Large-size high-quality magnetic wurtzite semimetal co3sn2s2 single crystal and preparation method thereof

Abstract

This invention discloses a large-size, high-quality magnetic Weyl half-metal Co3Sn2S2 single crystal and its preparation method. The single crystal has a diameter greater than 1 cm and a length greater than 5 cm, exhibiting high quality, a complete and crack-free appearance, and a smooth surface. X-ray rocking curve analysis confirmed its high quality. l The full width at half maximum (FWHM) of the diffraction peaks is only 0.02°. Furthermore, this crystal exhibits ferromagnetism and a Curie temperature of [missing value]. T c =174 K, exhibiting a significant anomalous Hall effect: the maximum anomalous Hall conductivity is approximately 1250 S / cm, and the anomalous Hall angle is 25%. The preparation method includes controlling the molar ratio of raw materials to synthesize polycrystalline raw materials through a high-temperature solid-state reaction; further, using a modified Bridgman process, optimizing the temperature gradient, controlling the growth rate, rotation rate, and vacuum sealing environment, ultimately preparing a Co3Sn2S2 single crystal. The Co3Sn2S2 single crystal of this invention can be used in novel low-power spintronic devices, topological thermoelectric devices, etc., providing a key material foundation for the practical research of magnetic Weyl half-metals.

Description

Technical Field

[0001] This invention relates to topological quantum materials and crystal growth technology, specifically to a large-size, high-quality magnetic Weyl half-metal Co3Sn2S2 single crystal and its preparation method. Background Technology

[0002] Weyl half-metals are a very important class of topological quantum materials, divided into non-magnetic and magnetic types. Magnetic Weyl half-metals possess both intrinsic long-range magnetic order and Weyl fermion topological states, and exhibit a series of novel physical effects through the enhanced Berry curvature resulting from electronic topological properties. In 2019, Liu Defa et al. experimentally confirmed that Co3Sn2S2 is the first magnetic Weyl half-metal material. Co3Sn2S2 exhibits a layered crystal structure with space group [space group missing]. The Sn atom is located at the center of the Kagome lattice composed of Co atoms, forming a sandwich structure of S-Sn-Co3Sn, i.e., a quasi-two-dimensional lattice structure of Sn-[S-(Co3Sn)-S] along the

[0001] direction. Resistivity and magnetic measurements indicate that Co3Sn2S2 undergoes a ferromagnetic phase transition at 175 K, with an effective magnetic moment of approximately 0.3 mB for the Co atom, and the magnetic moment direction is perpendicular to the Kagome crystal plane. Angle-resolved photoelectron spectroscopy experiments show a linearly dispersed Weyl body band near the Fermi level, with three Pyl points located 60 meV above the Fermi level. The unique electronic band structure enables the magnetic Weyl half-metal Co3Sn2S2 to exhibit superior topologically enhanced transport properties, such as high carrier mobility, low effective mass, huge anomalous Hall conductance and anomalous Hall angle, significant negative magnetoresistance effect, and greatly enhanced anomalous Nernst effect. These superior properties are far superior to those of traditional magnetic materials, and it has important application prospects in low-power spintronic devices, topological magnetoelectric devices, thermoelectric power generation, and solid-state refrigeration.

[0003] However, to date, most of the Co3Sn2S2 single crystal samples reported in the literature are very small (millimeter-scale). From an application perspective, the small size of these samples poses significant challenges to subsequent device fabrication, including cutting, polishing, orientation, device fabrication, and assembly, making it difficult to meet the basic size requirements for large-area device processing and integration. Furthermore, commonly used growth methods reported in the literature (flux method, chemical vapor transport method) struggle to achieve precise control over composition, defects, stress, and grain boundaries. This results in significant differences in physical properties such as residual resistivity ratio, carrier mobility, anomalous Hall effect, and anomalous Nernst effect among samples obtained from different batches and research groups, making it difficult to corroborate experimental data and severely interfering with the accurate analysis of intrinsic topological physical mechanisms. Therefore, achieving the controllable preparation of large-size, high-quality Co3Sn2S2 single crystals is not only crucial for overcoming current experimental bottlenecks but also a necessary prerequisite for deeply revealing novel physical effects of magnetic Weyl half-metals and promoting their practical applications in spintronics and thermoelectric devices, possessing significant scientific value and application prospects. Summary of the Invention

[0004] Objective of the Invention: The objective of this invention is to provide a large-size, high-quality magnetic Weyl half-metal Co3Sn2S2 single crystal and a preparation method based on the improved Bridgman process. Specifically, by controlling a reasonable temperature gradient in the growth region and parameters such as the descent and rotation speeds suitable for the crystal, a large-size, high-quality Co3Sn2S2 single crystal was successfully prepared.

[0005] Technical solution: The large-size, high-quality magnetic Weyl half-metal Co3Sn2S2 single crystal of this invention is a centimeter-sized single crystal with a diameter of more than 1 cm and a length of more than 5 cm. It is columnar, has a metallic luster, and a complete shape.

[0006] Preferably, the easily dissociable plane of the Co3Sn2S2 crystal is (00... l )noodle.

[0007] Preferably, the Co3Sn2S2 crystal is easily dissociated (00 l The half-width at half-maximum (FWHM) of the X-ray diffraction rocking curve is only 0.02°-0.05°.

[0008] Preferably, the Co3Sn2S2 crystal exhibits ferromagnetism, and its Curie temperature is [insert temperature here]. T c = 174 K, and also has a significant anomalous Hall effect: the maximum anomalous Hall conductance under zero magnetic field is about 1250 S / cm and the anomalous Hall angle is 25%.

[0009] The present invention also provides a method for preparing Co3Sn2S2 single crystal as described above, comprising: high-temperature solid-state synthesis of polycrystalline raw materials and improved Bridgman method for growing large-size, high-quality Co3Sn2S2 crystals; The high-temperature solid-state method for synthesizing polycrystalline raw materials includes the following steps: 1) Preparation of growth raw materials: Co, Sn, and S powder are used as initial raw materials, and are prepared according to the stoichiometric ratio of Co:Sn:S = 3:2:2. To compensate for Sn volatilization, Sn is weighed in excess at 2-5 at % mol / L. The raw materials are mixed evenly by grinding and placed into a quartz tube. The mixture is then grown under vacuum (1000 ppm). -3 -10 -4 The mixture was sealed (Pa) and then polycrystalline Co3Sn2S2 was synthesized by solid-state sintering reaction. 2) Co3Sn2S2 crystal growth: The polycrystalline Co3Sn2S2 raw material prepared in step 1) is ground into powder of 50-200 mesh, and then placed into a quartz tube under vacuum (10... -3 -10 -4 (Pa) Seal; place the sealed quartz tube in a three-temperature zone descending furnace, set the temperature program, and descend at a suitable position to grow large-size, high-quality Co3Sn2S2 single crystals.

[0010] Preferably, the quartz tube used in step 1) is a round-bottomed ordinary quartz tube with a length of 10-20 cm and a diameter of 2-3 cm; the quartz tube used in step 2) is a conical-bottomed quartz tube with a length of 10-20 cm and a diameter of 1-3 cm.

[0011] Preferably, in steps 1 and 2), the sealing methods are the same or different, and they independently adopt a gas flame, an acetylene flame, or a hydrogen flame.

[0012] Preferably, in step 1), the temperature of the high-temperature solid-state sintering reaction is 800-900 ℃; the reaction time is 5-10 days.

[0013] Preferably, in step 2), the three temperature zones of the descending furnace are a high-temperature melting zone (relative position above 600 mm), a gradient cooling zone (relative position between 400-600 mm), and a low-temperature annealing zone (relative position between 0-400 mm).

[0014] Preferably, the growth temperature program in step 2) is set as follows: high temperature melting zone 900-1100 ℃, gradient cooling zone 700-900 ℃, low temperature annealing zone 400-700 ℃, and growth cycle is 7-15 days.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The large-size, high-quality magnetic Weyl half-metal Co3Sn2S2 single crystal provided by this invention solves the problems of small size and difficulty in precise quality control in existing technologies. The large-size, high-quality single crystal prepared by this invention can not only be directly used to study the intrinsic topological electronic states and topological properties of Co3Sn2S2 (such as the anomalous Hall effect and the anomalous Nernst effect), but can also be cut, polished, oriented, and assembled into prototype devices for high-efficiency spintronic devices and thermoelectric devices, and to study the application potential of magnetic Weyl half-metal Co3Sn2S2.

[0016] (2) The growth method for large-size, high-quality magnetic Weyl half-metal Co3Sn2S2 single crystals provided by this invention overcomes the limitation of small (millimeter-scale) Co3Sn2S2 single crystals prepared by commonly used techniques (such as flux method and chemical vapor transport method), and realizes the large-size preparation of Co3Sn2S2 single crystals for the first time. This method has the advantages of fast growth rate, good crystal uniformity, high quality, and the potential for controllable preparation of large-size, high-quality single crystals. By optimizing the temperature gradient, growth rate, raw material ratio, and sealing process of the Bridgman process, this invention successfully prepared large-size, high-quality Co3Sn2S2 single crystals with a diameter ≥1 cm and a length ≥5 cm, providing a solid material foundation for its practical application. Attached Figure Description

[0017] Figure 1 The image shows the X-ray diffraction (XRD) pattern of the Co3Sn2S2 polycrystalline powder synthesized in Example 1 of this invention.

[0018] Figure 2 (a) is an optical photograph of the Co3Sn2S2 crystal grown in Example 1 of the present invention; Figure 2 (b) is the EDS spectrum of the Co3Sn2S2 crystal grown in Example 1 of this invention; Figure 2 (c) in the figure is the XRD pattern of the Co3Sn2S2 single crystal grown in Example 1 of the present invention, which is the easily dissociable surface. All diffraction peaks are (0, 0, 0). l Diffraction peaks on the surface; Figure 2 (d) in the figure represents the Co3Sn2S2 crystal (00) grown in Example 1 of this invention. l The single-crystal rocking curve of the surface has a full width at half maximum (FWHM) of only 0.02°.

[0019] Figure 3 In Figure (a), the resistivity curve of the Co3Sn2S2 crystal grown in Example 1 of this invention is shown, with the transition point... T c =174 K; Figure 3 (b) in the figure is the magnetization curve of the Co3Sn2S2 crystal grown in Example 1 of the present invention; Figure 3(c) in the figure is the curve of the anomalous Hall conductivity of the Co3Sn2S2 crystal grown in Example 1 of the present invention as a function of temperature; Figure 3 In Figure (d), the curve of the anomalous Hall angle of the Co3Sn2S2 crystal grown in Example 1 of the present invention as a function of temperature is shown.

[0020] Figure 4 (a) is an optical photograph of the Co3Sn2S2 crystal grown in Example 2 of the present invention; Figure 4 (b) in the figure is the EDS spectrum of the Co3Sn2S2 crystal grown in Example 2 of the present invention; Figure 4 (c) in the figure is the XRD pattern of the Co3Sn2S2 single crystal grown in Example 2 of the present invention, which is the easily dissociable surface. All diffraction peaks are (0, 0, 0). l Diffraction peaks on the surface; Figure 4 (d) in the figure represents the Co3Sn2S2 crystal (00) grown in Example 2 of this invention. l The single-crystal rocking curve of the surface has a full width at half maximum (FWHM) of 0.05°.

[0021] Figure 5 In Figure (a), the resistivity curve of the Co3Sn2S2 crystal grown in Example 2 of this invention is shown, with the transition point... T c =177 K; Figure 5 (b) in the figure is the magnetization curve of the Co3Sn2S2 crystal grown in Example 2 of the present invention; Figure 5 (c) in the figure is the curve of the anomalous Hall conductivity of the Co3Sn2S2 crystal grown in Example 2 of the present invention as a function of temperature; Figure 5 In Figure (d), the curve of the anomalous Hall angle of the Co3Sn2S2 crystal grown in Example 2 of the present invention as a function of temperature is shown. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. Unless otherwise stated, the raw materials and reagents used in the following embodiments are commercially available products or can be prepared by known methods.

[0023] In the experiment, high-purity (above 3N) Co, Sn, and S powders were used as initial raw materials to synthesize polycrystalline raw materials. The round-bottomed quartz tubes used were made of high-purity (above 3N) quartz. The synthesized Co3Sn2S2 polycrystalline powder was used as raw material to grow the crystals. The conical-bottomed quartz tubes used were made of high-purity (above 3N) quartz.

[0024] Example 1: Co3Sn2S2 polycrystalline powder was prepared using Co, Sn, and S powder as initial raw materials via a high-temperature solid-state method. Specifically, 0.15 mol of Co powder (8.8395 g), 0.102 mol of Sn powder (12.1074 g), and 0.1 mol of S powder (3.2060 g) were weighed, with Sn in excess at 2 at% to compensate for Sn volatilization in the mixture. The mixture was thoroughly mixed and placed into a pre-prepared quartz tube. The tube was sealed under vacuum using a mechanical pump and a molecular pump, and a high-temperature solid-state sintering reaction was carried out at 800°C for 10 days to obtain Co3Sn2S2 polycrystalline powder, which was then used as the growth raw material. Figure 1 As shown, X-ray powder diffraction (XRD) analysis indicates that the prepared Co3Sn2S2 polycrystalline powders are all pure phases and no impurity peaks are observed.

[0025] Next, using Co3Sn2S2 polycrystalline powder as raw material, a modified Bridgman process was employed to grow Co3Sn2S2 crystals. Specifically, approximately 15 g of high-purity Co3Sn2S2 polycrystalline powder was weighed and placed into a prepared quartz tube (10 cm in length, 1 cm in diameter, with a conical bottom). After sealing, the quartz tube was placed in a vertical three-zone descending furnace. Temperature programs were set for each zone: the high-temperature melting zone was positioned above 600 mm, with a temperature range of 900-1100 ℃; the gradient cooling zone was positioned between 400-600 mm, with a temperature range of 700-900 ℃, and the growth zone temperature gradient was 10 ℃ / cm; the low-temperature annealing zone was positioned between 0-400 mm, with a temperature range of 400-700 ℃. The raw material was first raised to the high-temperature melting zone at 700 mm for melting and held at that position for 24 hours to ensure complete melting. The raw material was then rapidly lowered to a temperature gradient zone at 580 mm, followed by annealing at a rate of 0.1 mm / h to 350 mm for 12 h to eliminate internal stress in the crystal. The annealing temperature was 600 °C. The rotation speed was maintained at 4 rpm throughout the growth process. Finally, the furnace heating system was shut off, and the crystal was allowed to cool naturally to room temperature. The quartz tube was then removed, and the growth cycle was 15 days. Finally, high-quality, centimeter-sized Co3Sn2S2 single crystals were obtained. Figure 2 As shown in (a). Energy-dispersive X-ray spectroscopy (EDS) elemental analysis revealed that the crystal is composed of Co, Sn, and S, with no impurities. Quantitative calculations showed that the proportions of the three elements were close to the stoichiometric ratios. Figure 2 As shown in (b). XRD analysis of the easily dissociated surface of the crystal revealed diffraction peaks at (00°). l ) surface, such as Figure 2 (c) shows the easy dissociation of Co3Sn2S2 crystal (00 l X-ray diffraction rocking curve test was performed on the surface, such as... Figure 2 As shown in (d), the full width at half maximum (FWHM) of the diffraction peak is only 0.02°, indicating that the grown crystal has high quality.

[0026] Simultaneously, the physical properties of the grown Co3Sn2S2 crystals were characterized, and the results are as follows: Figure 3 As shown, the resistivity curve is as follows Figure 3 (a) shows the Curie temperature transition point. T c = 174 K; Magnetization curve as shown Figure 3 As shown in (b); the curves of anomalous Hall conductance and anomalous Hall angle as a function of temperature are respectively shown in Figure 1. Figure 3 As shown in (c) and (d), it exhibits a significant anomalous Hall effect: the maximum anomalous Hall conductance under zero magnetic field is approximately 1250 S / cm and the anomalous Hall angle is 25%.

[0027] Example 2: First, Co3Sn2S2 polycrystalline powder was prepared using Co, Sn, and S powder as initial raw materials via a high-temperature solid-state method. Specifically, 0.15 mol of Co powder (8.8395 g), 0.105 mol of Sn powder (12.432 g), and 0.1 mol of S powder (3.2060 g) were weighed, with Sn in excess at 5 at% to compensate for Sn volatilization in the mixture. The mixture was thoroughly mixed and placed into a pre-prepared quartz tube. The tube was sealed under vacuum using a mechanical pump and a molecular pump, and a high-temperature solid-state sintering reaction was carried out at 900°C for 5 days to obtain Co3Sn2S2 polycrystalline powder as the growth raw material.

[0028] Next, using Co3Sn2S2 polycrystalline powder as raw material, a modified Bridgman process was employed to grow Co3Sn2S2 crystals. Specifically, approximately 15 g of high-purity Co3Sn2S2 polycrystalline powder was weighed and placed into a prepared quartz tube (15 cm in length, 1 cm in diameter, with a conical bottom). After sealing, the quartz tube was placed in a vertical three-zone descending furnace. Temperature programs were set for each zone: the high-temperature melting zone was positioned above 600 mm, with a temperature range of 900-1100 ℃; the gradient cooling zone was positioned between 400-600 mm, with a temperature range of 800-900 ℃, and a temperature gradient of 5 ℃ / cm in the growth zone; the low-temperature annealing zone was positioned between 0-400 mm, with a temperature range of 300-800 ℃. The raw material was first raised to the high-temperature melting zone at 700 mm for melting and held at this position for 24 hours to ensure complete melting. The raw material was then rapidly lowered to a temperature gradient zone at 580 mm, followed by annealing at a rate of 2 mm / h to 300 mm for 72 h to eliminate internal stress in the crystal. The annealing temperature was 500 °C. The rotation speed was maintained at 10 rpm throughout the growth process. Finally, the furnace heating system was shut off, and the crystal was allowed to cool naturally to room temperature. The quartz tube was then removed, and the growth cycle was 7 days. Finally, high-quality, centimeter-sized Co3Sn2S2 single crystals were obtained. Figure 4 As shown in (a). Energy-dispersive X-ray spectroscopy (EDS) elemental analysis revealed that the crystal is composed of Co, Sn, and S, with no impurities. Quantitative calculations showed that the proportions of the three elements were close to the stoichiometric ratios. Figure 4 As shown in (b). XRD analysis of the easily dissociated surface of the crystal revealed diffraction peaks at (00°). l ) surface, such as Figure 4 (c) shows the easy dissociation of Co3Sn2S2 crystal (00 l X-ray diffraction rocking curve test was performed on the surface, such as... Figure 4 As shown in (d), the full width at half maximum (FWHM) of the diffraction peak is 0.05°, indicating that the grown crystal has high quality.

[0029] Simultaneously, the physical properties of the grown Co3Sn2S2 crystals were characterized, and the results are as follows: Figure 5 As shown, the resistivity curve is as follows Figure 5 (a) shows the Curie temperature transition point. T c = 177 K; Magnetization curve as shown Figure 5 As shown in (b); the curves of anomalous Hall conductance and anomalous Hall angle as a function of temperature are respectively shown in Figure 1. Figure 5 As shown in (c) and (d), it exhibits a significant anomalous Hall effect: the maximum anomalous Hall conductance under zero magnetic field is approximately 1250 S / cm and the anomalous Hall angle is 25%.

Claims

1. A large-size, high-quality magnetic Weyl half-metal Co3Sn2S2 single crystal, characterized in that, The Co3Sn2S2 crystal is a large single crystal with a diameter of more than 1 cm and a length of more than 5 cm.

2. The Co3Sn2S2 single crystal according to claim 1, characterized in that, The Co3Sn2S2 crystal has a complete appearance without cracks, and the half-width at half-maximum (FWHM) of the single-crystal X-ray rocking curve is 0.02-0.05°.

3. The Co3Sn2S2 single crystal according to claim 1, characterized in that, The Co3Sn2S2 crystal is ferromagnetic, and its Curie temperature is [insert temperature here]. T c = 174-177 K; The Co3Sn2S2 crystal exhibits an anomalous Hall effect: the maximum anomalous Hall conductance is 1250 S / cm and the anomalous Hall angle is 25%.

4. The method for preparing the Co3Sn2S2 single crystal according to claim 1, characterized in that, Includes the following steps: 1) Co3Sn2S2 polycrystalline material was prepared by high-temperature solid-state reaction and used as raw material for growing single crystals; 2) Using the improved Bridgman method to grow Co3Sn2S2 single crystals: Co3Sn2S2 polycrystalline material is loaded into a quartz tube with a conical bottom, vacuum sealed, placed in a descending furnace, and the growth temperature program is set. Co3Sn2S2 single crystals are obtained by descending directional solidification. The growth cycle is 7-15 days.

5. The preparation method according to claim 4, characterized in that, In step 1), the preparation method of the Co3Sn2S2 polycrystalline powder is as follows: Co, Sn and S powder are used as initial raw materials and weighed according to stoichiometric ratio. In order to compensate for the volatilization of Sn, Sn is weighed in excess of 2-5 at % and mixed evenly into a quartz tube. The tube is sealed under vacuum using a mechanical pump or a molecular pump and subjected to high-temperature solid-state sintering reaction at 800-900℃ for 5-10 days to obtain Co3Sn2S2 polycrystalline powder.

6. The preparation method according to claim 4, characterized in that, In step 2), the specific preparation method of the Co3Sn2S2 single crystal is as follows: Co3Sn2S2 polycrystalline powder is weighed and placed into a quartz tube, and the quartz tube is placed in a vacuum-sealed environment (10... -3 -10 -4 After sealing, the furnace is placed in a vertical three-temperature zone descending furnace; the temperature program for each temperature zone is set, and growth is carried out through reasonable temperature gradient, descending rate, rotation rate, annealing temperature and annealing time.

7. The preparation method according to claim 6, characterized in that, The quartz tube has a diameter of 1-3 cm, a length of 10-20 cm, a purity of 3N, and a conical bottom.

8. The preparation method according to claim 6, characterized in that, The descent rate is 0.1-2 mm / h, the rotation rate is 4-10 rpm, the annealing temperature is 300-700 ℃, and the annealing time is 12-72 h.

9. The preparation method according to claim 6, characterized in that, The temperature gradient for crystal growth satisfies: axial 5-10℃ / cm, radial ≤2℃ / cm.

10. The application of the large-size, high-quality magnetic Weyl half-metal Co3Sn2S2 single crystal as described in claim 1 in novel low-power spintronic devices, topological magnetoelectric devices, and topological thermoelectric devices.

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