Current induced spin-momentum transfer stack with dual insulating layers
A high speed, low power method to control and switch the magnetization direction of a magnetic region in a magnetic device for memory cells using spin polarized electrical current. The magnetic device comprises a pinned magnetic layer, a reference magnetic layer with a fixed magnetization direction and a free magnetic layer with a changeable magnetization direction. The magnetic layers are separated by insulating non-magnetic layers. A current can be applied to the device to induce a torque that alters the magnetic state of the device so that it can act as a magnetic memory for writing information. The resistance, which depends on the magnetic state of the device, can be measured to read out the information stored in the device.
1. A magnetic device comprising:
a pinned magnetic layer with a first magnetization vector with a first magnetization direction that is fixed;
a free magnetic layer with a second magnetization vector with a changeable second magnetization direction;
a first non-magnetic insulating layer that spatially separates the free magnetic layer and the pinned magnetic layer, wherein the first non-magnetic insulating layer is sufficiently thin such that electrons traverse the first non-magnetic layer by quantum mechanical tunneling;
a read-out magnetic layer with a third magnetization vector with a third magnetization direction that is fixed, wherein the first magnetization vector is orthogonal to the second magnetization vector and the third magnetization vector; and
a second non-magnetic insulating layer that spatially separates the free magnetic layer and the read-out magnetic layer, wherein the second non-magnetic insulating layer is sufficiently thin such that electrons traverse the second non-magnetic layer by quantum mechanical tunneling.
2. The magnetic device of claim 1 , wherein the first non-magnetic insulating layer comprises one of more of magnesium oxide, MgO, aluminum oxide, AlO, or silicon oxide, SiO, wherein the proportion of oxygen to the first element need not be in the ratio of one to one.
3. The magnetic device of claim 1 , wherein the first non-magnetic insulating layer comprises MgO that has an epitaxial lattice arraignment with at least the free magnetic layer or the pinned magnetic layer.
4. The magnetic device of claim 1 , wherein the second non-magnetic insulating layer comprises one of more of magnesium oxide, MgO, aluminum oxide, A 10 , or silicon oxide, SiO, wherein the proportion of oxygen to the first element need not be in the ratio of one to one.
5. The magnetic device of claim 1 , wherein the first magnetization vector is perpendicular to a plane of the pinned layer.
6. The magnetic device of claim 1 , wherein the pinned magnetic layer, the free magnetic layer, and the read-out magnetic layer are comprised of Co, Ni, Fe, an alloy of Co and Ni, an alloy of Co and Fe, an alloy of Ni and Fe, an alloy of Co, Ni, Fe, or permalloy Nil-xFex.
7. The magnetic device of claim 1 , wherein the pinned magnetic layer, the free magnetic layer, and the read-out magnetic layer are comprised of a non-magnetic metal and an alloy, wherein the alloy comprises an alloy of Co and Ni, an alloy of Co and Fe, an alloy of Ni and Fe, or an alloy of Co, Ni and Fe, such that the non-magnetic metal and the alloy are ferromagnetically ordered at room temperature.
8. The magnetic device of claim 7 , wherein the non-magnetic metal comprises Cu, Pd or Pt.
9. The magnetic device of claim 1 , wherein the pinned magnetic layer, the free magnetic layer, and the read-out magnetic layer are comprised of NiMnSb and a conducting magnetic oxide.
10. The magnetic device of claim 9 , wherein the conducting magnetic oxide comprises CrO2 or Fe3O4.
11. The magnetic device of claim 1 , wherein spin transfer torques associated with the pinned magnetic layer is described by,
ⅆ
m
^
ⅆ
t
=
-
γμ
0
m
^
×
H
→
eff
+
α
m
^
×
ⅆ
m
^
ⅆ
t
+
γα
J
m
^
×
(
m
^
×
m
^
P
)
-
βγα
J
m
^
×
(
m
^
×
m
^
R
)
where m represents the magnetization direction of the free layer magnetization, a j is a term proportional to current and current spin-polarization, the second term d{circumflex over (m)}/dt being spin transfer from the pinned magnetic layer (m p ) and the third term begin spin transfer from the read-out magnetic layer (m r ), and β represents a ratio of magnitude m p /m r .
12. The magnetic device of claim 11 , wherein β>1 provides a range of current pulse amplitudes wherein switching of the magnetic device is directly from parallel to anti-parallel for a first current polarity and anti-parallel to parallel for a second current polarity.
13. The magnetic device of claim 12 , wherein the magnetic device switching is precessional and bipolar for both polarities.
14. The magnetic device of claim 11 , wherein β>1 provides reduced direct current switching errors.
15. The magnetic device of claim 11 , wherein β>1 and pulse polarity controls a final magnetization state of the free magnetic layer and the final magnetization state of the free layer is independent of current pulse durations longer than a minimum switching pulse duration.
16. The magnetic device of claim 15 , wherein spin polarization of the read-out magnetic layer is increased by selecting mating materials for the read-out magnetic layer and a magnetic tunnel junction layer adjacent thereto.
17. The magnetic device of claim 16 , wherein the mating materials are selected from the group of (a) CoFeB and MgO and (b) NiFe and MgO.
18. The magnetic device of claim 15 , wherein the pinned magnetic layer comprises a Co/Ni multilayer, Pt, Pd, Co/Pt, Co/Pd, or a combination of Pt and Pd that reduces spin polarization from the pinned magnetic layer.
19. A method of magnetic switching, the method comprising:
applying an electric current over a sub-nanosecond period of time to a magnetic device comprising a pinned magnetic layer with a first magnetization vector with a first magnetization direction that is fixed, a free magnetic layer with a second magnetization vector having at least two stable magnetic states, a read-out magnetic layer with a third magnetization vector with a third magnetization direction that is fixed, wherein the first magnetization vector is orthogonal to the second magnetization vector and the third magnetization vector wherein the pinned magnetic layer and the free magnetic layer are separated by a first non-magnetic insulating layer, wherein the free magnetic layer and the read-out magnetic layer are separated by a second non-magnetic insulating layer, wherein the current is applied through the pinned magnetic layer, the free magnetic layer, and the read-out magnetic layer, and wherein the first non-magnetic insulating layer and the second non-magnetic insulating layer are sufficiently thin such that electrons traverse the first non-magnetic layer and the second non-magnetic layer by quantum mechanical tunneling; and
stopping application of the electric current after the second magnetization vector changes from one of the two stable magnetic states to another of the two stable magnetic states.
20. The method of claim 19 , wherein the first non-magnetic insulating layer comprises one of more of magnesium oxide, MgO, aluminum oxide, AlO, or silicon oxide, SiO, wherein the proportion of oxygen to the first element need not be in the ratio of one to one.