A two-dimensional Janus structure construction method based on atomic layer removal and a magnetic regulation method

Abstract

The application relates to the technical field of two-dimensional material design and application, and particularly relates to a two-dimensional Janus structure construction method and magnetic regulation method based on atomic layer removal. In view of the problems of complex structure design path and high coupling degree in the regulation process in the existing two-dimensional Janus structure construction process, the method takes the MA2Z4 two-dimensional material with a multilayer atomic stacking structure as the basis, removes the atomic layer on one side of the surface of the material, breaks the out-of-plane symmetry, thereby constructs the Janus material with an asymmetric structure, and carries out first principle calculation optimization and electronic property analysis on the obtained structure. Researches show that in the VGe2N4 system, the Janus structure constructed by the method can cause the change of the local crystal field environment of the transition metal atom and the enhancement of the orbital hybridization, so that the spin polarization of the system is weakened and non-magnetic properties are shown. The method has clear structure regulation path and high repeatability, and can be used for guiding the design of two-dimensional Janus materials and the application of the two-dimensional Janus materials in spin electronic devices.

Description

Technical Field

[0001] This invention relates to the field of two-dimensional material design and application technology, specifically to a method for constructing two-dimensional Janus structures and a method for magnetic control based on atomic layer removal. Background Technology

[0002] Since the successful exfoliation of graphene, two-dimensional (2D) materials have sparked a research boom in condensed matter physics, materials science, and nanoelectronics due to their extreme physical thickness and unique quantum confinement effect. Subsequently, a series of 2D materials, such as transition metal chalcogenides (TMDs), black phosphorus, and hexagonal boron nitride (h-BN), have been discovered, greatly enriching the family of 2D materials and demonstrating enormous application potential in flexible electronic devices, photodetectors, and energy storage.

[0003] Among numerous physical properties, the intrinsic magnetism of two-dimensional materials plays an irreplaceable foundational role in realizing next-generation ultra-compact, low-power, high-speed spintronic devices (such as spin valves, magnetic tunnel junctions, and spin field-effect transistors). However, for a long time, according to the famous Mermin-Wagner theorem, under the thermodynamic limit, the isotropic two-dimensional Heisenberg model could not maintain long-range magnetic order at finite temperatures due to strong thermal fluctuations. This limited early research on two-dimensional materials to non-magnetic systems. Until recent years, the experimental synthesis of two-dimensional van der Waals (vdW) ferromagnets such as CrI3 and Cr2Ge2Te6 has confirmed that magnetocrystalline anisotropy can effectively resist thermal fluctuations, thereby stabilizing intrinsic long-range magnetic order under the two-dimensional limit. This breakthrough officially opened the prelude to research on two-dimensional spintronics.

[0004] While the discovery of two-dimensional intrinsically magnetic materials is exciting, the known candidate systems remain very limited. Therefore, how to introduce, modulate, and precisely control magnetism in emerging two-dimensional materials that possess both high stability and excellent semiconductor properties has become a key scientific problem that urgently needs to be solved in the fields of condensed matter physics and materials computation. MA2Z4-type two-dimensional materials, as a newly emerging class of layered materials in recent years, possess a stable seven-layer sandwich structure and excellent electronic properties. However, due to the high symmetry of their intrinsic structure, their magnetic modulation is still somewhat limited.

[0005] To endow or modulate the magnetic properties of these highly promising two-dimensional materials, traditional research approaches have mainly focused on the following methods:

[0006] (1) Chemical element doping / substitution: This involves introducing transition metal impurities with unpaired d or f electrons. However, this method is extremely difficult to precisely control the doping concentration and distribution in experimental operations, and impurity atoms are prone to agglomeration, leading to local structural distortion and enhanced carrier scattering in the material, which severely degrades its intrinsic carrier mobility.

[0007] (2) Defect engineering: Creating vacancies or gap defects to induce local magnetic moments. However, the randomness of defects makes the repeatability of the device extremely poor.

[0008] (3) External control field: Apply external strain, high-intensity electric field or heterojunction proximity effect. These methods often require extremely complex micro-nano fabrication processes and have extremely narrow control windows, making them difficult to integrate on a large scale in practical applications.

[0009] In recent years, Janus-structured two-dimensional materials have attracted widespread attention due to their breaking of out-of-plane inversion symmetry. For example, Janus transition metal chalcogenides (such as MoSSe) not only exhibit a significant Rashba spin-orbit coupling (SOC) effect due to the difference in electronegativity between the upper and lower surface atoms, but also generate a built-in electric field perpendicular to the basal plane. This structural asymmetry provides entirely new degrees of freedom for significantly reshaping the electronic band structure and valley spin degrees of freedom of the material. For the seven-layer MA2Z4 system, if its out-of-plane structural symmetry can be broken, placing the central M atom in an asymmetric local crystal field, it will drastically alter the degeneracy of d orbitals and the electron occupancy rules, thereby triggering an unprecedented magnetic phase transition.

[0010] In summary, there is an urgent need in existing technologies for a simpler, more theoretically predictable, and chemically-avoidable control method to systematically study and regulate the magnetic evolution of the MA2Z4 class of two-dimensional magnetic materials. This invention creatively proposes a "subtraction" physical model—using computational simulation to directly peel off the ZA passivation layer on one side of a seven-layer structure, thereby naturally exposing an asymmetric five-layer environment. This not only provides a universal method for achieving magnetic switching or excitation without doping, but also offers rigorous theoretical guidance and structural screening criteria for future experimental fabrication of low-dimensional magnetic devices via plasma etching or mechanical / chemical selective exfoliation. Summary of the Invention

[0011] The purpose of this invention is to solve the problem of difficult magnetic control caused by the complex structural design path and high coupling degree of the control process in the construction of existing two-dimensional Janus structures.

[0012] To achieve the above objectives, the present invention employs the following technical means:

[0013] This invention provides a method for constructing a two-dimensional Janus structure based on selective removal of atomic layers, comprising the following steps:

[0014] S1: Construct an initial structural model of a two-dimensional material of the MA2Z4 class with a seven-layer atomic stack configuration [ZAZMZAZ], where the transition metal M is a vanadium (V) atom;

[0015] S2: By selectively removing the ZA atomic layer on one side of the surface of the two-dimensional material, a five-layer Janus structure with out-of-plane inversion symmetry broken is constructed.

[0016] S3: Introduce a vacuum layer of not less than 15 Å in a direction perpendicular to the plane of the Janus configuration material to eliminate the influence of periodic boundary conditions on the out-of-plane direction of the two-dimensional material;

[0017] S4: The plane wave method based on density functional theory is used to calculate the system. The electron exchange-correlation interaction is treated by the generalized gradient approximation (GGA-PBE) functional, and the electron-ion interaction is described by the projected fused wave (PAW) method. The GGA+U method is introduced to correct the strong correlation effect of vanadium (V) atoms, and spin polarization calculation is enabled.

[0018] S5: Set the plane wave cutoff energy to be no less than 550 eV and the Brillouin zone K-point grid density to be no less than 13×13×1. Perform full relaxation on the Janus configuration until the total energy of the system and the atomic forces reach the convergence criterion to obtain the geometrically optimized Janus structure.

[0019] S6: Perform band structure calculation and projected density of states calculation on the geometrically optimized Janus configuration. By extracting and analyzing the occupied d orbitals and spin polarization characteristics of vanadium (V) atoms, the magnetic state can be evaluated and controlled.

[0020] S7: The kinetic and thermodynamic stability of the Janus configuration was verified using phonon spectrum calculations and ab initio molecular dynamics simulations.

[0021] The above scheme, specifically the verification of the kinetic and thermodynamic stability of the Janus configuration, includes:

[0022] Dynamic stability verification: The phonon dispersion curve of the system is calculated using density functional perturbation theory or finite displacement method. When the frequency values ​​of the phonon dispersion curve are all greater than or equal to zero in the entire Brillouin zone, it is determined that the phonon spectrum has no imaginary frequency, thus confirming that the Janus configuration has dynamic stability.

[0023] Thermodynamic stability verification: Ab initio molecular dynamics simulations were performed at 300 K using a canonical ensemble, with a total simulation time of no less than 5 ps. During this simulation, if the total energy and temperature of the system remained within the range of thermodynamic fluctuations, and the chemical bonds between the atoms constituting the Janus configuration did not break compared to the initial configuration, it was determined that the structure had not been reconstructed, confirming that the Janus configuration had thermodynamic stability.

[0024] In the above scheme, the controllable regulation of the magnetic state is achieved by changing the local crystal field environment of vanadium (V) atoms to enhance the hybridization between the d orbitals of vanadium (V) atoms and the p orbitals of neighboring nonmetal atoms.

[0025] In the above scheme, by introducing out-of-plane inversion symmetry breaking, the local symmetry of vanadium (V) atoms is reduced and the V–N bond length is contracted, which leads to weakening of exchange splitting and the spin-up and spin-down states near the Fermi level tend to be symmetrical, and the total magnetic moment of the system is reduced to 0 μB.

[0026] In the above scheme, the control of the magnetic state includes realizing the controllable transition of the system's magnetism from a ferromagnetic state to a non-magnetic state.

[0027] In the above scheme, the MA2Z4 type two-dimensional material includes one or more of VGe2N4, VSi2N4, TiGe2N4, and CrGe2N4.

[0028] This invention also provides a method for magnetic control of two-dimensional materials based on atomic layer selective removal. For the optimized Janus structure obtained using the above-mentioned two-dimensional Janus structure construction method, the implementation logic and verification steps for magnetic state control specifically include:

[0029] (1) After completing the static self-consistent calculation of the Janus structure, start the projection calculation, use the projection operator to project the wave function onto the spherical harmonic function of each atom, and extract the projected density of states data of the d orbital of vanadium (V) atom and the p orbital of adjacent nonmetal atom and the spin occupancy of the suborbital.

[0030] (2) Based on the extracted projected density of states data, the crystal field changes before and after layer removal were compared, and it was confirmed that the local crystal field of vanadium (V) atoms decreased from D3h to C3v symmetry, and the VN bond length shortened, resulting in enhanced hybridization between the d orbitals of vanadium (V) atoms and the p orbitals of nonmetal atoms.

[0031] (3) By comparing the electron state density distributions of spin-up and spin-down, when the vanadium (V) atom When the orbital spin asymmetry is significantly weakened, the spin-up and spin-down states near the Fermi level tend to be symmetrical, and the total magnetic moment of the system drops to 0 μB, it is determined that the system has completed the modulation transition from the ferromagnetic state to the nonmagnetic state.

[0032] Because the present invention employs the above-mentioned technical means, it has the following beneficial effects:

[0033] 1. The method of constructing Janus structures through atomic layer removal can effectively control the electronic structure and magnetic behavior of two-dimensional materials. Taking the VGe2N4 system as an example, in the original structure, the 3d orbitals of the V atom exhibit significant spin splitting near the Fermi level, making the system ferromagnetic. However, after constructing the Janus structure, due to the breaking of out-of-plane symmetry and the shortening of the V–N bond length, the hybridization between the V-3d orbitals and the N-2p orbitals is significantly enhanced. At the same time, orbital occupancy is rearranged, which weakens the original spin asymmetry. The spin-up and spin-down electronic states tend to be symmetrical, thus causing the system to lose its magnetism.

[0034] 2. Compared with existing technologies, this invention does not require the introduction of impurity doping or external control conditions. Effective switching of magnetism can be achieved through simple structural manipulation, offering advantages such as ease of operation, low cost, and good stability. It holds significant application potential in the design of two-dimensional spintronic devices and the development of functional materials. The structure obtained by this method can be used to guide the experimental preparation of two-dimensional materials, including but not limited to selective layer removal during plasma etching, molecular beam epitaxy, or chemical vapor deposition. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the atomic configuration of a seven-layer VGe2N4 monolayer structure in an embodiment of the present invention; the diagram is used to illustrate the out-of-plane inversion symmetry (D3h group) and complete layered crystallographic features of the initial structure;

[0036] Figure 2 This is a schematic diagram of the five-layer Janus-VGeN3 structure formed after removing the top N–Ge atomic layer in an embodiment of the present invention. This diagram is used to illustrate the out-of-plane inversion symmetry breaking (reduced to C3v group) introduced by the atomic layer removal operation, and the resulting contraction of interlayer distance and bond length.

[0037] Figure 3 The diagram shows the band structure and density of states of the seven-layer VGe2N4 structure in this embodiment of the invention (left diagram is the electronic band structure, right diagram is the density of states distribution). This diagram aims to demonstrate that the original structure has significant spin band splitting and electron occupancy asymmetry near the Fermi level, thus establishing its initial ferromagnetic state basis.

[0038] Figure 4The diagram shows the band structure and density of states of the Janus-VGeN3 structure in this embodiment of the invention (left diagram is the electronic band structure, right diagram is the density of states). This diagram aims to demonstrate that after constructing the Janus structure, the spin-up and spin-down electronic states near the Fermi level tend to completely coincide, which intuitively reflects the successful control of the total magnetic moment of the system to zero and the non-magnetic state.

[0039] Figure 5 This is a partial orbital projected density of states (PDOS) diagram of the 3d orbitals of vanadium (V) atoms in the VGe2N4 structure of this invention; this diagram further reveals that before modulation, the local magnetic moment mainly originates from... Strong spin polarization asymmetry occupies specific orbitals;

[0040] Figure 6 This is a partial orbital projection density of states (PDOS) diagram of the 3d orbitals of vanadium (V) atoms in the Janus-VGeN3 structure in this embodiment of the invention. The diagram aims to reveal the intrinsic microscopic mechanism of magnetic quenching, namely, the symmetry breaking leads to the rehybridization and charge transfer of the d orbitals of vanadium (V) atoms, which greatly weakens the original spin asymmetric occupation. Detailed Implementation

[0041] The embodiments of the present invention will be described in detail below. Although the present invention will be described and illustrated in conjunction with some specific embodiments, it should be noted that the present invention is not limited to these embodiments. On the contrary, any modifications or equivalent substitutions made to the present invention should be covered within the scope of the claims of the present invention.

[0042] To address the aforementioned technical problems, this invention discloses a simulation design method for constructing a two-dimensional Janus structure and achieving magnetic modulation based on selective atomic layer removal. Using MA2Z4-type two-dimensional materials with a seven-layer sandwich structure as a foundation, out-of-plane symmetry is broken by removing the top atomic layer, thereby altering the local crystal field environment and orbital coupling of the central transition metal atoms, and achieving controllable modulation of the material's magnetism. This method requires no doping or external field, and has advantages such as simple structure, high repeatability, and wide applicability.

[0043] Furthermore, to better illustrate the present invention, numerous specific details are provided in the following detailed embodiments.

[0044] This invention provides a simulation design method for two-dimensional Janus structure materials, comprising the following steps:

[0045] S1: Using structural modeling software, a preliminary single-layer structure of MA2Z4 two-dimensional material was constructed to obtain a two-dimensional material model with a seven-layer atomic stack configuration [ZAZMZAZ].

[0046] S2: Based on the seven-layer structure, the ZA atomic layer on one side surface is selectively removed to construct a five-layer Janus configuration with out-of-plane inversion symmetry broken.

[0047] S3: Import the above structure into the calculation software and introduce a vacuum layer of more than 15 Å in the direction perpendicular to the material plane to eliminate the influence of periodic boundary conditions on the interaction between the upper and lower layers.

[0048] S4: The system is described using a plane-wave method based on density functional theory. Electron exchange-correlation interactions are handled using the generalized gradient approximation (GGA-PBE), and electron-ion interactions are described using the projected fused wave (PAW) method. To address the strong correlation effects of transition metal atoms, the GGA+U method is introduced for correction. By comparing and analyzing the electronic structures at different U values, an effective U value that reasonably describes the electronic properties of the system is selected. For example, for V atoms, the U... eff The value is usually selected between 2.0 and 4.0 eV.

[0049] S5: Set appropriate plane wave cutoff energy and Brillouin zone K-point grid, fully relax the structure, and make the total energy of the system and the atomic forces reach the convergence standard;

[0050] S6: Perform electronic structure analysis on the optimized structure, including calculation of band structure and projected density of states, to determine the magnetic changes caused by symmetry breaking in the system.

[0051] S7: Phonon spectrum calculations and ab initio molecular dynamics simulations were used to verify the structural stability. The molecular dynamics simulations were performed at 300 K to evaluate the thermal stability of the system.

[0052] Furthermore, all geometric optimization and electronic structure calculation steps in this invention are recommended to be performed using mature commercial or open-source software packages based on density functional theory (DFT), such as the Vienna Ab initio Simulation Package (VASP, version 5.4.4 or higher recommended). To ensure the rigor of the screening results, the following core parameters must be set according to standard settings when performing steps S3 and S4:

[0053] (a) Pseudopotential and functional selection: The electron-ion core interaction is described using the Projected Augmented Wave (PAW) method. The exchange-correlation between electrons is described using the Perdew-Burke-Ernzerhof (PBE) functional under the generalized gradient approximation (GGA).

[0054] (b) Strong Correlation Correction (GGA+U): Considering that transition metals M (such as V, Ti, Cr, etc.) have 3d or 4d electrons with strong localization characteristics, standard DFT often severely underestimates their electronic correlation effects, leading to failure in magnetic ground state prediction. Therefore, LDAU = .TRUE. must be introduced in the INCAR setup file, and a reasonably tested Hubbard U value (i.e., effective parameter U) must be applied to the d orbitals of M atoms. eff = U - J). The value of U should be determined by comparing the band gap and magnetic moment convergence under different parameters (for example, for the V system, U can be taken as U - J). eff Tested in the range of 2.0 eV to 4.0 eV.

[0055] (c) Cut-off energy and K-point mesh: The kinetic cut-off energy (ENCUT) of the expanded plane wave basis set should be set to no less than 550 eV to ensure high accuracy of force and total energy. The Brillouin zone integral uses the Monkhorst-Pack method to generate a k-point mesh centered at the Gamma point. The mesh density should be no less than 13 × 13 × 1 for structural relaxation, static calculation, and density of states calculation.

[0056] (d) Convergence Criteria and Spin Polarization: To calculate magnetic properties, spin polarization calculations must be enabled (ISPIN = 2), and a reasonable initial magnetic moment conjecture (MAGMOM parameter) must be assigned at the beginning of the calculation. The energy convergence threshold for structural relaxation (ISIF = 3 for cell optimization, then ISIF = 2 for atomic coordinate optimization) must reach 10. -6 eV / atom, with the interatomic residual force convergence criterion strictly limited to 0.01 eV / Å.

[0057] In the Projected Density of States (PDOS) and visualization analysis workflow, steps S4 and S5 are crucial for obtaining magnetic conclusions through in-depth analysis of the electronic structure. The standard procedure for obtaining high-precision PDOS is as follows: After completing static self-consistent calculations, projective calculations are enabled in non-self-consistent calculations (setting LORBIT = 11 to project the wavefunction onto the spherical harmonics of each atom using the PAW projection operator). After the calculations are complete, a post-processing script (such as VASPKOT) is used to extract the energy distribution data for each atom (especially M and Z atoms) corresponding to the s, p, and d orbitals from the DOSCAR file. The data is then plotted using graphing software (such as Origin) into two curves: spin-up (usually assigned positive values) and spin-down (usually assigned negative values).

[0058] The VGe2N4 system is used as a specific example for illustration. In the original seven-layer structure, the V atom is in a D3h symmetric crystal field environment, its 3d orbitals are split, and it exhibits a significant spin asymmetry distribution near the Fermi level. PDOS results show that the V-3d state dominates near the Fermi level and exhibits significant spin splitting. The unpaired electrons generate a magnetic moment of about 1 μB, making the system ferromagnetic.

[0059] When the Janus-VGeN3 structure was constructed by removing the top N–Ge atomic layer, the out-of-plane symmetry of the system was broken, the local crystal field decreased from D3h to C3v, and the V–N bond length shortened from approximately 2.068 Å to approximately 1.928 Å. This structural change led to enhanced hybridization between the V-3d and N-2p orbitals and caused a redistribution of d orbital occupancy.

[0060] Orbital occupancy analysis shows that in the Janus structure, the difference in the number of spin-up and spin-down electrons in the 3d orbitals of the V atom is significantly reduced, and the electrons that were originally in the dz orbitals are now more concentrated in the V atom. 2 The spin asymmetric occupation of orbitals is weakened, and electrons are redistributed to other d orbitals. Meanwhile, PDOS results show that spin-up and spin-down states near the Fermi level tend to be symmetrical, indicating a significant reduction in exchange splitting.

[0061] Due to the disappearance of spin polarization, the total magnetic moment of the system drops to zero, exhibiting a non-magnetic state. These results demonstrate that the occupation and spin distribution of transition metal d orbitals can be effectively controlled through simple atomic layer removal operations, thereby achieving controllable adjustment of the magnetism of two-dimensional materials.

[0062] Furthermore, no imaginary frequencies were observed in the phonon spectrum calculations, indicating that the structure is dynamically stable. During molecular dynamics simulations at 300 K, the structure did not undergo significant reconstruction, further demonstrating its good thermal stability.

[0063] In summary, this invention achieves controllable adjustment of the magnetism of two-dimensional materials through structural layer subtraction. The method is simple and has good stability and repeatability.

Claims

1. A method for constructing a two-dimensional Janus structure based on atomic layer selective removal, characterized in that, Includes the following steps: S1: Construct an initial structural model of a two-dimensional material of the MA2Z4 class with a seven-layer atomic stacked configuration [ZAZMZAZ], where M is a transition metal element, A is a main group element, and Z is a non-metal element; S2: By selectively removing the ZA atomic layer on one side of the surface of the two-dimensional material, a five-layer Janus structure with out-of-plane inversion symmetry broken is constructed. S3: The obtained Janus configuration is geometrically optimized and its electronic structure is calculated using the plane wave method based on density functional theory. A vacuum layer of not less than 15 Å is introduced in the direction perpendicular to the material plane to obtain the optimized Janus structure.

2. The method according to claim 1, characterized in that: The geometric optimization in step 3 includes setting the plane wave cutoff energy to be no less than 550 eV and the grid density of the K-point in the Brillouin zone to be no less than 13×13×1.

3. The method according to claim 1, characterized in that: The electronic structure calculation in step 3 includes band structure calculation and projected density of states calculation.

4. The method according to claim 1, characterized in that: After performing step S3, the dynamic stability of the obtained Janus structure is verified.

5. The method according to claim 4, characterized in that: The stability verification includes: calculating the phonon dispersion curve of the system using density functional perturbation theory or the finite displacement method; when the frequency values ​​of the phonon dispersion curve are all greater than or equal to zero in the entire Brillouin zone, it is determined that the phonon spectrum has no imaginary frequencies, confirming that the Janus configuration has dynamic stability; performing ab initio molecular dynamics simulations using a canonical ensemble at 300 K, with a total simulation time of not less than 5 ps, during which the total energy and temperature of the system remain within the range of thermodynamic fluctuations, and compared with the initial configuration, the chemical bond relationships between the transition metal atoms constituting the Janus configuration and the adjacent non-metal atoms have not been broken, it is determined that the structure has not been reconstructed, confirming that the Janus configuration has thermodynamic stability.

6. The method according to claim 1, characterized in that: The MA2Z4 type two-dimensional materials include one or more of VGe2N4, VSi2N4, TiGe2N4, and CrGe2N4.

7. A method for controlling the magnetic properties of two-dimensional materials based on atomic layer selective removal, characterized in that, The method described herein uses the construction method described in any one of claims 1-6 to obtain an optimized Janus structure. The implementation logic and verification steps for the magnetic state modulation include: after completing the static self-consistent calculation of the Janus structure, starting the projection calculation, using the projection operator to project the wave function onto the spherical harmonic function of each atom, and extracting the projected density of states (PDOS) data of the d orbitals of the transition metal atom and the spin occupancy of the adjacent non-metal atom p orbitals; based on the extracted PDOS data, comparing the changes in the crystal field before and after layer removal; confirming that the local crystal field of the transition metal atom decreases from D3h to C3v symmetry, and that the bond length between the transition metal and non-metal atoms shortens, resulting in enhanced hybridization between the transition metal d orbitals and the non-metal p orbitals; by comparing the electronic state density distributions of spin-up and spin-down, when the spin asymmetric occupancy of the dz² orbitals of the transition metal atom is significantly weakened, the spin-up and spin-down states near the Fermi level tend to be symmetrical, and the total magnetic moment of the system decreases to 0 μB, it is determined that the system has completed the modulation transition from the ferromagnetic state to the non-magnetic state.

8. The method according to claim 7, characterized in that: The controllable regulation of the magnetic state is achieved by altering the local crystal field environment of the transition metal atoms, thereby enhancing the hybridization between the d orbitals of the transition metal atoms and the p orbitals of neighboring non-metal atoms.

9. The method according to claim 7, characterized in that: By introducing out-of-plane inversion symmetry breaking, the local symmetry of transition metal atoms is reduced and the ZM bond length is contracted, thereby weakening exchange splitting and enhancing electron delocalization.

10. The method according to claim 7, characterized in that: The control of the magnetic state includes achieving a controllable transition of the system's magnetism from a ferromagnetic state to a nonmagnetic state.

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