JP2018026481A - Magnetoresistance effect element, thermal history sensor, and spin glass utilization type magnetic memory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetoresistance effect element capable of new multivalued recording and analog recording.SOLUTION: The magnetoresistance effect element includes: a spin glass layer having a ferrimagnetic material as a host material; a nonmagnetic layer; and a first ferromagnetic layer having a fixed magnetization direction, in this order. The magnetization direction of the spin glass layer and the magnetization direction of the first ferromagnetic layer may be antiparallel.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a magnetoresistive element, a thermal history sensor, and a spin glass-based magnetic memory.

 As a next-generation non-volatile memory that replaces flash memories and the like that have seen limitations in miniaturization, a resistance change type memory that stores data using a resistance change type element, for example, MRAM (Magnetroresistive Random Access Memory), ReRAM (Resistancne) Random Access Memory) and PCRAM (Phase Change Random Access Memory) are attracting attention.

  As a method for increasing the density (capacity) of the memory, there are various methods in addition to a method of reducing the element itself constituting the memory, and a method of multi-valued recording bits per element constituting the memory. Multi-value conversion methods have been proposed (for example, Patent Documents 1 to 3).

One of the MRAMs is called a domain wall drive type or a domain wall displacement type (for example, Patent Document 4). In the domain wall drive type MRAM, current flows in the in-plane direction of the domain wall drive layer (magnetization free layer), the domain wall is moved by the spin transfer effect by spin-polarized electrons, and the magnetization of the ferromagnetic film corresponds to the direction of the write current. Data writing is performed by reversing the direction.
Patent Document 4 describes a multi-value recording and analog recording method for a domain wall drive type MRAM.
In MRAM, different data writing methods have been proposed. In addition to the domain wall drive type MRAM, magnetic field writing type, yoke magnetic field writing type, STT (Spin Transfer Torque) type, SOT (Spin Orbit Torque) type MRAM, etc. are known. It has been.

JP2015-088669A International Publication No. 2009/072213 JP, 2006-004924, A International Publication No. 2009/101827 JP-A-3-273540

However, in the conventional domain wall drive type MRAM, it is necessary to pass a current in the in-plane direction of the domain wall drive layer (magnetization free layer) at the time of reading, and therefore the domain wall of the domain wall drive layer may be moved by the current passed at the time of reading. There is sex. If the domain wall moves outside the portion where the domain wall drive layer (magnetization free layer) and the magnetoresistive effect element overlap, the signal finally becomes a digital signal of 0 or 1 in the domain wall drive MRAM, It was difficult to use as a memory. On the other hand, in a plan view, if the domain wall movement is not completed outside the portion where the domain wall drive layer (magnetization free layer) and the magnetoresistive effect element overlap, the domain wall moves during reading and erroneous writing or initial reading There is a problem that the signal of the time changes. Therefore, for the conventional domain wall drive type MRAM, development of a means for stably reading is desired.
On the other hand, development of an MRAM capable of unprecedented types of multi-value recording and analog recording is also desired.

  The present invention has been made in view of the above circumstances, and provides a novel magnetoresistive effect element capable of multi-value recording and analog recording, a heat history sensor using the same, and a spin glass-based magnetic memory. Objective.

  The present invention provides the following means in order to solve the above problems.

(1) A magnetoresistive effect element according to an aspect of the present invention includes a spin glass layer using a ferrimagnetic material as a base material, a nonmagnetic layer, and a first ferromagnetic layer whose magnetization direction is fixed in this order. The magnetization direction of the spin glass layer and the magnetization direction of the first ferromagnetic layer may be antiparallel.

(2) In the magnetoresistive element described in (1) above, a second ferromagnetic layer may be provided between the spin glass layer and the nonmagnetic layer.

(3) In the magnetoresistive element described in (1) or (2) above, a spin orbit torque layer may be provided on the surface of the spin glass layer opposite to the side provided with the nonmagnetic layer.

(4) In the magnetoresistive effect element according to any one of (1) to (3), the ferrimagnetic material is a spinel material represented by AB ₂ O _4-x or BA ₂ O _{4. The} reverse spinel material represented by _-x may be sufficient. However, A is one or more elements of Mn, Fe, Co, Ni, Cu, Zn, and Mg, and B is one or more elements of Fe, Cr, Ti, Mg, Mn, and Ni.

(5) In the magnetoresistive effect element according to (4), the spinel material or the reverse spinel material of the spin glass layer may be oxygen deficient.

(6) The thermal history sensor according to an aspect of the present invention uses the magnetoresistive element described in any one of (1) to (5) above.

(7) A spin glass-based magnetic memory according to an aspect of the present invention includes the magnetoresistive element according to any one of (1) to (5) above, and a stacking direction with respect to the magnetoresistive element. And a current source for supplying a current to.

(8) In the spin glass-based magnetic memory according to (7), a control circuit that controls the flow of a write current that allows the resistance value of the magnetoresistive effect element included in the spin glass to be used in a multivalued or analog manner. A current source may be provided.

(9) A magnetic neuron element according to an aspect of the present invention includes the spin glass-based magnetic memory according to (8), and the control circuit can read at least according to a difference in resistance value of the magnetoresistive element. Control can be performed so that a write current having the number of pulses corresponding to three resistance ranges flows.

  According to the magnetoresistive effect element of the present invention, a novel magnetoresistive effect element capable of multi-value recording and analog recording can be provided.

It is a cross-sectional schematic diagram of an example of the magnetoresistive effect element which concerns on one Embodiment of this invention. It is a schematic diagram for demonstrating a ferrimagnetism and a spin glass layer. It is a cross-sectional schematic diagram of an example of the magnetoresistive effect element which concerns on other embodiment of this invention. It is a cross-sectional schematic diagram of an example of the magnetoresistive effect element which concerns on other embodiment of this invention. It is a schematic diagram for demonstrating a spin Hall effect. It is a graph which shows notionally the relationship between the ratio of the spin glass area | region in a spin glass layer, and the resistance value of a magnetoresistive effect element. It is a figure which shows the concept of the artificial brain using the magnetic neuron element which concerns on one Embodiment of this invention.

  Hereinafter, a configuration of a magnetoresistive effect element to which the present invention is applied, a thermal history sensor using the magnetoresistive effect element, and a spin glass-based magnetic memory will be described with reference to the drawings. In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. . In addition, the materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited thereto, and can be implemented with appropriate modifications within the scope of the effects of the present invention. . In the element of the present invention, other layers may be provided as long as the effects of the present invention are achieved.

(Magnetoresistive element)
FIG. 1 is a schematic cross-sectional view of an example of a magnetoresistive element according to an embodiment of the present invention.
A magnetoresistive effect element 100 shown in FIG. 1 includes a spin glass layer 1 using a ferrimagnetic material as a base material, a nonmagnetic layer 2, and a first ferromagnetic layer 3 having a fixed magnetization direction in this order. The magnetization direction M1 of the spin glass layer 1 and the magnetization direction M2 of the first ferromagnetic layer are antiparallel.
In FIG. 1, the stacking direction of each layer, that is, the direction orthogonal to the main surface of each layer (plane normal direction) is defined as the Z direction. Each layer is formed in parallel to the XY plane orthogonal to the Z direction.
The “spin glass layer using a ferrimagnetic material as a base material” includes a nonmagnetic material or a magnetic material at a concentration sufficient to maintain the ferrimagnetism of the base material in the ferrimagnetic material as a base material. The magnetic material or a layer having a spin glass region around the localized spin of the magnetic material.
Further, “the magnetization direction is fixed” means that the magnetization direction does not change (magnetization is fixed) before and after writing using the write current.
The spin glass layer 1 and the first ferromagnetic layer 3 may be either an in-plane magnetization film whose magnetization direction is an in-plane direction parallel to the layer, or a perpendicular magnetization film whose magnetization direction is perpendicular to the layer.

  The ferrimagnetic material, which is the base material of the spin glass layer 1, is arranged in the opposite direction of the magnetic moments like the antiferromagnetic material, but their number (density) and size are different. Thus, the two sublattice magnetizations do not cancel each other, and the magnetic material exhibits magnetization as a whole. The sub-lattice is a virtual lattice obtained by taking out magnetic moments in the same direction.

FIG. 2 is a schematic diagram for explaining the ferrimagnetism and the spin glass layer.
In FIG. 2, the magnetic ordered region indicated by the symbol A schematically shows a ferrimagnetic region (region other than the spin glass region). In the case shown in FIG. 2, the magnetic moment shown by m1 and the magnetic moment shown by m2 have the same number (density), but their magnitudes are different, so that the magnetization M1 facing right as a whole (see FIG. 1). ) Is schematically shown.
On the other hand, in the case shown in FIG. 2, the region surrounded by the dotted line indicated by the symbol B is a region in which the magnetic order around it is disturbed because there are atoms (localized spins) P of the nonmagnetic material in the ferrimagnetic material. It is. The spin glass layer of the present invention refers to a layer having a locally stabilized region (spin glass region) in a state where the magnetic order is locally disturbed. Here, spin glass is a phenomenon that occurs when local correlation is disturbed or frustrated in a magnetic material. Thus, since the spin direction of the region where the spin glass is generated (the portion surrounded by the dotted line B in FIG. 2) is disturbed, the spin-polarized current that has passed through the spin glass region is almost due to the magnetoresistive effect. It is not scattered. On the contrary, since the spin that has passed through the region other than the spin glass region is scattered by a general magnetoresistive effect, the resistance value of the magnetoresistive effect changes depending on the ratio of the spin glass region B in the spin glass layer. Since the spin glass can exist stably below the spin glass transition temperature, the spin glass layer functions as a layer for holding nonvolatile information. When the direction of magnetization of the first ferromagnetic layer and the spin glass layer or the second ferromagnetic layer (described later) in contact with the nonmagnetic layer is opposite, when reading resistance by the magnetoresistive effect, the spin glass region According to the ratio, magnetic scattering is suppressed, and a nonvolatile and analog resistance value can be obtained.
By flowing a strong spin-polarized current between the first ferromagnetic layer and the spin glass layer, the spin glass can be induced by the STT effect, and the resistance of the element can be changed.

Ferrimagnetic material forming the spin glass _layer, the spinel material is represented by AB _{2 O 4-x,} or may be reversed spinel material represented by BA _{2 O 4-x.} Here, A is one or more elements of Mn, Fe, Co, Ni, Cu, Zn, and Mg, and B is one or more elements of Fe, Cr, Ti, Mg, Mn, and Ni.
A material having a spinel structure or an inverse spinel structure exhibits ferrimagnetism, and can exhibit a spin glass at a high temperature. The example of the material concerning patent document 5 is described.

  Of the non-magnetic materials or magnetic materials that cause the spin glass region in the material based on the ferrimagnetic material, a non-magnetic material such as Co and Zn becomes spin glass by mixing about several percent. If about% is mixed (added), the ferrimagnetism of the base material is lost. On the other hand, when a magnetic material is mixed, a larger amount can be mixed. However, these phenomena are not limited to the above because they vary quantitatively depending on the magnetic correlation in the base material and the material to be replaced.

  When the spin glass layer is a spinel oxide, Mg in the MgO tunnel layer diffuses into the spinel oxide when the spinel oxide is formed. Therefore, it is desirable to form MgO after forming the spinel oxide layer. Further, when annealing is performed in a structure in which the spinel oxide and the MgO tunnel layer are in contact with each other, the same effect is obtained. Therefore, it is desirable to take measures such as suppressing the diffusion of Mg by setting the annealing temperature to 400 ° C. or lower, or inserting a second ferromagnetic layer between the spinel oxide and the MgO tunnel layer.

  The spinel oxide uses reactive sputtering in which a metal target is formed with argon and oxygen plasma, and the substrate temperature during film formation is preferably at least 350 ° C., more preferably 400 ° C. or more. The spinel oxide can be obtained by reactive sputtering at least 350 ° C. or higher, and if it is 400 ° C. or higher, the spinel oxide can be stably obtained. Furthermore, a method of forming a film with a plasma of argon and oxygen using a spinel oxide as a target is also possible. Although it is difficult to adjust the oxidation degree of the spinel oxide by this method, the spinel oxide can be stably obtained even at 350 ° C.

  When the spin glass layer is a magnetic spinel material, the film thickness is preferably 3.5 nm or more. This is because the magnetic properties are not stable unless the film thickness is 3.5 nm or more.

The spinel layer spin spin material or reverse spinel material may be oxygen deficient.
The spinel material of spin glass layer or the reverse spinel material has a structure in which oxygen is deficient, so that the resistance of the spin glass layer can be reduced and the magnetoresistance ratio can be increased.
For example, the resistance of magnetite (FeFe ₂ O ₄ ) decreases to a resistivity about 100 times that of metal by oxygen deficiency.

  A known material can be used for the material of the first ferromagnetic layer 3. For example, a metal selected from the group consisting of Cr, Mn, Co, Fe, and Ni and an alloy that includes one or more of these metals and exhibits ferromagnetism can be used. An alloy containing these metals and at least one element of B, C, and N can also be used. Specifically, Co-Fe and Co-Fe-B are mentioned.

In order to obtain a higher output, it is preferable to use a Heusler alloy such as Co ₂ FeSi. The Heusler alloy includes an intermetallic compound having a chemical composition of X ₂ YZ, where X is a transition metal element or noble metal element of Co, Fe, Ni, or Cu group on the periodic table, and Y is Mn, V It is a transition metal of Cr, Ti or Ti, and can take the elemental species of X, and Z is a typical element of Group III to Group V. Examples thereof include Co ₂ FeSi, Co ₂ MnSi, and Co ₂ Mn _1-a Fe _a Al _b Si _1-b .

  In order to further increase the coercive force of the first ferromagnetic layer 3, an antiferromagnetic material such as IrMn or PtMn may be used as a material in contact with the first ferromagnetic layer 3. Further, in order to prevent the leakage magnetic field of the first ferromagnetic layer 3 from affecting the spin glass layer 1, a structure of a synthetic ferromagnetic coupling may be used.

Furthermore, when the direction of magnetization of the first ferromagnetic layer 3 is perpendicular to the laminated surface, it is preferable to use a laminated film of Co and Pt. Specifically, the first ferromagnetic layer 3 has [Co (0.24 nm) / Pt (0.16 nm)] ₆ / Ru (0.9 nm) / [Pt (0.16 nm) / Co (0.16 nm). ] _{4 /} Ta (0.2 nm) / FeB (1.0 nm).

A known material can be used for the nonmagnetic layer 2.
For example, when the nonmagnetic layer 2 is made of an insulator (when it is a tunnel barrier layer), as the material, Al ₂ O ₃ , SiO ₂ , Mg, MgAl ₂ O _4, or the like can be used. In addition to these, materials in which a part of Al, Si, Mg is substituted with Zn, Be, or the like can also be used. Among these, since MgO and MgAl ₂ O ₄ are materials that can realize a coherent tunnel, spin can be injected efficiently.
When the nonmagnetic layer 2 is made of metal, Cu, Au, Ag, or the like can be used as the material.

  Further, by forming the nonmagnetic layer 2 on the spin glass layer 1, it is possible to form a laminated film without diffusing other elements of the spin glass layer 1.

As shown in FIG. 3, a second ferromagnetic layer 4 may be provided between the spin glass layer 1 and the nonmagnetic layer 2.
By providing the second ferromagnetic layer 4 in addition to the spin glass layer 1 as the magnetization free layer for the first ferromagnetic layer 3 which is a magnetization fixed layer, the reversible magnetization is set to M1 and M3 to obtain a large magnetoresistance effect. Is possible. This requires a combination of a tunnel barrier layer and a ferromagnetic layer in order to cause the coherent tunnel effect, and the spin conduction between the spin glass layer 1 and the second ferromagnetic layer 4 is not a coherent tunnel but a normal TMR effect. This is because there is a possibility of occurrence. Since the spin glass layer 1 and the second ferromagnetic layer 4 are magnetically coupled, the spin glass layer is caused by the spin transfer torque (STT) effect between the first ferromagnetic layer 3 and the second ferromagnetic layer 4. It is possible to adjust the size of the spin glass region.

  As the material of the second ferromagnetic layer 4, a ferromagnetic material, particularly a soft magnetic material can be applied. For example, a metal selected from the group consisting of Cr, Mn, Co, Fe, and Ni, an alloy containing one or more of these metals, these metals and at least one element of B, C, and N are included. Alloys that can be used can be used. Specific examples include Co—Fe, Co—Fe—B, and Ni—Fe. Alternatively, an alloy containing a rare earth element is preferable. For example, an alloy such as Tb—Fe—Co can spontaneously develop perpendicular magnetic characteristics.

  In the case where the magnetization direction of the second ferromagnetic layer 4 is perpendicular to the laminated surface, the thickness of the second ferromagnetic layer is preferably 2.5 nm or less. Perpendicular magnetic anisotropy can be added to the second ferromagnetic layer 4 at the interface between the second ferromagnetic layer 4 and the nonmagnetic layer 2. In addition, since the effect of perpendicular magnetic anisotropy is attenuated by increasing the thickness of the second ferromagnetic layer 4, it is preferable that the thickness of the second ferromagnetic layer 4 is smaller. In addition, since the spin glass layer 1 and the second ferromagnetic layer 4 are thin, the influence of spin transfer becomes large, and magnetization reversal is possible even with a low spin polarization current.

As shown in FIG. 4, the magnetoresistive effect element shown in FIG. 3 may further include a spin orbit torque layer 5 on the surface of the spin glass layer 1 opposite to the side including the nonmagnetic layer 2. Although not shown, the magnetoresistive effect element shown in FIG. 1 may further include a spin orbit torque layer on the surface of the spin glass layer 1 opposite to the side including the nonmagnetic layer 2.
By passing a current through the spin orbit torque layer and injecting a pure spin current into the spin glass layer 1, a spin glass region can be induced in the spin glass layer.

The spin orbit torque wiring indicates the magnetoresistive effect element portion (the portion of the spin glass layer 1, the nonmagnetic layer 2, the first ferromagnetic layer 3, and the second ferromagnetic layer 4 (when the second ferromagnetic layer 4 is not included). Are extending in a direction crossing the stacking direction of the spin glass layer 1, the nonmagnetic layer 2 and the first ferromagnetic layer 3). The spin orbit torque wiring preferably extends in a direction orthogonal to the stacking direction. The spin orbit torque wiring is electrically connected to the spin orbit torque wiring to a power source that passes a current in a direction orthogonal to the stacking direction of the magnetoresistive effect element portion. It functions as a spin injection means for injecting a flow.
The spin orbit torque wiring may be directly connected to the spin glass layer 1 or may be connected via another layer.

The spin orbit torque wiring is made of a material that generates a pure spin current by a spin Hall effect when a current flows. As such a material, a material that generates a pure spin current in the spin orbit torque wiring is sufficient. Therefore, the material is not limited to a material composed of a single element, and may be a material composed of a portion made of a material that generates a pure spin current and a portion made of a material that does not generate a pure spin current.
The spin Hall effect is a phenomenon in which a pure spin current is induced in a direction orthogonal to the direction of the current based on the spin-orbit interaction when a current is passed through the material.

  FIG. 5 is a schematic diagram for explaining the spin Hall effect. Based on FIG. 5, the mechanism by which a pure spin current is produced by the spin Hall effect will be described.

As shown in FIG. 5, when the current I is passed in the extending direction of the spin-orbit torque line 5, the up spin S ⁺ and down spin S ^- is bent in a direction perpendicular to the current, respectively. The normal Hall effect and the spin Hall effect are common in that the moving (moving) charge (electrons) can bend in the moving (moving) direction, but the normal Hall effect is that the charged particles moving in the magnetic field exert Lorentz force. In contrast to this, the direction of motion is bent, but the spin Hall effect is greatly different in that the direction of movement is bent only by the movement of electrons (only the current flows) even though there is no magnetic field.
Magnetic body and the number of electrons spin-up S ⁺ in (ferromagnetic material not) spin-down S ^- since the number of electrons is equal to the up spin S ⁺ number of electrons and downward toward upward in the drawing It equals the number of electrons ^- down spin S toward. Therefore, the current as a net flow of charge is zero. This spin current without current is particularly called a pure spin current.
In contrast, when current is passed through a ferromagnet, upward spin electrons and downward spin electrons are bent in opposite directions, but in ferromagnets, upward spin electrons and downward spin electrons are the same. As a result, there is a difference in that a net flow of charges occurs (voltage is generated) as a result. Therefore, the material of the spin orbit torque wiring does not include a material made only of a ferromagnetic material.

Here, the electron flow of the upward spin S ⁺ is defined as J _↑ , the electron flow of the downward spin S ⁻ as J _↓ , and the spin current as J _S , and J _S = J _↑ −J _↓ . In FIG. 5, _JS flows upward in the figure as a pure spin current. Here, J _S is an electron flow having a polarizability of 100%.
In FIG. 5, when a ferromagnetic material is brought into contact with the upper surface of the spin orbit torque wiring 5, the pure spin current is diffused into the ferromagnetic material.
In this embodiment, a current is caused to flow through the spin orbit torque wiring to generate a pure spin current, and the pure spin current is diffused in the spin glass layer in contact with the spin orbit torque wiring. The spin glass region is induced in the spin glass layer by the spin orbit torque (SOT) effect caused by the flow.

(Heat history sensor)
A thermal history sensor according to an embodiment of the present invention uses the magnetoresistive effect element of the present invention.
If the spin glass region is induced in the spin glass layer using the ferrimagnetic material and then cooled, when the temperature is raised, the spin glass region decreases or disappears at the temperature at which the spin glass region is induced. This phenomenon occurs because the fluctuation due to temperature and the spin glass state are in an equilibrium state and stabilized at the temperature at which the spin glass region is induced. Therefore, when the temperature at which the spin glass region is induced is reached, the equilibrium state changes to a non-equilibrium state and the spin glass region decreases. The thermal history sensor of the present invention detects a change in the resistance value of the magnetoresistive effect element due to the phenomenon of the spin glass region due to the thermal history.

(Magnetic memory using spin glass)
A spin glass-based magnetic memory according to an embodiment of the present invention includes one or a plurality of magnetoresistive elements of the present invention and a stacking direction of layers constituting the magnetoresistive element with respect to each magnetoresistive element A current source for supplying a current, and at least the spin glass layer (in the case where the second ferromagnetic layer is provided) between the spin glass layer and the first ferromagnetic layer. The resistance of the magnetoresistive element is changed by applying a current larger than the critical current of spin injection magnetization reversal of the ferromagnetic layer.
The ratio of the spin glass layer can be increased or decreased by changing the direction of the current flowing through the magnetoresistive element. When a current is applied from the spin glass layer 1 to the first ferromagnetic layer 3, spin-polarized electrons flow from the first ferromagnetic layer 3 to the spin glass layer 1. Therefore, the spin-polarized electrons act to change the magnetization direction of the spin glass layer 1 in the same direction as the magnetization direction of the first ferromagnetic layer. At this time, the place where the spin glass is easily induced is that the magnetization direction changes with a current value smaller than the critical current value of the spin inflow magnetization reversal necessary for the entire spin glass layer 1 to reverse the magnetization, thereby inducing the spin glass. It is possible. Conversely, when a current is passed from the first ferromagnetic layer 3 to the spin glass layer 1, spin-polarized electrons flow from the spin glass layer 1 to the first ferromagnetic layer 3. Therefore, the spin-polarized electrons act to change the magnetization direction of the spin glass layer 1 in the direction opposite to the magnetization direction of the first ferromagnetic layer. By this effect, the portion where the spin glass is induced is magnetized in the same direction as the portion where the spin glass is not induced, and the spin glass region can be lost.

  The spin glass-based magnetic memory according to an embodiment of the present invention includes a magnetoresistive effect element including a spin glass layer as a magnetization free layer, and thus can output an analog resistance value as the resistance value of the magnetoresistive effect element. This principle will be described below.

FIG. 6 is a graph conceptually showing the relationship between the ratio of the spin glass region in the spin glass layer and the resistance value of the magnetoresistive effect element.
When the spin glass region is not generated in the spin glass layer, that is, when the ratio of the spin glass region in the spin glass layer is zero, the magnetization direction of the spin glass layer and the magnetization direction of the first ferromagnetic layer are antiparallel. And the resistance value of the magnetoresistive element portion is maximized.
On the other hand, when a spin polarization region (write current) is passed through the spin glass layer to generate a spin glass region in the spin glass layer, the proportion of the spin glass region in the spin glass layer increases. The horizontal axis (ratio of the spin glass region) of the graph corresponds to the number of pulses when a spin-polarized current (write current) is flowed in pulses. The spin glass region does not contribute to the magnetization of the spin glass layer because the magnetic order is disturbed. Therefore, if the proportion of the spin glass region increases, the region contributing to magnetization decreases, the magnetization of the spin glass layer decreases, and the magnetoresistance decreases. This decrease in magnetoresistance is analog, and the spin glass region exists stably as long as it is below the spin glass transition temperature. Therefore, in the spin glass-based magnetic memory including the magnetoresistive effect element of the present invention, data can be written in an analog manner depending on the magnitude of the spin polarization current (write current).

  In the magnetoresistive effect element of the present invention, it is assumed that the parent ferrimagnetic magnetic order is maintained in the entire layer. Therefore, the concentration of the non-matrix material that is the starting point of the spin glass region is The amount of magnetic ordering can be maintained. Therefore, the magnitude of the decrease in magnetoresistance of the magnetoresistive element due to the increase in the proportion of the spin glass region is also determined by the concentration of the non-matrix material.

Looking at the generation of the spin glass region at a microscopic level, spin-polarized electrons are injected into the spin glass layer, so that the localized spins of the ferrimagnetic material and non-matrix material constituting the spin glass layer are spin-polarized electrons. Around the localized spin of the non-matrix material that receives the spin angular momentum from the spin glass phenomenon, and the spin of the ferrimagnetic material is fixed in a state of losing the magnetic order as ferrimagnetism, and the spin glass region Is generated (see FIG. 2).
Regarding the reversal of the magnetization of the spin glass layer, when a spin polarization current having a current density exceeding the critical current density and for a sufficient time is applied, the magnetization of the spin glass layer is reversed by this magnetization reversal torque. On the other hand, in the case of a spin-polarized current that does not lead to magnetization reversal, the magnetization direction of the spin glass layer remains the same, but the magnitude is reduced by the amount of generation of the spin glass region. Since the transfer of spin angular momentum (spin transfer) is probabilistic, the higher the current density of the spin-polarized current, or the longer the flow time (in the case of current pulses, the pulse length) The proportion of the spin glass region increases.

  Writing and reading of the spin glass-based magnetic memory including the magnetoresistive effect element shown in FIG. 1 will be described below.

First, a conventional MRAM will be described.
The MRAM includes a magnetoresistive element using a magnetoresistive effect such as a GMR (Giant Magneto Resistance) effect and a TMR (Tunnel Magneto Resistance) effect as a memory cell. The magnetoresistive element has, for example, a laminated structure in which two ferromagnetic layers are laminated via a nonmagnetic layer. The two ferromagnetic layers are a magnetization fixed layer (pinned layer) whose magnetization direction is fixed and a magnetization free layer (free layer) whose magnetization direction can be reversed. The value of the electric resistance of the magnetoresistive element is larger when the magnetization directions of the magnetization fixed layer and the magnetization free layer are antiparallel than when they are parallel. In the magnetoresistive effect element which is an MRAM memory cell, by utilizing the difference in resistance value, the magnetization parallel state is associated with data “0” and the antiparallel state is associated with data “1”. The data is stored in a nonvolatile manner. Data is read by passing a read current so as to penetrate the magnetoresistive element (through the laminated structure) and measuring the resistance value of the magnetoresistive element. On the other hand, data is written by passing a spin-polarized current and reversing the magnetization direction of the magnetization free layer.

As the current mainstream data writing method, the “STT method” using spin transfer torque is known. In the STT method, a spin-polarized current is injected into the magnetization free layer, and a torque is generated in the magnetization free layer due to the interaction between the spin of conduction electrons carrying the current and the magnetic moment of the magnetization free layer. When it is sufficiently large, the magnetization is reversed. Since this magnetization reversal is more likely to occur as the current density increases, the write current can be reduced as the memory cell size is reduced. As the STT method, a method of flowing a write current so as to penetrate the magnetoresistive effect element (for example, Patent Document 1), or a method of flowing a write current in the in-plane direction of the magnetization free layer without penetrating the magnetoresistive effect element ( For example, Patent Document 4) is known.
Data is read by passing a read current so as to penetrate the magnetoresistive element (through the laminated structure) and measuring the resistance value of the magnetoresistive element. That is, it is performed by passing a current between the magnetization fixed layer and the magnetization free layer via the nonmagnetic layer and detecting a change in resistance according to the relative angle between the magnetization of the magnetization fixed layer and the magnetization of the magnetization free layer. .

On the other hand, the spin glass-based magnetic memory of the present invention is similar to the conventional MRAM described above in that data can be stored digitally, but in addition, data can be stored in an analog manner. Is different from the conventional MRAM.
That is, the critical current of the spin injection magnetization reversal of the spin glass layer (in the case of including the second ferromagnetic layer, the spin glass layer and the second ferromagnetic layer) that is a magnetization free layer so as to penetrate the magnetoresistive effect element By applying a larger write current and reversing the magnetization of the magnetization free layer, it is between the magnetization of the first ferromagnetic layer and the magnetization of the spin glass layer (or the spin glass layer and the second ferromagnetic layer). This is the same as the conventional MRAM in that data “0” or data “1” can be stored.
In addition, in the antiparallel state, a spin glass region is generated in the spin glass layer by flowing a write current to such an extent that the magnetization free layer is not reversed, so that the magnetic resistance value is lower than the magnetoresistance value in the antiparallel state. The resistance value can be stored. If the write current is controlled so that the magnetoresistive value is discrete, multi-level storage is possible, and if the write current is controlled so that the magnetoresistive value is substantially continuous, it is analog. Memory becomes possible. This is a control circuit that controls the spin glass-based magnetic memory of the present invention to flow a write current that allows the resistance value of the magnetoresistive effect element included in the spin glass-based magnetic memory to be used in a multivalued or analog manner. This is possible by providing a current source having

In order to eliminate the generated spin glass region, a current passing through the magnetoresistive effect element may be passed in a direction opposite to the direction in which the spin glass region is generated.
That is, when a current is passed from the first ferromagnetic layer 3 to the spin glass layer 1, spin-polarized electrons flow from the spin glass layer 1 to the first ferromagnetic layer 3. Therefore, the spin-polarized electrons act to change the magnetization direction of the spin glass layer 1 in the direction opposite to the magnetization direction of the first ferromagnetic layer. By this effect, the portion where the spin glass is induced is magnetized in the same direction as the portion where the spin glass is not induced, and the spin glass region can be lost.

  As another method, the magnetoresistive element may be set to a temperature exceeding the spin glass transition temperature. For example, the spin glass region generated by bringing the magnetoresistive element to a temperature exceeding the spin glass transition temperature by Joule heat due to the current passing through the magnetoresistive element can be eliminated.

  Similar to the above-described conventional MRAM, data is read by passing a read current so as to penetrate the magnetoresistive element (through the laminated structure) and measuring the resistance value of the magnetoresistive element. it can.

(Magnetic neuron element)
The magnetic neuron device of the present invention includes the spin glass-based magnetic memory of the present invention, and a write current that can use the resistance value of the magnetoresistive effect element included in the spin glass-based magnetic memory in a multivalued or analog manner. A current source having a control circuit that controls to flow, and the control circuit can control to flow a write current having a pulse number that makes at least three resistance ranges that can be read by the difference in resistance value of the magnetoresistive effect element Is.

  The spin glass-based magnetic memory of the present invention can be used as a magnetic neuron element that is an element that simulates synaptic operation. At the synapse, it is preferable to have a linear output with respect to external stimuli. In addition, when a reverse load is applied, it is preferable that there is no hysteresis and that the load is reversible. As shown in FIG. 6, in the magnetoresistive effect element of the present invention, the proportion of the spin glass region changes continuously. The horizontal axis in FIG. 6 can be regarded as the number of pulses of the write current, and can show a relatively linear resistance change. In addition, the resistance change can be changed depending on the magnitude of the current and the time of the applied current pulse, so that the magnitude and direction of the current and the time of the applied current pulse are regarded as an external load. Can do.

(Main memory stage)
When the reading resistance starts to change, an additional load is applied to the external load, resulting in a resistance change during reading that is proportional to the load to some extent. This is the main memory stage. That is, the case where the reading resistance changes can be called a main memory stage of memory. The stage immediately before the reading resistance starts to change can be defined as memory or no memory, and the stage at which the reading resistance stops changing can be defined as no memory or memory. Naturally, if the write current is reversed, the reverse effect is obtained.

(Forgetting memory stage)
By erasing the spin glass region, the memory can be forgotten. In the spin glass-based magnetic memory according to the present invention, since the output exhibits constant low resistance and high resistance values, memory and non-memory must be determined by definition. In addition, since the spin glass region is randomized when generated or lost, the information correlation between the plurality of spin glass-based magnetic memories is lost. These can be called the memory forgetting stage.

(Artificial brain using magnetic neuron elements)
The magnetic neuron device of the present invention is a memory that simulates synaptic movement and can undergo a main memory stage. The spin glass-based magnetic memory of the present invention can be installed on a plurality of circuits to simulate the brain. A brain with a high degree of integration can be formed with an arrangement in which the arrays are arranged vertically and horizontally like a general memory.
Further, as shown in FIG. 7, in the arrangement in which a plurality of magnetic neuron elements having specific circuits are arrayed as one lump, it is possible to form brains having different degrees of recognition from external loads. For example, it is possible to produce individuality such as a brain that is sensitive to color and a brain that has a high level of language understanding. In other words, information obtained from an external sensor is recognized in the five sense areas optimized for vision, taste, touch, smell, and auditory recognition, and further judged by the logical thinking area, It is possible to form a process of determining actions. Furthermore, if the material of the spin glass layer is changed, the generation rate of the spin glass region with respect to the load and the formation method of the spin glass region change, so that it becomes possible to form an artificial brain with such changes as individuality. .

DESCRIPTION OF SYMBOLS 1 Spin glass layer 2 Nonmagnetic layer 3 1st ferromagnetic layer 4 2nd ferromagnetic layer 5 Spin orbit torque layer 100 Magnetoresistive effect element

Claims (9)

A spin glass layer whose base material is a ferrimagnetic material, a nonmagnetic layer, and a first ferromagnetic layer whose magnetization direction is fixed are provided in this order,
A magnetoresistive effect element in which the magnetization direction of the spin glass layer and the magnetization direction of the first ferromagnetic layer can be antiparallel.   The magnetoresistive element according to claim 1, further comprising a second ferromagnetic layer between the spin glass layer and the nonmagnetic layer.   3. The magnetoresistive element according to claim 1, further comprising a spin orbit torque layer on a surface of the spin glass layer opposite to the side including the nonmagnetic layer. The ferrimagnetic _material, AB _{2 O} spinel materials represented by _4-x or _magnetic according to any one of claims 1 to 3 is an inverse spinel material represented by BA _{2 O 4-x,} Here, A is one or more elements of Mn, Fe, Co, Ni, Cu, Zn, and Mg, and B is one or more elements of Fe, Cr, Ti, Mg, Mn, and Ni. is there.   The magnetoresistive element according to claim 4, wherein the spinel material or the reverse spinel material of the spin glass layer is deficient in oxygen.   The thermal history sensor using the magnetoresistive effect element as described in any one of Claims 1-5.   A spin glass-based magnetic memory comprising: the magnetoresistive effect element according to any one of claims 1 to 5; and a current source for causing a current to flow in the stacking direction with respect to the magnetoresistive effect element.   A spin comprising a current source having a control circuit for controlling a write current that allows a multi-value or analog use of a resistance value of a magnetoresistive effect element included in the spin glass-based magnetic memory according to claim 7 Glass-based magnetic memory. A spin glass-based magnetic memory according to claim 8,
A magnetic neuron element that can be controlled so that the control circuit passes a write current having a pulse number in at least three resistance ranges that can be read depending on a difference in resistance value of the magnetoresistive element.

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