Spin device and magnetization reversal measuring method

Abstract

To easily determine the magnetization reversal of a spin-orbit material.SOLUTION: A spinning device first includes a laminated structure 103 including an Fe single crystal layer 101 and a spin orbital layer 102 formed on the Fe single crystal layer 101. The Fe single crystal layer 101 has a main surface that is a (100) plane. The Fe single crystal layer 101 can be formed on a substrate 111 made of a single crystal of MgAl2O4, for example. This spinning device also includes: a high-frequency generator 104 that applies a high-frequency current to the laminated structure 103; a magnetic field application mechanism 105 that applies a magnetic field (external magnetic field) to the laminated structure 103; and a voltmeter 106 that measures a change in DC voltage generated in the laminated structure 103.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a spinning apparatus and a method for measuring magnetization reversal. [Background technology]

[0002] In recent years, magnetoresistive random access memory (MRAM), which has been attracting attention as a non-volatile memory, has been actively developed and semiconductor manufacturers are now in mass production. As a result, it has been estimated that the market value of MRAM will reach several hundred billion yen by 2030 (Non-Patent Document 1). Against this background, active research has been conducted on spin currents that can operate MRAM, a killer device in the electronics industry, with high efficiency, and it has been demonstrated that magnetization reversal, which corresponds to the operating principle of MRAM, can actually be induced (Non-Patent Document 2: L. Liu et al., Science 336, 555 (2012)].

[0003] To demonstrate this spin-current induced magnetization reversal, a two-layer structure consisting of a spin orbital material that generates a spin current and a magnetic material with perpendicular magnetization is generally used, but the formation of perpendicular magnetization depends on the compatibility with the upper and lower layers that sandwich the magnetic layer, so the spin orbital materials that can be used are limited. Therefore, in order to verify whether the spin current generated by the new spin orbital material is useful for magnetization reversal, it is an urgent task to develop an electrical detection method using a magnetic material with magnetic anisotropy that is not dependent on compatibility with the spin orbital material. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] "Magneto Resistive RAM (MRAM) Market (By Product: Toggle Magneto Resistive RAM and Second-Generation Magneto Resistive RAM; By Application; By Geography) Global Scenario, Market Size, Outlook, Trend and Forecast, 2015-2024", Kenneth Research, [Retrieved July 19, 2023], (https: / / www.kennethresearch.com / report-details / magneto-resistive-ram-mram-market / 10325521). [Non-Patent Document 2] L. Liu et al., "Spin-Torque Switching with the Giant Spin Hall Effect of Tantalum", SCIENCE, vol. 336, pp. 555-555, 2012. [Non-Patent Document 3] Y. Takahashi et al., "Spin-orbit torque-induced switching of in-plane magnetized elliptic nanodot arrays with various easy-axis directions measured by differential planar Hall resistance", Applied Physics Letters, vol. 114, 012410, 2019. Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, a plane-perpendicular magnetization film with perpendicular magnetic anisotropy is used in the spin-current induced magnetization reversal by the technique of Non-Patent Document 2. In order to form plane-perpendicular magnetization, the combination of a buffer layer and a capping layer adjacent to a magnetic material is limited, and this magnetization reversal could only be demonstrated in a limited system.

[0006] In light of this background, there have been some attempts to use in-plane magnetization to reverse magnetization, but it is not easy to electrically detect in-plane magnetization. First, in the case of in-plane magnetization, it is usually not possible to provide magnetic anisotropy within the film plane, so it is not possible to define a binary state that is characteristic of magnetization reversal. Therefore, in order to provide magnetic anisotropy, it is necessary to process the magnetic material into a minute elliptical shape using electron beam exposure technology, thereby providing shape magnetic anisotropy (Non-Patent Document 3). With this technology, versatility is lost at the element fabrication stage.

[0007] In addition, even if an elliptical magnetic element is fabricated, it is difficult to electrically detect in-plane magnetization with DC. In the case of perpendicular magnetization, magnetization reversal can be easily detected by observing the anomalous Hall effect of the magnetic material, but in the case of in-plane magnetization, even if the planar Hall effect is used, the signal output upon reversal is the same, making it difficult to determine reversal.

[0008] To overcome this difficulty, a method was proposed in which an external magnetic field is applied after magnetization reversal to detect the magnetization direction, and the magnetization direction is detected by measuring the differential planar Hall voltage (Non-Patent Document 3). However, this method has the drawback of complicating the measurement process.

[0009] As described above, conventional techniques have had problems such as compatibility issues with spin orbital materials, the difficulty of forming elements for measuring magnetization reversal, and complicated measurement processes, making it difficult to determine the magnetization reversal of spin orbital materials.

[0010] The present invention has been made to solve the above problems, and has an object to make it possible to more easily determine the magnetization reversal of a spin-orbit material. [Means for solving the problem]

[0011] The spin device of the present invention includes a laminated structure composed of an Fe single crystal layer whose main surface is a (100) plane and a spin orbital layer made of a spin orbital material formed on the Fe single crystal layer, a high-frequency generator that applies a high-frequency current to the laminated structure, a magnetic field application mechanism that applies a magnetic field to the laminated structure, and a voltmeter that measures changes in DC voltage generated in the laminated structure.

[0012] In addition, the magnetization reversal measurement method of the present invention includes a current application step of applying a high-frequency current to a layered structure including an Fe single crystal layer whose main surface is a (100) plane and a spin orbital layer made of a spin orbital material formed on the Fe single crystal layer, a magnetic field application step of applying a magnetic field to the layered structure, and a measurement step of measuring a change in DC voltage generated in the layered structure to which the high-frequency current is applied. Effect of the Invention

[0013] As described above, according to the present invention, a spin orbital layer made of a spin orbital material is laminated on an Fe single crystal layer having a (100) major surface, so that the magnetization reversal of the spin orbital material can be determined more easily. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing the configuration of a spinning apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a flowchart illustrating a magnetization reversal measuring method according to an embodiment of the present invention. [Diagram 3] FIG. 3 shows diffraction images of the surfaces of the Fe single crystal layer 101(a) and the spin orbital layer 102(b) observed by reflection high-energy electron diffraction under high vacuum while each layer was being formed. [Figure 4] FIG. 4 is a characteristic diagram showing the results of observation of the Fe single crystal layer 101 and the spin orbital layer 102 by X-ray diffraction. [Diagram 5] FIG. 5 is a diagram showing a more detailed configuration of the spin device. [Figure 6] FIG. 6 is an explanatory diagram for explaining the relationship between magnetization easy axes 151a and 151b in an Fe single crystal, a current direction 131, and an application direction 132 of an external magnetic field. [Figure 7] FIG. 7 is a characteristic diagram showing the measurement results of the rectified voltage measured by the spinning apparatus according to the embodiment. [Figure 8] FIG. 8 is an explanatory diagram showing the relationship between the state of the spin current in the spin orbital layer 102 and the state of magnetization of the Fe single crystal layer 101. As shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] A spin device according to an embodiment of the present invention will be described below with reference to FIG. 1. This spin device includes a layered structure 103 including an Fe single crystal layer 101 and a spin orbital layer 102 formed on the Fe single crystal layer 101. The Fe single crystal layer 101 has a main surface that is a (100) plane. The Fe single crystal layer 101 is made of, for example, MgAl 2 O 4 The semiconductor device can be formed on a substrate 111 made of a single crystal.

[0016] This spinning device also includes a high-frequency generator 104 that applies a high-frequency current to the laminated structure 103, a magnetic field application mechanism 105 that applies a magnetic field (external magnetic field) to the laminated structure 103, and a voltmeter 106 that measures changes in DC voltage generated in the laminated structure 103.

[0017] The magnetic field application mechanism 105 applies a magnetic field in the direction of the easy axis of magnetization in a plane parallel to the main surface of the Fe single crystal layer 101. The direction of the magnetic field application can be at a certain angle to the easy axis of magnetization rather than being completely parallel to the easy axis of magnetization. It is important that the direction of the magnetic field application is at a significantly different angle from the hard axis of magnetization.

[0018] The voltmeter 106 measures a change in a DC voltage flowing in a direction perpendicular to the direction of application of the magnetic field in a plane parallel to the main surface of the Fe single crystal layer 101. The spinning apparatus may also include a determination circuit 107 that determines magnetization reversal of the stacked structure 103 based on the change in the DC voltage measured by the voltmeter 106.

[0019] Application of high-frequency current generates a heat flow perpendicular to the plane (layering direction) in the layered structure 103, which is made up of materials with different electrical conductivities. This heat flow generates a rectified voltage perpendicular to the magnetization direction due to the anomalous Nernst effect, depending on the magnetization direction controlled by an external magnetic field. Due to this relationship, the in-plane magnetization direction of the plane of the layered structure 103 can be electrically measured as a change in DC voltage generated in the layered structure 103, and the state of magnetization reversal can be determined.

[0020] Next, a magnetization reversal measuring method according to an embodiment of the present invention will be described with reference to Fig. 2. First, in a first step S101, a high frequency current is applied by using a high frequency generator 104 to a laminated structure 103 composed of an Fe single crystal layer 101 having a (100) plane as its main surface and a spin orbital layer 102 made of a spin orbital material formed on the Fe single crystal layer 101.

[0021] Next, in a second step S102, a magnetic field is applied to the laminated structure 103 using a magnetic field application mechanism 105. In the second step S102, a magnetic field is applied in the direction of the easy axis of magnetization in a plane parallel to the main surface of the Fe single crystal layer 101. The direction of the magnetic field application can be at a certain angle to the easy axis of magnetization rather than being completely parallel to the easy axis of magnetization. The direction of the magnetic field application is at an angle significantly different from the hard axis of magnetization.

[0022] Next, in a third step S103, a change in DC voltage occurring in the multilayer structure 103 to which the high-frequency current is applied is measured using a voltmeter 106. In the third step S103, a change in the DC voltage flowing in a plane parallel to the main surface of the Fe single crystal layer 101 and in a direction perpendicular to the direction in which the magnetic field is applied is measured.

[0023] Next, in a fourth step S104, the magnetization reversal of the laminated structure 103 is determined based on the change in the measured DC voltage.

[0024] This will be explained in more detail below. First, the fabrication of the laminated structure 103 will be explained.

[0025] MgAl 2 O 4 An Fe single crystal layer 101 having a (100) plane as its main surface is formed on a substrate 111 made of a single crystal of MgAl. 2 O 4 is a crystalline material that has high lattice matching with Fe. For example, an Fe single crystal layer 101 can be formed on a substrate 111 by high-frequency magnetron sputtering. Base vacuum: 10×10 -6 Under the conditions of: 1 Pa, operating vacuum: 0.3 Pa, Ar flow rate: 10 sccm, high frequency power: 300 W, target-substrate distance: 100 mm, and substrate temperature: 600° C., a 5 nm thick Fe single crystal layer 101 can be formed on the substrate 111.

[0026] Next, a spin orbital layer 102 made of a spin orbital material to be measured is formed on the Fe single crystal layer 101. The spin orbital material can be, for example, platinum (Pt). For example, the spin orbital layer 102 made of Pt can be formed on the Fe single crystal layer 101 by radio frequency magnetron sputtering. The spin orbital layer 102 can be formed to a thickness of 5 nm on the Fe single crystal layer 101 under the conditions of operating vacuum: 0.5 Pa, Ar flow rate: 15 sccm, radio frequency power: 50 W, target-substrate distance: 100 mm, and substrate temperature: 300°C.

[0027] The surfaces of the fabricated Fe single crystal layer 101 and spin orbital layer 102 were observed by reflection high energy electron diffraction (RHEED) under high vacuum while each layer was being formed. The RHEED observation results are shown in Figure 3. Figure 3(a) shows the RHEED observation results of the surface of the Fe single crystal layer 101. Figure 3(b) shows the RHEED observation results of the surface of the spin orbital layer 102. Both show clear streak patterns, suggesting epitaxial growth.

[0028] Next, the results of X-ray diffraction observation of the Fe single crystal layer 101 and the spin orbital layer 102 after each layer was formed are shown in Figure 4. As shown in Figure 4, diffraction patterns derived from Fe(100) and Pt(111) were obtained, indicating that epitaxial growth was successful. In Figure 4, "Fe(200)" is the diffraction pattern indicating the Fe(100) surface.

[0029] Next, a more detailed configuration of the spin device will be described with reference to Fig. 5. A laminated structure 103 consisting of an Fe single crystal layer 101 and a spin orbital layer 102 is microfabricated into a fine wire structure by Ar ion milling using a mask pattern created by optical exposure. The wire structure is processed so that the axial direction is the

[0100] direction (direction of easy axis of magnetic field) of the Fe single crystal (extending in the direction of easy axis of magnetic field). The crystal direction of the Fe single crystal can be determined by measuring the magnetic field.

[0030] One end of the thin-line laminated structure 103 is connected to the SIGNAL terminal of the measuring circuit 121, and the other end is connected to the GND wiring. A high-frequency current with a frequency of 20 GHz and a power of 6 dBm is applied from the high-frequency generator 104 via the SIGNAL terminal and the bias tee 122 to one end of the thin-line laminated structure 103. In this state, an external magnetic field is applied to the laminated structure 103. In order to induce reversal of the in-plane magnetization, the externally applied magnetic field is swept in the range of, for example, ±290 mT. With the external magnetic field applied in this manner, the DC voltage in the laminated structure 103 was measured by the voltmeter 106.

[0031] 6, the current direction 131 can be the easy axis 151a, and the application direction 132 of the external magnetic field can be the easy axis 151b, relative to the easy axis 151a and the hard axis 152 of the Fe single crystal. However, for the reasons described below, the application direction 132 of the external magnetic field can be angled at a predetermined angle φ from the easy axis 151b. H The position is shifted.

[0032] Application of high-frequency current generates a heat flow perpendicular to the surface in laminated structure 103 with different electrical conductivities. This heat flow generates a rectified voltage in laminated structure 103 due to the anomalous Nernst effect according to the magnetization direction of the external magnetic field. Here, when the magnetization direction is parallel to the easy axis of magnetization, the direction in which the rectified voltage is generated is the width direction of laminated structure 103 with a thin-wire structure. The rectified voltage generated in this way in the width direction cannot be measured by measurement circuit 121 shown in FIG. 5, which attempts to detect the rectified voltage in the axial direction of laminated structure 103 with a thin-wire structure. Therefore, the direction of application of the external magnetic field is set at a predetermined angle φ from the axial direction (direction of the easy axis of magnetization) of laminated structure 103 with a thin-wire structure so that the rectified voltage can be measured by measurement circuit 121. H It is desirable to shift the

[0033] The measurement results of the rectified voltage measured by the above method are shown in Figure 7. As shown in Figure 7, magnetization reversal with a coercive force of approximately 50 mT was observed. In this way, by using a layered structure in which a spin orbital layer made of a spin orbital material is formed on an Fe single crystal layer with a (100) main surface, it is possible to demonstrate spin-current induced magnetization reversal for any spin orbital material.

[0034] According to the above-mentioned embodiment, the state of magnetization reversal of the adjacent magnetic layer (Fe single crystal layer) can be determined more easily by the spin current generated by a wide variety of spin orbital materials. In the conventional technology, there were problems in obtaining perpendicular magnetic anisotropy and electrically detecting in-plane magnetization, and the material system was limited. However, by combining the in-plane crystalline magnetic anisotropy of the Fe single crystal layer whose main surface is the (100) plane and the high-frequency thermomagnetic effect, it becomes possible to determine the magnetization reversal more generally and easily. For example, as shown in FIG. 8, the state of the spin current in the spin orbital layer 102 reverses the magnetization state of the Fe single crystal layer 101 (0→1), and this state can be determined.

[0035] As described above, according to the present invention, a spin orbital layer made of a spin orbital material is laminated on an Fe single crystal layer having a (100) major surface, making it easier to determine the magnetization reversal of the spin orbital material.

[0036] It should be noted that the present invention is not limited to the above-described embodiments, and it is apparent that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention. [Explanation of symbols]

[0037] 101: Fe single crystal layer, 102: spin-orbital layer, 103: laminated structure, 104: high-frequency generator, 105: magnetic field application mechanism, 106: voltmeter, 107: determination circuit.

Claims

1. A laminated structure including an Fe single crystal layer having a (100) plane as a main surface, and a spin orbital layer made of a spin orbital material formed on the Fe single crystal layer; a high frequency generator for applying a high frequency current to the laminated structure; a magnetic field application mechanism that applies a magnetic field to the laminated structure; a voltmeter for measuring a change in DC voltage occurring in the laminate structure; A spin device comprising:

2. 2. The spinning apparatus of claim 1, The spin apparatus further includes a determination circuit for determining magnetization reversal of the laminated structure based on a change in the DC voltage measured by the voltmeter.

3. 3. The spinning device according to claim 1, The magnetic field application mechanism is a spinning device that applies a magnetic field in a plane parallel to a main surface of the Fe single crystal layer in the direction of an easy axis of magnetization.

4. 3. The spinning device according to claim 1, The voltmeter is a spinning apparatus that measures the change in the DC voltage flowing in a plane parallel to a main surface of the Fe single crystal layer and in a direction perpendicular to the direction in which the magnetic field is applied.

5. a current application step of applying a high frequency current to a laminate structure including an Fe single crystal layer having a (100) plane as a main surface and a spin orbital layer made of a spin orbital material formed on the Fe single crystal layer; a magnetic field application step of applying a magnetic field to the laminated structure; A measuring step of measuring a change in DC voltage occurring in the laminated structure to which a high frequency current is applied; A magnetization reversal measuring method comprising:

6. 6. The magnetization reversal measuring method according to claim 5, The magnetization reversal measuring method further comprises a determining step of determining magnetization reversal of the laminated structure based on a change in the measured DC voltage.

7. 7. The magnetization reversal measuring method according to claim 5, In the magnetic field application step, a magnetic field is applied in a plane parallel to a main surface of the Fe single crystal layer in a direction of an easy axis of magnetization.

8. 7. The magnetization reversal measuring method according to claim 5, The measuring step measures a change in the DC voltage flowing in a direction perpendicular to a direction in which a magnetic field is applied within a plane parallel to a main surface of the Fe single crystal layer.

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