A half-metal compensated ferrimagnetic material, its preparation and use

Abstract

The application provides a semi-metal compensation ferrimagnetic material, the chemical formula of the semi-metal compensation ferrimagnetic material is CrFeS2, the semi-metal compensation ferrimagnetic material has a hexagonal NiAs type crystal structure and belongs to the 194th space group, and a preparation method thereof comprises the following steps: sealing Cr powder, Fe powder and sulfur blocks and a transmission medium iodine in a vacuum quartz tube; placing the vacuum quartz tube in a heating furnace and heating at 780-920 DEG C for 4-30 days, and then quenching to a warm house. The semi-metal compensation ferrimagnetic material provided by the application has the characteristics of great perpendicular magnetic anisotropy and magnetic compensation characteristics, so that the material can realize zero-field cold exchange bias, and a unidirectional magnetic field with different sizes can control the direction of the exchange bias, and thus the material has a wide application prospect in the field of spintronics.

Description

Technical Field

[0001] This invention relates to a semi-metallic compensated ferrimagnetic material with extremely high vertical magnetic anisotropy and zero field cold exchange bias, as well as its preparation method and applications. Background Technology

[0002] Half-metals are a class of materials with 100% spin polarization, exhibiting metallic behavior in one spin direction and semiconductor or insulator behavior in the other spin direction. They are important materials in spintronic device applications.

[0003] Most of the half-metal materials discovered so far are ferromagnetic. As the requirements for device integration density continue to increase, ferromagnetic materials will struggle to meet these requirements, and the stray fields they generate will hinder device integration. Compensating ferrimagnets and antiferromagnets with very small or even zero magnetic moments are more ideal materials. Due to the high symmetry of antiferromagnets, their upper and lower spin lattices are equivalent and have the same density of states, restricting spin polarization to zero, making it impossible to realize a half-metallic antiferromagnet. On the other hand, ferrimagnets have low symmetry; even with magnetic compensation, the two sets of spin lattices are not equivalent, allowing for the realization of a half-metallic compensated ferrimagnet.

[0004] Semimetallic compensated ferrimagnets combine 100% polarizability and zero stray field, offering broad application prospects, such as being ideal materials for the tips of spin-polarized scanning tunneling microscopes and anchoring layers in spin valve devices. Developing and synthesizing novel semimetallic compensated ferrimagnets is a crucial step towards realizing their applications.

[0005] The phenomenon of a hysteresis loop shifting along a magnetic field axis is called exchange bias. Although the origin of exchange bias remains unclear, it has been widely applied in scientific and technological fields, such as high-density magnetic storage. Exchange bias can be achieved on ferromagnetic / antiferromagnetic or subferromagnetic thin-film heterojunctions using field cooling. Overall, the exchange bias effect is related to the unidirectional anisotropy formed by the interaction between different magnetic phases. Currently, commonly used methods for forming unidirectional anisotropy, besides field cooling, include depositing an antiferromagnetic layer on a saturated ferromagnetic layer and utilizing zero-field cooling with remanent magnetization.

[0006] Recently, in compensating for the hypoferromagnetic Mn-Pt-Ga system and the antiferromagnetic Fe... x A large exchange bias effect was discovered in NbS2. In these systems, the ferromagnetic or spin-glass order introduced by position disorder interacts with the subferromagnetic or antiferromagnetic order, resulting in a large exchange bias effect.

[0007] Theoretically, through material configuration, a large exchange bias can be achieved by utilizing positional disorder in a semimetallic compensated ferrimagnet. Currently, the only experimentally synthesized semimetallic compensated ferrimagnet is Mn2Ru. 0.5 Ga thin film, Mn 1.5 FeV0.5 Al and Mn2Co 0.5 V 0.5 Al alloys. No exchange bias effect was found in these semi-metallic compensated ferrimagnetic materials. Therefore, it is necessary to explore semi-metallic compensated ferrimagnets with exchange bias effect. Summary of the Invention

[0008] Therefore, the purpose of this invention is to develop and synthesize a semimetallic compensated ferrimagnet with a huge zero-field cold exchange bias effect.

[0009] Through extensive experimental research, the inventors of this invention discovered that CrFeS2 single crystals with a hexagonal NiAs-type crystal structure possess not only extremely high perpendicular magnetic anisotropy but also a huge zero-field cold exchange bias effect, thus having broad application prospects in the field of spintronics.

[0010] In a first aspect, the present invention provides a semi-metallic compensating ferrimagnetic material, the chemical formula of which is CrFeS2, and which has a hexagonal NiAs-type crystal structure belonging to space group 194.

[0011] The present invention provides a semi-metallic compensated subferromagnetic material, wherein the material exhibits extremely high perpendicular magnetic anisotropy. In various embodiments of the present invention, the easy axis of magnetization of the material is parallel to the c-axis of the crystal structure, and the coercive field is 6T at 5K. The easy axis of magnetization refers to the axis along which a ferromagnetic material is most easily magnetized.

[0012] The present invention provides a semi-metallic compensated ferrimagnetic material, wherein the material has magnetically compensated ferrimagnetic properties. In various embodiments of the present invention, the Curie temperature of the material is >350K, and the magnetic compensation temperature is 185±2K.

[0013] The semi-metallic compensated ferrimagnetic material provided by the present invention still exhibits the anomalous Hall effect when magnetic compensation occurs.

[0014] The present invention provides a semi-metallic compensated ferrimagnetic material having a large exchange bias field. In various embodiments of the invention, the exchange bias field of the material can reach 0.8T at 5K.

[0015] The semi-metallic compensated ferrimagnetic material provided by this invention has the characteristics of both extremely large perpendicular magnetic anisotropy and magnetic compensation properties, which enables the material to achieve zero-field cold large exchange bias, and the direction of exchange bias can be controlled by unidirectional magnetic fields of different magnitudes.

[0016] In a first aspect, the present invention provides a method for preparing the above-mentioned semi-metallic compensating ferrimagnetic material, the method comprising:

[0017] (1) The raw materials Cr powder, Fe powder and sulfur block and the transmission medium iodine are encapsulated in a vacuum quartz tube;

[0018] (2) Place the quartz tube containing the raw material in a heating furnace and heat it at 780-920°C for 4-30 days to synthesize CrFeS2 single crystals by chemical vapor transport method. Then quench it at a room temperature to obtain the semi-metallic compensated ferrimagnetic material.

[0019] According to the preparation method provided by the present invention, the molar ratio of Cr powder, Fe powder and sulfur block in step (1) can be 20-25:20-25:50-60, and most preferably 23:23:54. Preferably, the purity of the raw materials in step (1) is >99.9%.

[0020] According to the preparation method provided by the present invention, step (1) further includes cleaning the quartz tube with an inert gas after loading the raw material.

[0021] In a preferred embodiment of the present invention, the vacuum pressure inside the vacuum quartz tube after encapsulation in step (1) is less than 2 × 10⁻⁶. -3 Pa.

[0022] According to the preparation method provided by the present invention, the heating furnace in step (2) can be a muffle furnace, a pit furnace and / or a zone furnace.

[0023] In some embodiments of the present invention, the heating process described in step (2) may include: placing the quartz tube containing the raw material into a pit furnace, heating it from room temperature to 780-820°C for 2-6 days, then heating it to 880-920°C for another 2-6 days, and then holding it at 880-920°C for 2-6 days.

[0024] In some other embodiments of the present invention, the heating process described in step (2) may include: placing the quartz tube containing the raw material into a muffle furnace and preheating it from room temperature to 780-900°C for 2-6 days, and then placing it into a temperature zone furnace, so that the high temperature end of the temperature zone furnace is heated to 905-915°C for 2-4 hours, and the low temperature end is heated to 885-895°C for 2-4 hours, and then maintained at this temperature for 10-30 days.

[0025] In some other embodiments of the present invention, the heating process described in step (2) may include: placing a quartz tube containing the raw material into a temperature zone furnace, raising the temperature of the high-temperature end of the temperature zone furnace to 905-915°C over 2-6 days, raising the temperature of the low-temperature end to 885-895°C over 2-6 days, and then maintaining the temperature at that temperature for 10-30 days.

[0026] Thirdly, the present invention provides the application of the semi-metallic compensated ferrimagnetic material of the present invention or the semi-metallic compensated ferrimagnetic material prepared according to the method of the present invention as a hard magnetic material.

[0027] Fourthly, the present invention provides the application of the semi-metallic compensated ferrimagnetic material of the present invention or the semi-metallic compensated ferrimagnetic material prepared according to the method of the present invention in spintronic devices.

[0028] Compared with existing materials, the CrFeS2 material provided by this invention has the following beneficial effects:

[0029] 1. The material of the present invention has extremely high vertical magnetic anisotropy and zero-field cold exchange bias, with a coercive field of 6T at 5K and a zero-field cold exchange bias field of up to 0.8T at 5K.

[0030] 2. The material of the present invention can be cooled by unidirectional magnetic fields of different magnitudes to control the direction of the exchange bias.

[0031] 3. The material of the present invention has magnetic compensation properties, and even with compensation, it exhibits an anomalous Hall effect.

[0032] 4. The raw materials used in this invention do not contain rare earth elements, which reduces the dependence of hard magnetic materials on rare earth elements and lowers the material preparation cost.

[0033] The CrFeS2 semimetallic compensated ferrimagnetic material provided by this invention can be applied to rare-earth-free hard magnets or spintronics. In hard magnets, it reduces the dependence of hard magnetic materials on rare earth elements, lowering material preparation costs. In spintronics, it enables the development of novel compensated ferrimagnetic tunnel junctions. The material's semimetallic properties, strong perpendicular magnetic anisotropy, and zero-field cold exchange bias correspond to the tunnel junction's characteristics of high tunneling magnetoresistance, insensitivity to external magnetic field interference, and simple structure requiring no additional exchange bias structure. The material's strong perpendicular magnetic anisotropy, with an internal magnetic anisotropy field exceeding 30T at room temperature, is expected to correspond to resonance frequencies exceeding 1THz, enabling the development of picosecond-level ultrafast spin switches. The material's semimetallic properties eliminate some spin scattering channels, potentially reducing the material's magnetic damping coefficient. Combined with the material's small net magnetic moment, it is expected to excite oscillations with a small spin current, thus making it suitable for terahertz-band spin-transfer torque nano-oscillators and spin-orbit torque nano-oscillators. Attached Figure Description

[0034] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0035] Figure 1 Photograph (a), structural schematic diagram (b), and X-ray diffraction pattern (c) of the CrFeS2 sample prepared in Example 1 of this invention.

[0036] Figure 2 The thermomagnetic curve of the CrFeS2 sample prepared in Example 1 of this invention.

[0037] Figure 3 The magnetization curves and saturation magnetic moment of the CrFeS2 sample prepared in Example 1 of this invention at different temperatures are shown.

[0038] Figure 4 The Hall resistivity of the CrFeS2 sample prepared in Example 1 of this invention varies with magnetic field at different temperatures.

[0039] Figure 5 The results show the influencing factors of the exchange bias effect in the CrFeS2 sample prepared in Example 1 of this invention. (a) shows the result of the exchange bias effect and the direction of the initial magnetic field; (b) shows the result of the training effect of the exchange bias.

[0040] Figure 6 The figures show the low-temperature Hall curves of the CrFeS2 sample prepared in Example 1 of this invention, cooled with different magnetic fields. (a) The figure shows the Hall curves obtained by cooling to 5K with different fields after being magnetized with a positive field at room temperature; (b) The figure shows the Hall curves obtained by cooling to 5K with different fields after being magnetized with a negative field at room temperature.

[0041] Figure 7 The results show the changes in coercive field and exchange bias field of the CrFeS2 sample prepared in Example 1 of this invention at 5K with the field cooling field, wherein... Figure 7 Figure (a) shows the curve of coercive field versus field cooling field at 5K, with the horizontal axis representing field cooling field and the vertical axis representing coercive field. Figure 7 Figure (b) shows the curve of the exchange bias field changing with the field cooling field at 5K. The horizontal axis is the field cooling field and the vertical axis is the exchange bias field. Detailed Implementation

[0042] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0043] The raw materials and equipment used in the embodiments of the present invention include:

[0044] High-purity elemental Cr powder, Fe powder, S blocks, and elemental iodine.

[0045] The muffle furnace was manufactured by Tianjin Kaiheng Electric Heating Technology Co., Ltd., model KLJ-13Y; the magnetic measurement system (MPMS (SQUID-VSM)) and the comprehensive physical property measurement system (PPMS-16T and PPMS-9T) were manufactured by Quantum Design (USA).

[0046] Example 1

[0047] 1. A total of 1g of Cr powder, Fe powder, and sulfur block in a molar ratio of 23:23:54, along with 0.1g of iodine as the transmission medium, is encapsulated in a quartz tube with an outer diameter of 20mm, an inner diameter of 18mm, and a length of 120mm. After cleaning with Ar gas, a high vacuum (vacuum degree lower than 2×10⁻⁶) is evacuated. -3 Pa) and seal.

[0048] 2. Place the quartz tube containing the raw material into a pit furnace and heat it. The heating process is as follows: start from room temperature and heat to 800℃ for 96 hours, then heat to 900℃ for another 96 hours, and maintain at 900℃ for 96 hours.

[0049] 3. The heated quartz tube was placed in water and quenched to room temperature to obtain the CrFeS2 sample of the semi-metallic compensating ferrimagnetic material of the present invention.

[0050] Performance testing

[0051] I. Structural Characterization

[0052] The CrFeS2 single crystal sample grown by chemical vapor transport in Example 1 was observed using an optical microscope, as shown below. Figure 1 As shown in Figure (a), the side length of the squares is 1 mm. This sample has a NiAs-like structure, space group P63 / mmc (No. 194), with Cr and Fe atoms occupying 2a (0,0,0) positions and S atoms occupying 2c (1 / 3,2 / 3,1 / 4) positions. Its side and top views are shown below. Figure 1 As shown in Figure (b), its single-crystal X-ray diffraction pattern is as follows: Figure 1 As shown in Figure (c).

[0053] II. Magnetic Measurement

[0054] The CrFeS2 sample prepared in Example 1 of this invention was measured using a superconducting quantum interference vibrational magnetometer. After magnetizing the sample at a low temperature of 5K with a 7T magnetic field, the field was reduced to zero. The thermomagnetic curve (MT curve) of zero-field heating is shown below. Figure 2 As shown.

[0055] The magnetic moment on the MT curve changes from positive to negative as it crosses zero, confirming that the material is a compensated ferrimagnet. The magnetic compensation temperature T is [missing information]. comp It is approximately 185±2K. Since the magnetic moment at 350K has a certain non-zero value, it can be confirmed that the Curie temperature of this material is greater than 350K.

[0056] The magnetization curves (MH curves) of the CrFeS2 sample of this invention at different temperatures were determined using a vertical 9T magnetic field, as shown below. Figure 3As shown in Figure (a). The saturation magnetic moment can be extracted from the MH curve as follows: Figure 3 As shown in Figure (b). Wherein, Figure 3 (a) shows the magnetization curves at different temperatures, where the horizontal axis represents the magnetic field and the vertical axis represents the magnetization intensity. Figure 3 (b) is a scatter plot of saturation magnetization as a function of temperature, where the horizontal axis represents temperature and the vertical axis represents saturation magnetization.

[0057] As the temperature rises, the saturation magnetic moment increases slightly and then decreases, dropping to zero at the magnetic compensation temperature. Later, as the temperature rises to 300K, the saturation magnetic moment increases.

[0058] III. Transport Measurement

[0059] The Hall curves of the CrFeS2 samples prepared in the embodiments of the present invention at different temperatures were determined using a comprehensive physical property measurement system, such as... Figure 4 As shown, the horizontal axis represents the magnetic field, and the vertical axis represents the Hall resistivity. Figure 4 The results show that the Hall signals at 80K and 240K are opposite, further confirming the magnetic compensation properties of the material. The sample has a coercive field of 6T at 5K and 2T at 300K.

[0060] The influencing factors of the exchange bias effect in the CrFeS2 sample prepared in the embodiments of the present invention were determined using a comprehensive physical property measurement system. The results of the exchange bias effect and the initial magnetic field direction are as follows: Figure 5 As shown in Figure (a), after magnetizing the sample with a positive field at room temperature, the field was reduced to zero, and then the sample was cooled to 5 K with zero field. Hall curves were then measured starting from both positive and negative fields. This result shows that the initial magnetic field direction has almost no effect on the exchange bias effect at low temperatures. The results of the exchange bias training effect are as follows... Figure 5 As shown in Figure (b), after magnetizing the sample with a positive field at room temperature, the field was reduced to zero, and then the sample was cooled to 5K with zero field. The Hall curves were measured three times in a row. The results show that the sample has no obvious training effect due to the exchange bias.

[0061] The Hall curves of the samples after magnetization, cooling under different magnetic fields, and at 5K are shown below. Figure 6 As shown, Figure 6 Figure (a) shows the Hall curves obtained by applying a positive field magnetization at room temperature and then cooling to 5K with different fields. Figure 6 Figure (b) shows the Hall curves obtained by magnetizing at room temperature with a negative field and then cooling to 5K with different fields. Figure 6 The results show that the cold field can significantly affect the exchange bias field.

[0062] The results of the changes in the 5K coercive field and commutative bias with the field cold field are as follows: Figure 7Figures (a) and (b) show the results. The results show that the field cooling field has almost no effect on the magnitude of the coercive field, while the field cooling field can significantly change the magnitude and direction of the exchange bias field. Field cooling fields of different magnitudes in one direction can control the magnitude and direction of the exchange bias field. The exchange bias field of this sample with zero field cooling can reach 0.8T.

[0063] Although the invention has been described to a certain extent, it is apparent that appropriate variations in various conditions may be made without departing from the spirit and scope of the invention. It is understood that the invention is not limited to the described embodiments, but falls within the scope of the claims, which include equivalent substitutions for each of the elements.

Claims

1. A semi-metallic compensated ferrimagnetic single crystal material, wherein the chemical formula of the semi-metallic compensated ferrimagnetic single crystal material is CrFeS2, it has a hexagonal NiAs type crystal structure, belongs to space group 194, and at 5 K, the exchange bias field of the single crystal material is 0.8 T, wherein the exchange bias field is achieved through zero-field cooling, is in the same direction as the initial magnetic field, and has no tempering effect. in, The method for preparing the single crystal material includes: (1) The raw materials Cr powder, Fe powder and sulfur block and the transmission medium iodine are encapsulated in a vacuum quartz tube; (2) The quartz tube containing the raw material is placed in a heating furnace and heated at 780~920℃ for 4~30 days to synthesize CrFeS2 single crystals by chemical vapor transport method. Then, it is quenched to room temperature to obtain the semi-metallic compensated ferrimagnetic single crystal material. The magnetization easy axis of the single crystal material is parallel to the c-axis of the crystal structure, and the coercive field is 6T at 5K.

2. The semi-metallic compensated ferrimagnetic single crystal material according to claim 1, wherein, The single-crystal material has a Curie temperature >350K and a magnetic compensation temperature of 185±2 K.

3. The semi-metallic compensated ferrimagnetic single crystal material according to claim 1, wherein, The single-crystal material exhibits an anomalous Hall effect when magnetic compensation occurs.

4. The semi-metallic compensated ferrimagnetic single crystal material according to claim 1, wherein the molar ratio of Cr powder, Fe powder and sulfur block in step (1) of its preparation method is 20~25:20~25:50~60.

5. The semi-metallic compensated ferrimagnetic single crystal material according to claim 4, wherein the molar ratio of Cr powder, Fe powder and sulfur block is 23:23:

54.

6. The semi-metallic compensated ferrimagnetic single crystal material according to claim 1, wherein step (1) of the preparation method further includes cleaning the quartz tube with an inert gas after loading the raw material.

7. The semi-metallic compensated ferrimagnetic single crystal material according to claim 1, wherein the vacuum pressure inside the encapsulated vacuum quartz tube in step (1) of its preparation method is less than 2 × 10⁻⁶. -3 Pa.

8. The semi-metallic compensated ferrimagnetic single crystal material according to claim 1, wherein the heating furnace in step (2) of the preparation method is a muffle furnace, a pit furnace or a temperature zone furnace.

9. The heating process in step (2) of the preparation method of the semi-metallic compensated ferrimagnetic single crystal material according to claim 1 includes: Quartz tubes containing raw materials are placed in a pit furnace and heated from room temperature to 780-820°C for 2-6 days, then heated to 880-920°C for another 2-6 days, and then kept at 880-920°C for 2-6 days.

10. The semi-metallic compensated ferrimagnetic single crystal material according to claim 1, wherein the heating process in step (2) of its preparation method includes: Quartz tubes containing raw materials are placed in a muffle furnace and preheated from room temperature to 780-900°C for 2-6 days. Then they are placed in a temperature zone furnace, where the high-temperature end is heated to 905-915°C for 2-4 hours and the low-temperature end is heated to 885-895°C for 2-4 hours. The temperature is then maintained at this temperature for 10-30 days.

11. The semi-metallic compensated ferrimagnetic single crystal material according to claim 1, wherein the heating process in step (2) of its preparation method includes: The quartz tube containing the raw material is placed in a temperature zone furnace, and the high-temperature end of the furnace is heated to 905-915℃ over 2-6 days, and the low-temperature end is heated to 885-895℃ over 2-6 days. The furnace is then maintained at this temperature for 10-30 days.

12. The application of the semi-metallic compensated ferrimagnetic single crystal material according to any one of claims 1 to 11, the application including its use as a hard magnetic material and its use in spintronic devices.

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