Atmospheric stable two-dimensional room-temperature ferromagnetic nanosheets, preparation method and application thereof

Abstract

This invention belongs to the field of magnetic materials technology, and discloses an atmospherically stable two-dimensional room-temperature ferromagnetic nanosheet, its preparation method, and its applications. The chemical formula of the two-dimensional ferromagnetic nanosheet is Cr. 1+δ Te2, where 0.65≤δ≤0.75. The two-dimensional ferromagnetic nanosheets exhibit room-temperature magnetism and stability in morphology and magnetic domain changes under atmospheric conditions. The initial magnetic domains of the two-dimensional ferromagnetic nanosheets are striped domains. This invention successfully prepared atmospherically stable Cr with room-temperature magnetism using a chemical deposition method. 1+δ Te nanosheets enable the controllable growth of two-dimensional room-temperature magnetic materials. The initial magnetic domains of the prepared nanosheets are striped domains, and the generation and annihilation of skyrmions can be controlled under the influence of an external magnetic field and thermal excitation. This material has broad application prospects in the fields of magnetic information storage and spintronic devices.

Description

Technical Field

[0001] This invention belongs to the field of magnetic materials technology, specifically relating to an atmospherically stable two-dimensional room-temperature ferromagnetic nanosheet, its preparation method, and its application. Background Technology

[0002] Two-dimensional magnetic materials, as a type of two-dimensional material, possess relatively weak interlayer van der Waals forces and can maintain spontaneous magnetization even at atomic layer thicknesses. These properties make two-dimensional magnetic materials easily modulated through electric fields, magnetic fields, and interfaces, providing a new platform for exploring spin-related physical phenomena and spintronic devices. In the study of chiral and polar magnetic materials, a spin structure with vortex-like topological properties and nanoscale dimensions—the magnetic skyrmion—has been observed. Skyrmions can be driven at high speeds by low-density currents, exhibiting rich dynamic characteristics. Using skyrmions as a next-generation information storage unit holds promise for solving the current energy consumption, quantum limit, and Moore's Law problems faced by memory devices. Therefore, skyrmion spintronic devices are expected to become a new generation of low-energy memory.

[0003] There are four main mechanisms for skyrmion generation: first, long-range magnetic dipole interaction, which competes with magnetic anisotropy to generate skyrmion arrays under the influence of a magnetic field; second, Dzyaloshinskii-Moriya interaction, originating from symmetry loss at the interface of magnetic lattices or magnetic thin films; third, frustrated exchange interaction; and fourth, four-spin exchange interaction. Besides being observed in some chiral magnets (MnSi, FeGe), skyrmions have also been observed in two-dimensional magnetic materials such as Cr2Te2Te6 and Fe3GeTe2 in recent years. This expands the study of magnetic skyrmions to two-dimensional magnetic materials, contributing to the device-level application of magnetic skyrmion materials. However, most two-dimensional magnetic materials have the following drawbacks when applied to practical applications: Curie temperature (T... c It exists below room temperature and cannot exist stably in the air.

[0004] Chromium tellurides, such as CrTe2, Cr2Te3, Cr3Te4, and CrTe, are a new class of two-dimensional magnetic materials with excellent environmental stability. c The Cr content can be adjusted to achieve temperatures above room temperature. Furthermore, research indicates that Cr prepared using the chemical vapor transport (CVT) method... 1.74 The observation of skyrmions in Te2 crystals at 298 K proves that chromium telluride is a potential material capable of generating skyrmion structures. However, the aforementioned Cr... 1.74Te2 crystals are bulk materials and difficult to dissociate into thin layers for use in miniaturized devices. Therefore, the controllable preparation of atmospherically stable, room-temperature magnetic thin-layer chromium telluride is of great significance. Based on this, this invention provides a novel atmospherically stable two-dimensional room-temperature magnetic material, its preparation method, and its applications. Summary of the Invention

[0005] The purpose of this invention is to provide an atmospherically stable two-dimensional room-temperature ferromagnetic nanosheet, its preparation method, and its applications. The chemical formula of the ferromagnetic nanosheet is Cr. 1+δ Te2, where 0.65≤δ≤0.75, this invention successfully prepared atmospherically stable Cr with room-temperature magnetic properties using a chemical deposition method. 1+δ Te nanosheets were prepared with initial magnetic domains of striped domains. Under the action of an external magnetic field and thermal excitation, the generation and annihilation of skyrmions can be controlled.

[0006] To achieve the above objectives, the technical solution adopted in this application is as follows:

[0007] The first objective of this invention is to provide an atmospherically stable two-dimensional room-temperature ferromagnetic nanosheet, wherein the chemical formula of the two-dimensional ferromagnetic nanosheet is Cr. 1+δ Te2, where 0.65≤δ≤0.75.

[0008] Furthermore, the morphology of the magnetic domains of the two-dimensional ferromagnetic nanosheets can be regulated by an external magnetic field or thermal excitation, causing the magnetic domains of the two-dimensional ferromagnetic nanosheets to transform from a striped domain structure to a skyrmion structure.

[0009] Furthermore, 0G < the magnitude of the external magnetic field ≤ 1000G, and the direction of the external magnetic field is perpendicular to the surface of the nanosheet, either upwards or downwards.

[0010] Furthermore, 300K ≤ the temperature of the thermal excitation ≤ 333K.

[0011] Furthermore, the chemical formula of the two-dimensional ferromagnetic nanosheets is Cr. 1+δ Te2, where δ is 0.65, 0.66, 0.70 or 0.75.

[0012] Furthermore, the two-dimensional ferromagnetic nanosheets exhibit room-temperature magnetism and stability in morphology and magnetic domain changes in an atmospheric environment. The initial magnetic domains of the two-dimensional ferromagnetic nanosheets are striped domains. The two-dimensional ferromagnetic nanosheets have a polygonal structure, which is hexagonal or triangular, with a lateral dimension of more than 10 μm and a thickness of 7-100 nm.

[0013] A second objective of this invention is to provide a method for preparing the aforementioned atmospherically stable two-dimensional room-temperature ferromagnetic nanosheets, comprising the following steps: placing a tellurium source and a chromium source in corresponding first and second temperature zones of a dual-temperature zone tube furnace. The tellurium source, heated in the first temperature zone, forms vapor and is carried by a carrier gas to the second temperature zone, where it reacts with the chromium source gas at 850-860°C, depositing onto a substrate surface to obtain two-dimensional room-temperature ferromagnetic Cr nanosheets. 1+δ Te2 nanosheets.

[0014] Furthermore, the mass ratio of the tellurium source to the chromium source is 20-40:1.5-3, the tellurium source is Te, and the chromium source is CrCl3;

[0015] The CrCl3 has a polished substrate on each side with the polished surface facing upwards, and the distance between the two substrates is 1 cm. At the same time, a polished substrate is placed on top of the CrCl3 with the polished surface facing downwards.

[0016] Furthermore, the temperature of the first temperature zone is 550-600℃, and the reaction holding time is 20 minutes;

[0017] The carrier gas is an argon-hydrogen mixture, with a hydrogen volume content of 15-20% and a carrier gas flow rate of 55-60 sccm.

[0018] A third objective of this invention is to provide the use of the above-described atmospherically stable two-dimensional room-temperature ferromagnetic nanosheets in magnetic information storage or spintronic devices.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] (1) This invention successfully prepared atmospherically stable two-dimensional room temperature magnetic material Cr using chemical vapor deposition. 1+δ Te2 enables the controllable growth of two-dimensional room temperature magnetic materials. The prepared two-dimensional ferromagnetic nanosheets exhibit room temperature magnetism and stability in morphology and magnetic domain changes in atmospheric environment. The initial magnetic domains of the two-dimensional ferromagnetic nanosheets are striped domain structures. The generation and annihilation of skyrmions can be controlled by magnetic field and thermal excitation, making it an ideal candidate material for skyrmion-based spintronic devices.

[0021] (2) This invention is of great significance for exploring the microscopic magnetic domain behavior of room-temperature magnetic materials and provides a reference for the manipulation and control of skyrmions at room temperature. This invention can be applied to skyrmion track memory, which has low power consumption, high magnetic storage density and stability, and is expected to become a new generation of information memory. Attached Figure Description

[0022] Figure 1 This invention employs a chemical vapor deposition method to grow Cr. 1+δ A schematic diagram of the Te2 device.

[0023] Figure 2 This invention employs a chemical vapor deposition method to grow Cr. 1+δ A schematic diagram of the substrate placement for Te2.

[0024] Figure 3 Cr prepared in Example 1 of this invention 1+δ Optical images of Te2.

[0025] Figure 4 Cr prepared in Example 1 of this invention 1+δ Thickness test chart for Te2.

[0026] Figure 5 Cr prepared in Example 2 of this invention 1+δ Elemental distribution test plot of Te2.

[0027] Figure 6 Cr prepared in Example 2 of this invention 1+δ Microscopic magnetic domain structure of Te2 at room temperature.

[0028] Figure 7 Cr prepared in Example 3 of this invention 1+δ Evolution of the microscopic magnetic domain structure of Te2 under an applied magnetic field.

[0029] Figure 8 Cr prepared in Example 4 of this invention 1+δ Evolution of the microscopic magnetic domain structure of Te2 under thermal excitation.

[0030] Figure 9 Cr prepared in Example 1 of this invention 1+δ Stability test chart for Te2.

[0031] Figure 10 The Cr prepared in Examples 1-4 of this invention 1+δ A schematic diagram of Te2's application in track memory. Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the data in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] It should be noted that the technical terms used in this invention are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased commercially or prepared by existing methods. The tellurium source used in this invention is CrCl3, provided by Alfa Isa, with a purity greater than 99.99%; the chromium source is Te powder, provided by McLean, with a purity of 99.99% and a particle size of 200 mesh.

[0034] Chromium-based tellurides, as a novel class of magnetic materials, have attracted increasing attention due to their high Curie temperatures (Tc) (180-340 K). 1+δ Te2 is formed by stacking Te-Cr-Te three-layer structures along the c-axis, with weak van der Waals forces binding the layers together. By intercalating chromium atoms at different positions within the interlayers, chromium-based tellurides with varying proportions can be achieved, such as CrTe2, Cr2Te3, Cr3Te4, and CrTe. Ferromagnetic coupling is maintained through Cr-Te-Cr superexchange interactions, while the intercalated Cr atoms exhibit antiferromagnetic coupling. The difference in the number of intercalated Cr atoms causes competition between these two coupling mechanisms, leading to Cr... 1+δ Te2 exhibits abundant magnetism. Simultaneously, due to the presence of intercalated atoms, the atomic configuration on the surface of chromium-based telluride exhibits diversity, potentially leading to different temperature coefficients (Tc) due to doping mechanisms or reconstruction of two-dimensional magnetic materials. For example, application number 202110299849.3 discloses a strain-sensitive two-dimensional ferromagnetic Cr2Te3 nanosheet and its preparation method. It proposes a strain-sensitive two-dimensional ferromagnetic Cr2Te3 nanosheet grown on a mica substrate. By applying bending strain to the nanosheet, the Tc can be controlled. Under tensile stress, the highest Curie temperature can reach 210 K, far below room temperature, which greatly limits its application. Therefore, the diversity of phases in the chromium telluride system is crucial for achieving atmospherically stable and room-temperature magnetic thin-layer chromium telluride (Cr2Te3) 1+δ One of the major challenges in controllable equipment for Te2 is...

[0035] On one hand, the present invention provides an atmospherically stable two-dimensional room-temperature ferromagnetic nanosheet, wherein the chemical formula of the two-dimensional ferromagnetic nanosheet is Cr. 1+δ Te2, where 0.65≤δ≤0.75.

[0036] In this invention, Cr 1+δ Te2 has the advantage of continuously adjustable composition, and its T c The value increases with increasing Cr content. When δ ≥ 0.65, Cr... 1+δ Te2's T c It can reach above room temperature. However, as δ decreases, such as to 0.4 or 0.5, the prepared nanosheets do not exhibit room-temperature magnetism. As δ increases, Cr...1+δ The more Cr in the van der Waals interstices of Te2, the more completely the layered properties are lost when δ approaches 1. Excessively high δ causes the nanosheets to tend to grow in three dimensions during preparation, making it difficult to obtain thin-layer nanosheets. Therefore, the composition is limited to 0.65 ≤ δ ≤ 0.75.

[0037] In some specific embodiments, the morphology of the magnetic domains of the two-dimensional ferromagnetic nanosheets can be regulated by an external magnetic field or thermal excitation, causing the magnetic domains of the two-dimensional ferromagnetic nanosheets to transform from a striped domain structure to a skyrmion structure.

[0038] In this invention, 0G < the magnitude of the external magnetic field ≤ 1000G, and the direction of the external magnetic field is perpendicular to the surface of the nanosheet, either upwards or downwards. When the applied magnetic field is perpendicular to the surface of the nanosheet and upwards, as the magnetic field increases from 0G to 1000G, the striped domain structure transforms into a skyrmion structure; when the magnetic field decreases to 0G, most skyrmions disappear. Conversely, when the magnetic field is applied in the opposite direction, i.e., perpendicular to the surface of the nanosheet and downwards, as the magnetic field increases to -1000G, the striped domain structure transforms into a skyrmion structure; when the magnetic field decreases to 0G, the skyrmion structure transforms back into a striped domain structure. Therefore, the Cr content can be controlled by adjusting the magnitude of the applied magnetic field. 1+δ The generation and disappearance of skyrmions in Te2 samples.

[0039] In this invention, 300K ≤ the thermal excitation temperature ≤ 333K. Thermal excitation involves heating the two-dimensional ferromagnetic nanosheets. When heated to 313K, the striped domain structure transforms into a skyrmion structure, which remains stable. Further increasing the temperature to 333K causes the skyrmion structure to disappear. This indicates that the sample exhibits magnetic stability beyond room temperature, with a Curie temperature of approximately 333K.

[0040] In this invention, atmospherically stable Cr with room-temperature magnetic properties was successfully prepared using a chemical deposition method. 1+δ Te nanosheets were prepared with initial magnetic domains of striped domains. Under the action of an external magnetic field and thermal excitation, the generation and annihilation of skyrmions can be controlled.

[0041] In some specific embodiments, the chemical formula of the two-dimensional ferromagnetic nanosheets is Cr. 1+δ Te2, where δ is 0.65, 0.66, 0.70 or 0.75.

[0042] In some specific embodiments, the two-dimensional ferromagnetic nanosheets exhibit room-temperature magnetism and stability in terms of morphology and magnetic domain changes in an atmospheric environment. The initial magnetic domains of the two-dimensional ferromagnetic nanosheets are striped domains. The two-dimensional ferromagnetic nanosheets have a polygonal structure, which is hexagonal or triangular, with a lateral dimension of more than 10 μm and a thickness of 7-100 nm. More preferably, the lateral dimension is 20-40 μm.

[0043] In summary, this invention successfully prepared atmospherically stable two-dimensional room-temperature magnetic material Cr using chemical vapor deposition. 1+δ Te2 enables the controllable growth of two-dimensional room temperature magnetic materials. The prepared two-dimensional ferromagnetic nanosheets exhibit room temperature magnetism and stability in morphology and magnetic domain changes in atmospheric environment. The initial magnetic domains of the two-dimensional ferromagnetic nanosheets are striped domain structures. The generation and annihilation of skyrmions can be controlled by magnetic field and thermal excitation, making it an ideal candidate material for skyrmion-based spintronic devices.

[0044] On the other hand, the present invention provides a method for preparing the above-mentioned atmospherically stable two-dimensional room-temperature ferromagnetic nanosheets, comprising the following steps: placing a tellurium source and a chromium source in corresponding first and second temperature zones of a dual-temperature zone tube furnace; the tellurium source, after being heated in the first temperature zone, forms vapor and is carried to the second temperature zone by a carrier gas, where it reacts with the chromium source gas at 850-860°C, and after deposition on the substrate surface, a two-dimensional room-temperature ferromagnetic Cr nanosheet is obtained. 1+δ Te2 nanosheets.

[0045] In this invention, Cr is prepared 1+δ A schematic diagram of the chemical vapor deposition apparatus for Te2 is shown below. Figure 1 A dual-temperature zone tube furnace was used. Quartz boats containing Te powder and CrCl3 powder were placed in the first and second temperature zones, respectively. The quartz boats containing Te powder and CrCl3 powder were sequentially fed into the tube furnace from the right side, with the distances between the Te powder and CrCl3 powder and the opening of the right-side quartz tube being 80 cm and 58 cm, respectively. The area containing the Te powder was the upstream zone, and the carrier gas entered from the left end of the quartz tube. Figure 2 For the growth of Cr by chemical vapor deposition 1+δ The Te2 substrate placement diagram shows two 0.5cm × 1cm substrates with polished surfaces facing upwards placed on either side of the CrCl3 powder, with a 1cm gap between them. A 1cm × 2cm substrate with polished surfaces facing downwards is placed on top. The substrates can be any of silicon oxide, mica, or sapphire. Before use, the substrates require a series of cleaning steps to ensure cleanliness. The substrates are cleaned using an ultrasonic cleaner. The silicon oxide substrate is placed in an acetone solution heated to 40°C for 10 minutes, followed by cleaning in a room-temperature isopropanol solution for 10 minutes, then in an ethanol solution for 10 minutes, and finally ultrasonically cleaned with deionized water for 10 minutes. After completion, it is dried with nitrogen gas.

[0046] In this invention, the temperature of the second temperature zone reaction can be any specific value between 850-860℃, such as 850℃, 851℃, 852℃, 853℃, 854℃, 855℃, 856℃, 857℃, 858℃, 859℃, or 860℃, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable and will not be elaborated here. More preferably, the temperature range is 550℃. The preparation process of this invention involves no complex operating steps or expensive raw materials, the equipment is simple, and the operation is straightforward.

[0047] In this invention, the tellurium source and chromium source are placed in front of a dual-temperature zone tube furnace. Argon gas is introduced into the tube furnace beforehand and the furnace is heated to 200°C and held for 10 minutes. At the same time, nitrogen gas is used to purge the furnace to ensure that the gas atmosphere inside the furnace is oxygen-free and water-free before the experiment.

[0048] In some specific implementations, the mass ratio of the tellurium source to the chromium source is 20-40:1.5-3, the tellurium source is Te powder, and the chromium source is CrCl3 powder. Polished substrates with their polished surfaces facing upwards are placed on both sides of the CrCl3 powder, with a 1cm gap between the two substrates. A polished substrate with its polished surface facing downwards is placed on top of the CrCl3 powder. In this invention, there are no strict requirements on the particle size of the raw materials CrCl3 powder and Te powder. Since CrCl3 is highly susceptible to hydrolysis, the raw materials must be kept away from air as much as possible during operation. The weighing process is completed in a nitrogen-filled glove box, and the CrCl3 powder is stored inside the glove box. The mass ratio of the tellurium source to the chromium source can be any specific ratio between 20-40:1.5-3, such as 40:2.4, 40:2.3, 20:1.9, or 20:2.5, but it is not limited to the listed ratios. Other unlisted values ​​within the above range are also applicable and will not be elaborated upon here.

[0049] In some specific implementations, the temperature of the first temperature zone is 550-600℃, and the reaction holding time is 20 minutes. In this invention, the temperature range can be any specific value between 550-600℃, such as 550℃, 560℃, 570℃, 580℃, 590℃, or 600℃, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable and will not be elaborated upon here. More preferably, the temperature range is 550℃.

[0050] In some specific implementations, the carrier gas is an argon-hydrogen mixture, in which the hydrogen volume content is 15-20%, and the carrier gas flow rate is 55-60 sccm. In this invention, the carrier gas flow rate can be any specific value between 55-60 sccm, such as 55 sccm, 56 sccm, 57 sccm, 58 sccm, 59 sccm, or 60 sccm, etc., and the hydrogen volume percentage in the argon-hydrogen mixture can be any value between 15-20%, such as 15%, 16%, 17%, 18%, 19%, or 20%, etc., but is not limited to the specific values ​​listed. Other unlisted values ​​within the above range are also applicable and will not be elaborated here.

[0051] The following specific examples will provide further explanation.

[0052] Example 1

[0053] A method for preparing atmospherically stable two-dimensional room-temperature ferromagnetic nanosheets includes the following steps:

[0054] S1. Before placing the quartz boat containing the raw materials into the tube furnace, the gas inside the tube furnace must be cleaned. The specific measures are to turn on the vacuum pump, heat the tube furnace to 200°C, keep it at that temperature for 10 minutes, and at the same time use nitrogen to purge to remove water vapor and oxygen from the quartz tube. After cooling, high-purity argon is introduced to restore the atmospheric pressure.

[0055] Before use, silicon oxide (SiO2) substrates need to be cleaned with an ultrasonic cleaner. Place the SiO2 substrate in an acetone solution heated to 40°C and clean for 10 minutes. Next, place it in a room temperature isopropanol solution and clean for 10 minutes. Then, place it in an ethanol solution and clean for 10 minutes. Finally, ultrasonically clean it with deionized water for 10 minutes. After the cleaning is completed, dry it with nitrogen gas.

[0056] S2. Weigh 40 mg of Te powder and transfer it to the corresponding quartz boat. Weigh 2.4 mg of CrCl3 powder in a glove box and transfer it to the corresponding quartz boat as well. Place the SiO2 substrate stably in the quartz boat inside the glove box. Finally, seal the quartz boat and remove it to avoid contact with air.

[0057] S3. Quartz boats containing Te powder and CrCl3 powder are sequentially fed into the right side of the tube furnace. The distances of the Te powder and CrCl3 powder from the right side quartz tube opening are 80cm and 58cm, respectively.

[0058] S4. Turn on the vacuum pump. When the resistance vacuum gauge reading is less than 10 Pa, the air inside the tube can be considered to have been purged. Close the vacuum pump valve and the vacuum pump. Adjust the gas mixing system to control the flow rate of high-purity argon at 500 sccm. When the gas pressure inside the quartz tube reaches one standard atmosphere, open the outlet valve. Continue to purge with Ar for 10 minutes to ensure the quartz tube is thoroughly purged.

[0059] S5. Adjust the gas mixing system to output a 20% argon-hydrogen mixture at a volume fraction of 60 sccm as the carrier gas. The first temperature zone of the tubular furnace is 550℃, and the second temperature zone is 850℃, with a heating time of 40 min and a holding time of 20 min for both zones. After the reaction, allow it to cool naturally. Cr will appear on the surface of the SiO2 substrate. 1.65 Te2 is generated. Preparation of Cr 1+δ A schematic diagram of the chemical vapor deposition apparatus for Te2 is shown below. Figure 1 .

[0060] Example 2

[0061] A method for preparing atmospherically stable two-dimensional room-temperature ferromagnetic nanosheets includes the following steps:

[0062] S1. Before placing the quartz boat containing the raw materials into the tube furnace, the gas inside the tube furnace must be cleaned. The specific measures are to turn on the vacuum pump, heat the tube furnace to 200°C, keep it at that temperature for 10 minutes, and at the same time use nitrogen to purge to remove water vapor and oxygen from the quartz tube. After cooling, high-purity argon is introduced to restore the atmospheric pressure.

[0063] Before use, the SiO2 substrate needs to be cleaned with an ultrasonic cleaner. Place the SiO2 substrate in an acetone solution and heat it to 40°C for 10 minutes. Then place it in a room temperature isopropanol solution for 10 minutes, followed by an ethanol solution for 10 minutes. Finally, ultrasonically clean it with deionized water for 10 minutes. After the cleaning is completed, dry it with nitrogen gas.

[0064] S2. Weigh 40 mg of Te powder and transfer it to the corresponding quartz boat. Weigh 2.3 mg of CrCl3 powder in a glove box and transfer it to the corresponding quartz boat as well. Place the SiO2 substrate stably in the quartz boat inside the glove box. Finally, seal the quartz boat and remove it to avoid contact with air.

[0065] S3. Quartz boats containing Te powder and CrCl3 powder are sequentially fed into the right side of the tube furnace. The distances of the Te powder and CrCl3 powder from the right side quartz tube opening are 80cm and 58cm, respectively.

[0066] S4. Turn on the vacuum pump. When the resistance vacuum gauge reading is less than 10 Pa, the air inside the tube can be considered to have been purged. Close the vacuum pump valve and the vacuum pump. Adjust the gas mixing system to control the flow rate of high-purity argon at 500 sccm. When the gas pressure inside the quartz tube reaches one standard atmosphere, open the outlet valve. Continue to purge with Ar for 10 minutes to ensure the quartz tube is thoroughly purged.

[0067] S5. Adjust the gas mixing system to output a 20% argon-hydrogen mixture at a volume fraction of 60 sccm as the carrier gas. The first temperature zone of the tubular furnace is 550℃, and the second temperature zone is 858℃, with a heating time of 40 min and a holding time of 20 min for both. After the reaction, allow it to cool naturally. Cr will appear on the surface of the SiO2 substrate. 1.66 Te2 is generated. Preparation of Cr 1+δ A schematic diagram of the chemical vapor deposition apparatus for Te2 is shown below. Figure 1 .

[0068] Example 3

[0069] A method for preparing atmospherically stable two-dimensional room-temperature ferromagnetic nanosheets includes the following steps:

[0070] S1. Before placing the quartz boat containing the raw materials into the tube furnace, the gas inside the tube furnace must be cleaned. The specific measures are to turn on the vacuum pump, heat the tube furnace to 200°C, keep it at that temperature for 10 minutes, and at the same time use nitrogen to purge to remove water vapor and oxygen from the quartz tube. After cooling, high-purity argon is introduced to restore the atmospheric pressure.

[0071] Before use, the SiO2 substrate needs to be cleaned with an ultrasonic cleaner. Place the SiO2 substrate in an acetone solution and heat it to 40°C for 10 minutes. Then place it in a room temperature isopropanol solution for 10 minutes, followed by an ethanol solution for 10 minutes. Finally, ultrasonically clean it with deionized water for 10 minutes. After the cleaning is completed, dry it with nitrogen gas.

[0072] S2. Weigh 20 mg of Te powder and transfer it to the corresponding quartz boat. Weigh 1.9 mg of CrCl3 powder in a glove box and transfer it to the corresponding quartz boat as well. Place the SiO2 substrate stably in the quartz boat inside the glove box. Finally, seal the quartz boat and remove it to avoid contact with air.

[0073] S3. Quartz boats containing Te powder and CrCl3 powder are sequentially fed into the right side of the tube furnace. The distances of the Te powder and CrCl3 powder from the right side quartz tube opening are 80cm and 58cm, respectively.

[0074] S4. Turn on the vacuum pump. When the resistance vacuum gauge reading is less than 10 Pa, the air inside the tube can be considered to have been purged. Close the vacuum pump valve and the vacuum pump. Adjust the gas mixing system to control the flow rate of high-purity argon at 500 sccm. When the gas pressure inside the quartz tube reaches one standard atmosphere, open the outlet valve. Continue to purge with Ar for 10 minutes to ensure the quartz tube is thoroughly purged.

[0075] S5. Adjust the gas mixing system to output a 20% argon-hydrogen mixture at a volume fraction of 60 sccm as the carrier gas. The first temperature zone of the tubular furnace is 550℃, and the second temperature zone is 858℃, with a heating time of 40 min and a holding time of 20 min for both. After the reaction, allow it to cool naturally. Cr will appear on the surface of the SiO2 substrate. 1.70 Te2 is generated. Preparation of Cr 1+δ A schematic diagram of the chemical vapor deposition apparatus for Te2 is shown below. Figure 1 .

[0076] Example 4

[0077] A method for preparing atmospherically stable two-dimensional room-temperature ferromagnetic nanosheets includes the following steps:

[0078] S1. Before placing the quartz boat containing the raw materials into the tube furnace, the gas inside the tube furnace must be cleaned. The specific measures are to turn on the vacuum pump, heat the tube furnace to 200°C, keep it at that temperature for 10 minutes, and at the same time use nitrogen to purge to remove water vapor and oxygen from the quartz tube. After cooling, high-purity argon is introduced to restore the atmospheric pressure.

[0079] Before use, the SiO2 substrate needs to be cleaned with an ultrasonic cleaner. Place the SiO2 substrate in an acetone solution and heat it to 40°C for 10 minutes. Then place it in a room temperature isopropanol solution for 10 minutes, followed by an ethanol solution for 10 minutes. Finally, ultrasonically clean it with deionized water for 10 minutes. After the cleaning is completed, dry it with nitrogen gas.

[0080] S2. Weigh 20mg of Te powder and transfer it to the corresponding quartz boat. Weigh 2.5mg of CrCl3 powder in a glove box and transfer it to the corresponding quartz boat as well. Place the SiO2 substrate stably in the quartz boat inside the glove box. Finally, seal the quartz boat and remove it to avoid contact with air.

[0081] S3. Quartz boats containing Te powder and CrCl3 powder are sequentially fed into the right side of the tube furnace. The distances of the Te powder and CrCl3 powder from the right side quartz tube opening are 80cm and 58cm, respectively.

[0082] S4. Turn on the vacuum pump. When the resistance vacuum gauge reading is less than 10 Pa, the air inside the tube can be considered to have been purged. Close the vacuum pump valve and the vacuum pump. Adjust the gas mixing system to control the flow rate of high-purity argon at 500 sccm. When the gas pressure inside the quartz tube reaches one standard atmosphere, open the outlet valve. Continue to purge with Ar for 10 minutes to ensure the quartz tube is thoroughly purged.

[0083] S5. Adjust the gas mixing system to output a 20% argon-hydrogen mixture at a volume fraction of 60 sccm as the carrier gas. The first temperature zone of the tubular furnace is 550℃, and the second temperature zone is 858℃, with a heating time of 40 min and a holding time of 20 min for both. After the reaction, allow it to cool naturally. Cr will appear on the surface of the SiO2 substrate. 1.75 Te2 is generated. Preparation of Cr 1+δ A schematic diagram of the chemical vapor deposition apparatus for Te2 is shown below. Figure 1 .

[0084] The properties of the chromium telluride nanosheets prepared in Examples 1-4 were measured, and the results are as follows.

[0085] Morphological determination:

[0086] Figure 3 The Cr prepared in Example 1 of this invention 1+δ Optical photographs of Te2. For example... Figure 3 As shown, Cr was observed 1+δ Te2 exhibits a hexagonal or triangular structure with a lateral dimension of 20-40 μm. Figure 3 The caliber bar is 20 μm. Figure 4 Cr prepared in Example 1 1+δ Thickness test chart for Te2. (See attached image) Figure 4 As shown, Figure 4 The thicknesses of (a), (b), (c), and (d) are 7.7 nm, 33 nm, 54 nm, and 76 nm, respectively. Cr 1+δ Te2 has a smooth and clean surface. Figure 4 The caliber bar is 10 μm. Figure 5 Cr prepared in Example 1 1+δ Te2 element distribution test plot, Figure 5 (a) is the Cr prepared in Example 1. 1+δ Scanning electron microscope image of Te2, (b) is Figure 5 (a) is the scanning electron microscope image of the area selected in the box, (c) is the Cr elemental distribution map, and (d) is the Te elemental distribution map. Figure 5 As shown, the uniform color distribution indicates that Cr 1+δ The two elements were evenly distributed in the Te2 sample. Figure 5 The caliber bar is 5μm.

[0087] Magnetic property measurement:

[0088] Magnetic force microscopy (MFM) was used to detect Cr prepared in Example 2. 1+δ The microscopic magnetic domain structure of Te2. During testing, the sample surface morphology information is first acquired using a first-line scan. Then, the probe is raised to a certain height to detect the magnetic signal. The magnetic field between the probe and the sample creates a magnetic gradient, which further causes a shift in the probe's resonant frequency. This frequency shift leads to a phase difference, thus revealing the magnetic domain distribution of the sample. A negative frequency shift indicates an attractive interaction between the probe tip and the sample, while a positive frequency shift indicates a repulsive interaction, presenting two distinct contrasts. Red represents the attractive interaction between the probe tip and the sample surface, while blue represents the repulsive interaction. Figure 6 Preparation of Cr in Example 2 of the present invention 1+δ The room temperature magnetic properties test graph of Te2, in which... Figure 6 In the middle (a), Cr 1+δ Thickness test images of Te2, (b) is Cr 1+δ Magnetic domain distribution diagram of Te2. (See diagram below.) Figure 6 As shown, the sample has a thickness of 77 nm and exhibits a well-defined striped domain structure, proving that Cr... 1+δ Te2 exhibits good room-temperature ferromagnetism. Figure 6 The caliber bar is 5μm.

[0089] An out-of-plane magnetic field was applied using the variable field module of a magnetic microscope to investigate the effects of the magnetic field on the preparation of Cr in Example 3. 1+δ Evolution of the microscopic magnetic domain structure of Te2. Figure 7 Cr prepared in Example 3 of this invention 1+δ Evolution of the microscopic magnetic domain structure of Te2 under an applied magnetic field. Figure 7 In the medium magnetic field, "+" and "-" indicate the direction of the magnetic field. "+" represents a direction perpendicular to the nanosheet surface, pointing upwards; "-" represents a direction perpendicular to the nanosheet surface, pointing downwards. For example... Figure 7 As shown, the sample exhibits a striped domain structure when no magnetic field is applied. As the magnetic field increases to 1000 G, the striped domain structure transforms into a skyrmion structure. When the magnetic field decreases to 0 G, most of the skyrmions disappear. Similarly, when a magnetic field is applied in the opposite direction, as the magnetic field increases to -1000 G, the striped domain structure transforms into a skyrmion structure. When the magnetic field decreases to 0 G, the skyrmion structure reverts to the striped structure. These phenomena indicate that the Cr content can be controlled by adjusting the magnitude of the applied magnetic field. 1+δ The generation and disappearance of skyrmions in Te2 samples.

[0090] The temperature of the sample stage was increased using the temperature-changing module of a magnetic microscope to investigate the preparation of Cr in Example 4 under thermal excitation. 1+δ Evolution of the microscopic magnetic domain structure of Te2. Figure 8 Cr prepared in Example 4 of this invention 1+δ Evolution of the microscopic magnetic domain structure of Te2 under thermal excitation. (See diagram.) Figure 8 As shown, at room temperature (300 K), the sample exhibits a striped domain structure. Heating the sample to 313 K transforms the striped domain structure into a skyrmion structure, which remains stable. Further increasing the temperature to 333 K causes the skyrmion structure to disappear. This indicates that the sample possesses magnetic stability beyond room temperature, with a Curie temperature of approximately 333 K, demonstrating the feasibility of temperature-controlled skyrmion structure generation.

[0091] Atmospheric environmental stability test:

[0092] Figure 9 Cr prepared in Example 1 of this invention 1+δ Stability test results for Te2. Figure (a) shows the results for Cr. 1+δ AFM images of Te2 nanosheets after heating at 100°C in air for 5 min and immersing in deionized water for 20 min showed that the nanosheets did not decompose and the surface was clean without adsorbing any impurities. Figure 9 (b) is fresh Cr 1+δ Te2 nanosheets and their Raman spectra after being exposed to air for six months. (See attached image.) Figure 9 As shown in (b), at 120.5cm -1 and 138.4cm -1 Two distinct characteristic peaks were observed at each location, with no significant changes, indicating that Cr 1+δ Te2 did not oxidize or deteriorate in air. The above tests demonstrate the excellent atmospheric stability of the sample.

[0093] Furthermore, this invention provides an application of two-dimensional room-temperature ferromagnetic nanosheets in race track memory. Figure 10 To utilize the Cr prepared in Examples 1-4 of this invention 1+δ A schematic diagram illustrating the application of Te2 in track memory. (See diagram for example.) Figure 10As shown, the track memory includes a substrate 2, on which a nanotrack 4 is disposed. A write head 3 and a read head 5 are respectively disposed on the upper walls of both ends of the nanotrack 4. A spin polarization current 1 is also disposed on one side of the substrate 2 and the nanotrack 4, and the spin polarization current 1 is electrically connected to the nanotrack 4. The complete read, write, and storage process of skyrmions includes: the track memory generates magnetic skyrmions by vertically injecting spin polarization current 1 into the write head 3; the magnetic skyrmions move along the nanotrack 4 under the drive of the in-plane current; and finally, the magnetic skyrmion signal is read by the read head 5. Information is stored equidistantly inside the magnetic track, where the presence of skyrmions is "1" and the absence of skyrmions is "0". Atmospherically stable two-dimensional room-temperature magnetic Cr 1+δ The key to applying Te2 to skyrmion memory lies in the controlled generation of skyrmion structures under an external magnetic field. In skyrmion memory, current drives magnetic skyrmions to move, and the recorded bit information moves along the track, but the track itself (including the read / write units) remains stationary. Due to the absence of moving mechanical parts, skyrmion memory exhibits extremely high shock and drop resistance, meeting the application requirements of mobile devices.

[0094] In summary, this invention has achieved atmospherically stable two-dimensional room-temperature magnetic material Cr through chemical vapor deposition. 1+δ Controlled growth of Te2 to prepare Cr 1+δ Te2 initially exhibits striated magnetic domains, and under the influence of an external magnetic field and thermal excitation, the generation and annihilation of skyrmions can be controlled. This material can be applied to skyrmion track memory.

[0095] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0096] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. An air-stable two-dimensional room-temperature ferromagnetic nanosheet, characterized in that, The chemical formula of the two-dimensional ferromagnetic nanosheets is Cr. 1+δ Te2, where 0.65≤ δ ≤0.75; The initial magnetic domains of the two-dimensional ferromagnetic nanosheets are striped domains. The morphology of the magnetic domains of the two-dimensional ferromagnetic nanosheets can be regulated by an external magnetic field or thermal excitation, so that the magnetic domains of the two-dimensional ferromagnetic nanosheets can be transformed from striped domain structure to skyrmion structure.

2. The atmospherically stable two-dimensional room-temperature ferromagnetic nanosheet according to claim 1, characterized in that, 0G < the magnitude of the external magnetic field ≤ 1000 G, and the direction of the external magnetic field is perpendicular to the surface of the nanosheet, either upward or downward.

3. The atmospherically stable two-dimensional room-temperature ferromagnetic nanosheet according to claim 1, characterized in that, 300K ≤ the temperature of the thermal excitation ≤ 333 K.

4. The air-stable, two-dimensional, room-temperature ferromagnetic nanoplatelets of claim 1, wherein, The two-dimensional ferromagnetic nanosheets have a chemical formula of Cr 1+δ Te2, wherein δ 0.65, 0.66, 0.70, or 0.

75.

5. The air-stable, two-dimensional, room-temperature ferromagnetic nanoplatelets of claim 1, wherein, The two-dimensional ferromagnetic nanosheets exhibit room-temperature magnetism and stability in morphology and magnetic domain changes in atmospheric environment. The initial magnetic domains of the two-dimensional ferromagnetic nanosheets are striped domains. The two-dimensional ferromagnetic nanosheets have a polygonal structure, which is hexagonal or triangular, with a lateral dimension of more than 10 μm and a thickness of 7-100 nm.

6. A process for the preparation of the atmospheric stable two-dimensional room-temperature ferromagnetic nanosheets according to any one of claims 1 to 5, characterized in that, Includes the following steps: The tellurium source and chromium source are placed in the first and second temperature zones of a dual-temperature zone tube furnace, respectively. The tellurium source vaporizes under heating in the first temperature zone and is carried to the second temperature zone by a carrier gas, where it reacts with the chromium source gas at 850-860 °C. This reaction results in the deposition of a two-dimensional room-temperature ferromagnetic Cr on the substrate surface. 1+δ Te2 nanosheets.

7. The method of claim 6, wherein the method further comprises the step of: The mass ratio of the tellurium source to the chromium source is 20-40:1.5-3, wherein the tellurium source is Te and the chromium source is CrCl3; The CrCl3 has a polished substrate on each side with the polished surface facing upwards, and the distance between the two substrates is 1 cm. At the same time, a polished substrate is placed on top of the CrCl3 with the polished surface facing downwards.

8. The method of claim 7, wherein the method is performed in the presence of a reducing agent. The temperature of the first temperature zone is 550-600 ℃, and the reaction holding time is 20 min; The carrier gas is an argon-hydrogen mixture, with a hydrogen volume content of 15-20% and a carrier gas flow rate of 55-60 sccm.

9. The use of an atmospherically stable two-dimensional room-temperature ferromagnetic nanosheet according to any one of claims 1-5 in a magnetic information storage device or a spintronic device.

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