U.S. patent application number 09/447944 was filed with the patent office on 2002-07-11 for method and system for reducing assymetry in a spin valve having a synthetic pinned layer.
Invention is credited to CHEN, WENJIE, HUAI, YIMING, RANA, AMRITPAL SINGH, ZHANG, JING, ZHU, NINGJIA.
Application Number | 20020090533 09/447944 |
Document ID | / |
Family ID | 23778384 |
Filed Date | 2002-07-11 |
United States Patent
Application |
20020090533 |
Kind Code |
A1 |
ZHANG, JING ; et
al. |
July 11, 2002 |
METHOD AND SYSTEM FOR REDUCING ASSYMETRY IN A SPIN VALVE HAVING A
SYNTHETIC PINNED LAYER
Abstract
A method and system for providing a spin valve for use in a
magnetoresistive head is disclosed. The method and system include
providing a synthetic pinned layer, a nonmagnetic spacer layer, and
a free layer. The free layer has a first magnetization canted from
a first direction by a first angle. The nonmagnetic spacer layer is
disposed between the free layer and the synthetic pinned layer. The
synthetic pinned layer has a second magnetization in a second
direction. The second direction is canted from a third direction
that is transverse to the first direction by a second angle. The
second magnetization is substantially orthogonal to the first
magnetization.
Inventors: |
ZHANG, JING; (SAN JOSE,
CA) ; ZHU, NINGJIA; (CUPERTINO, CA) ; HUAI,
YIMING; (PLEASANTON, CA) ; RANA, AMRITPAL SINGH;
(UNION CITY, CA) ; CHEN, WENJIE; (CUPERTINO,
CA) |
Correspondence
Address: |
JOSEPH A SAWYER JR
SAWYER & ASSOCIATES
P O BOX 51418
PALO ALTO
CA
94303
|
Family ID: |
23778384 |
Appl. No.: |
09/447944 |
Filed: |
November 23, 1999 |
Current U.S.
Class: |
428/810 ;
G9B/5.114 |
Current CPC
Class: |
B82Y 10/00 20130101;
G11B 5/3932 20130101; Y10T 428/1121 20150115; Y10S 428/90 20130101;
Y10T 428/11 20150115; G11B 5/3903 20130101 |
Class at
Publication: |
428/692 |
International
Class: |
G11B 005/39 |
Claims
What is claimed is:
1. A spin valve for use in a magnetoresistive head comprising: a
free layer having a first magnetization that is canted from a first
direction by a first angle; a synthetic pinned layer having a
second magnetization in a second direction, the second direction
being canted by a second angle from a third direction that is
transverse to the first direction, the second magnetization being
substantially orthogonal to the first magnetization; and a
nonmagnetic spacer layer disposed between the free layer and the
synthetic pinned layer.
2. The spin valve of claim 1 wherein the second angle is greater
than or equal to approximately ten degrees.
3. The spin valve of claim 2 wherein the second angle is at least
twenty degrees.
4. The spin valve of claim 2 wherein the second angle is
approximately thirty degrees.
5. The spin valve of claim 2 wherein the second angle is between
ten and thirty degrees.
6. The spin valve of claim 1 further comprising: an
antiferromagnetic layer adjacent to the synthetic pinned layer, the
antiferromagnetic layer for pinning the second magnetization of the
synthetic pinned layer in the second direction.
7. The spin valve of claim 6 wherein the antiferromagnetic layer
further includes a layer of PtMn.
8. The spin valve of claim 6 wherein the antiferromagnetic layer
further includes a layer of PtMn.
9. The spin valve of claim 6 wherein the antiferromagnetic layer
further includes a layer of PtPdMn.
10. The spin valve of claim 1 wherein the second angle and the
first angle are substantially the same.
11. A method for providing spin valve for use in a magnetoresistive
head comprising the steps of: (a) providing a free layer having a
first magnetization canted from a first direction by a first angle;
(b) providing a synthetic pinned layer having a second
magnetization in a second direction, the second direction being
canted from a third direction that is transverse to the first
direction by a second angle, the second magnetization being
substantially orthogonal to the first magnetization; and (c)
providing a nonmagnetic spacer layer disposed between the free
layer and the synthetic pinned layer.
12. The method of claim 11 wherein the second angle is greater than
or equal to approximately ten degrees.
13. The method of claim 11 wherein the second angle is at least
twenty degrees.
14. The method of claim 11 wherein the second angle is
approximately thirty degrees.
15. The method of claim 11 wherein the second angle is between ten
and thirty degrees.
16. The method of claim 11 wherein the step of providing the
synthetic pinned layer (b) further includes the steps of. (b1)
depositing the synthetic pinned layer; and (b2) annealing the
synthetic pinned layer in a magnetic field having a fourth
direction that is substantially the same as the second
direction.
17. The method of claim 11 further comprising the step of: (c)
providing an antiferromagnetic layer adjacent to the synthetic
pinned layer, the antiferromagnetic layer for pinning the second
magnetization of the synthetic pinned layer in the second
direction.
18. The method of claim 17 wherein the antiferromagnetic layer
further includes a layer of IrMn.
19. The method of claim 17 wherein the antiferromagnetic layer
further includes a layer of PtMn.
20. The method of claim 17 wherein the antiferromagnetic layer
further includes a layer of PtPdMn.
21. The method of claim 10 wherein the second angle and the first
angle are substantially the same.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to magnetoresistive heads, and
more particularly to a method and system for providing a spin valve
having a synthetic pinned layer which has reduced amplitude
asymmetry and, in one embodiment, improved amplitude of the
magnetoresistance.
BACKGROUND OF THE INVENTION
[0002] Currently, spin valves are typically used for the
magnetoresistive (MR) element in MR read heads. A spin valve
includes a free layer and a pinned layer which are both magnetic.
The free layer and pinned layer are separated by a nonmagnetic
spacer layer. A spin valve also includes a conventional pinning
layer, such as an antiferromagnetic (AFM) layer, that is used to
pin the magnetization of the pinned layer in the desired direction.
The pinned layer of a conventional spin valve is typically composed
of a single magnetic material. The magnetic moment of the pinned
layer is typically fixed by exchange coupling to the AFM layer. The
spin valve may also include a capping layer. When used in a MR
head, antiferromagnets or hard magnets are also typically used to
ensure that the free layer has a single domain structure.
[0003] The magnetizations of the pinned layer and free layer are
controlled in the conventional spin valve. The magnetizations of
the pinned layer and free layer are typically biased to be
orthogonal when no external field is applied. In other words, the
pinning layer typically pins the magnetization of the pinned layer
in a direction that is substantially ninety degrees from the
direction of magnetization of the free layer when no recording
media is being read. In a conventional MR head, the direction of
magnetization of the pinned layer is approximately transverse,
ninety degrees from the direction that current travels through the
conventional spin valve.
[0004] The free layer is also typically biased to set the direction
of magnetization of the free layer when no external field is
applied. The free layer is typically biased using a combination of
three fields. The combination of fields typically ensures that the
free layer is biased longitudinally when no external field, for
example from a recording media, is applied. Thus, the free layer is
biased so that the magnetization is approximately in the direction
that current flows through the conventional spin valve when no
external field is applied. The fields which bias the free layer
include a magnetic field generated by a bias current driven through
the spin valve during use, an interlayer coupling between the
pinned layer and the free layer, and the demagnetization field of
the pinned layer. The combination of these three fields bias the
free layer in the longitudinal direction In order to improve the
stability of the magnetization of the pinned layer, a synthetic
pinned layer is used in synthetic spin valves. Such synthetic spin
valves are substantially the same as conventional spin valves,
except for the use of a synthetic pinned layer in lieu of a
conventional pinned layer. Thus, the magnetization of the synthetic
pinned layer is pinned in the transverse direction, ninety degrees
from the longitudinal direction in which the magnetization of the
free layer lies. Such synthetic pinned valves will be referred to
as "synthetic spin valves having a transverse pinned layer" and the
synthetic pinned layers will be referred to as "transverse
synthetic pinned layers." The transverse synthetic pinned layer
includes two magnetic layers that are separated by a nonmagnetic
spacer layer. The two magnetic layers within the transverse
synthetic pinned layer are antiferromagnetically coupled.
Consequently, the net magnetic moment of the transverse synthetic
pinned layer is significantly less than the magnetic moment for the
conventional pinned layer.
[0005] Although the transverse synthetic pinned layer is more
magnetically stable, the synthetic spin valve having a transverse
pinned layer exhibits an undesirable asymmetry. The reduction in
the magnetic moment of the transverse synthetic pinned layer
results in a demagnetization field from the transverse synthetic
pinned layer that is less than the demagnetization field of the
conventional pinned layer of the a conventional spin valve.
Consequently, the combination of fields no longer biases the free
layer in the longitudinal direction. The combination of the fields
from the bias current and the interlayer coupling for the synthetic
spin valve having a transverse pinned layer may be approximately
the same as the demagnetization field of the conventional spin
valve having the conventional pinned layer. However, because the
demagnetization field of the transverse pinned layer is reduced,
the three fields no longer bias the free layer of the synthetic
spin valve having a transverse pinned layer longitudinally.
Instead, the free layer may be less than ninety degrees from the
transverse direction.
[0006] Because the magnetization of the free layer is tilted from
the longitudinal direction in the absence of an external field, the
response of the synthetic spin valve having a transverse pinned
layer is asymmetric. Stored data in a recording media generate a
magnetic field in a first direction or a magnetic field in a second
direction. The second direction is opposite to the first direction.
When the conventional spin valve reads the recording media, the
free layer experiences fields due to the recording media. Because
it is tilted from the longitudinal direction, the magnetization of
the free layer will rotate more due to the field in one direction
than the field in the other direction. The MR of the synthetic spin
valve having a transverse pinned layer depends upon the difference
in the directions of magnetization for the free layer and the
transverse synthetic pinned layer. Because the free layer rotates
more in one direction than the other, the MR of the synthetic spin
valve having a transverse pinned layer is larger for fields from
the recording media in one direction than the other. Consequently,
the response of the synthetic spin valve having a transverse pinned
layer is asymmetric. Asymmetry in the response is undesirable. If
the asymmetry is large enough, the synthetic spin valve having a
transverse pinned layer may be unusable.
[0007] Accordingly, what is needed is a system and method for
reducing the asymmetry in a spin valve having a synthetic pinned
layer. The present invention addresses such a need.
SUMMARY OF THE INVENTION
[0008] The present invention provides a method and system for
providing a spin valve for use in a magnetoresistive head. The
method and system comprise providing a synthetic pinned layer, a
nonmagnetic spacer layer, and a free layer. The free layer has a
first magnetization canted from a first direction by a first angle.
The nonmagnetic spacer layer is disposed between the free layer and
the synthetic pinned layer. The synthetic pinned layer has a second
magnetization in a second direction. The second direction is canted
from a third direction that is transverse to the first direction by
a second angle. The second magnetization is substantially
orthogonal to the first magnetization.
[0009] According to the system and method disclosed herein, the
present invention provides a spin valve utilizing a synthetic free
layer and which has reduced asymmetry. Furthermore, the amplitude
of the magnetoresistive signal is improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a diagram of a magnetoresistive head.
[0011] FIG. 2A is a diagram of a synthetic spin valve having a
transverse pinned layer.
[0012] FIG. 2B is another view of the synthetic spin valve having a
transverse pinned layer.
[0013] FIG. 3 is a flow chart of a conventional method for
providing the synthetic spin valve having a transverse pinned
layer.
[0014] FIG. 4A is a diagram of a MR head including a spin valve
having a canted synthetic pinned layer in accordance with the
present invention.
[0015] FIG. 4B is another view of the synthetic spin valve having a
pinned layer in accordance with the present invention.
[0016] FIG. 5A is a flow chart depicting one embodiment of a method
for providing a synthetic spin valve having a synthetic pinned
layer.
[0017] FIG. 5B is a flow chart depicting a preferred embodiment of
a method for providing the synthetic pinned layer having a canted
magnetization.
[0018] FIG. 6 is a graph depicting the modeled transfer curves for
various pinning angles.
[0019] FIG. 7 is a graph depicting the track average amplitude and
track average amplitude asymmetry versus pinning angle.
[0020] FIG. 8A is a histogram depicting the asymmetry for a
synthetic spin valve having a transverse pinned layer.
[0021] FIG. 8B is a histogram depicting the asymmetry for a spin
valve using a synthetic pinned layer in accordance with the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The present invention relates to an improvement in spin
valves which include synthetic pinned layers. The following
description is presented to enable one of ordinary skill in the art
to make and use the invention and is provided in the context of a
patent application and its requirements. Various modifications to
the preferred embodiment will be readily apparent to those skilled
in the art and the generic principles herein may be applied to
other embodiments. Thus, the present invention is not intended to
be limited to the embodiment shown, but is to be accorded the
widest scope consistent with the principles and features described
herein.
[0023] FIG. 1 is a block diagram of a magnetoresistance ("MR") head
10. The MR head includes a first shield 14 formed on a substrate
12. The MR head 10 also includes a first gap 16 separating a MR
sensor 30 from the first shield 14. The MR head 10 also includes a
pair of hard bias layers 18a and 18b. The hard bias layers 18a and
18b magnetically bias layers in the MR element 30. The MR head 10
also includes lead layers 19a and 19b, which conduct current to and
from the MR element 30. A second gap 20 separates the MR sensor 30
from a second shield 22. When brought in proximity to a recording
media (not shown), the MR head 10 reads data based on a change in
the resistance of the MR sensor 30 due to the field of the
recording media.
[0024] In conventional systems, the MR sensor 30 is a spin valve,
which senses magnetically stored data using giant magnetoresistance
("GMR"). FIG. 2A depicts a synthetic spin valve 30' which uses a
synthetic pinned layer that is pinned in the transverse direction.
The synthetic spin valve 30' will be referred to as "a synthetic
spin valve having a transverse pinned layer." FIG. 2B depicts a
portion of the synthetic spin valve having a transverse pinned
layer. Referring to FIG. 2A, the conventional spin valve 30'
typically includes a seed layer 31, an antiferromagnetic ("AFM")
layer 32, a synthetic pinned layer 34 ("transverse synthetic pinned
layer 34"), a spacer layer 36, a free layer 38, and a capping layer
40. The transverse synthetic pinned layer 34 includes magnetic
layers 33 and 37 separated by a nonmagnetic layer 35. The magnetic
layers 33 and 37 are separated by a distance such that the layers
33 and 37 are antiferromagnetically coupled. The seed layer is used
to ensure that the material used for the AFM layer 32 has the
appropriate crystal structure and is antiferromagnetic in nature.
The spacer layer 36 is a nonmagnetic metal, such as copper. The
transverse synthetic pinned layer 34 and the free layer 38 are
magnetic layers. The magnetization of the transverse synthetic
pinned layer 34 is pinned in place due to an exchange coupling
between the AFM layer 32 and the synthetic pinned layer 34. The
magnetization of the free layer 38 is free to rotate.
[0025] Referring again to FIGS. 2A and 2B, the magnetization of the
transverse synthetic pinned layer 34 is transverse, approximately
ninety degrees from the longitudinal direction. Because the
transverse synthetic pinned layer 34 is composed of the
antiferromagnetically coupled magnetic layers 33 and 37, the
magnetization of the transverse synthetic pinned layer 34 is more
securely pinned in the desired direction. Therefore, the magnetic
structure of the tranverse synthetic pinned layer 34 is more stable
than a conventional spin valve.
[0026] FIG. 3 depicts a conventional method 50 for providing the
synthetic spin valve having a transverse pinned layer 30'. The
optional seed layer 31 and AFM layer 32 are provided, via step 52.
The transverse synthetic pinned layer 34 having its magnetization
pinned in the transverse direction is provided, via step 54. Step
54 includes depositing the transverse synthetic pinned layer 34,
then annealing the transverse synthetic pinned layer 34 in a large
field that is in the transverse direction. The spacer layer 36 is
then typically provided, via step 56. The free layer 38 is then
provided, via step 38. The capping layer 40 may then be provided,
via step 60.
[0027] Although the synthetic spin valve having a transverse pinned
layer shown in FIGS. 2A and 2B and made in accordance with the
method shown in FIG. 3 functions, one of ordinary skill in the art
will readily realize that the synthetic spin valve having a
transverse pinned layer 30' has an asymmetric response. The
magnetization of the free layer 38 is desired to be longitudinal,
in the direction that current flows between the leads 19a and 19b
of FIG. 1. Referring back to FIGS. 2A and 2B, the net magnetization
of the transverse synthetic pinned layer 34 is reduced because it
includes antiferromagnetically coupled layers 33 and 37. Because of
the reduced magnetic moment of the transverse synthetic pinned
layer 34, the magnetization of the free layer 38 is tilted from
longitudinal when no external magnetic field is applied. This tilt
is depicted in FIG. 2B. Referring back to FIGS. 2A and 2B, if the
transverse synthetic pinned layer 34 did not have a reduced
magnetization, the interlayer coupling between the transverse
synthetic pinned layer 34 and the free layer 38, the
demagnetization field of the transverse synthetic pinned layer 34,
and the magnetic field due to the bias current driven through the
synthetic spin valve 30' having a transverse pinned layer 34 would
ensure that the magnetization of the free layer was biased in the
longitudinal direction. However, because the transverse synthetic
pinned layer 34 has a reduced magnetization, these magnetic fields
do not longitudinally bias the magnetization of the free layer
38.
[0028] Because the magnetization of the free layer 34 is tilted
from the longitudinal direction, an external magnetic field in one
direction will cause a greater rotation in the magnetization from
the longitudinal direction than an external magnetic field in the
opposite direction. The difference in directions of magnetization
between the transverse synthetic pinned layer 34 and the free layer
38 determines the MR and, therefore, the response of the synthetic
spin valve 30' having a transverse pinned layer 34 to an external
field. Thus, the response of the synthetic spin valve 30' having a
transverse pinned layer 34 to a magnetic recording media will be
asymmetric. Asymmetries in the response of the synthetic spin valve
30' having a transverse pinned layer 34 are undesirable. When the
asymmetry is large enough, the synthetic spin valve 30' having a
transverse pinned layer 34 is unusable.
[0029] The present invention provides a method and system for
providing a spin valve for use in a magnetoresistive head. The
method and system comprise providing a synthetic pinned layer, a
nonmagnetic spacer layer, and a free layer. The free layer has a
first magnetization canted from a first direction by a first angle.
The nonmagnetic spacer layer is disposed between the free layer and
the synthetic pinned layer. The synthetic pinned layer has a second
magnetization in a second direction. The second direction is canted
from a third direction that is transverse to the first direction by
a second angle. The second magnetization is substantially
orthogonal to the first magnetization.
[0030] The present invention will be described in terms of a
particular embodiment of a spin valve that includes particular
materials. The present invention will also be described in the
context of a particular method for providing the spin valve.
However, one of ordinary skill in the art will readily recognize
that this method and system will operate effectively for other
materials and other methods for providing the spin valve.
[0031] To more particularly illustrate the method and system in
accordance with the present invention, refer now to FIG. 4A,
depicting one embodiment of a spin valve 100 in accordance with the
present invention. The spin valve 100 could be used as the MR
sensor 30 in the MR head 10 depicted in FIG. 1. FIG. 4B depicts a
portion of the spin valve 100 in accordance with the present
invention. Referring to FIG. 4A, the spin valve 100 includes an
optional seed layer 102, an AFM layer 104, a synthetic pinned layer
110 in accordance with the present invention, a nonmagnetic spacer
layer 120, a free layer 122, and an optional capping layer 124. The
synthetic pinned layer 110 includes magnetic layers 112 and 116
separated by a nonmagnetic layer 114, such as Ru. The magnetic
layers 112 and 116, which preferably include CoFe, are separated by
a distance such that the magnetic layers 112 and 116 are
antiferromagnetically coupled. The spacer layer 120 is a
nonmagnetic metal, such as copper. The synthetic pinned layer 110
and the free layer 122 are magnetic layers. In one embodiment, the
free layer is a layer of NiFe. In another embodiment, the free
layer 122 could be a multilayer, such as a multilayer including
layers of CoFe and NiFe. The magnetization of the synthetic pinned
layer 110 is pinned in place due to an exchange coupling between
the AFM layer 104 and the synthetic pinned layer 110. The AFM layer
could include IrMn, PtMn, or PtPdMn. Although magnetically biased,
as discussed below, the magnetization of the free layer 122 is free
to rotate in response to an external field, for example from a
recording media.
[0032] Referring to FIGS. 4A and 4B, the magnetization of the free
layer 122 is biased generally in a longitudinal direction LD. The
magnetization of the free layer 122 is, however, canted from being
exactly in the longitudinal direction LD. In this respect, the spin
valve 100 is similar to the spin valve 30' having the transverse
pinned layer. However, the magnetization of the synthetic pinned
layer 110 is also canted from a transverse direction TD. In one
embodiment, the magnetization of the synthetic pinned layer 110 is
canted by at least approximately plus or minus ten degrees from the
transverse direction. Thus, the angle, .THETA., is at least ten
degrees in the direction shown, or in the opposite direction from
the transverse direction. In a preferred embodiment, the synthetic
pinned layer 110 is canted by approximately plus or minus thirty
degrees from the transverse direction. However, nothing prevents
the synthetic pinned layer 110 from being canted at another angle
from the transverse direction. Also in a preferred embodiment, the
magnetization of the synthetic pinned layer 110 is canted from the
transverse direction by approximately the same angle that the
magnetization of the free layer 122 is canted from the longitudinal
direction.
[0033] Because the magnetization of the pinned layer 110 is canted
at an angle from the transverse direction, the magnetization of the
free layer 122 is substantially orthogonal to the magnetization of
the pinned layer 110 when no external field is applied. Thus, the
demagnetization field of the synthetic pinned layer 110, the
interlayer coupling between the synthetic pinned layer 110 and the
free layer 122, and the bias current driving the spin valve 100
during use combine to bias the magnetization of the free layer 122
substantially perpendicular to the magnetization of the pinned
layer 110.
[0034] Because the free layer 122 is substantially perpendicular to
the magnetization of the pinned layer 110 in the absence of an
external field, the asymmetry in the response of the free layer 122
is reduced. The response of the spin valve 100 depends upon the
angle between the magnetization of the free layer 122 and the
pinned layer 110. The magnetizations of the free layer 122 and the
pinned layer 110 in the absence of an external field are
orthogonal. As a result, the magnitude of the angle between the
magnetization of the free layer 122 and the pinned layer 100 is
approximately the same for external fields of the same magnitude
but opposite directions. In other words, the relative angle between
the magnetization of the free layer 122 and the magnetization of
the pinned layer 110 is the same for media fields in both
directions. The response of the spin valve 100 has, therefore,
approximately the same magnitude for media fields in opposite
directions. Consequently, the MR of the spin valve 100 is
substantially symmetric, which is desirable.
[0035] FIG. 5A depicts on embodiment of a method 200 in accordance
with the present invention for providing the spin valve 100. The
optional seed layer 102 and AFM layer 104 are provided, via 202.
The synthetic pinned layer 110 having its magnetization pinned in a
direction that is canted from the transverse direction is then
provided, via step 210. The spacer layer 120 is provided, via step
220. The free layer 122 is provided, via step 222. The
magnetization of the free layer 122 is substantially in the
longitudinal direction. The optional capping layer 124 may then be
provided, via step 224.
[0036] FIG. 5B depicts a preferred embodiment of the step 210,
providing the synthetic pinned layer 110 having its magnetization
pinned in a direction that is canted from the transverse direction.
The synthetic pinned layer 110 is deposited, via step 212.
Preferably, step 212 includes depositing the first magnetic layer
112, depositing the nonmagnetic layer 114, then depositing the
second magnetic layer 116. The synthetic pinned layer 110 is then
annealed in a magnetic field in a direction canted from the
transverse direction, via step 214. In a preferred embodiment, this
will result in the magnetization of the synthetic pinned layer 110
being in substantially the same direction as the magnetic field
used in annealing. Thus, a sufficiently large field is desired to
be used in step 214. In one embodiment, the magnetic field is at
least 10,000 Oe. In one embodiment, the desired direction is
achieved by rotating the substrates on which the spin valves 100
are formed in a magnetic field that is otherwise set to be in a
transverse direction. In another embodiment, the direction of the
magnetic field may be rotated. However, in either case, the desired
direction of the magnetization of the pinned layer, canted from the
transverse direction by approximately ten degrees or more, can
easily be achieved.
[0037] Note, however, that nothing prevents the use of another
method for obtaining the desired direction for the magnetization of
the pinned layer 110. For example, the desired direction could be
obtained by annealing the synthetic pinned layer 110 in a lower
magnetic field that is in the transverse direction. For example, a
field of six thousand Oe rather than ten thousand Oe may be used.
If the magnetic field is sufficiently low, the magnetization of the
synthetic pinned layer 110 will only be partially aligned by the
annealing step. Thus, the magnetization of the synthetic pinned
layer 100 may be canted from the transverse direction by ten
degrees or more. However, this method is significantly more
difficult to control than the method 210 depicted in FIG. 5B.
[0038] FIGS. 6-9 depict the differences between embodiments of the
spin valve 100 and the synthetic spin valve having a transverse
pinned layer 30'. FIG. 6 depicts the modeled track average
amplitude ("TAA") versus media Mrt for the canted synthetic pinned
layer 110 or the transverse synthetic pinned layer 34. The TAA is
the peak to peak amplitude of the signal for a particular spin
valve. The Mrt for a media is the remanence magnetization
multiplied by the thickness. The curves in FIG. 6 are for spin
valves having angles of sixty, seventy, eighty, and ninety degrees
between the free layer and the synthetic pinned layer. Thus, the
spin valves having angles of sixty, seventy, or eighty degrees are
embodiments of the spin valve 100 in accordance with the present
invention. The spin valve having an angle of ninety degrees
corresponds to the synthetic spin valve 30' having a transverse
pinned layer 34. As can be seen in FIG. 6, the curves for spin
valves 100 having angles of sixty, seventy, or eighty degrees are
more symmetric.
[0039] FIG. 7 depicts the modeled TAA and track average amplitude
asymmetry ("TAAA") versus angle between the net magnetization of
the synthetic pinned layer 110 or 34 and the longitudinal direction
LD, shown in FIG. 4B. The TAAA is defined as (maximum
signal-minimum signal)/(maximum signal+minimum signal). An angle of
ninety degrees corresponds to the synthetic spin valve 30' having a
transverse pinned layer 34, while an angle other than ninety
degrees corresponds to an embodiment of the spin valve 100. As can
be seen in FIG. 7, the TAAA is reduced for embodiments of the spin
valve 100. In addition, the TAA is higher for embodiments of the
spin valve 100 having angles of sixty, seventy, or eighty degrees.
Thus, not only is asymmetry improved, but the amplitude is also
improved. Note that if free layer of the spin valve in accordance
with the present invention is initialized in the opposite
direction, the TAAA will be different. However, the principle of
operation remains unchanged.
[0040] FIGS. 8A and 8B depicted histograms of the TAAA in
percentage versus the frequency of occurrence for the conventional
spin valve 30' and the spin valve 100, respectively. As can be seen
in FIGS. 8A and 8B, there is a much higher number of spin valves
100 having close to zero TAAA than for the synthetic spin valve 30'
having a transverse pinned layer 34. Furthermore, if it is assumed
that plus or minus fifteen percent TAAA is unacceptable for use, as
is typically the case, a significantly higher number of
conventional spin valve 30' will be discarded as unusable. Thus,
the spin valves 30' also have a higher yield.
[0041] Furthermore, the method 200 results in the improved spin
valves 100 and yield without significantly complicating processing
of the spin valve 100. The reduced asymmetry (TAAA), improved
amplitude in some cases (TAA) and improved yield can be achieved
simply by rotating the direction of the applied field during
annealing, as discussed with respect to FIG. 5B. This procedure is
relatively simple and does not significantly complicate the process
for fabricating a spin valve, yet results in significant
improvement in performance. Consequently, the benefits of the spin
valve 100 may be relatively easily achieved.
[0042] A method and system has been disclosed for providing a spin
valve having a synthetic pinned layer that also has reduced
asymmetry. Although the present invention has been described in
accordance with the embodiments shown, one of ordinary skill in the
art will readily recognize that there could be variations to the
embodiments and those variations would be within the spirit and
scope of the present invention. Accordingly, many modifications may
be made by one of ordinary skill in the art without departing from
the spirit and scope of the appended claims.
* * * * *