Quaternary niobium-iron-cobalt sulfide crystal, preparation method and application

Abstract

The invention discloses a quaternary ferrocolumbium cobalt sulfide crystal, a preparation method and application, and belongs to the technical field of magnetic materials, the quaternary ferrocolumbium cobalt sulfide crystal has remarkable in-plane and out-of-plane magnetic anisotropy, and the chemical general formula of the quaternary ferrocolumbium cobalt sulfide crystal is Nb3 (Fe, Co) S6; the preparation method comprises the following steps: (1) preparing and packaging raw materials; (2) vacuum packaging; (3) carrying out CVT reaction; and (4) cooling and sampling. An improved double-temperature-zone chemical vapor transport (CVT) method is adopted, and a proper transport agent is selected, so that a multi-component raw material can be transported and recrystallized in a gaseous form at a relatively low temperature, and a single crystal with uniform components and a complete structure is obtained. The material can be applied to spintronics devices, high-density magnetic storage units and magnetic sensors; and a new platform is provided for researching complex magnetic interaction, magnetic anisotropy sources, potential superconductivity, topological properties and the like.

Description

Technical Field

[0001] This invention belongs to the technical field of magnetic materials, and in particular relates to a quaternary niobium-iron-cobalt sulfide crystal, its preparation method, and its application. Background Technology

[0002] Developing novel magnetic materials, especially those with low-dimensional properties, strong magnetic anisotropy, and high Curie / Nell temperatures, is one of the core challenges in condensed matter physics and materials science. These materials are fundamental to building next-generation spintronic devices such as magnetic random access memory (MRAM) and spin field-effect transistors. Currently, much research on magnetic materials focuses on binary or ternary systems, such as chalcogenides of Fe, Co, and Ni, and chalcogenides of niobium. However, binary and ternary systems have limitations in controlling quantum phenomena such as electron spin, magnetic anisotropy, and charge density waves. To obtain richer and more tunable physical properties, researchers have begun to focus on multi-component (quaternary and higher) systems.

[0003] However, synthesizing high-quality, atomically ordered quaternary crystal materials presents significant challenges, primarily in the following aspects: 1. Compositional complexity: The four elements possess different atomic radii, chemical valence states, reactivity, and vapor pressures. In traditional high-temperature solid-state reactions, multiphase mixtures are easily formed rather than a single phase, making it difficult to obtain pure crystals. 2. Homogeneity control: Ensuring the uniform distribution of the four elements at the atomic scale according to stoichiometry is extremely difficult; any segregation will lead to significant performance degradation. 3. Crystal growth challenges: Finding suitable crystal growth windows (temperature, pressure, transporter, etc.) for all components is very demanding. Conventional methods such as melting methods are prone to compositional deviations and increased defects.

[0004] The present invention aims to overcome the above-mentioned technical difficulties and provide a novel quaternary Nb-Fe-Co-S crystal material with unique out-of-plane ferromagnetism and in-plane antiferromagnetism synthesized by an improved CVT process, and reveals its potential application value. Summary of the Invention

[0005] The purpose of this invention is to provide a quaternary niobium-iron-cobalt sulfide crystal, its preparation method, and its applications. It has significant in-plane and out-of-plane magnetic anisotropy and can be applied to spintronic devices, high-density magnetic storage devices, and magnetic sensors.

[0006] This invention is achieved through the following technical solution: A quaternary niobium-iron-cobalt sulfide crystal with the general chemical formula Nb3(Fe,Co)S6; the molar ratio of Fe to Co is approximately Fe0. 67 Co0. 19The overall molar ratio is Nb : Fe : Co : S = 3 : 0.67 : 0.19 : 6; the crystal belongs to the hexagonal or orthorhombic crystal system. The crystal exhibits strong magnetic anisotropy; out-of-plane orientation: ferromagnetic (FM), with a magnetic order transition temperature (TC) of approximately 100 K; in-plane orientation: ferromagnetic (FM) or weakly ferromagnetic ordered, with a magnetic order transition temperature of approximately 45 K.

[0007] This characteristic, where the magnetic ordering temperature and type differ in different crystal orientations, indicates that the material possesses very strong magnetocrystalline anisotropy, making it an ideal candidate material for constructing anisotropic magnetic devices.

[0008] Its unique magnetic anisotropy stems from the ordered arrangement of atoms in the crystal structure and the specific occupancy of Fe and Co ions in the crystal lattice. In the out-of-plane direction, the magnetic moments of Fe and Co ions exhibit a high degree of uniformity, forming strong ferromagnetic coupling, resulting in a high magnetic order transition temperature in this direction. In the in-plane direction, due to the effect of the crystal field and possible variations in magnetic exchange interactions, the magnetic moment arrangement is relatively loose, exhibiting ferromagnetic or weakly ferromagnetic order, and the magnetic order transition temperature is relatively low. This significant difference in magnetic anisotropy provides a wealth of control methods for designing novel magnetic devices with specific functions.

[0009] A method for preparing a quaternary niobium-iron-cobalt sulfide crystal includes the following steps: (1) Raw material preparation and packaging: High-purity niobium powder (Nb), iron powder (Fe), cobalt powder (Co) and sulfur powder (S) are accurately weighed according to the molar ratio Nb : Fe : Co : S = 3 : 0.67 : 0.19 : 6, and thoroughly ground and mixed. A transport agent is added, and the mixture is placed in a quartz tube sealed at one end. (2) Vacuum sealing: Connect the quartz tube to the vacuum system, evacuate to a high vacuum state, and then use an oxyhydrogen flame to seal the other end of the quartz tube to ensure that the inside of the sealed quartz tube is in a high vacuum state; (3) CVT reaction: The packaged quartz tube is placed horizontally in a dual-temperature zone tube furnace, with the raw material end as the source region in the high-temperature zone and the crystal growth end as the deposition region in the low-temperature zone. First heating stage: The source region temperature is raised to the first temperature at the first heating rate and held for a first period of time to allow the multi-component raw materials to undergo a preliminary reaction, form a uniform polycrystalline precursor, and avoid the loss of some components due to excessive volatilization. Second heating and crystal growth stage: Subsequently, the source region temperature is raised to the second temperature at the second heating rate, while the deposition region temperature is maintained within a temperature gradient 80-150℃ lower than the source region. The second temperature is then maintained for a second period of time. During this stage, the transport agent and the raw material form a gaseous complex, which is transported through the concentration difference generated by the temperature gradient. A reverse reaction occurs in the cooler deposition region, precipitating atomically uniform Nb3(Fe,Co)S6 single crystals. (4) Cooling and sampling: After the reaction is complete, let the furnace cool naturally to room temperature, open the quartz tube, and you can observe shiny flake or rod-shaped single crystals in the deposition area.

[0010] Furthermore, the transport agent involved in steps (1) and (3) is tellurium tetrachloride (TeCl4), which accounts for approximately 5-10% of the total raw material mass.

[0011] Furthermore, the tube pressure corresponding to the high vacuum state in step (2) is ≤ 10. -3 Pa.

[0012] Further, in step (3), the first heating rate is 1-5℃ / min, the first temperature is 600-750℃, and the first time period is 12-48h; the second heating rate is 0.5-2℃ / min, the second temperature is 850-950℃, and the second time period is 120-200h.

[0013] Further, in step (3), the first heating rate is 2℃ / min, the first temperature is 700℃, and the first time period is 24h; the second heating rate is 1℃ / min, the second temperature is 900℃, the temperature of the deposition zone is 780℃, and the second time period is 168h.

[0014] An improved dual-temperature zone chemical vapor transport (CVT) method effectively solves the challenges in the synthesis of multi-component crystalline materials. This method utilizes a transport agent to form a gaseous complex with the raw materials, achieving directional transport and recrystallization of the raw materials under temperature gradient drive, thereby obtaining single crystals with uniform composition and complete structure. Specifically, this invention uses tellurium tetrachloride (TeCl4) as the transport agent, with its mass being approximately 5-10% of the total raw material mass. By precisely controlling parameters such as heating rate, temperature, and holding time, high-quality crystal growth is achieved at relatively low temperatures (source region temperature 850-950℃, deposition region temperature 80-150℃ lower than the source region). Furthermore, this method has advantages such as simple operation and high reproducibility, providing a new approach for the synthesis of other multi-component crystalline materials.

[0015] Applications of a quaternary niobium-iron-cobalt sulfide crystal include, but are not limited to, spintronic devices, high-density magnetic storage units, and magnetic sensors. Corresponding to spintronic devices, it is used to construct novel magnetic tunnel junctions (MTJs), in which the ferromagnetic layer can provide spin-polarized electrons, while the antiferromagnetic layer can be used to pin the magnetization direction of the ferromagnetic layer, thereby enhancing the thermal stability of the device. For high-density magnetic storage cells, by utilizing the strong magnetic anisotropy of the material, its magnetization direction can be stably controlled in the out-of-plane perpendicular direction, which meets the requirements of high-density perpendicular magnetic recording technology and can be used to manufacture magnetic random access memory (MRAM) with higher storage density. Corresponding to magnetic sensors, this material can be used to make high-sensitivity magnetic sensors and temperature sensors by utilizing its sensitive characteristics of magnetization intensity changing with temperature and magnetic field. The quaternary system corresponding to the material also provides a new platform for studying complex magnetic interactions, the origin of magnetic anisotropy, and potential superconductivity and topological properties.

[0016] This invention offers the following advantages: This study utilizes an improved dual-temperature zone chemical vapor transport (CVT) method to conduct related experiments. CVT, as a highly efficient and high-quality single-crystal growth technique, has significant advantages in component systems with high vapor pressures. Through rigorous selection of suitable transport agents, it is possible to promote the transport and recrystallization of multi-component raw materials in a gaseous state under relatively low-temperature conditions, ultimately obtaining single crystals with uniform composition and complete structure. This method not only facilitates atomic-level homogeneous mixing but also effectively improves the quality and efficiency of single-crystal growth, providing high-quality single-crystal materials for research and applications in related fields, and promoting the development and innovation of related technologies. In-depth exploration of the physical properties of this material is expected to reveal new quantum phenomena and physical mechanisms in multi-component systems, making significant contributions to the development of condensed matter physics and materials science. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0018] Figure 1 Hysteresis loop (MH) curves in the in-plane direction of the crystal under different temperature conditions (10K, 20K, 30K, 50K, and 100K, respectively).

[0019] Figure 2 Hysteresis loop (MH) curves in the out-of-plane direction of the crystal under different temperature conditions (10K, 20K, 30K, 40K, 50K, and 100K, respectively).

[0020] Figure 3 ZFC and FC magnetization-temperature (MT) curves in the in-plane direction of the crystal under different applied magnetic fields (100 Oe, 300 Oe, 1000 Oe, 6000 Oe).

[0021] Figure 4 ZFC and FC magnetization-temperature (MT) curves in the out-of-plane direction of the crystal under different applied magnetic fields (300 Oe, 1000 Oe, 3000 Oe).

[0022] Figure 5 EDS elemental distribution map of the S element corresponding to the Nb3(Fe,Co)S6 crystal prepared in the embodiments of the present invention.

[0023] Figure 6 EDS elemental distribution map of Nb element corresponding to the Nb3(Fe,Co)S6 crystal prepared in the embodiments of the present invention.

[0024] Figure 7 EDS elemental distribution map of Fe element corresponding to the Nb3(Fe,Co)S6 crystal prepared in the embodiments of the present invention.

[0025] Figure 8 EDS elemental distribution map of Co element in the Nb3(Fe,Co)S6 crystal prepared in the embodiments of the present invention. Figure 9 Mappinp element analysis diagram.

[0026] Figure 10 SEM image of the Nb3(Fe,Co)S6 crystal prepared in the embodiments of the present invention. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0028] (1) Accurately weigh Nb powder (3 mmol), Fe powder (0.67 mmol), Co powder (0.19 mmol), and S powder (6 mmol), with a total mass of approximately 0.5 g. Add 50 mg of TeCl4 as a transport agent. Grind and mix thoroughly in an argon glove box.

[0029] (2) Load the mixture into one end of a quartz tube with a length of 20 cm and an inner diameter of 1.5 cm. Connect the quartz tube to a vacuum system and evacuate to 5 × 10⁻⁶. -4 Pa followed by fusion sealing.

[0030] (3) Place the quartz tube in a dual-temperature zone furnace, with the raw material end in the center and the growth end in the low-temperature zone at the furnace opening. Heat the source zone to 700°C at a rate of 2°C / min and hold for 24 hours. Then heat the source zone to 900°C at a rate of 1°C / min, at which point the temperature of the growth end is approximately 780°C. Hold at this temperature for 168 hours.

[0031] (4) After the reaction is complete, turn off the power and let the furnace cool down to room temperature naturally.

[0032] (5) Take out the quartz tube and open it to obtain a large number of silver-black metallic luster plate-like crystals on the inner wall of the growth end.

[0033] Figure 1 The hysteresis loop (MH) curves in the in-plane direction of the crystal under different temperature conditions (10K, 20K, 30K, 50K, and 100K, respectively). Figure 2 These are the out-of-plane hysteresis loop (MH) curves of the crystal under different temperature conditions (10K, 20K, 30K, 40K, 50K, and 100K, respectively). Figure 1 This indicates that in the in-plane direction, the magnetization is much lower than in the out-of-plane direction, and the coercivity is very small, even linear, which is consistent with the characteristics of antiferromagnetism. Figure 2 This indicates that in the out-of-plane direction, at low temperatures (e.g., 10 K), a clear open hysteresis loop is observed, exhibiting large coercivity (Hc) and saturation magnetization (Ms), confirming ferromagnetic or subferromagnetic order. Furthermore, the ferromagnetism in the out-of-plane direction gradually weakens with increasing temperature, disappearing near 100 K.

[0034] Figure 3 The ZFC and FC magnetization-temperature (MT) curves are shown for the in-plane directions of the crystal under different applied magnetic fields (100 Oe, 300 Oe, 1000 Oe, 6000 Oe). Figure 4 The ZFC and FC magnetization-temperature (MT) curves are shown for the out-of-plane orientation of the crystal under different applied magnetic fields (300 Oe, 1000 Oe, 3000 Oe). Based on... Figure 3 and Figure 4 Zero-field cooling (ZFC) and field cooling (FC) measurements were performed in two directions: parallel to the crystal surface (in-plane) and perpendicular to the crystal surface (out-of-plane), respectively, under an applied magnetic field (H). Figure 4 The ZFC / FC curve shows a clear bifurcation at ~100 K in the out-of-plane direction, indicating that the magnetic order transition temperature is 100 K. Tests under various magnetic fields, including 300 Oe, 1000 Oe, and 3000 Oe, confirmed the robustness of this transition. Figure 3This indicates that in the in-plane direction, the ZFC / FC curve changes at ~45 K, which contrasts sharply with the out-of-plane direction, directly demonstrating strong magnetic anisotropy.

[0035] Figures 5-8 The EDS elemental distribution diagrams for the Nb3(Fe,Co)S6 crystal show that Nb, Fe, Co, and S are spatially uniformly distributed without obvious elemental segregation, forming a homogeneous and structurally stable single-phase compound rather than a simple mechanical mixture.

[0036] Table 1 shows the elemental contents of sulfur (S), iron (Fe), cobalt (Co), and niobium (Nb) as determined by energy dispersive spectroscopy.

[0037]

[0038] Figure 9 For the Mappinp element analysis diagram, combined with Figure 9 The energy dispersive spectroscopy (EDS) analysis of sulfur (S), iron (Fe), cobalt (Co), and niobium (Nb) in Table 1 confirms that this crystal material is a single crystal with niobium sulfide as the main phase and containing iron and trace amounts of cobalt.

[0039] Figure 10 This is a SEM image of the Nb3(Fe,Co)S6 crystal prepared in an embodiment of the present invention. It strongly demonstrates the uniformity of the sample surface.

[0040] These embodiments are selected and specifically described in this specification in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can better understand and utilize the present invention.

Claims

1. A quaternary niobium-iron-cobalt sulfide crystal, characterized in that: Its general chemical formula is Nb3(Fe,Co)S6; The molar ratio of Fe to Co is approximately Fe0. 67 Co0. 19 ; The overall molar ratio is Nb : Fe : Co : S = 3 : 0.67 : 0.19 : 6; The crystal belongs to the hexagonal or orthorhombic crystal system.

2. The quaternary niobium-iron-cobalt sulfide crystal according to claim 1, characterized in that: Crystals exhibit strong magnetic anisotropy; Out-of-plane orientation: It exhibits ferromagnetism, and its magnetic order transition temperature is approximately 100 K; In-plane orientation: exhibits ferromagnetic or weakly ferromagnetic order, with a magnetic order transition temperature of approximately 45 K.

3. A method for preparing a quaternary niobium-iron-cobalt sulfide crystal, characterized in that: It includes the following steps, (1) Raw material preparation and packaging: High-purity niobium powder, iron powder, cobalt powder and sulfur powder are accurately weighed according to the molar ratio Nb : Fe : Co : S = 3 : 0.67 : 0.19 : 6, and thoroughly ground and mixed. A transport agent is added, and the mixture is placed in a quartz tube sealed at one end. (2) Vacuum sealing: Connect the quartz tube to the vacuum system, evacuate to a high vacuum state, and then use an oxyhydrogen flame to seal the other end of the quartz tube to ensure that the inside of the sealed quartz tube is in a high vacuum state; (3) CVT reaction: The packaged quartz tube is placed horizontally in a dual-temperature zone tube furnace, with the raw material end as the source region in the high-temperature zone and the crystal growth end as the deposition region in the low-temperature zone. First heating stage: The source region temperature is raised to the first temperature at the first heating rate and held for a first period of time to allow the multi-component raw materials to undergo a preliminary reaction, form a uniform polycrystalline precursor, and avoid the loss of some components due to excessive volatilization. Second heating and crystal growth stage: Then, the source region temperature is raised to the second temperature at the second heating rate, while the deposition region temperature is maintained within a temperature gradient 80-150℃ lower than the source region, and the temperature is kept at the second temperature for a second period of time. During this stage, the transport agent forms a gaseous complex with the raw material, which is transported by the concentration difference generated by the temperature gradient, and a reverse reaction occurs in the cooler deposition zone to precipitate atomically uniform Nb3(Fe,Co)S6 single crystals. (4) Cooling and sampling: After the reaction is complete, let the furnace cool naturally to room temperature, open the quartz tube, and you can observe shiny flake or rod-shaped single crystals in the deposition area.

4. The method for preparing a quaternary niobium-iron-cobalt sulfide crystal according to claim 3, characterized in that: The transport agent involved in steps (1) and (3) is tellurium tetrachloride, which accounts for about 5-10% of the total raw material mass.

5. The method for preparing a quaternary niobium-iron-cobalt sulfide crystal according to claim 3, characterized in that: In step (2), the pressure inside the tube corresponding to the high vacuum state is ≤ 10. -3 Pa.

6. The method for preparing a quaternary niobium-iron-cobalt sulfide crystal according to claim 3, characterized in that: In step (3), the first heating rate is 1-5℃ / min, the first temperature is 600-750℃, and the first time period is 12-48h; the second heating rate is 0.5-2℃ / min, the second temperature is 850-950℃, and the second time period is 120-200h.

7. The method for preparing a quaternary niobium-iron-cobalt sulfide crystal according to claim 6, characterized in that: In step (3), the first heating rate is 2℃ / min, the first temperature is 700℃, and the first time period is 24h; the second heating rate is 1℃ / min, the second temperature is 900℃, the temperature of the deposition zone is 780℃, and the second time period is 168h.

8. An application of a quaternary niobium-iron-cobalt sulfide crystal, characterized in that: Including but not limited to spintronic devices, high-density magnetic storage units, and magnetic sensors; Corresponding to spintronic devices, it is used to construct novel magnetic tunnel junctions, in which the ferromagnetic layer can provide spin-polarized electrons, while the antiferromagnetic layer can be used to pin the magnetization direction of the ferromagnetic layer, thereby enhancing the thermal stability of the device. Corresponding to high-density magnetic storage cells, by utilizing the strong magnetic anisotropy of materials, the magnetization direction can be stably controlled in the out-of-plane perpendicular direction, which meets the requirements of high-density perpendicular magnetic recording technology and can be used to manufacture magnetic random access memory with higher storage density. Corresponding to magnetic sensors, this material can be used to make high-sensitivity magnetic sensors and temperature sensors by taking advantage of the sensitive characteristics of its magnetization intensity changing with temperature and magnetic field. The quaternary system corresponding to the material also provides a new platform for studying complex magnetic interactions, the origin of magnetic anisotropy, and potential superconductivity and topological properties.

Images