Application of hexagonal crystal system material GdAl3 (BO3) 4 in field of extremely low temperature magnetic refrigeration

Abstract

The invention discloses application of a hexagonal crystal system material GdAl3 (BO3) 4 in the field of extremely low temperature magnetic refrigeration, and relates to the technical field of magnetic refrigeration materials. The hexagonal crystal system material GdAl3 (BO3) 4 applied to the field of extremely low temperature magnetic refrigeration, provided by the invention, can show excellent magnetocaloric performance and stability under the condition of extremely low temperature (less than or equal to 300mK). According to the material, Gd < 3 + > is introduced as magnetic ions, Al < 3 + >, borate ions and other ions with small relative molecular mass are introduced as ligands, the mass ratio of the magnetic ions is guaranteed, and the material has a higher magnetic entropy change value. The phase change temperature is low, no phase change occurs at the temperature of 300 mK or above, lambda phase change occurs at the temperature of 300 mK, and the magnetic entropy is well reserved in an extremely low temperature region. Crystal water is not contained, and the structural stability and thermal stability are high. The magnetic refrigeration device has a remarkable magnetothermal effect in an extremely low temperature region, and can realize efficient, stable and convenient magnetic refrigeration application in sub-Kelvin or even lower temperature regions.

Description

Technical Field

[0001] This invention relates to the field of magnetic refrigeration materials technology, and in particular to the application of hexagonal crystal material GdAl3(BO3)4 in the field of ultra-low temperature magnetic refrigeration. Background Technology

[0002] Cryogenic technology is a crucial component of scientific research and high-tech applications, particularly in advanced fields such as condensed matter physics, quantum information science, and space science. With the increasing demands for technologies like superconducting quantum computing and deep space exploration, the need for more efficient and reliable cryogenic refrigeration technologies is also growing. Therefore, obtaining and maintaining a reliable cryogenic environment over the long term has become one of the core issues restricting the development of related technologies. Currently, cryogenic refrigeration technologies mainly include dilution refrigeration (DR) and adiabatic demagnetization refrigeration (ADR). While dilution refrigeration can provide a stable cryogenic environment, its dependence on expensive and scarce helium-3 gas and its complex mechanical structure limit its applicability in specific environments, especially in microgravity environments such as space applications. In contrast, adiabatic demagnetization refrigeration (ADR), as a solid-state refrigeration method, achieves cooling by utilizing the magnetocaloric effect of magnetic materials in an applied magnetic field. It offers advantages such as compact structure, independence from gravity, and precise temperature control, making it more suitable for applications in space and high-tech fields. The core of adiabatic demagnetization refrigeration technology relies heavily on the magnetocaloric effect performance of magnetic refrigeration materials. The efficiency and reliability of magnetic refrigeration systems also depend to a large extent on the magnetocaloric performance of these materials under low temperature and low magnetic field conditions. Ideally, magnetic refrigeration materials should possess large magnetic entropy changes and high thermal efficiency over a wide temperature range and under low magnetic fields, such as maintaining large magnetic entropy changes and good thermal stability even at milliKelvin (mK) and lower temperatures. However, current magnetic refrigeration materials often exhibit limited magnetic entropy changes at low temperatures and low magnetic fields, which restricts their application potential in cryogenic refrigeration technology.

[0003] In related technologies, materials used in cryogenic adiabatic demagnetization refrigeration are mainly paramagnetic salts. While these materials exhibit good magnetocaloric properties within a certain temperature range, they generally contain a large amount of water of crystallization, making them prone to water loss under high vacuum or long-term operating conditions. This leads to changes in the material structure and magnetocaloric properties, severely affecting the refrigeration effect and system stability. Furthermore, the presence of water of crystallization also results in low thermal conductivity at extremely low temperatures. To improve thermal conductivity, auxiliary structures such as metal wires are typically introduced, which not only increases manufacturing difficulty but also significantly raises operating costs. On the other hand, paramagnetic salts also have limitations in mechanical strength, chemical stability, and processing performance, making it difficult to meet the comprehensive requirements of next-generation cryogenic refrigeration devices for long-term stable operation, structural reliability, and environmental adaptability. To address these issues, researchers have developed anhydrous inorganic magnetic compounds, multi-component rare earth compounds, and novel structural magnetic material systems. However, these materials generally suffer from insufficient magnetic entropy retention in ultra-low temperature regions (e.g., ≤300 mK), poor material stability, high preparation costs, and significant environmental impact.

[0004] Therefore, developing magnetic refrigeration materials that can be applied to the field of ultra-low temperature magnetic refrigeration, and that meet the requirements of being free of crystallization water, having a stable structure, being more efficient, environmentally friendly, cost-effective, and still having excellent magnetocaloric properties under ultra-low temperature conditions, is of great practical significance for promoting the development of related high-end technologies. Summary of the Invention

[0005] This invention aims to address at least one of the technical problems existing in the prior art. To this end, this invention proposes the application of hexagonal material GdAl3(BO3)4 in the field of ultra-low temperature magnetic refrigeration, aiming to solve the problems of insufficient magnetic entropy retention, poor material stability, high preparation cost, and environmental unfriendliness of current magnetic refrigeration materials under ultra-low temperature conditions (≤300mK). The invention seeks to develop a more stable and efficient magnetic refrigeration material that is free of crystallization water and can be applied to the field of ultra-low temperature magnetic refrigeration.

[0006] An embodiment of the first aspect of the present invention provides an application of a hexagonal crystal material in the field of ultra-low temperature magnetic refrigeration, wherein the chemical formula of the hexagonal crystal material is GdAl3(BO3)4, and the ultra-low temperature is ≤300mK.

[0007] According to the first aspect of the present invention, the application has at least the following beneficial effects: The hexagonal crystal material provided by the present invention for use in the field of ultra-low temperature magnetic refrigeration has the chemical formula GdAl3(BO3)4 and can exhibit excellent magnetocaloric properties and stability under ultra-low temperature (≤300mK) conditions, providing a new material option for ultra-low temperature magnetic refrigeration technology. The beneficial effects of this material are as follows: (1) The hexagonal gadolinium aluminum borate material provided by the present invention introduces Gd 3+ As a magnetic ion, Al3+ The use of ions with relatively small molecular weights, such as borate ions, as ligands ensures the mass ratio of magnetic ions, thereby ensuring that the material has a higher magnetic entropy change value. (2) The specific heat measurement results show that the magnetic refrigeration material with the chemical formula GdAl3(BO3)4 provided by this invention does not undergo a phase transition above 300mK, but undergoes a λ phase transition at 300mK. The magnetic entropy is well preserved in the extremely low temperature range, providing favorable conditions and material basis for the efficient magnetic refrigeration process in the sub-Kelvin or even lower temperature range, and has extremely high practical application value. (3) The material has a significant magnetocaloric effect in the extremely low temperature range. At temperatures of 1K and below, under a magnetic field change of 0~1T, the maximum magnetic entropy change that the material can achieve is 24.54 J·kg. -1 ·K -1 Or 106.51 mJ·cm -3 ·K -1 Under magnetic field variations of 0–2 T, the maximum magnetic entropy change achievable by this material is 32.52 J·kg⁻¹. -1 ·K -1 Or 141.16 mJ·cm -3 ·K -1 Under magnetic field variations of 0–3 T, the maximum magnetic entropy change achievable by this material is 34.05 J·kg⁻¹. -1 ·K -1 Or 147.77 mJ·cm -3 ·K -1 Under magnetic field variations of 0–4 T, the maximum magnetic entropy change achievable by this material is 34.74 J·kg⁻¹. -1 ·K -1 Or 150.81 mJ·cm -3 ·K -1 (4) Gd 3+ The ions have a large spin number (S = 7 / 2) and are almost unaffected by the anisotropy of the crystal field, making GdAl3(BO3)4 exhibit near-isotropic magnetic properties. Therefore, in practical magnetic refrigeration applications, this material does not require strict orientation treatment of the single crystal and can be placed in any direction in the magnetic field, which significantly reduces the complexity of the single crystal orientation and assembly process, reduces the operational difficulty and usage cost in engineering applications, and improves the convenience of engineering applications. (5) The GdAl3(BO3)4 crystal structure does not contain water of crystallization, which has higher structural stability and thermal stability, and is more suitable for use in vacuum environments. This material is not prone to structural degradation under high vacuum, extremely low temperature and relatively high preparation or use temperature conditions, avoiding the problem of magnetic refrigeration performance decay or even failure due to the removal of water of crystallization, thus making it more suitable for long-term stable operation of extremely low temperature magnetic refrigeration systems.

[0008] In summary, the GdAl3(BO3)4 material provided by this invention for use in ultra-low temperature magnetic refrigeration exhibits significant advantages in this field by optimizing the mass ratio of magnetic ions, low phase transition temperature, concentrated release behavior of magnetic entropy in the ultra-low temperature region, near-isotropic magnetic characteristics, and excellent structural stability. It can achieve efficient, stable, and convenient magnetic refrigeration applications in sub-Kelvin and even lower temperature regions, and has broad engineering application prospects.

[0009] In some embodiments of the present invention, the extremely low temperature is ≤300mK. Exemplarily, it can be 300mK, 250mK, 200mK, 150mK, 100mK, 50mK, or within the range of any two of the above values.

[0010] In some embodiments of the present invention, the extremely low temperature is ≤250mK.

[0011] In some embodiments of the present invention, the extremely low temperature is ≤200mK.

[0012] In some embodiments of the present invention, the extremely low temperature is ≤150mK.

[0013] In some embodiments of the present invention, the extremely low temperature is ≤100mK.

[0014] In some embodiments of the present invention, the extremely low temperature is ≤50mK.

[0015] In some embodiments of the present invention, the space group of the hexagonal crystal system material is R32(155).

[0016] In some embodiments of the present invention, the cell parameters of the hexagonal crystal system material are: a=b=9.2990Å, c=7.2597Å, α=β=90°, γ=120°.

[0017] Hexagonal crystal is a crystal system in crystallography characterized by sixfold rotation or sixfold reversal axes, with unit cell parameters a=b≠c, α=β=90°, and γ=120°. The gadolinium aluminum borate magnetic refrigeration material GdAl3(BO3)4 proposed in this invention is a hexagonal crystal material that exhibits excellent magnetocaloric properties and stability under extremely low temperatures, providing a new material option for ultra-low temperature magnetic refrigeration technology.

[0018] In some embodiments of the present invention, the phase transition temperature of the hexagonal crystal system material is ≤300 mK. Specific heat tests show that GdAl3(BO3)4 does not undergo a phase transition above 300 mK, but undergoes a λ phase transition at 300 mK. The magnetic entropy can be well preserved to the extremely low temperature range, providing favorable conditions and a material basis for efficient magnetic refrigeration processes in the sub-Kelvin or even lower temperature ranges. It also provides sufficient usable magnetic entropy resources for adiabatic demagnetization refrigeration processes, possessing extremely high practical application value.

[0019] In some embodiments of the present invention, under a temperature range of 0.5~1.5K and a magnetic field variation of 0~4T, the maximum magnetic entropy change of the hexagonal crystal material is ≤35 J·kg. -1 ·K -1 .

[0020] In some embodiments of the present invention, at a temperature ≤1K and a magnetic field variation of 0~1T, the maximum magnetic entropy change of the hexagonal crystal material is ≤24.54 J·kg. -1 ·K -1 .

[0021] In some embodiments of the present invention, at a temperature ≤1K and a magnetic field variation of 0~2T, the maximum magnetic entropy change of the hexagonal crystal material is ≤32.52 J·kg. -1 ·K -1 .

[0022] In some embodiments of the present invention, at a temperature ≤1K and a magnetic field variation of 0~3T, the maximum magnetic entropy change of the hexagonal crystal material is ≤34.05 J·kg. -1 ·K -1 .

[0023] In some embodiments of the present invention, at a temperature ≤1K and a magnetic field variation of 0~4T, the maximum magnetic entropy change of the hexagonal crystal material is ≤34.74 J·kg. -1 ·K -1 .

[0024] In some embodiments of the present invention, the specific heat behavior of an ultra-low temperature magnetic refrigeration material with the chemical formula GdAl3(BO3)4 was studied within a temperature range of 0.1–15 K and a magnetic field range of 0–4 T, yielding the magnetic specific heat of the aforementioned ultra-low temperature magnetic refrigeration material. It can be seen that, under a fixed magnetic field and within the test temperature range, the magnetic specific heat of the material first increases and then decreases as the temperature decreases. Integrating the magnetic specific heat with respect to temperature yields the curves showing the relationship between the magnetic entropy and temperature under different magnetic fields. The magnetic entropy can be well maintained in the ultra-low temperature range, proving that the material can be used for adiabatic demagnetization refrigeration in the ultra-low temperature range. Based on the curves showing the relationship between the magnetic entropy and temperature under different magnetic fields, the curves showing the relationship between the magnetic entropy change and temperature under different magnetic field changes can be calculated. It can be seen that the material exhibits a large magnetocaloric effect near 1 K, and the maximum magnetic entropy changes under magnetic field changes of 0–1, 0–2, 0–3, and 0–4 T are 106.51 mJ·cm⁻¹, respectively. -3 ·K -1 Or 24.54 J·kg -1 ·K -1 141.16 mJ·cm -3 ·K -1 Or 32.52 J·kg -1 ·K -1 and 147.77 mJ·cm -3 ·K -1 Or 34.05 J·kg -1 ·K -1 and 150.81 mJ·cm -3 ·K -1 Or 34.74 J·kg -1 ·K -1 The above results indicate that the material exhibits a large magnetocaloric effect in the low-temperature range, making it suitable for adiabatic demagnetization refrigeration in extremely low-temperature regions.

[0025] In some embodiments of this invention, the applications include those in the fields of cryogenic physics, deep space exploration, superconductivity, or aerospace and space science. The development of these novel ultra-low temperature magnetic refrigeration materials will have a profound impact on scientific research and future technological applications, promoting the widespread application of cryogenic technology in quantum technology, space exploration, superconductivity, and other high-tech fields.

[0026] The development of magnetic refrigeration technology faces the dual challenges of material performance and cost-effectiveness. In the field of ultra-low temperature magnetic refrigeration, the development of magnetic refrigeration materials not only needs to consider improving magnetic entropy change, but also needs to pay attention to the chemical stability, preparation cost, and environmental impact of the materials. These materials must exhibit excellent magnetocaloric properties at extremely low temperatures while meeting the requirements of sustainable development. Furthermore, traditional ultra-low temperature magnetic refrigeration materials are usually paramagnetic salts containing water of crystallization. The presence of water of crystallization leads to structural instability, long growth cycles, and complex processing and encapsulation techniques. Therefore, the field of ultra-low temperature magnetic refrigeration technology is seeking new material solutions. How to prepare ultra-low temperature magnetic refrigeration materials that are simple to prepare, have short cycles, are more stable, more efficient, environmentally friendly, cost-effective, and suitable for industrial production has become an urgent problem to be solved.

[0027] Based on this, a second aspect of the present invention provides a method for preparing an ultra-low temperature magnetic refrigeration material, comprising the following steps: Using Gd-containing compounds, Al-containing compounds, and B-containing compounds as raw materials, they are weighed according to the molar ratio of Gd, Al, and B elements of 1:3:(4~4.2), mixed evenly, and pre-fired at 550~650℃ for 2~6 hours, and then heated to 1000~1200℃ for sintering for 24~48 hours to obtain the ultra-low temperature magnetic refrigeration material.

[0028] In some embodiments of the present invention, the ultra-low temperature magnetic refrigeration material is hexagonal with the chemical formula GdAl3(BO3)4.

[0029] This invention synthesizes GdAl3(BO3)4 using Gd-containing compounds, Al-containing compounds, and B-containing compounds as raw materials via a high-temperature solid-state reaction method. The process is short, simple, cost-effective, and has significant industrial application potential. Furthermore, it is environmentally friendly, meets environmental protection requirements, satisfies sustainable development needs, and is suitable for large-scale industrial production. The development of this material provides a simple, environmentally friendly, and cost-effective option for cryogenic refrigeration systems, and has broad application prospects in high-end technology fields such as cryogenic physics, space exploration, and aerospace.

[0030] In some embodiments of the present invention, the Gd-containing compound includes at least one of Gd2O3 or Gd powder, but is not limited thereto.

[0031] In some embodiments of the present invention, the Al-containing compound includes Al2O3, but is not limited thereto.

[0032] In some embodiments of the present invention, the B-containing compound includes at least one of H3BO3 or B2O3, but is not limited thereto.

[0033] In some embodiments of the present invention, Gd2O3, Al2O3 and H3BO3 are used as raw materials.

[0034] Specifically, the stoichiometric molar ratio of Gd2O3, Al2O3 and H3BO3 is 1:3:8.

[0035] Specifically, the stoichiometric molar ratio of Gd2O3, Al2O3 and H3BO3 is 1:3:8.4.

[0036] In some embodiments of the present invention, Gd2O3, Al2O3 and B2O3 are used as raw materials.

[0037] Specifically, the stoichiometric molar ratio of Gd2O3, Al2O3 and B2O3 is 1:3:4.

[0038] In some embodiments of the present invention, Gd powder, Al2O3 and H3BO3 are used as raw materials.

[0039] Specifically, the stoichiometric molar ratio of the Gd powder, Al2O3, and H3BO3 is 2:3:8.

[0040] In some embodiments of the present invention, Gd powder, Al2O3 and B2O3 are used as raw materials.

[0041] Specifically, the stoichiometric molar ratio of the Gd powder, Al2O3, and B2O3 is 2:3:4.

[0042] In some embodiments of the present invention, the raw materials are thoroughly ground and mixed evenly.

[0043] In some embodiments of the present invention, after the raw materials are thoroughly ground and mixed evenly, a tablet press is used to compress the mixed raw materials into blocks.

[0044] In some embodiments of the present invention, the pressing conditions are not limited, as long as the sheet can be pressed into a sheet and placed in a muffle furnace for sintering. For example, it can be pressed into a sheet at 18 tons for 5 minutes.

[0045] In some embodiments of the present invention, the preheating temperature is 550~650°C. Exemplarily, it can be 550°C, 560°C, 570°C, 580°C, 590°C, 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, or a range consisting of any two of the above values. Preferably, it is 600°C.

[0046] In some embodiments of the present invention, the preheating time is 2 to 6 hours. Exemplarily, it can be 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or within any two of the above values.

[0047] In some embodiments of the present invention, the sintering temperature is 1000~1200℃. Exemplarily, it can be 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, 1050℃, 1060℃, 1070℃, 1080℃, 1090℃, 1100℃, 1110℃, 1120℃, 1130℃, 1140℃, 1150℃, 1160℃, 1170℃, 1180℃, 1190℃, 1200℃, or a range consisting of any two of the above values. Preferably, it is 1100℃.

[0048] In some embodiments of the present invention, the sintering time is 24 to 48 hours. Exemplarily, it can be 24 hours, 25 hours, 26 hours, 27 hours, 28 hours, 29 hours, 30 hours, 31 hours, 32 hours, 33 hours, 34 hours, 35 hours, 36 hours, 37 hours, 38 hours, 39 hours, 40 hours, 41 hours, 42 hours, 43 hours, 44 hours, 45 hours, 46 hours, 47 hours, or 48 hours, or within any two of the above values.

[0049] The sintering step of the present invention is maintained at 1100°C for 24 to 48 hours to optimize the microstructure of the material.

[0050] In some embodiments of the present invention, sintering is carried out in a sintering furnace.

[0051] Specifically, the sintering furnace includes a muffle furnace, a tube furnace, or a vacuum furnace.

[0052] In some embodiments of the invention, grinding is performed at least once before or after the sintering step. The method for preparing the material includes grinding at least once before and after sintering to improve the uniformity and reaction integrity of the material.

[0053] In some specific embodiments of the present invention, the preparation method of the ultra-low temperature magnetic refrigeration material GdAl3(BO3)4 includes the following steps: Using Gd2O3, Al2O3 and H3BO3 as raw materials, they are mixed in a stoichiometric molar ratio of 1:3:8. The mixed raw materials are thoroughly ground, pressed into blocks, pre-fired at 600℃ for 2-6 hours, then heated to 1100℃ for sintering for 24-48 hours, with multiple grindings during the process. Finally, the mixture is slowly cooled to room temperature to obtain a pure phase powder material with the chemical formula GdAl3(BO3)4.

[0054] In some embodiments of the present invention, the pressing conditions are not limited, as long as the sheet can be pressed into a sheet and placed in a muffle furnace for sintering. For example, it can be pressed into a sheet at 18 tons for 5 minutes.

[0055] In some embodiments of the present invention, the raw material block is pre-fired at 600°C for 2-6 hours in an oxygen-containing environment, then slowly cooled and ground before being pressed into a block again. The block is then heated at 1100°C again in an oxygen-containing environment and held for 24-48 hours, during which multiple grinding processes are performed to improve the crystallinity of the material. After being slowly cooled to room temperature, a hexagonal gadolinium aluminum borate magnetic refrigeration material with the chemical formula GdAl3(BO3)4 is obtained.

[0056] In some embodiments of the present invention, the space group of the hexagonal crystal system material is R32(155).

[0057] In some embodiments of the present invention, the cell parameters of the ultra-low temperature magnetic refrigeration material are: a=b=9.2990Å, c=7.2597Å, α=β=90°, γ=120°.

[0058] In some embodiments of the present invention, the phase transition temperature of the ultra-low temperature magnetic refrigeration material is ≤300 mK. Specific heat tests show that the ultra-low temperature magnetic refrigeration material GdAl3(BO3)4 does not undergo a phase transition above 300 mK, but undergoes a λ phase transition at 300 mK. The magnetic entropy can be well preserved in the ultra-low temperature range, providing favorable conditions and a material basis for efficient magnetic refrigeration processes in the sub-Kelvin or even lower temperature ranges. It also provides sufficient usable magnetic entropy resources for adiabatic demagnetization refrigeration processes, possessing extremely high practical application value.

[0059] In some embodiments of the present invention, under a temperature range of 0.5~1.5K and a magnetic field variation of 0~4T, the maximum magnetic entropy change of the ultra-low temperature magnetic refrigeration material is ≤35 J·kg. -1 ·K -1 .

[0060] In some embodiments of the present invention, at a temperature ≤1K and a magnetic field variation of 0~1T, the maximum magnetic entropy change of the ultra-low temperature magnetic refrigeration material is ≤24.54 J·kg. -1 ·K -1 .

[0061] In some embodiments of the present invention, at a temperature ≤1K and a magnetic field variation of 0~2T, the maximum magnetic entropy change of the ultra-low temperature magnetic refrigeration material is ≤32.52 J·kg. -1 ·K -1 .

[0062] In some embodiments of the present invention, at a temperature ≤1K and a magnetic field variation of 0~3T, the maximum magnetic entropy change of the ultra-low temperature magnetic refrigeration material is ≤34.05 J·kg. -1 ·K -1 .

[0063] In some embodiments of the present invention, under a magnetic field variation of 0~4T at a temperature ≤1K, the maximum magnetic entropy change of the ultra-low temperature magnetic refrigeration material is ≤34.74 J·kg. -1 ·K -1 .

[0064] An embodiment of the third aspect of the present invention provides an application of the above-mentioned method for preparing ultra-low temperature magnetic refrigeration materials in the field of ultra-low temperature magnetic refrigeration.

[0065] The method for preparing ultra-low temperature magnetic refrigeration materials provided by this invention introduces Gd into hexagonal gadolinium aluminum borate magnetic refrigeration materials. 3+ As a magnetic ion, Al 3+ The use of ions with relatively small molecular weights, such as borate ions, as ligands ensures the mass ratio of magnetic ions, thereby guaranteeing a higher magnetic entropy change value for the material. This material is waterless, making it structurally more stable and suitable for vacuum environments compared to traditional paramagnetic salt magnetic refrigeration materials containing crystal water. Furthermore, its short growth cycle and simple preparation process significantly reduce production costs, making it suitable for large-scale industrial production. The novel hexagonal polycrystalline magnetic refrigeration material obtained by the above method has the chemical formula GdAl3(BO3)4. It exhibits a large magnetocaloric effect in the low-temperature range, making it suitable for adiabatic demagnetization refrigeration in extremely low-temperature regions. Specific heat tests show that this material has a phase transition temperature as low as 300 mK and achieves a maximum magnetic entropy change of 150 mJ·cm⁻¹ within a magnetic field variation range of 0–4 T at 1 K. -3 ·K -1 Or 35 J·kg -1 ·K -1 This remarkable magnetocaloric effect makes it particularly suitable for applications in cryogenic magnetic refrigeration, applicable to technical fields where functionality, performance, or stable operation is required under extremely low or ultra-low temperature conditions.

[0066] In some embodiments of the present invention, the applications include applications in the fields of cryogenic physics, deep space exploration, superconductivity, or aerospace and space science.

[0067] In some embodiments of the present invention, the application includes use in a single-stage adiabatic demagnetizing refrigeration system or as a pre-stage magnetic refrigeration material in a multi-stage magnetic refrigeration system.

[0068] According to a fourth aspect of the present invention, an ultra-low temperature magnetic refrigeration device is provided, comprising a substrate and an ultra-low temperature magnetic refrigeration material, wherein the ultra-low temperature magnetic refrigeration material is prepared by the above-described preparation method.

[0069] The low-temperature magnetic refrigeration material prepared by this invention can be used to manufacture magnetic refrigeration systems, and is particularly suitable for low-temperature environments in aerospace and satellite technology.

[0070] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the description, claims, and drawings. Attached Figure Description

[0071] Figure 1 The X-ray diffraction pattern is shown for the hexagonal ultra-low temperature magnetic refrigeration material with the chemical formula GdAl3(BO3)4 prepared in Example 1 of this invention.

[0072] Figure 2 The magnetic susceptibility and reciprocal curve of the hexagonal crystal system ultra-low temperature magnetic refrigeration material with the chemical formula GdAl3(BO3)4 prepared in Example 1 of the present invention under zero-field cooling (ZFC) in a magnetic field of 0.1T are shown.

[0073] Figure 3 The magnetic susceptibility and reciprocal curve of the hexagonal crystal system ultra-low temperature magnetic refrigeration material with the chemical formula GdAl3(BO3)4 prepared in Example 1 of the present invention under field cooling (FC) in a magnetic field of 0.1T.

[0074] Figure 4 The image shows the isothermal magnetization curves of the hexagonal ultra-low temperature magnetic refrigeration material with the chemical formula GdAl3(BO3)4 prepared in Example 1 of this invention, under magnetic field variations of 0~9T and 2K~20K.

[0075] Figure 5 The curves show the relationship between the magnetic specific heat and temperature of the hexagonal ultra-low temperature magnetic refrigeration material with the chemical formula GdAl3(BO3)4 prepared in Example 1 of this invention under different magnetic fields.

[0076] Figure 6 The curves show the relationship between magnetic entropy and temperature of the hexagonal ultra-low temperature magnetic refrigeration material with the chemical formula GdAl3(BO3)4 prepared in Example 1 of this invention under different magnetic fields.

[0077] Figure 7 The graph shows the magnetic entropy change of the hexagonal crystal system ultra-low temperature magnetic refrigeration material with the chemical formula GdAl3(BO3)4 prepared in Example 1 of this invention. Detailed Implementation

[0078] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0079] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0080] In the description of this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. Unless otherwise stated, the various reaction or operation steps may be performed sequentially or not. Preferably, the reaction methods in this invention are performed sequentially.

[0081] Experimental methods in the following examples, unless otherwise specified, are generally performed under standard conditions or as recommended by the manufacturer. Unless otherwise specified, the materials and reagents used in these examples are commercially available.

[0082] Example 1 Preparation of hexagonal material GdAl3(BO3)4: The dried raw materials Gd2O3 (99.99%), Al2O3 (99.99%), and H3BO3 (99.99%) were accurately weighed according to the stoichiometric molar ratio of 1:3:8 and thoroughly ground and mixed. The raw materials were then compressed into blocks using a tablet press, and the initial raw material blocks were placed in a muffle furnace and heated to 600℃ for 5 hours for pre-calcination. After being slowly cooled to room temperature, the blocks were ground evenly and compressed into blocks again. The pre-calcined raw material blocks were then placed in a muffle furnace and heated to 1100℃ for 48 hours for sintering. During this period, the blocks were ground twice to obtain a pure-phase hexagonal crystal system ultra-low temperature magnetic refrigeration material with the chemical formula GdAl3(BO3)4.

[0083] Example 2 Preparation of hexagonal material GdAl3(BO3)4: The dried raw materials Gd2O3 (99.99%), Al2O3 (99.99%), and H3BO3 (99.99%) were accurately weighed according to the stoichiometric molar ratio of 1:3:8.4 and thoroughly ground and mixed. The raw materials were pressed into blocks using a tablet press, and the initial raw material blocks were placed in a muffle furnace and heated to 600℃ at a uniform rate for 5 hours for pre-calcination. After being slowly cooled to room temperature, the blocks were ground evenly and pressed into blocks again. The pre-calcined raw material blocks were then placed in a muffle furnace and heated to 1100℃ at a uniform rate for sintering for 48 hours, with two grinding operations during the process. Finally, a pure-phase hexagonal crystal system ultra-low temperature magnetic refrigeration material with the chemical formula GdAl3(BO3)4 was obtained.

[0084] Example 3 Preparation of hexagonal material GdAl3(BO3)4: The dried raw materials Gd2O3 (99.99%), Al2O3 (99.99%), and B2O3 (99.99%) were accurately weighed according to the stoichiometric molar ratio of 1:3:4 and thoroughly ground and mixed. The raw materials were then compressed into blocks using a tablet press, and the initial raw material blocks were placed in a muffle furnace and heated at a uniform rate to 1100℃ for sintering for 48 hours, with one grinding during the process. Finally, a pure-phase hexagonal crystal system ultra-low temperature magnetic refrigeration material with the chemical formula GdAl3(BO3)4 was obtained.

[0085] Example 4 Preparation of hexagonal material GdAl3(BO3)4: Dry raw materials Gd powder (99.99%), Al2O3 (99.99%), and H3BO3 (99.99%) were accurately weighed according to a stoichiometric molar ratio of 2:3:8 and thoroughly ground and mixed. The raw materials were then compressed into blocks using a tablet press, and the initial raw material blocks were placed in a muffle furnace and heated to 600°C for 5 hours for pre-calcination. After being slowly cooled to room temperature, the blocks were ground uniformly and compressed again. The pre-calcined raw material blocks were then placed in a muffle furnace and heated to 1100°C for 48 hours for sintering, with two grinding operations performed during the process. Finally, a pure-phase hexagonal crystal system ultra-low temperature magnetic refrigeration material with the chemical formula GdAl3(BO3)4 was obtained.

[0086] Example 5 Preparation of hexagonal material GdAl3(BO3)4: Dry raw materials Gd powder (99.99%), Al2O3 (99.99%), and B2O3 (99.99%) were accurately weighed according to a stoichiometric molar ratio of 2:3:4 and thoroughly ground and mixed. The raw materials were then compressed into blocks using a tablet press, and the initial raw material blocks were placed in a muffle furnace and heated at a uniform rate to 1100℃ for sintering for 48 hours. During this period, the materials were ground twice to finally obtain a pure-phase hexagonal crystal system ultra-low temperature magnetic refrigeration material with the chemical formula GdAl3(BO3)4.

[0087] Test case 1. Structural characterization: The ultra-low temperature magnetic refrigeration material with the chemical formula GdAl3(BO3)4 obtained in Example 1 was characterized by XRD, and the XRD characterization results were analyzed using the Rietveld refinement method. Figure 1 The results shown are the XRD test results and the refined fitting results. The test and refined results prove that the ultra-low temperature magnetic refrigeration material with the chemical formula GdAl3(BO3)4 prepared in Example 1 of this invention is a pure phase material.

[0088] 2. Magnetic test: The magnetic properties of the ultra-low temperature magnetic refrigeration material with the chemical formula GdAl3(BO3)4 prepared in Example 1 were studied using the Quantum Design PPMS DynaCool integrated property measurement system. The zero-field cooling (ZFC) and band-field cooling (FC) magnetic susceptibility curves of the ultra-low temperature magnetic refrigeration material with the chemical formula GdAl3(BO3)4 prepared in Example 1 were tested in a temperature range of 2~300 K and a magnetic field of 0.1 T. Figure 2 , Figure 3 The Curie-Weiss law was used to fit the reciprocals of the zero-field cooling (ZFC) and band-field cooling (FC) magnetic susceptibility curves, revealing that the compound is a paramagnetic material within the test temperature range. The fitted Curie constant was C = 7.92 emu·K·mol⁻¹. -1 The effective magnetic moment μ obtained by fitting eff = 7.96, which is very close to the calculated value of 7.94, the Werther constant θ CW =0.227 K, which indicates that the material has extremely weak ferromagnetic interaction and the magnetic entropy can be retained to the extremely low temperature range, so it can be used for extremely low temperature magnetic refrigeration.

[0089] The isothermal magnetization curves of the ultra-low temperature magnetic refrigeration material with the chemical formula GdAl3(BO3)4 prepared in Example 1 were tested within a temperature range of 2–20 K and a magnetic field range of 0–9 T. Figure 5 At a fixed temperature, the magnetization of the material gradually increases with the increase of the magnetic field. At 2K, it reaches the saturation magnetization value of 7 μ at a magnetic field of 7T. B It is exactly the same as the theoretical saturation magnetization value.

[0090] 3. Specific heat test: The specific heat of the ultra-low temperature magnetic refrigeration material with the chemical formula GdAl3(BO3)4 prepared in Example 1 was studied using the Quantum Design PPMS DynaCool integrated property measurement system and a dilution refrigerator (DR). The specific heat behavior of the ultra-low temperature magnetic refrigeration material with the chemical formula GdAl3(BO3)4 prepared in Example 1 was studied within a temperature range of 0.1–15 K and a magnetic field range of 0–4 T. After deducting the phonon specific heat, the following results were obtained: Figure 5 The magnetic specific heat is shown. It can be seen that, under a fixed magnetic field and within the test temperature range, the magnetic specific heat of this material first increases and then decreases as the temperature decreases. Integrating the magnetic specific heat over temperature yields the following... Figure 6 The curves showing the relationship between magnetic entropy and temperature under different magnetic fields demonstrate that the magnetic entropy can be well maintained up to the extremely low temperature range, proving that the material can be used for thermal insulation, demagnetization, and refrigeration in the extremely low temperature range.

[0091] according to Figure 6 The curves showing the relationship between magnetic entropy and temperature for this material under different magnetic fields can be used to calculate the curves showing the relationship between magnetic entropy change and temperature for this material under different magnetic field variations, such as... Figure 7 As shown, the material exhibits a large magnetocaloric effect near 1 K, with maximum magnetic entropy changes of 106.51 mJ·cm under magnetic field variations of 0–1 T, 0–2 T, 0–3 T, and 0–4 T, respectively. -3 ·K -1 Or 24.54 J·kg -1 ·K -1 141.16 mJ·cm -3 ·K -1 Or 32.52 J·kg -1 ·K -1 147.77 mJ·cm -3 ·K -1 Or 34.05 J·kg -1 ·K -1 150.81 mJ·cm -3 ·K -1 Or 34.74 J·kg -1 ·K -1 .

[0092] The above is a detailed description of the preferred embodiments of this application. However, this application is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of this application. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. The application of a hexagonal crystal material in the field of ultra-low temperature magnetic refrigeration, wherein the chemical formula of the hexagonal crystal material is GdAl3(BO3)4, and the ultra-low temperature is ≤300mK.

2. The application according to claim 1, characterized in that, The space group of the hexagonal crystal system material is R32(155); And / or, the cell parameters of the hexagonal crystal system material are: a=b=9.2990Å, c=7.2597Å, α=β=90°, γ=120°.

3. The application according to claim 1, characterized in that, The phase transition temperature of the hexagonal crystal system material is ≤300 mK.

4. The application according to claim 1, characterized in that, Within a temperature range of 0.5–1.5 K and a magnetic field variation of 0–4 T, the maximum magnetic entropy change of the hexagonal crystal material is ≤35 J·kg. -1 ·K -1 .

5. The application according to claim 1, characterized in that, Including at least one of (a1) to (a4): (a1) At a temperature ≤ 1 K, under a magnetic field variation of 0 ~ 1 T, the maximum magnetic entropy change of the hexagonal crystal material is ≤ 24.54 J·kg. -1 ·K -1 ; (a2) At a temperature ≤1K, under a magnetic field variation of 0~2T, the maximum magnetic entropy change of the hexagonal crystal material is ≤32.52 J·kg. -1 ·K -1 ; (a3) At a temperature ≤1K, under a magnetic field variation of 0~3T, the maximum magnetic entropy change of the hexagonal crystal material is ≤34.05 J·kg. -1 ·K -1 ; (a4) At a temperature ≤1K, under a magnetic field variation of 0~4T, the maximum magnetic entropy change of the hexagonal crystal material is ≤34.74 J·kg. -1 ·K -1 .

6. The application according to any one of claims 1-5, characterized in that, The applications include those in the fields of low-temperature physics, deep space exploration, superconductivity, or aerospace and space science.

7. A method for preparing an ultra-low temperature magnetic refrigeration material, characterized in that, Including the following steps: Using Gd-containing compounds, Al-containing compounds, and B-containing compounds as raw materials, weigh them according to the molar ratio of Gd, Al, and B elements of 1:3:(4~4.2), mix them evenly, pre-fire them at 550~650℃ for 2~6 hours, and then sinter them at 1000~1200℃ for 24~48 hours to obtain the ultra-low temperature magnetic refrigeration material. The ultra-low temperature magnetic refrigeration material is hexagonal with the chemical formula GdAl3(BO3)4.

8. The method for preparing the ultra-low temperature magnetic refrigeration material according to claim 7, characterized in that, Including at least one of (b1) to (b8): (b1) The Gd-containing compound includes at least one of Gd2O3 or Gd powder; (b2) The Al-containing compound includes Al2O3; (b3) The B-containing compound includes at least one of H3BO3 or B2O3; (b4) Grinding shall be performed at least once before or after the sintering step; (b5) The space group of the ultra-low temperature magnetic refrigeration material is R32(155); (b6) The cell parameters of the ultra-low temperature magnetic refrigeration material are: a=b=9.2990Å, c=7.2597Å, α=β=90°, γ=120°; (b7) The phase transition temperature of the ultra-low temperature magnetic refrigeration material is ≤300 mK; (b8) Under a temperature range of 0.5~1.5K and a magnetic field variation of 0~4T, the maximum magnetic entropy change of the ultra-low temperature magnetic refrigeration material is ≤35 J·kg. -1 ·K -1 .

9. The application of a method for preparing an ultra-low temperature magnetic refrigeration material as described in any one of claims 7-8 in the field of ultra-low temperature magnetic refrigeration.

10. A cryogenic magnetic refrigeration device, characterized in that, It includes a matrix and an ultra-low temperature magnetic refrigeration material, wherein the ultra-low temperature magnetic refrigeration material is prepared by the preparation method described in any one of claims 7-8.

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