Title: Magnetic memory, magnetic memory array, method for fabricating a magnetic memory, method for recording in a magnetic memory and method for reading out from a magnetic memory
Abstract: A magnetic memory includes a magnetic substance composed of a disc-shaped first magnetic layer and a ring-shaped second magnetic layer which is formed on the first magnetic layer.
Patent Number: 6,940,750 Issued on 09/06/2005 to Yamamoto, et al.
| Inventors:
|
Yamamoto; Masahiko (Minoo, JP);
Nakatani; Ryoichi (Toyonaka, JP);
Endo; Yasushi (Toyonaka, JP)
|
| Assignee:
|
Osaka University (Osaka, JP)
|
| Appl. No.:
|
680157 |
| Filed:
|
October 8, 2003 |
Foreign Application Priority Data
| Oct 18, 2002[JP] | 2002-304124 |
| Current U.S. Class: |
365/173; 365/48; 365/33; 365/55; 365/74; 365/97; 365/171; 365/66; 365/209 |
| Intern'l Class: |
G11C 011/15 |
| Field of Search: |
365/73,48,33,55,74,97,171,66,209
|
References Cited [Referenced By]
U.S. Patent Documents
| 5432373 | Jul., 1995 | Johnson.
| |
| 5475304 | Dec., 1995 | Prinz.
| |
| 5486967 | Jan., 1996 | Tanaka et al.
| |
| 5587943 | Dec., 1996 | Torok et al.
| |
| 5673220 | Sep., 1997 | Gendlin.
| |
| 5718983 | Feb., 1998 | Gendlin.
| |
| 6351410 | Feb., 2002 | Nakao et al.
| |
| 6743340 | Jun., 2004 | Fu.
| |
| 2004/0094785 | May., 2004 | Zhu et al.
| |
| 2004/0165426 | Aug., 2004 | Yamamoto et al.
| |
| Foreign Patent Documents |
| 0 375 646 | Jun., 1990 | EP.
| |
| WO 00/1017/8 | Feb., 2000 | WO.
| |
| WO 03/032336 | Apr., 2003 | WO.
| |
Other References
Jian-Gang Zhu et al. "Ultrahigh Density Vertical Magnetoresistive Random Access
Memory (Invited)," Journal of Applied Physics, vol. 87, No. 9, May 1, 2000, pp. 6668-6673.
M. Kläui et al. "Vortex Circulation Control in Mesoscopic Ring Mangets,"
Applied Physics Letters, vol. 78, No. 21, May 21, 2001, pp. 3268-3270.
M. Schneider et al. "Magnetic Switching of Single Vortex Permalloy Elements,"
Applied Physics Letters, vol. 79, No. 19, Nov. 5, 2001, pp. 3113-3115.
M. Schneider et al.; "Lorentz microscopy of circular ferromagnetic permalloy
nanodisks"; Applied Physics Letters; American Institute of Physics., New York,
US, vol. 77, No. 18; Oct. 30, 2000; pp 2909-2911.
|
Primary Examiner: Nguyen; Viet Q.
Attorney, Agent or Firm: Oliff & Berridge, PLC
Claims
1. A magnetic memory comprising a magnetic substance composed of a disc-shaped
first magnetic layer and a ring-shaped second magnetic layer which is formed on
said first magnetic layer.
2. The magnetic memory as defined in claim 1, wherein ratio (D
2/D
1)
is set within 0.1-0.8 on condition that an outside diameter and an inside diameter
of said second magnetic layer are designated by D
1 and D
2, respectively.
3. The magnetic memory as defined in claim 2, wherein said outside diameter D
1
of said second magnetic layer is set within 100-1500 nm and said inside diameter
D
2 of said second magnetic layer is set within 10-1200 nm.
4. The magnetic memory as defined in claim 1, wherein ratio (t
1/t
2)
is set within 1/5-5 on condition that thicknesses of said first magnetic layer
and said second magnetic layer are designated by t
1 and t
2, respectively.
5. The magnetic memory as defined in claim 4, wherein said thickness t
1
of said first magnetic layer t
1 is set within 4-20 nm, and said thickness
t
2 of said second magnetic layer t
2 is set within 4-20 nm.
6. The magnetic memory as defined in claim 1, wherein said first magnetic layer
and said second magnetic layer are made of room temperature ferromagnetic material.
7. The magnetic memory as defined in claim 1, wherein a magnetization of said
second magnetic layer is rendered right handed (clockwise) direction or left handed
(anticlockwise) direction along surfaces of said second magnetic layer.
8. The magnetic memory as defined in claim 1, wherein a periphery of said magnetic
substance is notched.
9. The magnetic memory as defined in claim 8, wherein ratio (h/H) is set to 0.006
or over on condition that a height of a notch of said periphery of said magnetic
substance is designated by h, and an outside diameter of said magnetic substance
is designated by H.
10. The magnetic memory as defined in claim 1, further comprising a ring-shaped
third magnetic layer on said magnetic substance via a non-magnetic layer.
11. The magnetic memory as defined in claim 10, wherein a thickness t
3
of said third magnetic layer is set within 5-20 nm.
12. The magnetic memory as defined in claim 10, wherein said third magnetic layer
is made of room temperature ferromagnetic material.
13. The magnetic memory as defined in claim 10, further comprising an antiferromagnetic
layer so as to be adjacent to a main surface of said third magnetic layer remote
from said magnetic substance.
14. The magnetic memory as defined in claim 10, wherein a magnetization of said
third magnetic layer is rendered right handed (clockwise) direction or left handed
(anticlockwise) direction along surfaces of said third magnetic layer.
15. The magnetic memory as defined in claim 14, wherein said direction of said
third magnetic layer is pinned.
16. A magnetic memory array comprising a plurality of magnetic memories as defined
in claim 1 which are arranged regularly.
17. A method for fabricating a magnetic memory, comprising the steps of:
preparing a given substrate,
forming a mask with circular openings on a main surface of said substrate,
introducing magnetic particles into said openings of said mask on said main surface
of said substrate at a given inclination angle from a normal line to said main
surface with rotating said substrate, to form a magnetic substance composed of
a disc-shaped first magnetic layer and a ring-shaped second magnetic layer which
are successively stacked.
18. The fabricating method as defined in claim 17, wherein said inclination angle
is set within 30-60 degrees from said normal line to said main surface.
19. A method for recording in a magnetic memory, comprising the steps of:
stacking a disc-shaped first magnetic layer and a ring-shaped second magnetic
layer successively to form a magnetic substance,
applying an external magnetic field to said magnetic substance to generate a
vortex magnetization in said first magnetic layer,
generating a right handed (clockwise) vortex magnetization or a left handed (anticlockwise)
vortex magnetization in said second magnetic layer along surfaces of said magnetic
layer by utilizing said vortex magnetization of said first magnetic layer as nucleus,
and
storing information "0" or "1" on said right handed (clockwise) vortex magnetization
or said left handed (anticlockwise) vortex magnetization of said second magnetic
layer.
20. The recording method as defined in claim 19, wherein ratio (D
2/D
1)
is set within 0.1-0.8 on condition that an outside diameter and an inside diameter
of said second magnetic layer are designated by D
1 and D
2, respectively.
21. The recording method as defined in claim 20, wherein said outside diameter
D
1 of said second magnetic layer is set within 100-1500 nm and said inside
diameter D
2 of said second magnetic layer is set within 10-1200 nm.
22. The recording method as defined in claim 19, wherein ratio (t
1/t
2)
is set within 1/5-5 on condition that thicknesses of said first magnetic layer
and said second magnetic layer are designated by t
1 and t
2, respectively.
23. The recording method as defined in claim 22, wherein said thickness t
1
of said first magnetic layer t
1 is set within 4-20 nm, and said thickness
t
2 of said second magnetic layer t
2 is set within 4-20 nm.
24. The recording method as defined in claim 19, wherein said first magnetic
layer and said second magnetic layer are made of room temperature ferromagnetic material.
25. The recording method as defined in claim 19, wherein a periphery of said
magnetic substance is notched.
26. The recording method as defined in claim 25, wherein ratio (h/H) is set to
0.006 or over on condition that a height of a notch of said periphery of said magnetic
substance is designated by h, and an outside diameter of said magnetic substance
is designated by H.
27. A method for reading out from a magnetic memory, comprising the steps of:
stacking a disc-shaped first magnetic layer and a ring-shaped second magnetic
layer successively to form a magnetic substance,
forming a ring-shaped third magnetic layer on said magnetic substance via a non-magnetic
layer, to complete said magnetic memory,
applying an external magnetic field to said magnetic substance to generate a
vortex magnetization in said first magnetic layer,
generating a right handed (clockwise) vortex magnetization or a left handed (anticlockwise)
vortex magnetization in said second magnetic layer along surfaces of said magnetic
layer by utilizing said vortex magnetization of said first magnetic layer as nucleus,
storing information "0" or "1" on said right handed (clockwise) vortex magnetization
or said left handed (anticlockwise) vortex magnetization of said second magnetic
layer, and
detecting a change in electric current due to a change in electric resistance
of said magnetic memory on relative direction of a magnetization of said second
magnetic layer for a magnetization of said third magnetic layer.
28. The reading out method as defined in claim 27, further comprising the step
of forming an antiferromagnetic layer so as to be adjacent to a main surface of
said third magnetic layer remote from said magnetic substance to pin said magnetization
of third magnetic layer.
29. The reading out method as defined in claim 27, wherein ratio (D
2/D
1)
is set within 0.1-0.8 on condition that an outside diameter and an inside diameter
of said second magnetic layer are designated by D
1 and D
2, respectively.
30. The reading out method as defined in claim 29, wherein said outside diameter
D
1 of said second magnetic layer is set within 100-1500 nm and said inside
diameter D
2 of said second magnetic layer is set within 10-1200 nm.
31. The reading out method as defined in claim 27, wherein a periphery of said
magnetic substance is notched.
32. The reading out method as defined in claim 31, wherein ratio (h/H) is set
to 0.006 or over on condition that a height of a notch of said periphery of said
magnetic substance is designated by h, and an outside diameter of said magnetic
substance is designated by H.
33. The reading out method as defined in claim 27, wherein a thickness t
1
of said first magnetic layer t
1 is set within 4-20 nm, and a thickness t
2
of said second magnetic layer t
2 is set within 4-20 nm.
34. The reading out method as defined in claim 27, wherein said first magnetic
layer, said second magnetic layer and said third magnetic layer are made of room
temperature ferromagnetic material.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a nonvolatile magnetic memory and a nonvolatile magnetic
memory array which are preferably usable as a magnetic random access memory (MRAM).
Also, this invention relates to a method for fabricating the nonvolatile magnetic
memory. Moreover, this invention relates to a method for recording in the nonvolatile
magnetic memory and a method for reading out from the nonvolatile magnetic memory.
2. Description of the Prior Art
Various electronic devices have been employed under a specific condition
such as an aero-space, and thus, it is desired to establish a recording device
where once stored information can not be deleted by the irradiation of a radioactive
ray. In this point of view, large radioactive-resistance and nonvolatile MRAMs
having their respective simply structured magnetic memory cells are researched
and developed.
Conventionally, such a magnetic memory cell is shaped rectangular,
and information "0" or "1" is stored on the magnetic direction of the magnetic
memory cell. With the conventional magnetic memory cell, however, the magnetic
flux originated from the magnetization is leaked outside from the magnetic memory
cell due to the configuration thereof. In order to increase the recording capacity
of the MRAM, in contrast, such an attempt is made as to arrange a plurality of
magnetic memory cells in high density. In this case, however, the leaked magnetic
flux affects significantly on the adjacent magnetic memory cells, and thus, the
intended high density MRAM can not be realized.
In this point of view, the inventors have developed a ring-shaped magnetic memory
where a right handed (clockwise) magnetization or a left-handed (anticlockwise)
magnetization is created in vortex, and information "0" or "1" is stored on the
rotative direction of the magnetization thereof (Japanese Patent application 2002-73681).
In this case, since a magnetic flux is not leaked from the magnetic memory, if
a plurality of magnetic memory are arranged in high density as mentioned above,
the leaked magnetic flux can not almost affect on the adjacent magnetic memories,
so that a high density MRAM can be realized.
With the ring-shaped magnetic memory, however, the motion of the magnetic domain
wall is prevented due to the inside external wall, so that the magnetization can
not be easily inverted. In order to control the right handed magnetization and
the left handed magnetization, it is required to flow current perpendicular to
the ring-shaped magnetic memory and thus, to generate rotative magnetic field in
the magnetic memory along the ring-shaped configuration, as indicated in "Journal
of Applied Physics, 87, 9, p6668-6673(2001)". Therefore, the control of the magnetic
condition of the ring-shaped magnetic memory is very difficult and complicated,
so that the ring-shaped magnetic memory can not be practically employed.
SUMMERY OF THE INVENTION
It is an object of the present invention to provide a magnetic memory and a magnetic
memory array which can generate a right handed (clockwise) vortex magnetization
and a left handed (anticlockwise) vortex magnetization easily to realize stable
recording performance on the direction of the vortex magnetization. It is another
object of the present invention to provide a method for fabricating the magnetic
memory, a method for recording in the magnetic memory and a method for reading
out from the magnetic memory.
In order to achieve the above-mentioned objects, this invention relates to a
magnetic
memory comprising a magnetic substance composed of a disc-shaped first magnetic
layer and a ring-shaped second magnetic layer which is formed on the first magnetic layer.
The inventors found out through vast researches and developments that if the
ring-shaped magnetic layer is formed adjacent to, concretely on the disc-shaped
magnetic layer, to constitute the magnetic memory, and a given external magnetic
field is applied to the magnetic memory, the disc-shaped magnetic layer is magnetized
in vortex. In this case, the vortex magnetization of the disc-shaped magnetic layer
functions as nucleus to generate the right handed (clockwise) magnetization and
the left handed (anticlockwise) magnetization easily in the ring-shaped magnetic
layer along the surfaces thereof.
If the polarity of the external magnetic field is varied, the direction of the
vortex magnetization can be varied in the disc-shaped magnetic layer, so that the
direction of the vortex magnetization of the ring-shaped magnetic layer can be
easily varied to the left handed (anticlockwise) magnetization from the right handed
(clockwise) magnetization or to the right handed (clockwise) magnetization from
the left handed (anticlockwise) magnetization. Therefore, if the information "0"
or "1" is stored on the direction of the vortex magnetization of the ring-shaped
magnetic layer, the magnetic memory, including the magnetic substance composed
of the disc-shaped magnetic layer and the ring-shaped magnetic layer, can be employed practically.
In the magnetic memory of the present invention, since the ring-shaped magnetic
layer is formed, magnetic flux can not be leaked from the vortex magnetization.
Therefore, if the magnetic memories are arranged in high density to constitute
the magnetic memory array, the leaked magnetic flux can not affect on the adjacent
magnetic memories. As a result, the magnetic memory array can be employed practically
as a high density magnetic memory array.
In a preferred embodiment of the present invention, the periphery of the magnetic
substance composed of the disc-shaped magnetic layer and the ring-shaped magnetic
layer is notched. In this case, the right handed (clockwise) vortex magnetization
and the left handed (anticlockwise) vortex magnetization can be easily generated
in the ring-shaped magnetic layer of the magnetic memory, and information "0" or
"1" can be easily stored in the magnetic memory on the direction of the vortex
magnetization on good control of the direction of the vortex magnetization. Therefore,
the magnetic memory can be employed more practically.
Other features and advantages of the magnetic memory of the present invention
will be described below. Also, a fabricating method, a recording method and a reading
method for the magnetic memory will be described below.
BRIEF DESCRIPTION OF THE DRAWINGS
For better understanding of the present invention, reference is made to the attached
drawings, wherein
FIG. 1 is a top plan view showing a magnetic substance constituting a magnetic
memory according to the present invention,
FIG. 2 is a cross sectional view of the magnetic substance shown in FIG. 1,
taken on line "A—A",
FIG. 3 is a cross sectional view showing one step in fabricating the magnetic
memory of the present invention,
FIG. 4 is a cross sectional view showing the step after the step shown in FIG. 3,
FIG. 5 is a cross sectional view showing the step after the step shown in FIG. 4,
FIG. 6 is a cross sectional view showing the step after the step shown in FIG. 5,
FIG. 7 is a top plan view showing another magnetic substance constituting another
magnetic memory according to the present invention,
FIG. 8 is a cross sectional view of the magnetic substance shown in FIG. 7,
taken on line "B—B",
FIG. 9 is a top plan view showing a concrete magnetic memory including the magnetic
substance shown in FIGS. 7 and 8,
FIG. 10 is a cross sectional view showing the magnetic memory shown in FIG.
9, taken on line "C—C",
FIG. 11 is a schematic view showing the magnetization state of the first magnetic
layer of the magnetic substance constituting the magnetic memory of the present
invention when an external magnetic field is applied,
FIG. 12 is a schematic view showing the magnetization state of the second magnetic
layer of the magnetic substance constituting the magnetic memory of the present
invention when the external magnetic field is applied,
FIG. 13 is a simulated map showing the magnetization switching process of the
second magnetic layer of the magnetic substance constituting the magnetic memory
of the present invention, and
FIG. 14 is a simulated map showing the magnetization switching process of the
first magnetic layer of the magnetic substance constituting the magnetic memory
of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
This invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a top plan view showing a magnetic substance constituting a magnetic
memory according to the present invention, and FIG. 2 is a cross sectional view
of the magnetic substance shown in FIG. 1, taken on line "A—A". The magnetic
substance
110 illustrated in FIGS. 1 and 2 includes a disc-shaped first
magnetic layer
101 and a ring-shaped magnetic layer
102 formed on
the first magnetic layer
101.
It is desired to set the ratio (D
2/D
1) of the inside diameter D
2
to the outside diameter D
1 of the second magnetic layer
102 within
0.1-0.8, particularly within 0.3-0.6. In this case, when an external magnetic field
is applied to the magnetic substance
110, in the second magnetic layer
102,
the magnetic domain wall can be moved easily without the influence of the inside
external wall. Therefore, the vortex magnetization of the first magnetic layer
101 which is generated by the external magnetic field functions as nucleus
to form a given vortex magnetization in the first magnetic layer
101 along
the surfaces thereof. In this case, the direction of the vortex magnetization in
the second magnetic layer
102 can be easily controlled.
Concretely, the outside diameter D
1 of the second magnetic layer
102 is preferably set within 100-1500 nm, and the inside diameter of the
second magnetic layer
102 is preferably set within 10-1200 nm. Also, it
is desired to set the ratio (t
1/t
2) of the thickness t
1 of
the first magnetic layer
101 to the thickness t
2 of the second magnetic
layer
102 within ⅕-5, particularly within ½-2. In this case,
the first magnetic layer
101 is magnetically combined with the second magnetic
layer
102 in good condition, so that the vortex magnetization can be easily
formed in the second magnetic layer
102, originated from the vortex magnetization
of the first magnetic layer
101 as nucleus. In this case, the direction
of the vortex magnetization in the second magnetic layer
102 can be easily controlled.
Concretely, the thickness t
1 of the first magnetic layer
101
is preferably set within 4-20 nm, and the thickness t
2 of the second magnetic
layer
102 is preferably set within 4-20 nm.
The first magnetic layer
101 and the second magnetic layer
102
may be made of room temperature ferromagnetic material such as Ni—Fe, Ni—Fe—Co,
Co—Fe or Ni—Fe—Co. Herein, the "room temperature ferromagnetic
material" means a ferromagnetic material which can exhibit ferromagnetic properties
at room temperature, and thus, encompasses another well known magnetic material
in addition to the above-mentioned magnetic materials.
The magnetic memory illustrated in FIGS. 1 and 2 can be fabricated as follows.
FIGS. 3-6 are process drawings showing the fabricating method of the magnetic memory.
As shown in FIG. 1, first of all, a given substrate
201 is prepared, and
a mask
203 with circular openings
204 is formed of resist on the
main surface
202 of the substrate
201. Then, magnetic particles
205
are introduced into the openings
204 of the mask
203 on the main
surface
202 of the substrate
201 by the inclination angle of 0 from
the normal line to the main surface
202 of the substrate
201 while
the substrate
201 is rotated at a predetermined velocity, e.g., 60 rpm.
As shown in FIGS. 4 and 5, in this case, the magnetic particles
205 are
deposited on the main surface
202 of the substrate
201 and the side
surfaces of the openings
204 of the mask
204.
Then, after a predetermined amount of magnetic particles
205 is deposited
in the openings
204, the mask
203 is dissolved with a given solvent
such as acetone, to complete a magnetic substance
210 where a disc-shaped
first magnetic layer
207 and a ring-shaped second magnetic layer
209
are successively stacked, as shown in FIG.
6.
The magnetic particles
205 may be deposited by a well known means such
as vacuum deposition or sputtering. Herein, the angle θ is preferably set
within 30-60 degrees. In this case, the magnetic particles
205 can be deposited
on the main surface
202 and the side surfaces of the openings
204
efficiently, and then, the intended magnetic substance
210 can be made easily.
FIG. 7 is a top plan view showing another magnetic substance constituting another
magnetic memory according to the present invention, and FIG. 8 is a cross sectional
view of the magnetic substance shown in FIG. 7, taken on line "B—B". The
magnetic substance
310 illustrated in FIGS. 7 and 8 includes a disc-shaped
first magnetic layer
301 and a ring-shaped magnetic layer
302 formed
on the first magnetic layer
301. The periphery of the magnetic substance
310, that is, the peripheries of the first magnetic layer
301 and
the second magnetic layer
302 are notched.
Since the periphery of the magnetic substance
310 is notched, the right
handed (clockwise) vortex magnetization and the left handed (anticlockwise) vortex
magnetization can be easily generated in the ring-shaped second magnetic layer
302, and information "0" or "1" can be easily stored in the direction of
the vortex magnetization on good control of the direction of the vortex magnetization.
The height h of the notch
305 is set so as to satisfy the relation of
the ratio (h/H)≧0.006 (H: the outside diameter of the magnetic substance
310). Not necessarily restricted, the ratio (h/H) is preferably set to 0.2
or below. If the ratio (h/H) is set beyond 0.2, the above-mentioned function can
not be enhanced, and the vortex magnetization may not be formed in the second magnetic
layer
302, resulting in the malfunction of the magnetic substance
310
as a magnetic memory.
The first magnetic layer
301 and the second magnetic layer
302
of the magnetic substance
310 may be made in the same manner as in the previous
embodiment relating to FIGS. 1 and 2.
FIG. 9 is a top plan view showing a concrete magnetic memory including the magnetic
substance shown in FIGS. 7 and 8, and FIG. 10 is a cross sectional view showing
the magnetic memory shown in FIG. 9, taken on line "C—C").
With a magnetic memory
420 shown in FIGS. 9 and 10, a ring-shaped third
magnetic layer
404 is formed via a ring-shaped non-magnetic layer
403
on a magnetic substance
410 composed of a disc-shaped first magnetic layer
401 and a ring-shaped second magnetic layer
402 which are successively
stacked. Also, a ring-shaped antiferromagnetic layer
405 is formed on the
third magnetic layer
404. The non-magnetic layer
403 through the
antiferromagnetic layer
405 are formed concentrically for the magnetic substance
410.
The magnetic substance
410 may be made in the same manner as in the previous
embodiment relating to FIGS. 7 and 8, and satisfies the above-mentioned requirements.
In this point of view, if the thickness t
1 of the first magnetic layer
401
and the thickness t
2 of the second magnetic layer
402 which constitute
the magnetic substance
410 are set within 4-20 nm, respectively, the thickness
t
3 of the third magnetic layer
404 is preferably set within 5-20
nm. Therefore, the reading operation for the magnetic memory can be performed in
good condition as will be described hereinafter.
The third magnetic layer
404 may be made of the same room temperature
ferromagnetic material as the first magnetic layer
401 and the second magnetic
layer
402. The non-magnetic layer
403 may be made of non-magnetic
material such as Cu, Ag or Au. The antiferromagnetic layer
405 may be made
of antiferromagnetic material such as Mn—Ir, Mn—Pt or Fe—Mn.
The thicknesses of the non-magnetic layer
403 and the antiferromagnetic
layer
405 are appropriately determined so as to magnetically divide the
magnetic substance
410 and the third magnetic layer
404 and magnetically
pin the magnetization of the third magnetic layer
404 through exchange interaction.
The recording operation for the magnetic memory
420 shown in FIGS. 9 and
10 will be carried out as follows. FIG. 11 is a schematic view showing the magnetization
state of the first magnetic layer
401 of the magnetic substance
410
when an external magnetic field is applied, and FIG. 12 is a schematic view showing
the magnetization state of the second magnetic layer
402 of the magnetic
substance
410 when the external magnetic field is applied. Herein, the arrow
designates the direction of magnetization.
When an external magnetic field is applied to the magnetic memory
420
shown in FIGS. 9 and 10, as is apparent from FIG. 7, a right handed (clockwise)
vortex magnetization X
1 (FIG.
11(
a)) or a left handed (anticlockwise)
vortex magnetization X
2 (FIG.
11(
b)) are generated in the
disc-shaped first magnetic layer
401 on the polarity of the external magnetic
field. Since the first magnetic layer
401 are magnetically combined with
the second magnetic layer
402, the vortex magnetization of the first magnetic
layer
401 functions as nucleus to generate a corresponding right handed
(clockwise) vortex magnetization Y
1 (FIG.
12(
a)) or a corresponding
left handed (anticlockwise) vortex magnetization Y
2 (FIG.
12(
b))
in the second magnetic layer
402 along the surfaces thereof. In this way,
the vortex magnetization can be formed easily in the second magnetic layer
402.
The vortex magnetizations X
1 and X
2 of the first magnetic layer
401 can be switched by the polarity of the external magnetic field, the
vortex magnetizations Y
1 and Y
2 can be also switched easily on the
switching of the vortex magnetizations X
1 and X
2. Therefore, the
direction of the vortex magnetization of the second magnetic layer
402 can
be controlled easily. As a result, if information "0" or "1" is stored on the vortex
magnetization Y
1 or Y
2, the recording operation for the magnetic
memory
420 can be performed stably, so that the magnetic memory
420
can be practically employed.
The reading operation for the magnetic memory
420 will be carried out
as follows. The magnetization of the third magnetic layer
404 is pinned
in a given direction, e.g., the right handed (clockwise) direction or the left
handed (anticlockwise) direction through the exchange interaction with the antiferromagnetic
layer
405. In this case, the electric resistance of the magnetic memory
420 depends on the relative direction of the vortex magnetization of the
second magnetic layer
402 for the vortex magnetization of the third magnetic
layer
404.
When the vortex magnetization of the second magnetic layer
402 is in
parallel with the vortex magnetization of the third magnetic layer
404,
the electric resistance of the magnetic memory
420 is rendered minimum,
and when the vortex magnetization of the second magnetic layer
402 is in
anti-parallel with the vortex magnetization of the third magnetic layer
404,
the electric resistance of the magnetic memory
420 is rendered maximum.
Therefore, if the above-mentioned recording operation is carried out for the magnetic
memory
420 to generate the vortex magnetization while the magnetization
of the third magnetic layer
404 is pinned in a predetermined direction,
the reading operation can be performed by detecting the change in electric current
due to the change in electric resistance of the magnetic memory
420.
EXAMPLE
The disc-shaped first magnetic layer and the ring-shaped second magnetic layer
were made of Ni-20 at % alloy in thicknesses of 8 nm and 16 nm, respectively, and
the outside diameter and the inside diameter of the second magnetic layer were
set to 500 nm and 300 nm, respectively, to complete the magnetic substance as shown
in FIGS. 1 and 2. Then, the variations in magnetization state of the first magnetic
layer and the second magnetic layer were simulated.
FIG. 13 is a simulated map showing the magnetization switching process of the
second magnetic layer, and FIG. 14 is a simulated map showing the magnetization
switching process of the first magnetic layer. As is apparent from FIG. 13, the
right handed (clockwise) vortex magnetization is induced in the second magnetic
layer as the external magnetic field is increased from -3000 Oe, and then, the
right handed (clockwise) vortex magnetization is clearly generated in the second
magnetic layer at the magnetic field of about 170 Oe. As is apparent from FIG.
14, the right handed (clockwise) vortex magnetization is also clearly generated
in the first magnetic layer at the magnetic field of about 170 Oe. Therefore, it
was turned out that the right handed (clockwise) magnetization of the second magnetic
layer was generated from the right handed (clockwise) vortex magnetization of the
first magnetic layer as nucleus.
Although the present invention was described in detail with reference to
the above examples, this invention is not limited to the above disclosure and every
kind of variation and modification may be made without departing from the scope
of the present invention.
As mentioned above, according to the present invention can be provided a magnetic
memory and a magnetic memory array which can generate a right handed (clockwise)
vortex magnetization and a left handed (anticlockwise) vortex magnetization easily
to realize stable recording performance on the direction of the vortex magnetization.
Moreover, a method for fabricating the magnetic memory, a method for recording
in the magnetic memory and a method for reading out from the magnetic memory can
be provided.
*
