Heavy metal / ferromagnetic heterojunction spin-orbit torque efficiency regulation and control method

Abstract

The invention provides a heavy metal / ferromagnetic heterojunction spin orbit torque efficiency regulation and control method, and relates to the field of spin electronic devices, and the method comprises the steps: introducing a vanadium-based oxide with an electronic phase change characteristic at a heavy metal side, and preparing a vanadium-based oxide layer / heavy metal layer / ferromagnetic layer multilayer film heterojunction; current is applied to the vanadium-based oxide layer, orbital flow perpendicular to the current direction is generated based on the orbital Hall effect, the orbital flow flows into the heavy metal layer through interlayer coupling and is converted into spin current perpendicular to the film surface, the spin current and spin current generated by the spin Hall effect of the heavy metal layer are overlaid and then injected into the ferromagnetic layer, and spin orbital torque is enhanced; the spin-orbit torque efficiency is improved; the electronic phase change of the vanadium-based oxide layer is triggered through external excitation, the orbital flow density is dynamically adjusted, and the spin-orbit torque efficiency is regulated and controlled. According to the invention, the dynamic regulation and control of the spin-orbit torque efficiency can be realized by introducing the phase-change material without changing the component or structure of the heterojunction material.

Description

Technical Field

[0001] The present invention relates to the technical field of spintronic devices, and in particular to a method for regulating the efficiency of a heavy metal / ferromagnetic heterojunction spin-orbit torque. Background Art

[0002] Spin-orbit torque (SOT) is an emerging and highly efficient tool for manipulating the magnetization state of magnetic materials, with significant application prospects in nonvolatile magnetic storage and low-power logic operations. SOT manipulation is typically achieved using non-magnetic / ferromagnetic multilayer systems. A non-magnetic layer (NM) with strong spin-orbit coupling (SOC) can generate a pure spin current perpendicular to the current direction when driven by an electric current, due to factors such as the spin Hall effect in the layer or the Rashba-Edelstein effect at the interface. This spin current is then transferred to the adjacent ferromagnetic layer (FM). The spin-orbit torque generated by this spin current effectively flips the magnetic moment in the FM, enabling data writing. Therefore, improving the efficiency of SOT conversion is key to optimizing SOT device performance.

[0003] Currently, research on improving spin-orbit torque conversion efficiency focuses primarily on exploring novel non-magnetic materials, including traditional heavy metals (such as Pt, Ta, and W), metal oxides with strong spin-orbit coupling (such as IrO2 and SrIrO3), topological insulators (such as Bi2Se3, Bi2Te3, and BiSb), and van der Waals transition metal dichalcogenides (such as MoS2, WTe2, and PtTe2). Furthermore, recent studies have shown that even light metals without strong spin-orbit coupling (such as Zr, Cr, and Ru) can enhance the SOT efficiency of heavy metal / ferromagnetic heterojunctions through the orbital Hall effect (OHE) and orbital Rashba–Edelstein effect (OREE), further expanding the range of materials available. However, the SOT efficiency of these materials depends primarily on their inherent physical properties. Once the material system is determined, the scope for efficiency optimization is limited. Existing technologies typically improve performance by adjusting material composition, optimizing interface engineering, or introducing multilayer structures. However, these approaches often involve complex processes and irreversible device design, making it difficult to achieve SOT efficiency control. In addition, complex multilayer structures or interface modifications may introduce additional scattering effects and reduce device reliability. Summary of the Invention

[0004] In view of this, an embodiment of the present invention provides a method for regulating the spin-orbit torque efficiency of a heavy metal / ferromagnetic heterojunction to solve the problems that the existing spin-orbit torque efficiency regulation technology relies on fixed material properties, is difficult to regulate, has complex and irreversible optimization methods, and lacks flexible external regulation dimensions.

[0005] In one aspect, the present invention provides a method for regulating the spin-orbit torque efficiency of a heavy metal / ferromagnetic heterojunction. The method is applied to a pre-prepared multilayer heterojunction, wherein the multilayer heterojunction comprises, from bottom to top, a vanadium-based oxide layer, a heavy metal layer, and a ferromagnetic layer, wherein the heavy metal layer and the ferromagnetic layer constitute a heavy metal / ferromagnetic heterojunction. The method comprises: Applying a current to the vanadium-based oxide layer, the vanadium-based oxide layer generates an orbital current perpendicular to the current direction based on the orbital Hall effect, and the orbital current flows into the heavy metal layer through interlayer coupling; the heavy metal layer converts the orbital current into a spin current perpendicular to the film surface, and superimposes the spin current perpendicular to the film surface with the spin current generated by the heavy metal layer based on the spin Hall effect, and the spin currents flow into the ferromagnetic layer together as an effective spin current, thereby generating a spin-orbit torque; By triggering the electronic phase transition state of the vanadium-based oxide layer through external excitation, the resistivity of the vanadium-based oxide layer changes, and then the density of the orbital flow, the density of the effective spin current flowing into the ferromagnetic layer, and the size of the spin-orbit torque are sequentially regulated to achieve the regulation of the spin-orbit torque efficiency of the heavy metal / ferromagnetic heterojunction.

[0006] In some embodiments of the present invention, the method further comprises preparing the multilayer film heterojunction, and preparing the multilayer film heterojunction comprises: Depositing a vanadium-based oxide on the pretreated substrate using a first predetermined deposition method to form a vanadium-based oxide thin film as the vanadium-based oxide layer; wherein the phase transition temperature of the vanadium-based oxide layer is controlled within a predetermined range based on deposition parameters and deposition process; Depositing a heavy metal material on the surface of the vanadium-based oxide film using a second predetermined deposition method to form a heavy metal film as the heavy metal layer; Depositing a ferromagnetic material on the surface of the heavy metal film using the second preset deposition method to form a ferromagnetic film as the ferromagnetic layer; Among them, the first preset deposition method includes a pulsed laser deposition method, a magnetron sputtering method and an atomic layer deposition method, and the second preset deposition method includes a magnetron sputtering method, a molecular beam epitaxy method and an electron beam evaporation method.

[0007] In some embodiments of the present invention, the pulsed laser deposition method is used to deposit the vanadium-based oxide thin film, including: The substrate is placed in a pulsed laser deposition system chamber, the chamber is evacuated to a vacuum state, and the substrate is heated to 500-550° C. The substrate is made of aluminum oxide single crystal; Oxygen is introduced into the chamber and the oxygen pressure is maintained at 0.8-1.5 Pa; a pulsed laser is used to strike a vanadium-based oxide target to form the vanadium-based oxide film, and the thickness of the vanadium-based oxide film is controlled by adjusting the number of laser pulses; wherein the repetition frequency of the pulsed laser is 1-5 Hz, the pulse energy is 400-550 mJ, and the distance between the vanadium-based oxide target and the substrate is less than 5 cm.

[0008] In some embodiments of the present invention, forming the heavy metal film and the ferromagnetic film by the magnetron sputtering method includes: placing the substrate on which the vanadium-based oxide thin film is deposited in a magnetron sputtering system chamber, and evacuating the chamber to a vacuum state; Argon gas is introduced into the chamber and the argon pressure is maintained at 0.4-1.2 Pa; the heavy metal film and the ferromagnetic film are sequentially deposited on the surface of the vanadium-based oxide film by DC sputtering; wherein the deposition power is 10-40 W and the deposition temperature is 20-30° C.

[0009] In some embodiments of the present invention, the vanadium-based oxide layer uses vanadium dioxide or vanadium-based oxide doped with other elements to have electronic phase change characteristics and orbital Hall effect; wherein the other elements include tungsten, titanium, molybdenum, niobium, zirconium, ruthenium and chromium.

[0010] In some embodiments of the present invention, materials used for the heavy metal layer include platinum, palladium, iridium, tantalum and tungsten.

[0011] In some embodiments of the present invention, the ferromagnetic layer adopts a ferromagnetic metal material with in-plane magnetic anisotropy or a ferromagnetic metal material with perpendicular magnetic anisotropy, wherein the cobalt and ferromagnetic metal materials with in-plane magnetic anisotropy include cobalt iron boron, cobalt iron and nickel iron, and the ferromagnetic metal materials with perpendicular magnetic anisotropy include cobalt / nickel multilayer films, cobalt / platinum multilayer films, cobalt iron boron / magnesium oxide heterojunctions, cobalt platinum alloys, cobalt palladium alloys, iron platinum alloys, and two-dimensional van der Waals ferromagnets.

[0012] In some embodiments of the present invention, the thickness of the metal layer is 2-10 nm, and the thickness of the ferromagnetic layer is 1-10 nm.

[0013] In some embodiments of the present invention, the external stimulus includes changing the ambient temperature, applying an electric field, irradiating light, and applying stress.

[0014] In some embodiments of the present invention, the method further comprises determining the spin-orbit torque efficiency by harmonic measurement, comprising: Applying an alternating current excitation to the multilayer film heterojunction and applying an external magnetic field with a variable angle to the alternating current in a plane parallel to the film surface; measuring the second harmonic resistance in a direction perpendicular to the alternating current; By fitting the functional relationship between the second harmonic resistance and the variable angle of the external magnetic field, the damping-type torque component and the field-type torque component are separated, and based on the damping-type torque component and the field-type torque component, the damping-type torque efficiency and the field-type torque efficiency are calculated respectively; wherein, the damping-type torque efficiency and the field-type torque efficiency jointly characterize the spin-orbit torque efficiency of the heavy metal / ferromagnetic heterojunction.

[0015] The present invention provides a method for regulating the spin-orbit torque efficiency of a heavy metal / ferromagnetic heterojunction, comprising: introducing a vanadium-based oxide with electronic phase transition characteristics on the heavy metal side to prepare a vanadium-based oxide layer / heavy metal layer / ferromagnetic layer multilayer heterojunction; applying a current to the vanadium-based oxide layer to generate an orbital current perpendicular to the current direction based on the orbital Hall effect, which flows into the heavy metal layer through interlayer coupling and is converted into a spin current perpendicular to the film surface. The spin current is superimposed with the spin current generated by the spin Hall effect of the heavy metal layer and then injected into the ferromagnetic layer, thereby enhancing the spin-orbit torque and improving the spin-orbit torque efficiency; and triggering the electronic phase transition of the vanadium-based oxide layer through external excitation to dynamically regulate the orbital current density and achieve regulation of the spin-orbit torque efficiency. The present invention does not require changing the heavy metal / ferromagnetic heterojunction material composition or structure, nor does it require optimizing the heavy metal / ferromagnetic heterojunction interface. Dynamic regulation of the spin-orbit torque efficiency can be achieved simply by introducing a phase change material. The method has a simple structure and is easy to implement, and can be applied to the design of new magnetic storage and computing devices.

[0016] Additional advantages, objects, and features of the present invention will be set forth in part in the following description and will become apparent to those skilled in the art upon examination of the following or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained by the structures particularly pointed out in the description and drawings.

[0017] Those skilled in the art will understand that the purposes and advantages that can be achieved by the present invention are not limited to the above specific descriptions, and the above and other purposes that can be achieved by the present invention will be more clearly understood based on the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings described herein are used to provide a further understanding of the present invention, constitute a part of this application, and do not constitute a limitation of the present invention. In the drawings: Figure 1 Schematic diagram of the structure of a multilayer heterojunction in one embodiment of the present invention.

[0019] Figure 2Schematic diagram of the principle of a method for controlling the spin-orbit torque efficiency of a heavy metal / ferromagnetic heterojunction according to one embodiment of the present invention.

[0020] Figure 3 FIG. 5 is a RT curve diagram of a VO2 thin film in one embodiment of the present invention.

[0021] Figure 4 Schematic diagram of harmonic measurement of the spin-orbit torque efficiency of a heavy metal / ferromagnetic heterojunction according to one embodiment of the present invention.

[0022] Figure 5 1 and 2 are harmonic test results and fitting curves before and after phase change temperature in one embodiment of the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and the accompanying drawings. Here, the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0024] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, the accompanying drawings only show structures and / or processing steps closely related to the solutions according to the present invention, while other details that are not closely related to the present invention are omitted.

[0025] It should be emphasized that the term "include / comprises" when used herein refers to the existence of features, elements, steps or components, but does not exclude the existence or addition of one or more other features, elements, steps or components.

[0026] It should also be noted that, unless otherwise specified, the term "connection" herein may refer not only to a direct connection but also to an indirect connection involving an intermediate.

[0027] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the accompanying drawings, the same reference numerals represent the same or similar components, or the same or similar steps.

[0028] It should be emphasized here that the step marks mentioned below do not limit the order of the steps, but it should be understood that the steps can be executed in the order mentioned in the embodiment, or in a different order from the embodiment, or several steps can be executed simultaneously.

[0029] In order to solve the problem that the existing spin-orbit torque efficiency control technology relies on fixed material properties, is difficult to control, has complex and irreversible optimization methods, and lacks flexible external control dimensions, the present invention provides a heavy metal / ferromagnetic heterojunction spin-orbit torque efficiency control method, which introduces a vanadium-based metal oxide with electronic phase change characteristics on the heavy metal side of the heavy metal / ferromagnetic heterojunction, and utilizes the orbital flow generated by the vanadium-based metal oxide to enhance the net spin flow of the heavy metal layer to improve the spin-orbit torque efficiency of the heavy metal / ferromagnetic heterojunction. At the same time, the spin-orbit torque efficiency of the heavy metal / ferromagnetic heterojunction is controlled by utilizing the sudden change in the size of the orbital flow generated before and after the phase change of the vanadium-based metal oxide. Specifically, the method includes: When current is applied to the vanadium-based oxide layer, it generates an orbital current perpendicular to the current direction due to the orbital Hall effect. This current flows into the heavy metal layer through interlayer coupling. The heavy metal layer converts the orbital current into a spin current perpendicular to the film surface. This spin current is then superimposed with the spin current generated by the heavy metal layer due to the spin Hall effect. Together, these two currents flow into the ferromagnetic layer as an effective spin current, generating a spin-orbit torque.

[0030] By triggering the electronic phase transition state of the vanadium-based oxide layer through external excitation, the resistivity of the vanadium-based oxide layer changes, and then the density of the orbital flow, the density of the effective spin current flowing into the ferromagnetic layer, and the size of the spin-orbit torque are regulated in turn, thereby realizing the regulation of the spin-orbit torque efficiency of the heavy metal / ferromagnetic heterojunction.

[0031] To facilitate understanding, the multilayer film heterojunction is first further explained.

[0032] In some embodiments, the vanadium-based oxide layer uses vanadium dioxide (VO2) or vanadium-based oxides doped with other elements to achieve electronic phase transition properties and the orbital Hall effect. Other elements include tungsten (W), titanium (Ti), molybdenum (Mo), niobium (Nb), zirconium (Zr), ruthenium (Ru), and chromium (Cr). It should be noted that when describing materials, the chemical formula of the corresponding material is in parentheses, and the same applies to the following text.

[0033] In some embodiments, the heavy metal layer is made of platinum (Pt), palladium (Pd), iridium (Ir), tantalum (Ta), tungsten (W), etc., so as to have a stronger spin-orbit coupling effect.

[0034] In some embodiments, the ferromagnetic layer is made of a ferromagnetic metal material with in-plane magnetic anisotropy or a ferromagnetic metal material with perpendicular magnetic anisotropy. Among them, the ferromagnetic metal material with in-plane magnetic anisotropy includes cobalt (Co), cobalt iron boron (CoFeB), cobalt iron (CoFe), nickel iron (NiFe), etc. The ferromagnetic metal material with perpendicular magnetic anisotropy includes cobalt platinum multilayer film ([Co / Pt] n )、Cobalt / Nickel Multilayer ([Co / Ni] n), cobalt iron boron / magnesium oxide heterojunction (CoFeB / MogO), cobalt platinum alloy (CoPt), cobalt palladium alloy (CoPd), iron platinum alloy (FePt), two-dimensional van der Waals ferromagnet (Fe3GaTe2 or Fe3GeTe2), etc.

[0035] In some embodiments, the preparation of a multilayer heterojunction comprises the following steps: A vanadium-based oxide is deposited on a substrate after pretreatment (e.g., cleaning) using a first predetermined deposition method to form a vanadium-based oxide thin film as a vanadium-based oxide layer. The phase transition temperature of the vanadium-based oxide layer is controlled within a predetermined range based on deposition parameters and the deposition process. For example, the phase transition temperature of the vanadium-based oxide layer is controlled to be near room temperature by regulating the oxygen pressure, stress effects, element doping, and deposition process during deposition, ensuring that the device can achieve phase transition control without additional temperature control conditions. Room temperature is typically defined as 25°C.

[0036] A heavy metal material is deposited on the surface of the vanadium-based oxide film using a second preset deposition method to form a heavy metal film as a heavy metal layer.

[0037] A ferromagnetic material is deposited on the surface of the heavy metal film using a second preset deposition method to form a ferromagnetic film as a ferromagnetic layer.

[0038] Thus, a multilayer heterojunction is prepared, which includes a vanadium-based oxide layer, a heavy metal layer and a ferromagnetic layer from bottom to top.

[0039] In some embodiments, the thickness of the metal layer is 2-10 nm, and the thickness of the ferromagnetic layer is 1-10 nm.

[0040] In some embodiments, the first preset deposition method includes at least a pulsed laser deposition method, a magnetron sputtering method, and an atomic layer deposition method, and the second preset deposition method includes at least a magnetron sputtering method, a molecular beam epitaxy method, and an electron beam evaporation method.

[0041] The following takes the preparation of VO2 / Pt / Co / Pt multilayer heterojunction by the first preset deposition method being a pulsed laser deposition method and the second preset deposition method being a magnetron sputtering method as an example for further explanation, and the preparation steps include: A cleaned (0001) oriented aluminum oxide (Al2O3) single crystal substrate is placed in the pulsed laser deposition system chamber. After the chamber is evacuated to a vacuum state, the substrate is heated to 500-550°C.

[0042] Oxygen was introduced into the chamber and maintained at a pressure of 0.8-1.5 Pa. A pulsed laser was used to strike a VO2 target, forming a vanadium-based oxide film. The thickness of the film was controlled by adjusting the number of laser pulses. During deposition, the pulsed laser had a repetition rate of 1-5 Hz and a pulse energy of 400-550 mJ. The distance between the VO2 target and substrate was less than 5 cm.

[0043] After the pulse laser strike is completed, wait for the pulse laser deposition system cavity to cool naturally to room temperature, take out the substrate with the vanadium-based oxide film deposited on it and transfer it to the magnetron sputtering system cavity, and then evacuate the cavity to a vacuum state.

[0044] Argon gas is introduced into the chamber and maintained at a pressure of 0.4-1.2 Pa. A Pt / Co / Pt heterojunction thin film is deposited on the surface of the vanadium-based oxide film using DC sputtering. The deposition power is 10-40 W, and the deposition temperature is room temperature, e.g., 20-30°C.

[0045] like Figure 1 As shown in the figure, a VO2 / Pt / Co / Pt multilayer heterojunction is finally obtained. Among them, the vanadium-based oxide film is made of VO2 material with a thickness of 10nm, the heavy metal film is made of Pt material with a thickness of 3nm, and the ferromagnetic film is made of Co / Pt material with thicknesses of 1nm and 1nm respectively.

[0046] like Figure 2 The figure shows the principle diagram of the method for regulating the spin-orbit torque efficiency of the heavy metal / ferromagnetic heterojunction, which includes, from bottom to top, a vanadium-based oxide layer (VO2), a heavy metal layer (HM), and a ferromagnetic layer (FM).

[0047] In step S101, the vanadium-based oxide layer is Figure 2 The current is applied in the x-axis direction as shown, and based on its orbital Hall effect, an orbital current with an orbital polarization vector in the y-axis direction (perpendicular to the applied current) is generated, and flows into the heavy metal layer through interlayer coupling. For example, the orbital polarization vector is recorded as , the orbital flow is denoted as The orbital Hall effect refers to the phenomenon in which, when driven by an electric current, the orbital angular momentum (not spin) of electrons in a material undergoes spatial separation, resulting in a net orbital flow perpendicular to the direction of the current. The orbital polarization vector is used to describe the collective orientation of the orbital angular momentum of electrons in the orbital flow.

[0048] The heavy metal layer, based on its strong spin-orbit coupling effect, associates orbital angular momentum with spin angular momentum to convert the orbital flow into a direction perpendicular to the film surface ( Figure 2 The spin current in the z-axis direction is consistent with the direction of the spin polarization vector of the heavy metal layer. For example, the converted spin current is recorded as , the spin polarization vector is denoted as , the conversion efficiency from orbital current to spin current is recorded as .

[0049] The converted spin current is superimposed on the spin current generated by the heavy metal layer based on the spin Hall effect, and flows into the ferromagnetic layer as an effective spin current, generating a spin-orbit torque. For example, the spin current generated by the heavy metal layer based on the spin Hall effect is denoted as .

[0050] Compared to traditional heavy metal / ferromagnetic heterojunctions, the addition of a vanadium-based oxide layer generates an orbital current that superimposes with the spin current of the heavy metal layer, increasing the effective spin current flowing into the ferromagnetic layer and thereby enhancing the spin-orbit torque, ultimately improving the spin-orbit torque efficiency of the heavy metal / ferromagnetic heterojunction. The spin-orbit torque efficiency measures the ability to generate an effective spin current per unit charge flow. A higher spin-orbit torque efficiency (greater spin-orbit torque) results in faster magnetization reversals and lower energy consumption.

[0051] In step S102, the electronic phase transition state of the vanadium-based oxide layer is triggered by external excitation. The change in the band gap of the vanadium-based oxide leads to a change in resistivity, which affects the density of the generated orbital flow, thereby regulating the density of the effective spin current flowing into the ferromagnetic layer, and then regulating the size of the spin-orbit torque, thereby realizing the regulation of the spin-orbit torque efficiency of the heavy metal / ferromagnetic heterojunction.

[0052] In some embodiments, the external stimulation method includes changing the ambient temperature, applying an electric field, irradiating light, applying stress, etc.

[0053] The present invention will be further described below with reference to a specific embodiment.

[0054] Use Figure 1 The VO2 / Pt / Co / Pt multilayer film heterojunction shown in the figure has an external excitation method of changing the ambient temperature.

[0055] like Figure 3 The figure shows the RT curve of a 10nm thick VO2 film in this embodiment. At low temperatures, the VO2 film exhibits a high resistance state. As the temperature rises, the resistance drops sharply near the transition temperature, transforming into a low resistance metallic phase. The temperature jump of the VO2 film resistance is close to 10 3 Ω order of magnitude, and there is an obvious hysteresis effect. Figure 2 The illustration in the upper right corner is the first-order derivative function of resistance changing with temperature. According to the temperature corresponding to its valley value, it can be seen that the transition temperature of the VO2 thin film grown in this example is 300K (cooling) and 313K (heating).

[0056] like Figure 4As shown in FIG, it is a schematic diagram of harmonic measurement of the spin-orbit torque efficiency of the heavy metal / ferromagnetic heterojunction in this embodiment. Figure 4 As shown, an AC current is applied along the x-axis and a variable angle with the x-axis is applied in a plane parallel to the membrane surface. The external magnetic field . In the direction perpendicular to the alternating current (i.e. Figure 4 The second harmonic resistance is measured using the y-axis in the figure. When current flows through a nonmagnetic layer with strong spin-orbit coupling, a spin accumulation effect occurs at the interface between the nonmagnetic layer and the ferromagnetic layer, injecting an effective spin current into the ferromagnetic layer. This process generates two types of spin-orbit torque: a damping-like torque and a field-like torque. Therefore, by fitting the functional relationship between the second harmonic resistance and the angle of the applied magnetic field, the damping-like torque component and the field-like torque component are separated. Based on these components, the damping-like torque efficiency and the field-like torque efficiency are calculated, respectively. This yields the spin-orbit torque efficiency of the heavy metal / ferromagnetic heterojunction, characterized by both the damping-like torque efficiency and the field-like torque efficiency.

[0057] like Figure 5 As shown in FIG, the harmonic test results and fitting curves before and after the phase change temperature in this embodiment are shown. Figure 5 As shown in a, an in-plane magnetic field is applied in the x direction, and the second harmonic resistance under large field The difference is approximately zero, indicating that in the device of the present invention (i.e., VO2 / Pt / Co / Pt multilayer heterojunction), the anomalous Nernst effect (ANE) and the spin Seebeck effect (SSE) have very weak interference on the measurement results. Figure 5 As shown in b, the device of the present invention is shown in Figure 2, which shows the in-plane angle dependence of the device under the current excitation of 3 mA. Measurement results, where the black solid line is The fitting results of the components, the red solid line is The fitting results of the components.

[0058] in, Variable angle The function is shown in formula (1): ; (1) in, represents the second harmonic resistance; represents the anomalous Hall resistance; Represents a damping-type moment; Indicates the intensity of the external magnetic field; represents the effective magnetic anisotropy field; The thermoelectric term represents the contribution of the anomalous Nernst effect and the spin Seebeck effect; represents the angle between the external magnetic field and the current direction; represents the planar Hall resistance; represents the field-type moment; represents the Oersted field.

[0059] like Figure 5 As shown in b, The contribution of the term (mainly from the damping-type moment) is significantly greater than The former is almost two orders of magnitude higher than the latter (mainly from the field-type torque). Therefore, the spin-orbit torque in this device mainly comes from the damping-type torque.

[0060] like Figure 5 The c in the figure shows the phase transition temperature before and after. and The relationship diagram and fitting curve are shown in Figure 2. The slope of the fitting curve can be used to further calculate the magnitude of the damping-type torque efficiency before and after the phase change, as shown in formula (2): ; (2) in, Indicates damping-type torque efficiency; represents the charge of an electron; represents the reduced Planck constant; represents the saturation magnetization of the ferromagnetic layer; represents the thickness of the ferromagnetic layer; represents the vacuum permeability; Represents the charge current density flowing through the heavy metal layer.

[0061] like Figure 5 Figure d shows the calculated quasi-damped spin-orbit torque efficiency at different temperatures for the VO2 / Pt / Co / Pt multilayer heterojunction device of this embodiment and a pure Pt / Co / Pt heterojunction device. Compared to the pure Pt / Co / Pt heterojunction device, the quasi-damped spin-orbit torque efficiency of the device of this embodiment is significantly improved at all temperatures. Furthermore, when the temperature reaches 300 K (the phase transition temperature of VO2), the spin-orbit torque efficiency shows a step-like increase. Below the phase transition temperature of VO2, the orbital flux generated by the VO2 layer decreases, resulting in a low spin-orbit torque efficiency. As the temperature rises, the VO2 layer undergoes an electronic phase transition, generating an increase in the orbital flux. The spin-orbit torque efficiency of the device of this embodiment significantly improves, from 0.16 to 0.50, an increase of over 300%.

[0062] It should be apparent to those skilled in the art that the various exemplary components, systems, and methods described in conjunction with the embodiments disclosed herein can be implemented in hardware, software, or a combination of both.

[0063] It should be understood that the present invention is not limited to the specific configurations and processes described above and illustrated in the figures. For the sake of brevity, a detailed description of known methods is omitted. In the above embodiments, several specific steps are described and illustrated as examples. However, the method of the present invention is not limited to the specific steps described and illustrated. Those skilled in the art may make various changes, modifications, and additions, or change the order of the steps after understanding the spirit of the present invention.

[0064] In the present invention, features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, and / or combined with or replace features of other embodiments.

[0065] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations to the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for controlling the spin-orbit torque efficiency of a heavy metal / ferromagnetic heterojunction, characterized in that: The method is applied to a pre-prepared multilayer heterojunction, wherein the multilayer heterojunction comprises, from bottom to top, a vanadium-based oxide layer, a heavy metal layer, and a ferromagnetic layer, wherein the heavy metal layer and the ferromagnetic layer constitute a heavy metal / ferromagnetic heterojunction, and the method comprises: Applying a current to the vanadium-based oxide layer, the vanadium-based oxide layer generates an orbital current perpendicular to the current direction based on the orbital Hall effect, and the orbital current flows into the heavy metal layer through interlayer coupling; the heavy metal layer converts the orbital current into a spin current perpendicular to the film surface, and superimposes the spin current perpendicular to the film surface with the spin current generated by the heavy metal layer based on the spin Hall effect, and the spin currents flow into the ferromagnetic layer together as an effective spin current, thereby generating a spin-orbit torque; By triggering the electronic phase transition state of the vanadium-based oxide layer through external excitation, the resistivity of the vanadium-based oxide layer changes, and then the density of the orbital flow, the density of the effective spin current flowing into the ferromagnetic layer, and the size of the spin-orbit torque are sequentially regulated to achieve the regulation of the spin-orbit torque efficiency of the heavy metal / ferromagnetic heterojunction.

2. The method for controlling the spin-orbit torque efficiency of a heavy metal / ferromagnetic heterojunction according to claim 1, characterized in that: The method further includes preparing the multilayer film heterojunction, and preparing the multilayer film heterojunction includes: Depositing a vanadium-based oxide on the pretreated substrate using a first predetermined deposition method to form a vanadium-based oxide thin film as the vanadium-based oxide layer; wherein the phase transition temperature of the vanadium-based oxide layer is controlled within a predetermined range based on deposition parameters and deposition process; Depositing a heavy metal material on the surface of the vanadium-based oxide film using a second predetermined deposition method to form a heavy metal film as the heavy metal layer; Depositing a ferromagnetic material on the surface of the heavy metal film using the second preset deposition method to form a ferromagnetic film as the ferromagnetic layer; Among them, the first preset deposition method includes a pulsed laser deposition method, a magnetron sputtering method and an atomic layer deposition method, and the second preset deposition method includes a magnetron sputtering method, a molecular beam epitaxy method and an electron beam evaporation method.

3. The method for controlling the spin-orbit torque efficiency of a heavy metal / ferromagnetic heterojunction according to claim 2, wherein: The pulsed laser deposition method is used to deposit and form the vanadium-based oxide thin film, comprising: The substrate is placed in a pulsed laser deposition system chamber, the chamber is evacuated to a vacuum state, and the substrate is heated to 500-550° C. The substrate is made of aluminum oxide single crystal; Oxygen is introduced into the chamber and the oxygen pressure is maintained at 0.8-1.5 Pa; a pulsed laser is used to strike a vanadium-based oxide target to form the vanadium-based oxide film, and the thickness of the vanadium-based oxide film is controlled by adjusting the number of laser pulses; wherein the repetition frequency of the pulsed laser is 1-5 Hz, the pulse energy is 400-550 mJ, and the distance between the vanadium-based oxide target and the substrate is less than 5 cm.

4. The method for controlling the spin-orbit torque efficiency of a heavy metal / ferromagnetic heterojunction according to claim 2, wherein: The heavy metal film and the ferromagnetic film are formed by the magnetron sputtering method, comprising: placing the substrate on which the vanadium-based oxide thin film is deposited in a magnetron sputtering system chamber, and evacuating the chamber to a vacuum state; Argon gas is introduced into the chamber and the argon pressure is maintained at 0.4-1.2 Pa; the heavy metal film and the ferromagnetic film are sequentially deposited on the surface of the vanadium-based oxide film by DC sputtering; wherein the deposition power is 10-40 W and the deposition temperature is 20-30° C.

5. The method for controlling the spin-orbit torque efficiency of a heavy metal / ferromagnetic heterojunction according to claim 1, wherein: The vanadium-based oxide layer uses vanadium dioxide or vanadium-based oxide doped with other elements to have electronic phase change characteristics and orbital Hall effect; wherein the other elements include tungsten, titanium, molybdenum, niobium, zirconium, ruthenium and chromium.

6. The method for controlling the spin-orbit torque efficiency of a heavy metal / ferromagnetic heterojunction according to claim 1, wherein: Materials used for the heavy metal layer include platinum, palladium, iridium, tantalum and tungsten.

7. The method for controlling the spin-orbit torque efficiency of a heavy metal / ferromagnetic heterojunction according to claim 1, wherein: The ferromagnetic layer is made of a ferromagnetic metal material with in-plane magnetic anisotropy or a ferromagnetic metal material with perpendicular magnetic anisotropy, wherein the ferromagnetic metal material with in-plane magnetic anisotropy includes cobalt, cobalt iron boron, cobalt iron and nickel iron, and the ferromagnetic metal material with perpendicular magnetic anisotropy includes cobalt / nickel multilayer film, cobalt / platinum multilayer film, cobalt iron boron / magnesium oxide heterojunction, cobalt platinum alloy, cobalt palladium alloy, iron platinum alloy, and two-dimensional van der Waals ferromagnet.

8. The method for controlling the spin-orbit torque efficiency of a heavy metal / ferromagnetic heterojunction according to claim 1, wherein: The thickness of the metal layer is 2-10 nm, and the thickness of the ferromagnetic layer is 1-10 nm.

9. The method for controlling the spin-orbit torque efficiency of a heavy metal / ferromagnetic heterojunction according to claim 1, wherein: The external stimulation includes changing the ambient temperature, applying an electric field, irradiating light and applying stress.

10. The method for controlling the spin-orbit torque efficiency of a heavy metal / ferromagnetic heterojunction according to claim 1, wherein: The method further includes determining the spin-orbit torque efficiency by harmonic measurement, including: Applying an alternating current excitation to the multilayer film heterojunction and applying an external magnetic field with a variable angle to the alternating current in a plane parallel to the film surface; measuring the second harmonic resistance in a direction perpendicular to the alternating current; By fitting the functional relationship between the second harmonic resistance and the variable angle of the external magnetic field, the damping-type torque component and the field-type torque component are separated, and based on the damping-type torque component and the field-type torque component, the damping-type torque efficiency and the field-type torque efficiency are calculated respectively; wherein, the damping-type torque efficiency and the field-type torque efficiency jointly characterize the spin-orbit torque efficiency of the heavy metal / ferromagnetic heterojunction.

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