Magnetic memory element, information processing system, and method for controlling magnetic memory element

Abstract

A magnetic memory element (100) comprises: a substrate (10); a spin Hall layer (12) which is stacked on the substrate (10) and is made of a material that exhibits the spin Hall effect (for example, a non-magnetic heavy metal) , the spin Hall layer (12) generating a spin flow when a write current Iwrite flows in an in-plane direction thereof; and an antiferromagnetic layer (14) which is stacked on the spin Hall layer (12), has a tensile strain ε in the in-plane direction, and is made of an antiferromagnetic metal including manganese (for example, Mn3Sn), wherein the magnetization of the antiferromagnetic metal can be inverted by a spin orbit torque produced by the spin flow.

Description

[Technical Field]

[0001] The present invention relates to a magnetic memory element, an information processing system, and a method for controlling a magnetic memory element. [Background technology]

[0002] Magnetic random access memory (MRAM) using ferromagnetic materials is attracting attention as a non-volatile memory that can realize low-power information processing. In fact, various semiconductor manufacturers are adopting MRAM as a replacement for volatile memory such as static random access memory (SRAM). Examples of such MRAM include STT-MRAM, which uses spin-transfer torque (STT) to reverse the magnetization of a ferromagnetic material, and SOT-MRAM, which uses spin-orbit torque (SOT) to reverse the magnetization of a ferromagnetic material (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 9,837,602 Summary of the Invention [Problem to be solved by the invention]

[0004] However, because current MRAM uses ferromagnetic materials, the magnetization reversal speed is limited to about 1 nanosecond, which poses a particular challenge in that it cannot handle the THz band (picoseconds), which will become increasingly important in the future as optical communications speeds increase.

[0005] The present invention has been made in view of the above-mentioned problems, and has as its object to enable high-speed write and read operations by a magnetic memory element using an antiferromagnetic material. [Means for solving the problem]

[0006] A magnetic memory element according to one aspect of the present invention includes an antiferromagnetic layer having uniaxial strain and made of an antiferromagnetic metal containing manganese, the magnetic order of which can be controlled by spin torque.

[0007] According to another aspect of the present invention, there is provided a magnetic memory element comprising: a spin Hall layer made of a material exhibiting the spin Hall effect, in which a spin current is generated when a write current flows in an in-plane direction; a free layer stacked on the spin Hall layer, having uniaxial strain and containing an antiferromagnetic metal containing manganese, in which the magnetic order of the antiferromagnetic metal can be reversed by the spin-orbit torque generated by the spin current; a non-magnetic layer stacked on the free layer; and a reference layer stacked on the non-magnetic layer, made of a ferromagnetic metal or an antiferromagnetic metal containing manganese, in which the magnetic order of the ferromagnetic metal or antiferromagnetic metal is fixed.

[0008] According to yet another aspect of the present invention, there is provided a magnetic memory element comprising: a reference layer made of a ferromagnetic metal or an antiferromagnetic metal containing manganese, in which the magnetic order of the ferromagnetic metal or the antiferromagnetic metal is fixed; a non-magnetic layer stacked on the reference layer; and a free layer stacked on the non-magnetic layer, the free layer having uniaxial strain and containing an antiferromagnetic metal containing manganese, in which the magnetic order of the antiferromagnetic metal can be reversed by spin transfer torque when a write current flows in the perpendicular direction.

[0009] An information processing system according to yet another aspect of the present invention is an information processing system including the magnetic memory element described above.

[0010] An information processing system according to yet another aspect of the present invention is an information processing system including a magnetic memory device having a plurality of the above-described magnetic memory elements arranged in a matrix.

[0011] A method for controlling a magnetic memory element according to yet another aspect of the present invention is a method for controlling a magnetic memory element having an antiferromagnetic layer having uniaxial strain and made of an antiferromagnetic metal containing manganese, in which the magnetic order of the antiferromagnetic metal is controlled by spin torque.

[0012] According to yet another aspect of the present invention, there is provided a method for controlling a magnetic memory element comprising: a spin Hall layer made of a material exhibiting the spin Hall effect; a free layer stacked on the spin Hall layer, having uniaxial strain, and comprising an antiferromagnetic metal containing manganese; a non-magnetic layer stacked on the free layer; and a reference layer stacked on the non-magnetic layer, made of a ferromagnetic metal or an antiferromagnetic metal containing manganese, in which the magnetic order of the ferromagnetic metal or antiferromagnetic metal is fixed. The method comprises the steps of: generating a spin current by passing a write current in an in-plane direction in the spin Hall layer; and reversing the magnetic order of the antiferromagnetic metal in the free layer by the spin-orbit torque generated by the spin current.

[0013] A method for controlling a magnetic memory element according to yet another aspect of the present invention is a method for controlling a magnetic memory element comprising: a reference layer made of a ferromagnetic metal or an antiferromagnetic metal containing manganese, in which the magnetic order of the ferromagnetic metal or antiferromagnetic metal is fixed; a non-magnetic layer stacked on the reference layer; and a free layer stacked on the non-magnetic layer, having uniaxial strain and containing an antiferromagnetic metal containing manganese, wherein a write current is passed in a direction perpendicular to the surface of the magnetic memory element, thereby reversing the magnetic order of the antiferromagnetic metal of the free layer by spin transfer torque. [Effects of the Invention]

[0014] According to the present invention, a magnetic memory element has an antiferromagnetic layer that has uniaxial strain and is made of an antiferromagnetic metal containing manganese, and the magnetic order of the antiferromagnetic metal can be controlled by spin torque, thereby increasing the magnetization reversal speed and enabling high-speed write and read operations. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view of a magnetic memory element according to a first embodiment of the present invention. [Figure 2] 1 is a schematic diagram showing the crystal structure and magnetic structure of Mn3Sn. [Figure 3]1 is a schematic diagram for explaining control of the magnetic state when in-plane tensile strain is present in the Mn3Sn layer of an MgO substrate / W / Mn3Sn multilayer film. [Figure 4A] 1 is a graph showing X-ray diffraction patterns of 2θ / ω scans for an MgO substrate / W / Mn3Sn / MgO sample and an MgO substrate. [Figure 4B] 1 is a graph showing φ scan X-ray diffraction patterns for an Mn3Sn layer, a W layer, and an MgO substrate. [Figure 4C] 1 is a cross-sectional transmission electron microscope (TEM) image of a Mn3Sn layer. [Figure 5] FIG. 1 is a schematic diagram for explaining tensile strain in an Mn3Sn layer in an epitaxial film. [Figure 6A] 1 is a schematic diagram showing the spin structure of the Kagome layer when there is no strain in the Mn3Sn layer (ε=0). [Figure 6B] Schematic diagram showing the binary state of the Kagome layer stabilized by epitaxial uniaxial tensile strain (ε>0) in the Mn3Sn layer. [Figure 7] FIG. 1 is a schematic diagram showing the configuration of a magnetic memory element having a Hall bar structure. [Figure 8A] 1 is a graph showing the magnetic field dependence of the Hall voltage of a W / Mn3Sn multilayer film on an MgO substrate. [Figure 8B] 1 is a graph showing the write current dependence of the Hall voltage of a W / Mn3Sn multilayer film on an MgO substrate. [Figure 9] 10 is a schematic diagram for explaining the piezoelectric effect of Mn3Sn in the second embodiment of the present invention. FIG. [Figure 10] FIG. 1 is a schematic diagram showing the structures of two Mn3Sn samples (M1 and M2) compressed in different directions. [Figure 11] 10 is a graph showing the magnetic field dependence of magnetization at various uniaxial stresses for each sample. [Figure 12] 10 is a graph showing the temperature dependence of magnetization at various uniaxial stresses for each sample. [Figure 13] 1 is a graph showing the uniaxial stress dependence of spontaneous magnetization and magnetic susceptibility for each sample. [Figure 14] FIG. 1 is a schematic diagram for explaining the measurement of the Hall effect for two Mn3Sn samples (H1 and H2) with different strain directions. [Figure 15A] 10 is a graph showing the magnetic field dependence of Hall resistivity at various strains for sample H1. [Figure 15B] 10 is a graph showing the magnetic field dependence of Hall resistivity at various strains for sample H2. [Figure 16] FIG. 10 is a cross-sectional view of a magnetoresistive element constituting a magnetic memory element according to a third embodiment of the present invention. [Figure 17] 17 is a schematic diagram for explaining the resistance state of the magnetoresistive element of FIG. 16. FIG. [Figure 18] FIG. 1 is a schematic diagram showing the configuration of a magnetic memory element of an SOT-MRAM. [Figure 19] FIG. 1 is a schematic diagram showing the configuration of a magnetic memory element of an STT-MRAM. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or similar components are designated by the same reference numerals throughout the drawings. The drawings are schematic, and the relationship between planar dimensions and thickness, and the thickness ratio of each component, differ from the actual ones. Furthermore, it goes without saying that the dimensional relationships and ratios of each component differ between the drawings.

[0017] In this embodiment, a multilayer film may be expressed by the material of each layer that constitutes the multilayer film. For example, if a layer of material b and a layer of material c are stacked in this order on a layer of material a, the multilayer film will be expressed as "material a / material b / material c." The thickness (nm) of each layer may be written in parentheses after the name of the material. For example, a layer made of material j with a thickness of ti (nm) will be expressed as "material j(ti)."

[0018] In this embodiment, an antiferromagnetic material is used instead of a ferromagnetic material to realize a nonvolatile memory that can operate at high speed. The reason is that the spin response speed of an antiferromagnetic material is in the THz range (picoseconds), which is two to three orders of magnitude faster than that of a ferromagnetic material, and the interaction between magnetic materials is small, so there is a possibility that magnetic devices can be made even faster and more highly integrated.

[0019] First Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 to 8B.

[0020] First, the configuration of a magnetic memory element 100 according to the first embodiment will be described with reference to Fig. 1. The magnetic memory element 100 includes a substrate 10, a spin Hall layer 12 on the substrate 10, and an antiferromagnetic layer 14 on the spin Hall layer 12.

[0021] The substrate 10 is made of an insulator such as MgO. The spin Hall layer 12 is made of a substance (spin Hall material) that exhibits the spin Hall effect, such as a non-magnetic heavy metal such as tantalum (Ta), tungsten (W), or platinum (Pt), or a chalcogenide material such as a topological insulator. The antiferromagnetic layer 14 is a thin film made of an antiferromagnetic metal containing manganese (Mn). Examples of such antiferromagnetic metals include Mn3X (X = Sn, Ge, Ga, Rh, Pt, Ir), Mn3XN (X = Ga, Sn, Ni), and gamma-type Mn alloys with a face-centered cubic (fcc) structure. Examples of gamma-type Mn alloys include Mn 1-x Fe x , Mn 1-x Rh x , Mn 1-x Pd x Alternatively, the antiferromagnetic layer 14 may be made of a mixture of different Mn3X (e.g., a mixture of Mn3Sn and Mn3Ga), or Mn3X mixed with a trace amount of another element (e.g., Mn3Sn mixed with a trace amount of Cr).

[0022] When a write current is passed in the in-plane direction through the spin Hall layer 12 of the magnetic memory element 100, a spin current is generated in the perpendicular direction due to the spin Hall effect, and the spin-orbit torque (SOT) acts on the magnetization of the antiferromagnetic layer 14, thereby reversing the magnetization.

[0023] Instead of the magnetic memory element 100 shown in Fig. 1, a configuration in which a spin Hall layer is stacked on an antiferromagnetic layer (substrate / antiferromagnetic layer / spin Hall layer) may be adopted. Also, the antiferromagnetic layer may be sandwiched between two spin Hall layers made of spin Hall materials with spin Hall angles of different signs. The following mainly describes the magnetic memory element 100 shown in Fig. 1.

[0024] Next, a method for fabricating the magnetic memory element 100 will be described. An example will be given below in which a W (7 nm) / Mn3Sn (30 nm) / MgO (5 nm) multilayer film is formed on an MgO (110) substrate. Here, the MgO (5 nm) layer is provided to prevent oxidation of the Mn3Sn layer. The thickness (nm) of each layer in the magnetic memory element 100 is merely an example and is not limited thereto.

[0025] First, the MgO substrate is annealed in an ultra-high vacuum chamber at 800 °C for 10 minutes. The W (7 nm) / Mn3Sn (30 nm) / MgO (5 nm) multilayer film is grown at a base pressure of 2 × 10 -8 The films were fabricated on MgO(110) substrates by molecular beam epitaxy (MBE) under ultra-high vacuum at 100 Pa. A W (7 nm) layer was deposited at 300 °C at a rate of 0.1 Å / s and then annealed at 800 °C for 10 minutes. A Mn3Sn (30 nm) layer was fabricated by co-evaporation of Mn and Sn at a rate of 0.25 Å / s. First, a Mn3Sn (5 nm) layer was deposited at room temperature and then annealed at 400 °C. An additional Mn3Sn (25 nm) layer was then deposited at approximately 260 °C.

[0026] Here, a clear stripe pattern can be observed from the in-situ reflection high-energy electron diffraction (RHEED) image, which indicates that the W and Mn3Sn layers are epitaxially grown during this fabrication process.

[0027] Then, an MgO layer is grown at room temperature at a rate of 0.1 Å / s. Finally, the MgO(110) substrate / W(7 nm) / Mn3Sn(30 nm) / MgO(5 nm) multilayer is annealed at 650 °C for 30 minutes. It should be noted that a multilayer with similar properties to that fabricated by MBE can also be fabricated by sputtering instead of MBE by using the same annealing process.

[0028] Next, with reference to FIG. 2, the characteristics of Mn3Sn as an example of an antiferromagnetic metal that forms the antiferromagnetic layer 14 will be described.

[0029] Mn3Sn is an antiferromagnetic material with a triangular crystal structure called the kagome lattice. As shown in Figure 2, the kagome lattice is stacked in the

[0001] direction. Due to geometric frustration, the Mn atoms located at the vertices of the kagome lattice exhibit a non-collinear magnetic structure at temperatures below 420 K, in which the magnetic moments (localized spin orientations) are inclined 120 degrees relative to each other. Three types of six-spin units arranged on a bilayer kagome lattice form a spin order called a cluster magnetic octupole, represented by a hexagon. This non-collinear magnetic structure can be regarded as a ferromagnetic order of the cluster magnetic octupole. This ferromagnetic order breaks time-reversal symmetry macroscopically.

[0030] The cluster magnetic octopole corresponds to the orientation of Weyl points, which are topological electronic structures, and the virtual magnetic field in momentum space (equivalent to 100-1000 Tesla (T) in real space), and the response derived from the Weyl points and the virtual magnetic field can be controlled by the orientation of the cluster magnetic octopole.

[0031] The magnetic structure shown in Figure 2 has orthorhombic symmetry, with only one of the three magnetic moments of Mn located at the vertices of the triangle parallel to the easy axis of magnetization. The other two magnetic moments are canted with respect to the easy axis, which is thought to induce a weak ferromagnetic moment. An antiferromagnet with a canted magnetic moment and thus a small magnetization is called a canted antiferromagnet.

[0032] The crystal orientation of Mn3Sn plays an important role in enhancing the readout signal of magnetic memory elements. For example, in the measurement of the anomalous Hall effect described below, only crystal grains with a component of the magnetic order of the cluster magnetic octupole in the perpendicular direction (perpendicular to the surface of the substrate 10) contribute to the Hall voltage.

[0033] When a W / Mn3Sn layer is fabricated on an MgO substrate as described above, a tensile strain ε is generated in the Mn3Sn layer along the [2-1-10] direction (in-plane direction), as shown in Figure 3. In this case, the magnetic order of the cluster magnetic octupole is oriented perpendicular to the plane. This determines the binary state (up or down) on the kagome layer (see Figure 6B).

[0034] X-ray diffraction is used to investigate the crystal structure of the Mn3Sn layer. Figure 4A shows the 2θ / ω scan X-ray diffraction patterns for the MgO(110) substrate / W(7 nm) / Mn3Sn(30 nm) / MgO(5 nm) sample and the MgO(110) substrate. For the MgO(110) substrate / W(7 nm) / Mn3Sn(30 nm) / MgO(5 nm) sample, the temperature T A The X-ray diffraction patterns at temperatures of 650 and 700 °C are shown. The bottom panel of Figure 4A shows the X-ray diffraction patterns at temperatures of 650 and 700 °C. 19 The theoretical spectra of α-Mn3Sn and α-W are shown in Fig. 4B. The φ-scan X-ray diffraction patterns for the {02-21} plane of the Mn3Sn layer, the {110} plane of the W layer, and the {200} plane of the MgO substrate are also shown in Fig. 4B.

[0035] The X-ray spectrum in FIG. 4A shows that the W layer has a peak at (211), and the Mn3Sn layer has main peaks at (01-10), (02-20), and (04-40). This indicates that the Mn3Sn layer has a hexagonal D0 19 As shown in Figure 4A, the Mn3Sn layer has a T A = 650℃, there are minor peaks at (0002) and (02-21), but T A At 700°C, these minor peaks disappear.

[0036] The X-ray spectra in Figure 4B show that the {110} peak of the W layer and the {021} peak of the Mn3Sn layer appear to be shifted by 90 degrees from the {200} peak of the MgO substrate. These results indicate that the Mn3Sn layer is preferentially oriented as MgO(110)

[0001] ||W(211)[01-1]||Mn3Sn(01-10)

[0001] . This confirms that the kagome planes confining the cluster magnetic octopole are perpendicular to the film plane, as shown in Figure 3.

[0037] Figure 5 shows the atomic arrangement of the Mn3Sn layer in the MBE-grown film. X-ray diffraction for the (02-20), (20-20), and (-2200) planes of the Mn3Sn layer revealed the interatomic distances d1 and d2 in each triangle constituting the hexagon, as well as the angle θ 12 The other interatomic distance d3 and the length parallel to the [2-1-10] direction (x direction) d in are d1, d2, θ 12 It can be found from

[0038] In the case of bulk Mn3Sn, the lattice constants are known to be a = 5.665 Å, c = 4.531 Å, d1 = 4.903 Å, d2 = 4.909 Å, d3 = 4.906 Å, d in = 4.251 Å, θ 12 On the other hand, for the Mn3Sn layer in the MBE grown film, d1 = 4.904 Å, d2 = 4.916 Å, d3 = 4.939 Å, and d in = 4.261 Å, θ 12= 60.4°. Compared to bulk Mn3Sn, the Mn3Sn layer grown by MBE has almost the same d1, but d2 is longer, and θ 12 is getting larger, and d in increases from 4.251 Å to 4.261 Å. This indicates the presence of a tensile strain (epitaxial strain) ε of approximately 0.2% in the [2-1-10] direction (x direction). The presence of a similar strain can also be assessed from the cross-sectional transmission electron microscope (TEM) image of the Mn3Sn layer shown in Figure 4C. In Figure 4C, the diamond represents the unit cell of Mn3Sn.

[0039] When the Mn3Sn layer is unstrained (ε = 0), the spin structure on the kagome layer takes six degenerate states, with the magnetic order of the cluster magnetic octopoles oriented along six equivalent {2-1-10} directions, as shown in Figure 6A. On the other hand, when the Mn3Sn layer is subjected to in-plane epitaxial uniaxial tensile strain (ε > 0), the magnetic order of the cluster magnetic octopoles takes two states, parallel (upward) and antiparallel (downward) to the [01-10] direction, as shown in Figure 6B. This allows binary data ("0" and "1") to be represented.

[0040] Next, the anomalous Hall effect, write and read operations of the magnetic memory element 100 will be described with reference to FIGS. 7, 8A and 8B.

[0041] 7 shows the configuration of a magnetic memory element 100 with a Hall bar structure. Electrodes 16a and 16b made of Au / Ti are arranged at both ends of the sample in the longitudinal direction (x direction) of the magnetic memory element 100, and electrodes 18a and 18b made of Au / Ti are arranged in the lateral direction (y direction). A write current I write or read current I read flows, and a Hall voltage V H is detected.

[0042] When writing data to the magnetic memory element 100, a write current Iwrite A pulse current (pulse current) is applied in the longitudinal direction (x direction). This generates a spin current in the perpendicular direction (z direction) due to the spin Hall effect, and the SOT acts on the magnetization of the antiferromagnetic layer 14, thereby reversing the magnetization. At this time, a weak bias magnetic field H x By applying a bias magnetic field H x The direction of magnetization rotation is determined by the influence of

[0043] In this way, data (“0” or “1”) can be written to the antiferromagnetic layer 14. The write current I write The magnetization direction of the antiferromagnetic layer 14 can be controlled by the direction of the write current I write When a write current I flows, the magnetization is reversed from the +z direction ("1") to the -z direction ("0"), and the write current I write When a current is applied, the magnetization reverses from the -z direction ("0") to the +z direction ("1").

[0044] When reading data stored in the antiferromagnetic layer 14, a read current I read (DC) flows in the x direction. This generates a Hall voltage V in the y direction due to the anomalous Hall effect. H The Hall voltage V H The sign of is determined by the z component of the magnetization of the antiferromagnetic layer 14. For example, when the magnetization of the antiferromagnetic layer 14 is oriented in the +z direction, it corresponds to "1," and when it is oriented in the -z direction, it corresponds to "0."

[0045] 8A and 8B, the measurement results of the anomalous Hall effect for the magnetic memory element 100 will be described. Here, the multilayer film of the magnetic memory element 100 used for the measurement is W (7 nm) / Mn3Sn (30 nm) on an MgO substrate.

[0046] Figure 8A shows the Hall voltage V versus the perpendicular magnetic field H (magnetic field in the z direction) at room temperature. H As shown in Figure 8A, the Hall voltage V HA clear hysteresis is observed in the Hall voltage V when the magnetic field H is swept from negative to positive. H and the Hall voltage V when the magnetic field H is swept from positive to negative. H The difference (Hall voltage change) ΔV H field is about 40 μV.

[0047] Figure 8B shows the write current I at room temperature when a bias magnetic field μH of 0.1 T is applied to the W (7 nm) / Mn3Sn (30 nm) multilayer film in the x direction. write Hall voltage V H Here, the Hall voltage V H To measure the write current I write After applying the read current I read As shown in Figure 8B, a clear hysteresis is observed, and the write current I write Hall voltage V H The jump corresponds to the reversal of the magnetic order (magnetization reversal) of the cluster magnetic octupole.

[0048] Write current I write The Hall voltage V when sweeping from negative to positive H and the write current I write The Hall voltage V when sweeping from positive to negative H The difference (change in Hall voltage) is ΔV H current The ratio ΔV H current / |ΔV H field | indicates the ratio of the actually reversed magnetic domains to the total reversible magnetic domains (reversal ratio). H current is about 40μV, so ΔV H current / |ΔV H field | is 1 (i.e., the reversal ratio is 100%). This means that in the 30 nm Mn3Sn layer, all magnetic domains that can be reversed by a perpendicular magnetic field are write This shows that it can be inverted by

[0049] The results in Figures 8A and 8B show that perpendicular magnetic anisotropy is effectively achieved in the Mn3Sn layer due to in-plane epitaxial strain. This can be attributed to the control of magnetic anisotropy by the piezoelectric effect described in the second embodiment below. This allows for a stable binary antiferromagnetic state to be obtained, eliminating signal variations even when the magnetic memory element 100 is miniaturized, and improving operational reliability.

[0050] In the above experiment, an epitaxial strain of approximately 0.2% was applied to the Mn3Sn layer using an MgO substrate. It is known that epitaxial strain can usually be increased to several percent. Thus, by using epitaxial strain, it is possible to increase the magnetization reversal speed of the antiferromagnetic layer 14 to approximately 1 ps to 10 ps (10 GHz to 1 THz).

[0051] As described above, in the magnetic memory element according to the first embodiment, when the antiferromagnetic layer has an epitaxial strain in the in-plane direction, the magnetic order of the cluster magnetic octupole that characterizes the antiferromagnetic state is oriented perpendicular to the strain direction, thereby determining a binary state. Therefore, the magnetic memory element using the antiferromagnetic material enables high-speed write and read operations.

[0052] Second Embodiment A second embodiment of the present invention will be described with reference to FIGS. 9 to 15B.

[0053] In the second embodiment, we will explain the control of magnetic anisotropy of an antiferromagnetic layer based on the piezoelectric effect. Conventionally, research on the piezoelectric effect has been limited mainly to antiferromagnetic insulators at extremely low temperatures, but the inventors of the present application have discovered the piezoelectric effect of antiferromagnetic metals at room temperature or above, as described below.

[0054] The magnetic memory element according to the second embodiment has the same configuration as the magnetic memory element 100 according to the first embodiment (FIG. 1), and the material of the multilayer film constituting the magnetic memory element is also the same as that of the first embodiment. In the second embodiment, Mn3Sn will be used as an example of an antiferromagnetic metal.

[0055] When uniaxial strain is applied to a magnetic memory element from the outside, the magnetic anisotropy can be controlled by the piezoelectric effect in the antiferromagnetic layer. As shown in the center of Figure 9, when there is no strain in the Mn3Sn layer, as mentioned above, the small spontaneous magnetization M S (In Figure 9, the [2-1-10] direction (+x direction) exists. When uniaxial stress is applied to a sample of a magnetic memory element, the nearest neighbor exchange interactions become anisotropic. For example, as shown in the left diagram of Figure 9, under horizontal (x direction) compression in zero magnetic field, the horizontal bond distance becomes shorter, the exchange interaction between these bonds increases, and the horizontally coupled spins rotate and become nearly antiparallel along the y direction. This results in the spontaneous magnetization M S On the other hand, under zero magnetic field and horizontal tensile strain, the spontaneous magnetization M S The -x component of increases.

[0056] Next, magnetization measurements for two samples M1 and M2, which are compressed in different directions, will be described. Both samples M1 and M2 are single crystals made of Mn3Sn. As shown in Figure 10, sample M1 is subjected to a uniaxial stress σ xx is applied from both sides, and specimen M2 is subjected to uniaxial stress σ in the y direction. yy The samples M1 and M2 are subjected to a magnetic field H in the [2-1-10] direction (+x direction). x , magnetic field H in the [01-10] direction (+y direction) y A uniaxial stress is applied to these samples using, for example, a piston-cylinder pressure cell as described in the following non-patent document: Kittaka, S., Taniguchi, H., Yonezawa, S., Yaguchi, H. & Maeno, Y. “Higher-Tc superconducting phase in Sr2RuO4induced by uniaxial pressure” Phys. Rev. B 81, 180510 (2010)

[0057] In the following, negative strain indicates compressive strain, and positive strain indicates tensile strain. xx The magnetic field dependence of magnetization M under conditions of 0 MPa, -107 MPa, and -270 MPa, and σ at 300 K (room temperature) for sample M2 yy Fig. 12 shows the magnetic field dependence of the magnetization M under various uniaxial stresses (σ xx μH at (=0 to -270MPa) x The temperature dependence of the magnetization M under a magnetic field of 1 T and the uniaxial stress (σ yy μH at (=0 to -101MPa) y Fig. 13 shows the temperature dependence of the magnetization M under a magnetic field of 1 T. For samples M1 and M2, the spontaneous magnetization M at 300 K is S 13 shows the uniaxial stress dependence of the magnetic susceptibility χ. In FIG. 13, for sample M2, the stress in the x direction and the magnetic field H x The data with applied stress (black circles) and the stress and magnetic field H y The data shown are those with and without the application of voltage (white circles).

[0058] From Figure 11, zero stress (σ xx =0), M of sample M1 S is 3.6mμ B / fu, and the coercive force is very small at 0.03 T. On the other hand, σ xx M of sample M1 under -270 MPa S is 10.7mμ B / fu, which shows an increase of about three times. In both samples M1 and M2, the magnetization M increases linearly with the magnetic field except in the low magnetic field region, and the slope of this curve represents the magnetic susceptibility χ. The dotted lines in each graph in Figure 11 show the linear approximation formula in the positive magnetic field region, M(H)=M S +χ·H. Here, for sample M1, χ=μ0 -1 (∂M / ∂H x )=14.3mμ B / fuT -1 , for sample M2, χ = μ0 -1 (∂M / ∂H y )=13.5mμ B / fuT -1 As is clear from Figure 11, the shape of the hysteresis loop and the magnetic susceptibility χ do not change with stress. This indicates that the quality of each sample does not deteriorate below the yield stress, and that the magnetization M is that of a single magnetic domain.

[0059] As can be seen from Fig. 12, both samples M1 and M2 have the incommensurate transition temperature T H It can be seen that at temperatures exceeding (=270K to 280K), the magnetization M increases with increasing stress.

[0060] From the upper graph of Figure 13, M S The stress dependence of is linear for both specimen M1 and specimen M2, and specimen M2 is almost isotropic in the xy plane. From the linear approximation (dotted line), in the tensile stress region (σ>0), M S The critical stress σ at which c It is estimated that the magnetic susceptibility χ is approximately 120 MPa. Furthermore, the bottom graph in Figure 13 shows that the magnetic susceptibility χ is constant regardless of the stress. Each sample is crushed by applying a stress exceeding 300 MPa.

[0061] Next, the anomalous Hall effect of two samples H1 and H2 with different strain directions will be described. As shown in Fig. 14, both samples H1 and H2 have single-crystal antiferromagnetic layers 20 made of Mn3Sn. Sample H1 has strain ε in the x and y directions, respectively. xx , magnetic field H yis applied to sample H2, and strains ε yy , magnetic field H x The anomalous Hall effect under various strains is measured using a piezoelectric strain device described in the following non-patent document: Hicks, CW, Barber, ME, Edkins, SD, Brodsky, DO & Mackenzie, AP “Piezoelectric-based apparatus for strain tuning” Rev. Sci. Instrum. 85, 065003 (2014)

[0062] A current I flows in the strain direction in specimens H1 and H2, and a Hall voltage V perpendicular to the current I flows in the plane. H is measured. When the thickness (length in the direction perpendicular to the surface) of the antiferromagnetic layer 20 is t and the Hall resistivity is ρ, V H = ρ·I / t.

[0063] Figure 15A shows the results of various strains ε xx Hall resistivity ρ at 300K in zx Figure 15B shows the magnetic field dependence of the strain ε yy Hall resistivity ρ at 300K in zy From Fig. 15A, when there is no strain (ε xx =0%), Hall resistivity ρ zx shows a sharp hysteresis curve, and the Hall resistivity at zero magnetic field is ρ zx (H y = 0) = -3.85 μΩcm, and the coercive force is approximately 0.04 T. xx Under tensile strain of ρ = 0.194%, the shape of the hysteresis curve is maintained, and zx (H y = 0) = -4.2 μΩ cm, which indicates that the magnitude of the Hall resistivity increases by approximately 10% compared to when there is no strain. xx <0%, ρ zx (H y =0) gradually decreases as the compression increases, and εxx <-0.2% becomes zero. xx <-0.06%, ρ zx There is a region where the magnetic field is linear. xx =-0.21%, ρ zx is the slope μ0 -1 (∂ρ zx / ∂H y ) is approximately 1μΩcmT -1 increases with μ0H y = +3.8T and positive saturation value ρ zx As shown in FIG. 15B, the Hall resistivity ρ zy behaves almost the same as sample H1.

[0064] As described above, the magnetic order of the cluster magnetic octopoles is oriented in the direction of the applied compressive strain, and the signals read out by the anomalous Hall effect and magnetoresistance effect (described later) can be increased in the direction of the applied compressive strain. In this way, the magnitude of the magnetization, the anomalous Hall effect, and the magnetoresistance effect can be controlled by applying compressive strain. This enables high-speed write and read operations in magnetic memory elements using antiferromagnetic materials.

[0065] The antiferromagnetic layer described in the first and second embodiments may be a single crystal film or a polycrystalline film, and the same applies to the free layer (antiferromagnetic layer) in the third embodiment below.

[0066] <Third embodiment> A third embodiment of the present invention will be described with reference to Figures 16 to 19. The third embodiment is directed to a magnetic memory element including a magnetoresistive element.

[0067] As shown in FIG. 16, the magnetoresistive element 30 includes a free layer 32 whose magnetization is reversible, a nonmagnetic layer 34 in contact with the free layer 32, and a reference layer 36 in contact with the nonmagnetic layer 34, whose magnetization is fixed in the in-plane or perpendicular direction. The nonmagnetic layer 34 is made of an insulator (e.g., MgO, AlOx, MgAl2O4). Both the free layer 32 and the reference layer 36 are thin films made of the same antiferromagnetic metal as the antiferromagnetic layer 14 in FIG. 1, but the reference layer 36 has a larger coercive force than the free layer 32. The free layer 32 preferably has uniaxial strain (epitaxial strain or compressive strain) as described in the first or second embodiment. The magnetoresistive element 30 functions as a magnetic tunnel junction (MTJ) element.

[0068] Data "0" or "1" is assigned to the magnetoresistive element 30 depending on the resistance state. For example, when the free layer 32 and the reference layer 36 are made of Mn3Sn, as shown in FIG. 17, the magnetoresistive element 30 is in a low resistance state when the magnetic order of the cluster magnetic octopoles in the reference layer 36 and the magnetic order of the cluster magnetic octopoles in the free layer 32 are in the same direction (parallel state), and is in a high resistance state when they are in opposite directions (antiparallel state). Data in the parallel state can be assigned as "0," and data in the antiparallel state as "1." Experiments have shown that the magnetoresistive element 30 can be in a high resistance state when in the parallel state and in a low resistance state when in the antiparallel state.

[0069] It has been observed that the tunneling magnetoresistance effect (TMR) in a ferromagnetic / non-magnetic / ferromagnetic magnetoresistance element is proportional to the spin polarization of the ferromagnetic material. On the other hand, in an antiferromagnetic / non-magnetic / antiferromagnetic magnetoresistance element, TMR is not observed because the spin polarization of the antiferromagnetic material is usually negligible. For example, the spin polarization of the antiferromagnetic material Mn3Sn is three orders of magnitude smaller than that of the ferromagnetic material iron (Fe).

[0070] However, in the Mn3Sn / MgO / Mn3Sn multilayer film, large TMR has been observed even without net spin polarization. H , the tunnel resistance in the low resistance state is R L The TMR rate (%) is expressed as {(RH -R L ) / R H}×100(%). A TMR ratio of approximately 1% was observed in the Mn3Sn / MgO / Mn3Sn multilayer, which is larger than that observed in the Fe / MgO / Mn3Sn multilayer. This indicates that the TMR in the Mn3Sn / MgO / Mn3Sn multilayer is dominated by the contribution of the cluster magnetic octupole polarization rather than the spin polarization. Furthermore, it is expected that the TMR ratio will be even higher if the magnetization is oriented in-plane.

[0071] The magnetic memory element according to the third embodiment can function as a magnetic random access memory (MRAM) element. Hereinafter, the magnetic memory element of MRAM will be described with reference to FIGS.

[0072] 18 shows the configuration of an SOT-MRAM magnetic memory element 200. The magnetic memory element 200 includes a magnetoresistive element 210, a spin Hall layer 220, a first terminal 231, a second terminal 232, a third terminal 233, and transistors Tr1 and Tr2.

[0073] 1, the spin Hall layer 220 is made of a non-magnetic heavy metal (W, Ta, etc.) or a chalcogenide material that exhibits the spin Hall effect. The magnetoresistive element 210 is stacked on the spin Hall layer 220 and includes a free layer 212 whose magnetization is reversible, a non-magnetic layer 214 stacked on the free layer 212, and a reference layer 216 stacked on the non-magnetic layer 214 and whose magnetization is fixed in the perpendicular direction. The free layer 212, the non-magnetic layer 214, and the reference layer 216 are made of the same materials as the free layer 32, the non-magnetic layer 34, and the reference layer 36 in FIG. 16, respectively.

[0074] The first terminal 231, the second terminal 232, and the third terminal 233 are made of metal. The first terminal 231 is connected to the reference layer 216, the second terminal 232 is connected to one end of the spin Hall layer 220, and the third terminal 233 is connected to the other end of the spin Hall layer 220. The first terminal 231 is connected to a ground line 240. The ground line 240 is set to the ground voltage. The ground line 240 may also be set to a reference voltage other than the ground voltage.

[0075] The transistors Tr1 and Tr2 are, for example, N-channel metal oxide semiconductor (NMOS) transistors. The second terminal 232 is connected to the drain of the transistor Tr1, and the third terminal 233 is connected to the drain of the transistor Tr2. The gates of the transistors Tr1 and Tr2 are connected to the word line WL. The source of the transistor Tr1 is connected to the first bit line BL1, and the source of the transistor Tr2 is connected to the second bit line BL2.

[0076] When the magnetizations of the free layer 212 and the reference layer 216 are perpendicular to the surface, a write current I write A weak bias magnetic field is applied in the direction of the arrow A, the word line WL is set to a high level to turn on the transistors Tr1 and Tr2, and one of the first bit line BL1 and the second bit line BL2 is set to a high level and the other is set to a low level. This causes a write current I write The flow of the write current I generates a spin current, which reverses the magnetization of the free layer 212 by SOT, allowing data to be written. write The data to be written can be changed depending on the direction of the

[0077] When reading data stored in the magnetoresistive element 210, the word line WL is set to a high level to turn on the transistors Tr1 and Tr2, one bit line (the second bit line BL2) is set to a high level, and the other bit line (the first bit line BL1) is set to an open state. As a result, a read current I flows from the high-level second bit line BL2 to the third terminal 233, the spin Hall layer 220, the free layer 212, the nonmagnetic layer 214, the reference layer 216, the first terminal 231, and the ground line 240. read The read current I read By measuring the magnitude of the resistance, the resistance state of the magnetoresistive element 210, that is, the stored data, can be determined.

[0078] 19 shows the configuration of a magnetic memory element 300 of an MRAM (STT-MRAM) that reverses magnetization using spin transfer torque (STT). The magnetic memory element 300 includes a magnetoresistive element 310, a first terminal 321, a second terminal 322, and a transistor Tr.

[0079] The magnetoresistive element 310 includes a reference layer 316 whose magnetization is fixed in the perpendicular direction, a non-magnetic layer 314 stacked on the reference layer 316, and a free layer 312 whose magnetization is reversible and stacked on the non-magnetic layer 314. The free layer 312, the non-magnetic layer 314, and the reference layer 316 are made of the same materials as the free layer 32, the non-magnetic layer 34, and the reference layer 36 in FIG. 16, respectively.

[0080] The first terminal 321 and the second terminal 322 are made of metal. The free layer 312 is connected to the first terminal 321, and the reference layer 316 is connected to the second terminal 322. The first terminal 321 is connected to the bit line BL, and the second terminal 322 is connected to the transistor Tr.

[0081] The transistor Tr is, for example, an NMOS transistor. The drain of the transistor Tr is connected to the second terminal 322, the source is connected to a source line SL, and the gate is connected to a word line WL.

[0082] When writing data to the magnetoresistive element 310, the word line WL is set to a high level to turn on the transistor Tr, and a write current I is supplied perpendicular to the surface between the bit line BL and the source line SL. write This causes the magnetization of the free layer 312 to be reversed by STT, allowing data to be written. write The data to be written can be changed depending on the direction of the

[0083] When reading data stored in the magnetoresistive element 310, the word line WL is set to a high level to turn on the transistor Tr, and a read current I read The read current I read By measuring the magnitude of the resistance, the resistance state of the magnetoresistive element 310, that is, the stored data, can be determined.

[0084] 16, 18, and 19 show examples in which the magnetoresistive elements 30, 210, and 310 are MTJ elements, but they can also function as giant magnetoresistive (GMR) elements. In this case, the nonmagnetic layers 34, 214, and 314 are made of metal (conductor). In the third embodiment, the reference layer 216 in FIG. 18 and the reference layer 316 in FIG. 19 are made of antiferromagnetic metal, but these reference layers may be ferromagnetic layers made of a ferromagnetic material (e.g., CoFeB). In FIG. 18, a very thin ferromagnetic layer made of a ferromagnetic material (e.g., CoFeB) of 2 nm or less may be stacked on the antiferromagnetic layer serving as the free layer 212, resulting in a magnetoresistive element consisting of [antiferromagnetic layer / ferromagnetic layer] (free layer) / nonmagnetic layer / ferromagnetic layer (reference layer). This stacked structure can be turned upside down to adopt a magnetoresistive element consisting of a ferromagnetic layer (reference layer) / non-magnetic layer / [ferromagnetic layer / antiferromagnetic layer (free layer)] as shown in Figure 19. In this way, when an antiferromagnetic layer and a very thin ferromagnetic layer are magnetically coupled, high-speed control comparable to that of an antiferromagnetic material can be achieved, and the spin polarization of the ferromagnetic material can be used, which makes it possible to anticipate high-speed memory.

[0085] 18, a magnetic memory device may be configured in which a plurality of magnetic memory elements 200 are arranged in a matrix. Similarly, in FIG. 19, a magnetic memory device may be configured in which a plurality of magnetic memory elements 300 are arranged in a matrix. Furthermore, a computer system or an information processing system may be configured that includes such a magnetic memory device.

[0086] The present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the present invention. [Explanation of symbols]

[0087] 10 Substrate 12, 220 Spin Hall Layer 14, 20 antiferromagnetic layer 100, 200, 300 Magnetic memory elements 16a, 16b, 18a, 18b electrode 30, 210, 310 magnetoresistive element 32, 212, 312 free layer 34, 214, 314 non-magnetic layer 36, 216, 316 reference layer

Claims

1. A magnetic memory element comprising an antiferromagnetic layer having uniaxial strain, which is tensile strain in the in-plane direction or compressive strain in the in-plane direction or perpendicular to the plane, and which is made of an antiferromagnetic metal containing manganese, the magnetic order of which can be controlled by spin torque, and in which the magnetic order is oriented in a direction perpendicular to the direction of the tensile strain or in the direction of the compressive strain.

2. 2. The magnetic memory element according to claim 1, wherein the antiferromagnetic layer is an epitaxial film.

3. 10. The magnetic memory element of claim 1, wherein the antiferromagnetic metal exhibits an anomalous Hall effect.

4. 2. The magnetic memory element according to claim 1, wherein the antiferromagnetic metal has a spin order of cluster magnetic octopoles.

5. 5. The magnetic memory element according to claim 4, wherein the magnetic order of the cluster magnetic octopoles of the antiferromagnetic layer is oriented in a direction perpendicular to the direction of the tensile strain.

6. 5. The magnetic memory element according to claim 4, wherein the magnetic order of the cluster magnetic octupole of the antiferromagnetic layer is oriented in the direction of the compressive strain.

7. a spin Hall layer in contact with the antiferromagnetic layer, the spin Hall layer being made of a material exhibiting the spin Hall effect, and in which a spin current is generated when a write current flows in an in-plane direction; 7. The magnetic memory element according to claim 1, wherein in the antiferromagnetic layer, the magnetic order can be reversed by a spin-orbit torque generated by the spin current acting on the magnetic order.

8. a spin Hall layer made of a material that exhibits the spin Hall effect, in which a spin current is generated when a write current flows in the in-plane direction; a free layer stacked on the spin Hall layer, the free layer having a uniaxial strain of tensile strain in an in-plane direction or compressive strain in an in-plane direction or a direction perpendicular to the plane, the free layer including an antiferromagnetic metal containing manganese, the magnetic order of the antiferromagnetic metal being reversible by a spin-orbit torque generated by the spin current, the magnetic order being oriented in a direction perpendicular to the tensile strain direction or in the direction of the compressive strain; a nonmagnetic layer stacked on the free layer; a reference layer stacked on the nonmagnetic layer and made of a ferromagnetic metal or an antiferromagnetic metal containing manganese, in which the magnetic order of the ferromagnetic metal or the antiferromagnetic metal is fixed; A magnetic memory element comprising:

9. a reference layer made of a ferromagnetic metal or an antiferromagnetic metal containing manganese, in which the magnetic order of the ferromagnetic metal or the antiferromagnetic metal is fixed; a nonmagnetic layer stacked on the reference layer; and a free layer stacked on the non-magnetic layer, the free layer having a uniaxial strain of tensile strain in an in-plane direction or compressive strain in an in-plane direction or a direction perpendicular to the plane, the free layer including an antiferromagnetic metal containing manganese, the free layer being such that when a write current flows in the direction perpendicular to the plane, the magnetic order of the antiferromagnetic metal can be reversed by spin transfer torque, and the magnetic order is oriented in a direction perpendicular to the direction of the tensile strain or in the direction of the compressive strain; A magnetic memory element comprising:

10. An information processing system comprising the magnetic memory element according to any one of claims 1 to 6.

11. 7. An information processing system comprising a magnetic memory device having a plurality of magnetic memory elements according to claim 1 arranged in a matrix.

12. A method for controlling the magnetic memory element according to claim 1, comprising: A method for controlling a magnetic memory element, which controls the magnetic order of the antiferromagnetic metal by spin torque.

13. A method for controlling a magnetic memory element according to claim 8, comprising: generating the spin current by passing a write current in an in-plane direction in the spin Hall layer; reversing the magnetic order of the antiferromagnetic metal of the free layer by a spin-orbit torque induced by the spin current; A method for controlling a magnetic memory element, comprising:

14. A method for controlling a magnetic memory element according to claim 9, comprising: A method for controlling a magnetic memory element, wherein a write current is passed in a direction perpendicular to the surface of the magnetic memory element, thereby reversing the magnetic order of the antiferromagnetic metal of the free layer by spin transfer torque.

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