U.S. patent application number 16/151696 was filed with the patent office on 2020-04-09 for tubular nanosized magnetic wires with 360.degree. magnetic domain wallu.
This patent application is currently assigned to Universitat Duisburg-Essen. The applicant listed for this patent is Universitat Duisburg-Essen. Invention is credited to Michael FARLE, Thomas FEGGELER, Irene IGLESIAS, Benjamin ZINGSEM.
Application Number | 20200111536 16/151696 |
Document ID | / |
Family ID | 70052383 |
Filed Date | 2020-04-09 |
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United States Patent
Application |
20200111536 |
Kind Code |
A1 |
ZINGSEM; Benjamin ; et
al. |
April 9, 2020 |
TUBULAR NANOSIZED MAGNETIC WIRES WITH 360.degree. MAGNETIC DOMAIN
WALLU
Abstract
The present invention is directed towards a tubular nanosized
magnetic wire, wherein the nanosized magnetic wire comprises: a
tubular magnetic shell surrounding a longitudinal axis of the wire,
at least one region of the tubular magnetic shell is capable of
providing a 360.degree. magnetic domain wall, wherein the
360.degree. magnetic domain wall is self-stabilizing and has a
magnetization going from a parallel alignment to a perpendicular
alignment and to a parallel alignment with regards to the wire
axis. The present invention also provides a practical method
capable of making a tubular nanosized magnetic wire with a
self-stabilizing, 360.degree. magnetic domain wall. The present
invention also relates to the use of the tubular nanosized magnetic
wire in a racetrack memory device.
Inventors: |
ZINGSEM; Benjamin;
(Monchengladbach, DE) ; FARLE; Michael; (Mulheim
a. d. Ruhr, DE) ; FEGGELER; Thomas; (Essen, DE)
; IGLESIAS; Irene; (Duisburg, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Universitat Duisburg-Essen |
Essen |
|
DE |
|
|
Assignee: |
Universitat Duisburg-Essen
Essen
DE
|
Family ID: |
70052383 |
Appl. No.: |
16/151696 |
Filed: |
October 4, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G11C 11/1673 20130101;
G11C 11/14 20130101; G11C 11/155 20130101; G11C 11/161 20130101;
G11C 19/0808 20130101; G11C 11/1675 20130101 |
International
Class: |
G11C 19/08 20060101
G11C019/08; G11C 11/14 20060101 G11C011/14 |
Claims
1. A tubular nanosized magnetic wire, wherein the nanosized
magnetic wire comprises: a tubular magnetic shell surrounding a
longitudinal axis of the wire, wherein at least one region of the
tubular magnetic shell is capable of providing a 360.degree.
magnetic domain wall, wherein the 360.degree. magnetic domain wall
is self-stabilizing and has a magnetization going from a parallel
alignment to a perpendicular alignment and to a parallel alignment
with regards to the wire axis.
2. The tubular nanosized magnetic wire according to claim 1,
wherein the tubular nanosized magnetic wire is a coaxial wire
wherein a solid non-magnetic center core is surrounded by the
tubular magnetic shell.
3. The tubular nanosized magnetic wire according to claim 1,
wherein the shape of the cross section of the tubular nanosized
magnetic wire is circular or elliptical.
4. The tubular nanosized magnetic wire according to claim 1,
wherein the self-stabilizing, 360.degree. magnetic domain wall is a
Neel-type magnetic domain wall.
5. The tubular nanosized magnetic wire according to claim 1,
wherein the self-stabilizing, 360.degree. magnetic domain wall is a
Bloch-type magnetic domain wall.
6. A method of making a tubular nanosized magnetic wire with a
self-stabilizing, 360.degree. magnetic domain wall comprising the
following steps: producing the tubular nanosized magnetic wire,
nucleating the 360.degree. magnetic domain wall through vortex
formation, or magnetic fields.
7. A method according to claim 6, wherein the tubular nanosized
magnetic wire is made by inorganic chemical synthesis or colloidal
synthesis comprising the steps of: synthesis of a ferromagnetic
nanosized wire, coating the tubular nanosized magnetic wire with a
dia- or paramagnetic layer coating the outside of the tubular
nanosized magnetic wire with a ferromagnetic or ferrimagnetic layer
by inorganic colloidal synthesis or atomic layer deposition.
8. A method according to claim 6, wherein the step of producing the
tubular nanosized magnetic wire comprises the step of: producing
the tubular nanosized magnetic wire by template-assisted
electrochemical synthesis.
9. A method according to claim 6, wherein the step of producing the
tubular nanosized magnetic wire comprises the step of: producing
the tubular nanosized magnetic wire by in situ single-wire
electrochemical synthesis.
10. A method according to claim 6, wherein the step of producing
the tubular nanosized magnetic wire comprises the step of:
producing the tubular nanosized magnetic wire by additive
manufacturing with nanoparticles.
11. A method according to claim 6, wherein the step of producing
the tubular nanosized magnetic wire comprises the step of:
producing the tubular nanosized magnetic wire by use of biological
templates.
12. A method according to claim 6, wherein the step of producing
the tubular nanosized magnetic wire comprises the step of:
producing the tubular nanosized magnetic wire by standard electron
beam lithography and mask techniques with successive sputtering
steps.
13. The use of the tubular nanosized magnetic wire according to
claim 1 in a racetrack memory device.
Description
FIELD OF THE INVENTION
[0001] The invention relates to the field of tubular nanosized
magnetic wire and in particular to a tubular nanosized magnetic
wire comprising a tubular magnetic shell surrounding a longitudinal
axis of the wire, wherein at least one region of the tubular
magnetic shell is capable of providing a 360.degree. magnetic
domain wall. The invention also relates to a racetrack memory
device making use of tubular nanosized magnetic wires with
360.degree. magnetic domain walls.
BACKGROUND OF THE INVENTION
[0002] Magnetic materials have been used in functional devices for
decades, such as recording devices including hard disk drives
(HDDs), magnetoresistive random-access memory (MRAM), bubble and
thin-film data storage, sensor and domain shift register devices.
Most of these traditional functional devices are based on the
control of magnetic domains. For example, recording media use
single magnetic domain states with two opposite magnetization
directions to represent the information bits 0 and 1. Material
morphology, geometry and intrinsic parameters influence the
specific magnetic domain formation and shape, and hence, do
directly or indirectly affect the relevant functionalities based on
magnetic domains. Magnetic domain walls have been moved and
transformed by a magnetic field or a spin-polarized current in
planar magnetic wires and rods resulting in new concepts for
magnetic memory, storage and logic devices.
[0003] In the document by Fert, A., Cros, V. & Sampaio, J.
Skyrmions on the track. Nature Nanotechnology 8, 152 (2013),
magnetic skyrmions are described which are nanoscale spin
configurations that hold promise as information carriers in
ultradense memory and logic devices owing to the extremely low
spin-polarized currents needed to move them. Magnetic skyrmions are
chiral spin structures with a whirling configuration. As their
structure cannot be continuously deformed to a ferromagnetic or
other magnetic state, skyrmions are topologically protected and
relatively stable structures, in comparison with, for example,
magnetic vortices or bubbles. To figure out how to stabilize
skyrmions on tubular nanosized magnetic wires is still a big
challenge.
SUMMARY OF THE INVENTION
[0004] Much research into domain walls in magnetic nanowires has
focused on flat, planar domain wall guides that have potential
spintronic applications including racetrack memory, shift registers
and domain wall logic devices. Both the domain wall structure and
its chirality are important for applications since they have been
shown to influence the domain wall pinning potential. In addition,
a number of studies have shown the importance of metastable states,
particularly in dynamic systems, where the domain wall is shifted
using a spin-polarised current or applied magnetic field.
Experiments have shown that domain walls can change type during
propagation along the guide. Indeed, propagation of domain walls in
planar nanowires is ultimately limited by Walker breakdown, which
describes a process whereby an anti-vortex structure is
periodically nucleated and annihilated at the wire edges, causing
the motion of the domain wall to become non-uniform. The resulting
technical problem is the instability and slow speed of magnetic
domain walls.
[0005] The object of the invention is to provide a solution for the
problem of instability of magnetic domain walls against magnetic
stray fields.
[0006] According to the invention, this object is addressed by the
subject matter of the independent claims. Preferred embodiments of
the invention are described in the sub claims.
[0007] In one aspect of the present invention, the object is
achieved by a tubular nanosized magnetic wire, wherein the
nanosized magnetic wire comprises: a tubular magnetic shell
surrounding a longitudinal axis of the wire, wherein at least one
region of the tubular magnetic shell is capable of providing a
360.degree. magnetic domain wall, wherein the 360.degree. magnetic
domain wall is self-stabilizing and has a magnetization going from
a parallel alignment to a perpendicular alignment and to a parallel
alignment with regards to the wire axis.
[0008] The tubular geometry of the nanosized magnetic wire allows
for 360.degree. domain walls (i.e. domainwalls in which the local
magnetic polarization undergoes a 360.degree. rotation when
traversing from one domain to another) to be self stabilizing (i.e.
topologically stabilized) as the domain walls loop around the tube
and in on themselves.
[0009] Another advantage of the proposed tubular nanosized magnetic
wire comprising a self-stabilizing, 360.degree. magnetic domain
wall is that due to its chirality a 360.degree. domain wall can be
moved through the system using field and current pulses. The
proposed tubular nanosized magnetic wires are superior to current
cutting edge technology in that, compared to conventional
180.degree. domain walls, the 360.degree. domain walls are self
stabilizing, do not annihilate, and compared to other self
stabilizing spin textures like skyrmions are not subject to drift,
since any force acting perpendicular to the direction of motion
performs an isomorphism on the texture. The magnetic wire is a
magnetically hollow tube wherein magnetically hollow refers to the
case that the inner core of the tubular core-shell wire device can
be either empty or filled with a non-ferromagnetic, that is dia-,
para-, or antiferromagnetic material.
[0010] In another preferred embodiment the tubular nanosized
magnetic wire is a coaxial wire wherein a solid non-magnetic center
core is surrounded by the tubular magnetic shell. This is
advantageous because the 360.degree. domain walls can be nucleated
through vortex formation on the tips of the inner solid core.
[0011] In a preferred embodiment the tubular nano-sized magnetic
wire according to one of the previous claims wherein the shape of
the cross section of the tubular nanosized magnetic wire is
circular or elliptical.
[0012] In another preferred embodiment the self-stabilizing,
360.degree. magnetic domain wall is a Neel-type magnetic domain
wall.
[0013] In another preferred embodiment the self-stabilizing,
360.degree. magnetic domain wall is a Bloch-type magnetic domain
wall.
[0014] In another aspect of the invention, the object is achieved
by a method of making a tubular nanosized magnetic wire with a
self-stabilizing, 360.degree. magnetic domain wall comprising the
following steps: producing the nanowire, nucleating the 360.degree.
magnetic domain wall through vortex formation or magnetic
fields.
[0015] In a preferred embodiment the tubular nanosized magnetic
wire is made by inorganic chemical synthesis or colloidal synthesis
comprising the steps of: synthesis of a ferromagnetic tubular
nanosized wire, coating the tubular nanosized magnetic wire with a
dia- or paramagnetic layer, coating the outside of the tubular
nanosized magnetic wire with a ferromagnetic or ferrimagnetic layer
by inorganic colloidal synthesis or atomic layer deposition. There
are more thin film depsoition techniques for making tubular
nanosized magnetic wires, for example sputtering and molecular beam
epitaxy.
[0016] In another preferred embodiment the step of producing the
tubular nanosized magnetic wire comprises the step of: producing
the tubular nanosized magnetic wire by template-assisted
electrochemical synthesis. A first template-assisted
electrochemical synthesis method is the electrodeposition of a
non-magnetic nanosized wire inside a porous membrane template (e.g.
anodized alumina, polycarbonate, silica) and partial removal of the
membrane by plasma or chemical etching leaving the wires standing
with a controlled length and coating the magnetic wire with a
ferromagnetic or ferrimagnetic layer (by electrochemistry or
sputtering). A second method is the electrodeposition of a ferro-
or ferrimagnetic nanosized tube inside the pores of the template
followed by electrodeposition of a concentric inner dia- or
paramagnetic layer and followed by electrodeposition of a
ferromagnetic nanosized core magnetic filament inside the
concentric tubes.
[0017] In a preferred embodiment the step of producing the tubular
nanosized magnetic wire comprises the step of: producing the
tubular nanosized magnetic wire by in situ single-wire
electrochemical synthesis. Wherein, the in situ single-wire
electrochemical synthesis consists of the following steps:
electrodeposition of the tubular nanosized wire inside the template
in situ, single-wire electrochemical coating of the tubular
nanosized magnetic wire with a dia- or paramagnetic layer, in situ
single-wire electrochemical coating of the tubular nanosized
magnetic wire with a ferromagnetic or ferrimagnetic layer.
[0018] In a preferred embodiment the step of producing the tubular
nanosized magnetic wire comprises the step of: producing the
tubular nanosized magnetic wire by additive manufacturing with
nanoparticles. Additive Manufacturing techniques using nanoscale
heating via electron beam, near-field lasing and/or two photon
polymerization will be employed. Nanomagnetic core and magnetic
shell will be built by melting size-selected nanoparticles that
have the desired magnetic and non-magnetic properties either in the
form of metallic, insulating or polycarbonate form. Particles can
also be positioned by an ink-jet-like printing technology.
[0019] In another preferred embodiment the step of producing the
tubular nanosized magnetic wire comprises the step of: producing
the tubular nanosized magnetic wire by use of biological templates.
Biological structures (e.g. tobacco virus) form regular nanotubes
with nanoscale diameter and length and consist of non-ferromagnetic
material. The tubes can be filled and coated by magnetic materials
using depsoition techniques described above, i.e. colloidal
chemistry, electro deposition and thin film coating techniques.
[0020] In a preferred embodiment the step of producing the tubular
nanosized magnetic wire comprises the step of: producing the
tubular nanosized magnetic wire by standard electron beam
lithography and mask techniques with successive sputtering steps.
In another aspect of the invention the tubular nanosized magnetic
wire is used in a racetrack memory device. Racetrack memory devices
are gaining interest as high-density storage devices. The use of
tubular nanosized magnetic wires according to the invention is
advantageously due to their stability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] These and other aspects of the invention will be apparent
from and elucidated with reference to the embodiments described
hereinafter. Such an embodiment does not necessarily represent the
full scope of the invention, however, and reference is made
therefore to the claims and herein for interpreting the scope of
the invention.
[0022] In the drawings:
[0023] FIG. 1a) is a perspective view of one embodiment of the
present invention showing a magnetic wire with a tubular shell,
[0024] FIG. 1b) is a perspective view of another embodiment of the
present invention wherein the magnetic wire is a coaxial wire with
a tubular shell and a solid core,
[0025] FIG. 2 schematically depicts a racetrack memory device
making use of a tubular nanosized magnetic wire according to the
present invention,
[0026] FIG. 3 is a perspective view of still another embodiment of
the present invention showing a hollow tube with a tubular shell
and a read/write element that is part of a racetrack memory
device.
DETAILED DESCRIPTION OF EMBODIMENTS
[0027] FIG. 1a) is a perspective view of one embodiment of the
present invention showing a magnetic wire 100 with a tubular shell
101. According to FIG. 1a) the magnetic wire 100 is a magnetically
hollow tube 102. The wording "magnetically hollow" refers to the
case that the inner core 104 of the tubular magnetic wire 100 can
be either empty or filled with a non-ferromagnetic, that is dia-,
para-, or antiferromagnetic material.
[0028] The 360.degree. domain walls 10 are perpendicular to the
axis of the wire 100 with magnetization 107 going from parallel to
perpendicular, to parallel alignment with regard to the wire 100
axis. The 360.degree. domain walls 106 are stabilized by the
morphology of the tubular hollow shell 101. Therefore one advantage
of the proposed tubular nanosized magnetic wire 100 comprising a
self-stabilizing, 360.degree. magnetic domain wall 106 is that due
to its chirality a 360.degree. domain wall 106 can be moved through
the system using field and current pulses. The proposed tubular
nanosized magnetic wires 100 are superior to current cutting edge
technology in that, compared to conventional 180.degree. domain
walls, the 360.degree. domain walls 106 are self stabilizing, do
not annihilate, and compared to other self stabilizing spin
textures like skyrmions are not subject to drift, since any force
acting perpendicular to the direction of motion performs an
isomorphism on the texture.
[0029] The magnetic wire 100 can be designed with a length in the
order of 100 to 1000 nm and da diameter of the order of 10 to 100
nm, the underlying physical principle makes it scalable up to the
micrometer regime.
[0030] FIG. 1b) is a perspective view of another embodiment of the
present invention. The magnetic wire 100 as shown in FIG. 1b) has a
coaxial structure 103 with a tubular shell 101 and a solid core
105. According to FIG. 1b) the magnetic wire has a solid
non-magnetic core 105. This is advantageous because the 360.degree.
domain walls 106 can be nucleated through vortex formation on the
tips of the inner solid wire 105. The stray field of the inner wire
105 affects the outer tubular shell 101 in a way, that a
360.degree. domain wall 106 is nucleated. Once the domain wall 106
is created, it remains stable until the field becomes large enough
to break the stability and orient the magnetic moments along the
field
[0031] FIG. 2 schematically depicts a racetrack memory device 200
making use of a tubular nanosized magnetic wire 202 according to
the present invention. A racetrack memory device 200 is a magnetic
shift register that uses the inherent, natural properties of domain
walls 205 in magnetic materials to store data. The shift register
uses spin electronics without changing the physical nature of its
constituent materials. The shift register comprises a fine track or
strip of magnetic materials 201. Information is stored as domain
walls 205 in the track 201. An electric current 204 is applied to
the track 201 to move the magnetic moments along the track 201 past
a reading or writing device 203. In a magnetic material 201 with
domain walls 205, a current 204 passed across the domain wall 205
moves the domain wall 205 in the direction of the current flow 206.
As the current 204 passes through a domain, it becomes "spin
polarized". When this spin polarized current passes through the
next domain and across a domain wall, it develops a circle of spin
torque. This spin torque moves the domain wall 205.
[0032] FIG. 3 is a perspective view of still another embodiment of
the present invention showing a tubular magnetic 300 wire with a
tubular shell 301 and a read/write element 302 that is part of a
racetrack memory device 200. The tubular magnetic wire 300 forms
the racetrack 201 as shown in FIG. 2. According to FIG. 3 the
magnetic wire 300 has a tubular shell 301. A read/write element 302
from a racetrack memory device 200 is positioned around the shell
301. Writing domain walls 305 can be carried out with a variety of
schemes, including using the self-field of currents passed along
neighboring metallic nanowires; using the spin-momentum transfer
torque effect derived from current injected into the racetrack from
magnetic nanoelements; or using the fringing fields from the
controlled motion of a magnetic domain wall in a proximal nanowire
writing element. FIG. 3 also shows the axial magnetization
distribution 303 inside the shell 301 of the magnetic wire 300.
FIG. 3 further shows the magnetic texture of the 360.degree.
magnetic domain wall 304 inside the shell 301 of the magnetic wire
300.
[0033] While the invention has been illustrated and described in
detail in the drawings and foregoing description, such illustration
and description are to be considered illustrative or exemplary and
not restrictive; the invention is not limited to the disclosed
embodiments. Other variations to the disclosed embodiments can be
understood and effected by those skilled in the art in practicing
the claimed invention, from a study of the drawings, the
disclosure, and the appended claims. In the claims, the word
"comprising" does not exclude other elements or steps, and the
indefinite article "a" or "an" does not exclude a plurality. The
mere fact that certain measures are recited in mutually different
dependent claims does not indicate that a combination of these
measures cannot be used to advantage. Any reference signs in the
claims should not be construed as limiting the scope. Further, for
the sake of clearness, not all elements in the drawings may have
been supplied with reference signs.
REFERENCE SYMBOL LIST
[0034] tubular nanosized magnetic wire 100 [0035] tubular shell 101
[0036] hollow tube 102 [0037] coaxial wire 103 [0038] inner core
104 [0039] solid center core 105 [0040] 360.degree. magnetic domain
wall 106 [0041] axial magnetization distribution inside tubular
shell 107 [0042] racetrack memory device 200 [0043] racetrack 201
[0044] tubular magnetic wire 202 [0045] read/write element of
racetrack memory device 203 [0046] current 204 [0047] 360.degree.
magnetic domain wall 205 [0048] moving direction of the domain
walls 206 [0049] tubular nanosized magnetic wire 300 [0050] shell
301 [0051] read/write element of racetrack memory device 302 [0052]
axial magnetization distribution inside tubular shell 303 [0053]
magnetic texture of 360.degree. magnetic domain wall 304 [0054]
360.degree. magnetic domain wall 305
* * * * *