A cubic MnSe2 single crystal that can be used as an alternating magnetic material and a preparation method thereof

Abstract

The present invention provides a method for preparing magnetic materials, in particular a cubic MnSe2 single crystal that can be used as an alternating magnetic material and a method for preparing the same, which belongs to the field of magnetic materials. The method for preparing the MnSe2 single crystal provided by the present invention includes the following steps: S1, weighing manganese, selenium and iodine in a container, evacuating and encapsulating the container; S2, performing a heat preservation treatment on the container evacuated and encapsulated in step S1; S3, performing a cooling treatment on the container that has undergone the heat preservation treatment in step S2; S4, taking out the sample in the container after the cooling treatment in step S3, and obtaining a cubic MnSe2 single crystal that can be used as an alternating magnetic material after soaking the sample in an organic solvent; in step S1, the mass ratio of the manganese, selenium and iodine is 1:5:(1~2). The method for preparing the MnSe2 single crystal provided by the present invention has the advantages of simple operation and excellent product performance, and the product meets the requirements of conventional magnetic, electrical, thermal and other transport tests.

Description

Technical Field

[0001] The present invention relates to the field of magnetic materials, and in particular to a cubic MnSe2 single crystal that can be used as an alternating magnetic material and a preparation method thereof. Background Art

[0002] Altermagnetism is a new type of magnetism proposed recently. Its characteristics are alternating spin polarization in real space crystal structure and momentum space band structure. It not only has ferromagnetic spin band splitting, but also has zero net magnetic moment in antiferromagnetism. This material with ferromagnetic and antiferromagnetic properties is divided into a third magnetic phase (alternating magnetic phase) by the method of non-relativistic spin symmetry group. The magnetic unit cell of the alternating magnetic material is constructed by expanding the non-magnetic original unit cell, thereby obtaining a non-zero propagation vector of the magnetic structure. This connection between the magnetic structure and the order of the sublattice provides an additional degree of freedom for the super unit cell alternating magnet, so that the order parameter of the spatial direction can be controlled.

[0003] MnSe2 is a candidate material for the d-wave of super single-cell alternating magnets. MnSe2 single crystals have a cubic pyrite structure, which is very similar to the NaCl structure, and contain discrete Se2 groups. Mn atoms are located in octahedral positions with six nearest neighbor Se atoms, while Se coordination is tetrahedral (consisting of one selenium atom and three manganese atoms). At present, the method used to prepare MnSe2 single crystals is to prepare samples by chemical reduction in a high-temperature and high-pressure Teflon autoclave. However, the MnSe2 single crystals prepared by this method often have the disadvantages of irregular shape and a molar ratio of Mn to Se that is not 1:2, making them difficult to use as alternating magnetic materials. Therefore, preparing MnSe2 single crystals that meet the requirements is the first and most important step in the research.

[0004] At the same time, the existing technology can only prepare micron-sized MnSe2 single crystals, which cannot meet the conventional electrical performance transport test requirements. Summary of the invention

[0005] The technical problem to be solved by the present invention is how to prepare a MnSe2 single crystal with a large unit cell volume, regular morphology and meeting the conventional electrical performance transport test requirements.

[0006] In order to solve the above problems, the first aspect of the present invention provides a method for preparing a cubic MnSe2 single crystal that can be used as an alternating magnetic material, which specifically comprises the following steps:

[0007] S1. Weigh manganese, selenium and iodine into a container, evacuate the container and seal it;

[0008] S2, heating and heat-insulating the container that has been evacuated and packaged in step S1;

[0009] S3, cooling the container that has been heated and insulated in step S2;

[0010] S4, taking out the sample in the container after the temperature reduction treatment in step S3, and soaking the sample in an organic solvent to obtain a cubic MnSe2 single crystal that can be used as an alternating magnetic material.

[0011] The prior art often adopts a precipitation slow-release synthesis method to synthesize MnSe2 single crystals. Compared with the prior art, the present invention adopts a chemical vapor transport method to prepare MnSe2 single crystals that can be used as alternating magnetic materials. In step S1, the container is evacuated to remove air and other impurity gases therein, and then the container is sealed. The heating and heat preservation treatment and the subsequent cooling treatment in steps S2 and S3 can accurately control the crystal growth process, so that the obtained MnSe2 single crystal has good crystallinity and uniformity. Finally, the sample is immersed in an organic solvent to remove impurities or unreacted raw materials that may exist on the surface.

[0012] Preferably, the step S3 includes the following steps:

[0013] S31: cooling the temperature of the test tube to 500°C;

[0014] S32: keeping the test tube after cooling in step S31 at 500°C;

[0015] S33: The test tube that has been kept warm in the natural cooling step S32 is cooled to room temperature and then the cooling is stopped.

[0016] The present invention adopts precise temperature control in each step from heating to cooling, which is helpful to form high-quality crystals.

[0017] In step S33, the process of naturally cooling to room temperature can further reduce the stress inside the crystal and improve the integrity of the crystal.

[0018] Preferably, in step S31, the cooling rate of the test tube is (0.02295~0.03125) °C / min.

[0019] In step S31, MnSe2 single crystals with different unit cell volumes can be obtained by controlling the cooling rate in the range of 0.02295-0.03125 °C / min. Specifically, the slower the cooling rate, the larger the volume of the crystal finally obtained.

[0020] In step S32, the insulation time is 9 to 12 days.

[0021] In step S32, the long-term heat preservation at 500°C helps the crystal to grow and improve further, thereby obtaining a purer single crystal.

[0022] Preferably, in step S1, the mass ratio of the manganese element, the selenium element and the transport agent is 1: 5: (1-2). The present invention controls the mass ratio of the manganese element, the selenium element and the transport agent to 1: 5: (1-2), strictly controls the ratio of the reactants, and adopts vacuum packaging technology to prepare a single crystal that meets the conventional electrical performance transport test requirements and has a molar ratio of Mn to Se approaching 1: 2. The closer the molar ratio of Mn to Se is to 1: 2, the better the quality of the final crystal product.

[0023] In the step S1, the transport agent is iodine.

[0024] In the present invention, iodine element is used as a transport agent to catalyze the formation of the final product, MnSe2 single crystal.

[0025] Preferably, step S2 comprises the following steps:

[0026] S21: Heat the test tube to 1000 °C within 500 min;

[0027] S22: Keep the test tube heated in step S21 at 1000°C for 600-1200 minutes.

[0028] Preferably, in step S4, the organic solvent is selected from one of methanol, ethanol, carbon tetrachloride, acetone and gasoline.

[0029] Furthermore, the second aspect of the present invention provides a cubic MnSe2 single crystal that can be used as an alternating magnetic material, which is prepared using the preparation method described in the first aspect.

[0030] Preferably, the cubic MnSe2 single crystal has a square crystal or a hexagonal crystal with a length of 0.5 to 1 mm.

[0031] Compared with the prior art, the present invention has the following beneficial effects: the present invention adopts chemical vapor transport method to prepare MnSe2 single crystals that can be used as alternating magnetic materials, which is a new method for preparing MnSe2 single crystals. The method directly adopts manganese and selenium as raw materials, and finally prepares MnSe2 single crystals through transport agents and specific temperature control steps. In the preparation method provided by the present invention, by controlling the mass ratio of the raw materials, the molar ratio of Mn to Se in the final product MnSe2 single crystal is finally controlled to approach 1:2. Through fine temperature control steps, the volume of the final MnSe2 single crystal reaches the millimeter level and the shape is regular. The preparation method provided by the present invention is simple to operate and can be used to prepare square or hexagonal MnSe2 single crystals with a length of 0.5 to 1 mm. The prepared MnSe2 single crystals are sufficient to meet some basic physical property tests, such as the change of magnetic susceptibility with temperature (MT), the change of magnetic susceptibility with magnetic field (MH), the change of resistivity with temperature (ρ-T) and the Hall effect, etc., enriching the alternating magnetism research system. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the optical microscope imaging result of sample M1 in Example 2 of the specific implementation mode of the present invention;

[0033] Figure 2 The X-ray spectrometer diffractometer analysis test results of sample M1 in Example 2 of the specific implementation mode of the present invention;

[0034] Figure 3 The vibrating sample magnetometer test result of sample M1 in Example 2 of the specific implementation mode of the present invention;

[0035] Figure 4 The longitudinal resistance test result of sample M1 in Example 2 of the specific implementation mode of the present invention;

[0036] Figure 5 This is the optical microscope imaging result of sample M2 in Example 3 of the specific implementation mode of the present invention;

[0037] Figure 6 This is a microcrystal image of the sample in comparative example 1 of a specific embodiment of the present invention. DETAILED DESCRIPTION

[0038] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation method and typical parameters of the present invention, and are not used to limit the parameter range described in the present invention. Reasonable changes derived therefrom are still within the scope of protection of the claims of the present invention.

[0039] It should be noted that the endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this article.

[0040] Unless otherwise defined, all terms, symbols and other scientific terms used herein are intended to have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. In some cases, the terms with conventionally understood meanings are defined herein for the purpose of illustrating or facilitating reference, and such definitions herein should not be construed as indicating significant differences from conventional understandings in the art. The technical methods described or cited herein are generally well understood by those skilled in the art and are adopted by conventional methods. Unless otherwise stated, the use of commercially available reagents and instruments is carried out in accordance with the schemes and parameters given by the manufacturer.

[0041] As described in the background technology, the MnSe2 single crystals obtained by the prior art often have defects such as irregular shape and small unit cell volume. Based on this, the specific embodiment of the present invention provides a method for preparing a cubic MnSe2 single crystal that can be used as an alternating magnetic material, comprising the following steps:

[0042] S1: weigh manganese, selenium and iodine in a mass ratio of 1: 5: (1-2) into a test tube, and evacuate and seal the test tube;

[0043] S21: Heat the test tube to 1000 °C within 500 min;

[0044] S22: keeping the test tube heated in step S21 at 1000°C for 600-1200 minutes;

[0045] S31: cool the temperature of the test tube to 500 °C at a cooling rate of (0.02295~0.03125) °C / min;

[0046] S32: keeping the test tube after cooling in step S31 at 500° C. for 9 to 12 days;

[0047] S33: naturally cooling the test tube after the insulation in step S32 is completed to room temperature and then the cooling is stopped;

[0048] S4: Take out the sample in the test tube after the cooling in step S3, and soak the sample in an organic solvent to obtain a cubic MnSe2 single crystal that can be used as an alternating magnetic material.

[0049] In step S1 of the above embodiment, manganese and selenium are used as raw materials to directly participate in the synthesis of MnSe2 single crystals, and iodine is used as a transport agent to catalyze the formation of MnSe2 single crystals.

[0050] By controlling the mass ratio of manganese, selenium and iodine, the molar ratio of Mn to Se in the subsequent MnSe2 single crystal can be close to 1:2. The purpose of vacuuming is to prevent impurity gases such as oxygen from affecting the purity of the MnSe2 single crystal.

[0051] In step S31 of the above embodiment, the unit cell size of the final MnSe2 single crystal can be controlled by controlling different cooling rates. The lower the cooling rate, the larger the final unit cell volume.

[0052] The technical solution of the present invention is further described below through specific implementation methods.

[0053] Example 1

[0054] S1: In the glove box, the raw materials are placed in a test tube at a mass ratio of Mn: Se: I2 of 1: 5: 1 and evacuated, and the test tube is fired with a hydrogen-oxygen machine to isolate the sample from the outside;

[0055] S21: placing the packaged test tube in a high temperature tube furnace and heating it to 1000°C for 500 minutes;

[0056] S22: keeping the test tube heated in step S21 at 1000°C for 1000 minutes;

[0057] S31: Cool the temperature of the test tube to 500 °C at a cooling rate of 0.03125 °C / min;

[0058] S32: keeping the test tube after cooling in step S31 at 500° C. for 10 days;

[0059] S33: naturally cooling the test tube after the insulation in step S32 is completed to room temperature and then the cooling is stopped;

[0060] S4: Take out the sample in the test tube after cooling in step S33, soak the sample in alcohol to obtain a cubic MnSe2 single crystal that can be used as an alternating magnetic material. The sample material is marked as M1.

[0061] The following are sample characterizations:

[0062] Optical microscope imaging: Place sample M1 under an optical microscope and obtain its optical photograph as shown below: Figure 1 As shown, the average edge size is about 0.5 mm.

[0063] X-ray diffractometer (EDX) analysis test: Figure 2As shown, the EDX composition test of sample M1 showed that the composition of the MnSe2 single crystal obtained using the aforementioned method was 1:1.895, which is close to 1:2.

[0064] Vibrating Sample Magnetometer (VSM) Test: Figure 3 As shown in the figure, the MT curve of the tested sample shows that sample M1 has antiferromagnetic characteristics, and its magnetic transition temperature is around 50 K, which has the same magnetic properties as the theoretical MnSe2 single crystal.

[0065] Longitudinal resistance test: Figure 4 As shown, the low-temperature resistance curve of sample M1 tested by Quantum Design's comprehensive physical property measurement system (ppms) shows that sample M1 is a semiconductor and has insulating properties at low temperatures, and has the same electrical properties as the theoretical MnSe2 single crystal.

[0066] In summary, sample M1 is an alternating magnetism of millimeter-scale crystals, which meets the conventional magnetic, electrical, thermal and other transport test requirements.

[0067] Example 2

[0068] S1: In the glove box, the raw materials are placed in a test tube according to the mass ratio of Mn: Se: I2 of 1: 5: 2 and evacuated, and the test tube is fired with a hydrogen-oxygen machine to isolate the sample from the outside;

[0069] S21: placing the packaged test tube in a high temperature tube furnace and heating it to 1000°C for 400 minutes;

[0070] S22: keeping the test tube heated in step S21 at 1000°C for 1200 minutes;

[0071] S31: Cool the temperature of the test tube to 500 °C at a cooling rate of 0.02295 °C / min;

[0072] S32: keeping the test tube after cooling in step S31 at 500° C. for 9 days;

[0073] S33: naturally cooling the test tube after the insulation in step S32 is completed to room temperature and then the cooling is stopped;

[0074] S4: Take out the sample in the test tube after the cooling in step S33, soak the sample in acetone to obtain a cubic MnSe2 single crystal that can be used as an alternating magnetic material. The sample material is marked as M2.

[0075] Optical microscope imaging: Place sample M2 under an optical microscope and obtain its optical photograph as shown below: Figure 5 As shown, the average edge size is about 1 mm.

[0076] In summary, the MnSe2 single crystal prepared by the specific implementation mode of the present invention is sufficient to meet the physical property tests such as the change of magnetic susceptibility with temperature (MT), the change of magnetic susceptibility with magnetic field (MH), the change of resistivity with temperature (ρ-T) and the Hall effect (Halleffect), enriching the alternating magnetism research system.

[0077] Comparative Example 1

[0078] The existing precipitation slow-release synthesis method was used as a comparative example.

[0079] To prepare R-MnSe and MnSe2 microcrystals, MnSO4 (1.51 g, 0.01 mol) was placed in a 100 mL polytetrafluoroethylene-lined autoclave and dissolved in 60 mL of deionized water. A total of 0.86 g (0.005 mol) of Na2SeO3 and 10 mL of hydrazine hydrate (N2H4‚H2O) were added to the autoclave. After stirring for 5 min, the autoclave was sealed and heated at 100 °C (for MnSe2) or 180 °C (for R-MnSe) for about 24 h. The autoclave was allowed to cool naturally to room temperature after the heat treatment. The system was transferred to 200 mL of citric acid (1 M) solution and stirred until the Mn(OH)2 precipitate dissolved. The samples were collected by filtration (MnSe2 was black and R-MnSe was dark brown), washed with deionized water and anhydrous ethanol, and then dried at 60 °C.

[0080] Synthesis of microcrystals by precipitation slow-release synthesis Figure 6 As shown, Figure 6 a, b, and c are microcrystal photos at different magnifications.

[0081] pass Figure 6 It can be seen that the MnSe2 synthesized in Comparative Example 1 has good crystallinity. The average edge size of these cubes is about 30 µm, and the average volume is about 27000 µm 3 . However, the size of the MnSe2 crystal synthesized by the cube is micron-level, which is not enough to meet the conventional electrical performance transport test. In summary, compared with the prior art, the average volume (millimeter level) of the MnSe2 single crystal prepared by the MnSe2 single crystal preparation method provided in the specific embodiment of the present invention is much larger than the MnSe2 single crystal (micrometer level) prepared by the prior art. And the magnetic properties of the MnSe2 single crystal prepared by the specific embodiment of the present invention suggest that the MnSe2 single crystal can be used as an alternating magnet material.

[0082] Although the disclosure is disclosed as above, the protection scope of the disclosure is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the disclosure, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A method for preparing a cubic MnSe2 single crystal that can be used as an alternating magnetic material, characterized in that: The following steps are involved: S1. Weigh manganese, selenium and iodine in a mass ratio of 1:5:(1-2) into a container, evacuate the container and seal it; S2, heating and heat-insulating the container that has been evacuated and sealed in step S1, specifically comprising: S21: Heat the test tube to 1000°C within 500 minutes; S22: keeping the test tube heated in step S21 at 1000° C. for 600 to 1200 minutes; S3, cooling the container that has been heated and insulated in step S2, specifically comprising: S31: Cool the temperature of the test tube to 500°C at a cooling rate of (0.02295~0.03125)°C / min; S32: keeping the test tube after cooling in step S31 at 500° C. for 9 to 12 days; S33: naturally cooling the test tube after the insulation in step S32 is completed to room temperature and then the cooling is stopped; S4. Take out the sample in the container after the cooling treatment in step S3, and soak the sample in an organic solvent to obtain a cubic MnSe2 single crystal that can be used as an alternating magnetic material. The cubic MnSe2 single crystal that can be used as an alternating magnetic material has a square crystal or a hexagonal crystal with a length of 0.5~1 mm.

2. The preparation method according to claim 1, characterized in that In step S4, the organic solvent is selected from one of methanol, ethanol, carbon tetrachloride, acetone and gasoline.

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