U.S. patent application number 09/755730 was filed with the patent office on 2004-12-02 for gapless longitudinal magnetic recording head with flux cavity.
Invention is credited to Johns, Earl Chrzaszcz, Khizroev, Sakhrat, Litvinov, Dmitri.
Application Number | 20040240107 09/755730 |
Document ID | / |
Family ID | 33479806 |
Filed Date | 2004-12-02 |
United States Patent
Application |
20040240107 |
Kind Code |
A9 |
Khizroev, Sakhrat ; et
al. |
December 2, 2004 |
Gapless longitudinal magnetic recording head with flux cavity
Abstract
A longitudinal recording head for use with magnetic recording
media includes a gapless yoke with a cavity that expels magnetic
flux onto a small area of the magnetic recording medium.
Longitudinal recording heads incorporating the gapless yoke and
flux cavity are capable of improved recording densities.
Inventors: |
Khizroev, Sakhrat;
(Pittsburgh, PA) ; Litvinov, Dmitri; (Pittsburgh,
PA) ; Johns, Earl Chrzaszcz; (Sewickley, PA) |
Correspondence
Address: |
Alan G Towner
Pietragallo Bosick & Gordon
One Oxford Centre 38th Floor
301 Grant Street
Pittsburgh
PA
15219
US
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 0024341 A1 |
September 27, 2001 |
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Family ID: |
33479806 |
Appl. No.: |
09/755730 |
Filed: |
January 5, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09755730 |
Jan 5, 2001 |
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PCT/US00/27356 |
Oct 4, 2000 |
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60174524 |
Jan 5, 2000 |
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60175793 |
Jan 12, 2000 |
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60157883 |
Oct 5, 1999 |
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Current U.S.
Class: |
360/119.05 ;
G9B/5.04; G9B/5.051; G9B/5.052; G9B/5.082 |
Current CPC
Class: |
G11B 5/127 20130101;
G11B 5/23 20130101; G11B 5/232 20130101; G11B 5/1871 20130101; G11B
5/3116 20130101; G11B 5/187 20130101 |
Class at
Publication: |
360/125 |
International
Class: |
G11B 005/127 |
Claims
We claim:
1. A longitudinal recording head for use with a magnetic recording
medium, the longitudinal recording head comprising: a gapless
magnetic recording yoke; and means for expelling magnetic flux from
the yoke to produce a localized magnetic field in the magnetic
storage medium.
2. The longitudinal recording head according to claim 1, wherein
the means for expelling magnetic flux comprises a flux cavity in
the yoke.
3. The longitudinal recording head according to claim 2, wherein
the flux cavity is curved.
4. The longitudinal recording head according to claim 2, wherein
the flux cavity comprises a substantially ellipsoidal or
hemispherical shape.
5. The longitudinal recording head according to claim 4, wherein
the flux cavity comprises at least one inwardly curved wall.
6. The longitudinal recording head according to claim 2, wherein
the flux cavity has a length of from about 50 to about 300 nm, a
width of from about 50 to about 300 nm, and a depth of from about
50 to about 500 nm.
7. A longitudinal recording head for use with a magnetic recording
medium, the longitudinal recording head comprising: a gapless
magnetic recording yoke; and a flux cavity in the yoke.
8. The longitudinal recording head according to claim 7, wherein
the flux cavity is curved.
9. The longitudinal recording head according to claim 7, wherein
the flux cavity comprises a substantially ellipsoidal or
hemispherical shape.
10. The longitudinal recording head according to claim 9, wherein
the flux cavity comprises at least one inwardly curved wall.
11. The longitudinal recording head according to claim 7, wherein
the flux cavity has a length of from about 50 to about 300 nm, a
width of from about 50 to about 300 nm, and a depth of from about
50 to about 500 nm.
12. A method of making a flux cavity in a magnetic recording yoke
of a longitudinal recording head for use with a magnetic recording
medium, the method comprising the steps of: providing a gapless
magnetic recording yoke; and creating a flux cavity in the
yoke.
13. The method according to claim 12, wherein the step of creating
a flux cavity is accomplished by removing material from the
yoke.
14. The method according to claim 12, wherein the step of creating
a flux cavity is accomplished using focused ion beam direct
etching.
15. The method according to claim 12, wherein the flux cavity is
curved.
16. The method according to claim 15, wherein the flux cavity
comprises a substantially ellipsoidal or hemispherical shape.
17. The method according to claim 16, wherein the flux cavity
comprises at least one inwardly curved wall.
18. The method according to claim 12, wherein the flux cavity has a
length of from about 50 to about 300 nm, a width of from about 50
to about 300 nm, and a depth of from about 50 to about 500 nm.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 60/174,524 filed Jan. 5, 2000, and also
claims the benefit of U.S. Provisional Patent Application Ser. No.
60/175,793 filed Jan. 12, 2000.
FIELD OF THE INVENTION
[0002] This invention relates to magnetic recording heads, and more
particularly, relates to gapless longitudinal recording heads for
recording at high densities.
BACKGROUND INFORMATION
[0003] Magnetic hard disk drives incorporating longitudinal
recording heads are well known. However, conventional longitudinal
recording heads suffer from the disadvantage that at high recording
densities, e.g., exceeding 40 Gbit/in.sup.2, the track width is
relatively large. In particular, a track width cannot be defined
which is smaller than the head track width plus two times the gap
length of the head in conventional designs. This limitation results
from side fringing magnetic fields which spread at a distance on
the order of the gap length from the both track sides across the
track. Decreasing the gap length should reduce this characteristic
side fringing region. However, as the gap length is decreased, the
magnetic fields in the region of recording media along the track
are also reduced. For example, at a 50 nm gap length, the maximum
in-plane field component at a 10 nm flying height is less than
10,000 Oe, assuming a high moment (4 Ms.about.20 kG) pole tip
material is used. This field is not sufficient to record
transitions clear enough for such high densities. At such high
densities recording media are expected to have dynamic coercivity
above 5,000 Oe, and approximately two times the coercivity is
required to record sufficiently defined transitions. Therefore,
there is a trade-off in decreasing the gap length.
[0004] U.S. Pat. No. 5,621,595 to Cohen discloses a magnetic
recording head with a pinched gap which is said to reduce side
fringing magnetic fields in the gap region. While the disclosed
pinched gap design may reduce side fringing fields, the fields in
the track region are also reduced significantly, resulting in the
inability to record on high coercivity media. Furthermore, the
pinched gap design is extremely sensitive to write currents.
[0005] The present invention has been developed in view of the
foregoing, and to address other deficiencies of the prior art.
SUMMARY OF THE INVENTION
[0006] The present invention provides a longitudinal magnetic
recording head with a gapless yoke having a flux cavity. The cavity
acts to expel magnetic flux from the yoke in a manner which
concentrates the magnetic flux in the region below the cavity.
Strong localized magnetic fields are thereby generated in the
magnetic recording region under the flux cavity. The use of the
present gapless yoke and flux cavity significantly increases the
data storage densities while avoiding the necessity of making
substantial modifications to conventional longitudinal recording
head designs.
[0007] An aspect of the present invention is to provide a
longitudinal recording head for use with a magnetic recording
medium. The longitudinal recording head includes a gapless magnetic
recording yoke and a flux cavity in the yoke.
[0008] Another aspect of the present invention is to provide a
method of making a flux cavity in a yoke of a longitudinal
recording head for use with a magnetic recording medium. The method
includes the steps of providing a magnetic recording yoke, and
creating a flux cavity in the yoke.
[0009] These and other aspects of the present invention will be
more apparent from the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a top view of a typical computer hard disk drive
for which the present invention may be used, illustrating the disk
drive with its upper housing portion removed.
[0011] FIGS. 2a and 2b are partially schematic side and bottom
views, respectively, of poles of a conventional longitudinal
recording head having a uniform gap.
[0012] FIGS. 3a and 3b are partially schematic side and bottom
views, respectively, of a gapless longitudinal recording yoke
having an ellipsoidal flux cavity in accordance with an embodiment
of the present invention.
[0013] FIGS. 4a and 4b are partially schematic side and bottom
views, respectively, of a gapless longitudinal recording yoke
having a partially ellipsoidal flux cavity having inwardly curved
sidewalls in accordance with another embodiment of the present
invention.
[0014] FIG. 5 is a graph of magnetic field strength across the
track width for a longitudinal recording head having a gapless yoke
and flux cavity in accordance with an embodiment of the present
invention.
[0015] FIG. 6 is a partially schematic side sectional view of a
focused ion beam direct etching apparatus which may be used to
produce a cavity in the yoke of a gapless longitudinal recording
head in accordance with an embodiment of the present invention.
[0016] FIG. 7 is a photomicrograph of a longitudinal recording head
including a gapless yoke with a flux cavity in accordance with an
embodiment of the present invention.
[0017] FIG. 8 is a roll-off curve for a magnetic track written by
the recording head shown in FIG. 7 and read back by a conventional
narrow GMR reader.
[0018] FIG. 9 is a recording track profile for a narrow track
written by the recording head shown in FIG. 7 and read back by a
conventional narrow GMR reader.
[0019] FIG. 10 is a saturation current curve, illustrating the
dependence of readback signal on the amount of write current used
during writing by the recording head shown in FIG. 7 and read back
by a conventional narrow GMR reader.
DETAILED DESCRIPTION
[0020] The invention is described in relation to presently known
longitudinal recording heads used with a hard disk drive 10 for
computers, one of which is illustrated in FIG. 1. As used herein,
"recording head" means a head adapted for read and/or write
operations. The hard disk drive 10 includes a housing 12 (with the
upper portion removed and the lower portion visible in this view
for maximum clarity) dimensioned and configured to contain and
locate the various components of the disk drive 10. The disk drive
10 includes a spindle motor 14 for rotating at least one magnetic
storage medium 16 within the housing, in this case a magnetic disk.
At least one arm 18 is contained within the housing 12, with each
arm 18 having a first end 20 with a longitudinal recording head 22,
and a second end 24 pivotally mounted to a bearing 26. An actuator
motor 28, such as a movable coil DC motor, is located at the arm's
second end 24, pivoting the arm 18 to position the head 22 over a
desired sector of the disk 16. The actuator motor 28 is regulated
by a controller which is not shown, and which is well known.
[0021] Writing is accomplished by rotating the disk 16 relative to
recording head 22 so that the recording head 22 is located above
the appropriate sectors of tracks on the disk 16. Reading from the
disk 16 may be accomplished either using the same head 22, or with
a separate read head adjacent to the write head 22. If the
individual magnetic fields are too close to each other within the
magnetic layer of the disk 16, writing to the magnetic storage
medium will affect not only the desired location on the disk, but
also neighboring locations. Therefore, maximizing flux density
within a desired section of a track while minimizing flux density
within neighboring sections, permits the tracks to be smaller,
thereby permitting a greater number of tracks within a disk, and
allowing the disk to store additional information. Additionally,
concentrating the flux density within only the track directly below
the recording head 22 will permit the same flux density within the
track to be achieved by a lower power level. Alternatively,
concentrating the magnetic flux will increase flux density at the
same power level, thereby permitting a track to be magnetically
harder (have a higher coercivity) at the same power level.
[0022] In accordance with the present invention, a longitudinal
recording head may be modified by eliminating the gap between the
leading and trailing poles of the writer, and by providing a flux
cavity in the gapless yoke. By varying the flux cavity geometry in
the vertical direction of the yoke (perpendicular to the bottom or
air bearing surface) as well as the horizontal direction, the flux
pattern can be optimized. It should be noted that in conventional
designs, the gap geometry in the vertical direction remains
constant from the level of the bottom or air bearing surface to the
level of the throat height, as illustrated by the poles of a
conventional longitudinal head 36 of FIGS. 2a and 2b. As shown in
FIGS. 2a and 2b, the first and second poles 37 and 38 define a
uniform gap 39.
[0023] In accordance with an embodiment of the present invention,
the magnetic field is controlled by providing a gapless yoke design
and controlling the flux cavity shape in the vertical direction,
e.g., through the use of a generally ellipsoidal geometry, as shown
in FIGS. 3a and 3b. The recording yoke 56 includes first and second
portions 57 and 58 made of any suitable magnetically soft material
with an ellipsoidal flux cavity 59 therein. The ellipsoidal flux
cavity 59 defines a minimum yoke distance M which corresponds to
the location of maximum flux concentration below the cavity 59.
[0024] FIGS. 4a and 4b illustrate a recording yoke 60 in accordance
with another embodiment of the present invention. The yoke 60
includes first and second portions 61 and 62 made of magnetically
soft material with a contoured flux cavity 64 therein. The flux
cavity 64 has an elliptical shape at the lower air bearing surface
of the yoke 60, with inwardly curved sidewalls which form a narrow
hollow tip defining a minimum yoke distance M. The minimum yoke
distance M corresponds to the location of maximum flux
concentration below the flux cavity 64. The inwardly curved shape
of the flux cavity shown in FIGS. 4a and 4b compensates for spacing
losses. Another advantage of the inwardly curved walls in the
generally ellipsoidal flux cavity as shown in FIGS. 4a and 4b is to
increase the magnetic surface charge.
[0025] Because the recording yoke has no gap, the present yoke
structure can be saturated at a smaller coil current than an
equivalent conventional ring yoke with a gap. The smallest
cross-sectional area of the yoke M saturates at a smaller current
value than the rest of the yoke. A yoke geometry can be chosen such
that the narrowest yoke cross-section M is located above the
position of the flux cavity. As the current value is increased
above the saturation point, the yoke region around the cavity
starts to saturate. Before total saturation occurs this region is
relatively soft and the magnetic field outside the yoke is
perpendicular to the surface of the relatively soft pole material.
As this region saturates, the magnetic charge density at the flux
cavity surface reaches its maximum. The concave shape of the flux
cavity effectively focuses the along-the-track field component in
the media region. By adjusting the shape of the cavity, the fields
can be concentrated in a small region of a recording medium.
[0026] The magnetic fields are determined by the surface charge
density in the flux cavity of the yoke. The larger the surface
charge is, the larger the field is. In turn, the surface charge is
proportional to the value of the discontinuity of the magnetization
component normal to the surface. Hence, geometries such as that
shown in FIGS. 4a and 4b will promote a larger magnetic charge at
the flux cavity because the cavity surface on average is more
normal to the flux propagation direction, thus increasing the
magnetic charge.
[0027] Although generally hemispherical or elliptical flux cavity
geometries are primarily described herein, several other cavity
geometries may be used in gapless longitudinal recording heads to
improve their performance over conventional longitudinal recording
heads. Alternative embodiments include cavities having curved or
faceted walls of various shapes. For example, the flux cavity may
comprise a cylindrical hole having an axis perpendicular to the air
bearing surface. Alternatively, the axis of the cylindrical hole
may be parallel with the across-the-track direction of the head.
The cross-sectional shapes of such cylindrical holes may be
circular, ovular, elliptical, triangular, square, rectangular,
hexagonal, octagonal, etc. The various flux cavity geometries may
be symmetrical or asymmetrical, e.g., one side of the cavity may be
semi-circular and the other side may be flat or may have a
different shape. The flux cavities may be filled with air, or may
comprise other non-magnetic materials. Cavities having contoured
sides adapted to concentrate at least a portion of the magnetic
flux will be advantageous as compared to conventional uniform gap
longitudinal recording heads. This description and accompanying
figures therefore provide only representative examples of the many
possible cavity geometries, not an inclusive list of all that will
work.
[0028] A modeled along-the-track field component versus the
distance across the track for a gapless yoke of the present
invention is shown in FIG. 5. The maximum field in a localized
region of 60 nm.times.60 nm at a 10 nm flying height is
approximately 13,400 Oe, corresponding to a storage density of more
than 200 Gbit/in.sup.2.
[0029] Preferred methods of manufacturing the flux cavities of the
present invention include focused ion beam direct etching, electron
lithography and optical lithography, as well as mechanical
processes such as dimpling the yoke with a stylus made of silicon,
silicon nitride, tungsten or the like. An example of a focused ion
beam direct etching apparatus 72 is illustrated in FIG. 6.
Positively charged ions of liquid metals, for example gallium, are
focused onto the bottom surface of the first and second portions 67
and 68 of the yoke to etch the cavity 69. During the process, ions
are generated by an ion source 74, passing through a suppressor 76.
The ions then proceed through an extractor and spray aperture 78,
which begins the focusing process. Next, the ions pass through at
least one lens 80, thereby continuing to focus the ions. A
stigmator 82 is placed after the first group of lenses 80. The ions
then pass through any one of a plurality of limiting apertures 84,
which may be selected to further narrow the ion beam. After exiting
the aperture 84, the ions pass through a blanking deflector 86,
blanking aperture 88 and deflection assembly 90. Lastly, the ions
pass through at least one additional lens 80 before striking the
bottom surface of the first and second portions 67 and 68 of the
yoke to etch the cavity 69.
[0030] FIG. 7 is a photomicrograph of the bottom or air bearing
surface of a gapless longitudinal recording head, showing a flux
cavity (depicted by the arrow G) between first and second portions
P1 and P2 of the gapless recording yoke. The yoke portions P1 and
P2 were made by conventional deposition techniques. The flux cavity
G was made using focused ion beam direct etching as described
above. The flux cavity is generally ellipsoidal in shape with a
length of 180 nm measured in the along-the-track horizontal
direction in FIG. 7, a width of 200 nm measured in the
across-the-track horizontal direction in FIG. 7, and a depth of 250
nm measured in a vertical direction perpendicular to the air
bearing surface. When ellipsoidal or other flux cavities are used
in accordance with the present invention, they typically have
lengths of from about 50 to about 300 nm, widths of from about 50
to about 300 nm, and depths of from about 50 to about 500 nm.
[0031] FIG. 8 is a graph of playback versus linear density,
illustrating a favorable roll-off curve for a magnetic track
written by the recording head shown in FIG. 7 using a write current
of 50 mA. A conventional narrow GMR reader was used.
[0032] FIG. 9 is a graph of playback versus distance across the
track, which provides a recording track profile for a narrow track
written by the recording head shown in FIG. 7. The write current
was 50 mA and the track speed was 32 m/s. A conventional narrow GMR
reader was used.
[0033] FIG. 10 is a saturation current curve, illustrating the
dependence of readback signal on the amount of write current used
during writing by the recording head shown in FIG. 7 and read back
by a conventional narrow GMR reader.
[0034] The use of a gapless yoke with a flux cavity provides
several advantages. The present invention extends the high density
potential of conventional longitudinal write head designs by
forming a flux cavity in the gapless recording yoke, unlike the
two-dimensional gap slits in conventional designs. The contoured
cavity allows for more flexible control of the magnetic field
generated by the recording head. The flux cavity geometry allows
the magnetic flux to concentrate in the cavity region, thus causing
relatively strong and localized fields in the disk region under the
cavity. This solves the problem of conventional ring heads in which
the track width is limited by the gap length. Consequently,
longitudinal recording heads incorporating the present flux cavity
designs can be used at densities well beyond 100 Gbit/in.sup.2,
while the maximum density achievable with conventional ring heads
is approximately 30 Gbit/in.sup.2. Another advantage of the present
invention is that the longitudinal recording head is relatively
easy to fabricate and does not require the introduction of new
electronics. An additional benefit is that the absence of a write
gap significantly increases the efficiency of the recording head
because the currents necessary to saturate the yoke structure are
substantially less than in a conventional head. Furthermore,
processing steps required to define an ultra-thin write gap are
eliminated, thereby simplifying the manufacturing process.
[0035] Whereas particular embodiments of this invention have been
described above for purposes of illustration, it will be evident to
those skilled in the art that numerous variations of the details of
the present invention may be made without departing from the
invention as defined in the appended claims.
* * * * *