater distance from the magnetic recording layer
than in conventional perpendicular media.
[0044] More specifically, conventional perpendicular magnetic
recording media of the prior art generally comprise a SUL with a
magnetization-thickness product (M.sub.st) in the range from about
5 to about 60 memu/cm.sup.2, corresponding to Ms generally in the
range from about 1,000 to about 2,000 emu/cc.sup.2 and thickness
ranging from about 50 to about 300 nm, and the spacing between the
recording layer and the SUL is generally from about 5 to about 30
nm.
[0045] It has been determined, however, that perpendicular media
with a thin SUL having a M.sub.st product less than about 4
memu/cm.sup.2 utilized in combination with ring-type transducer
heads exhibit significantly improved system performance. Improved
system performance, relative to when no SUL is present in the
perpendicular media, is obtained with as little as 1 nm thickness
of a 1,000 emu/cc SUL material positioned at as great a spacing as
about 100 nm from the perpendicular recording layer. As a
consequence, it is evident that improved perpendicular magnetic
recording media can be designed and fabricated according to the
principles of the present invention so as to optimize the write
field tilt angle of a ring-type magnetic transducer head (such as
typically utilized with longitudinal media systems) and thereby
obtain significantly improved recording performance, including
higher areal recording densities than are obtainable from
conventional longitudinal or perpendicular magnetic recording media
and systems of the prior art.
[0046] Referring to FIG. 2, schematically illustrated therein, in
simplified cross-sectional view, is a portion of a magnetic
recording, storage, and retrieval system 20 according to an
illustrative, but non-limitative, embodiment of the present
invention, comprised of a perpendicular magnetic recording medium
11 structured for use with ring-type magnetic transducer head 19.
More specifically, medium 11 according to the present invention
generally resembles the conventional perpendicular medium 1 of FIG.
1, and comprises a series of thin film layers arranged in an
overlying (i.e., stacked) sequence on a non-magnetic substrate 2
comprised of a non-magnetic material selected from the group
consisting of: Al, Al--Mg alloys, other Al-based alloys, NiP-plated
Al or Al-based alloys, glass, ceramics, glass-ceramics, polymeric
materials, and composites or laminates of these materials.
[0047] The thickness of substrate 2 is not critical; however, in
the case of magnetic recording media for use in hard disk
applications, substrate 2 must be of a thickness sufficient to
provide the necessary rigidity. Substrate 10 typically comprises Al
or an Al-based alloy, e.g., an Al--Mg alloy, or glass or
glass-ceramics, and, in the case of Al-based substrates, includes a
plating layer, typically of NiP, on the surface of substrate 2 (not
shown in the figure for illustrative simplicity). An optional
adhesion layer 3, typically a less than about 100 .ANG. thick layer
of an amorphous metallic material or a fine-grained material, such
as a metal or a metal alloy material, e.g., Ti, a Ti-based alloy,
Ta, a Ta-based alloy, Cr, or a Cr-based alloy, may be formed over
the surface of substrate surface 2 or the NiP plating layer
thereon.
[0048] Overlying substrate 2 or optional adhesion layer 3 is a thin
magnetically soft underlayer (SUL) 4' formed according to the
principles of the present invention, wherein the SUL 4' is
sufficiently magnetically strong as to cause the head field near
the leading edge of the trailing pole of a magnetic transducer head
to be more vertical near the head gap, but not magnetically strong
enough as to induce a large vertical field at the trailing edge of
the trailing pole. According to embodiments of the present
invention, a saturation magnetization (M.sub.s)--thickness (t)
product (M.sub.st) of SUL 4' is less than about 4
memu/cm.sup.2.
[0049] In accordance with embodiments of the present invention, the
SUL 4' comprises a layer of a material from about 1 to about 40 nm
thick and having a saturation magnetization (M.sub.s) of about 500
to about 2,000 emu/cc, selected from the group consisting of: Ni,
Co, Fe, an Fe-containing alloy such as NiFe (Permalloy), FeN,
FeSiAl, FeSiAlN, a Co-containing alloy such as CoZr, CoZrCr,
CoZrNb, or a Co--Fe-containing alloy such as CoFeZrNb, CoFe, FeCoB,
and FeCoC; and is vertically spaced apart by about 5 to about 200
nm, illustratively from about 30 to about 100 nm, from the lower
edge of overlying perpendicular magnetic recording layer 6.
[0050] Preferably, SUL 4' has a saturation magnetization
(M.sub.s)-thickness (t) product (M.sub.st) less than about 1
memu/cm.sup.2 and comprises a material having a magnetic
permeability greater than about 10 and a thickness less than about
10 nm.
[0051] As before, an optional adhesion layer 3 may be included in
the layer stack of medium 11 between the surface of substrate
surface 2 and the SUL 4', the adhesion layer 3 being less than
about 200 .ANG. thick and comprised of a metal or a metal alloy
material such as Ti, a Ti-based alloy, Ta, a Ta-based alloy, Cr, or
a Cr-based alloy.
[0052] Still referring to FIG. 2, the layer stack of medium 11
further comprises a non-magnetic interlayer stack 5' between SUL 4'
and at least one overlying perpendicular magnetic recording layer
6, which interlayer stack 5' can be of substantially greater
thickness than that of conventional perpendicular media, e.g., SUL
4 of medium 1 shown in FIG. 1. According to a key feature of the
present invention, the relatively thick interlayer stack 5'
generally provides optimal performance at thicknesses from about 30
nm to about 100 nm, and in many instances, may provide a
performance benefit at thicknesses ranging from about 5 to about
200 nm. Interlayer stack 5', comprised of sequentially stacked
amorphous spacer layer 5.sub.C, optional seed layer 5.sub.B, and
interlayer 5.sub.A, is utilized, inter alia, for
determining/controlling the spacing s between the SUL 4' and the
lower edge of the at least one perpendicular magnetic recording
layer 6 to the above-described ranges, i.e., from about 5 to about
200 nm, including from about 30 to about 100 nm, and for
facilitating a preferred perpendicular growth orientation of the
overlying at least one perpendicular magnetic recording layer 6.
Suitable non-magnetic materials for use as interlayer 5.sub.A
adjacent the magnetically hard perpendicular recording layer 6
include hcp materials, such as Ru, TiCr, Ru/CoCr.sub.37Pt.sub.6,
RuCr/CoCrPt, etc.; suitable materials for use as optional seed
layer 5.sub.B typically include an fcc material, such as an alloy
of Cu, Ag, Pt, or Au, or an amorphous or fine-grained material,
such as Ta, TaW, CrTa, Ti, TiN, TiW, or TiCr; and amorphous spacer
layer 5.sub.C adjacent SUL 4', utilized for increasing the spacing
s between the lower edge of the perpendicular magnetic recording
layer 6 and the SUL 4', is from about 20 to about 100 nm thick, and
typically comprised of an amorphous material such as CrTa, TaW,
TiCr, or TiW. In this regard, the use of interlayer stacks 5' with
thicknesses as great as about 200 nm, as described above, enables
obtainment of performance advantages (e.g., use of ring-type
magnetic transducer heads) with perpendicular media designs
including thicker, higher M.sub.st product SUL's 4'.
[0053] According to embodiments of the present invention, the at
least one magnetically hard perpendicular magnetic recording
layer(s) 6 is (are) typically comprised of (an) about 10 to about
25 nm thick layer(s) of Co-based alloy(s) including one or more
elements selected from the group consisting of Cr, Fe, Ta, Ni, Mo,
Pt, W, Cr, Ru, Ti, Si, O, V, Nb, Ge, B, and Pd. Preferably, the at
least one perpendicular magnetic recording layer 6 comprises a
fine-grained hcp Co-based alloy with a preferred c-axis
perpendicular growth orientation; and the interlayer stack 5'
comprises a fine-grained hcp material with a preferred c-axis
perpendicular growth orientation. In addition, the at least one
perpendicular magnetic recording layer 6 is preferably comprised of
at least partially isolated, uniformly sized and composed, magnetic
particles or grains with c-axis growth orientation.
[0054] Finally, the layer stack of medium 11 includes a protective
overcoat layer 7 above the at least one perpendicular magnetic
recording layer 6 and a lubricant topcoat layer 8 over the
protective overcoat layer 7. Preferably, the protective overcoat
layer 7 comprises a carbon-based material, e.g., diamond-like
carbon ("DLC"), and the lubricant topcoat layer 8 comprises a
fluoropolymer material, e.g., a perfluoropolyether compound.
[0055] According to the invention, each of the layers 3, 4', 5', 6,
7, as well as the optional seed and adhesion layers (not shown in
the figure for illustrative simplicity), may be deposited or
otherwise formed by any suitable technique utilized for formation
of thin film layers, e.g., any suitable physical vapor deposition
("PVD") technique, including but not limited to, sputtering, vacuum
evaporation, ion plating, cathodic arc deposition ("CAD"), etc., or
by any combination of various PVD techniques. The lubricant topcoat
layer 8 may be provided over the upper surface of the protective
overcoat layer 7 in any convenient manner, e.g., as by dipping the
thus-formed medium into a liquid bath containing a solution of the
lubricant compound.
[0056] With continued reference to FIG. 2, as schematically
illustrated therein, magnetic data/information recording, storage,
and retrieval system 20 includes a ring-type magnetic transducer
head 19 positioned in close proximity to the upper surface of
medium 11, i.e., the upper surface of lubricant topcoat layer 8.
Ring-type magnetic transducer head 19 is of conventional design
according to the invention, i.e., similar to ring-type magnetic
transducer heads typically utilized with conventional longitudinal
magnetic recording media, and includes a leading pole 19.sub.L with
leading and trailing edges 19.sub.LL and 19.sub.LT, respectively,
and a trailing pole 19.sub.T with leading and trailing edges
19.sub.TL and 19.sub.TT, respectively. According to the invention,
in order to optimize writing of perpendicular media by means of
ring-type transducer head 19 such as is utilized with longitudinal
media, the magnetic field from transducer head 19 is altered by the
thin SUL 4' of the present invention to provide a greater
perpendicular component, preferably with a very high total field at
an angle approaching 45.degree. away from the horizontal.
Therefore, according to the invention, the SUL is sufficiently
magnetically strong as to cause the head field near the leading
edge 19.sub.TL of the trailing pole 19.sub.T of the ring-type
magnetic transducer head 19 to be more vertical near the head gap
between the lower end of the head poles and the medium surface, but
not magnetically strong enough as to induce a large vertical field
at the trailing edge 19.sub.TT of the trailing pole 19.sub.T. It is
important to note in this regard that application of the magnetic
field from transducer head 19 with a selected perpendicular
component or angle is set and constant, except as altered by the
SUL material.
[0057] It is also desirable, according to the invention, to
increase the vertical component in order to increase the size of
the recording "write bubble", and thereby reduce interaction
between the high field regions at the leading and trailing poles of
the ring type magnetic transducer head. As has been indicated
above, according to the invention, the vertical component of the
flinging magnetic field at the leading edge of the trailing pole is
increased, without causing a trailing edge vertical field
sufficient to overwrite the recorded data pattern, by fabricating
the perpendicular media with a much thinner SUL than utilized in
conventional perpendicular media, or by positioning the SUL at a
much greater distance from the magnetic recording layer than in
conventional perpendicular media.
[0058] Preferred embodiments of the invention include those wherein
the perpendicular media used in conjunction with a ring-type
magnetic transducer head have an orientation ratio greater than
about 10, wherein the latter term is a figure of merit commonly
utilized for describing longitudinal media for longitudinal
magnetic recording systems with ring-type transducer heads, and is
defined as the ratio of coercivity (or remanent magnetization) of
the medium measured parallel vs. measured perpendicularly to the
magnetization direction of the recorded data bits, i.e.,
H.sub.c.parallel./H.sub.c.perp. or
M.sub.rt.sub..parallel./M.sub.rt.perp.. In the instant case for
perpendicular media, the parallel direction is vertical (or normal)
to the plane of the medium and the perpendicular direction is in
the direction of the plane of the medium (i.e., parallel
thereto).
[0059] The efficacy of the present invention will now be described
with reference to FIGS. 3 and 4, wherein: FIG. 3 is a graph for
illustrating Bit Error Rate as a function of SUL thickness for
perpendicular magnetic recording media in a system according to the
invention utilizing a ring-type transducer head conventionally
utilized in systems comprising longitudinal magnetic recording
media; and FIG. 4 is a graph for illustrating Overwrite as a
function of SUL thickness for perpendicular magnetic recording
media in a system according to the invention utilizing a ring-type
transducer head conventionally utilized in systems comprising
longitudinal magnetic recording media.
[0060] In the following, media recording was performed using a
conventional ring-type recording head and channel of a longitudinal
type magnetic recording system. Performance of a prior art
perpendicular medium with no SUL is represented by the "0 nm" point
on the x-axis of each of FIGS. 3 and 4; performance of a prior art
perpendicular medium with a conventional thick SUL is represented
by the "160 nm" point on the x-axis of each of FIGS. 3 and 4;
performance of a prior art longitudinal medium is represented by
the "ref" point on the x-axis of each of FIGS. 3 and 4; and each of
the perpendicular media shown in FIGS. 3 and 4 had identical
microstructure independent of variation in SUL thickness.
[0061] Adverting to FIG. 3, an advantage demonstrated therein by
thin SUL media according to the present invention is an improved
ability to write data bits with significantly reduced error rates.
In particular, the 4 nm data point evidences a new design space,
and FIG. 3 as a whole demonstrates a dramatic improvement in
magnetic recording performance of perpendicular media with
ring-type transducer heads such as are employed in longitudinal
magnetic recording systems, which dramatic improvement is obtained
according to the invention by appropriately adjusting the head
field with a very thin soft magnetic underlayer (SUL) or by
increasing the spacing s between the perpendicular magnetic
recording layer(s) and the SUL.
[0062] Referring now to FIG. 4, an advantage of thin SUL
perpendicular magnetic recording media illustrated therein is an
improved ability to write data bits to the media. An approximate
measure of the ability to write data bits to magnetic media is
reverse overwrite for perpendicular media and standard overwrite
for longitudinal media. As indicated in the graph of FIG. 4, the
media with thinnest SUL's appear to have improved bit writing
capability compared to media with thicker SUL's, and comparable
write capability to longitudinal media.
[0063] Additional advantages of thin SUL perpendicular magnetic
recording media according to the present invention include:
[0064] 1. lower defect counts and higher production yields owing to
reduction in the amount of deposited material, specifically less
SUL material;
[0065] 2. improved performance with fewer changes to prior art
magnetic recording systems than previously required with
perpendicular media; and
[0066] 3. ability to use higher M.sub.rt products than longitudinal
media without incurring a performance penalty, thereby enabling
higher read-back amplitudes than with longitudinal media. Such
higher read-back amplitudes also enable obtainment of reduced
electronic component of recording noise.
[0067] Thus, the present invention advantageously provides improved
performance, high areal density, magnetic alloy-based perpendicular
magnetic media and data/information recording, storage, and
retrieval systems, which media include an improved, very thin soft
magnetic underlayers (SUL's) which afford improved performance
characteristics when utilized in combination with ring-type
magnetic transducer heads such as are typically employed with
longitudinal media. The media of the present invention enjoy
particular utility in high recording density systems for
computer-related applications. In addition, the inventive media can
be fabricated by means of conventional media manufacturing
technologies, e.g., sputtering.
[0068] In the previous description, numerous specific details are
set forth, such as specific materials, structures, processes, etc.,
in order to provide a better understanding of the present
invention. However, the present invention can be practiced without
resorting to the details specifically set forth. In other
instances, well-known processing materials and techniques have not
been described in detail in order not to unnecessarily obscure the
present invention.
[0069] Only the preferred embodiments of the present invention and
but a few examples of its versatility are shown and described in
the present disclosure. It is to be understood that the present
invention is capable of use in various other combinations and
environments and is susceptible of changes and/or modifications
within the scope of the inventive concept as expressed herein.
* * * * *