A method for realizing spin-orbital moment driven magnetic moment flip based on interface spin vorticity coupling effect

Abstract

The application belongs to the technical field of spintronics, and specifically forms a vortex of electron drift velocity at the interface of a magnetic layer and a metal layer by a difference in conductivity, further utilizes a spin vortex coupling effect to realize conversion of charge current to spin current, and thereby drives a magnetic moment to flip through a spin-orbit moment. As an example, the application deposits a Cu layer with high conductivity on a PtCo alloy layer with lower conductivity through magnetron sputtering, and constructs a heterostructure with a PtCo / Cu interface spin vortex coupling effect. By increasing the thickness of the Cu layer to improve the conductivity of the Cu layer, a significant improvement in the orbital moment efficiency can be observed. Not only does this provide valuable experimental evidence for in-depth understanding of the physical mechanism of interface-induced spin current, but also enriches the conversion approach between charge current and spin current, and opens up a simple and efficient new path for the research and design of a new generation of spintronic devices.

Description

Technical Field

[0001] This invention belongs to the field of spintronic device technology. Specifically, it uses the difference in conductivity at the interface of the magnetic layer / metal layer to form vorticity of electron drift velocity. Furthermore, it utilizes the spin vortex coupling effect to realize the conversion of charge flow into spin current, thereby driving magnetic moment reversal through spin orbital moment. Background Technology

[0002] Inducing magnetic layer reversal through electronic control is currently a cutting-edge and hot topic in spintronics research. Over the past decade, spin-transfer torque (STT) and spin-orbit torque (SOT), based on spin current-driven magnetic moment reversal, have received extensive research. The advantage of spin-transfer torque lies in its structure, which is consistent with magnetic tunnel junctions. It utilizes pinned ferromagnetic metal layers to convert charge flow into spin-polarized electron flow and inject it into the free layer. However, the high-density tunneling current easily breaks down the intermediate potential barrier, affecting device stability. Compared to spin-transfer torque, spin-orbit torque can be designed as a three-terminal storage unit to separate the information storage and retrieval paths, extending the device's lifespan. In recent years, orbital electronics has attracted considerable attention. It relies on the generation and injection of orbital currents to achieve spin-orbit torque-driven magnetic moment reversal. Unlike traditional spintronics, orbital electronics can achieve charge-to-spin conversion in light metal systems lacking strong spin-orbit coupling, thus greatly expanding the range of materials suitable for spintronic devices.

[0003] Studies have shown that orbital currents can be generated through chiral orbital textures associated with orbital hybridization in a material system under an applied electric field. For example, a recent work used magneto-optical Kerr microscopy to confirm the orbital Hall effect in the light metal titanium, consistent with the orbital textures under its face-centered cubic structure. Furthermore, the study also found similar effects in some naturally oxidized light metals, such as CuO. x Due to orbital hybridization between the Op and Cu-d states, a strong chiral orbital texture structure can be generated, leading to a significant enhancement of the orbital Lashba effect near the Fermi level. From an application perspective, orbital electronics offers the possibility of using orbital currents as information carriers. However, orbital electronics faces several challenges, particularly in orbital current generation and orbital-to-spin conversion efficiency, resulting in orbital torque efficiency that does not offer a significant advantage over traditional spintronics. These challenges necessitate a deeper understanding of orbital dynamics and the exploration of methods to improve orbital current generation and conversion efficiency. Summary of the Invention

[0004] To address the problem of improving the efficiency of orbital current generation and conversion, this invention proposes an innovative solution. This solution utilizes the interfacial spin vortex coupling effect to achieve efficient conversion of charge current into spin current, and then injects the generated spin current into the magnetic layer to drive magnetic moment reversal. The core of this method lies in constructing a heterostructure with significant conductivity differences, which, from bottom to top, can be a buffer layer, a magnetic layer, a metal layer, and a capping layer, or a buffer layer, a metal layer, a magnetic layer, and a capping layer. In this heterostructure, the significant resistivity difference between the magnetic layer and the metal layer becomes the key factor in inducing the interfacial spin vortex coupling effect. This effect broadens the orbital-spin conversion mechanism, not only significantly improving the spin-orbit moment efficiency, but also further enhancing the spin-orbit moment efficiency by continuously increasing the conductivity of the metal layer, thereby driving magnetic moment reversal more efficiently.

[0005] To achieve the above technical objectives, a method for realizing spin orbital moment-driven magnetic moment reversal based on interface spin vortex coupling effect is implemented through the following technical solution: (1) A magnetic heterostructure with out-of-plane magnetic anisotropy is prepared by using thin film growth methods such as magnetron sputtering, laser pulse deposition, molecular beam epitaxy, and electron beam evaporation. The structure consists of a buffer layer, a magnetic metal layer, a metal layer, and a capping layer from bottom to top, or a buffer layer, a metal layer, a magnetic metal layer, and a capping layer. The selection of the metal layer includes, but is not limited to, metals with low resistivity such as Cu, Ag, and Au. The selection of the magnetic metal layer includes, but is not limited to, Fe, Co, Ni, PtCo, FePt, and CoTb. In this invention, the sample is prepared by magnetron sputtering, and the metal layer and the magnetic metal layer are selected as Cu and PtCo, respectively. Specifically, in step (1), the substrate is Si(001), wherein the substrate surface is treated by thermal oxidation process to have 500nm dense SiO2, and it needs to be ultrasonically cleaned with anhydrous ethanol and acetone before use. Specifically, in step (1), the buffer layer is made of heavy metal Ta, which provides a smooth surface for the subsequent growth of the magnetic layer and enhances the out-of-plane magnetic anisotropy of the PtCo layer. Specifically, in step (1), the magnetic metal layer is selected from PtCo alloy. The alloy composition of this invention is specifically Pt(0.6nm) / Co(0.3nm) / Pt(0.6nm) / Co(0.3nm) / Pt(0.6nm) / Co(0.3nm) / Pt(0.6nm); Specifically, in step (1), Cu is selected as the metal layer, which has excellent conductivity. Its conductivity is significantly different from that of the PtCo alloy layer. At the PtCo / Cu interface, the spin vortex coupling effect is used to efficiently induce the conversion between charge current and spin current, and the induced spin current is injected into the magnetic layer to drive the magnetic moment to flip. Specifically, in step (1), silicon nitride is selected as the capping layer to prevent the functional layer from contacting the air and causing it to oxidize, thereby improving the stability of the heterostructure.

[0006] The mechanism of this invention is as follows: Figure 4 As shown, at the PtCo / Cu interface, the difference in conductivity leads to a non-uniform distribution of carrier velocities near the interface, forming a velocity gradient in the vertical direction of the interface, which in turn generates vorticity in the electron drift velocity. ω Due to the spin vorticity coupling effect, vorticity ω It is converted into a spin current; the spin current is injected into the PtCo layer to drive the magnetic moment to flip.

[0007] The beneficial effects of this invention are as follows: This invention proposes a method for achieving spin-orbit moment driven magnetic moment reversal based on the interface spin vortex coupling effect. Unlike traditional methods of generating spin current, this method does not rely on strong spin-orbit coupling effects. Instead, it generates electron migration velocity vorticity through the significant difference in conductivity between the metal layer and the magnetic metal layer, and combines this with the spin vortex coupling effect to achieve efficient conversion of charge current to spin current. The method proposed in this invention opens up a new approach for the design and fabrication of low-power, high-efficiency magnetic storage devices, providing a new idea and solution for the fabrication of next-generation spintronic devices. This invention has the advantages of high stability, simple structure, and easy fabrication. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of the Ta(3) / PtCo(3.3) / Cu(7) / SiN(3) structure.

[0009] Figure 2 The figure shows the test results of the magnetic moment reversal of Ta(3) / PtCo(3.3) / Cu(7) / SiN(3) driven by the current-induced spin-orbit torque under an in-plane auxiliary magnetic field Bx = ±50 mT.

[0010] Figure 3 Damping moment and field moment + Oersted field Efficiency diagram as a function of copper layer thickness

[0011] Figure 4 This is a schematic diagram of spin current generated by interfacial spin vortex coupling in a PtCo / Cu heterostructure. Detailed Implementation

[0012] To clarify the purpose of this patent application and the technical solutions and advantages described herein, a detailed explanation will be provided below with reference to examples and accompanying drawings. The embodiments described are merely examples and not the only possible solutions. Other solutions derived by those skilled in the art based on these embodiments without inventive effort are all within the scope of protection of this application.

[0013] Example 1: Fabrication and Current-Driven Magnetic Moment Reversal of a Ta(3nm) / [Pt(0.6nm) / Co(0.3nm)]3Pt(0.6nm) / Cu(7nm) / SiN(3nm) Heterostructure

[0014] (1) The substrate is Si(001) with a specification of 25mm*25mm*0.5mm. Its surface is treated with thermal oxidation process to have 500nm dense SiO2. Before use, it is ultrasonically cleaned with anhydrous ethanol, acetone and anhydrous ethanol for 5 minutes in sequence.

[0015] (2) Fix the substrate on the tray and place it in the sample chamber of the magnetron sputtering instrument. Use a mechanical pump and a molecular pump to remove the residual air in the sample chamber, so that the air pressure in the sample chamber is better than 10. -5 Torr, while the sputtering chamber pressure is better than 10. -8 Torr opens the baffle between the sample delivery chamber and the sputtering chamber, and sends the tray to the sputtering chamber along the x-axis using the sample delivery rod.

[0016] (3) Set the tray rotation angular velocity in the sputtering chamber to 15 rpm and introduce argon gas into the chamber at a certain flow rate. After the chamber meets the ignition pressure, turn on the power supply of sputtering targets Ta, Pt, Co, Pt, Co, Pt, Co, Pt, Cu, and SiN in sequence. Set the ignition power to 50W. After ignition, adjust the power supply of the target to the growth power and reduce the pressure in the chamber to the growth pressure. After stabilizing for a period of time, open the sample baffle. Sputter for a period of time according to the thickness to be grown, and then close the sample baffle in sequence to complete the thin film growth process. Ta, Co, and Cu were sputtered using DC sputtering, while Pt and SiN were sputtered using RF sputtering. The start-up gas pressure for the DC sputtering target was 10 mT, and the start-up gas pressure for the RF sputtering target was 15 mT. The growth gas pressure for both DC and RF targets was 3 mT. The stabilization time was 1 min. The growth power for Ta, Pt, Co, Cu, and SiN was 50 W, 40 W, 30 W, 20 W, and 30 W, respectively. The growth rates for Ta, Pt, Co, Cu, and SiN were 0.231 Å, 0.194275 Å, 0.15584 Å, 0.5413333 Å, and 0.02415 Å per second, respectively.

[0017] (4) After sputtering, the sample is transferred to the sampling chamber and taken out. The sample surface is observed by atomic force microscope. The root mean square roughness is 200 pm, indicating that the film surface has good flatness.

[0018] (5) The samples were micro- and nano-fabricated using a laser direct writing instrument and an ion beam etching machine. The anomalous Hall voltage and harmonic voltage of the samples were measured using a self-built electrical transport system. The current for testing the anomalous Hall effect was applied along the x-axis by a Keithley 6221 amplifier with a magnitude of 1 mA. The anomalous Hall voltage was read using a Keithley 2182A amplifier, and the harmonic voltage was read using a lock-in amplifier (SR830). Harmonic voltage is a way to quantify the effective field of the spin orbital moment. Measuring the second-order and first-order harmonic Hall voltages of the sample can fit the effective field of the sample's spin orbital moment. Here, we fabricated a Hall bar structure with a width of 5 μm and a length of 50 μm, where the current was applied along the x-axis, and the anomalous Hall voltage and harmonic voltage were measured along the y-axis.

Claims

1. A method for realizing spin orbital moment-driven magnetic moment reversal based on interface spin vortex coupling effect, characterized in that, The interface spin vortex coupling effect is caused by the resistivity mismatch between the magnetic layer and the metal layer. The intensity of the interface spin vortex coupling effect in the heterostructure can be achieved by changing the conductivity of the metal layer.

2. The interface spin vortex coupling effect according to claim 1, characterized in that, Due to the significant difference in conductivity between the magnetic layer and the metal layer, the rate of conduction electrons forms a gradient in the vertical direction of the magnetic layer / metal layer interface, resulting in an interfacial spin vortex coupling effect.

3. The method for realizing spin orbital moment driven magnetic moment reversal based on interface spin vortex coupling effect according to claim 1, characterized in that: The preparation methods include, but are not limited to, magnetron sputtering, molecular beam epitaxy, laser pulse deposition, etc. In this invention, a magnetic heterostructure is obtained by growing a thin film on a substrate using sputtering technology. The structure consists of a buffer layer, a magnetic layer, a metal layer, and a capping layer from bottom to top, or a buffer layer, a metal layer, a magnetic layer, and a capping layer. Furthermore, the introduction of a buffer layer can effectively reduce the lattice mismatch rate in the heterostructure, thereby optimizing the overall quality of the heterojunction. Furthermore, when selecting materials for the magnetic layer and the metal layer, special attention should be paid to avoiding combinations of materials with similar electrical conductivity. Instead, materials with significantly different electrical conductivity should be prioritized to generate a significant spin vortex coupling effect at the interface. Furthermore, the capping layer is grown on the metal layer to avoid direct contact between the metal layer and the air, effectively preventing oxidation of the metal layer and thus significantly improving the overall stability and durability of the heterostructure.

4. The method for achieving spin-orbit moment-driven magnetization reversal based on interface spin vortex coupling effect according to claim 1, characterized in that, Unlike traditional mechanisms for generating spin current, such as the spin Hall effect and Lashba effect, this invention provides a novel method for efficiently inducing spin current at the interface through differences in conductivity.

5. The method for realizing spin orbital moment driven magnetic moment reversal based on interface spin vortex coupling effect according to claim 1, characterized in that, Ultra-high efficiency of spin-orbit moment reversal magnetic moment is achieved at the interface. Specifically, the heterostructure designed and fabricated in this invention enhances the efficiency of unit electric field-like damping moment by two orders of magnitude compared to traditional heavy metal / ferromagnetic heterostructures. Therefore, the interface spin vortex coupling effect can efficiently induce the generation of spin current, significantly improve the efficiency of spin-orbit moment, and thus efficiently drive magnetization reversal.

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