A method for preparing hopfion topological magnetic structure based on electron beam irradiation damage

Abstract

The present application relates to the technical field of spintronics and nanomagnetic structure preparation. The existing three-dimensional topological magnetic structure preparation method depends on specific crystal symmetry or complex growth conditions, and it is difficult to realize the controllable writing and in-situ observation of local structure. The present application discloses a method for preparing hopfion topological magnetic structure based on electron beam irradiation damage, which prepares a semiconductor or insulator substrate into a thin sheet sample and irradiates the target area using a focused electron beam. By adjusting the beam current and irradiation time to control the cumulative electron dose, local amorphization and defects are induced, and the spin texture is guided to close along a specific spatial winding mode, thereby forming a hopfion structure with a predetermined topological charge. The present application converts electron beam irradiation damage into a controllable topological magnetic structure writing method, realizes in-situ preparation and characterization on the same platform, simplifies the preparation process, and can program the position and morphology of the magnetic structure, providing a new technical approach for the integration of topological spintronic devices.

Description

Technical Field

[0001] This invention relates to the field of spintronics and nanomagnetic structure fabrication technology, and in particular to a method for fabricating Hopfon topological magnetic structures based on electron beam irradiation damage. Background Technology

[0002] Three-dimensional topological magnetic structures possess nontrivial spatial spin configurations, holding significant application potential in high-density information storage, low-power logic devices, and topological spintronics. Hopfons are three-dimensional magnetic solitons with closed-loop or toroidal topological morphologies. Their topological properties can be characterized by the entanglement relationships of closed-loop spin textures, exhibiting higher stability and richer information encoding capabilities compared to two-dimensional skyrmions.

[0003] The formation of existing three-dimensional topological magnetic structures typically depends on specific crystal symmetries, external field paths, interfacial interactions, or complex material growth conditions. For materials with different conductivity types, such as metals, semiconductors, and insulators, carrier concentration, defect-induced local magnetic moments, local inversion symmetry breaking, and the spatial distribution of disordered / amorphous regions all affect Dzyaloshinskii-Moriya interactions, exchange interactions, and magnetic anisotropy, thus determining the formation paths of different topological magnetic structures. Currently, a universal and controllable method for selectively preparing Hopfons on substrates with different conductivity types is lacking.

[0004] Electron beams possess nanoscale spatial localization capabilities and dose controllability in transmission electron microscopy. Traditionally, electron beam irradiation has been considered a damage source in material characterization processes and should be avoided as much as possible. However, if electron beam-induced local disorder, defects, and amorphization processes can be used as controllable modulation methods, it is hoped that in-situ writing, real-time observation, and parameter optimization of three-dimensional topological magnetic structures can be achieved on the same platform. Therefore, there is an urgent need for a technique that can selectively prepare Hopfons in materials with different conductivity types using electron beam irradiation damage. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing Hopfons topological magnetic structures based on electron beam irradiation damage. This method overcomes the limitations of traditional material growth and interface engineering on substrate materials, and utilizes the irradiation damage effect of a focused electron beam in transmission electron microscopy to achieve controllable preparation and in-situ characterization of three-dimensional Hopfons topological magnetic structures in semiconductor or insulating materials.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing Hopf subtopological magnetic structures based on electron beam irradiation damage includes: irradiating a target region of a substrate material with a focused electron beam to induce the generation of localized amorphous regions and defects through electron beam induction; By adjusting the beam current intensity and irradiation duration of the focused electron beam, the cumulative electron dose is controlled, causing the local amorphous region and lattice defects to induce the breaking of local magnetic moments and inversion symmetry. This drives the spin texture to close along a predetermined spatial winding pattern under the combined action of exchange interaction, Dzyaloshinskii-Moriya interaction, and magnetic anisotropy, thereby forming a Hopf sub-three-dimensional topological magnetic structure with non-zero Hopf invariants in the substrate material. The substrate material is either a semiconductor material or an insulating material.

[0007] Furthermore, the substrate material is titanium dioxide, single-crystal silicon, or gallium arsenide.

[0008] Furthermore, the cumulative electron dose ranges from (3.5 to 5.0) × 10²³ e⁻ / cm².

[0009] Furthermore, with a beam spot diameter of 50 nm, the beam current is 4 nA to 5 nA, and the irradiation duration is 4 min to 5 min.

[0010] By using a focused electron beam to locally irradiate a target region on a semiconductor or insulator substrate, localized amorphous regions, defects, and regions with broken inversion symmetry are induced within the material, causing the electronic states to transition from extended states to localized states. When the spatial propagation degree of freedom of electrons is suppressed, the system mainly retains the spin degree of freedom. The spins rearrange under the combined effects of exchange interactions, Dzyaloshinskii-Moriya interactions, and magnetic anisotropy, evolving towards the lowest free energy state.

[0011] The electronic localization process can be represented as: ,in, Let ξ be the electron transition intensity, and ξ be the localization length. When electron localization is enhanced... The size of the electron is reduced, thus restricting its spatial movement.

[0012] Due to the spatially inhomogeneous effective field and topological constraints induced by localized defects, the spin texture gradually forms a closed, entangled structure, and further undergoes topological connections along the electron beam scanning path, ultimately yielding a stable Hopf subchain structure. The topological properties of the formed structure are characterized by Hopf invariants: ,in ≠0 indicates the formation of a Hopf subchain structure with non-trivial topological features.

[0013] Compared with the prior art, the present invention has the following beneficial effects: (1) Because this invention employs a technique of inducing localized amorphization and defects in semiconductor or insulator substrates by focused electron beam irradiation, it enables the direct fabrication of Hopfons three-dimensional topological magnetic structures in non-magnetic materials. Compared with existing methods that rely on specific crystal symmetry materials or complex multilayer film interface engineering, this invention overcomes the limitations of material systems. It utilizes electron beam damage, a process usually considered a negative effect, to transform it into a positive driving force for constructing topological magnetic structures, greatly broadening the range of materials to be selected for topological magnetic structures and reducing the difficulty and cost of material preparation.

[0014] (2) By setting the cumulative electron dose range, the efficient and stable preparation of Hopfons structure was achieved. The dose range can precisely balance the relationship between defect induction and structural integrity: sufficient electron dose can induce the generation of high-density local magnetic moments and inversion symmetry breaking, providing an energy potential well for the formation of Hopfons; at the same time, it avoids material ablation or structural collapse caused by excessive irradiation, thereby ensuring the topological stability of the magnetic structure.

[0015] (3) Compared with the random nucleation positions, uncontrollable morphology, or limitations imposed by the material lattice structure of the magnetic structure in the prior art, the present invention controls the distribution of local defects and the direction of spin rearrangement by pre-set electron beam scanning, thereby guiding the spin texture to close and entangle along a predetermined spatial path to form a Hopf submagnetic structure with controllable topological features and spatial configuration, providing a new technical means for the programmable design of topological magnetic structures in logic devices and information storage devices.

[0016] (4) Since the present invention prepares Hopfons in a semiconductor or insulator substrate, it takes advantage of the low free carrier concentration of such materials, which reduces the scattering and interference of conduction electrons on the magnetic structure, resulting in a Hopfon structure with better thermal stability and topological protection. This characteristic has important physical significance and application value for developing low-power, high-stability next-generation spintronic memory devices. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the toroidal magnetic domains and their topological magnetic structure in the electron beam-induced disordered region of the present invention.

[0018] Figure 2 This is a schematic diagram illustrating the preparation of Hopfons three-dimensional topological magnetic structures in titanium dioxide substrates, Si substrates, and GaAs substrates according to the present invention.

[0019] Figure 3 This is a schematic diagram illustrating the structural evolution of titanium dioxide substrate, Si substrate, and GaAs substrate materials under varying magnetic conditions according to the present invention. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0021] Example 1:

[0022] This invention provides a method for preparing Hopfons topological magnetic structures based on electron beam irradiation damage. Utilizing the irradiation damage effect of a focused electron beam in transmission electron microscopy, localized amorphous regions and defects are induced in semiconductor or insulator substrates. By precisely controlling the electron beam current intensity and irradiation time, the cumulative electron dose is modulated, thereby writing three-dimensional magnetic structures with specific topological charges into non-magnetic materials. This method overcomes the dependence of traditional topological magnetic structure preparation on materials with specific crystal symmetry, achieving in-situ preparation and characterization on the same platform.

[0023] This embodiment uses TiO2, single-crystal Si, and GaAs as semiconductor or insulator substrate materials to illustrate a method for preparing Hopfons using electron beam irradiation damage. The three substrate materials are prepared into transmission electron microscope thin-film samples with a thickness of approximately 80–100 nm after mechanical thinning, ion thinning, or focused ion beam thinning treatment.

[0024] Electron beam irradiation was performed using a FEI Titan Themis 300 transmission electron microscope at an accelerating voltage of 300 kV, a beam spot diameter of approximately 50 nm, a beam current of 5 nA, and an irradiation duration of 5 min. During irradiation, the thin-film sample was placed in a near-zero external magnetic field environment compensated by a Helmholtz coil. After irradiation, the magnetic structure was characterized using Lorentz transmission electron microscopy and intensity transport equation reconstruction.

[0025] After GaAs is irradiated with an electron beam, as Figure 1 As shown in the figure, a locally disordered region is formed at the location indicated by the red circle. This region can be regarded as a localized amorphization and defect-rich area induced by the electron beam. Within this disordered region, a significant toroidal magnetic contrast is further observed, indicating that electron beam irradiation not only alters the local microstructure but also induces an observable localized magnetic response. TIE reconstruction results show that this structure corresponds to a closed rotating toroidal magnetic domain: the in-plane magnetic induction direction continuously changes along the circumference and forms a closed rotation, exhibiting typical characteristics of a flux-closed vortex toroidal magnetic domain. From a magnetic structural perspective, this magnetic domain can be simply described as a closed toroidal topological magnetic structure; in simulation, it can be approximated as a toroidal three-dimensional spin texture composed of a closed skyrmion string, i.e., a hopfion-like toroidal magnetic structure. This result is consistent with the proposed technical approach of "electron beam inducing localized amorphization and defects, and further inducing localized magnetic moments and inversion symmetry breaking, thereby driving the spin texture closure to form a topological magnetic structure."

[0026] Multi-angle closed projection in semiconductor or insulator substrates, structural stability under varying magnetic fields, and cross-material consistency together constitute the experimental criteria for Hopfons formation.

[0027] like Figure 2 As shown, the structure exhibits typical Hopfion three-dimensional topological magnetic texture features. The presence of closed loop or elliptical magnetic contrast in the image indicates that the magnetic structure is spatially locally closed, more closely resembling a three-dimensional topological loop structure composed of closed skyrmion strings. The morphologies in different substrates all share the common characteristics of locally closed, continuously rotating, and topologically entangled magnetic moment distributions.

[0028] Figure 3 This reflects the tunability and stability of the Hopfion substructure's three-dimensional topological magnetic structure under an applied magnetic field. Under varying magnetic conditions, the Hopfion magnetic structures in different substrates all exhibited stable morphological evolution characteristics. With changes in the applied magnetic field, the morphology of the magnetic structure maintained its overall closed magnetic structure. These results indicate that titanium dioxide, Si, and GaAs substrates can provide a certain pinning effect for the Hopfion substructure, enabling it to maintain high stability in varying magnetic environments.

[0029] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing Hopf subtopological magnetic structures based on electron beam irradiation damage, characterized in that, include: A focused electron beam is used to irradiate a target area of ​​a substrate material, thereby inducing the generation of localized amorphous regions and defects through electron beam induction. By adjusting the beam current intensity and irradiation duration of the focused electron beam, the cumulative electron dose is controlled, causing the local amorphous region and lattice defects to induce the breaking of local magnetic moments and inversion symmetry. This drives the spin texture to close along a predetermined spatial winding pattern under the combined action of exchange interaction, Dzyaloshinskii-Moriya interaction, and magnetic anisotropy, thereby forming a Hopf sub-three-dimensional topological magnetic structure with non-zero Hopf invariants in the substrate material. The substrate material is either a semiconductor material or an insulating material.

2. The method for preparing Hopf subtopological magnetic structures based on electron beam irradiation damage according to claim 1, characterized in that, The substrate material is titanium dioxide, single-crystal silicon, or gallium arsenide.

3. The method for preparing Hopf subtopological magnetic structures based on electron beam irradiation damage according to claim 1, characterized in that, The cumulative electron dose ranges from (3.5 to 5.0) × 10⁻⁶. 23 e⁻ / cm 2 .

4. The method for preparing Hopf subtopological magnetic structures based on electron beam irradiation damage according to claim 1, characterized in that, With a beam diameter of 50 nm, the beam current is 4 nA to 5 nA, and the irradiation duration is 4 min to 5 min.

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