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

Abstract

The present invention provides a method for regulating the spin-orbit torque efficiency of a heavy metal / ferromagnetic heterojunction, relating to the field of spintronic devices. The method comprises: introducing a vanadium-based oxide with electronic phase change 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 change of the vanadium-based oxide layer through external excitation to dynamically adjust the orbital current density and achieve regulation of the spin-orbit torque efficiency. The present invention does not require changing the heterojunction material composition or structure, and can achieve dynamic regulation of the spin-orbit torque efficiency by introducing a phase change 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, the embodiment of the present application provides a heavy metal / ferromagnetic heterojunction spin-orbit torque efficiency regulation method to solve the problem that the existing spin-orbit torque efficiency regulation technology relies on fixed material characteristics, is difficult to regulate and optimize, has a complex and irreversible means, and lacks flexible external regulation dimensions.

[0005] In one aspect, the present application provides a heavy metal / ferromagnetic heterojunction spin-orbit torque efficiency regulation method, which is applied to a pre-prepared multilayer film heterojunction. The multilayer film heterojunction is composed of a vanadium-based oxide layer, a heavy metal layer, and a ferromagnetic layer from bottom to top. The heavy metal layer and the ferromagnetic layer form a heavy metal / ferromagnetic heterojunction. The method comprises:

[0006] An electric current is applied to the vanadium-based oxide layer. The vanadium-based oxide layer generates an orbital current perpendicular to the direction of the electric current based on the orbital Hall effect and 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 a spin current generated by the heavy metal layer based on the spin Hall effect to flow into the ferromagnetic layer as an effective spin current, generating a spin-orbit torque.

[0007] The electronic phase change state of the vanadium-based oxide layer is triggered by external excitation, so that the resistivity of the vanadium-based oxide layer changes, and then the density of the orbital current, the density of the effective spin current flowing into the ferromagnetic layer, and the size of the spin-orbit torque are regulated in sequence, realizing the regulation of the spin-orbit torque efficiency of the heavy metal / ferromagnetic heterojunction.

[0008] In some embodiments of the present application, the method further comprises preparing the multilayer film heterojunction, which comprises:

[0009] A vanadium-based oxide is deposited on the pretreated substrate using a first preset deposition method to form a vanadium-based oxide film as the vanadium-based oxide layer. The phase change temperature of the vanadium-based oxide layer is controlled within a preset range based on deposition parameters and deposition process.

[0010] 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 the heavy metal layer.

[0011] A ferromagnetic material is deposited on the surface of the heavy metal film using the second preset deposition method to form a ferromagnetic film as the ferromagnetic layer.

[0012] The first preset deposition method includes a pulsed laser deposition method, a magnetron sputtering method, and an atomic layer deposition method. The second preset deposition method includes a magnetron sputtering method, a molecular beam epitaxy method, and an electron beam evaporation method.

[0013] In some embodiments of the present application, the vanadium-based oxide film is formed by the pulsed laser deposition method, which comprises:

[0014] The substrate is placed in a chamber of a pulsed laser deposition system, and the chamber is pumped to a vacuum state, and the substrate is heated to 500-550℃.

[0015] Oxygen is introduced into the chamber and maintained at a pressure of 0.8-1.5 Pa, and 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 pulses of the laser; 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.

[0016] In some embodiments of the present application, the heavy metal film and the ferromagnetic film are formed by the magnetron sputtering method, which comprises:

[0017] The substrate on which the vanadium-based oxide film is deposited is placed in a chamber of a magnetron sputtering system, and the chamber is pumped to a vacuum state.

[0018] Argon is introduced into the chamber and maintained at a pressure of 0.4-1.2 Pa, and a direct current sputtering is used to sequentially deposit the heavy metal film and the ferromagnetic film on the surface of the vanadium-based oxide film; wherein the deposition power is 10-40 W, and the deposition temperature is 20-30℃.

[0019] In some embodiments of the present application, the vanadium-based oxide layer uses vanadium dioxide or vanadium-based oxide doped with other elements to have electronic phase transition characteristics and orbital Hall effect; wherein the other elements include tungsten, titanium, molybdenum, niobium, zirconium, ruthenium and chromium.

[0020] In some embodiments of the present application, the material of the heavy metal layer includes platinum, palladium, iridium, tantalum and tungsten.

[0021] In some embodiments of the present application, the ferromagnetic layer uses 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-iron-boron, cobalt-iron and nickel-iron, and the ferromagnetic metal material with perpendicular magnetic anisotropy includes a cobalt / nickel multilayer film, a cobalt / platinum multilayer film, a cobalt-iron-boron / magnesium oxide heterojunction, a cobalt-platinum alloy, a cobalt-palladium alloy, an iron-platinum alloy and a two-dimensional van der Waals ferromagnet.

[0022] In some embodiments of the present application, the thickness of the metal layer is 2-10 nm, and the thickness of the ferromagnetic layer is 1-10 nm.

[0023] In some embodiments of the application, the external stimulus comprises changing ambient temperature, applying an electric field, illumination, and applying stress.

[0024] In some embodiments of the application, the method further comprises determining the spin-orbit torque efficiency by harmonic measurement, comprising:

[0025] An alternating current excitation is applied to the multilayer film heterojunction, and an external magnetic field is applied at a variable angle with the alternating current in a plane parallel to the film surface; a second harmonic resistance is measured in a direction perpendicular to the alternating current;

[0026] By fitting the function relationship between the second harmonic resistance and the variable angle of the external magnetic field, the damping-like torque component and the field-like torque component are separated, and the damping-like torque efficiency and the field-like torque efficiency are calculated based on the damping-like torque component and the field-like torque component, respectively; wherein the damping-like torque efficiency and the field-like torque efficiency together represent the spin-orbit torque efficiency of the heavy metal / ferromagnetic heterojunction.

[0027] The application provides a heavy metal / ferromagnetic heterojunction spin-orbit torque efficiency regulation method, 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 film 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, flowing into the heavy metal layer through interlayer coupling and converting into a spin current perpendicular to the film surface, and then injecting the ferromagnetic layer after superimposing with the spin current generated by the spin Hall effect of the heavy metal 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 adjust the orbital current density and regulate the spin-orbit torque efficiency. The application does not need to change the material composition or structure of the heavy metal / ferromagnetic heterojunction or optimize the heavy metal / ferromagnetic heterojunction interface, but only needs to introduce a phase change material to dynamically regulate the spin-orbit torque efficiency, and the structure is simple and convenient to implement, which can be applied to the design of new magnetic storage and operation devices.

[0028] Additional advantages, objects, and features of the application will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or can be learned by practice of the application. The objects and other advantages of the application can be realized and attained by the structure particularly pointed out in the specification as well as in the appended claims.

[0029] Those skilled in the art will appreciate that the objects and advantages of the application can be realized and attained by means summarized fully in the following description, and particularly pointed out in the appended claims. Accordingly, the foregoing background of the application is intended for illustrative purposes only and is not intended to limit the scope of the application. BRIEF DESCRIPTION OF DRAWINGS

[0030] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the principles of the application. In the drawings:

[0031] Figure 1 Structure diagram of a multilayer film heterojunction in an embodiment of the present application.

[0032] Figure 2 Principle diagram of a heavy metal / ferromagnetic heterojunction spin-orbit torque efficiency regulation method in an embodiment of the present application.

[0033] Figure 3 R-T curve diagram of a VO2 thin film in an embodiment of the present application.

[0034] Figure 4 Harmonic measurement diagram of a heavy metal / ferromagnetic heterojunction spin-orbit torque efficiency in an embodiment of the present application.

[0035] Figure 5 Harmonic test results and fitting curves before and after a phase transition temperature in an embodiment of the present application. DETAILED DESCRIPTION

[0036] In order to make the objectives, technical solutions, and advantages of the present application clearer, the present application will be described in further detail below with reference to the embodiments and drawings. Here, the illustrative embodiments of the present application and the descriptions thereof are used to explain the present application, but are not intended to limit the present application.

[0037] It should also be noted that, in order to avoid obscuring the present application due to unnecessary details, only structures and / or processing steps closely related to the solutions according to the present application are shown in the drawings, and other details not closely related to the present application are omitted.

[0038] It should be emphasized that the terms “comprises / comprising” when used in this text indicate the presence of the stated features, elements, steps or components, but do not exclude the presence or addition of one or more other features, elements, steps or components.

[0039] It should also be noted that, unless otherwise specified, the term “connected” in this text can not only mean direct connection, but also mean indirect connection in the presence of an intermediate.

[0040] In the following, embodiments of the present application will be described with reference to the drawings. In the drawings, the same reference numerals represent the same or similar parts or the same or similar steps.

[0041] It should be emphasized here that the step designations mentioned in the following are not intended to limit the order of the steps, but it should be understood that the steps can be performed in the order mentioned in the embodiments, or in a different order from the embodiments, or several steps can be performed simultaneously.

[0042] In order to solve the problems that the existing spin-orbit torque efficiency regulation technology relies on fixed material characteristics, is difficult to regulate and optimize, the means is complex and irreversible, and lacks flexible external regulation dimension, the present application provides a heavy metal / ferromagnetic heterojunction spin-orbit torque efficiency regulation method. A vanadium-based metal oxide with electronic phase transition characteristics is introduced on the heavy metal side of the heavy metal / ferromagnetic heterojunction. The generated orbital flow enhances 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 orbital flow size generated before and after the phase transition of the vanadium-based metal oxide is used to regulate the spin-orbit torque efficiency of the heavy metal / ferromagnetic heterojunction. Specifically, the method comprises:

[0043] An electric current is applied to the vanadium-based oxide layer. The vanadium-based oxide layer generates an orbital flow perpendicular to the direction of the electric current based on the orbital Hall effect, and flows into the heavy metal layer through interlayer coupling. The heavy metal layer converts the orbital flow into a spin flow perpendicular to the film surface, and superimposes the spin flow perpendicular to the film surface with the spin flow generated by the heavy metal layer based on the spin Hall effect, as an effective spin flow, and flows into the ferromagnetic layer together to generate spin-orbit torque.

[0044] The electronic phase transition state of the vanadium-based oxide layer is triggered by external excitation to change the resistivity of the vanadium-based oxide layer, and then the density of the orbital flow, the density of the effective spin flow flowing into the ferromagnetic layer, and the size of the spin-orbit torque are regulated in turn to regulate the spin-orbit torque efficiency of the heavy metal / ferromagnetic heterojunction.

[0045] For the sake of understanding, first, the multilayer film heterojunction is further described.

[0046] In some embodiments, the vanadium-based oxide layer adopts vanadium dioxide (VO2) or a vanadium-based oxide doped with other elements to have electronic phase transition characteristics and orbital Hall effect. The other elements include tungsten (W), titanium (Ti), molybdenum (Mo), niobium (Nb), zirconium (Zr), ruthenium (Ru), chromium (Cr), etc. It should be noted that when referring to materials, the chemical formula of the corresponding material is in the brackets, and the same applies hereinafter.

[0047] In some embodiments, the material of the heavy metal layer includes platinum (Pt), palladium (Pd), iridium (Ir), tantalum (Ta), tungsten (W), etc. to have a strong spin-orbit coupling effect.

[0048] In some embodiments, the ferromagnetic layer adopts a ferromagnetic metal material with in-plane magnetic anisotropy or a ferromagnetic metal material with perpendicular magnetic anisotropy. 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 a cobalt-platinum multilayer film ([Co / Pt]n cobalt / nickel multilayer film ([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 (Fe3GaTe2or Fe3GeTe2), etc.

[0049] In some embodiments, the preparation of the multilayer film heterojunction comprises the following steps:

[0050] A vanadium-based oxide is deposited on the substrate after pretreatment (such as cleaning treatment) using a first preset deposition method to form a vanadium-based oxide film as a vanadium-based oxide layer. The phase transition temperature of the vanadium-based oxide layer is controlled within a preset range based on deposition parameters and deposition process. For example, by adjusting the oxygen pressure, stress effect, element doping and deposition process during deposition, the phase transition temperature of the vanadium-based oxide layer is controlled near room temperature, ensuring that the device can realize phase transition control without additional temperature control. Room temperature is usually defined as 25°C.

[0051] 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.

[0052] 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.

[0053] Thus, a multilayer film heterojunction is prepared, which has a vanadium-based oxide layer, a heavy metal layer and a ferromagnetic layer from bottom to top.

[0054] In some embodiments, the thickness of the metal layer is 2-10 nm, and the thickness of the ferromagnetic layer is 1-10 nm.

[0055] In some embodiments, the first preset deposition method includes at least pulsed laser deposition method, magnetron sputtering method and atomic layer deposition method, and the second preset deposition method includes at least magnetron sputtering method, molecular beam epitaxy method and electron beam evaporation method.

[0056] The following takes the first preset deposition method as the pulsed laser deposition method and the second preset deposition method as the magnetron sputtering method to prepare a VO2 / Pt / Co / Pt multilayer film heterojunction as an example for further description, and the preparation steps include:

[0057] The cleaned (0001) oriented aluminum trioxide (Al2O3) single crystal substrate is placed in the cavity of the pulsed laser deposition system, and the cavity is pumped to a vacuum state, and then the substrate is heated to 500-550°C.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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).

[0063] 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.

[0064] 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 denoted as .

[0065] The spin current generated by the spin Hall effect of the heavy metal layer is superimposed on the spin current converted from the orbital current, and the superimposed spin current flows into the ferromagnetic layer as effective spin current, thereby generating spin-orbit torque. .

[0066] Compared with the conventional heavy metal / ferromagnetic heterojunction, the orbital current generated by the vanadium-based oxide layer is superimposed on the spin current of the heavy metal layer, thereby increasing the effective spin current flowing into the ferromagnetic layer, enhancing the spin-orbit torque, and finally improving the spin-orbit torque efficiency of the heavy metal / ferromagnetic heterojunction.

[0067] In step S102, the electronic phase change state of the vanadium-based oxide layer is triggered by external excitation, the band gap of the vanadium-based oxide layer changes, the resistivity changes, the density of the generated orbital current changes, the density of the effective spin current flowing into the ferromagnetic layer changes, the size of the spin-orbit torque changes, and the spin-orbit torque efficiency of the heavy metal / ferromagnetic heterojunction is controlled.

[0068] In some embodiments, the external excitation mode includes changing the ambient temperature, applying an electric field, light, applying stress, etc.

[0069] The application will be further described below in combination with a specific embodiment.

[0070] As shown in Figure 1 , a VO2 / Pt / Co / Pt multilayer film heterojunction is used, and the external excitation mode is to change the ambient temperature.

[0071] As shown in Figure 3 , the R-T curve of the VO2 film with a thickness of 10 nm in this embodiment is shown. At low temperature, the VO2 film shows a high resistance state. As the temperature rises, the resistance suddenly decreases near the transition temperature, and the VO2 film changes into a low resistance state metal phase. The jump of the VO2 film resistance with temperature is close to 10 3 Ω order of magnitude, and there is a significant hysteresis effect. Figure 2 The upper right corner of the drawing is the first derivative function of the resistance with respect to temperature, and according to the temperature corresponding to the valley value, it can be seen that the transition temperature of the VO2 film grown in this embodiment is 300K (cooling) and 313K (heating).

[0072] As shown in 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.

[0073] 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.

[0074] in, Variable angle The function is shown in formula (1):

[0075] ; (1)

[0076] 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.

[0077] 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.

[0078] 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):

[0079] ; (2)

[0080] 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.

[0081] 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%.

[0082] Those of ordinary skill in the art will appreciate that the various illustrative components, systems and methods described in connection with the embodiments disclosed herein can be implemented as hardware, software, or hardware and software in combination.

[0083] It is to be expressly understood that the invention is not limited to the specific configurations and process described hereinabove and shown in the drawings. The detailed description of known methods is omitted for the sake of brevity. In the above embodiments, several specific steps are described and shown as examples. However, the method processes of the present invention are not limited to the specific steps described and shown, and various changes, modifications and additions can be made thereto by one of ordinary skill in the art without departing from the spirit of the present invention.

[0084] In the present invention, features described and / or illustrated in connection with one embodiment can be used in the same or similar manner or in conjunction with or in place of features of other embodiments.

[0085] The above description is merely illustrative of the application, and is not intended to limit the scope of the application. Various modifications and changes can be made by those of ordinary skill in the art without departing from the spirit and scope of the application. Any modification, equivalent replacement, improvement, and the like made within the spirit and principle of the application shall fall within the scope of the protection of the application.

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 pulses of the pulsed laser; 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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