Method for enhancing spin-orbit coupling effect in ferromagnetic metal film system based on stress

Abstract

The invention discloses a method for enhancing a spin-orbit coupling effect in a ferromagnetic metal film system based on stress. According to the method, the spin-orbit coupling effect in a ferromagnetic metal film system is enhanced in a mode of applying prestress in the ferromagnetic metal film growth process by utilizing the bendable characteristic of a flexible substrate. The method is simple and easy to implement, effective regulation and detection of the spin-orbit coupling effect can be achieved, and development of novel magnetoelectric devices based on the spin-orbit coupling effect is facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of spin electronics and relates to a method for enhancing the spin-orbit coupling effect in a ferromagnetic metal film system based on stress. Background Art

[0002] Traditional electronic devices based on manipulating electron charge have the disadvantage of high power consumption due to the Joule heating effect of charge flow. Spintronic devices use both the charge and spin properties of electrons to generate and process information. Compared with traditional electronic devices, they have advantages such as low power consumption and non-volatility, and have become one of the core competitive technologies in the emerging electronic information era.

[0003] Spin-orbit coupling (SOC) describes the interaction between the electron spin and orbital degrees of freedom. It is a relativistic effect that can be viewed as the effective magnetic field experienced by the electron spin in a stationary reference frame. Since SOC connects the electron spin and its orbit, it is very sensitive to the lattice and band structure in condensed matter, playing a fundamental role in a rich variety of phenomena: from magnetic anisotropy, anomalous Hall effect (AHE), and anisotropic magnetoresistance (AMR) observed centuries ago to the recently discovered spin Hall effect in heavy metals and topological insulators. Many of these phenomena are crucial to several technological revolutions in the field of magnetic sensors and magnetic storage. Therefore, since its emergence a century ago, SOC has been at the core of the field of magnetism and spin electronics. The effective manipulation of SOC in magnetic materials is a key scientific issue that needs to be urgently addressed in current spin electronics research.

[0004] Existing methods for enhancing the spin-orbit coupling effect mainly focus on introducing elements with large atomic numbers, such as combining heavy metals (HM) with thin ferromagnets (FM) to drive stronger SOC at the HM / FM interface, or directly doping heavy elements into ferromagnets or ferromagnetic semiconductors. However, the introduction of expensive heavy metals inevitably increases the cost of related devices. In addition, the above methods also have a series of problems such as complex processes and limited application conditions. How to more effectively enhance the spin-orbit coupling effect in ferromagnetic metal thin film systems under simple and convenient conditions and in a low-cost manner has become one of the major challenges facing the current field of spin electronics technology. Summary of the invention

[0005] The present invention aims to provide a method for enhancing the spin-orbit coupling effect in a ferromagnetic metal film system based on stress, which method can achieve effective regulation and detection of the spin-orbit coupling effect in the ferromagnetic metal film system.

[0006] The technical solution to achieve the purpose of the present invention is:

[0007] Based on the method of stress-enhanced spin-orbit coupling effect in ferromagnetic metal thin film systems, the spin-orbit coupling effect in the ferromagnetic metal thin film system is enhanced by applying prestress to the ferromagnetic metal thin film system during its growth process through a flexible and bendable substrate.

[0008] Furthermore, in the above method, prestress is applied and regulated during the growth process of the ferromagnetic metal film system by controlling the curvature radius of the flexible bendable substrate.

[0009] Furthermore, the method for applying and regulating prestress during the growth process of the ferromagnetic metal film system by controlling the curvature radius of the flexible bendable substrate is as follows: before the growth of the ferromagnetic metal film, the flexible bendable substrate is fixed on a non-magnetic metal mold with a corresponding curvature radius, and after the growth of the ferromagnetic metal film is completed, the ferromagnetic metal film is removed from the mold and naturally flattened, wherein the prestress is expressed as strain, and the relationship between the strain and the curvature radius is: Where L is the arc length of the mold, ε is the compressive strain or tensile strain, r is the radius of curvature of the mold, T is the total thickness of the substrate and film, and t is the film thickness.

[0010] Furthermore, in the above method, the flexible and bendable substrate is a substrate conventionally used in the art, such as a mica sheet, etc.; the ferromagnetic metal is a Permalloy (Py, Ni 80 Fe 20 ), CoFeB, etc.

[0011] Furthermore, the specific steps of the above method are:

[0012] (1) fixing the flexible bendable substrate on a non-magnetic metal mold with a corresponding curvature radius;

[0013] (2) Ultra-high vacuum magnetron sputtering technology is used, and the background vacuum degree of the deposition chamber is not less than 4×10 -5 Pa, argon pressure is 0.2-0.3 Pa, Ta or Cu target is sputtered, and a metal buffer layer is sputtered and deposited on the surface of a flexible and bendable substrate. The sputtering power is 30-50 W, and the sputtering deposition rate is 1-2 nm / min;

[0014] (3) Ultra-high vacuum magnetron sputtering technology is used, and the background vacuum degree of the deposition chamber is not less than 4×10 -5 Pa, argon pressure is 0.2-0.3Pa, ferromagnetic metal target is sputtered, sputtering power is 30-50W, sputtering deposition rate is 1-2nm / min, and after the ferromagnetic metal film is grown, it is removed from the mold and flattened naturally.

[0015] Preferably, in step (1), the thickness of the flexible bendable substrate is 10 to 30 μm, and the radius of curvature of the non-magnetic metal mold is 10 to 40 mm.

[0016] Preferably, in step (2), the thickness of the metal buffer layer is 3 to 10 nm.

[0017] Preferably, in step (3), the thickness of the ferromagnetic metal film is 3 to 50 nm.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) The present invention can effectively enhance the spin-orbit coupling effect in the system by only applying prestress during the growth of the ferromagnetic metal film, and can realize controllable modulation of the spin-orbit coupling effect in the system by changing the magnitude of the prestress.

[0020] (2) The present invention does not need to destroy the organizational structure and composition of ferromagnetic metals or heavy metals, and does not need to introduce expensive heavy metals. It has the characteristics of simple structure, low cost, convenient implementation, and significant effect, which meets the requirements of practical application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of applying prestress to the ferromagnetic metal film system in the embodiment, wherein 101 is a solid mica substrate on a non-magnetic metal mold, 102 is a non-magnetic metal convex mold with a curvature radius of 10 mm, and 103 is a non-magnetic metal concave mold with a curvature radius of 10 mm.

[0022] Figure 2 201 is an electromagnet with a curvature radius of 10 mm, 202 is a Helmholtz coil, and 203 is a magnetic metal film sample to be measured.

[0023] Figure 3 is the thin film ferromagnetic resonance field H in the embodiment res The relationship between the change of film resonance damping α and the change of film strain (a) and (b).

[0024] Figure 4 The effective magnetization intensity in the embodiment is 4πM eff and the perpendicular anisotropy field H k ⊥ The relationship between the change of spin-orbit coupling effect intensity with film strain (a) and the change of spin-orbit coupling effect intensity with film strain (b). DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0026] The present invention provides a method for enhancing the spin-orbit coupling effect of a ferromagnetic metal thin film system by applying prestress to the system during its growth process through a flexible and bendable substrate. The specific process of applying prestress is as follows: Figure 1As shown: before film deposition, the flexible substrate mica is fixed on a non-magnetic metal convex mold (102) or concave mold (103), and then a ferromagnetic metal film system is deposited on the flexible substrate. After the film deposition is completed, the flexible substrate with the ferromagnetic metal film system is taken out of the convex mold and naturally flattened, so that a pre-compression strain can be applied to the film system; the flexible substrate with the ferromagnetic metal film system is taken out of the concave mold and naturally flattened, so that a pre-tension strain can be applied to the film system. The magnitude of the pre-strain in the ferromagnetic metal film system in the present invention is achieved by changing the radius of curvature of the convex mold.

[0027] Example 1

[0028] The ferromagnetic metal film system is prepared by magnetron sputtering. The specific steps are as follows:

[0029] (1) The flexible and bendable substrate used is a mica sheet. Before the film is grown, the mica sheet is fixed on a non-magnetic metal mold with different curvature radii. The thickness of the mica sheet is 20 μm, and the curvature radius of the convex mold is 10 to 40 mm.

[0030] (2)Using ultra-high vacuum magnetron sputtering technology, the background vacuum of the deposition chamber is 2×10 -5 Pa, the argon pressure is 0.25 Pa, and the Ta target is DC sputtered to sputter-deposit a metal buffer Ta layer on the surface of the above-mentioned flexible substrate. The DC sputtering power is 30 W, the sputtering deposition rate is 1.5 nm / min, and the thickness of the metal buffer Ta layer is 4 nm.

[0031] (3)Using ultra-high vacuum magnetron sputtering technology, the background vacuum of the deposition chamber is 2×10 -5 Pa, argon pressure is 0.0.3Pa, DC sputtering of ferromagnetic metal target Permalloy Py, DC sputtering power is 50W, sputtering deposition rate is 1nm / min, and the thickness of ferromagnetic metal Py is 10nm.

[0032] The strength of the spin-orbit coupling effect in the ferromagnetic metal film system is evaluated by measuring the magnitude of the ferromagnetic resonance field offset and magnetic damping of the ferromagnetic metal film system. Figure 2 As shown. The sample is placed on a coplanar waveguide in the middle of the electromagnet (201), and a DC magnetic field is applied to the sample through a DC power supply. At the same time, a microwave power supply applies a microwave magnetic field to the sample through the coplanar waveguide, and the direction of the DC magnetic field is 90 degrees to the direction of the microwave magnetic field. The frequency f of the microwave field or the magnitude of the DC magnetic field is changed to excite the ferromagnetic resonance effect in the sample and measure its ferromagnetic resonance spectrum. The resonance field H is read from the ferromagnetic resonance spectrum. res ( Figure 3 a) and the resonance line width ΔH. The perpendicular anisotropy field H is calculated based on the resonance field and the resonance line width.k ⊥ (F=(γ / 2π)[H res (H res +4πM eff )] 1 / 2 , ) and resonance damping α( Figure 3 b). Due to the spin-orbit coupling effect and the perpendicular anisotropy field H k ⊥ and the resonance damping α, so it can be measured by measuring the perpendicular anisotropy field H k ⊥ Or the change in the resonance damping α can be used to evaluate the strength of the spin-orbit coupling effect.

[0033] With perpendicular anisotropy field H k ⊥ For example:

[0034]

[0035] where A is a constant that depends on the electronic structure and is between 0 and 0.2; N and V represent the number of atoms per unit cell and the volume of the unit cell, respectively; μ0 is the magnetic permeability of the vacuum; M s is the saturation magnetization; is the self-selected coupling related term; μ B is the Bohr magneton.

[0036] Ferromagnetic resonance analysis was used to measure the H content of thin films at different strain states. k ⊥ The spin-orbit coupling strength can be obtained by changes, such as Figure 4 b, where the spin-orbit coupling strength It increases with the increase of compressive strain and tensile strain, and the enhancement reaches 250% under the compressive strain ε=1.5‰.

Claims

1. A method for stress-enhanced spin-orbit coupling effect in a ferromagnetic metal film system, characterized in that: The spin-orbit coupling effect in the ferromagnetic metal thin film system is enhanced by applying prestress to the ferromagnetic metal thin film system during its growth process through a flexible and bendable substrate.

2. The method according to claim 1, characterized in that Prestress is applied and regulated during the growth process of the ferromagnetic metal film system by controlling the curvature radius of the flexible bendable substrate.

3. The method according to claim 2, characterized in that The method of applying and regulating prestress during the growth process of the ferromagnetic metal film system by controlling the curvature radius of the flexible bendable substrate is as follows: before the growth of the ferromagnetic metal film, the flexible bendable substrate is fixed on a non-magnetic metal mold with a corresponding curvature radius; after the growth of the ferromagnetic metal film is completed, the ferromagnetic metal film is removed from the mold and naturally flattened, wherein the prestress is expressed as strain, and the relationship between strain and curvature radius is: ,in L is the arc length of the die, ε is the compressive strain or the tensile strain, r is the radius of curvature of the die, T is the total thickness of the substrate and the film, t is the film thickness.

4. The method according to claim 1, characterized in that The flexible and bendable substrate is a mica sheet; the ferromagnetic metal is Permalloy or CoFeB.

5. The method according to claim 1, characterized in that The specific steps are: (1) Fixing the flexible bendable substrate on a non-magnetic metal mold with a corresponding curvature radius; (2) Ultra-high vacuum magnetron sputtering technology is used, and the background vacuum degree of the deposition chamber is not less than 4×10 -5 Pa, argon pressure is 0.2~0.3 Pa, sputtering Ta or Cu target, sputtering depositing metal buffer layer on the surface of flexible and bendable substrate, sputtering power is 30~50W, sputtering deposition rate is 1~2 nm / min; (3) Ultra-high vacuum magnetron sputtering technology is used, and the background vacuum degree of the deposition chamber is not less than 4×10 -5 Pa, the argon pressure is 0.2~0.3Pa, the ferromagnetic metal target is sputtered, the sputtering power is 30~50W, the sputtering deposition rate is 1~2 nm / min, and after the ferromagnetic metal film is grown, it is removed from the mold and flattened naturally.

6. The method according to claim 5, characterized in that In step (1), the thickness of the flexible bendable substrate is 10-30 μm, and the radius of curvature of the non-magnetic metal mold is 10-40 mm.

7. The method according to claim 5, characterized in that In step (2), the thickness of the metal buffer layer is 3-10 nm.

8. The method according to claim 5, characterized in that In step (3), the thickness of the ferromagnetic metal film is 3 to 50 nm.

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