Magnetic refrigeration material

Abstract

To provide, in a magnetic refrigeration material that provides a large magnetic entropy change in the vicinity of a liquefaction temperature of hydrogen, a magnetic refrigeration material of a system containing a kind of material which has heretofore been unknown, to provide a magnetic refrigeration apparatus using such a magnetic refrigeration material, and to investigate a method for exploring a magnetic refrigeration material comprising a heretofore unknown kind of material.SOLUTION: Provided is a magnetic refrigeration material comprising a metal alloy represented by AuxAlyRz, where R is at least one of Gd, Tb, and Dy; and x, y, and z satisfy 64-9≤x≤64+7.5, 22-7.5≤y≤22+9, and 14-0.5≤z≤14+0.5.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a magnetic refrigeration material, a method for manufacturing the same, a method for using the same, and a magnetic refrigeration apparatus using the same.

Background Art

[0002] For the widespread use of hydrogen, which is promising as one of the energy carriers, it is desirable to utilize it in the "liquid" state that enables high-density storage and transportation. At this time, since the liquefaction temperature of hydrogen is about 20 Kelvin (minus 253 degrees) at normal pressure, which is the second lowest after helium, the development and improvement of its liquefaction technology are essential. In the conventional liquefaction method using compression and expansion of gas, the cost of hydrogen liquefaction has remained high due to the theoretical upper limit of liquefaction efficiency (about 40%). On the other hand, magnetic refrigeration technology using the magnetocaloric effect, which utilizes the magnetic entropy change accompanying magnetization (heat generation) and demagnetization (heat absorption) of a magnetic material by using a magnetic field, can theoretically achieve a liquefaction efficiency of up to 90%, and is expected to contribute to the widespread use of hydrogen. In addition, this technology is expected to be used at various temperatures, not only at 20 Kelvin but also in the extremely low temperature region below 1 Kelvin and in the region of liquefied natural gas temperature (110 Kelvin). In this way, there is a demand for magnetic refrigeration materials that can be effectively used in the extremely low temperature region for hydrogen liquefaction of next-generation clean energy and for helium replacement.

[0003] In the development of magnetic refrigeration materials, it is first important to bring about a large magnetic entropy change when the magnetic field is turned on and off in the magnetic material near the target temperature (20 Kelvin in the case of hydrogen liquefaction). So far, material development has been carried out for room-temperature magnetic refrigeration materials, represented by (La(FeSi) 13 ). Also, even near the hydrogen liquefaction temperature, it has been reported that materials such as the Raves phase (ErCo2) (although not reported with awareness of magnetic refrigeration materials) have a large magnetic entropy change. These reported materials are crystalline substances in a conventional framework with a periodic atomic arrangement.

[0004] In recent years, as the third solid state following crystals and amorphous substances, the existence of quasicrystals has been recognized in metals. Not only are there specificities in their structures, but also electrical specificities such as high electrical resistance have been observed, and their applications are expected. In such metals, if the composition for forming a quasicrystalline structure is slightly changed, it is possible to create a crystal structure that has a local structure reflecting quasicrystallinity and also has periodicity like a crystal, which is called a approximant crystal. Further research on these quasicrystals and approximant crystals is highly desired.

[0005] As described above, in magnetic refrigeration materials, it is desired that the magnetic entropy change is large when the magnetic field is turned on and off for the magnetic material at a predetermined temperature. For example, in a room-temperature magnetic refrigeration material (La(Fe,Si) 13 ), although a magnetocaloric effect has been observed, in attempts to control the desired magnetic transition temperature, the magnetization history has been an issue (for example, Non-Patent Document 1). Also, in the Laves phase (ErCo2), although a magnetic entropy change is observed, there is a risk of material damage due to a large magnetovolume effect (a rapid change in the crystal lattice due to a magnetic transition by a magnetic field) accompanying the first-order transition (for example, Non-Patent Document 2). Also, an Er 5+x Pd2 (-0.5 ≤ x ≤ 0.5) represented magnetic refrigeration material has been proposed (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Non-Patent Documents

[0007]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] Thus, although various magnetic refrigeration materials have been proposed, it is of course desirable to obtain a large magnetic entropy change, and magnetic refrigeration materials in different systems are required in consideration of applications under various application conditions and environments.

Means for Solving the Problems

[0009] Under such circumstances, as a result of intensive research, the present inventors have successfully provided a magnetic refrigeration material containing a metallic alloy represented by the Au x Al y R z system. Here, R may be at least one of rare earth elements. For example, it may be at least one of rare earth elements having lone pairs of electrons. For example, it may be at least one of Gd, Tb, and Dy, and x = 64 ± 9, y = 22 ± 9, z = 14 ± 0.5 may be satisfied. This metallic alloy may be a quasicrystal or an approximant crystal.

[0010] Specifically, it may contain the following. Au x Al y R z A magnetic refrigeration material containing a metallic alloy represented by, where R is at least one of Gd, Tb, and Dy, and x, y, and z satisfy 64 - 9 ≤ x ≤ 64 + 7.5, 22 - 7.5 ≤ y ≤ 22 + 9, and 14 - 0.5 ≤ z ≤ 14 + 0.5. In any of the above magnetic refrigeration materials, a magnetic refrigeration material characterized in that R contains Dy. In any of the above magnetic refrigeration materials, a magnetic refrigeration material characterized in that R contains Gd. In any of the above magnetic refrigeration materials, a magnetic refrigeration material characterized in that R contains Tb. In any of the above-described magnetic refrigeration materials, the magnetic refrigeration material is characterized in that the metal alloy contains a quasicrystal or an approximant crystal phase. In any of the above-described magnetic refrigeration materials, the ferromagnetic transition temperature is from 2 K to 50 K, and the maximum value (-ΔSmax) of the magnetic entropy change amount (-ΔSM) in a magnetic field change up to 7 Tesla is 4 J / molK or more. The magnetic refrigeration material is characterized by this. In any of the above-described magnetic refrigeration materials, the ferromagnetic transition temperature is from 2 K to 50 K. The magnetic refrigeration material is characterized by this. In any of the above-described magnetic refrigeration materials, the form is spherical approximation, and the magnetic refrigeration material is characterized by presenting a particulate shape having a diameter of 200 μm to 500 μm. A method for manufacturing any of the above-described magnetic refrigeration materials, the method including: mixing at least one selected from Au, Al, and at least one selected from Gd, Tb, and Dy to form a mixture; and heating and melting the mixture. A magnetic refrigeration device including: a heat exchanger filled with any of the above-described magnetic refrigeration materials; and magnetic field generating means for applying or removing a magnetic field to the magnetic refrigeration materials in the heat exchanger. The magnetic refrigeration device is characterized by this. A method for exploring a magnetic refrigeration material, the method including: mixing x moles of Au or Pt (platinum), y moles of Al or Ga (gallium), and z moles of at least one selected from rare earth elements to form R, and melting to form an alloy; and confirming that the alloy contains a quasicrystal or an approximant crystal phase. In any of the above-described methods, the step of confirming includes detecting that the alloy contains a regular icosahedron cluster with rare earth atoms. The method is characterized by this. Here, the above-described rare earth elements may include scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

[0011] Generally, a quasicrystal is an aperiodic crystal that is said to have rotational symmetries not allowed in crystals. Or, it is also a general term for substances that exhibit non-crystallographic rotational symmetry and have a quasi-periodic regular structure. And, self-similarity has an irrational ratio such as τ = (1 + √5) / 2. Also, the structure of a quasicrystal is described by a combination of a quasi-periodic lattice as a framework and atomic clusters that modify it. On the other hand, when this τ is approximated by a rational number, the arrangement in physical space becomes periodic and is called an approximant. An approximant has the same or similar clusters as the quasicrystal as its basic structure and has a structure in which they are periodically arranged.

[0012] Here, Gd, Tb, and Dy can bear magnetism, in this case, ferromagnetism that can be expected to have a large magnetic entropy change. It can be mentioned that they have a quantum mechanical multiplicity for extracting such a large entropy change. This multiplicity is considered to be related to the control of the ferromagnetic transition temperature. Therefore, even other elements, for example, rare earth elements, may be able to replace them if they can bear ferromagnetism that can be expected to have a large magnetic entropy change. Thus, elements with magnetism can be candidates. Also, in the formation of magnetic order, the exchange interaction is an important factor, and approximate crystals or quasi-crystals are also considered to be related to this. In Au and Al, the valences are different, and by changing the ratio, the total number of electrons in the crystal can be changed. Thereby, it is considered that the control of the ferromagnetic transition temperature becomes possible, and conversely, when there is a desired ferromagnetic transition temperature, the ratio of Au and Al can also be adjusted accordingly. However, regarding the ranges of x, y, and z described above, 64 - 15 ≤ x is preferable, 64 - 10 ≤ x is preferable, 64 - 9 ≤ x is preferable. Also, x ≤ 64 + 11 is preferable, x ≤ 64 + 10 is preferable, x ≤ 64 + 7.5 is preferable. 22 - 11 ≤ y is preferable, 22 - 10 ≤ y is preferable, 22 - 7.5 ≤ y is preferable. Also, y ≤ 22 + 15 is preferable, y ≤ 22 + 10 is preferable, y ≤ 22 + 9 is preferable. For x and y, they can also be adjusted according to the ratios described above. In such ranges, approximate crystals are likely to be formed. Also, ferromagnetic correlations are likely to be present. And 14 - 1 ≤ z is preferable, 14 - 0.7 ≤ z is preferable, 14 - 0.5 ≤ z is preferable. Also, z ≤ 14 + 1 is preferable, z ≤ 14 + 0.7 is preferable, z ≤ 14 + 0.5 is preferable. In particular, considering the stability of the approximate crystal, z = 14 or in its vicinity is preferable.

Advantages of the Invention

[0013] As described above, in the embodiment of the present invention, when R is at least one of Gd, Tb, and Dy, and x, y, and z are 64 - 9 ≤ x ≤ 64 + 7.5, 22 - 7.5 ≤ y ≤ 22 + 9, and 14 - 0.5 ≤ z ≤ 14 + 0.5, then Au x Al y Rz A magnetic refrigeration material containing a metal alloy represented by z exhibits a large magnetic entropy change. In particular, it is excellent as a magnetic refrigeration material in hydrogen liquefaction technology.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4A

Figure 4B

Figure 5A

Figure 5B

Figure 6A

Figure 6B

Figure 7

Modes for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same elements are denoted by the same numbers, and the description thereof will be omitted.

[0016] FIG. 1 shows Au in the embodiment of the present invention. x Al y R zIt is a diagram showing the composition of the Au-Al-R alloy system. The numerical values are expressed in %. Here, R is Gd, Tb, or Dy. The ratio of each element is expressed in moles. For example, 16.9, 25.6, and 36.0 between Au and Al at the bottom where the R composition concentration is 0 mean, in molar ratio, that Au to Al is 83.1 to 16.9, 74.4 to 25.6, and 64.0 to 36.0, respectively. Similarly, between Au and R, Au:R is 83.6:16.4, 82.1:17.9, and 79.7:20.3. Also, between Al and R, Al:R is 68.9:31.1, 61.1:38.9, and 49.1:50.9. And at points u, v, and w, the composition formulas are Au 71.5 Al 14.5 R 14 、Au 64 Al 22 R 14 、Au 55 Al 31 R 14 、respectively. The composition of the Au-Al-R alloy system on the line uvw connecting these points is particularly preferable. In terms of the composition formula, it is Au x Al y R z 、satisfying -7.5 ≤ α ≤ 9. Also, if a width (e.g., ±0.5) is given to R 64-α Al 22+α R 14 、it can also be set as Au 14 Al 64-α+β Al 22+α+β R 14-2β (-7.5 ≤ α ≤ 9 and -0.25 ≤ β ≤ 0.25).

[0017] More specifically, it is Au 64-α Al 22+α Gd 14 (-7.5 ≤ α ≤ 9), Au 64-α Al 22+α Tb 14 (-7.5 ≤ α ≤ 9), or Au 64-α Al 22+α Dy 14 (-7.5 ≤ α ≤ 9). Also, Au 64-α+β Al 22+α+β Gd 14-2β (-7.5 ≤ α ≤ 9 and -0.5 / 2 ≤ β ≤ 0.5 / 2), Au64-α+β Al 22+α+β Tb 14-2β (-7.5 ≦ α ≦ 9 and -0.5 / 2 ≦ β ≦ 0.5 / 2), and Au 64-α+β Al 22+α+β Dy 14-2β (-7.5 ≦ α ≦ 9 and -0.5 / 2 ≦ β ≦ 0.5 / 2). These alloys may contain a quasicrystalline or approximant crystalline phase. Thus, as R, it may contain a single rare earth element, or it may contain two or more rare earth elements. For example, taking p and q as parameters, Au 64-α Al 22+α Gd p Tb q Dy 14-p-q (-7.5 ≦ α ≦ 9, 0 ≦ p, 0 ≦ q, p + q ≦ 14) may be applicable. Also, Au 64-α+β Al 22+α+β Gd p Tb q Dy 14-2β-p-q (-7.5 ≦ α ≦ 9, -0.25 ≦ β ≦ 0.25, 0 ≦ p, 0 ≦ q, p + q ≦ 14 - 2β) may be applicable. When p = 0 and 0 < q < 14 - 2β, it is a composite of two rare earth elements, Au 64-α+β Al 22+α+β Tb q Dy 14-2β-q and when q = 0 and 0 < p < 14 - 2β, it is a composite of two rare earth elements, Au 64-α+β Al 22+α+β Gd p Dy 14-2β-p and when p + q = 14 - 2β and p > 0 and q > 0, it is a composite of two rare earth elements, Au 64-α+β Al 22+α+β Gd p Tb q and when p + q < 14 - 2β and p > 0 and q > 0, it is a composite of three rare earth elements, Au 64-α+β Al 22+α+β Gd p Tb q Dy 14-2β-p-qThat is. Quasi-crystals refer to a group of substances that have a local structure similar to that of quasicrystals (e.g., icosahedral symmetry) while having the same translational symmetry as ordinary crystals. These approximate crystals may include Tsai-type 1 / 1 approximate crystals. They may have a structure in which rare-earth atoms responsible for magnetism are arranged at the vertices of an icosahedron. On the other hand, quasicrystals may have a structure based on a local structure similar to that of approximate crystals and translational symmetry in a high-dimensional space (hyperspace) called quasi-periodicity. At this time, the functional properties resulting from the unique crystal structure and magnetic structure, different from those of conventional crystals, are expected for these quasicrystals and approximate crystals, collectively called "hypermaterials," which can be described as the real-space cross-section of the periodic approximation of the hyperspace, common to both approximate crystals and quasicrystals. Here, Au, which is an approximate crystal among hypermaterials x Al y R z In the system, a magnetic ordered state has been found. The number of conduction electrons per atom (e / a) corresponds to 1.57 to 1.9, and Au satisfies x + y = 86 and z = 14 x Al y R z has been found to exhibit ferromagnetic order.

[0018] Fig. 2 schematically shows the crystal structure of the approximate crystal in this study. In order from the left, (a) the first shell (tetrahedron), (b) the second shell (dodecahedron), (c) the third shell (icosahedron), (d) the fourth shell (dodecahedron·icosahedron), and (e) the fifth shell (rhombic triacontahedron) structures are shown. (a) is surrounded by (b), (b) is surrounded by (c), (c) is surrounded by (d), and (d) is surrounded by (e). (a) to (d) are in a nested state and enter (e) the fifth shell (rhombic triacontahedron) (nested multi-layer shell-like clusters). Such multi-layer shell-like clusters are arranged on a body-centered cubic lattice (Fig. 2(f)). Among them, only (c) is taken out for clarity, and (c) forms the approximate crystal of (f) by forming a lattice. Here, (c) is taken out because it is a particularly important part. Rare-earth atoms are arranged at each point of this icosahedron, which is considered to be the cause of ferromagnetism and the magnetocaloric effect in the invention of the present application.

[0019] In particular, Au64 Al 22 Gd 14 The approximate crystal of 14 22 64 has the crystal structure parameters as shown in Table 1. Here, it is the case of R = Gd, but when R = Tb or Dy, only the lattice constant a is slightly different, and the others are the same.

[0020]

Table 1

[0021] [Experimental Example] (Synthesis of Au x Al y Gd z , Au x Al y Tb z , Au x Al y Dy z ) Au grains (shape: irregular grains, purity: 99.99%) manufactured by Tanaka Precious Metals Industry Co., Ltd. were used as the Au raw material, Al grains (shape: Grains 2-5mm, purity: 99.99%) manufactured by High Purity Chemical Research Institute were used as the aluminum (Al) raw material, a grain (shape: irregular lump of 5-10mm, purity: 99.9%, packaging form: oil immersion) manufactured by Nippon Yttrium Co., Ltd. was used as the gadolinium (Gd) raw material, a grain (shape: irregular lump of 5-10mm, purity: 99.9%, packaging form: oil immersion) manufactured by Nippon Yttrium Co., Ltd. was used as the terbium (Tb) raw material, and a grain (shape: irregular lump of 5-10mm, purity: 99.9%, packaging form: oil immersion) manufactured by Nippon Yttrium Co., Ltd. was used as the dysprosium (Dy) raw material, and each was prepared. For the Gd, Tb, and Dy raw materials, acetone manufactured by Godo Co., Ltd. was put into a beaker (B-200 SCI, manufactured by HARIO Co., Ltd.) together with the above raw materials to remove the oil, and ultrasonic cleaning was performed for 15 minutes using an ultrasonic cleaner (Au-16C, manufactured by Iwamedical Industry Co., Ltd.). For the Al, Gd, Tb, and Dy raw materials, nippers (N-31, manufactured by Hozan Co., Ltd.) were used to cut them into a size of 1-3mm × 1-3mm × 1-3mm to obtain samples. Also, since the Au raw material is particles with a diameter of about 1-3mm, it was used as an Au sample as it was. The Au sample, Al sample, Gd sample, Tb sample, and Dy sample were weighed to a total of 1g so that it would be Au 64 Al 22 R 14 (R = Gd, Tb, or Dy), and three mixed samples were obtained.

[0022] Next, using an ultra-small vacuum arc melting device (NEV-AD 03 type, manufactured by Nisshin Koken Co., Ltd.), the mixed samples weighed as described above were each placed on a water-cooled copper hearth, and evacuated for about 2 hours until the pressure reached 3×10 -3 Pa. After that, in an argon atmosphere, the current value was adjusted to about 50A - 100A to arc-melt each mixed sample. In order to melt the sample homogeneously, after irradiating the sample with an arc, the sample was inverted using an inversion rod and irradiated with an arc again, and this procedure was performed three times. As a result, three types of button-shaped alloy samples with a diameter of 5mm - 7mm, Au 64 Al 22 R 14(R = Gd, Tb, and Dy) was obtained (see Table 2).

[0023]

Table 2

[0024] Molybdenum (Mo) foil manufactured by NILACO Corporation (shape: 0.05 mm × 200 mm × 500 mm, purity: 99.95%) was prepared. Three pieces with a size of 30 mm × 20 mm were cut out using metal scissors to produce Mo foil pieces, and then each of the above alloy samples was wrapped with a Mo foil piece. The samples wrapped with Mo foil were placed in a quartz tube (inner diameter: 15Φ, outer diameter: 13Φ) manufactured by Eikou Corporation, and the inside of the quartz tube was evacuated for about 1 hour using a high-vacuum pumping device (DS-A412Z, manufactured by Daiya Vacuum Co., Ltd.) until the pressure reached 3×10 -3 Pa. After that, Ar was filled inside, and the quartz tube was sealed using a hydrogen-oxygen burner (KBSS-800, manufactured by Kinoshita Rika Kogyo Co., Ltd.) to obtain a quartz tube with a sample inside having a length of 80 mm. The obtained quartz tube with the sample inside was placed in an electric furnace (FO200, manufactured by YAMATO Scientific Co., Ltd.) and annealed at 1073 Kelvin for 50 hours. After cooling the annealed sample, it was taken out at room temperature, opened, and the taken-out sample was cut using an Isomet (manufactured by Buehler).

[0025] (X-ray diffraction analysis) A part of the cut material was powdered in a mortar, and the obtained powder was filled into a non-reflective sample plate of 0.2×5 mmΦ. The material was evaluated using a powder X-ray diffractometer (MiniFlex600, manufactured by Rigaku Corporation, radiation source: CuKα). The results are shown in Fig. 3. Even when R is Dy, Tb, or Gd, they all show almost the same X-ray diffraction pattern. The numbers attached to each peak are the corresponding plane indices. The lower figure marked "Cal" is the calculation result using the crystal structure parameters in Table 1. It can be seen that it is in good agreement with the experimental data. By analyzing this pattern, the crystal structure in Fig. 2 can be obtained. And when an X-ray diffraction pattern like Fig. 3 is obtained, it has a crystal structure like Fig. 2, and by examining its constituent elements simultaneously, it can be seen that something like the embodiment of the invention of this application is formed. For example, when the indices considered to be the main peaks in the X-ray diffraction pattern of Fig. 3, 503, 532, 631, 604, and 1031, match or are almost the same, it can be determined that it is such an approximate crystal. As a result of this X-ray diffraction analysis, each sample had a cubic crystal structure, and the lattice constant a of each was 1.472 nm (Gd), 1.468 nm (Tb), and 1.467 nm (Dy). Thus, from the approximation of the crystal structure and the approximation of the lattice constant due to the X-ray diffraction pattern, Gd, Tb, and Dy can form a composite crystal that can be mutually substituted. Such a state can also be represented by the above-described composition formula.

[0026] (Measurement of magnetization) The temperature dependence of magnetization was measured by the DC method using a magnetization measurement device (MPMS3, manufactured by Quantum Design). An approximately 15 mg sample cut after annealing was set in a quartz holder, and after attaching the measurement probe, it was set in the temperature variable part and the magnetic field center part inside the device. The sample measurement range was carried out between a temperature of 2 - 120 Kelvin and a magnetic field of 0.01 - 7 Tesla. The measurement data was analyzed, and the magnetic entropy change ΔS was obtained using the relationship ∂M / ∂T = ∂S / ∂H of Maxwell's relational expression. The obtained results are shown in Figs. 4A to 6B.

[0027] Au 64 Al22 Gd 14 showed a ferromagnetic transition at about 27 K (Fig. 4A), and ΔS reached its maximum at about 27 K (Fig. 4B). At this time, the temperature range corresponding to the full width at half maximum was 18 K to 42 K at 7 T. Also, Au 64 Al 22 Tb 14 showed a ferromagnetic transition at about 15 K (Fig. 5A), and ΔS reached its maximum at about 15 K (Fig. 5B). At this time, the temperature range corresponding to the full width at half maximum was 10 K to 42 K at 7 T. And, Au 64 Al 22 Dy 14 showed a ferromagnetic transition at about 9.5 K (Fig. 6A), and ΔS reached its maximum at about 9.5 K (Fig. 6B). At this time, the temperature range corresponding to the full width at half maximum was 5 K to 38 K at 7 T.

[0028] (Specific heat measurement) Using the same samples as those used in the magnetization measurement described above, the specific heat (Cp) was measured by the relaxation method using the PPMS specific heat measurement option (manufactured by Quantum Design). The measurement temperature (T) range was 2 - 120 Kelvin. Combining with the magnetization measurement, the adiabatic temperature change ΔT was obtained from ΔT = (T / C p )×ΔS. The obtained results are summarized in Table 3. Here, ΔT can be used as an index indicating how much temperature change can be expected with an actual magnetic field change (for example, from 0 to 7 T). Generally speaking, a large value means a large temperature change, and it can be said that the material has a high magnetocaloric effect.

[0029]

Table 3

[0030] As can be seen from this table, all showed a ferromagnetic transition temperature Tc at a temperature close to the hydrogen liquefaction temperature, and it can be seen that the entropy change is also extremely large. Furthermore, the adiabatic temperature change ΔT is also a large value when viewed from the ratio of rare earth elements to the total number of lattice points (14 / 100), and it was found to be preferable for magnetic refrigeration because a temperature change associated with a magnetic field change up to 5 tesla can be observed.

[0031] Here, consider the average valence electron concentration: e / a. The number of conduction electrons per atom in each sample corresponds to e / a = 1.72. Au x Al y R z (where x = 64, y = 22, z = 14, R = Gd, Tb, Dy), respectively, in materials having ferromagnetic transition temperatures of 27 Kelvin (Au 64 Al 22 Gd 14 ), 15 Kelvin (Au 64 Al 22 Tb 14 ), 9.5 Kelvin (Au 64 Al 22 Dy 14 ), it was found that there are magnetic entropy changes of 6.4 J / K mol - Gd, 4.5 J / K mol - Tb, and 4.8 J / K mol - Dy. Ferromagnetic order in the approximate crystal is supposed to be obtained at 1.57 < e / a < 1.9, but by changing the composition ratio, the number of conduction electrons per atom can be controlled, and thereby the magnetic properties can be predicted. Here, for example, by changing the ratio of monovalent Au to trivalent Al, it is considered that the total number of electrons in the material can be controlled. In this way, it is considered that the ferromagnetic transition temperature can be controlled. Thus, it can be expected to develop hypermaterials with even higher - efficiency magnetic entropy changes, taking into account not only conventional crystal materials but also approximate crystals. Also, since element substitution such as changing Au to Pt and Al to Ga is possible, the functional expression of various materials in hypermaterials can be expected.

[0032] Au x Al y R zIn a composition range that satisfies x + y = 86, z = 14, and also satisfies 55 < x < 71.5, 14.5 < y < 31, it is said to exhibit ferromagnetic order in a range where the number of conduction electrons per atom (e / a) corresponds to 1.57 to 1.9. In addition to the example of e / a = 1.72 (x = 64, y = 22, z = 14) this time, through various selections of x, y, z, and the element substitution effect of changing Au to Pt or the like, and also Al to Ga or the like, more practical magnetic refrigeration materials can be found. And in "hypermaterials" including approximate crystals and further quasicrystals, guidelines have been obtained for exploring materials suitable as magnetic refrigeration materials.

[0033] FIG. 7 is a schematic diagram showing the main part of a magnetic refrigeration device. A magnetic refrigeration material containing the materials of the above-described embodiments can be used. As one form of this magnetic refrigeration material, particles having a particle diameter in the range of 50 μm or more and 1000 μm or less may be used. For example, in a spherical approximation, it may be 50 μm or more, 100 μm or more, 200 μm or more, and may be in the form of particles having a diameter of 2000 μm or less, 1000 μm or less, 500 μm or less. Further, these lower and upper limits may be appropriately combined to form a predetermined range. When adopting a particle form, the filling rate into the AMR bed can be increased, and the heat exchange cross-sectional area and pressure loss with the heat transfer refrigerant can be changed according to the particle diameter. The smaller the particle diameter, the larger the heat exchange cross-sectional area, which is effective for improving the refrigeration performance from this viewpoint. On the other hand, the smaller the particle diameter, the higher the pressure loss, which deteriorates the refrigeration performance. The actual magnitude of the pressure loss depends not only on the particle diameter but also on the type of heat transfer refrigerant and the operating conditions. Here, the particle size is the median diameter (d50) based on volume, and the measurement of the average particle diameter based on volume can be measured, for example, by Microtrac or the laser scattering method. More specifically, a static image analysis method and a dynamic image analysis method can be adopted. The former can take a large number of particle images (such as SEM images) and obtain the particle diameter converted into a circle from the area of each particle using image analysis software. Such a magnetic refrigeration device 200 equipped with a magnetic refrigeration material can be used for generating ultra-low temperatures, for example, for liquefying hydrogen. The magnetic refrigeration device 200 further includes an AMR bed 220 filled with a magnetic refrigeration material 210, a magnetic field applying means 230 for applying a magnetic field thereto, a cooling stage 290 for cooling an object to be cooled by cold temperature, and a heat exchanger 240 for exhausting the heat generated by the magnetic refrigeration work in the AMR bed 220.

[0034] As the magnetic field applying means 230, any means for applying a magnetic field to the AMR bed 220 can be applied. For example, it is realistic to use a magnetic field having an intensity of about 1 to 10 T (tesla). As the magnetic field applying means 230, a superconducting magnet, a permanent magnet, etc. can be adopted. Further, by a drive mechanism (not shown), the relative position between the magnetic field applying means 230 and the AMR bed 220 can be changed to change the magnitude of the magnetic field applied to the AMR bed 220.

[0035] A pre-cooling stage 260 is provided on the high-temperature side of the AMR bed 220, an 80K shield 270 is connected to the low-temperature side of the pre-cooling stage 260, and a 300K shield 280 is connected to the high-temperature side of the pre-cooling stage 260. Further, a cooling stage 290 is provided on the low-temperature side of the AMR bed 220, and a liquefaction container 250 is provided in thermal connection with the cooling stage 290. That is, a gas to be cooled is supplied to the liquefaction container 250 and liquefied. Also, the AMR bed 220 is provided with an inlet and outlet for a heat transfer refrigerant, and the heat transfer refrigerant can flow back and forth inside the AMR bed 220 through the gaps of the magnetocaloric material 210.

[0036] A gas 310 (for example, hydrogen, helium (He), etc.) to be liquefied is supplied to the liquefaction container 250 from a tank (not shown). The magnetocaloric refrigeration device 200 may operate as follows. A magnetic field is applied to the AMR bed 220 filled with the magnetocaloric material 210 by a magnetic field application means 230 to raise the temperature of the magnetocaloric material 210. Next, a heat transfer refrigerant is caused to flow in a direction 300A from the low-temperature end side to the high-temperature end side of the AMR bed 220. The heat transfer refrigerant exchanges heat with the magnetocaloric material 210 filled inside the AMR bed 220, receives heat, flows through the gaps of the magnetocaloric material 210, and flows out from the high-temperature end portion of the AMR bed 220. The heat transfer refrigerant flowing out from the high-temperature end portion of the AMR bed 220 flows into a heat exchanger 240 that exhausts heat through the pre-cooling stage 260, and the excess heat is exhausted to the outside. Next, the magnetic field filled with the magnetocaloric material 210 is removed (decreased) to lower the temperature of the magnetocaloric material 210.

[0037] Then, a heat transfer refrigerant is caused to flow in a direction 300B from the high-temperature end side to the low-temperature end side of the AMR bed 220. The heat transfer refrigerant flows into the high-temperature end portion of the AMR bed 220 through the pre-cooling stage 260, exchanges heat with the magnetocaloric material 210 filled therein, is cooled while flowing through the gaps of the magnetocaloric material 210, and reaches the low-temperature end portion of the AMR bed 220. Incidentally, the flow of the heat transfer refrigerant is driven by refrigerant driving means (not shown). The refrigerant driving means is not particularly limited as long as it can drive a vibration flow in which the heat transfer refrigerant reciprocally flows in synchronization with the AMR cycle, and examples thereof include a method of combining a piston, a blower, and a valve.

[0038] When the temperature of the low-temperature end portion of the AMR bed 220 drops below the boiling point of liquid hydrogen (20 K at atmospheric pressure), the hydrogen gas supplied to the liquefaction container 250 is cooled by heat exchange with the cooling stage 290 provided on the low-temperature end side of the AMR bed 220 and concentrated and liquefied. By repeating such a process, the gas is periodically liquefied or cooled inside the liquefaction container 250.

Industrial Applicability

[0039] As described above, the magnetocaloric material is used in a magnetic refrigeration device and effectively functions for liquefaction of hydrogen and the like. Thereby, it is possible to contribute to the spread of hydrogen, which is promising as one of the energy carriers.

Explanation of Reference Numerals

[0040] 200 Magnetic refrigeration device 220 AMR bed 230 Magnetic field applying means 240 Heat exchanger 250 Liquefaction container 260 Pre-cooling stage 270 80K shield 280 300K shield 290 Cooling stage 300A Movement direction of heat transfer refrigerant 300B Movement direction of heat transfer refrigerant

Claims

1. Au ｘ Al ｙ R ｚ and containing a metal alloy represented by R is at least one of Gd, Tb, and Dy; x, y, and z, which represent the molar ratios of the respective elements, are 64-9≦x≦64+7.5, 22-7.5≦y≦22+9, and 14-0.5≦z≦14+0.5, Satisfying the above, magnetic refrigeration materials.

2. 2. The magnetic refrigeration material according to claim 1, wherein R contains Dy.

3. 2. The magnetic refrigeration material according to claim 1, wherein R contains Gd.

4. 2. The magnetic refrigeration material according to claim 1, wherein R contains Tb.

5. 5. The magnetic refrigeration material according to claim 1, wherein the metal alloy contains a quasicrystalline or approximate crystalline phase.

6. 6. A magnetic refrigeration material according to any one of claims 1 to 5, characterized in that the ferromagnetic transition temperature is from 2 K to 50 K, and the maximum value (-ΔSmax) of the magnetic entropy change (-ΔSM) in a magnetic field change up to 7 Tesla is 4 J / molK or more.

7. 7. The magnetic refrigeration material according to claim 1, wherein the ferromagnetic transition temperature is from 2K to 50K.

8. 8. The magnetic refrigeration material according to claim 1, wherein the magnetic refrigeration material is in the form of particles having a diameter of 200 μm to 500 μm in approximate spherical shape.

9. A method for producing the magnetic refrigeration material according to any one of claims 1 to 8, comprising the steps of: mixing Au, Al, and at least one selected from Gd, Tb, and Dy to form a mixture; heating and melting the mixture; The method includes:

10. A heat exchanger filled with the magnetic refrigeration material according to any one of claims 1 to 8; a magnetic field generating means for applying or removing a magnetic field to the magnetic refrigeration material in the heat exchanger; A magnetic refrigeration device comprising:

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