MAGNETIC MEMORY ELEMENT, MAGNETIC MEMORY DEVICE, AND METHOD FOR STORING DATA IN A MAGNETIC MEMORY ELEMENT - Patent application

Abstract

To provide a layer structure of a magnetic memory element and a magnetic memory element provided with the same, in which a drive current required for magnetic wall movement and controllability of magnetic wall movement are improved.SOLUTION: A layer structure 9 of a magnetic memory element 10 includes a plurality of first ferromagnetic layers 1 with switchable spin states and a boundary layer 2 that is disposed between the plurality of first ferromagnetic layers 1 and constitutes a magnetic wall. The boundary layer 2 generates a ferromagnetic interaction Aex between the plurality of first ferromagnetic layers 1.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a magnetic memory element, and more particularly to a layer structure of a magnetic memory element that transfers information based on domain wall motion, a magnetic memory element, a magnetic memory device, and a method for storing data in a magnetic memory element. [Background technology]

[0002] With the dramatic increase in the amount of information, there is a need for memory devices that can record information at high density. Currently, flash memory is widely used as such a memory device. However, due to the operating principle of flash memory, there are drawbacks in that the number of times that data can be written is limited due to the deterioration of the oxide film, and that the writing speed slows down as information is repeatedly written. For this reason, various magnetic memories have been proposed in recent years as replacements for existing flash memories.

[0003] For example, Patent Document 1 discloses a linear racetrack memory proposed as a three-dimensional magnetic memory, and Patent Document 2 discloses a magnetic storage device using spin transfer torque for the recording method.

[0004] In the racetrack memory of Patent Document 1, ferromagnetic materials are separated by magnetic domains and arranged in stacks or lines. A bit is defined for each magnetic domain, and data is stored by the direction 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, and a torque is generated between adjacent magnetic layers at each position by spin momentum transfer to determine the direction of magnetization, thereby storing data bits. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent No. 6,834,005 [Patent Document 2] JP 2009-239282 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the racetrack memory of Patent Document 1, magnetic domain walls are moved by passing an electric current through a ferromagnetic thin wire (magnetic nanowire). This causes the magnetization in the magnetic domains to move in one direction all at once, transmitting data. In the magnetic storage device of Patent Document 2, spin transfer torque is used for the recording method, but magnetic domain walls are not generated in the stack memory.

[0007] The information transmission method based on domain wall motion as shown in Patent Document 1 still has problems such as a high driving current for domain wall motion and poor controllability of domain wall motion. Thus, there is a demand for improving the driving current required for domain wall motion and the controllability of domain wall motion in magnetic memory elements.

[0008] An object of the present invention is to provide a layer structure of a magnetic memory element that improves the drive current required for domain wall motion and the controllability of domain wall motion, and a magnetic memory element including the layer structure. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention includes, for example, the following aspects. (Section 1) a plurality of first ferromagnetic layers having switchable spin states; a boundary layer disposed between the first ferromagnetic layers and forming a domain wall; Equipped with The boundary layer generates ferromagnetic interactions between the first ferromagnetic layers. (Section 2) Item 2. The layer structure according to item 1, wherein the boundary layer is formed using a non-magnetic material. (Section 3) Item 2. The layer structure according to item 1, wherein the boundary layer is formed using a ferromagnetic material different from that of the first ferromagnetic layer. (Section 4) The layer structure according to any one of items 1 to 3, a second ferromagnetic layer having a switchable spin state, the second ferromagnetic layer being disposed on one side of the first ferromagnetic layer with the boundary layer therebetween; a first electrode disposed adjacent to the second ferromagnetic layer for switching the spin state of the second ferromagnetic layer by a spin-orbit torque; a second electrode disposed on a side of the other of the first ferromagnetic layers farthest from the one of the first ferromagnetic layers; A magnetic memory element comprising: (Section 5) 5. The magnetic memory element according to item 4, wherein the second ferromagnetic layer has a higher coercivity than the first ferromagnetic layer. (Section 6) an insulating film disposed between the other of the first ferromagnetic layers farthest from the one of the first ferromagnetic layers and the second electrode; a third ferromagnetic layer having a fixed spin state, the third ferromagnetic layer being disposed between the insulating film and the second electrode; Further equipped with Item 6. The magnetic memory element according to item 4 or 5, wherein the spin state of the other of the first ferromagnetic layers is read out via the second electrode. (Section 7) Item 6. The magnetic memory element according to item 6, a current source for applying a current through the first electrode and from the second electrode to the first electrode; a sensor for reading data represented by spin states stored in the magnetic memory element; A magnetic memory device comprising: (Section 8) A method for storing data represented by a spin state in the magnetic memory element according to any one of items 4 to 6, applying a current through the first electrode to set the spin state of the second ferromagnetic layer via a spin-orbit torque; a step of passing a current between the second electrode and the first electrode to transfer the spin state of the second ferromagnetic layer to one of the first ferromagnetic layers by a spin transfer torque; 16. A method for storing data in a magnetic memory element, comprising: Effect of the Invention

[0010] 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 domain wall motion are improved, and a magnetic memory element including the layer structure. [Brief description of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of a magnetic memory element according to one embodiment of the present invention. [Diagram 2] 5A and 5B are schematic diagrams for explaining the operation of a magnetic memory element according to one embodiment of the present invention. [Diagram 3] 5A and 5B are schematic diagrams for explaining the operation of a magnetic memory element according to one embodiment of the present invention. [Figure 4] 4 is a flowchart for explaining a procedure for storing data in a magnetic memory element according to an embodiment of the present invention. [Diagram 5] 1 is a diagram illustrating a schematic configuration of a magnetic memory device according to an embodiment of the present invention; [Figure 6] FIG. 2 is a diagram showing a schematic layer structure used in a numerical simulation of a magnetic memory element according to one embodiment of the present invention. [Figure 7] 4 is a graph showing the results of a numerical simulation regarding the layer structure of a magnetic memory element according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, embodiments of the present invention will 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 thus redundant descriptions of the same or similar components will be omitted. [Configuration of Memory Element]

[0013] FIG. 1 is a cross-sectional view schematically showing a schematic configuration of a magnetic memory element according to an embodiment of the present invention.

[0014] A magnetic memory element 10 according to an embodiment of the present invention includes a plurality of first ferromagnetic layers 1 (1a to 1d), a plurality of boundary layers 2 (2a to 2d), a second ferromagnetic layer 3, a first electrode 4, an insulating film 5, a third ferromagnetic layer 6, and a second electrode 7. In the illustrated magnetic memory element 10, the second ferromagnetic layer 3, the layer structure 9 of the plurality of boundary layers 2 and the plurality of first ferromagnetic layers 1, the insulating film 5, and the third ferromagnetic layer 6 are stacked in order from the lower side in the figure between the first electrode 4 and the second electrode 7 to have a three-dimensional structure.

[0015] The plurality of first ferromagnetic layers 1 (1a to 1d) are ferromagnetic layers whose spin states are switchable. In the illustrated aspect, the spin state can have two states, for example, the arrow of the spin is upward or downward, and one first ferromagnetic layer 1 functions as a memory cell that stores 1-bit binary information. Exemplarily, the first ferromagnetic layer 1 can be formed using a single metal such as iron and cobalt, or an alloy of these metals, such as Fe 1-x Ni x ,Fe 1-x Co x ,Co 1-x Pt x ,CoFeB. Here, x is the composition ratio of the alloy and takes a value in the range of 0 < x < 1.

[0016] The boundary layer 2 is disposed between a plurality of first ferromagnetic layers 1 to form a magnetic domain wall. In the illustrated embodiment, the spin state of the boundary layer 2 can have three states, for example, the spin arrow pointing upward, downward, and horizontal. When a magnetic domain wall is formed in the boundary layer 2, the spin state of the boundary layer 2 is represented by a horizontal arrow. For convenience of explanation, the state in which the spin arrow points horizontally is only to the right. In this embodiment, the boundary layer 2 is formed using a non-magnetic material. For example, the non-magnetic material of the boundary layer 2 can be a single metal that is not a ferromagnetic material, such as copper or platinum, or an alloy of cobalt and platinum whose composition is controlled as described later. In this embodiment, even if the boundary layer 2 is a non-magnetic material, its thickness is made thin, so that the ferromagnetic layer (the first ferromagnetic layer 1 or the second ferromagnetic layer 3) adjacent to the boundary layer 2 causes the proximity effect to cause the boundary layer 2 to become a ferromagnetic material with a weak exchange stiffness constant.

[0017] In the layer structure 9, the description will be focused on one boundary layer 2 and a pair of first ferromagnetic layers 1 (1a, 1b) sandwiching the boundary layer 2. In the layer structure 9 of the magnetic memory element 10 according to the embodiment, the boundary layer 2 generates a ferromagnetic interaction (magnetic stiffness) Aex between the first ferromagnetic layers 1. More specifically, the boundary layer 2 has a thickness or composition that generates a ferromagnetic interaction Aex between the first ferromagnetic layers 1. The ferromagnetic interaction Aex is an interaction for aligning the direction of spin. Since the ferromagnetic interaction Aex occurs between the first ferromagnetic layers 1, the drive current required for domain wall movement and the controllability of the domain wall movement are improved in the magnetic memory element 10. The ferromagnetic interaction Aex also occurs between the first ferromagnetic layer 1a and the second ferromagnetic layer 3 sandwiching the boundary layer 2.

[0018] When a simple metal is used as the non-magnetic material of the boundary layer 2, the boundary layer 2 is formed using a simple metal with a thickness that generates ferromagnetic interaction Aex between the multiple first ferromagnetic layers 1. For example, when the boundary layer 2 is formed using copper, the thickness of the boundary layer 2 is preferably within the range of 1 to 3 copper atoms. More preferably, the thickness of the boundary layer 2 is within the range of 1 to 2 copper atoms. For example, when the boundary layer 2 is formed using platinum, the thickness of the boundary layer 2 is preferably within the range of 1 to 4 platinum atoms. More preferably, the thickness of the boundary layer 2 is within the range of 1 to 3 platinum atoms.

[0019] When an alloy is used for the nonmagnetic material of the boundary layer 2, the boundary layer 2 is formed using an alloy having a composition that generates a ferromagnetic interaction Aex between the multiple first ferromagnetic layers 1. The magnitude of the ferromagnetic interaction Aex generated between the multiple first ferromagnetic layers 1 is controlled by controlling the composition ratio of the alloy used to form the boundary layer 2. Since the Curie temperature Tc is the transition temperature at which a ferromagnetic material changes into a paramagnetic material, it is possible to control whether the alloy exhibits the properties of a ferromagnetic material or a paramagnetic material (i.e., a nonmagnetic material) by controlling the Curie temperature Tc of the alloy. The Curie temperature Tc and the ferromagnetic interaction Aex are proportional. On the other hand, the Curie temperature Tc of the alloy can be controlled by controlling the composition ratio of the alloy. For example, SA Ahern, MJC Martin and Willie Sucksmith, “The spontaneous magnetization of nickel + copper alloys”, Proc. Math. Phys. Eng. Sci., United Kingdom, The Royal Society, 11 November 1958, Volume 248, Issue 1253, p.145-152, https: / / doi.org / 10.1098 / rspa.1958.0235, Fig. 3 shows the magnetization of Ni 1-x Cu x The composition dependence of the Curie temperature Tc in alloys is described. Ni 1-x Cu xNot limited to alloys, Co 1-x Pt x The same control can be applied to the alloy. Therefore, by controlling the composition ratio of the alloy used to form the boundary layer 2, it is possible to control the Curie temperature Tc of the alloy and to control whether the alloy exhibits ferromagnetic or paramagnetic properties, thereby controlling the magnitude of the ferromagnetic interaction Aex.

[0020] The second ferromagnetic layer 3 is a ferromagnetic layer whose spin state is switchable. The second ferromagnetic layer 3 is disposed on the side of the first ferromagnetic layer 1a located at the lower side in the layer structure 9 in the figure, with the boundary layer 2 sandwiched therebetween. The second ferromagnetic layer 3 functions as a layer for writing one bit of binary information to the first ferromagnetic layer 1a. Exemplarily, the second ferromagnetic layer 3 can be formed using an alloy of cobalt and platinum, or an alloy of iron and nickel. The material of the second ferromagnetic layer 3 can be various materials used for the magnetization fixed phase in magnetoresistive memories (MRAMs: Magnetoresistive Random Access Memory).

[0021] The second ferromagnetic layer 3 has a higher coercive force than the first ferromagnetic layer 1. For example, when at least one of the following three conditions is satisfied, the second ferromagnetic layer 3 has a higher coercive force than the first ferromagnetic layer 1. The first condition is that the second ferromagnetic layer 3 is formed thicker than the first ferromagnetic layer 1 even if the second ferromagnetic layer 3 and the first ferromagnetic layer 1 are formed using the same material. The second condition is that the second ferromagnetic layer 3 is formed using a material having a higher magnetic anisotropy than the first ferromagnetic layer 1 even if the thickness of the second ferromagnetic layer 3 is the same as the thickness of the first ferromagnetic layer 1. The third condition is that the second ferromagnetic layer 3 is formed using a material having a sufficiently higher magnetic anisotropy than the first ferromagnetic layer 1 even if the thickness of the second ferromagnetic layer 3 is thinner than the thickness of the first ferromagnetic layer 1, and as a result, the coercive force of the second ferromagnetic layer 3 is higher than the first ferromagnetic layer 1.

[0022] The first electrode 4 is disposed adjacent to the second ferromagnetic layer 3 and uses spin-orbit torque to switch the spin state of the second ferromagnetic layer 3. The first electrode 4 includes a spin-orbit torque (SOT) layer 41 and two bottom electrodes 42 (42a, 42b) electrically connected to the spin-orbit torque layer 41.

[0023] By passing a drive current for switching the spin state of the second ferromagnetic layer 3 between the terminal 11 and the terminal 12 of the first electrode 4, a write current Iw shown by a dashed line in the figure flows through the spin orbit torque layer 41, and the spin orbit torque generated by the spin orbit interaction switches the spin state of the second ferromagnetic layer 3. The spin state of the second ferromagnetic layer 3 is determined according to the direction of the write current Iw. In this embodiment, the write current Iw is pulsed. Exemplarily, the spin orbit torque layer 41 can be formed using a heavy metal such as platinum. The bottom electrode 42 can be formed using various conductive metals such as gold and copper.

[0024] The insulating film 5 and the third ferromagnetic layer 6 function as a magnetic tunnel junction (MTJ) for reading the spin state of the first ferromagnetic layer 1d in combination with the first ferromagnetic layer 1d located at the upper side in the layer structure 9 in the figure. The first ferromagnetic layer 1d functions as a free layer of the magnetic tunnel junction. The spin state of the first ferromagnetic layer 1d is read by measuring the magnitude of the current flowing through the first ferromagnetic layer 1d, the insulating film 5, and the third ferromagnetic layer 6. The method of reading the spin state by the magnetic tunnel junction is well known, so further detailed description will be omitted in this specification.

[0025] The insulating film 5 functions as a tunnel layer of the magnetic tunnel junction. The insulating film 5 is disposed between the first ferromagnetic layer 1d located at the upper side in the layer structure 9 in the figure and the second electrode 7. The third ferromagnetic layer 6 is a layer in which the spin state is fixed (upward arrow in the illustrated embodiment), and functions as a fixed layer of the magnetic tunnel junction. In this embodiment, the spin state of the third ferromagnetic layer 6 is fixed in a state in which the spin arrow points upward. The third ferromagnetic layer 6 is disposed 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 third ferromagnetic layer 6 can be formed using CoFeB, which is an alloy of cobalt, iron, and boron. Various materials used for the magnetization fixed phase in MRAM can be used as the material of the third ferromagnetic layer 6.

[0026] The second electrode 7 reads out the spin state of the first ferromagnetic layer 1d located at the upper side in the layer structure 9. The second electrode 7 is disposed adjacent to the third ferromagnetic layer 6 on the side of the first ferromagnetic layer 1d located at the upper side in the figure.

[0027] By passing a driving current for moving the domain wall between one of the terminals 11 and 12 of the first electrode 4 and the terminal 13 of the second electrode 7, a domain wall driving current Id shown by a dashed line in the figure flows between the second electrode 7 and the first electrode 4. This allows the domain wall to be moved in the multiple boundary layers 2 (2a to 2d) located between the second electrode 7 and the first electrode 4, and the spin states of the multiple first ferromagnetic layers 1 (1a to 1d) can be shifted in a racetrack manner and moved sequentially. The insulating film 5 and the third ferromagnetic layer 6 function as a magnetic tunnel junction for reading. As a result, the spin state of the first ferromagnetic layer 1d located at the upper side in the layer structure 9 in the figure is read out via the second electrode 7. In this embodiment, the domain wall driving current Id is pulsed. Exemplarily, the second electrode 7 can be formed using various conductive metals such as gold and copper. [Memory element operation]

[0028] Fig. 2 and Fig. 3 are schematic diagrams for explaining the operation of the magnetic memory element according to one embodiment of the present invention. Fig. 4 is a flow chart for explaining the procedure for storing data in the magnetic memory element according to one embodiment of the present invention.

[0029] A method for storing data in a magnetic memory element 10 according to one embodiment includes a step (step S1) of passing a current between the bottom electrodes 42a and 42b of the first electrode 4 to set the spin state of the second ferromagnetic layer 3 by spin-orbit torque, and a step (step S2) of passing a domain wall driving current Id between the second electrode 7 and the first electrode 4 to transfer the spin state of the second ferromagnetic layer 3 to the first ferromagnetic layer 1 (1d) by spin transfer torque.

[0030] 2 and 3, a procedure shown in FIG. 4 for storing data in the magnetic memory element 10 according to one embodiment and a procedure for reading data from the magnetic memory element 10 will be described below. In the illustrated embodiment, the magnetic memory element 10 includes four memory cells (cell No. 1 to cell No. 4) and stores a total of four bits of binary information. For ease of explanation, the upward state of the spin arrow means a value of "0" and the downward state means a value of "1" below.

[0031] - Initialize data FIG. 2A shows the magnetic memory element 10 in an initialized state. In each of the four first ferromagnetic layers 1 and the second ferromagnetic layer 3, the spin arrow points upward and a value of "0" is stored. In each of the four boundary layers 2, the spin arrow also points upward, and no domain wall is formed in the boundary layer 2 in the initialized state. The magnetic memory element 10 can be initialized, for example, by continuously passing a pulsed domain wall driving current Id from the first electrode 4 to the second electrode 7 a predetermined number of times. Note that the spin state of the third ferromagnetic layer 6 is fixed to the upward direction in this embodiment, and does not change even by initialization.

[0032] Write data Data is written to the magnetic memory element 10 via the second ferromagnetic layer 3. In this embodiment, since the second ferromagnetic layer 3 is disposed below the layer structure 9, data is written from the first ferromagnetic layer 1a corresponding to cell No. 1. When attempting to write a value "1" to cell No. 1, first, a value "1" is set in the second ferromagnetic layer 3. Next, the value "1" set in the second ferromagnetic layer 3 is transferred to cell No. 1.

[0033] 2B, when a write current Iw is applied to the first electrode 4 in the rightward direction, the spin state of the second ferromagnetic layer 3 is switched from an upward spin arrow to a downward spin arrow due to the spin orbit torque caused by the write current Iw. A value of "1" is set and stored in the second ferromagnetic layer 3. Accordingly, a domain wall is formed in the boundary layer 2a located between the second ferromagnetic layer 3 and the first ferromagnetic layer 1a.

[0034] As shown in FIG. 2C, when a pulsed domain wall driving current Id is applied from the second electrode 7 to the first electrode 4, the domain wall formed in the boundary layer 2a moves to the boundary layer 2b located between the first ferromagnetic layer 1a and the first ferromagnetic layer 1b. As a result, the spin states of the second ferromagnetic layer 3 and the four first ferromagnetic layers 1 (1a to 1d) are sequentially shifted to the upper layers in the figure by the domain wall movement caused by the spin transfer torque by the domain wall driving current Id. In this way, the spin state is sequentially shifted by the domain wall movement caused by the spin transfer torque, so that the spin state of the second ferromagnetic layer 3 is shifted to the first ferromagnetic layer 1a, and the spin state of the first ferromagnetic layer 1a is switched from the state in which the spin arrow points upward to the state in which the spin arrow points downward. The value "1" set in the second ferromagnetic layer 3 is written to the first ferromagnetic layer 1a, and the value "1" is stored in cell No. 1. Similarly, as the spin state shifts sequentially, the value stored in cell No. 1 is transferred and stored in cell No. 2, the value stored in cell No. 2 is transferred and stored in cell No. 3, and the value stored in cell No. 3 is transferred and stored in cell No. 4.

[0035] When a pulsed domain wall-driving current Id is applied from the first electrode 4 to the second electrode 7 in the direction opposite to the direction shown in the figure, the spin states of the second ferromagnetic layer 3 and the four first ferromagnetic layers 1 (1a-1d) are sequentially shifted to the lower layers in the figure by domain wall motion caused by spin transfer torque due to the domain wall-driving current Id. In this embodiment, the second ferromagnetic layer 3 used for writing data is disposed below the layer structure 9, and the insulating film 5 and the third ferromagnetic layer 6 used for reading data, which will be described later, are disposed above the layer structure 9. Therefore, the domain wall-driving current Id is applied from the second electrode 7 to the first electrode 4, and the spin states are sequentially shifted to the upper layers in the figure.

[0036] Subsequently, as shown in FIG. 3D, when a pulsed domain wall-driving current Id is applied from the second electrode 7 to the first electrode 4, the domain wall formed in the boundary layer 2b moves to the boundary layer 2c located between the first ferromagnetic layer 1b and the first ferromagnetic layer 1c, and the sequential transition of the spin state described with reference to FIG. 2C continues. The spin state of the first ferromagnetic layer 1a transitions to the first ferromagnetic layer 1b, and the spin state of the first ferromagnetic layer 1b is switched from an upward spin arrow state to a downward spin arrow state. The value "1" stored in the first ferromagnetic layer 1a is transferred to the first ferromagnetic layer 1b, and the value "1" is stored in cell No. 2.

[0037] In this manner, while the value "1" is set in the second ferromagnetic layer 3, the value "1" set in the second ferromagnetic layer 3 is written to the first ferromagnetic layer 1a, and the value "1" is stored in cell No. 1. Similarly, by sequentially shifting the spin state, the value stored in cell No. 2 is transferred to and stored in cell No. 3, and the value stored in cell No. 3 is transferred to and stored in cell No. 4. The value stored in cell No. 4 is sequentially read out by passing a domain wall driving current Id from the second electrode 7 to the first electrode 4.

[0038] When writing a value "0" into cell No. 1, first, a value "0" is set in the second ferromagnetic layer 3. Then, the value "0" set in the second ferromagnetic layer 3 is transferred to cell No. 1.

[0039] 3E, when a write current Iw is applied to the first electrode 4 in the leftward direction, the spin state of the second ferromagnetic layer 3 is switched from a state in which the spin arrow points downward to a state in which the spin arrow points upward due to the spin orbit torque caused by the write current Iw. The value "0" is set and stored in the second ferromagnetic layer 3. Accordingly, a domain wall is formed in the boundary layer 2a located between the second ferromagnetic layer 3 and the first ferromagnetic layer 1a.

[0040] As shown in FIG. 3F, when a pulsed domain wall driving current Id is applied from the second electrode 7 to the first electrode 4, the domain wall formed in the boundary layer 2a moves to the boundary layer 2b, and the domain wall formed in the boundary layer 2c moves to the boundary layer 2d located between the first ferromagnetic layer 1c and the first ferromagnetic layer 1d. As a result, the spin states of the second ferromagnetic layer 3 and the four first ferromagnetic layers 1 (1a to 1d) sequentially move to the upper layers in the figure due to the domain wall movement caused by the spin transfer torque caused by the domain wall driving current Id. The spin state of the second ferromagnetic layer 3 moves to the first ferromagnetic layer 1a, and the spin state of the first ferromagnetic layer 1a is switched from a state in which the spin arrow points downward to a state in which the spin arrow points upward. The value "0" set in the second ferromagnetic layer 3 is written to the first ferromagnetic layer 1a, and the value "0" is stored in cell No. 1. Similarly, as the spin state shifts sequentially, the value stored in cell No. 1 is transferred and stored in cell No. 2, the value stored in cell No. 2 is transferred and stored in cell No. 3, and the value stored in cell No. 3 is transferred and stored in cell No. 4.

[0041] By sequentially applying the write operations to the magnetic memory element 10 as described above, it is possible to write 4 bits of data with values ​​of "0", "1", "1", and "0" in sequence to the magnetic memory element 10, which has four memory cells (cell No. 1 to cell No. 4).

[0042] - Reading data Data is read from the magnetic memory element 10 via the insulating film 5 and the third ferromagnetic layer 6. In this embodiment, since the insulating film 5 and the third ferromagnetic layer 6 are disposed above the layer structure 9, data is read from the first ferromagnetic layer 1d corresponding to cell No. 4. The spin state of the first ferromagnetic layer 1d is read by measuring the magnitude of the read current Ir flowing through the first ferromagnetic layer 1d, the insulating film 5, and the third ferromagnetic layer 6 using a magnetic tunnel junction. 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 memory element 10.

[0043] In the state of the magnetic memory element 10 shown in FIG. 3(F), first, the spin state of the first ferromagnetic layer 1d corresponding to cell No. 4 is measured using a magnetic tunnel junction to read out the value "0."

[0044] Next, a pulsed domain wall-drive current Id is passed from the second electrode 7 to the first electrode 4. This causes the domain wall to move due to the spin transfer torque, and the spin state is transferred sequentially to the upper layers in the figure. The value "0" stored in cell No. 1 is transferred to and stored in cell No. 2, the value "1" stored in cell No. 2 is transferred to and stored in cell No. 3, and the value "1" stored in cell No. 3 is transferred to and stored in cell No. 4. The value stored in cell No. 4 is destroyed by passing the pulsed domain wall-drive current Id, but the value stored in cell No. 4 has already been read out using the magnetic tunnel junction before passing the pulsed domain wall-drive current Id.

[0045] Thereafter, by repeatedly applying a read operation including a step of measuring the spin state of the first ferromagnetic layer 1d corresponding to cell No. 4 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, four bits of data having values ​​of “0”, “1”, “1”, and “0” can be read from the memory element 10.

[0046] In the example of the operation of the magnetic memory element 10 described above, data is read from the first ferromagnetic layer 1d using a destructive read method similar to that of a DRAM (Dynamic Random Access Memory), so it is advisable to write the data again after the read operation. [Configuration of magnetic memory device]

[0047] FIG. 5 is a diagram showing a schematic configuration of a magnetic memory device according to one embodiment of the present invention.

[0048] The magnetic memory device 20 according to the embodiment includes a magnetic memory element 10 , a current source 14 and a sensor 15 .

[0049] The current source 14 passes a current between the bottom electrode 42a and the bottom electrode 42b of the first electrode 4 of the magnetic memory element 10 and from the second electrode 7 to the first electrode 4. The sensor 15 reads data represented by a spin state stored in the magnetic memory element 10. The sensor 15 measures the current value of the read current Ir flowing through the magnetic memory element 10, and can detect the resistance value from the current value to read the spin state of the magnetic memory element. The current source 14 and the sensor 15 are connected to a memory controller 16. The memory controller 16 controls the write operation to the magnetic memory element 10 and the read operation from the magnetic memory element 10 described with reference to FIG. 2 and FIG. 3 by controlling the operation of the current source 14 and the sensor 15. The data read through the sensor 15 is transmitted and received through a data bus 17. The connection from the current source 14 to the first electrode 4 and the second electrode 7 of the magnetic memory element 10 is switched using, for example, switches 18a and 18b. The operations of the switches 18a and 18b are controlled by, for example, the memory controller 16. A plurality of the magnetic memory elements 10 can be arranged in an array to form a memory array. [Numerical simulation of layered structure]

[0050] FIG. 6 is a schematic diagram showing the layer structure used in a numerical simulation of a magnetic memory element according to one embodiment of the present invention, and FIG. 7 is a graph showing the results of a numerical simulation of the layer structure of a magnetic memory element according to one embodiment of the present invention.

[0051] The vertical axis of the graph in Fig. 7 is the current density Jc [A / m 2 ], and the horizontal axis of the graph represents the ferromagnetic interaction Aex [×10 12 ·J / m]. In the numerical simulation, the magnitude of the ferromagnetic interaction Aex shown on the horizontal axis is used as a free parameter to calculate the magnitude of the current density Jc required for operation shown on the vertical axis.

[0052] The conditions for the numerical simulation are as follows: The simulation parameters are assumed to be typical MRAM materials. Layer Shape and Size Each layer is a disk shape with a diameter of 20 nm and a thickness of 3 nm, composed of cells of 1 nm x 1 nm x 1 nm. [Number of layers and layer structure] The layer structure shown in Figure 6 is a total of 12 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. Since the value of Ku in the domain wall layer is zero, the domain wall is trapped in the domain wall layer rather than in the recording layer. This improves the controllability of the domain wall position. Layers 3, 5, 7, 9, 11 (magnetic wall layers) Ms = 8 × 10 5 [A / m], Ku=0 The domain wall layer corresponds to the boundary layer 2 in the magnetic memory element 10 according to one embodiment of the present invention. Aex introduced into the domain wall layer is a free parameter in the simulation, and corresponds to the horizontal axis of the graph shown in FIG. Layers 2, 4, 6, 8, 10, 12 (recording layers) Ms = 8 × 10 5 [A / m], Ku=1×106 [J / m 3 ], Aex = 1 × 10 -11 [J / m] The recording layer corresponds to the first ferromagnetic layer 1 in the magnetic memory element 10 according to one embodiment of the present invention. Layer 1 (pin layer) Ms = 8 × 10 5 [A / m], Ku=1×10 7 [J / m 3 ], Aex = 1 × 10 -11 [J / m] The pinned layer corresponds to the second ferromagnetic layer 3 in the magnetic memory element 10 according to one embodiment of the present invention.

[0053] Consider the graph shown in Fig. 7. In the graph of Fig. 7 showing the results of the numerical simulation, when the value of the ferromagnetic interaction Aex is zero, the magnitude of the operating current density Jc is about 10 14 In a conventional magnetic memory element in which the ferromagnetic interaction Aex is not introduced, the magnitude of the operating current density Jc is 10 14 In contrast, in the magnetic memory element 10 according to an embodiment of the present invention in which the ferromagnetic interaction Aex is introduced between the first ferromagnetic layers 1, the magnitude of the operating current density Jc is on the order of 10 10 This means that by introducing ferromagnetic interaction Aex between the first ferromagnetic layers 1, it is possible to reduce the operating current density Jc to a maximum of about 1 / 10,000, or at least about 1 / 100 of the conventional level. If the operating current density Jc is reduced, the drive current required for domain wall motion and the controllability of the domain wall motion are improved.

[0054] As described above, according to the present invention, it is possible to provide a layer structure of a magnetic memory element with improved drive current required for domain wall motion and controllability of domain wall motion, and a magnetic memory element including the layer structure. In the layer structure 9 of the magnetic memory element 10 according to one embodiment, the boundary layer 2 generates ferromagnetic interaction Aex between the multiple first ferromagnetic layers 1. Since the ferromagnetic interaction Aex occurs between the multiple first ferromagnetic layers 1, the drive current required for domain wall motion and controllability of domain wall motion are improved in the magnetic memory element 10. [Other formats]

[0055] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

[0056] The number of memory cells included in the magnetic memory element 10 is not limited to four, and the magnetic memory element 10 can include a greater number of memory cells.

[0057] In the above-described embodiment, the boundary layer 2 is formed using a non-magnetic material, but the material of the boundary layer 2 is not limited to the non-magnetic material. The boundary layer 2 constituting the domain wall may be formed using a different type of ferromagnetic material or a ferromagnetic material with a different composition from that of the first ferromagnetic layer 1. For example, the first ferromagnetic layer 1 can be formed using a CoFeB alloy, and the boundary layer 2 can be formed using an elemental metal of cobalt. In such a case, the boundary layer 2 can be expressed as a fourth ferromagnetic layer in the magnetic memory element 10 according to the above-described embodiment. Examples of ferromagnetic materials that can be used as the material of the boundary layer 2 include Ni 1-x Cu x Alloys and Co 1-x Cu x Alloy, Co 1-x Pt x As mentioned above, these Ni alloys can be exemplified. 1-x Cu x Alloy and Co 1-x Pt xBy controlling the composition ratio of the alloy, it is possible to control the Curie temperature Tc of the alloy, thereby controlling whether the alloy exhibits ferromagnetic or paramagnetic properties, and to control the magnitude of the ferromagnetic interaction Aex. Therefore, these alloys whose composition ratios are controlled so as to exhibit ferromagnetic properties and have an appropriate magnitude of the ferromagnetic interaction Aex can be used as the material for the boundary layer 2.

[0058] In the above embodiment, data is read from the magnetic memory element 10 in a destructive manner, but by changing the arrangement of the insulating film 5 and the third ferromagnetic layer 6, data can be read in a non-destructive manner. For example, the third ferromagnetic layer 6 formed in a ring shape concentric with the layer structure 9 can be arranged in the center of the height direction of the layer structure 9, and the insulating film 5 can be arranged between the wall of the layer structure 9 and the third ferromagnetic layer 6. With such a structure, the first ferromagnetic layer 1 in the layer structure 9 located below the third ferromagnetic layer 6 can function as a data buffer.

[0059] In the above embodiment, when reading data from the magnetic memory element 10, the data is moved by one memory cell at a time by the pulsed domain wall drive current Id, and the values ​​stored in the memory cells are read one by one in the magnetic tunnel junction, but the procedure for reading data from the magnetic memory element 10 is not limited to this. By passing a plurality of pulsed domain wall drive currents Id, a plurality of data stored in a plurality of memory cells can be moved at once, and the plurality of data can be sequentially read in the magnetic tunnel junction using the domain wall drive current Id. When data is read using a current, the change in the magnitude of the domain wall drive current Id over time can be used, and when the magnitude of the domain wall drive current Id does not change over time, the change in the magnitude of the voltage of the magnetic tunnel junction over time can be used.

[0060] In the above embodiment, the magnetic memory element 10 includes the insulating film 5, and the spin state of the first ferromagnetic layer 1d is read by the TMR (tunnel magnetoresistance) effect, but the method of reading the spin state of the first ferromagnetic layer 1d is not limited to this. For example, a layer of a nonmagnetic metal such as copper may be provided in the magnetic memory element instead of the insulating film 5, and the spin state of the first ferromagnetic layer 1d may be read by the GMR (giant magnetoresistance) effect. By utilizing the GMR effect to read the spin state, it becomes possible to pass a relatively large current.

[0061] In the above embodiment, the structure of the magnetic memory element 10 is a three-dimensional structure in which various layers are stacked vertically, but the structure of the magnetic memory element can also be a structure in which regions corresponding to various layers are arranged horizontally and mounted on a plane. The layer structure described in the claims does not only mean a three-dimensional structure in which various layers are stacked vertically, but also means a structure in which various regions are arranged horizontally in this way and mounted on a plane. [Explanation of symbols]

[0062] 1(1a-1d) First ferromagnetic layer 2 Boundary layer 3 Second ferromagnetic layer 4 First electrode 5. Insulating film 6 Third ferromagnetic layer 7 Second electrode 9 layer structure 10 Magnetic memory elements Terminals 11-13 14 Current source 15 Sensors 16 Memory Controller 17 Data Bus 18(18a,18b) Switch 20 Magnetic memory device 41 Spin-orbit torque layer 42(42a,42b) Bottom electrode Aex ferromagnetic interaction Id Domain wall driving current Iw Write current Ir Read current

Claims

1. a plurality of first ferromagnetic layers having switchable spin states; a boundary layer disposed between the first ferromagnetic layers and forming a domain wall; a first electrode and a second electrode for passing a drive current for moving the domain wall; a second ferromagnetic layer having a switchable spin state, the second ferromagnetic layer being disposed on one side of the first ferromagnetic layer with the boundary layer therebetween; Equipped with the first electrode is disposed adjacent to the second ferromagnetic layer and switches the spin state of the second ferromagnetic layer by a spin-orbit torque; the second electrode is disposed on a side of the other of the first ferromagnetic layers that is farthest from the one of the first electrodes; A magnetic memory element, wherein a spin transfer torque generated by passing the drive current between the second electrode and the first electrode moves the domain wall to the adjacent boundary layer, and the movement of the domain wall moves the spin state to the adjacent first ferromagnetic layer.

2. 2. The magnetic memory element according to claim 1, wherein the boundary layer is made of a non-magnetic material.

3. 2. The magnetic memory element according to claim 1, wherein the boundary layer is formed using a ferromagnetic material different from that of the first ferromagnetic layer.

4. The magnetic memory element according to claim 1 , wherein the second ferromagnetic layer has a higher coercivity than the first ferromagnetic layer.

5. an insulating film disposed between the other of the first ferromagnetic layers farthest from the one of the first ferromagnetic layers and the second electrode; a third ferromagnetic layer having a fixed spin state, the third ferromagnetic layer being disposed between the insulating film and the second electrode; Further equipped with The magnetic memory element according to claim 1 , wherein the spin state of the other of the first ferromagnetic layers is read out via the second electrode.

6. A magnetic memory element according to claim 5 ; a current source for passing a current through the first electrode and from the second electrode to the first electrode; a sensor for reading data represented by spin states stored in the magnetic memory element; A magnetic memory device comprising:

7. A method for storing data represented by spin states in a magnetic memory element according to any one of claims 1 to 5, comprising the steps of: applying a current through the first electrode to set a spin state of the second ferromagnetic layer via a spin-orbit torque; a step of passing a drive current between the second electrode and the first electrode to transfer the spin state of the second ferromagnetic layer to one of the first ferromagnetic layers by a spin transfer torque; 16. A method for storing data in a magnetic memory element, comprising:

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