US 7,889,543 B2 · Magnetic memory element and magnetic memory apparatus

Abstract

A magnetic memory element is provided with first and second ferromagnetic fixed layers, a ferromagnetic memory layer, nonmagnetic first and second intermediate layers. The memory layer is disposed between the first and second fixed layers, and has a variable magnetization direction. In order to cancel asymmetry of a write-in current of the element, the element is provided so that the memory layer receives a larger perpendicular stray field from the first fixed layer than from the second fixed layer, and then a magnetization direction of a portion of the memory layer being nearest to the first intermediate layer and the magnetization direction of the first fixed layer are antiparallel to each other whenever a magnetization direction of a portion of the memory layer being nearest to the second intermediate layer and the magnetization direction of the second fixed layer are parallel to each other, and vice versa.

A magnetic memory element, comprising:

a multilayer including:
a working surface;
a first fixed layer including a first ferromagnetic material and having a first magnetization direction fixed substantially perpendicular to the working surface;
a second fixed layer including a second ferromagnetic material and having a second magnetization direction fixed substantially in a direction opposite to the first magnetization direction;
a memory layer disposed between the first fixed layer and the second fixed layer, the memory layer including a third ferromagnetic material and having a magnetization direction that is variable;
a first intermediate layer disposed between the first fixed layer and the memory layer, the first intermediate layer made essentially of one or more nonmagnetic materials, the nonmagnetic materials including one or both of insulators and semiconductors;
and
a second intermediate layer disposed between the second fixed layer and the memory layer, the second intermediate layer being nonmagnetic,
wherein the magnetization direction of a portion of the memory layer being nearest to the first intermediate layer and the magnetization direction of the first fixed layer are anti-parallel to each other whenever the magnetization direction of a portion of the memory layer being nearest to the second fixed layer and the magnetization direction of the second fixed layer are parallel to each other, and vice versa;
wherein the memory layer receives a larger perpendicular component of a stray field from the first fixed layer than from the second fixed layer;
wherein a current is configured to be passed bi-directionally between the first fixed layer and the second fixed layer;
wherein the current is passed in a first direction over a first threshold to make a magnetization direction of the memory layer in the first direction;
wherein the current is passed in a second direction over a second threshold to make the magnetization direction of the memory layer in the direction opposite to the first direction;
wherein a current is passed between the first fixed layer and the second fixed layer to detect the magnetization direction of the memory layer;
wherein an electric conductivity of a nonmagnetic material to constitute the first intermediate layer is lower than an electric conductivity of a nonmagnetic material to constitute the second intermediate layer;
wherein a thickness of the first intermediate layer is 1 nm or less;
wherein the first fixed layer includes N first ferromagnetic sublayers (N is an integer of 1 or more);
wherein the second fixed layer includes M second ferromagnetic sublayers (M is an integer of 1 or more);
wherein the memory layer includes P memory ferromagnetic sublayers (P is an integer of 1 or more);
and
wherein
the mathematical formula 2 including the function φ(a, b, d) defined by the mathematical formula 1 is satisfied by a1i, b1i, t1i, a2j, b2j, t2j, d1ik, d2jk, M1i, M2j, Msk and HKk,
when
an i-th first ferromagnetic sublayer of the N first ferromagnetic sublayers is approximated by a i-th first rectangular parallelepiped;
a j-th second ferromagnetic sublayer of the M second ferromagnetic sublayers is approximated by a j-th second rectangular parallelepiped;
a1i, b1i and t1i represent a height, a width and a thickness of the i-th first rectangular parallelepiped, respectively;
M1i represents saturation magnetization of the i-th first ferromagnetic sublayer;
a2j, b2j and t2j represent a height, a width and a thickness of the j-th second rectangular parallelepiped, respectively;
M2j represents saturation magnetization of the j-th second ferromagnetic sublayer;
Msk and HKk represent saturation magnetization and an anisotropy field of a k-th memory ferromagnetic layer of the P memory ferromagnetic sublayers, respectively;
d1ik represents a distance between the i-th first ferromagnetic sublayer and the k-th memory ferromagnetic sublayer;
d2jk represents a distance between the j-th second ferromagnetic sublayer and the k-th memory ferromagnetic sublayer,
ϕ
⁡
(
a
,
b
,
d
)
=
2
π
×
arctan
(
ab
2
⁢
d
⁢
a
2
+
b
2
+
4
⁢
d
2
)
[
formula
⁢
⁢
1
]
0.75
×
∑
k
=
1
P
⁢
∑
i
=
1
N
⁢
2
⁢
π
⁢
⁢
M
1
⁢
⁢
i
⁡
(
ϕ
⁢
(
a
1
⁢
⁢
i
,
b
1
⁢
⁢
i
,
d
1
⁢
⁢
ik
)
-
ϕ
⁡
(
a
1
⁢
⁢
i
,
b
1
⁢
⁢
i
,
t
1
⁢
⁢
i
+
d
1
⁢
⁢
ik
)
)
-
0.75
×
∑
k
=
1
P
⁢
∑
j
=
1
M
⁢
2
⁢
π
⁢
⁢
M
2
⁢
⁢
j
⁡
(
ϕ
⁢
(
a
2
⁢
⁢
j
,
b
2
⁢
⁢
j
,
d
2
⁢
jk
)
-
ϕ
⁡
(
a
2
⁢
⁢
j
,
b
2
⁢
⁢
j
,
t
2
⁢
⁢
j
+
d
2
⁢
jk
)
)
≥
0.052
×
∑
k
=
1
P
⁢
(
H
Kk
-
4
⁢
π
⁢
⁢
M
Sk
)
.
[
formula
⁢
⁢
2
]

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Magnetic memory element and magnetic memory apparatus

Life of this patent

Magnetic memory element and magnetic memory apparatus

Life of this patent

Abstract

Claims6