JP2023094193A - Layer structure of magnetic memory element, magnetic memory element, magnetic memory device, and method for storing data to magnetic memory element - Google Patents

Abstract

To provide a layer structure of a magnetic memory element with improved drive current required for a magnetic domain wall movement and controllability of the magnetic domain wall movement, and a magnetic memory element including the same.SOLUTION: A layer structure 9 of a magnetic memory element 10 includes a plurality of antiferromagnetic layers 1 and a boundary layer 2 that is arranged between a plurality of antiferromagnetic layers 1,1 and configures a magnetic domain wall. The thickness of the boundary layer 2 is 2.0 nanometers or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a magnetic memory element, and more particularly to a layer structure of a magnetic memory element that transmits information based on domain wall motion, a magnetic memory element, a magnetic memory device, and a method of storing data in the magnetic memory element.

With the dramatic increase in the amount of information, there is a need for memory devices that can record information at high density. As such a memory device, flash memory is currently widely used. However, due to its operating principle, the flash memory has the drawback that the number of times it can be written is limited due to deterioration of the oxide film, and that the write speed slows down while the information is repeatedly written. For this reason, in recent years, various magnetic memories have been proposed to replace existing flash memories.

For example, Patent Document 1 discloses a linear racetrack memory proposed as a three-dimensional magnetic memory. Further, Patent Document 2 discloses a magnetic storage device using spin transfer torque as a recording method.

In the racetrack memory of Patent Document 1, ferromagnetic materials are separated by magnetic domains and arranged in a stack or in a line. A bit is defined for each magnetic domain, and data is stored according to the orientation of magnetization in the magnetic domain. In the magnetic storage device of Patent Document 2, a current is passed through the stack from a current source to generate torque between the magnetic layers adjacent to each position due to spin momentum transfer, thereby determining the direction of magnetization, thereby storing data and data. remember bits.

U.S. Pat. No. 6,834,005 JP 2009-239282 A

In the racetrack memory of Patent Literature 1, a domain wall is moved by applying a current to a ferromagnetic fine wire (magnetic nanowire). This causes the magnetization in the magnetic domains to move in one direction all at once, thereby transmitting data. In the magnetic storage device of Patent Document 2, although spin transfer torque is used in the recording method, no domain wall occurs in the stack memory.

The information transmission method based on domain wall motion, such as that shown in Patent Document 1, still has the problem of high drive current for domain wall motion and poor controllability of domain wall motion. are doing. Thus, in the magnetic memory element, it is required to improve the controllability of the drive current required for the domain wall motion and the domain wall motion.

An object of the present invention is to provide a layered structure of a magnetic memory element with improved controllability of the driving current required for domain wall motion and domain wall motion, and a magnetic memory element having the layered structure.

The present invention for achieving the above object includes, for example, the following aspects.
(Section 1)
a plurality of antiferromagnetic layers;
a boundary layer disposed between the plurality of antiferromagnetic layers and forming a domain wall;
with
A layered structure of a magnetic memory element, wherein the boundary layer has a thickness of 2.0 nanometers or less.
(Section 2)
Item 2. The layer structure of item 1, wherein the antiferromagnetic layer comprises a plurality of ferromagnetic layers that are stacked.
(Section 3)
Item 3. The layer structure according to item 2, wherein the antiferromagnetic layer further includes a nonmagnetic layer between the plurality of ferromagnetic layers.
(Section 4)
4. Layered structure according to any one of clauses 1 to 3, wherein the boundary layer has a thickness of 0.5 nanometers or less.
(Section 5)
A layer structure according to any one of Items 1 to 4;
a first ferromagnetic layer capable of switching a spin state, disposed on one side of the antiferromagnetic layer with the boundary layer interposed therebetween;
a first electrode positioned adjacent to the first ferromagnetic layer for switching the spin state of the first ferromagnetic layer by spin-orbit torque;
a second electrode disposed on the side of the other antiferromagnetic layer farthest from the one;
A magnetic memory element.
(Section 6)
an insulating film disposed between the other antiferromagnetic layer farthest from the one and the second electrode;
a second ferromagnetic layer having a fixed spin state disposed between the insulating film and the second electrode;
further comprising
Item 6. The magnetic memory element according to item 5, wherein the spin state of the other antiferromagnetic layer is read via the second electrode.
(Section 7)
Item 6. The magnetic memory element according to Item 6;
a current source that directs current into and from the first electrode and from the second electrode;
a sensor that reads data represented by a spin state stored in the magnetic memory element;
a magnetic memory device.
(Section 8)
7. A method for storing data represented by a spin state in the magnetic memory element according to item 5 or 6, comprising:
setting the spin state of the first ferromagnetic layer by a spin-orbit torque by passing a current through the first electrode;
applying a current between the second electrode and the first electrode to transfer the spin state of the first ferromagnetic layer to one of the antiferromagnetic layers by spin transfer torque;
A method of storing data in a magnetic memory element, comprising:

According to the present invention, it is possible to provide a layered structure of a magnetic memory element with improved controllability of the drive current required for the domain wall motion and the domain wall motion, and a magnetic memory element having the layered structure.

1 is a cross-sectional view schematically showing a schematic configuration of a magnetic memory element according to an embodiment of the invention; FIG. 4A and 4B are schematic diagrams for explaining the operation of a magnetic memory element according to an embodiment of the present invention; FIG. 4 is a flow chart for explaining a procedure for storing data in a magnetic memory element according to an embodiment of the invention; 1 is a diagram schematically showing a schematic configuration of a magnetic memory device according to one embodiment of the present invention; FIG. 4 is a graph showing the results of numerical simulations of the ratio Mz/Ms between magnetization in the z-axis direction and saturation magnetization over time. 5 is a graph showing the results of numerical simulations relating to the relationship between the interaction Jex occurring in the antiferromagnetic layer and the current density Jc required for the operation of the layer structure; 5 is a graph showing the results of numerical simulation comparing the current density Jc required for operation of the layer structure between the antiferromagnetic layer and the ferromagnetic layer. It is the result of numerical simulation regarding the thickness of the boundary layer, and is a graph showing the result of calculating the ratio Mz/Ms between the magnetization in the z-axis direction and the saturation magnetization using the ferromagnetic interaction Aex as a free parameter. 9 is a graph plotting the thickness of the boundary layer required for the spin arrow to change in the horizontal direction in the graph shown in FIG. 8 for each value of ferromagnetic interaction Aex. 1 is a cross-sectional view schematically showing a schematic configuration of a magnetic memory element using a ferromagnetic material for a recording layer; FIG.

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In the following description and drawings, the same reference numerals denote the same or similar components, and redundant description of the same or similar components will be omitted.

In this specification, the term "layer" does not mean only a layer that is distinguished from other layers by physical and chemical properties such as materials used for formation and magnetism and conductivity. It also means a film or region formed on or in a material such as a metal or alloy, for example by a method such as sputtering. The term "layer" in the claims is to be interpreted to include "film" and "region".
[Configuration of memory device]

FIG. 1 is a cross-sectional view schematically showing a schematic configuration of a magnetic memory element according to one embodiment of the present invention.

A magnetic memory element 10 according to an embodiment of the present invention includes a plurality of antiferromagnetic layers 1 (1a to 1e), a plurality of boundary layers 2 (2a to 2e), a first ferromagnetic layer 3, a 1 electrode 4 , an insulating film 5 , a second ferromagnetic layer 6 , and a second electrode 7 . In the illustrated magnetic memory element 10, the first ferromagnetic layer 3, the layer structure 9 of the plurality of boundary layers 2 and the plurality of antiferromagnetic layers 1, the insulating film 5, and the second ferromagnetic layer 6 are It has a three-dimensional structure laminated between the first electrode 4 and the second electrode 7 in order from the bottom in the drawing. As will be described below, the layer structure 9 of the magnetic memory element 10 according to the present invention includes an antiferromagnetic layer 1 as a recording layer, and the thickness of the boundary layer 2 is such that domain walls are formed therein. It is the thickness that can operate as a domain wall layer.

The plurality of antiferromagnetic layers 1 (1a to 1e) are layers whose spin states can be switched. One antiferromagnetic layer 1 functions as a memory cell that stores 1-bit binary information. In a ferromagnet, multiple spins are arranged so as to align with each other. For example, one bit of binary information can be generated by the direction of magnetization of the entire ferromagnetic material, which is represented by two states in which the spin arrow points upward or downward. express. On the other hand, an antiferromagnetic material does not have magnetization as a whole, but it has a microscopic magnetic order, and one-bit binary information of "0" or "1" can be assigned to this state. . That is, the antiferromagnetic layer 1 whose spin state can be switched can be expressed as a layer to which a spin state corresponding to 1-bit binary information is assigned.

The antiferromagnetic layer 1 includes a plurality of laminated ferromagnetic layers 11 and 12 and a non-illustrated non-magnetic layer disposed between the ferromagnetic layers 11 and 12 . The non-magnetic layer in the antiferromagnetic layer 1 is optional, and may be omitted in another embodiment. In the antiferromagnetic layer 1, an interaction Jex that maintains the spin directions in opposite directions occurs between the laminated ferromagnetic layers 11 and 12. As shown in FIG. Thus, in one antiferromagnetic layer 1, the spin direction in one ferromagnetic layer 11 and the spin direction in the other ferromagnetic layer 12 are maintained in opposite directions. For example, in the antiferromagnetic layer 1, binary information “0” can be assigned to a state in which the spin arrow in the ferromagnetic layer 11 points upward and the spin arrow in the ferromagnetic layer 12 points downward. The binary information "1" can be assigned to the state where the spin arrows in the magnetic layer 11 point downwards and the spin arrows in the ferromagnetic layer 12 point upwards. The allocation of binary information in the antiferromagnetic layer 1 is not limited to this example, and the logic opposite to the example of the binary information to be assigned may be used.

For example, the antiferromagnetic layer 1 has a Co/Pt/Gd laminated structure in which cobalt, platinum, and gadolinium are laminated, or (Co/Pt) ₆ in which iridium is laminated between two laminated layers of cobalt and platinum. It can be formed using a laminated structure of /Ir/(Co/Pt) ₆ . The symbol "/" means stacking of layered structures. These laminated structures can be formed by sputtering, for example. In the Co/Pt/Gd laminated structure forming the antiferromagnetic layer 1, the Co layer and the Gd layer correspond to the ferromagnetic layers 11 and 12, and the Pt layer corresponds to the nonmagnetic layer. Illustratively, the Co layer is about 1 nm thick, the Pt layer is about 0.1 nm thick, and the Gd layer is about 1 nm thick. In the (Co/Pt) ₆ /Ir/(Co/Pt) ₆ layer structure, the two (Co/Pt) layers correspond to the ferromagnetic layers 11 and 12 and the Ir layer corresponds to the nonmagnetic layer. Illustratively, the (Co/Pt) ₆ layer is about 2.4 nm thick and the Ir layer is about 0.5 nm thick.

The boundary layer 2 is arranged between the plurality of antiferromagnetic layers 1 to form a domain wall. In the illustrated embodiment, the spin state of the boundary layer 2 can have three states, with the spin arrow pointing up, down, and sideways, for example. When a domain wall is formed in the boundary layer 2, the spin state of the boundary layer 2 is represented by horizontal arrows. For convenience of explanation, the state in which the spin arrow points sideways is only to the right. In this embodiment, the boundary layer 2 is formed using an oxide film such as magnesium oxide (MgO). Illustratively, the thickness of the MgO layer used for boundary layer 2 is about 1 nm. The boundary layer 2 can be formed, for example, by a sputtering method.

The first ferromagnetic layer 3 is a ferromagnetic layer whose spin state can be switched. The first ferromagnetic layer 3 is arranged on the side of the antiferromagnetic layer 1a located on the lower side in the drawing in the layer structure 9 with the boundary layer 2 interposed therebetween. The first ferromagnetic layer 3 functions as a layer for writing 1-bit binary information in the antiferromagnetic layer 1a. Illustratively, the first ferromagnetic layer 3 can be formed using an alloy of cobalt and platinum or an alloy of iron and nickel. As a material for the first ferromagnetic layer 3, various materials used for a magnetization fixed layer in a magnetoresistive memory (MRAM: Magnetoresistive Random Access Memory) can be used.

A first electrode 4 is arranged adjacent to the first ferromagnetic layer 3 and switches the spin state of the first ferromagnetic layer 3 by spin-orbit torque. The first electrode 4 comprises a spin-orbit torque (SOT) layer 41 and two bottom electrodes 42 ( 42 a, 42 b ) electrically connected to the spin-orbit torque layer 41 .

By passing a drive current for switching the spin state of the first ferromagnetic layer 3 between the terminal 21 and the terminal 22 of the first electrode 4, the write current Iw indicated by a dashed line in the figure changes the spin state. The spin state of the first ferromagnetic layer 3 is switched by the spin-orbit torque flowing in the orbital torque layer 41 and caused by the spin-orbit interaction. The spin state of the first ferromagnetic layer 3 is determined according to the direction of the write current Iw. In this embodiment, the write current Iw is pulsed. Illustratively, the spin-orbit torque layer 41 can be formed using a heavy metal such as platinum. Bottom electrode 42 may be formed using a variety of conductive metals such as gold and copper.

The insulating film 5 and the second ferromagnetic layer 6 are combined with the upper antiferromagnetic layer 1d in the layer structure 9 to form a magnetic tunnel for reading the spin state of this antiferromagnetic layer 1d. It functions as a junction (MTJ: Magnetic Tunnel Junction). The antiferromagnetic layer 1d functions as a free layer of the magnetic tunnel junction. The spin state of the antiferromagnetic layer 1d is read by measuring the magnitude of the current (readout current) flowing through the antiferromagnetic layer 1d, the insulating film 5, and the second ferromagnetic layer 6. FIG. Since the method of reading the spin state by magnetic tunnel junction is well known, further detailed description is omitted here.

The insulating film 5 functions as a tunnel layer of the magnetic tunnel junction. The insulating film 5 is arranged between the antiferromagnetic layer 1 d located on the upper side in the drawing in the layer structure 9 and the second electrode 7 . The second ferromagnetic layer 6 is a layer whose spin state is fixed (the arrow points upward in the illustrated embodiment), and functions as a fixed layer of the magnetic tunnel junction. In this embodiment, the spin state of the second ferromagnetic layer 6 is fixed such that the spin arrow points upward. A second ferromagnetic layer 6 is arranged between the insulating film 5 and the second electrode 7 . The insulating film 5 can be formed using an oxide film such as magnesium oxide (MgO). The second ferromagnetic layer 6 can be formed using, for example, CoFeB, which is an alloy of cobalt, iron and boron. As the material of the second ferromagnetic layer 6, various materials used for the fixed magnetization layer in MRAM can be used.

The second electrode 7 reads out the spin state of the antiferromagnetic layer 1d located on the upper side of the layer structure 9 in the figure. The second electrode 7 is arranged adjacent to the second ferromagnetic layer 6 on the side of the antiferromagnetic layer 1d located on the upper side in the figure.

By passing a driving current for moving the domain wall between either one of the terminals 21 and 22 of the first electrode 4 and the terminal 23 of the second electrode 7, A domain wall drive current Id shown flows between the second electrode 7 and the first electrode 4 . As a result, domain walls can be moved in a plurality of boundary layers 2 (2a to 2d) located between the second electrode 7 and the first electrode 4, and a plurality of antiferromagnetic layers 1 (1a to 1d) can be moved. ) can be shifted sequentially in a racetrack fashion. The insulating film 5 and the second ferromagnetic layer 6 function as a magnetic tunnel junction for reading. As a result, the spin state of the antiferromagnetic layer 1 d located on the upper side in the drawing in the layer structure 9 is read out via the second electrode 7 . In this embodiment, the domain wall driving current Id is pulsed. Illustratively, the second electrode 7 can be formed using various conductive metals such as gold and copper.
[Operation of memory device]

FIG. 2 is a schematic diagram for explaining the operation of the magnetic memory device according to one embodiment of the present invention. FIG. 3 is a flowchart for explaining the procedure for storing data in the magnetic memory element according to one embodiment of the invention.

A method for storing data in the magnetic memory element 10 according to one embodiment is to apply a current between the bottom electrodes 42a and 42b of the first electrode 4 to change the spin state of the first ferromagnetic layer 3 by spin-orbit torque. In the step of setting (step S1), the domain wall driving current Id is passed between the second electrode 7 and the first electrode 4, and the spin state of the first ferromagnetic layer 3 is changed to antiferromagnetic by the spin transfer torque. and a step of transitioning to layer 1 (1a) (step S2).

The procedure shown in FIG. 3 for storing data in the magnetic memory element 10 according to one embodiment and the procedure for reading data from the magnetic memory element 10 will be described below. In the illustrated embodiment, magnetic memory element 10 includes five memory cells to store a total of five bits of binary information.

Data Initialization In describing the operation of the magnetic memory element 10, it is assumed that the magnetic memory element 10 is in the initial state shown in FIG. 2(I). The magnetic memory element 10 can be initialized, for example, by continuously supplying a pulsed domain wall driving current Id from the first electrode 4 to the second electrode 7 for a predetermined number of times. The spin state of the second ferromagnetic layer 6 is fixed in advance in a predetermined direction (for example, upward), and therefore does not change even after initialization.

Data Writing Data is written to the magnetic memory element 10 via the first ferromagnetic layer 3 . In this embodiment, since the first ferromagnetic layer 3 is arranged below the layer structure 9, data is written in the lowest position among the plurality of antiferromagnetic layers 1 (1a to 1e). This is done from the antiferromagnetic layer 1a. When a rightward write current Iw is applied to the first electrode 4, as shown in FIG. arrow is switched from downward to upward. Along with this, a domain wall indicated by a horizontal spin arrow is formed in the boundary layer 2a positioned between the first ferromagnetic layer 3 and the antiferromagnetic layer 1a.

Movement of Domain Wall When a pulse-like domain wall driving current Id is passed from the second electrode 7 to the first electrode 4, the domain wall formed in the boundary layer 2a moves in a reverse direction as shown in FIG. 2(III). It moves to the boundary layer 2b located between the ferromagnetic layer 1a and the antiferromagnetic layer 1b. As a result, the spin state of each of the first ferromagnetic layer 3 and the plurality of antiferromagnetic layers 1 (1a to 1e) is shifted to the upper layer in the figure by the domain wall displacement caused by the spin transfer torque caused by the domain wall drive current Id. It will gradually shift to a racetrack system. As described above, the spin state of the first ferromagnetic layer 3 is shifted to the antiferromagnetic layer 1a by the sequential shift of the spin state due to the magnetic domain wall motion caused by the spin transfer torque.

When a pulsed domain wall driving current Id flows from the first electrode 4 to the second electrode 7 in the opposite direction to the above explanation, the first ferromagnetic layer 3 and the plurality of antiferromagnetic layers 1 ( Each of the spin states 1a to 1e) is sequentially transferred to the lower layer in the drawing in a racetrack manner due to the domain wall displacement caused by the spin transfer torque caused by the domain wall driving current Id. In this embodiment, the first ferromagnetic layer 3 used for writing data is arranged below the layer structure 9, and the insulating film 5 and the second ferromagnetic layer 6 used for reading data are arranged above the layer structure 9. , the domain wall driving current Id is passed from the second electrode 7 to the first electrode 4 to sequentially shift the spin state to the upper layer in the figure.

Subsequently, when a pulsed domain wall driving current Id is passed from the second electrode 7 to the first electrode 4, the domain wall formed in the boundary layer 2b becomes antiferromagnetic as shown in FIG. 2(IV). Moving to the boundary layer 2c located between the layer 1b and the antiferromagnetic layer 1c, the sequential transition of spin states described with reference to state (II) in FIG. 2 also continues. The spin state of the antiferromagnetic layer 1a shifts to the antiferromagnetic layer 1b.

Data Reading Data is read from the magnetic memory element 10 via the insulating film 5 and the second ferromagnetic layer 6 . In this embodiment, since the insulating film 5 and the second ferromagnetic layer 6 are arranged above the layer structure 9, data is read from the most antiferromagnetic layer 1 (1a to 1e). This is done from the antiferromagnetic layer 1e positioned above. The spin state of the antiferromagnetic layer 1e is read by measuring the magnitude of the readout current flowing through the antiferromagnetic layer 1e, the insulating film 5, and the second ferromagnetic layer 6 using a magnetic tunnel junction. be Since the sequential transition of the spin state occurs for each pulse, only one magnetic tunnel junction for reading the spin state is required for each magnetic memory element 10 .

First, the spin state of the antiferromagnetic layer 1e is measured using a magnetic tunnel junction to read binary information corresponding to the spin state. Next, a pulsed domain wall driving current Id is passed from the second electrode 7 to the first electrode 4 . As a result, the spin state is sequentially transferred to the upper layer in the figure in a racetrack manner due to domain wall movement due to the spin transfer torque. Binary information corresponding to the spin state stored in the antiferromagnetic layer 1e is destroyed by applying the pulsed domain wall driving current Id. have already been read out using magnetic tunnel junctions.

Thereafter, a read operation including a step of measuring the spin state of the antiferromagnetic layer 1e using a magnetic tunnel junction and a step of passing a pulsed domain wall driving current Id from the second electrode 7 to the first electrode 4. is repeatedly applied, binary information corresponding to the spin states of a plurality of antiferromagnetic layers 1 can be read from the magnetic memory element 10 .

In the example of the operation of the magnetic memory element 10 described above, data is read from the antiferromagnetic layer 1e by a destructive read method similar to that of a DRAM (Dynamic Random Access Memory). Write the data again.
[Configuration of magnetic memory device]

FIG. 4 is a diagram schematically showing a schematic configuration of a magnetic memory device according to one embodiment of the present invention.

A magnetic memory device 20 according to one embodiment includes a magnetic memory element 10 , a current source 24 and a sensor 25 .

The current source 24 causes current to flow between the bottom electrodes 42 a and 42 b of the first electrode 4 of the magnetic memory element 10 and from the second electrode 7 to the first electrode 4 . The sensor 25 reads data represented by spin states stored in the magnetic memory element 10 . The sensor 25 can measure the current value of the read current flowing through the magnetic memory element 10, detect the resistance value from the measured value, and read the spin state of the magnetic memory element. Current source 24 and sensor 25 are connected to memory controller 26 . The memory controller 26 controls write operations to the magnetic memory element 10 and read operations from the magnetic memory element 10 by controlling the operations of the current source 24 and the sensor 25 . Data read through sensor 25 is transmitted and received through data bus 27 . The connection from the current source 24 to the first electrode 4 and the second electrode 7 of the magnetic memory element 10 is switched using switches 28a and 28b, for example. The operations of the switches 28a and 28b are controlled by the memory controller 26, for example. A plurality of magnetic memory elements 10 can be arranged in an array to form a memory array.
[Numerical simulation of layer structure]

5 to 9 are results of various numerical simulations regarding the layer structure of the magnetic memory element according to one embodiment of the present invention. Simulation conditions common to various numerical simulations described below are as follows. The simulation parameters assume typical MRAM materials.
[Layer shape and size]
Each layer is disc-shaped with a diameter of 20 nm and a thickness of 3 nm, composed of cells of 1 nm×1 nm×1 nm.
[Number of layers and layer structure]
This is the layered structure shown in FIG. 4, with a total of 16 layers. The material parameters for each layer are as follows. Here, Ms means the magnitude of saturation magnetization, Ku means the magnitude of magnetic anisotropy, and Aex means the magnitude of ferromagnetic interaction (Magnetic Stiffness). The ferromagnetic interaction Aex is an interaction for aligning the directions of spins. Jex means the magnitude of interaction that maintains the spin directions in opposite directions. The interaction Jex and the ferromagnetic interaction Aex are independent interactions. Since the value of Ku in the domain wall layer is zero, the domain wall is trapped in the domain wall layer instead of the recording layer. This improves the controllability of the domain wall position.
・Layers 2, 5, 8, 11, 14 (domain wall layers)
Aex=1×10 ⁻¹² [J/m], Ku=0, Ms=8×10 ⁵ [A/m]
The domain wall layer corresponds to the boundary layer 2 in the magnetic memory element 10 according to one embodiment of the invention.
・Layers 3, 4, 6, 7, 9, 10, 12, 13, 15, 16 (recording layers)
Aex=1×10 ⁻¹¹ [J/m], Ku=1×10 ⁶ [J/m ³ ], Ms=8×10 ⁵ [A/m], Jex=−3.0 [erg/cm ² ]
The recording layers correspond to the ferromagnetic layers 11 and 12 in the magnetic memory element 10 according to one embodiment of the present invention. configure. By introducing an interaction Jex between two adjacent recording layers that maintains the spin directions in opposite directions, it is simulated that these two adjacent recording layers operate as one antiferromagnetic layer 1. .
・Layer 1 (pin layer)
Aex=1×10 ⁻¹¹ [J/m], Ku=1×10 ⁷ [J/m ³ ], Ms=8×10 ⁵ [A/m]
The pinned layer corresponds to the first ferromagnetic layer 3 in the magnetic memory element 10 according to one embodiment of the invention.

Various numerical simulation results regarding the layer structure 9 of the magnetic memory element 10 according to one embodiment of the present invention will be described below with reference to FIGS.
[Operation of layer structure]

FIG. 5 is a graph showing the result of numerical simulation regarding the passage of time of the ratio Mz/Ms between the magnetization in the z-axis direction and the saturation magnetization. In the first numerical simulation, the operation of the layer structure is simulated by applying a pulsed domain wall driving current Id to the layer structure 9 of the magnetic memory element 10 shown in FIG. The results of numerical simulation are shown in FIG.

In FIG. 5, the upper stage shows the simulation results for the boundary layer 2 (domain wall layer DW), and the lower stage shows the simulation results for the antiferromagnetic layer 1 (AFM: antiferromagnetic). Layer numbers correspond between FIGS. 2 and 5, and states (II) to (IV) also correspond between FIGS. The value of the magnetization ratio Mz/Ms shown on the vertical axis of the graph of FIG. 5 corresponds to the direction of the spin arrow shown in the layer structure of FIG. The values '1', '0' and '-1' of the magnetization ratio Mz/Ms mean the upward, sideways and downward directions of the spin arrow, respectively. When a domain wall is formed in the boundary layer 2, the spin state of the boundary layer 2 is represented by horizontal arrows.

Movement of Domain Wall Constructed in Boundary Layer 2 Movement of the domain wall constructed in the boundary layer 2 will be described with reference to FIGS. 5 and 2. FIG. In the state shown in FIG. 2(II), the boundary layer 2a of the layer number 2 forms a domain wall indicated by the horizontal spin arrow. Next, in the state shown in (III) in which the domain wall driving current Id is passed through the layer structure, domain walls indicated by horizontal spin arrows are formed in the boundary layer 2b of layer number 5. FIG. Next, in the state shown in (IV) in which the domain wall driving current Id is passed through the layer structure, domain walls indicated by horizontal spin arrows are formed in the boundary layer 2c of layer number 8. FIG.

Referring to the upper part of FIG. 5 showing the simulation results for the boundary layer 2, for each layer number constituting the boundary layer 2, the value of the magnetization ratio Mz/Ms along the time course of the state (II) to the state (IV) to confirm. In state (II), the boundary layer 2a of layer number 2 denoted by reference numeral 52 has a value of "0", and in state (III), the boundary layer 2b of layer number 5 denoted by reference numeral 55 has a value of "0". , and in state (IV), it is confirmed that the boundary layer 2c of layer number 8 denoted by reference numeral 58 has a value of "0". In the boundary layers 2a, 2b, and 2c of layer numbers 2, 5, and 8, the value of the magnetization ratio Mz/Ms before or after the movement of the domain wall is "1" or "-1". , it is confirmed that the spin state is appropriately changed without maintaining the value "0".

As a result, it is confirmed by the numerical simulation that the domain wall formed in the boundary layer 2 shifts to the upper boundary layer 2 in the figure in a racetrack manner every time the domain wall driving current Id flows through the layer structure.

Change in Spin State in Antiferromagnetic Layer 1 A change in spin state in the antiferromagnetic layer 1 will be described with reference to FIGS. 5 and 2. FIG. Referring to the state shown in FIG. 2(II) in which the domain wall is formed in the boundary layer 2a of the layer number 2, the opposite layers of the layer numbers 3 and 4 located above the boundary layer 2a of the layer number 2 in which the domain wall is formed. In the ferromagnetic layer 1a, the spin arrows are in an antiparallel combination in which they point outward. Next, in the state shown in (III) in which the domain wall driving current Id is passed through the layer structure, the domain wall formed in the boundary layer 2a of the layer number 2 moves to the boundary layer 2b of the layer number 5, and the layer number 3, In the antiferromagnetic layer 1a of No. 4, the spin state changes and becomes an antiparallel combination state in which the spin arrows point inward. In the antiferromagnetic layers 1b of layer numbers 6 and 7 located above the boundary layer 2b of layer number 5 in which domain walls are formed, the spin arrows are in an antiparallel combination state in which they point inward. Next, in the state shown in (IV) in which the domain wall driving current Id is supplied to the layer structure, the domain wall formed in the boundary layer 2b of the layer number 5 moves to the boundary layer 2c of the layer number 8, and the layer number 6, In the antiferromagnetic layer 1b of 7, the spin state changes and becomes an antiparallel combination state in which the spin arrows point outward.

Referring to the lower part of FIG. 5 showing the simulation results for the antiferromagnetic layer 1, for each layer number constituting the antiferromagnetic layer 1, the magnetization ratio Check the change in the value of Mz/Ms. As for layer numbers 3 and 4 constituting the antiferromagnetic layer 1a, the spin state changes from state (II) to state (III). From state (II) to state (III), the ferromagnetic layer of layer number 3 denoted by reference numeral 53 changes from the value “−1” to the value “1”, and the ferromagnetic layer of layer number 4 denoted by reference numeral 54 changes from the value “−1” to the value “1”. has changed from value "1" to value "-1". As for layer numbers 6 and 7 constituting the antiferromagnetic layer 1b, the spin state changes from state (III) to state (IV). From state (III) to state (IV), the ferromagnetic layer of layer number 6 denoted by reference numeral 56 changes from the value "1" to the value "-1", and the ferromagnetic layer of layer number 7 denoted by reference numeral 57 changes from the value "1" to the value "-1". has changed from the value "-1" to the value "1".

As a result, the domain wall driving current Id flows through the layer structure, and the spin state of the antiferromagnetic layer 1 is reversed each time the domain wall formed in the boundary layer 2 moves across the antiferromagnetic layer 1. Confirmed by numerical simulation.
[Interaction Jex Dependencies]

FIG. 6 is a graph showing the results of numerical simulations relating to the relationship between the interaction Jex occurring in the antiferromagnetic layer and the current density Jc required for the operation of the layer structure. A second numerical simulation simulates the dependence of the interaction Jex on the current density Jc. The results of numerical simulation are shown in FIG.

In FIG. 6, the vertical axis of the graph indicates the current density Jc [A/m ² ] required for the operation of the layer structure, and the horizontal axis of the graph indicates that the spin directions are kept opposite to each other in the antiferromagnetic layer 1. It shows the magnitude of the interaction Jex [erg/cm ² ]. In this numerical simulation, the magnitude of the current density Jc required for the operation indicated on the vertical axis is calculated using the magnitude of the interaction Jex indicated on the horizontal axis as a free parameter. For the value of the interaction Jex, the four values shown in FIG. 6 are used with reference to the following numerical ranges published in academic papers.
・Co/Pt/Gd: 0 to 40 erg/cm ² (IEEE Translation Journal on Magnetics in Japan, 9, 164 (1994))
・(Co/Pt) ₆ /Ir/(Co/Pt) ₆ : 2.6 erg/cm ² (Appl. Phys. Lett. 110, 092406 (2017))

Consider the graph shown in FIG. The numerical simulation results shown in FIG. 6 show that the current density Jc required for the operation of the layer structure decreases as the interaction Jex that maintains the spin directions opposite to each other in the antiferromagnetic layer 1 increases. When the operating current density Jc is reduced, the drive current required for the domain wall motion and the controllability of the domain wall motion are improved.
[Comparison of current density Jc with ferromagnetic layer]

FIG. 7 is a graph showing the results of numerical simulation comparing the current density Jc required for the operation of the layer structure between the antiferromagnetic layer and the ferromagnetic layer. (A) is the result of numerical simulation of the current density Jc when using an antiferromagnetic layer for the recording layer. (B) is the result of a numerical simulation of the current density Jc when a ferromagnetic layer is used as the recording layer.

In the third numerical simulation, the ferromagnetic interaction Aex is used as a reference to compare the current density Jc required for the operation of the layer structure between the antiferromagnetic layer and the ferromagnetic layer. The ferromagnetic interaction Aex is an interaction for aligning the directions of spins. In the case of the magnetic memory element 90 shown in FIG. 10 using the ferromagnetic material 91 in the recording layer, a ferromagnetic interaction Aex occurs between the laminated ferromagnetic materials 91 , 91 . Similarly, in the case of the magnetic memory element 10 according to the present invention shown in FIG. has a ferromagnetic interaction Aex.

The results of the numerical simulation shown in FIG. 7 show the following two matters. First, in the region where the ferromagnetic interaction Aex is small (0<Aex<1 pJ/m), the value of the current density Jc required for the operation of the layer structure is is smaller by one order of magnitude (10 ⁻¹ ) than the case where a ferromagnetic layer is used as the recording layer shown in (B). From the viewpoint of current density Jc, it is advantageous to use an antiferromagnetic layer for the recording layer. When the operating current density Jc is reduced, the drive current required for the domain wall motion and the controllability of the domain wall motion are improved.

Secondly, when the ferromagnetic interaction Aex is small, the thickness of the boundary layer 2 can be made thin. In a racetrack memory constructed by laminating a plurality of ferromagnetic materials, the thickness of a boundary layer in which domain walls are formed is proportional to the magnitude of ferromagnetic interaction Aex. This makes it possible to reduce the thickness of the layer structure in the stacking direction, and to increase the density of the magnetic memory element. Since the ferromagnetic interaction Aex of the domain wall layer can be reduced by using an antiferromagnetic layer as the recording layer, it is advantageous to use the antiferromagnetic layer as the recording layer from the viewpoint of increasing the density of the magnetic memory element. is.
[Thickness of boundary layer capable of operating as domain wall layer]

8 and 9 are graphs showing the results of numerical simulations regarding the thickness of the boundary layer. In the fourth numerical simulation, an antiferromagnetic layer is used as the recording layer, and the ferromagnetic interaction Aex is used as a free parameter to calculate the ratio Mz/Ms between the magnetization in the z-axis direction and the saturation magnetization. The results of numerical simulation are shown in FIG.

In FIG. 8, the vertical axis of the graph indicates the magnetization ratio Mz/Ms. The value of the magnetization ratio Mz/Ms corresponds to the direction of the spin arrow, as in FIG. The horizontal axis of the graph indicates the number of cells used for simulation. In this numerical simulation, one layer is subdivided into a plurality of finer cells, and one layer is described using seven cells. Note that since the first ferromagnetic layer 3 functioning as a magnetization fixed layer is omitted in this numerical simulation, layer numbers do not correspond between FIG. 8 and FIG.

In a certain layer (layer number 4 in the illustrated example) of the layer structure shown in the graph of FIG. The arrow changes from upward to sideways to downward. The graph shown in FIG. 9 is a graph in which the thickness of the boundary layer required for the spin arrow to change in the horizontal direction in the graph shown in FIG. 8 is plotted for each value of the ferromagnetic interaction Aex.

The numerical simulation results shown in FIGS. 8 and 9 suggest the thickness (central portion) of the boundary layer 2 that can operate as a domain wall layer when the antiferromagnetic layer 1 is used as the recording layer. Referring to FIG. 8, if the value of the magnetization ratio Mz/Ms is in the range of −0.75 to +0.75 and an operable domain wall is constructed in the boundary layer 2, ferromagnetic An operable domain wall is formed in the boundary layer 2 if the value of the interaction Aex is less than or equal to about 0.3-0.4 pJ/m. Therefore, when the antiferromagnetic layer 1 is used as the recording layer, the thickness of the boundary layer 2 that can operate as a domain wall layer is preferably about 2.0 nm (nanometers) or less, and more preferably, referring to FIG. is about 0.5 nm or less.

As described above, according to the present invention, it is possible to provide a layer structure of a magnetic memory element in which the drive current required for domain wall motion and the controllability of the domain wall motion are improved, and a magnetic memory element having the layer structure. The layer structure 9 of the magnetic memory element 10 according to the present invention includes an antiferromagnetic layer 1 as a recording layer, and the thickness of the boundary layer 2 is such that a domain wall is formed therein and can operate as a domain wall layer. It is. By providing the antiferromagnetic layer 1 as the recording layer, the magnetic memory element 10 according to the present invention can obtain, for example, the following two effects.

First, it is possible to reduce the ferromagnetic interaction Aex acting between the configurations of the magnetic memory element. In the region where the ferromagnetic interaction Aex is small, the value of the current density Jc required for the operation of the layer structure is one order of magnitude ( 10 ⁻¹ ). As a result, in the magnetic memory element 10, the controllability of the drive current required for the domain wall motion and the domain wall motion is improved. Also, if the ferromagnetic interaction Aex of the domain wall layer can be reduced, the thickness of the boundary layer 2 can be reduced. In a racetrack memory constructed by laminating a plurality of ferromagnetic materials, the thickness of a boundary layer in which domain walls are formed is proportional to the magnitude of ferromagnetic interaction Aex. This makes it possible to reduce the thickness of the layer structure in the stacking direction, and to increase the density of the magnetic memory element.

Second, it is possible to reduce the influence of the leakage magnetic field from the magnetic memory element on the bit operation. In the magnetic memory element 90 using the ferromagnetic material 91 as a recording layer, as shown in FIG. bit behavior. On the other hand, in the magnetic memory device 10 according to the present invention, the antiferromagnetic layer 1 is used instead of the ferromagnetic material 91 as the recording layer. be able to.

[Other forms]
Although the present invention has been described in terms of specific embodiments, the present invention is not limited to the embodiments described above.

The number of memory cells included in the magnetic memory element 10 is not limited to the illustrated five, and the magnetic memory element 10 can include more memory cells.

In the above-described embodiment, data is read from the magnetic memory element 10 by a destructive read method. can be For example, the second ferromagnetic layer 6 formed in a ring shape concentric with the layer structure 9 is arranged at the center of the layer structure 9 in the height direction, and the wall of the layer structure 9 and the second ferromagnetic layer 6 are arranged. An insulating film 5 can be arranged in between. With such a structure, the antiferromagnetic layer 1 in the layer structure 9 located below the second ferromagnetic layer 6 can act as a data buffer.

In the above-described embodiment, when data is read from the magnetic memory element 10, the data is moved by one memory cell by the pulsed domain wall driving current Id, and the value stored in the memory cell is transferred to the magnetic tunnel junction. , the procedure for reading data from the magnetic memory element 10 is not limited to this. A plurality of pulsed domain wall drive currents Id are applied to move a plurality of data stored in a plurality of memory cells at once, and the domain wall drive currents Id are used to sequentially transfer a plurality of data in the magnetic tunnel junction. It can also be read. When data is read by current, the time change in the magnitude of the domain wall driving current Id can be utilized. It is possible to use the time change of the

In the above embodiment, the magnetic memory element 10 includes the insulating film 5, and the spin state of the antiferromagnetic layer 1d is read by the TMR (tunnel magnetoresistance) effect. The reading method is not limited to this. For example, instead of the insulating film 5, a layer of nonmagnetic metal such as copper may be provided in the magnetic memory element, and the spin state of the antiferromagnetic layer 1d may be read out by the GMR (giant magnetoresistance) effect. By using the GMR effect to read out the spin state, it becomes possible to pass a relatively large current.

In the above-described embodiment, the structure of the magnetic memory element 10 is a three-dimensional structure in which various layers are stacked vertically. A structure in which they are arranged side by side and mounted on a plane is also possible. The layer structure described in the claims does not mean only a three-dimensional structure in which various layers are stacked vertically, but various regions are horizontally arranged in this way and mounted on a plane. Also means structure.

1 (1a to 1d) antiferromagnetic layer 2 boundary layer 3 first ferromagnetic layer 4 first electrode 5 insulating film 6 second ferromagnetic layer 7 second electrode 9 layer structure 10 magnetic memory element 11 ferromagnetism layer 12 ferromagnetic layer 20 magnetic memory device 21-23 terminal 24 current source 25 sensor 26 memory controller 27 data bus 28 (28a, 28b) switch 41 spin orbit torque layer 42 (42a, 42b) bottom electrode 90 magnetic memory element 91 strong Magnetic body 99 Leakage magnetic field Id Domain wall drive current Iw Write current

Claims (8)

a plurality of antiferromagnetic layers;
a boundary layer disposed between the plurality of antiferromagnetic layers and forming a domain wall;
with
A layered structure of a magnetic memory element, wherein the boundary layer has a thickness of 2.0 nanometers or less. 2. The layer structure of claim 1, wherein the antiferromagnetic layer comprises a plurality of ferromagnetic layers stacked. 3. The layer structure of claim 2, wherein said antiferromagnetic layer further comprises a non-magnetic layer between said plurality of ferromagnetic layers. 4. A layered structure according to any one of claims 1 to 3, wherein the boundary layer has a thickness of 0.5 nanometers or less. A layered structure according to any one of claims 1 to 4;
a first ferromagnetic layer capable of switching a spin state, disposed on one side of the antiferromagnetic layer with the boundary layer interposed therebetween;
a first electrode positioned adjacent to the first ferromagnetic layer for switching the spin state of the first ferromagnetic layer by spin-orbit torque;
a second electrode disposed on the side of the other antiferromagnetic layer farthest from the one;
A magnetic memory element. an insulating film disposed between the other antiferromagnetic layer farthest from the one and the second electrode;
a second ferromagnetic layer having a fixed spin state disposed between the insulating film and the second electrode;
further comprising
6. The magnetic memory element according to claim 5, wherein said spin state of said other antiferromagnetic layer is read through said second electrode. a magnetic memory device according to claim 6;
a current source that directs current into and from the first electrode and from the second electrode;
a sensor that reads data represented by a spin state stored in the magnetic memory element;
a magnetic memory device. A method for storing data represented by a spin state in the magnetic memory element according to claim 5 or 6,
setting the spin state of the first ferromagnetic layer by a spin-orbit torque by passing a current through the first electrode;
applying a current between the second electrode and the first electrode to transfer the spin state of the first ferromagnetic layer to one of the antiferromagnetic layers by spin transfer torque;
A method of storing data in a magnetic memory element, comprising:

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