Two-dimensional multiferroic material with multiple polarization states and preparation method thereof

Abstract

The invention discloses a two-dimensional multiferroic material with multiple polarization states and a preparation method thereof. According to the two-dimensional multiferroic material, magnetic elements are introduced into a two-dimensional ferroelectric material CuInP2S6 with an intrinsic sextuple polarization state, so that the two-dimensional multiferroic material has superparamagnetism while keeping the sextuple polarization state. The two-dimensional multiferroic material has potential application value in high-density data storage and multifunctional transistors.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of two-dimensional materials, and particularly relates to a two-dimensional multiferroic material with multiple polarization states and a preparation method thereof. BACKGROUND

[0002] With the rapid development of information technology, the demand for data storage is growing exponentially, and traditional storage technology is gradually facing the bottleneck of density, speed and energy consumption. In order to break through these limitations, researchers have begun to explore new storage materials and technologies, mainly in two ways: one is to optimize the manufacturing process to continuously reduce the size of the unit storage unit to increase the integration; the second is to increase the storage density of each storage unit. For the first scheme, as the process node shrinks, the complexity and cost of photolithography technology increase significantly, and the manufacturing yield decreases, making the size gradually approach the physical limit. Therefore, non-volatile multistate memory can store multiple bits in a single unit, which can greatly increase the storage density without shrinking the size of the storage unit, and has gradually become a research hotspot.

[0003] Two-dimensional multiferroic materials refer to materials with two or more long-range ferroelectricity, of which the most widely studied is the magnetoelectric multiferroic material with both ferroelectricity and magnetism. Due to the multiple degrees of freedom, it is a good carrier for the development of multistate memory devices. Ferroelectric materials have spontaneous polarization characteristics, and the polarization direction can be reversibly switched by an external electric field, thereby realizing non-volatile data storage. Compared with traditional oxide ferroelectric materials, two-dimensional van der Waals ferroelectric materials have emerged in recent years due to their characteristics such as no dangling bonds and weak interlayer coupling, which are not limited by the substrate and are easy to integrate, and have gradually become a research hotspot.

[0004] Among them, CuInP2S6 is a room-temperature ferroelectric material with relatively high polarization strength. Recent studies have shown that this material system has intrinsic six-fold polarization states, exhibiting great potential for multistate information storage. At the same time, multiferroic materials have opened up new ways for designing multifunctional, low-power devices due to their electric and magnetic dual degrees of freedom. If ferroelectricity and magnetism can be integrated in the same material, it is expected to realize a new type of storage technology with high density, high speed and low power consumption.

[0005] At present, most multiferroic materials are difficult to meet the requirements of room-temperature operation, intrinsic multiple polarization states, excellent two-dimensional characteristics and magnetoelectric coupling. In particular, how to effectively introduce magnetism while maintaining the intrinsic multiple polarization characteristics of materials such as CuInP2S6, and prepare two-dimensional multiferroic single crystals with excellent ferroelectric and magnetic properties, is still an important challenge in this field.

[0006] Therefore, it is of great significance to develop a new two-dimensional multiferroic material with intrinsic multi-polarization ferroelectric state and superparamagnetism at room temperature and realize controllable synthesis of high-quality single crystal, so as to promote the development of high-density multi-state memory and multifunctional electronic devices. SUMMARY

[0007] In order to overcome the above problems, the application provides a two-dimensional multiferroic material with multiple polarization states and a preparation method thereof. The two-dimensional multiferroic material is obtained by introducing a magnetic element into a two-dimensional ferroelectric material CuInP2S6 with intrinsic six-polarization state, so that the two-dimensional multiferroic material has superparamagnetism while retaining the six-polarization state. The two-dimensional multiferroic material has potential application value in high-density data storage and multifunctional transistors.

[0008] Specifically, the application aims to provide the following aspects:

[0009] In a first aspect, a two-dimensional multiferroic material is provided, which is obtained by introducing a magnetic element into a two-dimensional ferroelectric material CuInP2S6 with intrinsic six-polarization state, so that the two-dimensional multiferroic material has superparamagnetism while retaining the six-polarization state.

[0010] Optionally, the magnetic element is dysprosium.

[0011] Optionally, the two-dimensional multiferroic material has the following expression: CuDy x In 1-x P2S6, wherein x is in the range of 0.05 to 0.5.

[0012] Optionally, the two-dimensional multiferroic material has a layered single crystal structure.

[0013] Optionally, the two-dimensional multiferroic material layers are combined by van der Waals force.

[0014] In a second aspect, a method for preparing the two-dimensional multiferroic material of the first aspect is provided, and the method comprises the following steps:

[0015] In step 1, copper powder, indium powder, phosphorus powder, sulfur powder and magnetic element elemental powder are mixed to obtain a mixed powder.

[0016] In step 2, the mixed powder is grown in a double-temperature zone by chemical vapor transport method to obtain the two-dimensional multiferroic material.

[0017] Optionally, in step 1, the purity of the copper powder, indium powder, phosphorus powder, sulfur powder and magnetic element elemental powder is not less than 98.9%.

[0018] Optionally, in step 1, the amount of the copper powder, indium powder, phosphorus powder, sulfur powder and magnetic element elemental powder satisfies: CuDy x In1-x P2S6, x is in the range of 0.05-0.5.

[0019] Optionally, in step 1, the mixed powder further comprises a chemical transport agent.

[0020] In a third aspect, a nonvolatile memory device is provided, comprising the two-dimensional multiferroic material of the first aspect.

[0021] The present application has the beneficial effects including:

[0022] (1) The two-dimensional multiferroic material provided by the present application realizes superparamagnetism while retaining excellent ferroelectric properties by introducing a magnetic rare earth element into a two-dimensional ferroelectric material CuInP2S6 with intrinsic six-fold polarization state.

[0023] (2) The two-dimensional multiferroic material provided by the present application is mechanically exfoliated, easy to integrate, and not limited by substrates, and has potential application value in high-density memory devices, flexible devices, etc.; and its preparation method is simple, pollution-free, highly reproducible, and has excellent crystal quality. BRIEF DESCRIPTION OF DRAWINGS

[0024] Various other advantages and benefits of the present application will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included solely for purposes of illustrating the preferred embodiments and are not to be construed as a limitation of the present application. It should be readily understood that the drawings depicted are only some embodiments of the present application and that any other drawings, which are similar to those included, can also be derived by one of ordinary skill in the art without paying creative effort.

[0025] In the drawings:

[0026] Figure 1 X-ray diffraction comparison chart of the two-dimensional multiferroic material and CuInP2S6 in Example 1 is shown;

[0027] Figure 2 CuDy 0.5 In 0.5 Fourier transform diffraction spot image of the scanning transmission electron microscope atomic image of the P2S6 two-dimensional multiferroic nanosheet material;

[0028] Figure 3 X-ray photoelectron spectrogram of the two-dimensional multiferroic material in Example 1 is shown;

[0029] Figure 4 CuDy 0.5 In 0.5 Piezoelectric force microscope amplitude response distribution chart of the P2S6 two-dimensional multiferroic nanosheet material;

[0030] Figure 5 CuDy is shown in Example 1 0.5 In 0.5 piezoelectric microscopy hysteresis loop test results of P2S6 two-dimensional multiferroic nanosheets;

[0031] Figure 6 CuDy is shown in Example 1 0.5 In 0.5 Comparison of MH curves between P2S6 two-dimensional multiferroic nanosheets and CuInP2S6;

[0032] Figure 7 The MH curves of the two-dimensional multiferroic materials prepared in Examples 1-4 and CuInP2S6 are shown in comparison. Detailed Implementation

[0033] The following will refer to the appendix. Figures 1 to 7 Specific embodiments of the invention will be described in more detail below. While specific embodiments of the invention are shown in the accompanying drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0034] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0035] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "front," and "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship in the working state of this invention, and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. Furthermore, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0036] To facilitate understanding of the embodiments of the present invention, further explanations and descriptions will be provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0037] In a first aspect, according to the present invention, a two-dimensional multiferroic material is provided, in which magnetic elements are introduced into a two-dimensional ferroelectric material CuInP2S6 having an intrinsic six-fold polarization state, so that the two-dimensional multiferroic material retains the six-fold polarization state while also possessing superparamagnetism.

[0038] Furthermore, the magnetic element is preferably dysprosium, which replaces In ions to achieve superparamagnetism.

[0039] The core of this invention lies in achieving the synergistic coexistence of multiple ferroelectric polarization states and magnetism in two-dimensional materials. The intrinsic sixfold polarization of CuInP2S6 originates from Cu + The ordered displacement of ions in the crystal lattice and the resulting distortion of the non-centrosymmetric structure. Dysprosium was chosen as the dopant element because its ionic radius is similar to that of the In it is substituted. 3+ The results are relatively close, with small local lattice strain caused by doping, which will not significantly disturb Cu. + The migration path and polarization reversal barrier. Meanwhile, Dy 3+ The 4f electrons are trapped in the outer 5s shell. 2 5p 6 Electron shielding and highly localized electron clouds result in weak orbital hybridization with the valence band apex (mainly composed of S-3p and Cu-3d orbitals), thus limiting the impact on the stability of the ferroelectric polarization direction. These factors effectively preserve the sixfold polarization state of the two-dimensional multiferroic material.

[0040] Dy 3+ The magnetic moment is relatively large, when it replaces In 3+ After entering the crystal lattice, local magnetic moments are formed. Due to the controllable doping concentration, the magnetic ions are sparsely distributed, and CuInP2S6 has a van der Waals layered structure with extremely weak interlayer exchange interactions, making it difficult to establish long-range order among the magnetic moments. Under room temperature thermal perturbation, these magnetic moments macroscopically exhibit magnetization behavior without coercivity and remanence, i.e., superparamagnetism. The saturation magnetic moment of the two-dimensional multiferroic material at 2K is 5 × 10⁻⁶. -4 ~7×10 -4 emu, the saturation magnetic moment at 300K is 7×10 -5 ~9×10 -5 The magnetic moment at 2K and 10000 Oe is 0.3~0.85 emu / g.

[0041] In this invention, the two-dimensional multiferroic material has a layered single-crystal structure, space group P31c, and is expressed as follows: CuDy x In1-x P2S6, where x ranges from 0.05 to 0.5. The constraint on this parameter is: when x < 0.05, effective superparamagnetic properties cannot be achieved, and the functional significance of "multiferroic coupling" is lost; excessive Dy... 3+ Doping causes significant changes in local bond lengths and bond angles, disrupting the Cu bond structure. + The lattice symmetry upon which the ordered migration of ions depends leads to significant lattice distortion. When x is between 0.05 and 0.5, magnetism can be effectively introduced without destroying the intrinsic ferroelectric order, thus achieving coordinated control of electrical and magnetic degrees of freedom.

[0042] In this invention, the two-dimensional multiferroic material is bonded between its layers by van der Waals forces, and then mechanically exfoliated to obtain two-dimensional multiferroic nanosheets. The thickness of the exfoliated nanosheets is typically 50-300 nm. The resulting two-dimensional multiferroic nanosheets retain the ferroelectric and magnetic properties of the bulk material, making them suitable for constructing miniaturized and flexible electronic devices.

[0043] In a second aspect, according to the method for preparing the two-dimensional multiferroic material described in the first aspect of the present invention, the method includes:

[0044] Step 1: Mix copper powder, indium powder, phosphorus powder, sulfur powder and elemental magnetic powder to obtain a mixed powder;

[0045] Step 2: The mixed powder is grown in a dual-temperature zone using chemical vapor transport method to obtain the two-dimensional multiferroic material.

[0046] Specifically:

[0047] In step 1, the magnetic element powder is any element that can introduce a local magnetic moment without significantly disrupting the ferroelectric order of CuInP2S6, preferably dysprosium powder.

[0048] In step 1, in order to ensure the purity of the two-dimensional multiferroic material, the purity of the copper powder, indium powder, phosphorus powder, sulfur powder and magnetic element powder is not less than 98.9%.

[0049] In one embodiment, the amounts of copper powder, indium powder, phosphorus powder, sulfur powder, and magnetic element powder satisfy the following: CuDy x In 1-x P2S6, where x ranges from 0.05 to 0.5.

[0050] In step 1, the mixed powder also includes a chemical transport agent. This chemical transport agent does not participate in the crystal lattice structure of the final product; it only reacts with the raw materials at high temperatures to generate volatile intermediate species, achieving gas-phase transport and promoting crystal growth.

[0051] Furthermore, the chemical transport agent is selected from any one of iodine, iodine chloride, and ammonium chloride, preferably iodine.

[0052] In this invention, iodine is used as a preferred chemical transport agent, which has the advantages of mild reaction and no damage to the PS backbone structure, and is particularly suitable for the CuDy described in this invention. x In 1-x Single crystal growth of the P2S6 system. Using iodine as a chemical transport agent, the resulting two-dimensional multiferroic materials are large in size, have high crystal quality, and smooth surface, which is beneficial for subsequent mechanical exfoliation and device applications.

[0053] In one embodiment, step 2 includes the following sub-steps:

[0054] Step 2-1: Load the mixed powder into one end of the reaction tube and evacuate to 10°C. -2 Below Pa, seal the tube;

[0055] Step 2-2: Place the reaction tube in a dual-temperature zone tube furnace, with one end containing the mixed powder in the high-temperature zone and the other end in the low-temperature zone.

[0056] Steps 2-3: Set the temperature of the high-temperature zone to 850-900℃ and the temperature of the low-temperature zone to 600-650℃. After isothermal growth for 5-10 days using chemical vapor transport method, the material is naturally cooled to room temperature to obtain a two-dimensional multiferroic material.

[0057] In step 2-1, the amount of chemical transport agent is determined based on the effective volume of the reaction tube. Theoretically, the relationship between the amount of chemical transport agent and the volume of the reaction tube is (1.8~2.5) mg / cm³. 3 For example, 2.0 mg / cm 3 The constraints for selecting this parameter are: this dosage can establish a stable vapor pressure environment, promote the reversible transport of raw materials between the hot and cold ends, and at the same time avoid corrosion of the reaction tube or splashing of raw materials due to excessive chemical transport agent.

[0058] Furthermore, the raw material loading volume does not exceed half of the effective volume of the reaction tube to ensure sufficient gas diffusion space and crystal growth area.

[0059] In step 2-1, the reaction tube is typically a quartz tube with good high-temperature resistance and chemical stability.

[0060] In step 2-1, the tube is typically sealed by heating, for example by heating the tube with an oxyhydrogen flame generator.

[0061] In step 2-2, the reaction tube is typically placed horizontally in a dual-temperature zone tube furnace to ensure a uniform temperature gradient along the axial direction. The high-temperature zone serves as the "source zone," where the raw materials react with the chemical transport agent to generate gaseous intermediates; the low-temperature zone serves as the "growth zone," where the decreasing temperature causes the reaction equilibrium to shift in the reverse direction, promoting the slow precipitation of the target crystal in this region. Without a significant temperature difference, continuous mass transport cannot be formed.

[0062] In steps 2-3, the constraint condition for setting the high-temperature zone temperature to 850-900℃ is as follows: if the temperature is too low, the raw materials, especially phosphorus and sulfur, will not volatilize sufficiently, the formation rate of the complex of the chemical transport agent will be slow, and the transport efficiency will be low; if the temperature is too high, it may cause CuInP2S6 to decompose (such as the PS bond breaking and releasing P2 or S2 gas), or cause the quartz tube to soften and deform; 850-900℃ is the optimal temperature in this system, which can ensure sufficient reaction without destroying the integrity of the crystal structure.

[0063] In steps 2-3, the constraint condition for setting the low-temperature zone temperature to 600-650℃ is as follows: if the temperature is too low, the reaction is too fast, and polycrystalline or powdery products are easily formed; if the temperature is too high, the temperature difference between the high-temperature end and the low-temperature end is insufficient (<200℃), and an effective transport driving force cannot be established; 600-650℃ is conducive to slow crystallization and the formation of layered single crystals with regular morphology.

[0064] In steps 2-3, the constraint condition for the growth time of 5-10 days is as follows: chemical vapor transport is a slow diffusion-controlled process. If the time is too short, the crystal size will be small and the yield will be low; if the time is too long, secondary nucleation or impurity precipitation may occur, affecting the purity; 5-10 days is the optimal balance point, which can obtain single crystals.

[0065] In steps 2-3, the temperature is raised from room temperature to the specified temperature, which typically takes 1 to 1.5 hours, for example, 1 hour. This is to avoid excessively rapid heating that could cause a large temperature difference between the inside and outside of the reaction tube, leading to cracking.

[0066] In one embodiment, the high-temperature zone temperature is set to 880°C and the low-temperature zone temperature is set to 630°C. The temperature is increased for 1 hour, and after reaching the temperature, it is kept at that temperature for 168 hours (7 days). Then, it is naturally cooled to room temperature to obtain a two-dimensional multiferroic material.

[0067] In this invention, a chemical vapor transport method is used to grow crystals, which realizes the directional transport and slow crystallization of raw materials, which is beneficial to obtaining large-size, high-crystal-quality single crystal materials.

[0068] Thirdly, according to the present invention, a non-volatile storage device comprises a two-dimensional multiferroic material as described in the first aspect.

[0069] The present invention is further described below through specific examples; however, these examples are merely exemplary and do not constitute any limitation on the scope of protection of the present invention.

[0070] Example 1

[0071] (1) Copper powder (purity 99.80%), indium powder (purity 99.99%), phosphorus powder (purity 98.90%), sulfur powder (purity 99.9%), and dysprosium powder (purity 99.9%) are mixed in a stoichiometric ratio CuDy 0.5 In 0.5 P2S6 was weighed, and the mass of other elements was calculated using 1g of sulfur powder as the standard.

[0072] Prepared quartz tubes with an outer diameter of 20 mm and a length of 300 mm, necked at 130 mm from the opening for easy sealing. The internal volume below the sealed portion of the quartz tube used in this study was measured to be 38 cm³ using the displacement method. 3 The relationship between iodine dosage and quartz tube volume is 2 mg / cm³. 3 The amount of iodine (99.9% purity) required was calculated to be 0.076 g.

[0073] (2) Weigh out copper powder, indium powder, phosphorus powder, sulfur powder, dysprosium powder and iodine and feed them into the bottom of the quartz tube. Then, place a quartz column 30 mm high at the neck of the quartz tube. Connect the quartz tube filled with raw materials to the vacuum sealing system. First, reduce the gas pressure inside the tube to 10. -2 When the pressure is below Pa, turn on the oxyhydrogen flame generator, aim it at the sealing area, and fuse the quartz column to the tube wall to complete the sealing. After cooling, add an appropriate amount of water above the sealed quartz column and observe for 12 hours to check for leaks. During the leak check, calibrate the temperature of the tube furnace. Set the resistance wires at both ends of the dual-temperature zone tube furnace to 880℃ and 630℃ respectively, with a heating time of 1 hour.

[0074] (3) After the water leakage inspection process is completed, the temperature is raised. The temperature of the high temperature zone is 880℃ and the temperature of the low temperature zone is 630℃. The temperature is raised for 1 hour and then kept at the temperature for 168 hours (7 days). Then it is naturally cooled to room temperature to obtain a two-dimensional multiferroic material with a layered single crystal structure.

[0075] A small piece of two-dimensional multiferroic material was placed on a blue adhesive tape. Mechanical cleavage was performed by repeatedly folding and peeling the tape. Finally, the tape, retaining a thin layer of material, was adhered to a heavily doped n-type silicon substrate and left for 30 minutes before being peeled off, leaving CuDy on the substrate. 0.5 In 0.5 P2S6 two-dimensional multiferroic nanosheet material.

[0076] Figure 1The X-ray diffraction comparison diagrams of the two-dimensional multiferroic material and CuInP2S6 are shown. It can be seen that the crystal structure of the two-dimensional multiferroic material does not change significantly after doping with dysprosium, and no new phase is generated. In addition, the peak positions of the two-dimensional multiferroic material (x=0.5) at (004) and (006) show a significant tendency to shift to a lower angle compared with CuInP2S6 (x=0), which is due to the lattice expansion caused by the doping of Dy element.

[0077] Figure 2 CuDy 0.5 In 0.5 Fourier transform diffraction pattern of P2S6 two-dimensional multiferroic nanosheets atomic image obtained by scanning transmission electron microscopy shows that the material is a single crystal with the corresponding space group P31c.

[0078] Figure 3 The X-ray photoelectron spectrum of the two-dimensional multiferroic material is shown, which shows that Dy 3+ The binding energy peak of the ions indicates that dysprosium exists in the crystal lattice in ionic form.

[0079] Figure 4 CuDy 0.5 In 0.5 The piezoelectric microscopy amplitude response distribution of P2S6 two-dimensional multiferroic nanosheet material shows that it has a ferroelectric domain structure, that is, the material has a spontaneous ferroelectric response.

[0080] Figure 5 The CuDy layer with a thickness of 101.57 nm is shown. 0.5 In 0.5 The piezoelectric microscopy hysteresis loop test results of P2S6 two-dimensional multiferroic nanosheets show that its polarization state can be reversed under an electric field, and it exhibits six distinguishable polarization orientations, confirming that it retains its intrinsic sixfold polarization characteristics.

[0081] Figure 6 CuDy 0.5 In 0.5 A comparison of the MH curves of P2S6 two-dimensional multiferroic crystal (shown as x=0.5 in the figure) and CuInP2S6 measured by a superconducting quantum interference device shows that it exhibits superparamagnetism at low temperature (2K) and room temperature (300K), with saturation magnetic moments of 6×10⁻⁶ and 6×10⁻⁶, respectively. -4 emu, 8×10 -5 emu.

[0082] Example 2

[0083] Two-dimensional multiferroic materials were prepared in a manner similar to that of Example 1, except that x was 0.05. Specifically:

[0084] (1) Copper powder (purity 99.80%), indium powder (purity 99.99%), phosphorus powder (purity 98.90%), sulfur powder (purity 99.9%), and dysprosium powder (purity 99.9%) are mixed in a stoichiometric ratio CuDy 0.05 In 0.95 P2S6 was weighed, and the mass of other elements was calculated using 1g of sulfur powder as the standard.

[0085] Prepared quartz tubes with an outer diameter of 20 mm and a length of 300 mm, necked at 130 mm from the opening for easy sealing. The internal volume below the sealed portion of the quartz tube used in this study was measured to be 38 cm³ using the displacement method. 3 The relationship between iodine dosage and quartz tube volume is 2 mg / cm³. 3 The amount of iodine (99.9% purity) required was calculated to be 0.076 g.

[0086] (2) Weigh out copper powder, indium powder, phosphorus powder, sulfur powder, dysprosium powder and iodine and feed them into the bottom of the quartz tube. Then, place a quartz column 30 mm high at the neck of the quartz tube. Connect the quartz tube filled with raw materials to the vacuum sealing system. First, reduce the gas pressure inside the tube to 10. -2 When the pressure is below Pa, turn on the oxyhydrogen flame generator, aim it at the sealing area, and fuse the quartz column to the tube wall to complete the sealing. After cooling, add an appropriate amount of water above the sealed quartz column and observe for 12 hours to check for leaks. During the leak check, calibrate the temperature of the tube furnace. Set the resistance wires at both ends of the dual-temperature zone tube furnace to 880℃ and 630℃ respectively, with a heating time of 1 hour.

[0087] (3) After the water leakage inspection process is completed, the temperature is raised. The temperature of the high temperature zone is 880℃ and the temperature of the low temperature zone is 630℃. The temperature is raised for 1 hour and then kept at the temperature for 168 hours (7 days). Then it is naturally cooled to room temperature to obtain a two-dimensional multiferroic material with a layered single crystal structure.

[0088] A small piece of two-dimensional multiferroic material was placed on a blue adhesive tape. Mechanical cleavage was performed by repeatedly folding and peeling the tape. Finally, the tape, retaining a thin layer of material, was adhered to a heavily doped n-type silicon substrate and left for 30 minutes before being peeled off, leaving CuDy on the substrate. 0.05 In 0.95 P2S6 two-dimensional multiferroic nanosheet material.

[0089] Example 3

[0090] Two-dimensional multiferroic materials were prepared in a manner similar to that of Example 1, except that x was 0.1. Specifically:

[0091] (1) Copper powder (purity 99.80%), indium powder (purity 99.99%), phosphorus powder (purity 98.90%), sulfur powder (purity 99.9%), and dysprosium powder (purity 99.9%) are mixed in a stoichiometric ratio CuDy 0.1 In 0.9 P2S6 was weighed, and the mass of other elements was calculated using 1g of sulfur powder as the standard.

[0092] Prepared quartz tubes with an outer diameter of 20 mm and a length of 300 mm, necked at 130 mm from the opening for easy sealing. The internal volume below the sealed portion of the quartz tube used in this study was measured to be 38 cm³ using the displacement method. 3 The relationship between iodine dosage and quartz tube volume is 2 mg / cm³. 3 The amount of iodine (99.9% purity) required was calculated to be 0.076 g.

[0093] (2) Weigh out copper powder, indium powder, phosphorus powder, sulfur powder, dysprosium powder and iodine and feed them into the bottom of the quartz tube. Then, place a quartz column 30 mm high at the neck of the quartz tube. Connect the quartz tube filled with raw materials to the vacuum sealing system. First, reduce the gas pressure inside the tube to 10. -2 When the pressure is below Pa, turn on the oxyhydrogen flame generator, aim it at the sealing area, and fuse the quartz column to the tube wall to complete the sealing. After cooling, add an appropriate amount of water above the sealed quartz column and observe for 12 hours to check for leaks. During the leak check, calibrate the temperature of the tube furnace. Set the resistance wires at both ends of the dual-temperature zone tube furnace to 880℃ and 630℃ respectively, with a heating time of 1 hour.

[0094] (3) After the water leakage inspection process is completed, the temperature is raised. The temperature of the high temperature zone is 880℃ and the temperature of the low temperature zone is 630℃. The temperature is raised for 1 hour and then kept at the temperature for 168 hours (7 days). Then it is naturally cooled to room temperature to obtain a two-dimensional multiferroic material with a layered single crystal structure.

[0095] A small piece of two-dimensional multiferroic material was placed on a blue adhesive tape. Mechanical cleavage was performed by repeatedly folding and peeling the tape. Finally, the tape, retaining a thin layer of material, was adhered to a heavily doped n-type silicon substrate and left for 30 minutes before being peeled off, leaving CuDy on the substrate. 0.1 In 0.9 P2S6 two-dimensional multiferroic nanosheet material.

[0096] Example 4

[0097] Two-dimensional multiferroic materials were prepared in a manner similar to that of Example 1, except that x was 0.15. Specifically:

[0098] (1) Copper powder (purity 99.80%), indium powder (purity 99.99%), phosphorus powder (purity 98.90%), sulfur powder (purity 99.9%), and dysprosium powder (purity 99.9%) are mixed in a stoichiometric ratio CuDy 0.15 In 0.85 P2S6 was weighed, and the mass of other elements was calculated using 1g of sulfur powder as the standard.

[0099] Prepared quartz tubes with an outer diameter of 20 mm and a length of 300 mm, necked at 130 mm from the opening for easy sealing. The internal volume below the sealed portion of the quartz tube used in this study was measured to be 38 cm³ using the displacement method. 3 The relationship between iodine dosage and quartz tube volume is 2 mg / cm³. 3 The amount of iodine (99.9% purity) required was calculated to be 0.076 g.

[0100] (2) Weigh out copper powder, indium powder, phosphorus powder, sulfur powder, dysprosium powder and iodine and feed them into the bottom of the quartz tube. Then, place a quartz column 30 mm high at the neck of the quartz tube. Connect the quartz tube filled with raw materials to the vacuum sealing system. First, reduce the gas pressure inside the tube to 10. -2 When the pressure is below Pa, turn on the oxyhydrogen flame generator, aim it at the sealing area, and fuse the quartz column to the tube wall to complete the sealing. After cooling, add an appropriate amount of water above the sealed quartz column and observe for 12 hours to check for leaks. During the leak check, calibrate the temperature of the tube furnace. Set the resistance wires at both ends of the dual-temperature zone tube furnace to 880℃ and 630℃ respectively, with a heating time of 1 hour.

[0101] (3) After the water leakage inspection process is completed, the temperature is raised. The temperature of the high temperature zone is 880℃ and the temperature of the low temperature zone is 630℃. The temperature is raised for 1 hour and then kept at the temperature for 168 hours (7 days). Then it is naturally cooled to room temperature to obtain a two-dimensional multiferroic material with a layered single crystal structure.

[0102] A small piece of two-dimensional multiferroic material was placed on a blue adhesive tape. Mechanical cleavage was performed by repeatedly folding and peeling the tape. Finally, the tape, retaining a thin layer of material, was adhered to a heavily doped n-type silicon substrate and left for 30 minutes before being peeled off, leaving CuDy on the substrate. 0.15 In 0.85 P2S6 two-dimensional multiferroic nanosheet material.

[0103] The above examples clearly demonstrate that the two-dimensional multiferroic materials prepared by introducing the magnetic element Dy into CuInP2S6 not only possess six-fold polarized ferroelectric states but also exhibit superparamagnetism.

[0104] Figure 7The diagram shows a comparison of the MH curves of the two-dimensional multiferroic materials prepared in Examples 1-4 (shown as x=0.5, x=0.05, x=0.1, and x=0.15 respectively) and CuInP2S6 (shown as x=0) at a temperature of 2K measured by a superconducting quantum interference device. It can be seen that the two-dimensional multiferroic materials prepared in Examples 1-4 all exhibit superparamagnetism at low temperatures, and the corresponding magnetic moment values ​​at 10000 Oe are 0.84 emu / g, 0.53 emu / g, 0.3 emu / g, and 0.71 emu / g, respectively.

[0105] The present invention has been described in detail above with reference to preferred embodiments and exemplary examples. However, it should be noted that these specific embodiments are merely illustrative explanations of the invention and do not constitute any limitation on the scope of protection of the invention. Various improvements, equivalent substitutions, or modifications can be made to the technical content and embodiments of the present invention without departing from the spirit and scope of protection of the invention, and all such modifications fall within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A two-dimensional multiferroic material, characterized in that, Introducing magnetic elements into CuInP2S6, a two-dimensional ferroelectric material with intrinsic six-fold polarization, allows the two-dimensional multiferroic material to retain the six-fold polarization while also exhibiting superparamagnetism.

2. The two-dimensional multiferroic material according to claim 1, characterized in that, Preferably, the magnetic element is dysprosium.

3. The two-dimensional multiferroic material according to claim 1, characterized in that, The two-dimensional multiferroic material has the following expression: CuDy x In 1-x P2S6, where x takes values ​​from 0.05 to 0.

5.

4. The two-dimensional multiferroic material according to claim 1, characterized in that, The two-dimensional multiferroic material has a layered single-crystal structure and a space group of P31c.

5. The two-dimensional multiferroic material according to claim 4, characterized in that, The two-dimensional multiferroic material is bonded between its layers by van der Waals forces.

6. A method for preparing the two-dimensional multiferroic material according to any one of claims 1 to 5, characterized in that, The method includes: Step 1: Mix copper powder, indium powder, phosphorus powder, sulfur powder and elemental magnetic powder to obtain a mixed powder; Step 2: The mixed powder is grown in a dual-temperature zone using chemical vapor transport method to obtain the two-dimensional multiferroic material.

7. The method according to claim 6, characterized in that, In step 1, the purity of the copper powder, indium powder, phosphorus powder, sulfur powder, and magnetic element powder is not less than 98.9%.

8. The method according to claim 6 or 7, characterized in that, In step 1, the amounts of copper powder, indium powder, phosphorus powder, sulfur powder, and magnetic element powder satisfy the following: CuDy x In 1-x P2S6, where x ranges from 0.05 to 0.

5.

9. The method according to claim 8, characterized in that, In step 1, the mixed powder also includes a chemical transporter.

10. A non-volatile storage device, characterized in that, Includes the two-dimensional multiferroic material as described in any one of claims 1 to 5.

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