Magnetic refrigeration material, production method therefor, and magnetic refrigeration device

Abstract

A magnetic refrigeration material that includes a tetragonal Eu-Ti-O–based compound containing europium (Eu), titanium (Ti) and oxygen (O) as constituent elements.

Description

Magnetic refrigeration material, method for manufacturing the same, and magnetic refrigeration apparatus

[0001] This disclosure relates to a magnetic refrigeration material, a method for manufacturing the same, and a magnetic refrigeration apparatus using the magnetic refrigeration material.

[0002] The use of hydrogen as an energy source is attracting attention as we move towards realizing a decarbonized society. For the storage and transportation of large quantities of hydrogen, the liquid state is more advantageous than the gaseous state in terms of volume and safety. However, hydrogen has an extremely low liquefaction temperature of 20K (-253°C), making it difficult to liquefy efficiently and at low cost. For hydrogen to become widespread, a reduction in the production and storage costs of liquid hydrogen is necessary.

[0003] Magnetic refrigeration is a well-known technology for liquefying hydrogen. Magnetic refrigeration utilizes the phenomenon (magnetocaloric effect) in which, when a magnetic field is applied, the orientation of the magnetic spins of a magnetic material aligns and becomes ordered in one direction, decreasing magnetic entropy and generating heat. When the magnetic field is removed, the orientation of the magnetic spins becomes irregular (disordered), increasing magnetic entropy and causing heat absorption.

[0004] In magnetic refrigeration technology, efforts are underway to develop magnetic refrigeration materials that generate large entropy changes through excitation and demagnetization around 20K, the temperature at which hydrogen liquefies. In particular, there is a need for magnetic refrigeration materials that can provide good cooling effects in the temperature range from 77K (-196°C), the liquefaction temperature of nitrogen, to 20K, the liquefaction temperature of hydrogen.

[0005] Various ceramic materials containing rare earth elements have been proposed as magnetic refrigeration materials, such as gadolinium gallium garnet (Gd ３ Ga ５ O １２ A garnet-structured magnetic compound based on (commonly known as GGG) is known (see Patent Document 1). Also, for example, Patent Document 2 describes GdTiO ３ Such cubic magnetic refrigeration materials are disclosed.

[0006] JP-A-61-97132 JP-A-1-46545

[0007] The magnetic refrigeration material of this disclosure includes a tetragonal Eu-Ti-O compound containing europium (Eu), titanium (Ti), and oxygen (O) as constituent elements.

[0008] This is a graph (S-T curve) showing the entropy versus temperature plot of the magnetic refrigeration material of Example 5.

[0009] The garnet-structured magnetic compounds described in Patent Document 1 do not exhibit a sufficiently large change in magnetic entropy during the Carnot cycle. This disclosure provides a magnetic refrigeration material with a large change in magnetic entropy in the cryogenic region below 77 K, a method for producing the same, and a magnetic refrigeration apparatus using the magnetic refrigeration material.

[0010] The present disclosure will be described in detail below with reference to one embodiment. The meaning and definition of terms used in this disclosure are as follows: The notation "X to Y" (where X and Y are numerical values) means a numerical range with X as the lower limit and Y as the upper limit. Within a numerical range (for example, a range of content, etc.), the lower and upper limits described in steps may be combined independently of each other. The lower and upper limits of the numerical range may be replaced with the numerical values ​​described in the examples.

[0011] [Magnetic Refrigeration Material] The magnetic refrigeration material of this disclosure includes a tetragonal Eu-Ti-O compound containing Eu, Ti, and O as constituent elements. The Eu-Ti-O compound contained in the magnetic refrigeration material may be a single compound or two or more compounds.

[0012] The Eu-Ti-O compounds relating to this disclosure are tetragonal. Tetragonal Eu-Ti-O compounds include garnet structures such as GGG, which are conventionally known as magnetic refrigeration materials, and GdTiO ３ , EuTiO ３ These magnetic materials exhibit a greater cooling effect in the cryogenic region compared to cubic perovskite magnetic compounds such as GGG and EuTiO. ３One reason why tetragonal Eu-Ti-O compounds are superior as magnetic refrigeration materials compared to GGG is that while GGG is paramagnetic, tetragonal Eu-Ti-O compounds are ferromagnetic, and therefore the applied magnetic field is more easily amplified. In addition, tetragonal Eu-Ti-O compounds have a larger number of magnetic atoms in their unit cell than conventional cubic magnetic compounds, so the change in magnetic entropy in the cryogenic region is thought to be greater.

[0013] Furthermore, the tetragonal crystal structure of Eu-Ti-O compounds can be confirmed by X-ray diffraction (XRD) measurements based on the Powder Diffraction File (PDF), a database of the ICDD (International Centre for Powder Diffraction Data).

[0014] The Eu-Ti-O compound according to this disclosure has Eu, Ti, and O as its main constituent elements, and the total content of Eu, Ti, and O in all constituent elements may be 80 to 100% by mass, 90 to 100% by mass, or 95 to 100% by mass.

[0015] Eu-Ti-O compounds may contain at least one element selected from the group consisting of Dy, Gd, Ho, Tb, Nb, V, and Al as a constituent element other than Eu, Ti, and O, or they may contain at least one of Dy and Gd. Including any of these elements increases the amount of magnetic entropy change in the cryogenic region during isothermal changes due to excitation and demagnetization. Furthermore, since the peak temperature of the magnetic entropy change in the cryogenic region approaches the liquefaction temperature of hydrogen, it is easier to obtain magnetic refrigeration materials suitable for hydrogen liquefaction.

[0016] If an Eu-Ti-O compound contains constituent elements other than Eu, Ti, and O, a portion of the Eu in the Eu-Ti-O compound may be substituted with at least one element selected from the group consisting of Dy, Gd, Ho, and Tb. Furthermore, a portion of the Ti in the Eu-Ti-O compound may be substituted with at least one element selected from the group consisting of Nb, V, and Al.

[0017] While it is currently difficult to directly confirm that Eu-Ti-O compounds are substitutional solid solutions containing the elements mentioned above through direct observation using a transmission electron microscope, etc., this can be indirectly inferred by the following method, based on the fact that the measured lattice constants obtained by XRD analysis change continuously up to the solid solution limit. For example, if the Eu-Ti-O compound contains Dy, Eu-Ti-O compound samples are prepared, each containing 0, 3, 7, 10, 13, or 16 mol% of Dy relative to a total of 100 mol% of Eu and Dy (the molar ratio of the total content of Eu and Dy to the content of Ti is constant). For each sample, the a-axis length and c-axis length of the tetragonal lattice constant of the Eu-Ti-O compound are measured by XRD. When at least one of the a-axis length and c-axis length continuously increases or decreases in the range of 0 to 10 mol% for Dy content, and no substantial change is observed at Dy content of 13 mol% and 16 mol%, then the maximum amount of Dy that can be substituted and dissolved in an Eu-Ti-O compound, i.e., the solubility limit, can be said to be 10 mol%. Therefore, by analogy, an Eu-Ti-O compound containing 10 mol% or less of Dy relative to a total of 100 mol% of Eu and Dy can be inferred to be a substitutional solid solution.

[0018] Eu-Ti-O compounds may have oxygen vacancies. These vacancies may be oxygen-deficient or oxygen-excessive. The presence of oxygen vacancies in Eu-Ti-O compounds increases the peak temperature of the magnetic entropy change in the cryogenic region, and this peak temperature approaches the hydrogen liquefaction temperature, making it easier to obtain magnetic refrigeration materials suitable for hydrogen liquefaction.

[0019] The Eu-Ti-O compound may be represented by at least one of the compositional formulas (1a) and (1b). ２＋ｘ Ti１＋ｙ O ４＋ｚ (1a) Eu ３＋ｕ Ti ２＋ｖ O ７＋ｗ (1b)

[0020] In formula (1a), -0.2 ≤ x ≤ 0.2, -0.2 ≤ y ≤ 0.2, -0.2 ≤ z ≤ 0.2, and x, y, and z may each independently be -0.1 ≤ x ≤ 0.1, -0.1 ≤ y ≤ 0.1, -0.1 ≤ z ≤ 0.1, or x = 0, y = 0, z = 0. In formula (1b), -0.2 ≤ u ≤ 0.2, -0.2 ≤ v ≤ 0.2, -0.2 ≤ w ≤ 0.2, and u, v, and w may each independently be -0.1 ≤ u ≤ 0.1, -0.1 ≤ v ≤ 0.1, -0.1 ≤ w ≤ 0.1, or u = 0, v = 0, w = 0.

[0021] The Eu-Ti-O compound may be a non-stoichiometric compound having oxygen defects and lattice defects, etc. The Eu-Ti-O compound may be a compound in which x = y = z = 0 in formula (1a), that is, Eu ２ TiO ４ or may be a compound in which u = v = w = 0 in formula (1b), that is, Eu ３ Ti ２ O ７ .

[0022] The cubic Eu-Ti-O compound represented by at least one of the composition formulas of (1a) and (1b) has a large density of magnetic ions Eu ２＋ per unit volume, and due to the relationship between the distance and angle between the magnetic ions Eu ２＋ and oxygen ions in the crystal structure, the magnetic moment is large, so the magnetic entropy change amount in the extremely low temperature region tends to be large.

[0023] From the perspective that the magnetic refrigeration material of the present disclosure not only has a large magnetic entropy change amount in the extremely low temperature region but also has a sufficiently large magnetic entropy change amount in the Carnot cycle, the content of the Eu-Ti-O compound may be 50% by mass or more, may be 80 - 100% by mass, or may be 90 - 100% by mass.

[0024] From the same viewpoint, the magnetic refrigeration material may have a total content of the compound represented by either formula (1a) or (1b) of 70% by mass or more, 80 to 100% by mass, or 90 to 100% by mass.

[0025] The aforementioned magnetic refrigeration material may contain components other than Eu-Ti-O compounds, as long as it can ensure a sufficiently large change in magnetic entropy of the Eu-Ti-O compound in the cryogenic region, and can also increase the change in magnetic entropy in the cryogenic region.

[0026] Eu-Ti-O compounds are Eu ２＋ It may include, Eu ３＋ It may also include. ３＋ The inclusion of this material promotes sintering during the firing process when manufacturing magnetic refrigeration materials, which makes it easier to improve the bulk density of the magnetic refrigeration material and increase the amount of change in magnetic entropy per unit volume in the cryogenic region.

[0027] The magnetic refrigeration material may contain, for example, an oxide of Eu in addition to an Eu-Ti-O compound. The inclusion of an oxide of Eu in the magnetic refrigeration material improves its bulk density, making it easier to increase the change in magnetic entropy per unit volume in the cryogenic region.

[0028] If the magnetic refrigeration material contains an oxide of Eu, its content may be less than 30% by mass, greater than 0% by mass and 20% by mass or less, or 1 to 20% by mass. If the content of the oxide of Eu is within the above range, the change in magnetic entropy of the Eu-Ti-O compound in the cryogenic region tends to be sufficiently large. The oxide of Eu may be a single type or two or more types.

[0029] The oxide of Eu may be represented by at least one of the compositional formulas (2a), (2b), and (2c). １＋ｐ O (2a) Eu ２＋ｑ O ３ (2b) EU ３＋ｒ O ４ (2c)

[0030] In equation (2a), -0.2 ≤ p ≤ 0.2, and it is also possible that -0.1 ≤ p ≤ 0.1, and p = 0. In equation (2b), -0.2 ≤ q ≤ 0.2, and it is also possible that -0.1 ≤ q ≤ 0.1, and q = 0. In equation (2c), -0.2 ≤ r ≤ 0.2, and it is also possible that -0.1 ≤ r ≤ 0.1, and r = 0.

[0031] The oxide of Eu may be an oxide in which the oxidation state of Eu is +2, +3, or +4, and may be derived from the raw materials used in the manufacture of the magnetic refrigeration material. The oxide of Eu may be a compound in formula (2a) where p=0, i.e., EuO, and a compound in formula (2b) where q=0, i.e., Eu ２ O ３ It may also be the case that, in formula (2c), the compound is r=0, i.e., Eu ３ O ４ That's fine.

[0032] The magnetic refrigeration material can be effectively used for cryogenic cooling, and the applicable cooling temperature range may be below 77K, which is the liquefaction temperature of nitrogen, or it may be in the range of around 20K (e.g., 18K) to 77K, which is the liquefaction temperature of hydrogen. By applying it to cooling within the above temperature range, it can contribute to reducing the cost of liquid hydrogen production and storage.

[0033] [Manufacturing Method] The magnetic refrigeration material of the present disclosure described above can be manufactured by a manufacturing method of the present disclosure, comprising the steps of (1) mixing an Eu compound and a Ti compound to obtain a mixture, (2) molding the mixture to obtain a molded body, and (3) firing the molded body under an inert gas or vacuum atmosphere, wherein the oxidation number of Ti in the Ti compound is less than +4. By using a Ti compound in which the oxidation number of Ti is less than +4 as a raw material, a magnetic refrigeration material containing a tetragonal Eu-Ti-O compound can be obtained.

[0034] (Step (1)) First, in step (1), the Eu compound and the Ti compound are mixed to obtain a mixture.

[0035] The Eu compound used as a raw material to obtain tetragonal Eu-Ti-O compounds may be an oxide of Eu, for example, EuO, Eu ２ O ３ , Eu ３ O ４ Examples include: The raw material EU compound may be a single type or two or more types may be used in combination. From the viewpoint of ease of handling and availability, etc., EU ２ O ３ That's fine.

[0036] For the Ti compound mixed with the EU compound, a compound in which the oxidation state of Ti is less than +4 is used. Although Ti can have oxidation states of +2, +3, or +4, a compound with an oxidation state of +4 is used, such as titanium dioxide (TiO2). ２ ) is a very stable compound, and by using a Ti compound with a lower oxidation state than this as a starting material, tetragonal Eu-Ti-O compounds can be easily obtained. Such a Ti compound may be a compound in which the oxidation state of Ti is +2 or +3, for example, titanium(II) oxide (TiO), titanium(III) oxide (Ti ２ O ３ ) may also be used, and from the viewpoint of ease of handling and availability, TiO may also be used.

[0037] The oxidation state of Ti in a Ti compound can be determined as follows. For example, if the Ti compound is a Ti oxide, heating the Ti compound in an oxidizing atmosphere will cause it to oxidize to a stable TiO ２ This process generates a compound, increasing its mass. Based on the change in mass before and after oxidation, the oxidation number of Ti in the Ti compound can be calculated.

[0038] The compound in which Ti has an oxidation state of less than +4 may be used alone or in combination of two or more. For example, as the raw material powder for the Ti compound, TiO powder or Ti ２ O ３ Only one type may be used, TiO ２ A mixture of powder and Ti powder (with an average oxidation state of Ti less than +4) may be used. From the viewpoint of ease of handling and availability, TiO powder alone may be used as the raw material powder for the Ti compound.

[0039] A mixture of Eu and Ti compounds can be obtained, for example, by mixing the respective powders using a ball mill or other mixer. From the viewpoint of homogeneous mixing, it may also be obtained as a slurry using a wet ball mill. The dispersion medium for obtaining the slurry can be an organic solvent that is volatile at 100°C, such as isopropyl alcohol, which can prevent the raw material powders from agglomerating and also reduces oxidation of the Ti compound and is easy to handle.

[0040] When obtaining a mixture as a slurry using a wet ball mill, from the viewpoint of homogeneous mixing and ease of handling, the raw material powder may have a median diameter on a volume basis of 0.3 to 20.0 μm, 0.5 to 15.0 μm, or 0.7 to 10.0 μm. The median diameter referred to here is a value based on the volume-based particle size distribution measured by laser diffraction scattering.

[0041] The slurry of the thoroughly mixed mixture may be granulated to a particle size larger than that of the raw material powder by volatilizing the dispersion medium of the slurry by heating (e.g., 100°C) to facilitate molding in step (2). At that time, an organic binder may be added to facilitate granulation. The organic binder may be, for example, paraffin wax. The organic binder is burned off during calcination in step (3), and only a sufficient amount is needed for easy molding and granulation. It may be 0 to 20 parts by mass, 0 to 15 parts by mass, or 0 to 10 parts by mass per 100 parts by mass of the total of the Eu compound and Ti compound of the raw material powder.

[0042] (Step (2)) Next, in step (2), the mixture obtained in step (1) is molded to obtain a molded body.

[0043] As described above, the mixture may be granulated. From the viewpoint of obtaining a magnetic refrigeration material with high bulk density, reduced porosity, good thermal conductivity, and good cooling effect, the mixture may be pressure-molded, for example, using a press. The molding pressure may be 90 to 200 MPa, 100 to 180 MPa, or 120 to 150 MPa. The shape and size of the molded body are not particularly limited and may be any desired form.

[0044] (Step (3)) In step (3), the molded body obtained in step (2) is fired in an inert gas or vacuum atmosphere. This yields a magnetic refrigeration material as a fired body.

[0045] The molded body may be pre-sintered to remove any contained organic binder before firing. Pre-sintering may be carried out in an inert gas (e.g., argon gas, helium gas) or vacuum atmosphere at, for example, 200-800°C, 300-700°C, or 400-600°C.

[0046] The firing may be carried out in an inert gas (e.g., argon gas, helium gas) or vacuum atmosphere at a temperature higher than the pre-firing temperature, for example, at 800 to 1600°C, 900 to 1500°C, or 1000 to 1400°C. The vacuum atmosphere in the firing atmosphere may be 10 Pa or less. －２ It may be less than or equal to Pa, 10 －３ It may be less than or equal to Pa.

[0047] The firing atmosphere may be a vacuum atmosphere followed by an inert gas purging atmosphere. In this case, the oxygen partial pressure may be 0.02 to 20 Pa, 0.05 to 15 Pa, or 0.1 to 10 Pa, from the viewpoint of good regularity of the atomic arrangement in the crystal structure. The firing time may be 1 to 36 hours, 2 to 30 hours, or 3 to 24 hours, from the viewpoint of sufficient firing, with the holding time at the maximum temperature being 1 to 36 hours, 2 to 30 hours, or 3 to 24 hours.

[0048] The sintered body obtained in step (3) may be subjected to grinding or other processing as necessary when applied as a magnetic refrigeration material.

[0049] [Magnetic Refrigeration Apparatus] The magnetic refrigeration apparatus of this disclosure uses the magnetic refrigeration material of this disclosure described above. By using the magnetic refrigeration material of this disclosure, a good magnetocaloric effect can be obtained in repeated cycles of magnetic field application and demagnetization, and a magnetic refrigeration apparatus that provides an efficient cooling effect can be provided. The basic configuration of the magnetic refrigeration apparatus includes a magnetic refrigeration material arranged in a state where a magnetic field can be applied and demagnetized, and a medium that is cooled by the heat absorption of the magnetic refrigeration material. Since the magnetic refrigeration material of this disclosure provides a good cooling effect around 20K, it can be used in the technology of liquefying hydrogen gas cooled with liquid nitrogen. For this reason, the magnetic refrigeration apparatus may be a Carnot magnetic refrigeration apparatus (CMR). The structure of the CMR is not particularly limited.

[0050] Next, the present disclosure will be specifically described by examples. The present disclosure is not limited in any way by these examples.

[0051] [Manufacturing of magnetic refrigeration materials]

[0052] (Example 1) Eu ２ O ３ A slurry was obtained by mixing 50 parts by mass of powder (median diameter 0.747 μm), 50 parts by mass of TiO powder (median diameter 12.89 μm) (raw material mass ratio 1.000), and 50 parts by mass of isopropyl alcohol in a ball mill. ２ O ３ The median diameter of the powder and TiO powder was measured by laser diffraction scattering using a particle size distribution analyzer ("MT3300EX II", manufactured by Microtrac-Bell Co., Ltd.). The obtained slurry was then mixed with paraffin wax (Eu). ２ O ３ 10 parts by mass of isopropanol was added to 100 parts by mass of the total of the powder and TiO powder, and granulation was carried out at 100°C while volatilizing the isopropanol. The granulated mixture was pressure-molded at 147 MPa to produce a disc-shaped molded body with a diameter of 12 mm and a thickness of 3 mm. The obtained molded body was then subjected to a vacuum atmosphere (vacuum degree 10 －３After pre-sintering at 400°C for 1 hour (at an oxygen partial pressure of 10 Pa), the furnace was replaced with argon gas, and the material was fired at 1400°C for 24 hours at an oxygen partial pressure of 10 Pa to produce a magnetic refrigeration material.

[0053] Furthermore, the TiO powder used as a raw material was heated to 900°C in an oxygen atmosphere and oxidized to produce TiO ２ The mixture was generated (confirmed by XRD), and the mass increase was measured. Based on this mass increase, it was calculated that the oxidation state of Ti in the TiO powder was +2.

[0054] (Examples 2-10) In Example 1, the raw material mass ratio, firing temperature, firing time, and oxygen partial pressure were set to the conditions shown in Table 1, and all other conditions were the same as in Example 1 to produce each magnetic refrigeration material.

[0055] (Comparative Example 1) Gd ２ O ３ Powder 53.71 parts by mass, Ga ２ O ３ 46.29 parts by mass of powder (molar ratio 3 / 5) and 100 parts by mass of isopropyl alcohol were mixed in a ball mill to obtain a slurry. Paraffin wax (Gd ２ O ３ Powder and Ga ２ O ３ (10 parts by mass) was added to 100 parts by mass of the total powder, and granulation was carried out at 100°C while volatilizing the isopropanol. The granulated mixture was pressure-molded at 98 MPa to produce a disc-shaped molded body with a diameter of 12 mm and a thickness of 3 mm. The obtained molded body was fired at 1500°C for 1 hour in an air atmosphere, and Gd ３ Ga ５ O １２ We manufactured a magnetic refrigeration material containing a calcined body of (GGG).

[0056] [Measurement and Evaluation] The following describes various measurement and evaluation methods for the magnetic refrigeration materials produced in the examples and comparative examples.

[0057] (Crystal Phase Components and Crystal Constants) The content of constituent elements of the magnetic refrigeration material was measured by high-frequency inductively coupled plasma (ICP) emission spectroscopy and oxygen-nitrogen analysis (infrared absorption method, thermal conductivity method). In addition, powder XRD measurements were used to identify each crystal phase component and crystal structure from the ICDD database, the Powder Diffraction File (PDF). Furthermore, the content and lattice constant of each crystal phase component were measured by Rietveld method analysis in XRD (software RIETAN-FP).

[0058] (Bulk density and porosity) Measured using the Archimedes method in accordance with JIS R 1634:1998.

[0059] (Magnetic Entropy) The change in magnetic entropy ΔS is calculated using the following steps (1) to (3). Ｍ and the change in magnetic entropy in the Carnot cycle, Carnot ΔS Ｍ The following was determined. (1) Creation of the S-T curve at H=0[T] With no magnetic field applied (H=0[T]), the specific heat C was measured by changing the temperature T[K], and the S-T curve was created from the following relationship (I) with entropy S. Here, [K] is the unit of absolute temperature "Kelvin", and [T] is the unit of magnetic flux density "Tesla".

[0060]

[0061] The specific heat C was measured using the thermal relaxation method (equipment used: Physical Properties Measurement System (PPMS) (Quantum Design Co., Ltd.), sample: 2.0 mm x 2.0 mm, 1.1 mm thick flat plate, temperature T: 2-300 K).

[0062] (2) T-ΔS under the applied magnetic field H ＭDiagram Creation: Magnetization M was measured by applying a predetermined (constant) magnetic field H within the range of 0.1 to 5 [T] and varying the temperature T within the range of 0 to 50 [K] (Equipment used: Magnetic property measurement system (MPMS) using superconducting quantum interference devices (SQUID) (Quantum Design Co., Ltd.), Sample: Rod-shaped, 0.55 mm × 0.55 mm, 3.30 mm in length). Specifically, the magnetic field H was set to seven conditions: H = 0.1, 0.2, 1, 2, 3, 4, and 5 [T], and was applied along the length of the rod-shaped sample from the viewpoint of minimizing the effect of the demagnetizing field. M-T curves were created for each magnetic field H by plotting and connecting the measured values ​​of magnetization M at each temperature T. The entropy change ΔS was obtained by numerically integrating this M-T curve with equation (III), which is obtained by integrating Maxwell's relation (II) below, from H = 0 to the applied magnetic field H.

[0063]

[0064] Furthermore, since (∂M / ∂T) < 0, -ΔS is the change in magnetic entropy ΔS in the cryogenic region. Ｍ This is expressed as follows: Temperature T and calculated value ΔS Ｍ Therefore, T-ΔS for each magnetic field H Ｍ I created a diagram.

[0065] (3) Carnot ΔS Ｍ The measurement of the entropy S of the S-T curve at H=0[T] in (1) above, and T-ΔS at each temperature T[K] in (2) above. Ｍ ΔS in the diagram Ｍ By interpolating (adding) these values, S-T curves were created for each magnetic field H under different magnetic field conditions. Using these S-T curves under different magnetic field H conditions and the S-T curve without a magnetic field (H = 0 [T]), the Carnot ΔS was calculated. Ｍ They sought it.

[0066] Figure 1 shows a representative S-T curve for the magnetic refrigeration material of Example 5. The curve connecting the upper plots is the S-T curve when H = 0 [T]. The curve connecting the lower plots is the S-T curve when H = 5 [T], which is an example of a magnetic field H. From these S-T curves, the Carnot ΔS Ｍ They sought it.

[0067] The measurement and evaluation results for each magnetic refrigeration material are shown in Table 1. Note that the measurement of the crystal phase components and lattice constants for Comparative Example 1 has not been carried out.

[0068]

[0069] As shown in Table 1, the magnetic refrigeration materials of Examples 1, 2, and 4 to 10 contain Eu ２ TiO ４ and it was confirmed that the magnetic refrigeration materials of Examples 1 to 10 contain Eu ３ Ti ２ O ７ In addition, from the XRD analysis, Eu ２ TiO ４ , Eu ３ Ti ２ O ７ was confirmed to be tetragonal.

[0070] The magnetic refrigeration materials of Examples 1 to 10 have ΔS Ｍ and Carnot ΔS Ｍ both of which are larger than those of GGG (Comparative Example 1) and are 10 J / (kg·K) or more, so it can be said that a cooling effect can be obtained with higher efficiency.

[0071] When containing an oxide of Eu (Eu ２ O ３ ), in the case of Examples 1 to 3 and 7 to 10, it was confirmed that when Eu ２ TiO ４ in the Eu-Ti-O-based compound is more than Eu ３ Ti ２ O ７ , ΔS Ｍ and Carnot ΔS Ｍ tend to increase. On the other hand, when not containing Eu ２ O ３ (Examples 4 to 6), it was confirmed that as the content of Eu ３ Ti ２ O ７ in the Eu-Ti-O-based compound increases, ΔS Ｍ and Carnot ΔS Ｍ tend to increase. These tendencies are due to the magnetic atom Eu (or magnetic ion Eu ２＋This is presumed to be due to the density of the atoms, the distance between magnetic atoms and oxygen atoms, and their interactions.

Claims

1. A magnetic refrigeration material comprising a tetragonal Eu-Ti-O compound containing europium (Eu), titanium (Ti), and oxygen (O) as constituent elements.

2. The magnetic refrigeration material according to claim 1, wherein the content of the Eu-Ti-O compound is 50% by mass or more.

3. The magnetic refrigeration material according to claim 1 or 2, wherein the Eu-Ti-O compound comprises at least one element selected from the group consisting of dysprosium (Dy), gadolinium (Gd), holmium (Ho), terbium (Tb), niobium (Nb), vanadium (V), and aluminum (Al).

4. The magnetic refrigeration material according to any one of claims 1 to 3, wherein the Eu-Ti-O compound is represented by at least one of the following compositional formulas (1a) and (1b). ２＋ｘ Ti １＋ｙ O ４＋ｚ (1a) EU ３＋ｕ Ti ２＋ｖ O ７＋ｗ (1b) (wherein -0.2≦x≦0.2, -0.2≦y≦0.2, -0.2≦z≦0.2, -0.2≦u≦0.2, -0.2≦v≦0.2, -0.2≦w≦0.2) 5. The magnetic refrigeration material according to claim 4, wherein the total content of the compound represented by either of the compositional formulas (1a) and (1b) is 70% by mass or more.

6. The magnetic refrigeration material according to any one of claims 1 to 5, further comprising an oxide of europium (Eu).

7. The magnetic refrigeration material according to claim 6, wherein the content of europium (Eu) oxide is less than 30% by mass.

8. The magnetic refrigeration material according to claim 6 or 7, wherein the oxide of europium (Eu) is represented by at least one of the following compositional formulas (2a), (2b), and (2c). Eu １＋ｐ O (2a) Eu ２＋ｑ O ３ (2b) Eu ３＋ｒ O ４ (2c) (where -0.2 ≤ p ≤ 0.2, -0.2 ≤ q ≤ 0.2, -0.2 ≤ r ≤ 0.2) 9. A magnetic refrigeration material according to any one of claims 1 to 8, used for cooling to a temperature of 77K or lower.

10. A method for producing a magnetic refrigeration material according to any one of claims 1 to 9, comprising the steps of: mixing a europium (Eu) compound and a titanium (Ti) compound to obtain a mixture; molding the mixture to obtain a molded body; and firing the molded body under an inert gas or vacuum atmosphere, wherein the oxidation number of titanium (Ti) in the titanium (Ti) compound is less than +4.

11. The method for producing a magnetic refrigeration material according to claim 10, wherein the titanium (Ti) compound is titanium(II) oxide (TiO).

12. A magnetic refrigeration apparatus using the magnetic refrigeration material described in any one of claims 1 to 9.

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