Gadolinium boron molybdate magnetic refrigeration material with triangular magnetic resistance as well as preparation method and application of gadolinium boron molybdate magnetic refrigeration material

Abstract

The invention discloses a gadolinium boron molybdate magnetic refrigeration material with triangular magnetic resistance and a preparation method and application of the gadolinium boron molybdate magnetic refrigeration material. The chemical formula of the material is Gd2B2MoO9, the material belongs to a triclinic system, and the space group is P-1; the crystal structure has the characteristic that nearest rare earth Gd ions have magnetic resistance file; the material is prepared by a solid phase method or a sol-gel method; the magnetic phase change temperature of the material is 0.7-0.9 K, the material shows a remarkable magnetothermal effect at low temperature, the maximum isothermal magnetic entropy change values of the material are 30.0-35.0 J / kg.K and 51.0-55.0 J / kg.K respectively under the magnetic field change of 0-2T and 0-5T, and the material can be applied to low-temperature magnetic refrigeration. The gadolinium boron molybdate Gd2B2MoO9 material with triangular magnetoresistance provided by the invention has the advantages of low raw material price, simple process and lower equipment requirement, and is suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of rare earth magnetic functional materials, and in particular to a gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration, and a preparation method and application thereof. Background Art

[0002] In 1881, the German physicist Emil Warburg discovered the magnetocaloric effect, revealing the phenomenon of temperature change caused by the rearrangement of magnetic moments in magnetic materials in a magnetic field. The principle of the magnetocaloric effect is that when a magnetic material is placed in a magnetic field, the magnetic moments inside it will rearrange, resulting in a change in the temperature of the material. With the progress of science and technology, researchers have found that by precisely controlling the magnetic field and temperature, a new type of refrigeration technology can be developed using this effect. This technology not only has the characteristics of high efficiency and energy saving, but also can achieve a green and environmentally friendly refrigeration solution, reducing the dependence on traditional refrigerants, thereby reducing the impact on the environment. The application potential of magnetic materials in this field is huge, and it can provide sustainable solutions for future refrigeration technologies. Based on this principle, scientists have developed an efficient and energy-saving green refrigeration technology, reducing the dependence on traditional refrigerants. In the field of cryogenic technology, Peter Joseph William Debye and William Giauque proposed the adiabatic demagnetization refrigeration (ADR) theory for paramagnetic salts in 1926. In 1933, Giauque and D.P. MacDougall successfully conducted an experiment and achieved an extremely low temperature of 0.25K for the first time, marking a major breakthrough in this field. In particular, the application of Gd2(SO4)3·8H2O as a cooling medium has further developed and improved the adiabatic demagnetization technology for paramagnetic salts. This technology has not only promoted the frontier research of basic science, but also provided strong support for applications in quantum computing, superconducting materials and other high-tech fields.

[0003] Low-temperature magnetic refrigeration materials and the continuous progress of low-temperature refrigeration technology will open up new paths for future scientific exploration and technological innovation, facilitating humanity's in-depth exploration and discovery in unknown fields. In low-temperature magnetic refrigeration technology, hydrate paramagnetic salts such as FeNH4(SO4)2·12H2O (ammonium iron sulfate, FAA) and KCr(SO4)2·12H2O (potassium chromium sulfate, CPA) are widely used. However, the use of these materials in ultra-high vacuum environments is restricted to some extent, mainly due to the dehydration phenomenon of water molecules and the long preparation cycle, which pose certain challenges in practical applications. Therefore, finding new low-temperature magnetic refrigeration working fluids has become the focus of research. An ideal alternative material should have good chemical structure stability, be able to maintain its physical properties under ultra-high vacuum conditions, and also have a simple preparation method to improve production efficiency and reduce costs. By exploring new hydrate paramagnetic salts or other types of materials, researchers hope to overcome the current technical bottlenecks and promote the further development of low-temperature refrigeration technology. This is not only of great significance for scientific research but also provides more possibilities for practical applications, thus promoting the popularization and application of low-temperature technology in various fields. In short, the development of new low-temperature magnetic refrigeration working fluids is an important direction to improve the performance of ADR technology and will provide a broader prospect for future low-temperature research and related applications.

[0004] Magnetic frustrated materials have special crystal structures (such as triangular lattices, kagome lattices, or pyrochlore, etc.), which lead to the inability of the interactions between magnetic ions to simultaneously satisfy the condition of the lowest energy, thus forming geometric frustration or random frustration and suppressing the establishment of long-range magnetic order. In such materials, the synergistic effect of strong quantum fluctuations and frustration effects often results in an extremely low magnetic ordering temperature. For example, the two-dimensional triangular lattice material TmMgGaO4 (TMGO) exhibits long-range order only below 0.9 K and shows the disordered strong fluctuation characteristics of the Berezinskii-Kosterlitz-Thouless (BKT) phase in the range of 0.9 - 1.9 K; similarly, the striped antiferromagnetic order of CsCeSe2 appears only near 350 mK, and the magnetic excitation still shows anomalous kinetic behavior at extremely low temperatures. The number of known strong frustrated materials is limited, partly because it is difficult to synthesize materials with a high frustration coefficient. For example, the double perovskite structure material Pb2MnMoO6 can only achieve a frustration coefficient f > 12.5 through high-temperature and high-pressure preparation, and its long-range magnetic ordering temperature is still below 2 K. In addition, most of the similar materials have weak frustration effects (such as f of Pb2MnWO6 is only 3). Moreover, the quantum spin liquid state (QSL) in the frustrated system, as a novel quantum state with a highly entangled spin configuration, does not form a traditional long-range magnetic order even at absolute zero, further reducing the possibility of observable magnetic order. These characteristics make frustrated materials an ideal platform for exploring novel quantum states (such as spin liquids, topological magnetic structures) and developing extremely low-temperature solid-state refrigeration technology. Summary of the Invention

[0005] The object of the present invention is to provide a novel gadolinium boromolybdate material with a triangular magnetic frustration structure, its preparation method and its application in magnetic refrigeration, so as to solve the problems of small magnetic entropy, unstable chemical structure and complex preparation process of existing magnetic refrigeration materials.

[0006] The present invention provides a gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration, whose molecular formula is Gd2B2MoO9, which is composed of a single phase, belongs to the triclinic system, the space group is P-1, and the lattice constants are a = 5.2011(1), b = 6.9488(4), c = 10.3210(9), α = 74.557(6), β = 76.307(7) and γ = 73.065(6); among them, in the crystallographic data, the parentheses () after the lattice constants and angular parameters represent the uncertainty of the measured values, that is, the error range;

[0007] Gd atoms form two nearly equilateral triangles sharing an edge through covalent bonds, where the length of the shared edge is The lengths of the other two sides of one nearly equilateral triangle are both The lengths of the other two sides of the other nearly equilateral triangle are both and

[0008] Preferably, its magnetic transition temperature is 0.7 - 0.9K. Under an external magnetic field of 0 - 2T and 0 - 5T, its isothermal magnetic entropy changes are 30.0 - 35.0 J / kg·K and 51.0 - 55.0 J / kg·K respectively.

[0009] The present invention also provides a preparation method of the gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration, including the following steps:

[0010] Using Gd(NO3)3·6H2O, H3BO3 and (NH4)6Mo7O 24 ·4H2O as raw materials, where the dosages of Gd(NO3)3·6H2O and (NH4)6Mo7O 24 ·4H2O are determined according to the stoichiometric ratio of Gd and Mo elements in the molecular formula Gd2B2MoO9, and H3BO3 is in excess; grind and mix the raw materials evenly, first sinter at 650°C, cool and grind and mix evenly again, sinter at 750°C, and then sinter at a temperature not lower than 860°C to obtain the gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration.

[0011] Preferably, the specific dosage of H3BO3 is determined as follows: the dosage of H3BO3 I is determined according to the stoichiometric ratio of Gd, B, and Mo elements in the molecular formula Gd2B2MoO9, and the dosage of H3BO3 I is multiplied by 105% - 107% as the specific dosage of H3BO3.

[0012] Preferably, the sintering time at 650 °C is 5 hours, the sintering time at 750 °C is 5 hours, and the temperature not lower than 860 °C is specifically 860 - 900 °C for 8 hours of sintering.

[0013] The present invention also provides a preparation method of the gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration, comprising the following steps:

[0014] Using Gd(NO3)3·6H2O, H3BO3, and (NH4)6Mo7O 24 ·4H2O as raw materials, wherein the dosages of Gd(NO3)3·6H2O and (NH4)6Mo7O 24 ·4H2O are determined according to the stoichiometric ratio of Gd and Mo elements in the molecular formula Gd2B2MoO9, and H3BO3 is in excess;

[0015] After dissolving the raw materials and mixing them with citric acid and stirring, a gel-like mixture is formed.

[0016] After drying the gel-like mixture, it is sintered at 650 °C, cooled and ground again to be uniformly mixed, and then sintered at a temperature not lower than 800 °C; the gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration is obtained.

[0017] Preferably, the stirring time is 12 h; the sintering time at 650 °C is 5 hours, and the temperature not lower than 800 °C is specifically 800 - 900 °C for 5 hours of sintering.

[0018] Preferably, when dissolving the raw materials, the mass ratio of the raw materials used to deionized water is 1:30, and the molar ratio of citric acid to the cations in the solution obtained by dissolving the raw materials is 1:1.

[0019] Preferably, the purities of Gd2O3, H3BO3, (NH4)6Mo7O 24 ·4H2O, and Gd(NO3)3·6H2O are not lower than 99.95%; both drying and sintering are carried out in air.

[0020] The present invention also provides an application of the gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration in low-temperature magnetic refrigeration, which is characterized in that: at a temperature of 0.7 - 0.9 K, under an external magnetic field of 0 - 2 T and 0 - 5 T, the isothermal magnetic entropy changes of the gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration are 30.0 - 35.0 J / kg·K and 51.0 - 55.0 J / kg·K respectively.

[0021] The present invention has the following beneficial effects:

[0022] 1. The gadolinium boromolybdate magnetic refrigeration material Gd2B2MoO9 with triangular magnetic frustration according to the present invention; its magnetic transition temperature is 0.7 - 0.9 K; under 0 - 2 T and 0 - 5 T, its isothermal magnetic entropy changes are 30.0 - 35.0 J / kg·K and 51.0 - 55.0 J / kg·K respectively; greatly improving the magnetic entropy change of rare earth magnetic refrigeration materials.

[0023] 2. The gadolinium boromolybdate magnetic refrigeration material Gd2B2MoO9 with triangular magnetic frustration according to the present invention has the advantages of a large magnetic entropy change value, a simple preparation method, and a stable structure, and has very great application prospects in the field of magnetic refrigeration.

[0024] 3. The present invention prepares low-temperature magnetic refrigeration materials by traditional solid-phase method and sol-gel method, which has the characteristics of simple process, short production cycle, and low energy consumption, and is suitable for large-scale industrial application. Applying this material to the field of magnetic refrigeration has the advantages of low raw material price, simple process, and low equipment requirements, and is suitable for industrial production. It can not only promote the scientific and technological progress of our country in the fields of low-temperature physics, deep space exploration, and aerospace, but also promote the high-value utilization of rare earth resources, and further enhance the international competitiveness and technical strength of our country's rare earth industry.

[0025] The technical solution of the present invention will be further described in detail below through the accompanying drawings and embodiments. Description of the Drawings

[0026] Figure 1 XRD pattern of the gadolinium boromolybdate magnetic refrigeration material Gd2B2MoO9 with triangular magnetic frustration prepared in Example 1 of the present invention;

[0027] Figure 2 XRD pattern of the gadolinium boromolybdate magnetic refrigeration material Gd2B2MoO9 with triangular magnetic frustration prepared in Example 2 of the present invention;

[0028] Figure 3 XRD pattern of the gadolinium boromolybdate magnetic refrigeration material Gd2B2MoO9 with triangular magnetic frustration prepared in Example 3 of the present invention;

[0029] Figure 4Crystal structure diagram of gadolinium boromolybdate magnetic refrigeration material Gd2B2MoO9 with triangular magnetic frustration prepared in Example 1 of the present invention; it shows two edge-sharing near-equilateral triangles composed of 4 Gd atoms, and the side length of the edge-sharing is The lengths of the other two sides of a near-equilateral triangle are both The lengths of the other two sides of the other near-equilateral triangle are both and Their included angles are all about 60°, specifically 61.64(9)°, 59.17(6)°, 59.17(6)°, 61.65(0)°, 59.17(5)° and 59.17(5)° respectively;

[0030] Figure 5 Temperature-dependent magnetic susceptibility curve and Curie-Weiss fitting curve diagram of gadolinium boromolybdate magnetic refrigeration material Gd2B2MoO9 with triangular magnetic frustration prepared in Example 1 of the present invention;

[0031] Figure 6 ZFC-FC curve diagram of gadolinium boromolybdate magnetic refrigeration material Gd2B2MoO9 with triangular magnetic frustration prepared in Example 1 of the present invention at 0.05 T;

[0032] Figure 7 Temperature-dependent and field-dependent magnetization intensity diagram of gadolinium boromolybdate magnetic refrigeration material Gd2B2MoO9 with triangular magnetic frustration prepared in Example 1 of the present invention;

[0033] Figure 8 Magnetic entropy diagram of gadolinium boromolybdate magnetic refrigeration material Gd2B2MoO9 with triangular magnetic frustration prepared in Example 1 of the present invention. Detailed implementation manners

[0034] The technical solutions of the present invention are further described below through the accompanying drawings and embodiments.

[0035] Example 1

[0036] The Gd2B2MoO9 material was prepared by the traditional solid-phase method and tested, including the following steps:

[0037] S1. Weigh the starting materials including Gd2O3, H3BO3 and (NH4)6Mo7O 24 ·4H2O according to the stoichiometric values in the molecular formula, and weigh 7.0% more H3BO3 than its stoichiometric ratio to compensate for inevitable losses;

[0038] S2. Thoroughly mix all the chemical substances in an agate mortar;

[0039] S3. Put the mixture into a muffle furnace, gradually heat it to 650 °C, and keep it at this temperature for 5 hours;

[0040] S4. Grind and remix the mixture, and then sinter it at 750 °C for 5 hours;

[0041] S5. Then sinter the preheated mixture at 860 °C for 8 hours to obtain the final sample;

[0042] S6. Characterize the Gd2B2MoO9 material obtained in this example by XRD, and the results are as Figure 1 shown. It can be found that the measured sample basically coincides with the standard PDF card. The refined lattice constants are a = 5.2011(1), b = 6.9488(4), c = 10.3210(9), α = 74.557(6), β = 76.307(7) and γ = 73.065(6);

[0043] S7. Conduct structural characterization on the Gd2B2MoO9 material prepared in this example: The crystal structure diagram of the Gd2B2MoO9 material is as Figure 4 (b) shows that the Gd2B2MoO9 material is triclinic with a space group of P-1. Figure 4 In (a) of, it can be seen that Gd atoms form two edge-sharing equilateral triangles through covalent bonds, and the side lengths are with included angles of 61.64(9)°, 59.17(6)°, 59.17(6)°, 61.65(0)°, 59.17(5)° and 59.17(5)°, Figure 4 in (a) implies its geometric frustration property, and the existence of geometric frustration is beneficial to achieving a low magnetic ordering temperature.

[0044] S8. Measure the rare earth oxide magnetic refrigeration material prepared in the example using a vibrating sample magnetometer (VSM) measurement accessory produced by Quantum Design Corporation of the United States. Perform a linear fit on the reciprocal curve of the temperature-dependent magnetic susceptibility according to the Curie-Weiss theorem, and the result is Figure 3 , that is, the paramagnetic Curie temperature θ CW = -5.43 K. The negative θ P indicates that Gd2B2MoO9 has weak antiferromagnetic coupling and is suitable for use as a magnetic refrigeration material. To further determine the phase transition temperature of Gd2B2MoO9, the temperature-dependent magnetic susceptibility curve in the range of 0.4 - 1.2 K was measured, as shown in Figure 5 . The test results prove the antiferromagnetic ground state of Gd2B2MoO9, and from Figure 6 it can be seen that at 0.05 T, the antiferromagnetic transition temperature is T N = 0.84 K. In addition, the calculated frustration parameter f = |θ cw / T N | = 6.45. It shows that there is strong frustration property in Gd2B2MoO9.

[0045] Under the conditions of a temperature range of 0.4 - 22 K and a magnetic field range of 0 - 5 T, the temperature-dependent and magnetic field-dependent magnetization curves of Gd2B2MoO9 measured are as Figure 7 shown. As the magnetic field increases, the magnetization of the Gd2B2MoO9 alloy gradually increases and reaches saturation. According to the Maxwell relation, the magnetic entropy change of Gd2B2MoO9 is calculated, and the obtained results are as Figure 8 shown. It can be seen from the figure that the magnetic transition temperature of the Gd2B2MoO9 rare earth oxide magnetic refrigeration material in Example 1 is 0.84 K. Under 0 - 2 T and 0 - 5 T, its isothermal magnetic entropy changes can reach 33.07 J / kg·K and 53.05 J / kg·K respectively. This characterization shows that Gd2B2MoO9 can effectively absorb and release heat under magnetic field regulation to achieve the purpose of refrigeration.

[0046] Example 2

[0047] The Gd2B2MoO9 material is prepared by the traditional solid-phase method and tested, including the following steps:

[0048] S1. Weigh the starting materials including Gd2O3, H3BO3 and (NH4)6Mo7O 24 ·4H2O according to the stoichiometric values in the molecular formula, where H3BO3 is weighed 5.0% more than its stoichiometric ratio to compensate for inevitable losses;

[0049] S2. Thoroughly mix all the chemical substances in an agate mortar;

[0050] S3. Put the mixture into a muffle furnace, gradually heat it to 650 °C, and keep it at this temperature for 5 hours;

[0051] S4. Grind and remix the mixture, and then sinter it at 750 °C for 5 hours;

[0052] S5. Press the preheated mixture into tablets and sinter it at 900 °C for 8 hours to obtain the final sample;

[0053] S6. Characterize the Gd2B2MoO9 alloy obtained in this example by XRD, and the XRD refinement result is Figure 2 .

[0054] S7. Use the vibrating sample magnetometer (VSM) measurement accessory produced by Quantum Design Corporation of the United States to measure the rare earth oxide magnetic refrigeration material prepared in the example. According to the Curie-Weiss theorem, a linear fit is performed on the reciprocal curve of the temperature-dependent magnetic susceptibility. It can be calculated that the effective magnetic moment in paramagnetism μeff = 7.98, and the Curie temperature θ CW = -3.11 K. The negative θ PIt is explained that Gd2B2MoO9 has weak antiferromagnetic coupling and is suitable for use as a magnetic refrigeration material.

[0055] Example 3

[0056] Prepare the Gd2B2MoO9 material by the sol-gel method and conduct tests, including the following steps:

[0057] S1. Weigh according to the stoichiometric values in the molecular formula. The starting materials include Gd(NO3)3·6H2O, H3BO3, and (NH4)6Mo7O 24 ·4H2O, and the H3BO3 is weighed 5.0% more than its stoichiometric ratio to compensate for inevitable losses;

[0058] S2. Add deionized water according to the mass ratio of raw materials to deionized water of 1:30, stir evenly, and then add citric acid according to the ratio of citric acid to cations of 1:1. Stir the mixture for 12 h until it forms a gel;

[0059] S3. Place the mixture in an oven at 80 °C for 8 h, then put the mixture into a muffle furnace, gradually heat it to 650 °C, and keep it at this temperature for 5 h;

[0060] S4. Grind the mixture, remix it, and press it into tablets. Sinter it at 800 °C for 5 h to obtain the final sample;

[0061] S5. Characterize the Gd2B2MoO9 alloy obtained in this example by XRD. The refinement result is Figure 3 , as shown in the figure, the sample is impure and contains 3.14% of the impurity phase Gd3BMoO9.

[0062] Example 4

[0063] Prepare the Gd2B2MoO9 material by the sol-gel method and conduct tests, including the following steps:

[0064] S1. Weigh the starting materials according to the stoichiometric values in the molecular formula, including Gd(NO3)3·6H2O, H3BO3, and (NH4)6Mo7O 24 ·4H2O, and the H3BO3 is weighed 7.0% more than its stoichiometric ratio to compensate for inevitable losses;

[0065] S2. Add deionized water according to the mass ratio of raw materials to deionized water of 1:30, stir evenly, and then add citric acid according to the ratio of citric acid to cations of 1:1. Stir the mixture for 12 h until it forms a gel;

[0066] S3. Place the mixture in an oven and dry it at 80 °C for 8 h, then put the mixture into a muffle furnace, gradually heat it to 650 °C, and keep it at this temperature for 5 h;

[0067] S4. Grind the mixture, mix it again and tablet it, and sinter it at 900 °C for 5 hours to obtain the final sample;

[0068] S5. Characterize the Gd2B2MoO9 alloy obtained in this example by XRD, and the results are basically consistent with the theoretical pattern.

[0069] Use the X-ray diffractometer produced by Rigaku Corporation of Japan to perform XRD detection on the materials prepared in the examples, and the results are as Figure 1 、 3 shown. The Gd2B2MoO9 magnetic refrigeration material prepared by the method described in the present invention is single-phase, belongs to the triclinic system, and the space group is P-1.

[0070] Use the vibrating sample magnetometer (VSM) measurement accessory produced by Quantum Design Company of the United States to measure the rare earth oxide magnetic refrigeration material prepared in the example, and the magneto-entropy change results are as Figure 8 shown. In Example 1, under the magnetic field changes of 0-2T and 0-5T, the maximum values of the isothermal magneto-entropy change are 33.07 J / kg·K and 53.05 J / kg·K respectively. In Example 2, under the magnetic field changes of 0-2T and 0-5T, the maximum values of the isothermal magneto-entropy change are 30.86 J / kg·K and 52.45 J / kg·K respectively. In Example 3, under the magnetic field changes of 0-2T and 0-5T, the maximum values of the isothermal magneto-entropy change are 35.00 J / kg·K and 55.25 J / kg·K respectively. In this example, the XRD refinement results show that there is 3.14% of the impurity phase Gd3BMoO9, which should be the reason why the magneto-entropy change at 0-2T and 0-5T is greater than the normal value. In Example 4, under the magnetic field changes of 0-2T and 0-5T, the maximum values of the isothermal magneto-entropy change are 30.07 J / kg·K and 51.03 J / kg·K respectively. The magnetic transition temperatures of the Gd2B2MoO9 rare earth oxide magnetic refrigeration materials in the above four examples are all around 0.8K.

[0071] The gadolinium boromolybdate magnetic refrigeration material Gd2B2MoO9 with special triangular magnetic frustration prepared by the preparation method described in the present invention has maximum values of isothermal magneto-entropy change of 33.07 J / kg·K and 53.05 J / kg·K respectively under the magnetic field changes of 0-2T and 0-5T; greatly improving the magneto-entropy change of rare earth magnetic refrigeration materials. This characterization shows that the gadolinium boromolybdate magnetic refrigeration material Gd2B2MoO9 with triangular magnetic frustration can effectively absorb and release heat under magnetic field regulation to achieve the refrigeration purpose. And its preparation method is simple and the structure is stable. It not only has great application prospects in the field of magnetic refrigeration, but also can be applied to fields such as low-temperature physics, deep space exploration and aerospace, and can also promote the high-value utilization of rare earth resources, further enhancing the international competitiveness and technical strength of China's rare earth industry.

[0072] Therefore, by adopting the above preparation method, the present invention can prepare a gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration, which can solve the problems of low magnetic entropy and unstable structure of the existing magnetic refrigeration materials.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration, characterized in that: Its molecular formula is Gd2B2MoO9, which consists of a single phase, belongs to the triclinic system, the space group is P-1, and the lattice constants are a = 5.2011(1), b = 6.9488(4), c = 10.3210(9), α = 74.557(6), β = 76.307(7) and γ = 73.065(6); Two nearly equilateral triangles sharing a common side are formed by Gd atoms through covalent bonds, where the length of the common side is The lengths of the other two sides of one nearly equilateral triangle are both The lengths of the other two sides of the other nearly equilateral triangle are both and 2. The gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration according to claim 1, wherein: Its magnetic transition temperature is 0.7 - 0.9 K. Under the external magnetic field changes of 0 - 2 T and 0 - 5 T, its isothermal magnetic entropy changes are 30.0 - 35.0 J / kg·K and 51.0 - 55.0 J / kg·K respectively.

3. The preparation method of the gadolinium boromolybdate magnetocaloric material with triangular magnetic frustration according to claim 1, characterized in that, It includes the following steps: Using Gd(NO3)3·6H2O, H3BO3 and (NH4)6Mo7O 24 ·4H2O as raw materials, wherein the dosages of Gd(NO3)3·6H2O and (NH4)6Mo7O 24 ·4H2O are determined according to the stoichiometric ratio of Gd and Mo elements in the formula Gd2B2MoO9, and H3BO3 is in excess; the raw materials are ground and mixed evenly, sintered at 650 °C first, cooled and ground and mixed evenly again, sintered at 750 °C, and then sintered at a temperature not lower than 860 °C to obtain the gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration.

4. The preparation method of the gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration according to claim 3, characterized in that The specific dosage of H3BO3 is determined as follows: The dosage of H3BO3 one is determined according to the stoichiometric ratio of Gd, B, and Mo elements in the molecular formula Gd2B2MoO9, and the dosage of H3BO3 one is multiplied by 105% - 107% as the specific dosage of H3BO3.

5. The preparation method of the gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration according to claim 3, characterized in that, The sintering time at 650 °C is 5 hours, the sintering time at 750 °C is 5 hours, and the temperature not lower than 860 °C is specifically 860 - 900 °C for sintering for 8 hours.

6. The preparation method of the gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration according to claim 1, characterized in that, It includes the following steps: Using Gd(NO3)3·6H2O, H3BO3, and (NH4)6Mo7O 24 ·4H2O as raw materials, wherein the dosages of Gd(NO3)3·6H2O and (NH4)6Mo7O 24 ·4H2O are determined according to the stoichiometric ratio of Gd and Mo elements in the formula Gd2B2MoO9, and H3BO3 is in excess; After dissolving the raw materials, mix them with citric acid and stir to form a gel-like mixture. After drying the gel-like mixture, sinter it at 650 °C, cool and grind it again to mix evenly, and then sinter it at a temperature not lower than 800 °C; to obtain the gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration.

7. The preparation method of the gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration according to claim 6, characterized in that, The stirring time is 12 h; the sintering time at 650 °C is 5 hours, and the temperature not lower than 800 °C is specifically 800 - 900 °C for sintering for 5 hours.

8. The preparation method of the gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration according to claim 6, characterized in that, When dissolving the raw materials, the mass ratio of the raw materials used to deionized water is 1:30, and the molar ratio of citric acid to the cations in the solution obtained by dissolving the raw materials is 1:

1.

9. The preparation method of a gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration according to any one of claims 3 - 8, characterized in that: The purities of the Gd2O3, H3BO3, (NH4)6Mo7O 24 ·4H2O and Gd(NO3)3·6H2O are all not less than 99.95%; both the drying and the sintering are carried out in air.

10. Application of a gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration in low-temperature magnetic refrigeration, characterized in that: Under the condition of a temperature of 0.7 - 0.9 K, under the external magnetic fields of 0 - 2 T and 0 - 5 T, the isothermal magnetic entropy changes of the gadolinium boromolybdate magnetic refrigeration material with triangular magnetic frustration are 30.0 - 35.0 J / kg·K and 51.0 - 55.0 J / kg·K respectively.

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