U.S. patent application number 14/946069 was filed with the patent office on 2017-03-23 for spin hall effect magnetic structures.
The applicant listed for this patent is Regents of the University of Minnesota. Invention is credited to Mahdi Jamali, Angeline Klemm Smith, Jian-Ping Wang, Zhengyang Zhao.
Application Number | 20170082697 14/946069 |
Document ID | / |
Family ID | 58277092 |
Filed Date | 2017-03-23 |
United States Patent
Application |
20170082697 |
Kind Code |
A1 |
Wang; Jian-Ping ; et
al. |
March 23, 2017 |
SPIN HALL EFFECT MAGNETIC STRUCTURES
Abstract
An article may include a substantially perpendicularly
magnetized free layer having a first magnetic orientation in the
absence of an applied magnetic field. The article may also include
a spin Hall channel layer configured to conduct a spin current
configured to subject the perpendicularly magnetized free layer to
a magnetic switching torque and a substantially in-plane magnetized
bias layer configured to bias the substantially perpendicularly
magnetized free layer to a second magnetic orientation. The second
magnetic orientation is different than the first magnetic
orientation and is out of a plane of the substantially
perpendicularly magnetized free layer.
Inventors: |
Wang; Jian-Ping; (Shoreview,
MN) ; Smith; Angeline Klemm; (New Brighton, MN)
; Jamali; Mahdi; (Minneapolis, MN) ; Zhao;
Zhengyang; (Minneapolis, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Regents of the University of Minnesota |
Minneapolis |
MN |
US |
|
|
Family ID: |
58277092 |
Appl. No.: |
14/946069 |
Filed: |
November 19, 2015 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62220740 |
Sep 18, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 43/04 20130101;
G01R 33/077 20130101; G01R 33/075 20130101; H01L 43/06 20130101;
G01R 33/1284 20130101 |
International
Class: |
G01R 33/07 20060101
G01R033/07 |
Goverment Interests
GOVERNMENT SUPPORT
[0002] This invention was made with government funds under
Agreement No. HR0011-13-3-0002 awarded by DARPA. The U.S.
Government has rights in this invention.
Claims
1. An article comprising: a substantially perpendicularly
magnetized free layer having a first magnetic orientation in the
absence of an applied magnetic field; a spin Hall channel layer
configured to generate a spin current configured to subject the
perpendicularly magnetized free layer to a magnetic switching
torque; and a substantially in-plane magnetized bias layer
configured to bias the substantially perpendicularly magnetized
free layer to a second magnetic orientation that is different than
the first magnetic orientation, wherein the second magnetic
orientation is out of a plane of the substantially perpendicularly
magnetized free layer.
2. The article of claim 1, wherein the substantially
perpendicularly magnetized free layer is disposed between the
substantially in-plane magnetized bias layer and the spin Hall
channel layer and is dipole-coupled to the substantially in-plane
magnetized bias layer.
3. The article of claim 1, wherein the substantially
perpendicularly magnetized free layer is disposed adjacent the spin
Hall channel layer.
4. The article of claim 1, wherein the substantially in-plane
magnetized bias layer is disposed between the substantially
perpendicularly magnetized free layer and the spin Hall channel
layer.
5. The article of claim 4, further comprising a spacer layer
between the substantially perpendicularly magnetized free layer and
the substantially in-plane magnetized bias layer, wherein the
spacer layer has a predetermined thickness to control exchange
coupling between the substantially perpendicularly magnetized free
layer and the substantially in-plane magnetized bias layer.
6. The article of claim 4, wherein the substantially in-plane
magnetized bias layer is disposed adjacent the spin Hall channel
layer.
7. The article of claim 4, wherein the spacer layer comprises a
material that exhibits spin current polarization.
8. The article of claim 1, further comprising a substantially
perpendicularly magnetized pinned layer and an insulating barrier
layer between the substantially perpendicularly magnetized pinned
layer and the substantially perpendicularly magnetized free
layer.
9. An article comprising: an anisotropically graded free magnetic
layer; and a spin Hall channel layer configured to generate a spin
current configured to modify the magnetic orientation of the
anisotropically graded free magnetic layer.
10. The article of claim 9, wherein the anisotropic graded magnetic
layer exhibits a magnetic anisotropy gradient that varies from a
substantially perpendicular magnetic anisotropy at a surface
opposite the spin Hall channel layer to a non-perpendicular
magnetic anisotropy at a surface adjacent to the spin Hall channel
layer.
11. The article of claim 9, wherein the anisotropic graded magnetic
layer comprises at least one of a Heusler alloy,
Fe.sub.xPt.sub.1-x, or Fe.sub.xPd.sub.1-x, wherein x is between
about 0.4 and about 0.7.
12. The article of claim 9, further comprising a substantially
perpendicularly magnetized pinned layer and an insulating barrier
layer between the substantially perpendicularly magnetized pinned
layer and the anisotropically graded free magnetic layer.
13. A method comprising: biasing a substantially perpendicularly
magnetized free layer from a first magnetic orientation to a second
magnetic orientation that is different than the first magnetic
orientation by exerting a stray magnetic field from a substantially
in-plane magnetized bias layer on the substantially perpendicular
magnetized free layer, wherein the second magnetic orientation is
out of a plane of the substantially perpendicularly magnetized free
layer, and wherein the substantially perpendicularly magnetized
free layer has the first magnetic orientation in the absence of an
applied magnetic field; and generating a spin current through a
spin Hall channel layer to subject the substantially
perpendicularly magnetized free layer to a magnetic switching
torque.
14. The method of claim 13, wherein the substantially
perpendicularly magnetized free layer is disposed between the
substantially in-plane magnetized bias layer and the spin Hall
channel layer and is dipole-coupled to the substantially in-plane
magnetized bias layer.
15. The method of claim 13, wherein the substantially in-plane
magnetized bias layer is disposed between the perpendicularly
magnetized layer and the spin Hall channel layer, and wherein a
spacer layer having a predetermined thickness to facilitate
exchange-spring coupling between the substantially perpendicularly
magnetized free layer and the substantially in-plane magnetized
bias layer is disposed between the substantially perpendicularly
magnetized free layer and the substantially in-plane magnetized
bias layer.
16. The method of claim 13, further comprising switching the
substantially perpendicularly magnetized free layer from the first
magnetic orientation to the second magnetic orientation by
generating the spin current.
17. A method comprising: generating a spin current through a spin
Hall channel layer disposed adjacent an anisotropically graded free
magnetic layer, wherein the anisotropically graded magnetic layer
exhibits a magnetic anisotropy gradient that varies from
substantially perpendicular magnetic anisotropy at a surface
opposite the spin Hall channel layer to non-perpendicular magnetic
anisotropy at a surface adjacent to the spin Hall channel
layer.
18. The method of claim 17, further comprising switching the
anisotropically graded free magnetic layer from a first magnetic
configuration to a second magnetic configuration by generating the
spin current.
19. A method comprising: depositing a substantially perpendicularly
magnetized free layer over a spin Hall channel layer; depositing a
spacer layer on the substantially perpendicularly magnetized free
layer; and depositing a substantially in-plane magnetized bias
layer over the spacer layer, wherein the substantially
perpendicularly magnetized free layer is dipole-coupled to the
substantially in-plane magnetized bias layer, and wherein the
substantially in-plane magnetized bias layer is configured to
magnetically bias the substantially perpendicularly magnetized free
layer.
20. A method comprising: depositing a substantially in-plane
magnetized bias layer over a spin Hall channel layer; depositing a
spacer layer on the substantially in-plane magnetized bias layer;
and depositing a substantially perpendicularly magnetized free
layer on the spacer layer, wherein the spacer layer has a
predetermined thickness to control a strength of exchange coupling
between the substantially perpendicularly magnetized free layer and
the substantially in-plane magnetized bias layer.
Description
[0001] This application claims the benefit of Provisional U.S.
Patent Application No. 62/220,740, titled "SPIN HALL EFFECT
MAGNETIC STRUCTURES," filed 18 Sep. 2015, the entire content of
which is incorporated herein by reference.
TECHNICAL FIELD
[0003] This disclosure relates to articles including magnetic
structures that exhibit the spin Hall effect.
BACKGROUND
[0004] The scaling of conventional semiconductor devices may be
limited by factors including device reliability and increased power
consumption Improvement in the performance of memory and
computational devices is continuously pursued. Spin-based or
spintronic devices may be used as alternatives to or in conjunction
with electronic devices. Spin-based effects may be used by devices
such as spintronic devices that harness the intrinsic spin of
electrons and their associated magnetic moments, in addition to
electronic phenomena that arise from the fundamental electronic
charges of electrons. Magnetic structures may be used in spintronic
devices including memory and computational devices. For example,
memory devices such as magnetic random access memory (MRAM) or
spin-transfer torque random access memory (STT-RAM) may be based on
the relative magnetic orientation of multiple magnetic layers.
Computational devices such as spin logic or spin neuron device also
may be based on these layers. Reliable and cost-effective
fabrication of memory and computational devices using integrated
magnetic structures continues to pose difficulties.
SUMMARY
[0005] In some examples, the disclosure describes an article
including a substantially perpendicularly magnetized free layer
having a first magnetic orientation in the absence of an applied
magnetic field. The article includes a spin Hall channel layer
configured to generate a spin current configured to subject the
perpendicularly magnetized free layer to a magnetic switching
torque. The article also includes a substantially in-plane
magnetized bias layer configured to bias the substantially
perpendicularly magnetized free layer to a second magnetic
orientation that is different than the first magnetic orientation.
The second magnetic orientation is out of a plane of the
substantially perpendicularly magnetized free layer.
[0006] In some examples, the disclosure describes an article
including an anisotropically graded free magnetic layer and a spin
Hall channel layer configured to generate a spin current configured
to modify the magnetic orientation of the anisotropically graded
free magnetic layer.
[0007] In some examples, the disclosure describes a technique
including biasing a substantially perpendicularly magnetized free
layer from a first magnetic orientation to a second magnetic
orientation that is different than the first magnetic orientation
by exerting a stray magnetic field from a substantially in-plane
magnetized bias layer on the substantially perpendicular magnetized
free layer. The second magnetic orientation may be out of a plane
of the substantially perpendicularly magnetized free layer, and the
substantially perpendicularly magnetized free layer may have the
first magnetic orientation in the absence of an applied magnetic
field. The technique also may include generating a spin current
through a spin Hall channel layer to subject the substantially
perpendicularly magnetized free layer to a magnetic switching
torque.
[0008] In some examples, the disclosure describes a technique
including generating a spin current through a spin Hall channel
layer disposed adjacent an anisotropically graded free magnetic
layer. The anisotropic graded magnetic layer exhibits a magnetic
anisotropy gradient that varies from substantially perpendicular
magnetic anisotropy at a surface opposite the spin Hall channel
layer to non-perpendicular magnetic anisotropy at a surface
adjacent to the spin Hall channel layer.
[0009] In some examples, the disclosure describes a technique
including depositing a substantially perpendicularly magnetized
free layer over a spin Hall channel layer. The example technique
also includes depositing a spacer layer over the substantially
perpendicularly magnetized free layer. The example technique also
includes depositing a substantially in-plane magnetized bias layer
over the spacer layer. The substantially perpendicularly magnetized
free layer is dipole-coupled to the substantially in-plane
magnetized bias layer. The substantially in-plane magnetized bias
layer is configured to magnetically bias the substantially
perpendicularly magnetized free layer.
[0010] In some examples, the disclosure describes a technique
including depositing a substantially in-plane magnetized bias layer
over a spin Hall channel layer and depositing a spacer layer on the
substantially in-plane magnetized bias layer. The example technique
also includes depositing a substantially perpendicularly magnetized
free layer on the spacer layer. The spacer layer has a
predetermined thickness to tune a strength of exchange coupling
between the substantially perpendicularly magnetized free layer and
the substantially in-plane magnetized bias layer.
[0011] The details of one or more examples are set forth in the
accompanying drawings and the description below. Other features,
objects, and advantages will be apparent from the description and
drawings, and from the claims.
BRIEF DESCRIPTION OF DRAWINGS
[0012] FIG. 1 is a conceptual and schematic block diagram
illustrating an example spin Hall channel generating a spin
current.
[0013] FIGS. 2A and 2B are conceptual and schematic block diagrams
illustrating example articles including a substantially in-plane
magnetized bias layer coupled to a substantially perpendicularly
magnetized free layer.
[0014] FIG. 3A is a conceptual and schematic block diagram
illustrating an example article including a spin Hall channel layer
and an anisotropically graded free magnetic layer.
[0015] FIG. 3B is an enlarged illustration of the anisotropically
graded free magnetic layer of FIG. 3A.
[0016] FIG. 4 is a flow diagram illustrating an example technique
for switching a substantially perpendicularly magnetized free
layer.
[0017] FIG. 5 is a flow diagram illustrating an example technique
for preparing a magnetic structure including a spin Hall channel
layer.
[0018] FIG. 6 is a flow diagram illustrating an example technique
for preparing a magnetic structure including a spin Hall channel
layer.
[0019] FIG. 7A is a conceptual and schematic block diagram
illustrating an example magnetic structure dipole coupled with a
spin Hall channel layer.
[0020] FIG. 7B is an enlarged conceptual diagram illustrating the
magnetic structure of FIG. 7A.
[0021] FIG. 8A is a chart presenting vibrating sample magnetometer
measurements for the example structures of FIGS. 7A and 7B and a
reference structure.
[0022] FIG. 8B is a chart presenting a small field scan of the
example structures of FIGS. 7A and 7B and a reference
structure.
[0023] FIG. 9A is a chart presenting the anomalous Hall resistance
as a function of perpendicular field strength for a reference
structure.
[0024] FIG. 9B is a chart presenting the anomalous Hall resistance
as a function of perpendicular field strength for the example
structure of FIG. 7A.
[0025] FIG. 9C is a chart presenting spin current induced
magnetization switching of the example structure of 7A, in the
absence of an externally applied field.
DETAILED DESCRIPTION
[0026] The spin Hall effect (SHE) is a technique for generating a
spin current by passing a charge current through a non-magnetic
material utilizing spin-orbit interactions. FIG. 1 is a conceptual
and schematic block diagram illustrating an example spin Hall
channel generating a spin current. Input current 160 may be
injected into a spin Hall channel 120 (for example, a tantalum
layer). Spin-orbit coupling (SOC) splits the electrons from the
input charge current 160 according to their spin direction. For
example, electrons 124 with up-spin accumulate on one surface, for
example, the top surface 122 of the spin Hall channel 120, and
electrons 128 with down-spin accumulate on the other surface, for
example, the bottom surface 126 of the spin Hall channel 120. The
aligned spin may then exert a torque on a neighboring magnetic
structure (140) and may result in changes in magnetization of the
magnetic structure 140, for example, switching of a magnetic
orientation of a magnetic layer in magnetic structure 140. For
example, as shown in FIG. 1, the input charge current 160 may be
spin polarized in the Y-axis direction, which may exert on a
perpendicularly magnetized layer with magnetic orientation in the
Z-direction a spin Hall magnetic torque in the .+-.X-axis direction
(a cross product of the vector representing the spin polarization
and the vector representing the magnetization). In the case of
in-plane magnetized materials, the spin Hall effect may be
sufficient to cause even a reversal in magnetic orientation.
However, in the case of perpendicularly magnetized materials, the
application of an in-plane field may be required in addition to the
spin Hall current in order to break symmetry and achieve
deterministic switching using the spin Hall effect. Using
perpendicularly magnetized materials may help scale SHE devices for
high density and thermally stable memory applications, due to high
magnetic anisotropy values, and may achieve switching without an
external field, in contrast with conventional devices, which cannot
be switched without using an external field.
[0027] The spin Hall effect may be used to overcome problems such
as dielectric breakdown of the tunnel barrier at high current
densities required for write operations. For example, unlike in the
case of a STT-RAM cell in which current for writing is required to
pass through a high resistance tunnel barrier, in SHE devices, the
write current may not pass through a magnetic structure and may
instead only pass through the spin Hall channel adjacent a magnetic
layer or structure 140 (FIG. 1). Therefore, SHE memory devices may
be more reliable compared to STT-RAM. Moreover, due to the lower
resistivity of metals, less Joule heating may be involved during
the write process and utilizing the SHE may save energy compared to
STT-RAM. Additionally, since the read and write passes are
different, they can be independently optimized for better
performance. Spin Hall effect based devices may be more efficient
than STT-RAM due to geometrical gain of the spin Hall effect
magnetic torque.
[0028] The present disclosure describes switching, for example, a
reversal of magnetic orientation of a perpendicularly magnetized
layer in a magnetic structure, for example a CoFeB composite
structure, using the SHE, without an externally generated magnetic
field. Previous techniques for achieving switching in
perpendicularly magnetized materials without the assistance of an
externally applied field may utilize a wedge structure to achieve
external-field free switching. However, using wedge structures
limits scalability due to difficulty creating and reliably
controlling the wedge structure at the required dimensions for high
memory density and at wafer scale. Wedge structures also create
difficulties in preparing complex material stacks such as those
used in magnetic tunnel junctions (MTJ). The disclosure describes
magnetic structures that do not include a wedge structure, which
may allow advantages including uniform thickness and design across
the device and integration with full MTJ stacks.
[0029] FIG. 2A is a conceptual and schematic block diagram
illustrating an example article 200a including a substantially
in-plane magnetized bias layer 280 dipole coupled to a
substantially perpendicularly magnetized free layer 242. An article
200a includes a substantially perpendicularly magnetized free layer
242 having a first magnetic orientation in the absence of an
applied magnetic field. The substantially perpendicularly
magnetized free layer 242 includes a magnetic material formed in
such a manner to allow a magnetic moment of the layer to change
from the first magnetic orientation to another magnetic
orientation, for example, under the influence of a stray field or
under the influence of spin torque from exerted by spin polarized
current generated through spin Hall channel layer 220. The
substantially perpendicularly magnetized free layer 242 may be
formed so that its magnetic moment is oriented in the first
magnetic orientation in the absence of an external magnetic field,
for example, in a magnetically stable state. In some examples first
magnetic orientation is substantially parallel to the magnetic easy
axis of substantially perpendicularly magnetized free layer 242. In
the example shown in FIG. 2A, the first magnetic orientation is
substantially perpendicular to a major plane of the substantially
perpendicularly magnetized free layer 242, for example,
substantially perpendicular to the plane of the film layers of the
substantially perpendicularly magnetized free layer 242. For
example, the first magnetic orientation may be exactly at an angle
of 90.degree., or may slightly deviate from 90.degree., for
example, the first magnetic orientation may be within a in a range
of 90.degree..+-.10.degree., or 90.degree..+-.56.degree., or
90.degree..+-.3.degree., or 90.degree..+-.1.degree., or
90.degree..+-.0.5.degree., or 90.degree..+-.0.1.degree., or of from
about 80.degree., or from about 83.degree., or from about
85.degree., or from about 87.degree., or from about 89.degree., or
from about 89.5.degree., or from about 89.9.degree., to about
90.1.degree., or to about 90.5.degree., or to about 91.degree., or
to about 93.degree., or to about 95.degree., or to about
97.degree., or to about 100.degree..
[0030] The substantially perpendicularly magnetized free layer 242
may be formed of magnetic metals or alloys, such as, for example, a
CoFeB alloy. A thickness of the substantially perpendicularly
magnetized free layer 242 may be selected based on a number of
variables, including, for example, the expected magnitude of the
spin Hall torque, and thermal stability of the magnetic
orientation, or the like. For example, the substantially
perpendicularly magnetized free layer 242 may have a thickness of
about 1.2 nm.
[0031] Article 200a also includes spin Hall channel layer 220
configured to generate a spin current that subjects perpendicularly
magnetized free layer 242 to a magnetic switching torque. Spin Hall
channel layer 220 may include a material that exhibits spin current
polarization, for example, tantalum (Ta), chromium (Cr), bismuth
(Bi), bismuth selenide (Bi.sub.2Se.sub.3), gallium arsenide (GaAs),
indium gallium arsenide (InGaAs), tungsten (W), platinum (Pt), gold
(Au), and multilayers formed with one or more of these materials
and one or more of aluminum (Al), silver (Ag), copper (Cu), or the
like. In some examples, spin Hall channel layer 220 may have a
thickness of about 5 nm.
[0032] Article 200a also may include a substantially
perpendicularly magnetized pinned layer 246, which may be disposed
adjacent substantially perpendicularly magnetized free layer 242,
with an insulating barrier layer 230 disposed between substantially
perpendicularly magnetized pinned layer 246 and substantially
perpendicularly magnetized free layer 242. In some examples,
substantially perpendicularly magnetized pinned layer 246 may
include a magnetic material formed in a manner such that its
magnetic moment is substantially fixed in an orientation normal to
the plane of substantially perpendicularly magnetized pinned layer
246. In some examples, the magnetic moment substantially persists
in the fixed orientation even under the influence of external or
stray fields that may be experienced by substantially
perpendicularly magnetized pinned layer 246 during designed use.
For example, as shown in FIGS. 2A, a magnetic moment of
substantially perpendicularly magnetized pinned layer 246 is fixed
in a perpendicular direction (i.e., a direction normal to the major
plane of substantially perpendicularly magnetized pinned layer
246). In some examples, substantially perpendicularly magnetized
pinned layer 246 may include Fe.sub.0.5N.sub.0.5.
[0033] Insulating barrier layer 230 may include a nonmagnetic
material, such as, for example, an oxide or a dielectric material.
In some examples, insulating barrier layer 230 may act as a tunnel
barrier, for example, so that the stack of substantially
perpendicularly magnetized pinned layer 246 and substantially
perpendicularly magnetized free layer 242 forms a magnetic tunnel
junction. Insulating barrier layer 230 may be formed of a tunnel
barrier material, for example, MgO or the like. In some examples,
insulating barrier layer 230 may be sufficiently thin to allow
electrons to tunnel across insulating barrier layer 230. For
example, insulating barrier layer 230 may have a thickness of about
2 nm.
[0034] In some examples, article 200a further includes an
antiferromagnetic layer 250, which may be disposed adjacent
substantially perpendicularly magnetized pinned layer 246, and
serves to pin the magnetic moment of substantially perpendicularly
magnetized pinned layer 246 through antiferromagnetic coupling.
[0035] In some examples, article 200a also includes a capping layer
260, which may be disposed adjacent the magnetic tunnel junction
stack, or adjacent the antiferromagnetic layer 250. As shown in
FIG. 2A, in some examples, substantially in-plane magnetized bias
layer 280 is disposed on capping layer 260.
[0036] Article 200a also includes a substantially in-plane
magnetized bias layer 280. The substantially in-plane magnetized
bias layer 280 may exert a stray magnetic field effective to bias
substantially perpendicularly magnetized free layer 242 to a second
magnetic orientation that is different than the first magnetic
orientation. For example, the stray magnetic field may cause the
second magnetic orientation to be tilted away from the first
magnetic orientation even in the absence of an externally applied
magnetic field. In some examples, the second magnetic orientation
may be out of a plane of substantially perpendicularly magnetized
free layer 242, and is not perpendicular to the plane of
substantially perpendicularly magnetized free layer 242. For
example, the second magnetic orientation may be slightly different
from the first magnetic orientation, such that the second magnetic
orientation is out of the plane of the substantially
perpendicularly magnetized free layer. The deviation from the first
magnetic orientation may allow substantially perpendicularly
magnetized free layer 242 to be switched deterministically.
[0037] Substantially in-plane magnetized bias layer 280 may include
a magnetic material formed in a manner such that its magnetic
moment is substantially fixed in an orientation along the plane or
in the plane of substantially in-plane magnetized bias layer 280.
In some examples, the magnetic moment substantially persists in the
fixed orientation even under the influence of external or stray
fields that may be experienced by substantially in-plane magnetized
bias layer 280 during designed use. For example, as shown in FIG.
2A, a magnetic moment of substantially in-plane magnetized bias
layer 280 is fixed in an in-plane direction (i.e., a direction
within the major plane). However, the magnetic moment of
substantially in-plane magnetized bias layer 280 may be oriented in
a direction other than 0.degree. with respect to the plane of
substantially in-plane magnetized bias layer 280. For example, the
magnetic moment of the substantially in-plane magnetized bias layer
280 may be oriented at exactly at an angle of 0.degree. with
respect to the major plane of substantially in-plane magnetized
bias layer 280, or may be at an angle other than 0.degree., for
example, the magnetic moment may be oriented within a in a range of
0.degree..+-.10.degree., or 0.degree..+-.5.degree., or
0.degree..+-.3.degree., or 0.degree..+-.1.degree., or
0.degree..+-.0.5.degree., or 0.degree..+-.0.1.degree., or of from
about -10.degree., or from about -5.degree., or from about
-3.degree., or from about -1.degree., or from about -0.5.degree.,
or from about -0.1.degree., to about 0.1.degree., or to about
0.5.degree., or to about 1.degree., or to about 3.degree., or to
about 5.degree., or to about 10.degree. with respect to the plane
of substantially in-plane magnetized bias layer 280.
[0038] Various magnetic materials may be used for forming
substantially in-plane magnetized bias layer 280, including, for
example, cobalt-iron-boron (CoFeB) alloys, palladium/cobalt (Pd/Co)
multilayer structures, combinations thereof, or the like. The
thickness of substantially in-plane magnetized bias layer 280 may
be selected based on variables including, for example, the material
used to form substantially perpendicularly magnetized layer 242, a
thickness of the substantially perpendicularly magnetized layer
242, a thickness of spin Hall channel layer 220, separation or
spacing between a major surface of substantially in-plane
magnetized bias layer 280 and a major surface of one or both of
substantially perpendicularly magnetized fixed layer 242 and spin
Hall channel layer 220, or the like. In some examples,
substantially in-plane magnetized bias layer 280 may have a
thickness of about 3 nm.
[0039] In the absence of substantially in-plane magnetized bias
layer 280, the magnetic switching torque exerted by the
spin-polarized current generated in spin Hall channel layer 220
during a write technique may not deterministically switch a
magnetization of substantially perpendicularly magnetized layer
242. The effective torque associated with the spin Hall effect may
switch the magnetization in either a first direction or a second,
exactly opposite direction. For example, when the spin polarization
is in a transverse direction, such as along a Y-axis, the electron
current is along an X axis, and the initial magnetic orientation is
along a Z-axis (where orthogonal x-y-z axes are shown in FIG. 2A
for sake of illustration only), the effective spin Hall torque
switch the magnetization in either the X-Z plane or the negative
(-) X-Z plane. Thus, in some examples, substantially
perpendicularly magnetized free layer 242 may be dipole-coupled to
substantially in-plane magnetized bias layer 280. For example,
substantially in-plane magnetized bias layer 280 may exert a dipole
field or a stray field to bias substantially perpendicularly
magnetized layer 242 by breaking symmetry of the substantially
perpendicularly magnetized layer 242. Thus, substantially
perpendicularly magnetized layer 242 may be switched
deterministically under the influence of a switching magnetic
torque (spin torque) exerted by spin-polarized current generated in
spin Hall channel layer 220. Spin Hall channel layer 220 may not
influence the substantially in-plane magnetized bias layer 280,
since in some examples, the substantially in-plane magnetized bias
layer 280 is spaced in the Z-axis direction from spin Hall channel
layer 220 and does not contact spin Hall channel layer 220, as
shown in FIG. 2A. In some examples, substantially perpendicularly
magnetized free layer 242 is disposed between substantially
in-plane magnetized bias layer 280 and spin Hall channel layer 220,
for example, as shown in FIG. 2A. In some examples, the
substantially perpendicularly magnetized free layer 242 may be
disposed adjacent the spin Hall channel layer 220.
[0040] Electrically conductive leads may be disposed coupled to
opposite ends or side of spin Hall channel 220 to enable passing
current as required to switch the article 200a from the first
magnetic orientation to the second magnetic orientation. In some
examples, an STT-RAM device or a MTJ device may include article
200a. For example, a memory cell or a computational unit may
include article 200a.
[0041] In the example shown in FIG. 2A, substantially
perpendicularly magnetized free layer 242 is disposed between
substantially in-plane magnetized bias layer 280 and spin Hall
channel layer 220 and the substantially in-plane magnetized bias
layer 280 is dipole coupled to the substantially perpendicularly
magnetized free layer 242. In other examples, substantially
in-plane magnetized bias layer 280 may be exchange coupled to
substantially perpendicularly magnetized free layer 242, as shown
in FIG. 2B.
[0042] FIG. 2B is a conceptual and schematic block diagram
illustrating an example article 200b including substantially
in-plane magnetized bias layer 280 exchange coupled to a
substantially perpendicularly magnetized free layer 242. Similar to
article 200a of FIG. 2A, article 200b of FIG. 2B may include a spin
Hall channel layer 220, an insulating barrier layer 230, a
substantially perpendicularly magnetized free layer 242, a
substantially perpendicularly magnetized pinned layer 246, an
antiferromagnetic layer 250, and a capping layer 260, and an
substantially in-plane magnetized bias layer 280. The structure and
materials of these layers may be similar to or substantially the
same as described above with respect to FIG. 2A, aside from the
differences described herein.
[0043] Unlike article 200a of FIG. 2A, in article 200b,
substantially in-plane magnetized bias layer 280 is disposed
sufficiently close to substantially perpendicularly magnetized free
layer 242 to exchange couple the magnetic moments of substantially
in-plane magnetized bias layer 280 and substantially
perpendicularly magnetized free layer 242 near the adjacent
surfaces of substantially in-plane magnetized bias layer 280 and
substantially perpendicularly magnetized free layer 242. For
example, a spacer layer 270 may be disposed between substantially
in-plane magnetized bias layer 280 and substantially
perpendicularly magnetized free layer 242. In this way,
substantially in-plane magnetized bias layer 280 may bias the
magnetic moment of substantially perpendicularly magnetized free
layer 242 away from perpendicular, at least near the surface of
substantially perpendicularly magnetized free layer 242 near
substantially in-plane magnetized bias layer 280. Further, in some
examples, a spin polarized current generated in spin Hall channel
220 may switch an orientation of substantially in-plane magnetized
bias layer 280, which then exerts a magnetic torque on
substantially perpendicularly magnetized free layer 242. In one or
both of these ways, substantially in-plane magnetized bias layer
280, which is exchange coupled to substantially perpendicularly
magnetized layer 242, may facilitate deterministic switching of the
magnetization of substantially perpendicularly magnetized layer 242
by a spin polarized current generated in spin Hall channel 220.
[0044] In some examples, as shown in FIG. 2B, article 200b may
include spacer layer 270 between substantially in-plane magnetized
bias layer 280 and substantially perpendicularly magnetized free
layer 242. For example, spacer layer 270 may facilitate tuning of
the strength of exchange coupling between substantially
perpendicularly magnetized free layer 242 and substantially
in-plane magnetized bias layer 280. For example, a thicker spacer
layer 270 may result in weaker exchange coupling between
substantially perpendicularly magnetized free layer 242 and
substantially in-plane magnetized bias layer 280, while a thinner
spacer layer 270 may result in stronger exchange coupling between
substantially perpendicularly magnetized free layer 242 and
substantially in-plane magnetized bias layer 280. In some examples,
the thickness of spacer layer 270 may be greater than 0 nm and less
than about 1 nm. In some examples, spacer layer 270 may include a
material that exhibits spin current polarization, for example, Ta,
Ru, Cr, W, Pt, Au, Al, Ag, Cu, or the like. In some examples, the
material from which spacer layer 270 is formed may have an opposite
spin Hall angle polarity compared to the material from which spin
Hall channel layer 220 is formed. This may enhance the spin Hall
effect and facilitate switching of the magnetic moment of
substantially perpendicularly magnetized free layer 242.
[0045] Example articles including a substantially in-plane
magnetized bias layer magnetically coupled to a substantially
perpendicularly magnetized free layer have been described above.
Example articles including graded magnetic free layers are
described below.
[0046] FIG. 3A is a conceptual and schematic block diagram
illustrating an example article including a spin Hall channel layer
320 and an anisotropically graded free magnetic layer 344. Article
300 also includes an insulating barrier layer 330 on
anisotropically graded free magnetic layer 344, a substantially
perpendicularly magnetized pinned layer 346 on insulating barrier
layer 330, an antiferromagnetic layer 350 on substantially
perpendicularly magnetized pinned layer 346, and a cap layer 360 on
antiferromagnetic layer 350. Insulating barrier layer 330,
substantially perpendicularly magnetized pinned layer 346,
antiferromagnetic layer 350, and cap layer may be similar to or
substantially the same as the corresponding layers described in
FIGS. 2A and 2B.
[0047] Anisotropically graded free magnetic layer 344 may include
one or more of a Co-Pd alloy, an Fe-Pt alloy, an Fe-Pd alloy, or a
Heusler alloy. For example, anisotropically graded free magnetic
layer 344 may include Fe.sub.xPt.sub.1-x or Fe.sub.xPd.sub.1-x,
with x ranging from 0.4 to 0.7, or a Heusler alloy, such as
Cu.sub.2MnAl, Cu.sub.2MnIn, Cu.sub.2MnSn, MnBi, Ni.sub.2MnAl,
Ni.sub.2MnIn, Ni.sub.2MnSn, Ni.sub.2MnSb, Ni.sub.2MnGa,
Co.sub.2MnAl, Co.sub.2MnSi, Co.sub.2MnGa, Co.sub.2MnGe,
Pd.sub.2MnAl, Pd.sub.2MnIn, Pd.sub.2MnSn, Pd.sub.2MnSb,
Co.sub.2FeSi, Co.sub.2FeAl, Fe.sub.2Val, Mn.sub.2VGa, or
Co.sub.2FeGe. In some examples, the anisotropic graded magnetic
layer 344 may exhibit a magnetic anisotropy gradient that varies
from substantially perpendicular magnetic anisotropy at a surface
opposite spin Hall channel layer 320 to non-perpendicular magnetic
anisotropy at a surface adjacent to spin Hall channel layer 320, as
shown in FIG. 3B. FIG. 3B is an enlarged illustration of
anisotropically graded free magnetic layer 344 of FIG. 3A.
[0048] In article 300, anisotropically graded free magnetic layer
344 may exhibit a first magnetic configuration when no current is
passed through spin Hall channel layer 320, and in the absence of
an external field. The first magnetic configuration may include the
magnetic moments of the individual magnetic domains or grains
within anisotropically graded free magnetic layer 344 being
substantially parallel to their respective magnetic easy axes. For
example, the first magnetic configuration may include a first group
of magnetic domains within a first layer oriented substantially at
a first angle, a second group of magnetic domains within a second
layer oriented substantially at a second angle, and so on,
including an n-th group of magnetic domains within an n-th layer
oriented substantially at an n-th angle. In some examples, the
angle may vary from the first angle to the n-th angle, for example,
from 90.degree. to an angle that deviates from 90.degree. by
.+-.10.degree., or .+-.5.degree., or .+-.1.degree., or
.+-.0.1.degree.. When a spin polarized current is passed through
spin Hall channel layer 320, spin polarized current may exert a
magnetic switching torque effective to initiate switching of the
first group of magnetic domains, for example, in a boundary layer
near the surface of anisotropically graded free magnetic layer 344
adjacent spin Hall channel layer 320. As the angle of the first
group of magnetic domains changes, the magnetic torque from the
first group of magnetic domains, along with magnetic torque from
the spin polarized current may be sufficient to initiate switching
of the second group of magnetic domains, which may eventually
propagate to switching of the n-th group of magnetic domains.
Eventually, the entire anisotropically graded magnetic free layer
320 may switch to a second magnetic configuration including the
changed orientations of each group of magnetic domains. In some
examples, in the second magnetic configuration, the magnetic
moments of the respective magnetic domains are oriented
substantially anti-parallel to their orientations in the first
magnetic orientation. Thus, passing a current through spin Hall
channel layer 320 may switch the magnetic orientation of
anisotropically graded magnetic free layer 344 from the first
magnetic configuration to the second magnetic configuration.
[0049] FIG. 4 is a flow diagram illustrating an example technique
for switching a substantially perpendicularly magnetized free layer
using a spin polarized current generated in a spin Hall channel
layer. The technique of FIG. 4 will be described with concurrent
reference to article 200a of FIG. 2 for purposes of illustration
only, and it will be understood that other articles may implement
the technique of FIG. 4, and the article of FIG. 4 may be used to
implement other techniques. The example technique includes biasing
substantially perpendicularly magnetized free layer 242 to a second
magnetic orientation using a magnetic field from substantially
in-plane magnetized bias layer 280 (410). As described above, the
magnetic field from substantially in-plane magnetized bias layer
280 may bias the magnetic orientation of substantially
perpendicularly magnetized free layer 242 away from the first
magnetic orientation (e.g., away from the magnetic easy axis of
substantially perpendicularly magnetized free layer 242). In some
examples, the bias amount may be on the order of a few degrees. By
biasing the magnetic orientation of substantially perpendicularly
magnetized free layer 242 away from a substantially perpendicular
orientation, substantially in-plane magnetized bias layer 280 may
facilitate deterministic switching of the magnetic orientation of
substantially perpendicularly magnetized free layer 242 by the spin
polarized current generated in spin Hall channel 220.
[0050] The technique of FIG. 4 includes generating a spin polarized
current through spin Hall channel 220 (440). Generating the spin
polarized current may subject substantially perpendicularly
magnetized free layer 242 to a magnetic switching torque, which may
cause the magnetic orientation of substantially perpendicularly
magnetized free layer 242 to switch from the second magnetic
orientation to a third magnetic orientation that may be
substantially antiparallel to the second magnetic orientation. The
third magnetic orientation may be an energetically stable
orientation, in the direction of the magnetic easy axis of
substantially perpendicularly magnetized free layer 242, aside from
the bias caused by the magnetic field of substantially in-plane
magnetized bias layer 280.
[0051] In some examples, substantially perpendicularly magnetized
free layer 242 is disposed between substantially in-plane
magnetized bias layer 280 and spin Hall channel 220 and is
dipole-coupled to substantially in-plane magnetized bias layer 280,
as illustrated in FIG. 2A. In other examples, substantially
in-plane magnetized bias layer 280 is disposed between
substantially perpendicularly magnetized free layer 242 and spin
Hall channel 220, as illustrated in FIG. 2B. Substantially in-plane
magnetized bias layer 280 may be exchange coupled to substantially
perpendicularly magnetized free layer 242. A similar technique to
that illustrated in FIG. 4 may be used to switch substantially
perpendicularly magnetized free layer 242 in the example shown in
FIG. 2B, although the bias of the magnetic orientation of at least
part of substantially perpendicularly magnetized free layer 242 by
substantially in-plane magnetized bias layer 280 is due to exchange
coupling rather than dipole coupling.
[0052] FIG. 5 is a flow diagram illustrating an example technique
for preparing a magnetic structure including a spin Hall channel
layer. The example technique includes depositing a substantially
perpendicularly magnetized free layer on a spin Hall channel layer
(510). The technique may also include depositing a substantially
in-plane magnetized bias layer on the substantially perpendicularly
magnetized free layer (520). Alternatively, the technique may
include depositing a spacer layer on the spin Hall channel layer
after step 510, and depositing the substantially in-plane
magnetized bias layer on the spacer layer. The substantially
perpendicularly magnetized free layer may be dipole-coupled to the
substantially in-plane magnetized bias layer. The substantially
in-plane magnetized bias layer may be configured to exert a stray
magnetic field effective to bias the substantially perpendicularly
magnetized free layer. Techniques for depositing may include, for
example, sputtering, chemical vapor deposition, physical vapor
deposition, photolithography, ion milling, or the like.
[0053] FIG. 6 is a flow diagram illustrating an example technique
for preparing a magnetic structure including a spin Hall channel
layer. The example technique includes depositing a substantially
in-plane magnetized bias layer on a spin Hall channel layer (610).
The example technique may include depositing a spacer layer on the
substantially in-plane magnetized bias layer (620). The example
technique may further include depositing a substantially
perpendicularly magnetized free layer on the spacer layer. The
spacer layer may have a predetermined thickness to tune a strength
of exchange coupling between the substantially perpendicularly
magnetized free layer and the substantially in-plane magnetized
bias layer. Techniques for depositing may include the techniques
discussed above with reference to FIG. 5.
EXAMPLES
Example 1
[0054] FIG. 7A is a conceptual and schematic block diagram
illustrating an example magnetic structure dipole coupled with a
spin Hall channel layer. A magnetic structure 720 is disposed on a
spin Hall channel layer 710. Voltage V across the structure and
current I flowing through the spin Hall channel layer 710 may be
measured as shown in FIG. 7A. FIG. 7B is an enlarged conceptual
diagram illustrating the magnetic structure of FIG. 7A. A magnetic
stack structure included a 5 nm Ta layer for the spin Hall channel
layer 710, a 1.2 nm CoFeB perpendicularly magnetized free layer
730, a 2 nm MgO insulating layer 740, a 3 nm in-plane magnetized
bias layer 750, and a 2 nm MgO cap layer 760, as shown in FIG. 7B.
A reference structure included a 5 nm Ta spin Hall channel layer, a
1.2 nm CoFeB perpendicularly magnetized layer, and a 2 nm MgO cap
layer. For the fabrication of the example stack and the reference
structure, photolithography and ion milling were used to form a
Hall bar region of 30 .mu.m wide. Then, photolithography and ion
milling were used to pattern and define a circular magnetic pillar
in the center of each Hall bar region. The pillars had a diameter
of 4.times.6 .mu.m.sup.2.
[0055] FIG. 8A is a chart presenting vibrating sample magnetometer
measurements for the example structure of FIGS. 7A and 7B and the
reference structure. FIG. 8A indicates that both perpendicular and
in-plane magnetization components are present in the example stack
structure of FIGS. 7A and 7B. FIG. 8B is a chart presenting a small
field scan of the example structure of FIGS. 7A and 7B and the
reference structure. FIG. 8B indicates that the example stack
structure and the reference structure had substantially the same
perpendicular magnetic component. Thus, FIGS. 8A and 8B are
indicative of the perpendicular anisotropy of the 1.2 nm thick
CoFeB layer.
Example 2
[0056] The respective switching behaviors of the example stack
structure and the reference structure were investigated. The
anomalous Hall resistance was used to measure and determine changes
in the perpendicular magnetization. Changes in the measured
anomalous Hall resistance are indicative of changes in the
perpendicular component of the magnetization since R.sub.AHE
(=V.sub.H/I) is proportional to the perpendicular component of the
magnetization. FIGS. 9A and 9B show the anomalous Hall resistance
for the reference structure and the example stack structure,
respectively, when an externally applied perpendicular field is
swept from -700 Oe to +700 Oe. FIG. 9A is a chart presenting the
anomalous Hall resistance as a function of perpendicular field
strength for the reference structure. FIG. 9B shows a significant
reduction in the coercivity of the example stack structure compared
to the reference structure, which indicated interaction between
in-plane magnetic bias layer and the perpendicularly magnetized
free layer within the example stack structure.
[0057] Current induced switching was investigated in the example
stack structure of FIG. 7A. Current was applied and swept along the
Hall bar and the anomalous Hall resistance was measured to monitor
the change in magnetization. Before beginning the measurement, an
external perpendicular field was applied to ensure the
magnetization was saturated. No external field was applied during
the measurement. As shown in FIG. 9C, at a current strength of
about 6 mA, there is a change in R.sub.AHE which indicated a change
in the perpendicular magnetization direction of the CoFeB free
magnetic layer. As the current was then reduced, R.sub.AHE changed
back to the original value at about 3.5 mA, which corresponds to
the magnetization direction changing back to the original state.
Due to the composite structure of the example stack structure,
perpendicular magnetization switching was successfully achieved
without the use of any externally applied fields.
[0058] Various examples have been described. These and other
examples are within the scope of the following claims.
* * * * *