Screening method of heavy rare earth transition metal oxide magnetocaloric material

Abstract

The invention belongs to the technical field of condensed state physics and material research, and particularly relates to a heavy rare earth transition metal oxide magnetocaloric material screening method which comprises the following steps: obtaining zero field cooling of a test sample and a magnetization intensity-temperature curve of the field cooling, and deriving the magnetization intensity-temperature curve of the field cooling to obtain a magnetic field temperature curve of the field cooling; then the absolute value of the derivative of the field cooling magnetization intensity-temperature curve is obtained, and an absolute value curve is obtained; calculating an average magnetic phase transition temperature based on the absolute value curve; calculating the variance of the absolute value curve at the average magnetic phase transition temperature; calculating the dimensionless variance of the absolute value curve based on the variance of the absolute value curve at the average magnetic phase transition temperature; obtaining an isothermal magnetization curve of the test sample and calculating a magnetic entropy change value; and based on the dimensionless variance value, establishing a quantitative relationship between the magnetic phase change interaction intensity and the magnetic entropy change value, and further screening out a target sample. And theoretical support is provided for development and physical mechanism analysis of the low-temperature heavy rare earth based giant magnetocaloric material.

Description

Technical Field

[0001] This invention belongs to the field of condensed matter physics and materials research technology, specifically relating to a screening method for heavy rare earth transition metal oxide magnetocaloric materials. Background Technology

[0002] Magnetic refrigeration is a solid-state refrigeration technology based on the magnetocaloric effect. It utilizes an external magnetic field to control the magnetic order of magnetic materials, achieving a refrigeration cycle through magnetic entropy change. Compared to traditional gas compression refrigeration, magnetic refrigeration offers advantages such as high efficiency, low noise, and no greenhouse gas emissions, showing significant application potential, especially in the low-temperature range (<20 K) and room-temperature range. Due to the large magnetic moment characteristics of heavy rare earth elements Gd, Tb, Dy, Ho, and Er, heavy rare earth (4... f Transition metals (3) d Oxide materials possess strong magnetocaloric effects and have important applications in magnetic refrigeration (especially in low-temperature regions). Their unique 4... f -3 d Its electronic coupling, tunable magnetic phase transition, and low thermal hysteresis characteristics give it great potential in the field of cryogenic magnetic refrigeration.

[0003] The magnetic structure of heavy rare earth transition metal oxide magnetocaloric materials consists of rare earth and transition metal sublattices. Under normal circumstances, transition metal ions (3 d -3 d The exchange interaction between rare earth and transition metal ions (4) is greater than that between rare earth and transition metal ions (4) f -3 d The exchange interactions between them are much stronger, such as the superexchange interactions between Ni-O-Mn and Co-O-Mn (magnetic ions such as Ni, Mn, and Co are bridged by anions such as O). 2- Indirect coupling occurs, leading to a strong ferromagnetic phase transition in the high-temperature region (near room temperature). For second-order ferromagnetic phase transition materials (such as heavy rare earth transition metal oxides), critical behavior studies are an important means of exploring the physical mechanism of microscopic magnetic interactions near strong ferromagnetic phase transitions. However, critical behavior studies are no longer applicable to weaker ferromagnetic or subferromagnetic phase transitions and cases involving multiple magnetic phase transitions.

[0004] Furthermore, traditional characterization methods for magnetocaloric materials involve applying a specific magnetic field to the material. M ( T The magnetic phase transition is determined by the curve, and then a certain amount of isothermal magnetization is tested near the magnetic phase transition. M ( H The curve is then used to calculate the magnetic entropy change based on Maxwell's equations. It is evident that traditional characterization methods require significant time and resource investment. Summary of the Invention

[0005] The purpose of this invention is to provide a screening method for heavy rare earth transition metal oxide magnetocaloric materials, thereby overcoming the shortcomings of the prior art. This invention establishes a quantitative relationship between the strength of magnetic interaction and the magnetic entropy change value through dimensionless variance value, which is used for magnetic phase transition analysis and efficient screening of magnetocaloric materials. It has important scientific significance and research value for the exploration and development of magnetocaloric materials.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: This invention provides a method for screening heavy rare earth transition metal oxide magnetocaloric materials, comprising the following steps: The magnetization intensity-temperature curves of the test sample under zero field cooling and field cooling are obtained respectively. The derivative of the magnetization intensity-temperature curve under field cooling is calculated, and then the absolute value of the derivative of the magnetization intensity-temperature curve under field cooling is taken to obtain the absolute value curve. The average magnetic phase transition temperature is calculated based on the absolute value curve. Calculate the variance of the absolute value curve at the average magnetic phase transition temperature; The dimensionless variance of the absolute value curve is calculated based on the variance of the absolute value curve at the average magnetic phase transition temperature. Obtain the isothermal magnetization curve of the test sample and calculate the magnetic entropy change. Based on dimensionless variance, a quantitative relationship between the intensity of magnetic phase transition interaction and the magnetic entropy change is established, and target samples are screened based on the quantitative relationship.

[0007] This invention establishes a dimensionless quantitative relationship between the intensity of magnetic phase transition interactions and the magnetic entropy change. Based on revealing the relationship between the intensity of magnetic phase transition interactions and the magnetic entropy change, it achieves this relationship solely by measuring the sample under a specific magnetic field. M ( T The curve, based on the magnitude of the dimensionless variance, can quickly and efficiently perform preliminary screening, thereby selecting target samples and avoiding the waste of time and resources in traditional magnetic characterization, thus achieving efficient research and development of low-temperature magnetocaloric materials.

[0008] In some other implementations, the absolute value curves near the magnetic phase transition temperature conform to a Gaussian function distribution, the mathematical expression of which is as follows: (1) Among them: | M ( T )'| represents the absolute value curve. T m The average magnetic phase transition temperature determines the central location of the Gaussian function distribution. T For temperature testing, σ represents the standard deviation, which determines the dispersion of the distribution. The larger the standard deviation, the more dispersed the data distribution. 2 It is variance.

[0009] Based on the ideal ferromagnetic phase transition point ( T C The magnetization intensity of ) changes with temperature M ( T The slope of the curve is infinite, that is... M ( T The absolute value of the first derivative of the curve | M ( T The curve is a straight line perpendicular to the temperature axis, and its variance is zero. The dimensionless variance is also zero. ); while | at an infinite distance from the ferromagnetic phase transition point M ( T The variance of the curve is infinite. The dimensionless variance is 1 ( Other types of magnetic phase transitions | M ( T )'| curve Between 0 and 1.

[0010] In some other implementations, the average magnetic phase transition temperature is calculated using the following formula: (2) Among them, | M ( T )'| represents the absolute value curve. T m The average magnetic phase transition temperature. The interval between test temperature points.

[0011] In some other implementations, the formula for calculating the average magnetic phase transition temperature for discrete data is as follows: (3) In the calculation formula of the average magnetic phase transition temperature in this invention, formula (2) is used for integral calculation, representing an infinite number of data; formula (3) is used for discrete data calculation, where discrete data represents a finite number of data.

[0012] Among them, | M ( T )'| represents the absolute value curve. T m The average magnetic phase transition temperature. The interval between test temperature points.

[0013] In some other implementations, the variance of the absolute value curve near the average magnetic phase transition temperature is calculated using the following formula: (4) Among them, | M ( T )'| represents the absolute value curve.T m The average magnetic phase transition temperature. For the interval of the test temperature points, T To test the temperature, Let Variance be the variance.

[0014] In some other implementations, for discrete data, the variance of the absolute value curve near the average magnetic phase transition temperature is calculated using the following formula: (5) Among them, | M ( T )'| represents the absolute value curve. T m The average magnetic phase transition temperature. For the interval of the test temperature points, T To test the temperature, Let Variance be the variance.

[0015] In some other implementations, the formula for calculating the dimensionless variance of the absolute value curve is as follows: (6) in, For temperature comparison, T m The average magnetic phase transition temperature. T To test the temperature, For variance, To compare the absolute value curves of temperature, | M ( T )'| represents the absolute value curve. It is dimensionless variance.

[0016] In some other implementations, the isothermal magnetization curve is calculated using the following formula: (7) in, The magnetic entropy change values ​​under different magnetic field variations. T To test the temperature, H The magnetic field strength, M denoted as magnetization intensity.

[0017] In some other embodiments, the formula for screening Gd-based rare-earth transition metal oxide magnetocaloric materials is as follows: (8) in, This represents the maximum change in magnetic field value. It can take any real number greater than 0. for The corresponding maximum magnetic entropy change value, For Gd3+ The total angular momentum quantum number of an ion. transition metal ions M n+ Total angular momentum quantum number ( M n+ 3 d (ion with non-empty electron shell) For Gd 3+ The spin angular momentum quantum number of an ion. M r The relative molecular mass of the sample is denoted as . R It is the gas constant; RE The formula for screening heavy rare earth transition metal oxide magnetocaloric materials is as follows: (9) RE Selected from one or more of Tb, Dy, Ho, and Er; in, This represents the maximum change in magnetic field value. Take the value of any real number greater than 1. for The corresponding maximum magnetic entropy change value, for RE 3+ The total angular momentum quantum number of an ion. transition metal ions M n+ Total angular momentum quantum number ( M n+ 3 d (ion with non-empty electron shell) for RE 3+ The spin angular momentum quantum number of an ion. For Gd 3+ The spin angular momentum quantum number of an ion. M r The relative molecular mass of the sample is denoted as . R is the gas constant.

[0018] In some other implementations, for ≥ 3T any real number.

[0019] The beneficial effects of this invention are: (1) The screening method for heavy rare earth transition metal oxide magnetocaloric materials provided by the present invention has the characteristics of universality and high efficiency. It establishes a quantitative relationship between the magnetic phase transition interaction intensity and the magnetic entropy change value through dimensionless means, and measures the sample under a certain magnetic field. M ( TThe dimensionless variance of the curve, based on the derived pattern, can be used to predict and screen the magnitude of the magnetic entropy change value of magnetocaloric materials. This avoids the waste of time and resources in traditional magnetic characterization, thereby enabling efficient research and development of low-temperature magnetocaloric materials.

[0020] (2) This invention can also establish a quantitative relationship between the strength of magnetic interaction and the magnetic entropy change value through dimensionless variance value, thereby revealing the relationship between heavy rare earth transition metal oxide materials 4 f -3 d The magnetic interaction mechanism enables the efficient design of giant magnetocaloric materials based on heavy rare earth transition metal oxides. It also makes up for the shortcomings of critical behavior research, which is only applicable to the exploration of the physical mechanism of microscopic magnetic interaction near strong ferromagnetic phase transitions. This provides a new paradigm and theoretical support for the development and physical mechanism analysis of future low-temperature heavy rare earth-based giant magnetocaloric materials, and enriches the theoretical research methods of magnetic interaction analysis. Attached Figure Description

[0021] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0022] Figure 1 Schematic diagram of the ideal ferromagnetic phase transition model; Figure 2 field cold M ( T ) curve and | M ( T Example of a curve; Figure 3 The ZFC and FC curves of samples (a) Gd₂CoTiO₆, (b) Gd₂NiTiO₆, (c) Tb₂NiTiO₆, and (d) Dy₂NiTiO₆ in Examples 1-4 are shown below under a 0.05T magnetic field. The inset shows the ||F|| obtained by differentiating the FC curve and taking the absolute value. M ( T )'|curve; Figure 4 Isothermal magnetization curves of samples (a) Gd2CoTiO6, (b) Gd2NiTiO6, (c) Tb2NiTiO6 and (d) Dy2NiTiO6 in Examples 1-4 at different temperatures; Figure 5 The magnetic entropy change curves of samples (a) Gd2CoTiO6, (b) Gd2NiTiO6, (c) Tb2NiTiO6, and (d) Dy2NiTiO6 in Examples 1-4 are shown as the curves of magnetic entropy change with temperature under different magnetic field variations. Detailed Implementation

[0023] Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention. Specific conditions not specified in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Components whose manufacturers are not specified are all commercially available conventional products.

[0024] To address the limitation of critical behavior studies in handling weak ferromagnetic, subferromagnetic, and multi-magnetic phase transitions, this invention proposes a variance analysis mathematical model. The inventive concept is as follows: based on the schematic diagram of the ideal ferromagnetic phase transition (FM) model (e.g.,...). Figure 1 As shown in the figure, the magnetic moments at the ideal ferromagnetic phase transition point are completely ordered, while the magnetic moments at infinite distances from the ideal ferromagnetic phase transition point are completely disordered. The order of magnetic moments in antiferromagnetic phase transitions (AFM), ferrimagnetic phase transitions (FIM), and other types of magnetic phase transitions falls between these two extremes.

[0025] Variance is a mathematical characteristic that describes the degree to which a random variable deviates from its mean, reflecting the dispersion of the data. It is commonly represented by the symbol […]. This means that the larger the variance, the higher the dispersion of the data; the smaller the variance, the lower the dispersion of the data. Therefore, the ideal ferromagnetic phase transition point (… T C The magnetization intensity of ) changes with temperature M ( T The slope of the curve is infinite, that is... M ( T The absolute value of the first derivative of the curve | M ( T The curve is a straight line perpendicular to the temperature axis (e.g.) Figure 2 As shown), its variance is zero. The dimensionless variance is also zero. ); while | at an infinite distance from the ferromagnetic phase transition point M ( T The variance of the curve is infinite. The dimensionless variance is 1 ( Other types of magnetic phase transitions | M ( T )'| curve The value is between 0 and 1. The strength of magnetic interaction varies near different magnetic phase transitions, therefore its... The magnetocaloric effect will also change depending on the specific conditions.

[0026] This invention provides a screening method for heavy rare earth transition metal oxide magnetocaloric materials, which specifically includes the following steps: Step 1: Under a certain magnetic field, test the zero-field cooling (ZFC) and field cooling (FC) of the sample. M ( T The curve shows the temperature points spaced at intervals of ∆. T For the cold field M ( T Differentiating the curve yields the results near the magnetic phase transition. M ( T The curve is obtained by taking its absolute value. M ( T The curve '| is used to obtain the magnetic phase transition temperature. T m .

[0027] Near the magnetic phase transition temperature, | M ( T The curve follows a Gaussian distribution, and its mathematical expression is as follows: (1) in: T m σ is the average magnetic phase transition temperature, which determines the center of the Gaussian function distribution; σ is the standard deviation, which determines the dispersion of the distribution. The larger the standard deviation, the more dispersed the data distribution. 2 It is variance.

[0028] Step 2: Average magnetic phase transition temperature T m The calculation formula is as follows: (2) For discrete data, the average magnetic phase transition temperature T m The calculation formula is as follows: (3) in, The interval between test temperature points.

[0029] Step 3: Average magnetic phase transition temperature T m Nearby | M ( T variance of the curve The calculation formula is as follows: (4) For discrete data, the average magnetic phase transition temperature T m Nearby | M ( T variance of the curve The calculation formula is as follows: (5) Step 4: To eliminate the inconvenience caused by units in the calculation, a comparative temperature is used. As the independent variable, then, | M ( T The dimensionless variance of the curve The calculation formula is as follows: (6) Step 5: Test the isothermal magnetization curves of the sample at different temperatures near the low-temperature magnetic phase transition, using the following formula: (7) The magnetic entropy change of the sample under different magnetic field variations was calculated. The dimensionless variance corresponding to different types of magnetic phase transitions was also determined. The difference lies in the pursuit of... Then, through dimensionless variance The magnitude of the values, and the quantitative correlation between the magnetic phase transition interaction strength and the magnetic entropy change value, are established as follows: (8) in, This represents the maximum change in magnetic field value. It can take any real number greater than 0. for The corresponding maximum magnetic entropy change value, For Gd 3+ The total angular momentum quantum number of an ion. transition metal ions M n+ Total angular momentum quantum number ( M n+ 3 d (ion with non-empty electron shell) For Gd 3+ The spin angular momentum quantum number of an ion. M r The relative molecular mass of the sample is denoted as . R It is the gas constant; RE The formula for screening heavy rare earth transition metal oxide magnetocaloric materials is as follows: (9) RE Selected from one or more of Tb, Dy, Ho, and Er; in, This represents the maximum change in magnetic field value. Take the value of any real number greater than 1. for The corresponding maximum magnetic entropy change value, for RE 3+ The total angular momentum quantum number of an ion. transition metal ions M n+ Total angular momentum quantum number ( M n+ 3 d (ion with non-empty electron shell) for RE 3+ The spin angular momentum quantum number of an ion. For Gd 3+ The spin angular momentum quantum number of an ion. M r The relative molecular mass of the sample is denoted as . R is the gas constant.

[0030] Based on the analysis of variance and a deeper understanding of different magnetic interaction mechanisms, only measurements were taken under a specific magnetic field. M ( T The curve can predict and quickly and efficiently screen target samples based on the value, avoiding the waste of time and resources in traditional magnetic characterization, and thus realizing the efficient design of low-temperature magnetocaloric materials.

[0031] The technical solution of the present invention will be described below with reference to specific embodiments: Example 1 A screening method for heavy rare earth transition metal oxide magnetocaloric materials, taking Gd2CoTiO6 as an example, specifically includes the following steps: Step 1: First, under a magnetic field, test the zero-field cooling (ZFC) and field cooling (FC) properties of the Gd₂CoTiO₆ sample. M ( T The curve shows the temperature points at intervals of [missing information]. For the cold field M ( T Differentiating the curve yields the results near the magnetic phase transition. M ( T The curve is obtained by taking its absolute value. M ( T )'|Curve (e.g.) Figure 3 (as shown in a) Step 2: Calculate the average magnetic phase transition temperature T m The calculation formula is as follows:

[0032] Step 3: Average magnetic phase transition temperature T m Nearby | M ( T variance of the curve The calculation formula is as follows:

[0033] Step 4: | M ( T The dimensionless variance of the curve The calculation formula is as follows:

[0034] Finally, the dimensionless variance of Gd2CoTiO6 was obtained. The value is 0.3736.

[0035] Step 5: Test the isothermal magnetization curves of the sample at different temperatures near the low-temperature magnetic phase transition (e.g., Figure 4 (as shown in a), low-temperature magnetic phase transition The calculation formula is as follows:

[0036] Calculate the magnetic entropy change of the sample under different magnetic field variations. The dimensionless variance corresponding to different types of magnetic phase transitions. The difference lies in the pursuit of... Then, through dimensionless variance The magnitude of the value was used to establish a quantitative relationship between the strength of magnetic phase transition interaction and the magnetic entropy change value. The specific results are shown in Table 1.

[0037] The formula for screening Gd-based rare-earth transition metal oxide magnetocaloric materials is as follows:

[0038] in, This represents the maximum change in magnetic field value. It can take any real number greater than 0. for The corresponding maximum magnetic entropy change value, For Gd 3+ The total angular momentum quantum number of an ion. transition metal ions M n+ Total angular momentum quantum number ( M n+ 3 d (ion with non-empty electron shell) For Gd 3+ The spin angular momentum quantum number of an ion. M r The relative molecular mass of the sample is denoted as . R is the gas constant.

[0039] Example 2 A screening method for heavy rare earth transition metal oxide magnetocaloric materials, taking Gd2NiTiO6 as an example, specifically includes the following steps: Step 1: First, under a certain magnetic field, test the zero-field cooling (ZFC) and field cooling (FC) of the Gd2NiTiO6 sample. M ( T The curve shows the temperature points at intervals of [missing information]. The cold field M ( T Differentiating the curve yields the results near the magnetic phase transition. M ( T The curve is obtained by taking its absolute value. M ( T )'|Curve (e.g.) Figure 3 (as shown in b) Step 2: Average magnetic phase transition temperature T m The calculation formula is as follows:

[0040] Step 3: Average magnetic phase transition temperature T m Nearby | M ( T variance of the curve The calculation formula is as follows:

[0041] Step 4: | M ( T The dimensionless variance of the curve The calculation formula is as follows:

[0042] The dimensionless variance of Gd2NiTiO6 was finally obtained. The value is 0.3807.

[0043] Step 5: Test the isothermal magnetization curves of the sample at different temperatures near the low-temperature magnetic phase transition (e.g., Figure 4 (as shown in b), low-temperature magnetic phase transition The calculation formula is as follows:

[0044] The magnetic entropy change of the Gd2NiTiO6 sample under different magnetic field variations was calculated. The dimensionless variance corresponding to different types of magnetic phase transitions. The difference lies in the pursuit of... Then, through dimensionless variance The magnitude of the values ​​establishes a quantitative relationship between the strength of magnetic phase transition interaction and the magnetic entropy change value, as shown in Table 1.

[0045] The formula for screening Gd-based rare-earth transition metal oxide magnetocaloric materials is as follows:

[0046] in, This represents the maximum change in magnetic field value. It can take any real number greater than 0. for The corresponding maximum magnetic entropy change value, For Gd 3+ The total angular momentum quantum number of an ion. transition metal ions M n+ Total angular momentum quantum number ( M n+ 3 d (ion with non-empty electron shell) For Gd 3+ The spin angular momentum quantum number of an ion. M r The relative molecular mass of the sample is denoted as . R is the gas constant.

[0047] Example 3 A screening method for heavy rare earth transition metal oxide magnetocaloric materials, taking Tb2NiTiO6 as an example, specifically includes the following steps: Step 1: First, under a certain magnetic field, test the zero-field cooling (ZFC) and field cooling (FC) of the Tb2NiTiO6 sample. M ( T The curve shows the temperature points at intervals of [missing information]. For the cold field M ( T Differentiating the curve yields the results near the magnetic phase transition. M ( T The curve is obtained by taking its absolute value. M ( T )'|Curve (e.g.) Figure 3 (as shown in c) Step 2: Average magnetic phase transition temperature T m The calculation formula is as follows:

[0048] Step 3: Average magnetic phase transition temperature T m Nearby | M ( T variance of the curve The calculation formula is as follows:

[0049] Step 4: | M ( T The dimensionless variance of the curve The calculation formula is as follows:

[0050] The dimensionless variance of Gd2CuTiO6 was finally obtained. The value is 0.4522.

[0051] Step 5: Test the isothermal magnetization curves of the sample at different temperatures near the low-temperature magnetic phase transition (e.g., Figure 4 (as shown in c), low-temperature magnetic phase transition The calculation formula is as follows:

[0052] Calculate the magnetic entropy change of the sample under different magnetic field variations. The dimensionless variance corresponding to different types of magnetic phase transitions. The difference lies in the pursuit of... Then, through dimensionless variance The magnitude of the values ​​establishes a quantitative relationship between the strength of magnetic phase transition interaction and the magnetic entropy change value, as shown in Table 1.

[0053] The formula for screening Tb-based heavy rare earth transition metal oxide magnetocaloric materials is as follows:

[0054] RE For Tb; in, This represents the maximum change in magnetic field value. Take the value of any real number greater than 1. for The corresponding maximum magnetic entropy change value, for RE 3+ The total angular momentum quantum number of an ion. transition metal ions M n+ Total angular momentum quantum number ( M n+ 3 d (ion with non-empty electron shell) for RE 3+ The spin angular momentum quantum number of an ion. For Gd 3+ The spin angular momentum quantum number of an ion. M rThe relative molecular mass of the sample is denoted as . R is the gas constant.

[0055] Example 4 A screening method for heavy rare earth transition metal oxide magnetocaloric materials, taking Dy2NiTiO6 as an example, specifically includes the following steps: Step 1: First, under a certain magnetic field, test the zero-field cooling (ZFC) and field cooling (FC) of the Dy2NiTiO6 sample. M ( T The curve shows the temperature points at intervals of [missing information]. For the cold field M ( T Differentiating the curve yields the results near the magnetic phase transition. M ( T The curve is obtained by taking its absolute value. M ( T )'|Curve (e.g.) Figure 3 (as shown in c) Step 2: Average magnetic phase transition temperature T m The calculation formula is as follows:

[0056] Step 3: Average magnetic phase transition temperature T m Nearby | M ( T variance of the curve The calculation formula is as follows:

[0057] Step 4: | M ( T The dimensionless variance of the curve The calculation formula is as follows:

[0058] Finally, the dimensionless variance of Dy2NiTiO6 was obtained. The value is 0.3671.

[0059] Step 5: Test the isothermal magnetization curves of the Dy2NiTiO6 sample at different temperatures near the low-temperature magnetic phase transition (e.g., Figure 4 (as shown in c), low-temperature magnetic phase transition The calculation formula is as follows:

[0060] Calculate the magnetic entropy change of the sample under different magnetic field variations. The dimensionless variance corresponding to different types of magnetic phase transitions. The difference lies in the pursuit of... Then, through dimensionless variance The magnitude of the values ​​establishes a quantitative relationship between the strength of magnetic phase transition interaction and the magnetic entropy change value, as shown in Table 1.

[0061] The formula for screening Dy-based heavy rare earth transition metal oxide magnetocaloric materials is as follows:

[0062] RE For Dy; in, This represents the maximum change in magnetic field value. Take the value of any real number greater than 1. for The corresponding maximum magnetic entropy change value, for RE 3+ The total angular momentum quantum number of an ion. transition metal ions M n+ Total angular momentum quantum number ( M n+ 3 d (ion with non-empty electron shell) for RE 3+ The spin angular momentum quantum number of an ion. For Gd 3+ The spin angular momentum quantum number of an ion. M r The relative molecular mass of the sample is denoted as . R is the gas constant.

[0063] The relevant parameters of the samples in Examples 1-4 are shown in Table 1.

[0064] Table 1. Relevant parameters of samples in Examples 1-4

[0065] Based on the data in Table 1 and a large amount of magnetic data, correlation equations (8) and (9) are summarized. Under high magnetic fields, these equations are applicable to the prediction and calculation of magnetic entropy changes in Gd-based and Tb, Dy, Ho, and Er-based heavy rare earth transition metal oxide magnetocaloric materials, respectively. That is, the target samples with larger magnetic entropy changes can be screened by the magnitude of the dimensionless variance. for ≥ At 3 T, the maximum error range is less than 10%, and the minimum error range is within 1%.

[0066] The established formula for screening Gd-based rare-earth transition metal oxide magnetocaloric materials is as follows: (8) in, This represents the maximum change in magnetic field value. It can take the value of any real number greater than zero. for The corresponding maximum magnetic entropy change value, For Gd 3+ The total angular momentum quantum number of an ion. transition metal ions M n+ Total angular momentum quantum number ( M n+ 3 d (ion with non-empty electron shell) For Gd 3+ The spin angular momentum quantum number of an ion. M r The relative molecular mass of the sample is denoted as . R is the gas constant.

[0067] RE The formula for screening heavy rare earth transition metal oxide magnetocaloric materials is as follows: (9) RE Selected from one or more of Tb, Dy, Ho, and Er; in, This represents the maximum change in magnetic field value. Take the value of any real number greater than 1. for The corresponding maximum magnetic entropy change value, for RE 3+ The total angular momentum quantum number of an ion. transition metal ions M n+ Total angular momentum quantum number ( M n+ 3 d (ion with non-empty electron shell) for RE 3+ The spin angular momentum quantum number of an ion. For Gd 3+ The spin angular momentum quantum number of an ion. M r The relative molecular mass of the sample is denoted as . R is the gas constant.

[0068] As can be seen from Table 1, for ≥ When T is any real number, the formula for screening in this invention is used to calculate the result. It has higher accuracy.

[0069] Application examples Gd₂CuTiO₆, Gd₂ZnMnO₆, Dy₂NiTiO₆, and Ho₂NiTiO₆ samples were prepared using the sol-gel method. The dimensionless variance values ​​of each sample were obtained using steps (1) to (4). Their magnetic entropy changes were calculated using formulas (8) and (9). Comparison with reported values ​​in relevant literature showed that the results were largely consistent. The relevant parameter results are shown in Table 2. The results calculated using the application example further demonstrate that this screening method is reasonable and efficient.

[0070] Table 2 Relevant parameters of application example samples

[0071] As shown in Table 2, the results calculated using the screening formula of this invention are... RE rare earth transition metal oxide magnetocaloric materials The accuracy is relatively high.

[0072] The specific references cited in Table 2 are as follows: [1] YK Zhang, YZ Na, WX Hao, T. Gottschall, LW Li, EnhancedCryogenic Magnetocaloric Effect from 4 f -3 d Exchange Interaction in B -SiteOrdered Gd2CuTiO6Double Perovskite Oxide, Advanced Functional Materials 34(2024): 2409061. [2] LW Li, P. Xu, SK Ye, Y. Li, GD Liu, DX Huo, M. Yan, Magnetic properties and excellent cryogenic magnetocaloric performances in B -site ordered RE 2ZnMnO6( RE = Gd, Dy and Ho) perovskites, Acta Materialia 194(2020) 354-365. [3] ZQ Zhang, P. Xu, YS Jia, LW Li, Structural, magnetic and magnetocaloric properties in distorted RE 2NiTiO6double perovskite compounds, Journal of Physics: Energy 5 (2023) 014017. The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for screening heavy rare earth transition metal oxide magnetocaloric materials, characterized in that, Includes the following steps: The magnetization intensity-temperature curves of the test sample under zero field cooling and field cooling are obtained respectively. The derivative of the magnetization intensity-temperature curve under field cooling is calculated, and then the absolute value of the derivative of the magnetization intensity-temperature curve under field cooling is taken to obtain the absolute value curve. The average magnetic phase transition temperature is calculated based on the absolute value curve. Calculate the variance of the absolute value curve at the average magnetic phase transition temperature; The dimensionless variance of the absolute value curve is calculated based on the variance of the absolute value curve at the average magnetic phase transition temperature. Obtain the isothermal magnetization curve of the test sample and calculate the magnetic entropy change. Based on dimensionless variance, a quantitative relationship between the intensity of magnetic phase transition interaction and the magnetic entropy change is established, and target samples are screened based on the quantitative relationship.

2. The screening method for heavy rare earth transition metal oxide magnetocaloric materials according to claim 1, characterized in that, The absolute value curves near the magnetic phase transition temperature conform to a Gaussian function distribution, and their mathematical expression is as follows: （1） Among them: | M ( T )'| represents the absolute value curve. T m The average magnetic phase transition temperature. T For the test temperature, σ is the standard deviation. 2 It is variance.

3. The screening method for heavy rare earth transition metal oxide magnetocaloric materials according to claim 1, characterized in that, The formula for calculating the average magnetic phase transition temperature is as follows: （2） Among them, | M ( T )'| represents the absolute value curve. T m The average magnetic phase transition temperature. T To test the temperature, The interval between test temperature points.

4. The screening method for heavy rare earth transition metal oxide magnetocaloric materials according to claim 1, characterized in that, For discrete data, the formula for calculating the average magnetic phase transition temperature is as follows: （3） Among them, | M ( T )'| represents the absolute value curve. T m The average magnetic phase transition temperature. T To test the temperature, The interval between test temperature points.

5. The screening method for heavy rare earth transition metal oxide magnetocaloric materials according to claim 1, characterized in that, The formula for calculating the variance of the absolute value curve near the average magnetic phase transition temperature is as follows: （4） Among them, | M ( T )'| represents the absolute value curve. T m The average magnetic phase transition temperature. For the interval of the test temperature points, T To test the temperature, Let Variance be the variance.

6. The screening method for heavy rare earth transition metal oxide magnetocaloric materials according to claim 1, characterized in that, For discrete data, the variance of the absolute value curve near the average magnetic phase transition temperature is calculated using the following formula: （5） Among them, | M ( T )'| represents the absolute value curve. T m The average magnetic phase transition temperature. For the interval of the test temperature points, T To test the temperature, Let Variance be the variance.

7. The screening method for heavy rare earth transition metal oxide magnetocaloric materials according to claim 1, characterized in that, The formula for calculating the dimensionless variance of the absolute value curve is as follows: （6） in, For temperature comparison, T m The average magnetic phase transition temperature. T To test the temperature, For variance, To compare the absolute value curves of temperature, | M ( T )'| represents the absolute value curve. It is dimensionless variance.

8. The screening method for heavy rare earth transition metal oxide magnetocaloric materials according to claim 1, characterized in that, The formula for calculating the isothermal magnetization curve is as follows: （7） in, The magnetic entropy change values ​​under different magnetic field variations. T To test the temperature, H The magnetic field strength, M denoted as magnetization intensity.

9. The screening method for heavy rare earth transition metal oxide magnetocaloric materials according to claim 1, characterized in that, The formula for screening Gd-based rare-earth transition metal oxide magnetocaloric materials is as follows: （8） in, This represents the maximum change in magnetic field value. It can take any real number greater than 0. for The corresponding maximum magnetic entropy change value, For Gd 3+ The total angular momentum quantum number of an ion. transition metal ions M n+ The total angular momentum quantum number, M n + 3 d Ions with non-empty electron shells, For Gd 3+ The spin angular momentum quantum number of an ion. M r The relative molecular mass of the sample is denoted as . R It is the gas constant; RE The formula for screening heavy rare earth transition metal oxide magnetocaloric materials is as follows: （9） RE Selected from one or more of Tb, Dy, Ho, and Er; in, This represents the maximum change in magnetic field value. Take the value of any real number greater than 1. for The corresponding maximum magnetic entropy change value, for RE 3+ The total angular momentum quantum number of an ion. transition metal ions M n+ The total angular momentum quantum number, M n+ 3 d Ions with non-empty electron shells, for RE 3+ The spin angular momentum quantum number of an ion. For Gd 3+ The spin angular momentum quantum number of an ion. M r The relative molecular mass of the sample is denoted as . R is the gas constant.

10. The screening method for heavy rare earth transition metal oxide magnetocaloric materials according to claim 9, characterized in that, for ≥ 3T any real number.

Images