Cobalt-based layered ferromagnetic metal material KCo2S2 and single crystal growth method thereof

Abstract

The invention provides a cobalt-based layered ferromagnetic metal material KCo2S2 and a single crystal growth method thereof, the method comprises the following steps: using a fluxing agent method to grow a single crystal under a heating condition, the fluxing agent is CoS, the CoS fluxing agent does not introduce other impurity elements into the KCo2S2 single crystal, and the purity of the KCo2S2 single crystal is ensured. According to the method, the large-size and single-crystal cobalt-based layered material KCo2S2 is prepared, and the surface magnetic susceptibility of the material has obvious anisotropy.

Description

Technical Field

[0001] The present invention relates to the technical field of layered ferromagnetic metal materials, in particular to a cobalt-based layered ferromagnetic metal material KCo2S2 and a single crystal growth method thereof. Background Art

[0002] Layered compound AT2X2 type materials show rich physical properties. Among them, the parent of the "122" type iron-based superconductor AFe2As2 (A=K, Sr, Ba and Eu) is an antiferromagnetic metal. By introducing carriers by doping or pressurizing, the antiferromagnetic order can be suppressed to induce superconductivity. In addition, nickel-based layered materials BaNi2As2, SrNi2As2 and KNi2Se2 also show superconductivity. So far, the cobalt-based superconductors discovered in experiments are still very rare, mainly including hydrated layered cobaltates Na x CoO2·yH2O (K. Takada et al., Nature 422, 53-55 (2003)) and the recently discovered layered cobalt-based selenide oxide superconductor Na2CoSe2O (JW Cheng et al., JACS 146, 9 (2024)). Cobalt is close to iron in the periodic table, with only one more electron than iron. It also has a crystal structure and Fermi surface similar to those of iron-based compounds. Therefore, exploring new cobalt-based superconductors with similar structures will deepen our understanding of the mechanisms of unconventional superconductivity.

[0003] Single crystal materials have periodic arrangement of atoms, few impurities, and anisotropic physical properties, which can eliminate the influence of non-intrinsic factors such as grain boundary effects. They are of great value for measuring intrinsic physical properties and are indispensable for in-depth research on various novel quantum effects and rich physical phenomena. Summary of the Invention

[0004] The present invention provides a cobalt-based layered ferromagnetic metal material KCo2S2 and a single crystal growth method thereof, and prepares a large-sized single-crystal cobalt-based layered material KCo2S2, whose surface magnetic susceptibility has obvious anisotropy.

[0005] The technical solution of the present invention is achieved as follows: a method for growing a single crystal of a cobalt-based layered ferromagnetic metal material KCo2S2, the method comprising growing a single crystal using a flux method under heating conditions, wherein the flux is CoS.

[0006] CoS flux controls the melting point of KCo2S2 at 900-1200°C, and the elements of CoS are inherent in KCo2S2. CoS flux will not introduce other impurity elements into the KCo2S2 single crystal, thus ensuring the purity of the KCo2S2 single crystal.

[0007] The molar ratio of flux CoS to target substance KCo2S2 is (2-6):1, and the surface area of ​​the single crystal that can be grown is 1mm 2 ~1cm 2 Moreover, within this ratio range, it is conducive to the growth of single crystals and the formation of large-sized single crystals, avoiding the situation where there is too little flux and the purpose of fluxing cannot be achieved; at the same time, it also avoids excessive flux, which affects the nucleation of single crystals and is not conducive to the formation of large-sized single crystals.

[0008] Furthermore, the heating conditions are: keeping the temperature at 900-1200° C. for 10-30 hours under normal pressure, and then cooling to below 700° C. at a rate of 1-5° C. / hour.

[0009] Furthermore, the heating conditions are: keeping the temperature at 1000-1200° C. for 20-30 hours under normal pressure, and then cooling to below 700° C. at a rate of 2-3° C. / hour.

[0010] Furthermore, the single crystal growth method comprises the following steps:

[0011] (1) Co raw material and S raw material are mixed in a molar ratio of 1:1 to obtain a mixture, the mixture is evacuated under a sealed condition, and then flushed into a protective atmosphere;

[0012] (2) heating the mixture of step (1) to obtain a CoS precursor;

[0013] (3) The ground CoS precursor and K raw material are mixed, sealed, evacuated, and flushed into a protective atmosphere to grow a single crystal under heating conditions; the molar ratio of the K raw material to the CoS precursor is 1: (4-8), and the excess CoS in the CoS precursor serves as a flux;

[0014] (4) Dissociate the KCo2S2 single crystal from the flux CoS.

[0015] Furthermore, in step (2), the heating conditions are: maintaining the temperature at 500-800°C under normal pressure for 10-30 hours, and then cooling to room temperature at a rate of 1-5°C / min.

[0016] Furthermore, in steps (1) and (3), under sealed conditions, 10 -4 After high vacuum below Pa, fill with a protective atmosphere of 0 to 1 bar.

[0017] The cobalt-based layered ferromagnetic metal material KCo2S2 is prepared by adopting the single crystal growth method.

[0018] The cobalt-based ferromagnetic metal material KCo2S2 has a tetragonal ThCr2Si2 crystal structure with a spatial symmetry group of I4 / mmm. By performing Le Bail fitting on the diffraction data, the c-axis lattice constant range can be obtained as follows: Magnetic measurements show that its ferromagnetic transition temperature is 0~130K.

[0019] Furthermore, the cobalt-based ferromagnetic metal material KCo2S2, KCo2S2 single crystal is a sheet-like block material with a metallic luster on the surface and a size of 1mm 2 ~1cm 2 , mass is 0.001~0.1g.

[0020] Beneficial effects of the present invention:

[0021] The single crystal growth method of the present invention uses CoS flux, which prevents the introduction of other impurities into the KCo2S2 single crystal, thus ensuring the purity of the KCo2S2 single crystal. Furthermore, the molar ratio of the flux CoS to KCo2S2 is (2-6):1, which facilitates the production of large-sized single crystals. The KCo2S2 produced by the present invention is a cobalt-based matrix material with high-quality single crystals, low vacancies, and significant anisotropy in surface magnetic susceptibility, consistent with the general characteristics of single crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 This is a photo of a single crystal of KCo2S2 prepared in Example 1 of the present invention;

[0024] Figure 2 The X-ray diffraction spectrum of the single crystal KCo2S2 prepared in Example 1 of the present invention;

[0025] Figure 3 Energy dispersive X-ray spectrum of single crystal KCo2S2 prepared in Example 1 of the present invention;

[0026] Figure 4 The temperature-dependent magnetic susceptibility curve of single crystal KCo2S2 prepared in Example 1 of the present invention, wherein the magnetic field direction is parallel to the ab plane;

[0027] Figure 5 This is the temperature-dependent magnetic susceptibility curve of single crystal KCo2S2 obtained in Example 1 of the present invention, where the magnetic field direction is perpendicular to the ab plane. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0029] The present invention will be further described in detail below in conjunction with specific embodiments. The examples given are only for illustrating the present invention, not for limiting the scope of the present invention.

[0030] Example 1

[0031] A method for growing a single crystal of a cobalt-based layered ferromagnetic metal material KCo2S2 comprises the following steps:

[0032] (1) In an argon-filled glove box, Co powder and S powder with a purity higher than 99.9% were uniformly mixed in a molar ratio of 1:1 and placed in an alumina ceramic test tube;

[0033] Place the ceramic test tube containing the raw materials into the titanium tube, then transfer the titanium tube to the argon arc welding device and draw the vacuum degree to 10 -4 After the pressure is below Pa, fill it with 0.9 bar of argon and seal it;

[0034] (2) placing the sealed titanium metal tube in a high-temperature furnace, sintering it at 700°C for 20 hours, and then cooling it to room temperature at a rate of 4°C / min to obtain a CoS precursor;

[0035] (3) The CoS precursor is fully ground, and the ground CoS precursor is mixed with a K raw material with a purity higher than 99.9% at a molar ratio of 6:1, and then placed in an alumina ceramic test tube;

[0036] Place the ceramic test tube into the niobium metal tube, then transfer it to the argon arc welding device and draw the vacuum degree to 10 -4 Pa below, then fill with 0.9 bar argon and seal, then put the niobium metal tube into the quartz tube, and pump the vacuum degree to 10 -1 Pa below and sealed;

[0037] The sealed quartz tube was sintered in a high-temperature furnace at 1150°C for 20 hours, and then cooled to 700°C at a rate of 3°C / hour;

[0038] Separate the niobium metal tube, take out the alumina ceramic test tube and smash it open, and use a scalpel to dissociate the flaky single crystal to obtain a large-sized single crystal of KCo2S2.

[0039] Example 2

[0040] A method for growing a single crystal of a cobalt-based layered ferromagnetic metal material KCo2S2 comprises the following steps:

[0041] (1) In an argon-filled glove box, Co powder and S powder with a purity higher than 99.9% were uniformly mixed in a molar ratio of 1:1 and placed in an alumina ceramic test tube;

[0042] Place the ceramic test tube containing the raw materials into the titanium tube, then transfer the titanium tube to the argon arc welding device and draw the vacuum degree to 10 -4 After the pressure is below Pa, fill it with 0.9 bar of argon and seal it;

[0043] (2) placing the sealed titanium metal tube in a high-temperature furnace, sintering it at 700°C for 20 hours, and then cooling it to room temperature at a rate of 4°C / min to obtain a CoS precursor;

[0044] (3) Grinding the CoS precursor thoroughly, mixing the ground CoS precursor with a K raw material with a purity higher than 99.9% at a molar ratio of 4:1, and placing the mixture into an alumina ceramic test tube;

[0045] Place the ceramic test tube into the niobium metal tube, then transfer it to the argon arc welding device and draw the vacuum degree to 10 -4 Pa below, then fill with 0.9 bar argon and seal, then put the niobium metal tube into the quartz tube, and pump the vacuum degree to 10 -1 Pa below and sealed;

[0046] The sealed quartz tube was sintered in a high-temperature furnace at 1000°C for 20 hours, and then cooled to 700°C at a rate of 5°C / hour;

[0047] Separate the niobium metal tube, take out the alumina ceramic test tube and smash it open, and use a scalpel to dissociate the flaky single crystal to obtain a small-sized single crystal of KCo2S2.

[0048] Comparative Example 1

[0049] A method for growing a single crystal of a cobalt-based layered ferromagnetic metal material KCo2S2 comprises the following steps:

[0050] In an argon-filled glove box, Co powder, S powder, and K block with a purity higher than 99.9% were uniformly mixed in a molar ratio of 8:8:1 and placed in an alumina ceramic test tube;

[0051] Place the ceramic test tube into the niobium metal tube, then transfer it to the argon arc welding device and draw the vacuum degree to 10 -4 Pa below, then fill with 0.9 bar argon and seal, then put the niobium metal tube into the quartz tube, and pump the vacuum degree to 10 -1 Pa below and sealed;

[0052] The sealed quartz tube was heated to 500°C in a high-temperature furnace and kept at this temperature for 5 hours, then heated to 1000°C and kept at this temperature for 20 hours, and then cooled to 700°C at a rate of 5°C / hour;

[0053] After separating the niobium metal tube and smashing the alumina ceramic test tube, no single crystal of KCo2S2 was obtained.

[0054] Comparative Example 2

[0055] A method for growing a single crystal of a cobalt-based layered ferromagnetic metal material KCo2S2 comprises the following steps:

[0056] In an argon-filled glove box, Co powder, S powder, and K block with a purity higher than 99.9% were uniformly mixed in a molar ratio of 8:8:1 and placed in an alumina ceramic test tube;

[0057] Place the ceramic test tube into the niobium metal tube, then transfer it to the argon arc welding device and draw the vacuum degree to 10 -4 Pa below, then fill with 0.9 bar argon and seal, then put the niobium metal tube into the quartz tube, and pump the vacuum degree to 10 -1 Pa below and sealed;

[0058] The sealed quartz tube was heated to 1000°C in a high-temperature furnace and kept at this temperature for 20 hours, and then cooled to 700°C at a rate of 5°C / hour;

[0059] After separating the niobium metal tube, it was found that the alumina ceramic test tube was shattered.

[0060] Single crystal photo of single crystal KCo2S2 Figure 1 As shown, the larger one is approximately 2 mm × 2 mm × 0.2 mm.

[0061] X-ray diffraction test

[0062] Directly scan the single crystal in θ-2θ mode, i.e. powder X-ray diffraction mode, and obtain the diffraction spectrum as follows Figure 2 shown. Figure 2 All the diffraction peaks are from KCo2S2 material, with sharp peaks. Figure 2 The middle inset shows that the full width at half maximum of the 002 peak is only 0.03 degrees, indicating that the quality of the single crystal is very high; Figure 2 Only the (0 02n) peak appears, where n is an integer, indicating that the single crystal grows along the ab plane.

[0063] Energy spectrum analysis

[0064] The energy dispersion X-ray spectrum of KCo2S2 single crystal was obtained by scanning electron microscope. Figure 3 shown. Figure 3The peaks obtained by energy spectrum analysis come only from three elements: K, Co and S. Composition analysis shows that the atomic percentages of K, Co and S are close to 1:2:2, which further confirms that the single crystal obtained is indeed KCo2S2.

[0065] Magnetic susceptibility test

[0066] The temperature-dependent magnetic susceptibility of a single crystal sample is measured. When the magnetic field is applied in the direction parallel to the ab plane, the obtained magnetic susceptibility versus temperature curve is as follows: Figure 4 When the direction of the applied magnetic field is perpendicular to the ab plane, the obtained magnetic susceptibility temperature curve is as shown in Figure 5 As shown. Figure 4 and Figure 5 It can be clearly seen that the ferromagnetic transition Curie temperature of the single crystal is about 120K. In addition, it can be seen that the magnetic moment is quite different when the magnetic field is parallel and perpendicular to the ab plane, and there is obvious anisotropy in the surface magnetic susceptibility, which is consistent with the general characteristics of single crystals.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for growing a single crystal of a cobalt-based ferromagnetic metal material KCo2S2, characterized by: The method comprises growing a single crystal by using a flux method under heating conditions, wherein the flux is CoS.

2. The single crystal growth method according to claim 1, wherein: The molar ratio of flux CoS to KCo2S2 is (2-6):

1.

3. The single crystal growth method according to claim 1, wherein: The heating conditions are: keeping the temperature at 900-1200° C. under normal pressure for 10-30 hours, and then cooling to below 700° C. at a rate of 1-5° C. / hour.

4. The single crystal growth method according to claim 3, wherein: The heating conditions are: keeping the temperature at 1000-1200°C for 20-30 hours under normal pressure, and then cooling to below 700°C at a rate of 2-3°C / hour.

5. The single crystal growth method according to any one of claims 1 to 4, characterized in that: The single crystal growth method comprises the following steps: (1) Co raw material and S raw material are mixed in a molar ratio of 1:1 to obtain a mixture, the mixture is evacuated under a sealed condition, and then flushed into a protective atmosphere; (2) heating the mixture of step (1) to obtain a CoS precursor; (3) The ground CoS precursor and K raw material are mixed, sealed, evacuated, and flushed into a protective atmosphere to grow a single crystal under heating conditions; the molar ratio of the K raw material to the CoS precursor is 1: (4-8), and the excess CoS in the CoS precursor serves as a flux; (4) Dissociate the KCo2S2 single crystal from the flux CoS.

6. The single crystal growth method according to claim 5, wherein: In step (2), the heating conditions are: keeping the temperature at 500-800°C under normal pressure for 10-30 hours, and then cooling to room temperature at a rate of 1-5°C / min.

7. The single crystal growth method according to claim 5, wherein: In steps (1) and (3), under sealed conditions, 10 -4 After high vacuum below Pa, fill with a protective atmosphere of 0 to 1 bar.

8. A cobalt-based ferromagnetic metal material KCo2S2 prepared by the single crystal growth method according to any one of claims 1 to 7.

9. The cobalt-based layered ferromagnetic metal material KCo2S2 according to claim 8, characterized in that: It has a tetragonal ThCr2Si2 type crystal structure, the space symmetry group is I4 / mmm, and the c-axis lattice constant range is: Its ferromagnetic transition temperature is 0~130K.

10. The cobalt-based layered ferromagnetic metal material KCo2S2 according to claim 9, characterized in that: KCo2S2 single crystal is a flake-shaped block with a metallic luster on the surface.

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