U.S. patent application number 13/830810 was filed with the patent office on 2014-09-18 for microwave-assisted magnetic recording (mamr) head with highly resistive magnetic material.
This patent application is currently assigned to HGST NETHERLANDS B.V.. The applicant listed for this patent is HGST NETHERLANDS B.V.. Invention is credited to Tomoya Horide, Tomohiro Okada.
Application Number | 20140268404 13/830810 |
Document ID | / |
Family ID | 51526070 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140268404 |
Kind Code |
A1 |
Horide; Tomoya ; et
al. |
September 18, 2014 |
MICROWAVE-ASSISTED MAGNETIC RECORDING (MAMR) HEAD WITH HIGHLY
RESISTIVE MAGNETIC MATERIAL
Abstract
In one embodiment, a high-frequency magnetic field-assisted
magnetic recording (MAMR) head includes: a yoke adapted for
facilitating magnetic flux through the MAMR head; a main pole
magnetically coupled to the yoke and adapted for producing a
writing magnetic field; a return pole spaced from the main pole; a
spin torque oscillator (STO) positioned above the main pole; and a
back gap layer positioned between the yoke and the return pole,
where at least one of the yoke, the main pole, the return pole, and
the back gap layer comprises a highly resistive magnetic
material.
Inventors: |
Horide; Tomoya;
(Odawara-shi, JP) ; Okada; Tomohiro; (Odawara-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HGST NETHERLANDS B.V. |
Amsterdam |
|
NL |
|
|
Assignee: |
HGST NETHERLANDS B.V.
Amsterdam
NL
|
Family ID: |
51526070 |
Appl. No.: |
13/830810 |
Filed: |
March 14, 2013 |
Current U.S.
Class: |
360/75 ;
360/111 |
Current CPC
Class: |
G11B 2005/0024 20130101;
G11B 5/235 20130101; G11B 5/3146 20130101 |
Class at
Publication: |
360/75 ;
360/111 |
International
Class: |
G11B 5/235 20060101
G11B005/235 |
Claims
1. A high-frequency magnetic field-assisted magnetic recording
(MAMR) head, comprising: a yoke adapted for facilitating magnetic
flux through the MAMR head; a main pole magnetically coupled to the
yoke and adapted for producing a writing magnetic field; a return
pole spaced from the main pole; a spin torque oscillator (STO)
positioned above the main pole; and a back gap layer positioned
between the yoke and the return pole, wherein at least one of the
yoke, the main pole, the return pole, and the back gap layer
comprises a highly resistive magnetic material.
2. The head as recited in claim 1, wherein the highly resistive
magnetic material comprises a material selected from the group
consisting of: XFe.sub.2O.sub.4, RFe.sub.5O.sub.12, Fe, Co, Ni,
FeCoNi, iron oxides, nickel oxides, cobalt oxides and manganese
oxides; wherein X is an element selected from the group consisting
of: Mn, Co, Ni, Zn, Cu, Fe, and wherein R is a rare earth
element.
3. The head as recited in claim 1, wherein the highly resistive
material is characterized by a resistivity of not less than about
1.times.10.sup.-3 .OMEGA.m.
4. The head as recited in claim 1, wherein the highly resistive
material is characterized by a resistivity of about
1.times.10.sup.4 .OMEGA.m.
5. The head as recited in claim 4, wherein the highly resistive
material is further characterized by a saturation magnetic flux
density of not less than about 0.1 T.
6. The head as recited in claim 5 wherein the highly resistive
material is further characterized by a thickness not less than
about 10 nm.
7. The head as recited in claim 1, wherein the back gap layer
consists of the highly resistive material.
8. The head as recited in claim 1, wherein the yoke comprises the
highly resistive material.
9. The head as recited in claim 1, wherein the return pole
comprises the highly resistive material.
10. The head as recited in claim 1, further comprising a shield
positioned between the STO and the return pole, the shield
comprising the highly resistive material.
11. The head as recited in claim 1, further comprising a shield
positioned between the STO and the return pole, wherein two or more
of the yoke, the return pole, the main pole and the shield comprise
the highly resistive material.
12. The head as recited in claim 1, wherein the highly resistive
material is either XFe.sub.2O.sub.4 or RFe.sub.5O.sub.12, wherein X
is an element selected from the group consisting of: Mn, Co, Ni,
Zn, Cu, Fe, and wherein R is a rare earth element.
13. The head as recited in claim 1, wherein the highly resistive
material is a granular magnetic material selected from the group
consisting of: Fe, Co, Ni, FeCoNi, iron oxides, nickel oxides,
cobalt oxides and manganese oxides.
14. The head as recited in claim 1, wherein during operation of the
head, a current flowing through the back gap material flows along a
first current path characterized by a resistance in the range from
about 1.times.10.sup.8.OMEGA. to about 1.times.10.sup.9.OMEGA..
15. The head as recited in claim 1, wherein during operation of the
head, a current flowing through the STO along a second current path
is delivered to the STO with about 100% efficiency.
16. A magnetic data storage system, comprising: at least one head
as recited in claim 1; a magnetic medium; a drive mechanism for
passing the magnetic medium over the at least one head; and a
controller electrically coupled to the at least one head for
controlling operation of the at least one head.
17. A method for forming the head as recited in claim 1,
comprising: forming the yoke; forming the main pole above the yoke;
forming the STO above the main pole; forming the return pole above
the STO; and forming the back gap layer between the yoke and the
return pole.
18. A high-frequency magnetic field-assisted magnetic recording
(MAMR) head, comprising: a reproducing portion comprising: a first
sensor shield; a second sensor shield; and a sensor between the
first sensor shield and the second sensor shield; and a recording
portion positioned adjacent the reproducing portion, the recording
portion comprising: a yoke adapted for facilitating magnetic flux
through the MAMR head; a main pole positioned above the yoke and
adapted for producing a writing magnetic field; a spin torque
oscillator (STO) positioned above the main pole; an STO shield
positioned above the STO; a return pole positioned above the STO
shield; and a back gap layer positioned between the yoke and the
return pole, the back gap layer comprising at least one highly
resistive material selected from the group consisting of:
XFe.sub.2O.sub.4, RFe.sub.5O.sub.12, Fe, Co, Ni, FeCoNi, iron
oxides, nickel oxides, cobalt oxides and manganese oxides, wherein
X is an element selected from the group consisting of Mn, Co, Ni,
Zn, Cu, Fe, and wherein R is a rare earth element, wherein at least
two of the yoke, the return pole, the main pole and the STO shield
comprise at least one highly resistive material, wherein the highly
resistive material is characterized by a resistivity in a range
from about 1 .OMEGA.m to about 1.times.10.sup.4 .OMEGA.m, a
saturation magnetic flux density of not less than about 0.1 T, and
a thickness not less than about 10 nm, wherein during operation of
the head, a current flowing through the back gap material flows
along a first current path characterized by a resistivity in not
less than 1.times.10.sup.-3.OMEGA.m, and wherein during operation
of the head, a current flowing through the STO along a second
current path is delivered to the STO with about 100%
efficiency.
19. A magnetic data storage system, comprising: at least one head
as recited in claim 18; a magnetic medium; a drive mechanism for
passing the magnetic medium over the at least one head; and a
controller electrically coupled to the at least one head for
controlling operation of the at least one head.
20. A method for forming the head as recited in claim 18,
comprising: forming the yoke; forming the main pole above the yoke;
forming the STO above the main pole; forming the return pole above
the STO; and forming the back gap layer between the yoke and the
return pole.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to data storage systems, and
more particularly, this invention relates to microwave-assisted
magnetic recording heads, and methods of production and use
thereof.
BACKGROUND
[0002] The heart of a computer is a magnetic hard disk drive (HDD)
which typically includes a rotating magnetic disk, a slider that
has read and write heads, a suspension arm above the rotating disk
and an actuator arm that swings the suspension arm to place the
read and/or write heads over selected circular tracks on the
rotating disk. The suspension arm biases the slider into contact
with the surface of the disk when the disk is not rotating but,
when the disk rotates, air is swirled by the rotating disk adjacent
an air bearing surface (ABS) of the slider causing the slider to
ride on an air bearing a slight distance from the surface of the
rotating disk. When the slider rides on the air bearing the write
and read heads are employed for writing magnetic impressions to and
reading magnetic signal fields from the rotating disk. The read and
write heads are connected to processing circuitry that operates
according to a computer program to implement the writing and
reading functions.
[0003] The volume of information processing in the information age
is increasing rapidly. In particular, HDDs have been desired to
store more information in its limited area and volume. A technical
approach to this desire is to increase the capacity by increasing
the recording density of the HDD. To achieve higher recording
density, further miniaturization of recording bits is effective,
which in turn typically requires the design of smaller and smaller
components.
[0004] The further miniaturization and improvements to performance
of the various components, however, presents its own set of
challenges and obstacles.
[0005] In one approach, energy-assisted magnetic recording may be
employed to produce a high magnetic recording density. In
conventional microwave-assisted magnetic recording products and
applications, the typical magnetic recording is based on
superposing an assist magnetic field and a write magnetic field. In
order to adequately improve the performance of MAMR products, each
of the assist magnetic field characteristics and the write magnetic
field characteristics may be enhanced.
[0006] In order for a large current to flow efficiently to a spin
torque oscillator (STO) of a MAMR head, the back gap-side current
path must be electrically insulated. With this in mind, alumina
(Al.sub.2O.sub.3) is typically employed as the back gap material.
However, because alumina is a non-magnetic material, the magnetic
circuit of the recording head is magnetically separated in the
vicinity of the back gap. This produces a marked increase in the
magnetic circuit resistance in the back gap that precludes the
write magnetic field from being efficiently generated from the main
pole. Accordingly, conventional MAMR structures exhibit undesirably
low responsivity of the write magnetic field to the recording
current.
[0007] In other conventional perpendicular magnetic recording head
structures, an FeCoNi alloy may be employed for the back gap. Table
1 shows a comparison of the electrical and magnetic characteristics
when alumina is employed for the back gap and when a permalloy is
employed for the back gap.
TABLE-US-00001 TABLE 1 Electric resistance of current path and
response properties for conventional MAMR heads employing permalloy
(FeCoNi) and Al.sub.2O.sub.3 back gap materials. Permalloy Back gap
material (FeCoNi) Al.sub.2O.sub.3 Resistance (.OMEGA.) 5 .times.
10.sup.-4 5 .times. 10.sup.17 .DELTA.Heff/.DELTA.I (Oe/A) 2.4
.times. 10.sup.5 1.9 .times. 10.sup.5
[0008] These data refer to a conventional permalloy FeCoNi alloy
defined by the composition Fe.sub.80Ni.sub.20. The electrical
resistance when this permalloy is employed for the back gap is
5.times.10.sup.-4.OMEGA., and the responsivity thereof is
2.4.times.10.sup.5 Oe/A. The STO side resistance is 0.6.OMEGA..
Accordingly, because almost all the current flows along the current
path on the back gap side, the STO does not oscillate and, no
assist magnetic field is generated. Notably, because an equivalent
resistivity and a saturation magnetic flux density of not less than
0.1 T is produced when FeCoNi alloys having a composition other
than Fe.sub.80Ni.sub.20 are employed, this same conclusion may be
drawn for permalloy-containing MAMR head structures, regardless of
the specific composition.
[0009] As a result, there is little to no microwave-assisted effect
produced during magnetic recording in typical structures employing
permalloy as the back gap material.
[0010] On the other hand, in conventional MAMR head structures
where alumina is employed for the back gap material, an electrical
resistance of 5.times.10.sup.17.OMEGA. and a responsivity of
1.9.times.10.sup.5 Oe/A are produced. As a result of a marked
increase in the magnetic circuit resistance in the back gap as
described above, a write magnetic field cannot be efficiently
generated by conventional MAMR head structures employing alumina as
a back gap material.
[0011] Accordingly, the responsivity of the write magnetic field to
the recording current is undesirably low in conventional MAMR head
structures employing alumina as the back gap material. Moreover, a
microwave-assisted magnetic recording head in which the write
magnetic field responsivity is improved as much as with permalloy
back gap materials, while avoiding the electrical insulation
characteristics of the current path in the vicinity of alumina back
gap materials would be highly desirable.
SUMMARY
[0012] In one embodiment, a high-frequency magnetic field-assisted
magnetic recording (MAMR) head includes: a yoke adapted for
facilitating magnetic flux through the MAMR head; a main pole
magnetically coupled to the yoke and adapted for producing a
writing magnetic field; a return pole spaced from the main pole; a
spin torque oscillator (STO) positioned above the main pole; and a
back gap layer positioned between the yoke and the return pole,
wherein at least one of the yoke, the main pole, the return pole,
and the back gap layer comprises a highly resistive magnetic
material.
[0013] In another embodiment, a high-frequency magnetic
field-assisted magnetic recording (MAMR) head includes: a
reproducing portion comprising: a first sensor shield; a second
sensor shield; and a sensor between the first sensor shield and the
second sensor shield; and a recording portion positioned adjacent
the reproducing portion, the recording portion comprising: a yoke
adapted for facilitating magnetic flux through the MAMR head; a
main pole positioned above the yoke and adapted for producing a
writing magnetic field; a spin torque oscillator (STO) positioned
above the main pole; an STO shield positioned above the STO; a
return pole positioned above the STO shield; and a back gap layer
positioned between the yoke and the return pole, the back gap layer
comprising at least one highly resistive material selected from the
group consisting of: XFe.sub.2O.sub.4, RFe.sub.5O.sub.12, Fe, Co,
Ni, FeCoNi, iron oxides, nickel oxides, cobalt oxides and manganese
oxides, wherein X is an element selected from the group consisting
of: Mn, Co, Ni, Zn, Cu, Fe, and wherein R is a rare earth element,
wherein at least two of the yoke, the return pole, the main pole
and the STO shield comprise at least one highly resistive material,
wherein the highly resistive material is characterized by a
resistivity in a range from about 1 .OMEGA.m to about
1.times.10.sup.4 .OMEGA.m, a saturation magnetic flux density of
not less than about 0.1 T, and a thickness not less than about 10
nm, wherein during operation of the head, a current flowing through
the back gap material flows along a first current path
characterized by a resistivity in not less than 1.times.10.sup.-3
.OMEGA.m, and wherein during operation of the head, a current
flowing through the STO along a second current path is delivered to
the STO with about 100% efficiency.
[0014] Any of these embodiments may be implemented in a magnetic
data storage system such as a disk drive system, which may include
a magnetic head, a drive mechanism for passing a magnetic medium
(e.g., hard disk) over the magnetic head, and a controller
electrically coupled to the magnetic head.
[0015] Other aspects and advantages of the present invention will
become apparent from the following detailed description, which,
when taken in conjunction with the drawings, illustrate by way of
example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] For a fuller understanding of the nature and advantages of
the present invention, as well as the preferred mode of use,
reference should be made to the following detailed description read
in conjunction with the accompanying drawings.
[0017] FIG. 1 is a simplified drawing of a magnetic recording disk
drive system.
[0018] FIG. 2A is a schematic representation in section of a
recording medium utilizing a longitudinal recording format.
[0019] FIG. 2B is a schematic representation of a conventional
magnetic recording head and recording medium combination for
longitudinal recording as in FIG. 2A.
[0020] FIG. 2C is a magnetic recording medium utilizing a
perpendicular recording format.
[0021] FIG. 2D is a schematic representation of a recording head
and recording medium combination for perpendicular recording on one
side.
[0022] FIG. 2E is a schematic representation of a recording
apparatus adapted for recording separately on both sides of the
medium.
[0023] FIG. 3A is a cross-sectional view of one particular
embodiment of a perpendicular magnetic head with helical coils.
[0024] FIG. 3B is a cross-sectional view of one particular
embodiment of a piggyback magnetic head with helical coils.
[0025] FIG. 4A is a cross-sectional view of one particular
embodiment of a perpendicular magnetic head with looped coils.
[0026] FIG. 4B is a cross-sectional view of one particular
embodiment of a piggyback magnetic head with looped coils.
[0027] FIG. 5 depicts a schematic image of a microwave-assisted
magnetic recording head, according to one embodiment.
[0028] FIG. 6 depicts a schematic image of current paths in
microwave-assisted magnetic recording head, according to one
embodiment. The image is rotated and reversed from the view shown
in FIG. 5.
[0029] FIG. 7 depicts a microwave-assisted magnetic recording head
with ferrite back gap, according to one embodiment.
[0030] FIG. 8 depicts a microwave-assisted magnetic recording head
comprising ferrite in a portion of the back gap, according to one
embodiment.
[0031] FIG. 9 depicts a microwave-assisted magnetic recording head
comprising ferrite in the yoke, according to one embodiment.
[0032] FIG. 10 depicts a microwave-assisted magnetic recording head
comprising ferrite in the return pole, according to one
embodiment.
[0033] FIG. 11 depicts a microwave-assisted magnetic recording head
with a laminated back gap, according to one embodiment.
[0034] FIG. 12 depicts a microwave-assisted magnetic recording head
having ferrite in the back gap and the yoke, according to one
embodiment.
[0035] FIG. 13 depicts a STO current ratio as a function of
resistivity of back gap material, according to one embodiment.
[0036] FIG. 14 depicts a magnetic flux density in back gap for
Al.sub.2O.sub.3, Ferrite and permalloy, according to one
embodiment.
[0037] FIG. 15 depicts a write current dependence of the write
field, according to one embodiment.
[0038] FIG. 16 depicts a flowchart of a method, according to one
embodiment.
DETAILED DESCRIPTION
[0039] The following description is made for the purpose of
illustrating the general principles of the present invention and is
not meant to limit the inventive concepts claimed herein. Further,
particular features described herein can be used in combination
with other described features in each of the various possible
combinations and permutations.
[0040] Unless otherwise specifically defined herein, all terms are
to be given their broadest possible interpretation including
meanings implied from the specification as well as meanings
understood by those skilled in the art and/or as defined in
dictionaries, treatises, etc.
[0041] It must also be noted that, as used in the specification and
the appended claims, the singular forms "a," "an" and "the" include
plural referents unless otherwise specified.
[0042] The following description discloses several preferred
embodiments of disk-based storage systems and/or related systems
and methods, as well as operation and/or component parts
thereof.
[0043] In one general embodiment, a high-frequency magnetic
field-assisted magnetic recording (MAMR) head includes: a yoke
adapted for facilitating magnetic flux through the MAMR head; a
main pole magnetically coupled to the yoke and adapted for
producing a writing magnetic field; a return pole spaced from the
main pole; a spin torque oscillator (STO) positioned above the main
pole; and a back gap layer positioned between the yoke and the
return pole, wherein at least one of the yoke, the main pole, the
return pole, and the back gap layer comprises a highly resistive
magnetic material.
[0044] In another general embodiment, a high-frequency magnetic
field-assisted magnetic recording (MAMR) head includes: a
reproducing portion comprising: a first sensor shield; a second
sensor shield; and a sensor between the first sensor shield and the
second sensor shield; and a recording portion positioned adjacent
the reproducing portion, the recording portion comprising: a yoke
adapted for facilitating magnetic flux through the MAMR head; a
main pole positioned above the yoke and adapted for producing a
writing magnetic field; a spin torque oscillator (STO) positioned
above the main pole; an STO shield positioned above the STO; a
return pole positioned above the STO shield; and a back gap layer
positioned between the yoke and the return pole, the back gap layer
comprising at least one highly resistive material selected from the
group consisting of: XFe.sub.2O.sub.4, RFe.sub.5O.sub.12, Fe, Co,
Ni, FeCoNi, iron oxides, nickel oxides, cobalt oxides and manganese
oxides, wherein X is an element selected from the group consisting
of: Mn, Co, Ni, Zn, Cu, Fe, and wherein R is a rare earth element,
wherein at least two of the yoke, the return pole, the main pole
and the STO shield comprise at least one highly resistive material,
wherein the highly resistive material is characterized by a
resistivity in a range from about 1 .OMEGA.m to about
1.times.10.sup.4 .OMEGA.m, a saturation magnetic flux density of
not less than about 0.1 T, and a thickness not less than about 10
nm, wherein during operation of the head, a current flowing through
the back gap material flows along a first current path
characterized by a resistivity in not less than 1.times.10.sup.-3
.OMEGA.m, and wherein during operation of the head, a current
flowing through the STO along a second current path is delivered to
the STO with about 100% efficiency.
[0045] Referring now to FIG. 1, there is shown a disk drive 100 in
accordance with one embodiment of the present invention. As shown
in FIG. 1, at least one rotatable magnetic disk 112 is supported on
a spindle 114 and rotated by a disk drive motor 118. The magnetic
recording on each disk is typically in the form of an annular
pattern of concentric data tracks (not shown) on the disk 112.
[0046] At least one slider 113 is positioned near the disk 112,
each slider 113 supporting one or more magnetic read/write heads
121. As the disk rotates, slider 113 is moved radially in and out
over disk surface 122 so that heads 121 may access different tracks
of the disk where desired data are recorded and/or to be written.
Each slider 113 is attached to an actuator arm 119 by means of a
suspension 115. The suspension 115 provides a slight spring force
which biases slider 113 against the disk surface 122. Each actuator
arm 119 is attached to an actuator 127. The actuator 127 as shown
in FIG. 1 may be a voice coil motor (VCM). The VCM comprises a coil
movable within a fixed magnetic field, the direction and speed of
the coil movements being controlled by the motor current signals
supplied by controller 129.
[0047] During operation of the disk storage system, the rotation of
disk 112 generates an air bearing between slider 113 and disk
surface 122 which exerts an upward force or lift on the slider. The
air bearing thus counter-balances the slight spring force of
suspension 115 and supports slider 113 off and slightly above the
disk surface by a small, substantially constant spacing during
normal operation. Note that in some embodiments, the slider 113 may
slide along the disk surface 122.
[0048] The various components of the disk storage system are
controlled in operation by control signals generated by control
unit 129, such as access control signals and internal clock
signals. Typically, control unit 129 comprises logic control
circuits, storage (e.g., memory), and a microprocessor. The control
unit 129 generates control signals to control various system
operations such as drive motor control signals on line 123 and head
position and seek control signals on line 128. The control signals
on line 128 provide the desired current profiles to optimally move
and position slider 113 to the desired data track on disk 112. Read
and write signals are communicated to and from read/write heads 121
by way of recording channel 125.
[0049] The above description of a typical magnetic disk storage
system, and the accompanying illustration of FIG. 1 is for
representation purposes only. It should be apparent that disk
storage systems may contain a large number of disks and actuators,
and each actuator may support a number of sliders.
[0050] An interface may also be provided for communication between
the disk drive and a host (integral or external) to send and
receive the data and for controlling the operation of the disk
drive and communicating the status of the disk drive to the host,
all as will be understood by those of skill in the art.
[0051] In a typical head, an inductive write head includes a coil
layer embedded in one or more insulation layers (insulation stack),
the insulation stack being located between first and second pole
piece layers. A gap is formed between the first and second pole
piece layers by a gap layer at an air bearing surface (ABS) of the
write head. The pole piece layers may be connected at a back gap.
Currents are conducted through the coil layer, which produce
magnetic fields in the pole pieces. The magnetic fields fringe
across the gap at the ABS for the purpose of writing bits of
magnetic field information in tracks on moving media, such as in
circular tracks on a rotating magnetic disk.
[0052] The second pole piece layer has a pole tip portion which
extends from the ABS to a flare point and a yoke portion which
extends from the flare point to the back gap. The flare point is
where the second pole piece begins to widen (flare) to form the
yoke. The placement of the flare point directly affects the
magnitude of the magnetic field produced to write information on
the recording medium.
[0053] FIG. 2A illustrates, schematically, a conventional recording
medium such as used with magnetic disc recording systems, such as
that shown in FIG. 1. This medium is utilized for recording
magnetic impulses in or parallel to the plane of the medium itself.
The recording medium, a recording disc in this instance, comprises
basically a supporting substrate 200 of a suitable non-magnetic
material such as glass, with an overlying coating 202 of a suitable
and conventional magnetic layer.
[0054] FIG. 2B shows the operative relationship between a
conventional recording/playback head 204, which may preferably be a
thin film head, and a conventional recording medium, such as that
of FIG. 2A.
[0055] FIG. 2C illustrates, schematically, the orientation of
magnetic impulses substantially perpendicular to the surface of a
recording medium as used with magnetic disc recording systems, such
as that shown in FIG. 1. For such perpendicular recording the
medium typically includes an under layer 212 of a material having a
high magnetic permeability. This under layer 212 is then provided
with an overlying coating 214 of magnetic material preferably
having a high coercivity relative to the under layer 212.
[0056] FIG. 2D illustrates the operative relationship between a
perpendicular head 218 and a recording medium. The recording medium
illustrated in FIG. 2D includes both the high permeability under
layer 212 and the overlying coating 214 of magnetic material
described with respect to FIG. 2C above. However, both of these
layers 212 and 214 are shown applied to a suitable substrate 216.
Typically there is also an additional layer (not shown) called an
"exchange-break" layer or "interlayer" between layers 212 and
214.
[0057] In this structure, the magnetic lines of flux extending
between the poles of the perpendicular head 218 loop into and out
of the overlying coating 214 of the recording medium with the high
permeability under layer 212 of the recording medium causing the
lines of flux to pass through the overlying coating 214 in a
direction generally perpendicular to the surface of the medium to
record information in the overlying coating 214 of magnetic
material preferably having a high coercivity relative to the under
layer 212 in the form of magnetic impulses having their axes of
magnetization substantially perpendicular to the surface of the
medium. The flux is channeled by the soft underlying coating 212
back to the return layer (P1) of the head 218.
[0058] FIG. 2E illustrates a similar structure in which the
substrate 216 carries the layers 212 and 214 on each of its two
opposed sides, with suitable recording heads 218 positioned
adjacent the outer surface of the magnetic coating 214 on each side
of the medium, allowing for recording on each side of the
medium.
[0059] FIG. 3A is a cross-sectional view of a perpendicular
magnetic head. In FIG. 3A, helical coils 310 and 312 are used to
create magnetic flux in the stitch pole 308, which then delivers
that flux to the main pole 306. Coils 310 indicate coils extending
out from the page, while coils 312 indicate coils extending into
the page. Stitch pole 308 may be recessed from the ABS 318.
Insulation 316 surrounds the coils and may provide support for some
of the elements. The direction of the media travel, as indicated by
the arrow to the right of the structure, moves the media past the
lower return pole 314 first, then past the stitch pole 308, main
pole 306, trailing shield 304 which may be connected to the wrap
around shield (not shown), and finally past the upper return pole
302. Each of these components may have a portion in contact with
the ABS 318. The ABS 318 is indicated across the right side of the
structure.
[0060] Perpendicular writing is achieved by forcing flux through
the stitch pole 308 into the main pole 306 and then to the surface
of the disk positioned towards the ABS 318.
[0061] FIG. 3B illustrates a piggyback magnetic head having similar
features to the head of FIG. 3A. Two shields 304, 314 flank the
stitch pole 308 and main pole 306. Also sensor shields 322, 324 are
shown. The sensor 326 is typically positioned between the sensor
shields 322, 324.
[0062] FIG. 4A is a schematic diagram of one embodiment which uses
looped coils 410, sometimes referred to as a pancake configuration,
to provide flux to the stitch pole 408. The stitch pole then
provides this flux to the main pole 406. In this orientation, the
lower return pole is optional. Insulation 416 surrounds the coils
410, and may provide support for the stitch pole 408 and main pole
406. The stitch pole may be recessed from the ABS 418. The
direction of the media travel, as indicated by the arrow to the
right of the structure, moves the media past the stitch pole 408,
main pole 406, trailing shield 404 which may be connected to the
wrap around shield (not shown), and finally past the upper return
pole 402 (all of which may or may not have a portion in contact
with the ABS 418). The ABS 418 is indicated across the right side
of the structure. The trailing shield 404 may be in contact with
the main pole 406 in some embodiments.
[0063] FIG. 4B illustrates another type of piggyback magnetic head
having similar features to the head of FIG. 4A including a looped
coil 410, which wraps around to form a pancake coil. Also, sensor
shields 422, 424 are shown. The sensor 426 is typically positioned
between the sensor shields 422, 424.
[0064] In FIGS. 3B and 4B, an optional heater is shown near the
non-ABS side of the magnetic head. A heater (Heater) may also be
included in the magnetic heads shown in FIGS. 3A and 4A. The
position of this heater may vary based on design parameters such as
where the protrusion is desired, coefficients of thermal expansion
of the surrounding layers, etc.
Prior Art
[0065] FIG. 5 shows a conventional structure of a MAMR head. The
conventional magnetic head consists of a recording head portion 511
and a reproducing head portion 512. The recording head portion 511
is characterized by having, a main pole 513, a spin torque
oscillator (STO) 514, a STO shield 515, a return pole 516, a back
gap 517, a coil 518, a yoke 519, a lower electrode 520 and an upper
electrode 521, while the reproducing head portion 512 is
characterized by having a reproducing sensor 522 such as a CIP-GMR
sensor, a CPP-GMR sensor or a TMR sensor, according to the prior
art. Moreover, a lower reproducing shield 523 and an upper
reproducing shield 524 are positioned flanking the reproducing
sensor 522 in the conventional MAMR head structure, as can be seen
from FIG. 5.
[0066] FIG. 6 depicts the conventional structure shown in FIG. 5 in
operation from a view rotated 90.degree. to the right and inverted
along an axis perpendicular to the air-bearing surface (ABS),
according to the prior art. During a recording operation, such as a
write operation targeting a portion of a magnetic medium, current
flows through two paths in the MAMR head. In particular, a first
current flows through a first current path 532 from the yoke 519,
through the back gap 517 and into the return pole 516. In addition,
a second current flows through a second current path 531 through
the yoke 519 to the main pole 513, the STO 514, and the STO shield
515 into the return pole 516, according to the prior art.
Description of Inventive Embodiments
[0067] According to the inventive embodiments described herein, a
highly resistive material is disposed in at least one part of a
magnetic circuit including a main pole, return pole, yoke and a
back gap. The inventive structure advantageously improves the write
magnetic field responsivity while allowing a large current to flow
efficiently to the STO. In some approaches, a microwave-assisted
recording head also includes a structure in which an STO is
laminated between the main pole and a STO shield. FIGS. 7-12 depict
the highly resistive material 716 at various locations in the
magnetic circuit.
[0068] Preferably, the head is adapted for recording information on
a magnetic medium by a process involving using the main pole as one
electrode and the STO shield as another electrode for a STO. In
operation, the flow of a current to the STO enclosed between the
main pole and shield generates a microwave magnetic field.
Moreover, superposing this microwave magnetic field and the
magnetic field from the main pole results in improved write
magnetic field responsivity while allowing efficient flow of high
current to the STO.
[0069] In some embodiments, the highly resistive magnetic material
is characterized by a resistivity of not less than 10.sup.-3
.OMEGA.m. In one embodiment, the resistivity is in a range of
approximately 10.sup.-3 .OMEGA.m to 1 .OMEGA.m, in a preferred
embodiment a range of about 10.sup.2 .OMEGA.m to 10.sup.3 .OMEGA.m,
and in a particularly preferred embodiment a range of approximately
10.sup.3 .OMEGA.m to 10.sup.4 .OMEGA.m. Of course, other ranges of
resistivity may be employed without departing from the scope of the
present invention, as would be understood by one having ordinary
skill in the art upon reading the present descriptions.
[0070] Moreover, the saturation magnetic flux density of this
highly resistive material is desirably not less than 0.1 T. In some
embodiments, the flux density may be greater than about 1 T, in
others greater than about 10.sup.2 T, and in still others greater
than about 10.sup.4 T, as will be appreciated by skilled artisans
upon reading the present descriptions.
[0071] In addition, the thickness of the head portion(s) in which
the highly resistive material is employed is desirably not less
than 10 nm, although head portions with highly resistive material
therein and a thickness more than or less than 10 nm may be
employed without departing from the scope of the present
disclosures.
[0072] Particularly preferred embodiments employ ferrite (an Fe
oxide) as the highly resistive material 716. As understood herein,
ferrite is a ferric oxide which may be defined by a composition of
XFe.sub.2O.sub.4 where X is an element such as Mn, Co, Ni, Zn, Cu,
Fe, etc., as would be understood by the skilled artisan upon
reading the present descriptions. Alternatively, the ferrite may be
a ferric oxide defined by a composition of RFe.sub.5O.sub.12, where
R is a rare earth element.
[0073] Additionally and/or alternatively, a granular magnetic
material may be used as the highly resistive material 716. As
understood herein, a granular magnetic material is preferably
characterized by having small magnetized particles such as Fe, Co,
Ni, FeCoNi alloy, ferrite, etc. disposed in a non-magnetic
insulator material such as Al.sub.2O.sub.3, MgO, SiO.sub.2, etc.
and/or oxides containing Ni, Co, Mn or Fe etc., as would be
understood by one having ordinary skill in the art upon reading the
present descriptions.
[0074] Furthermore, in some approaches a structure comprising the
highly resistive material 716 may be formed by laminating at least
one layer of each of an FeCoNi alloy and any of the highly
resistive material 716 as noted above, and the laminate structure
may be employed as the highly resistive material 716. According to
one embodiment, the thickness of the highly resistive material 716
of this laminate structure is not less than 10 nm.
[0075] In preferred approaches, the highly resistive material 716
is disposed for use as the back gap. According to one embodiment,
the back gap may be constituted in its entirety from the highly
resistive material 716, or it may be partially constituted
therefrom.
[0076] FIG. 7 shows the structure of one exemplary inventive
embodiment. The inventive magnetic head includes a recording head
portion 700, and may include a reproducing head portion (not
shown). As an option, the present structure 700 may be implemented
in conjunction with features from any other embodiment listed
herein, such as those described with reference to the other FIGS.
Of course, however, such structure 700 and others presented herein
may be used in various applications and/or in permutations which
may or may not be specifically described in the illustrative
embodiments listed herein. Further, the structure 700 presented
herein may be used in any desired environment.
[0077] The recording head portion 700 is characterized by having, a
main pole 702, a spin torque oscillator (STO) 704, a STO shield
706, a return pole 708, a back gap 710, a coil (not shown), a yoke
712, a lower electrode (not shown) and an upper electrode (not
shown). A nonmagnetic, electrically conductive material or
materials 705, 707 of any known type, including materials
conventionally used in a write gap, may be positioned between the
STO and the main pole 702, as well as between the STO 704 and
shield 706. A current source 722 of known type for powering the STO
704 may be coupled to portions of the recording head portion 700,
such as the return pole 708 and yoke 712. Parameters such as
voltage, current level, etc. of the current source 722 may be
selected according to knowledge generally available to those
skilled in the art.
[0078] The reproducing head portion, if present, may be
characterized by having a reproducing sensor (not shown) such as a
CIP-GMR sensor, a CPP-GMR sensor or a TMR sensor, according to one
embodiment. Moreover, a lower reproducing shield (not shown) and an
upper reproducing shield (not shown) are positioned flanking the
reproducing sensor (not shown).
[0079] Additional elements not shown in FIG. 7 and in other
embodiments may be present, such as those found in FIG. 5. Such
additional elements may be arranged in a substantially similar
fashion as shown in FIG. 5, in various embodiments.
[0080] In one embodiment, the recording portion may be positioned
directly adjacent the reproducing portion, and in other embodiments
the recording portion may be spaced from the reproducing portion,
as would be understood by one having ordinary skill in the art upon
reading the present descriptions.
[0081] In preferred approaches, a highly resistive material 716 as
described herein may be employed for the back gap layer 710. In
particularly preferred embodiments, the highly resistive material
716 is ferrite. In one exemplary embodiment, when viewed from a
perspective as shown in FIG. 7 the back gap layer may be
characterized by an area of approximately 21 .mu.m, defined by a
height in a plane of deposition of about 7 .mu.m and a width in the
plane of deposition of about 3 .mu.m. Moreover, in some approaches
the back gap thickness (into the page as viewed from the
perspective shown in FIG. 7) is not less than about 1 .mu.m.
[0082] FIG. 13 shows the effect that the resistivity of the highly
resistive material has on the ratio of the current flowing to the
STO to the total current. In the experimental results discussed
below, the resistance was calculated employing these values. The
general embodiment shown in FIG. 7 as a representation of
components used in the following discussion of experimentation.
During experimentation, it was discovered that, in order for a
large current to flow efficiently along the second current path 720
to the STO 704 without a concurrent flow along the first current
path 718 into the back gap 710, the resistance of the first current
path may be increased.
[0083] As determined experimentally, the STO side resistance was
about 0.6.OMEGA. in various embodiments. Thus, in order for a large
current to flow efficiently to the STO side (second current path),
the resistance of the first current path is preferably suitably
higher than this value of 0.6.OMEGA.. In particularly preferred
embodiments, a suitable resistance of the first current path may be
achieved by employing a highly resistive material 716 in the back
gap 710 characterized by a resistivity of no less than about
10.sup.-3 .OMEGA.m. By employing such a highly resistive material
in the back gap 710, preferred embodiments of the inventive MAMR
head may achieve excellent, and preferably substantially perfect,
efficiency in delivering current to the STO 704. In other words, by
employing a highly resistive material 716 in the back gap 710
characterized by a resistivity of no less than about 10.sup.-3
.OMEGA.m, one may achieve near 100% efficiency in delivering
current to the STO 704 along the second current path 720, as can be
seen from the experimental results shown in FIG. 13. In some
embodiments, the current may flow along the second current path
with about 99% efficiency, in preferred embodiments with about
99.9% efficiency, and in particularly preferred embodiments with
about 99.99% efficiency.
[0084] Moreover, the use of a highly resistive material 716 having
a thickness of about 1 nm in the back gap 710 may generate a tunnel
current according to one embodiment that results in an undesirable
drop in the resistance of the back gap 710. Accordingly, the
thickness of the highly resistive material 716 in the back gap is
preferably at least a thickness at which the generation of a tunnel
current is avoided. In some approaches, a thickness of the order of
about 10 nm is sufficient to avoid the undesirable drop in
resistance caused by tunnel current.
[0085] One particularly effective approach to achieve suitable
resistance along the first current path 718 is to employ ferrite as
the highly resistive material 716 in the back gap 710. According to
one embodiment where ferrite is disposed in the back gap 710,
experimental results revealed that the resistivity of the ferrite
was about 10.sup.4 .OMEGA.m, and correspondingly the resistance
along the first current path 718 was about 5.times.10.sup.8.OMEGA..
This is several orders of magnitude higher than the exemplary
0.6.OMEGA. resistance of the STO 704, and is a sufficiently high
electrical resistance to achieve near-perfect (i.e. 100% efficient)
current delivery to the STO 704.
[0086] Additionally and/or alternatively, in some approaches a
granular magnetic material may be used as the highly resistive
material 716 in the back gap 710. As will be appreciated by the
skilled artisan reading the present descriptions, the magnetic
material in the grains confers the magnetic properties of a
granular magnetic material. Accordingly, the magnetic permeability
thereof is greater than in a vacuum, and as a result the magnetic
circuit resistance is reduced. In addition, because a non-magnetic
insulator interrupts the current-conducting path along a granular
magnetic material, the resistivity is concurrently higher than in
uniform materials. In some approaches, the granular magnetic
material therefore forms a highly resistive material 716 and
affords an effect similar to ferrite.
[0087] Additionally and/or alternatively, a compound having strong
magnetism at room temperature may be employed as the highly
resistive material 716. In some embodiments, oxides containing Mn,
Co, Ni, Fe, etc., as would be understood by one having ordinary
skill in the art upon reading the present descriptions, may be
employed as the highly resistive material 716.
[0088] Furthermore, materials constructed by the lamination of a
highly resistive material 716 and a magnetic alloy such as a FeCoNi
alloy may be employed as the highly resistive material 716 in the
back gap 710.
[0089] FIGS. 7-12 show various embodiments of the inventive
magnetic head as described herein having a highly resistive
material 716 disposed in one or more elements of the recording
portion 700 so as to generate the desirable high resistance along a
first current path 718 and responsivity along a second current path
720. As will be appreciated by the skilled artisan upon reading the
present descriptions, the various embodiments are not mutually
exclusive, and may be combined in any fashion desirable to improve
performance of a MAMR head by including highly resistive material
716 in any combination of the main pole 702, the STO shield 706,
the return pole 708, the yoke 712 and/or the back gap 710.
[0090] As shown in FIG. 8, a similar advantage in resistance and
responsivity is produced when a highly resistive material 716 is
employed in only a portion of the back gap. According to one
embodiment seen in FIG. 8, the back gap 710 may comprise a highly
resistive material 716 and an additional material. As will be
understood by the skilled artisan reading the present descriptions,
the additional material may be any material suitable for use in a
back gap 710 of a MAMR head, including those conventionally used
for such purpose.
[0091] As shown in FIG. 9, in other embodiments a highly resistive
material 716 may be disposed in all or part of the yoke 712 to
confer the desirably high resistance and responsivity on the
resulting MAMR head.
[0092] Additionally and/or alternatively, the employment of a
highly resistive material 716 in a part of the STO shield 706
affords a similar effect.
[0093] In addition, as shown in FIG. 10, the employment of a highly
resistive material 716 in a part of the return pole 708 affords the
same effect.
[0094] In addition, as shown in FIG. 11, the back gap 710 may be
constituted from the lamination of a highly resistive material 716
and a magnetic material such as a FeCoNi alloy.
[0095] Furthermore, as represented in FIG. 12, the arrangement of
highly resistive material 716 in two or more of the main pole 702,
the STO shield 706, the return pole 708, the yoke 712 and/or the
back gap 710 of the magnetic circuit affords similarly effective
improvements to MAMR head performance.
[0096] Notably, in embodiments where one or more portions of the
main pole 702, the STO shield 706, the return pole 708, the yoke
712 and/or the back gap 710 do not employ a highly resistive
material 716 as described herein, an additional material such as
FeCoNi alloy may be employed.
[0097] The adoption of the inventive configurations described
herein ensures an adequately advantageous increase in the
resistance of a first current path 718, e.g. a resistance of about
10.sup.-3.OMEGA. or more, as would be appreciated by the skilled
artisan reading the present descriptions. In turn, this large
resistance ensures that large amounts of current flow with
near-perfect efficiency (i.e. about 100% efficiency) to the STO 704
along the second current path 720. Moreover, this configuration
enables concurrent reduction in the magnetic circuit resistance
along the first current path 718. This ultimately results in a
microwave-assisted magnetic recording head that possesses a high
write magnetic field responsivity while maintaining the efficient
flow of a large current to the STO.
[0098] The employment of a ferrite in the back gap of a
microwave-assisted magnetic recording head in this way allows a
large current to be efficiently applied to the spin torque
oscillator in the absence of the flow of current to the back
portion, and improves the current responsivity of the recording
head magnetic field.
[0099] As described herein, according to some approaches the
inventive MAMR head structure may be produced by following a
process such as method 1600, depicted in FIG. 16. As will be
appreciated by one having ordinary skill in the art upon reading
the present descriptions, method 1600 may be performed in any
environment, including but not limited to those depicted in FIGS.
1-12, among others.
[0100] In one embodiment, method 1600 includes operation 1602 where
a yoke, such as yoke 712, is formed. The yoke may be formed by any
suitable method, including but not limited to sputtering, chemical
vapor deposition, ion beam deposition, etc. as would be appreciated
by one having ordinary skill in the art upon reading the present
descriptions. Moreover, the yoke may include a highly resistive
material 716 in some approaches, but need not have such a
composition to achieve the inventive MAMR head.
[0101] In operation 1604, a main pole, such as main pole 702 may be
formed above the yoke. The main pole may be formed by any suitable
method, including but not limited to sputtering, chemical vapor
deposition, ion beam deposition, etc. as would be appreciated by
one having ordinary skill in the art upon reading the present
descriptions. Moreover, the main pole may include a highly
resistive material 716 in some approaches, but need not have such a
composition to achieve the inventive MAMR head.
[0102] In operation 1606, a spin torque oscillator (STO) such as
STO 704 may be formed above the main pole. The STO may be formed by
any suitable method, including but not limited to sputtering,
chemical vapor deposition, ion beam deposition, etc. as would be
appreciated by one having ordinary skill in the art upon reading
the present descriptions.
[0103] In one approach an operation 1608 may be performed by
forming a return pole such as return pole 708 above the STO. The
return pole may be formed by any suitable method, including but not
limited to sputtering, chemical vapor deposition, ion beam
deposition, etc. as would be appreciated by one having ordinary
skill in the art upon reading the present descriptions. Moreover,
the return pole may include a highly resistive material 716 in some
approaches, but need not have such a composition to achieve the
inventive MAMR head.
[0104] In some approaches, a back gap such as back gap 710 may be
formed between the yoke and the return pole in operation 1610. The
back gap may be formed by any suitable method, including but not
limited to sputtering, chemical vapor deposition, ion beam
deposition, etc. as would be appreciated by one having ordinary
skill in the art upon reading the present descriptions. Moreover,
the back gap may include a highly resistive material 716 in some
approaches, but need not have such a composition to achieve the
inventive MAMR head.
Experimental Results
[0105] Turning now to the operation and functionality of the
inventive MAMR head as described herein, FIG. 13 shows a STO
current ratio as a function of resistivity of back gap material,
according to one embodiment. A person having ordinary skill in the
art will appreciate from reviewing the present disclosures, and
particularly the data shown in FIG. 13 that, for MAMR heads having
a resistance of about 10.sup.4 .OMEGA.m along the first current
path 718 (e.g., as represented in FIG. 7), essentially 100% of the
current flows to the STO along the second current path 720 (e.g.,
as represented in FIG. 7). Since ferrite as described herein
exhibits a resistivity well above this threshold when arranged in
one or more elements of a MAMR head according to the inventive
embodiments described above, sufficient electrical insulation
characteristics are maintained in the first current path to confer
the advantage of superior high-efficiency current flow to the STO
as compared to current flow efficiency of conventional MAMR head
structures.
[0106] FIG. 14 shows the saturation magnetic flux density in the
back gap as calculated using the finite element magnetic field
method. While the magnetic flux density using alumina was found to
be of the order of about 0.03 T, the magnetic flux density of the
permalloy was found to be of the order of about 0.14 T. This
difference in magnetic flux density is due to the magnetization of
the permalloy, and this indicates that the saturation magnetic flux
density of the magnetic material of the back gap is desirably not
less than about 0.1 T. The saturation magnetic flux density as
calculated for the ferrite was about 0.2 T--a comparatively much
larger figure than 0.1 T. When a ferrite was employed for the back
gap, the magnetic flux density of the back gap was found to be
about 0.14 T.
[0107] FIG. 15 shows the dependency of the recording head magnetic
field (Heft) as calculated using the finite element magnetic field
calculation with respect to a recording head current (Iw). As can
be seen from the experimental results, a back gap in which ferrite
is employed generates a higher recording head magnetic field with
respect to the recording current than a head in which alumina is
employed in the back gap. Without wishing to be bound to any
particular theory, the inventors believe this difference is due to
the magnetic coupling of the back gap and the reduction of the
magnetic circuit resistance in the back gap portion. In one
embodiment, the current responsivity (.DELTA.Heff*.DELTA.Iw) may be
improved by about 20% by changing the back gap material from
Al.sub.2O.sub.3 to a ferrite in this way.
[0108] While various embodiments have been described above, it
should be understood that they have been presented by way of
example only, and not limitation. Thus, the breadth and scope of an
embodiment of the present invention should not be limited by any of
the above-described exemplary embodiments, but should be defined
only in accordance with the following claims and their
equivalents.
* * * * *