Magnetic refrigerant, method of producing the same, AMR bed using the same, and magnetic refrigerator

Abstract

To provide a magnetic refrigerant having hydrogen-resistant barrier properties, a method of producing the same, an AMR bed using the same, and a magnetic refrigerator using the same.SOLUTION: A magnetic refrigerant in the present invention comprises a Laves phase compound that is represented by a general formula RT2 (where R is at least one or more rare earth elements and T is at least one or more elements selected from a group consisting of cobalt (Co), nickel (Ni), aluminum (Al) and iron (Fe)), and a barrier layer that covers over the Laves phase compound and includes a Cu layer consisting of copper (Cu) and a Ni layer consisting of nickel (Ni) positioned over the Cu layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a magnetic refrigeration material, a manufacturing method thereof, an AMR bed using the same, and a magnetic refrigeration device. [Background technology]

[0002] To realize a future hydrogen society with energy conservation and low carbonization, it is essential to utilize liquid hydrogen, which has 1 / 800 the volume of gaseous hydrogen, and features characteristics such as mass transportation, mass supply, mass storage, space saving, and ultra-high purity. However, the current hydrogen liquefaction technology using compressors has problems such as low liquefaction efficiency during production and loss due to evaporation. Here, magnetic refrigeration is a cooling technology that uses magnetic materials that exhibit the magnetocaloric effect as a refrigerant, and refrigeration is achieved by using the endothermic and exothermic reactions that occur as a result of ferromagnetic-paramagnetic phase transition caused by cycles of increasing and decreasing the magnetic field. Magnetic refrigerators are being developed as refrigerators that are more energy efficient and can liquefy hydrogen at low cost compared to refrigerators that use gas compression and expansion.

[0003] ErCo2 has been reported as a magnetic refrigeration material (e.g., Non-Patent Document 1). ErCo2 exhibits the largest entropy change among Laves phase compounds and has a desirable Curie temperature T C This indicates that it is a promising candidate for a giant magnetocaloric effect material for hydrogen liquefaction.

[0004] However, it is known that when such a magnetic refrigeration material is used in a hydrogen atmosphere, hydrogen penetrates into the magnetic refrigeration material, generating hydrides, which cause the magnetic refrigeration material to pulverize, and the magnetic properties of the magnetic refrigeration material to change significantly. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] H. Wada et al., Cryogenics 39, 1999, 915-919 Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above, an object of the present invention is to provide a magnetic refrigeration material having hydrogen barrier resistance, a manufacturing method thereof, an AMR bed using the same, and a magnetic refrigeration device. [Means for solving the problem]

[0007] The magnetic refrigeration material according to the present invention comprises a Laves phase compound represented by the general formula RT2 (wherein R is at least one rare earth element, and T is at least one element selected from the group consisting of cobalt (Co), nickel (Ni), aluminum (Al), and iron (Fe)), and a barrier layer including a Cu layer made of copper (Cu) covering the Laves phase compound, and a Ni layer made of nickel (Ni) located on the Cu layer, thereby solving the above-mentioned upper object. The thickness of the Cu layer may be in the range of 1 μm to 20 μm. The thickness of the Cu layer may be in the range of 3 μm to 7 μm. The thickness of the Ni layer may be in the range of 0.2 μm to 20 μm. The thickness of the Ni layer may be in the range of 1.5 μm to 4 μm. The insulating layer may further include an oxygen-rich layer between the Laves phase compound and the barrier layer. The oxygen-rich layer may have a thickness in the range of 3 μm to 20 μm. The oxygen-rich layer may have a thickness in the range of 5 μm to 10 μm. The semiconductor device may further include an interface layer containing palladium (Pd) and tin (Sn) at the interface between the Cu layer and the Ni layer. The thickness of the interface layer may be in the range of 30 nm to 200 nm. The thickness of the interface layer may be in the range of 50 nm to 150 nm. The particles may have a particle size in the range of 10 μm to 3000 μm. The method for producing a magnetic refrigeration material according to the present invention comprises forming a Cu layer made of copper (Cu) on the surface of a Laves phase compound represented by the above general formula RT2 (wherein R is at least one rare earth element and T is at least one element selected from the group consisting of cobalt (Co), nickel (Ni), aluminum (Al) and iron (Fe)), and forming a Ni layer made of nickel (Ni) on the Cu layer, thereby solving the above-mentioned problem. The formation of the Cu layer and the formation of the Ni layer may be performed by using an electroless plating method. The method may further include activating a surface of the Cu layer prior to forming the Ni layer. The activating step may use a catalyst containing tin (Sn) and palladium (Pd). The method may further include treating the surface of the Laves phase compound with an aqueous acid solution prior to forming the Cu layer. The method may further include subjecting the Laves phase compound to a homogenization treatment prior to treating the surface. The AMR bed according to the present invention includes the above-mentioned magnetic refrigeration material, thereby solving the above-mentioned problems. The magnetic refrigeration device according to the present invention includes the above-mentioned AMR bed, thereby solving the above-mentioned problems. Effect of the Invention

[0008] The magnetic refrigeration material according to the present invention comprises a Laves phase compound represented by the general formula RT2 (wherein R is at least one rare earth element, and T is at least one element selected from the group consisting of cobalt (Co), nickel (Ni), aluminum (Al), and iron (Fe)), and a barrier layer covering the surface of the compound, the barrier layer including a Cu layer made of copper (Cu) and a Ni layer made of nickel (Ni) located on the Cu layer. Since the Laves phase compound is the main component, the magnetic refrigeration material exhibits the maximum entropy change and has a desirable Curie temperature T CIt exhibits a large magnetocaloric effect for hydrogen liquefaction. Furthermore, by having a barrier layer consisting of a laminate of a Cu layer and a Ni layer on the surface, the hydrogen barrier resistance can be improved. Moreover, since the barrier layer is made of metal, the thermal conductivity performance is not impaired. Such a magnetic refrigeration material can be applied to an AMR bed and further provide a magnetic refrigeration device.

[0009] The manufacturing method of the above-mentioned magnetic refrigeration material according to the present invention includes forming a Cu layer made of copper (Cu) on the surface of a Laves phase compound represented by the general formula RT2 (wherein R is at least one rare earth element, and T is at least one element selected from the group consisting of cobalt (Co), nickel (Ni), aluminum (Al), and iron (Fe)), and forming a Ni layer made of nickel (Ni) on the Cu layer. Since existing techniques for forming metal films can be adopted, no special technique is required. In addition, since both Cu and Ni are easily available, it is possible to reduce costs and is advantageous for mass production. [Brief description of the drawings]

[0010] [Figure 1] Schematic diagram showing a magnetic refrigeration material according to the present invention. [Diagram 2] Schematic diagram showing the crystal structure of ErCo2 [Diagram 3] Schematic diagram showing another magnetic refrigeration material according to the present invention. [Figure 4] Schematic diagram showing another magnetic refrigeration material according to the present invention. [Diagram 5] A flow chart showing the steps of manufacturing the magnetic refrigeration material according to the present invention. [Figure 6] FIG. 13 is a schematic diagram showing a magnetic refrigeration device according to a second embodiment of the present invention; [Figure 7] Schematic diagram showing an AMR bed with multiple magnetic refrigeration materials [Figure 8] Schematic diagram showing the measurement device for hydrogen exposure testing [Figure 9] Figure showing the change in hydrogen pressure during hydrogen exposure testing using ErCo2 particles [Figure 10]Figure 1 shows an SEM image of the cross section of an ErCo2 particle after treatment with an acid aqueous solution. [Figure 11] FIG. 1 shows an SEM image of a cross section of the sample in Example 1. [Figure 12] FIG. 1 is an enlarged SEM image of a cross section of a sample in Example 1. [Figure 13] FIG. 1 shows an SEM image of a cross section of a sample of Example 3. [Figure 14] FIG. 1 is an enlarged SEM image of a cross section of a sample of Example 3. [Figure 15] Figure 1 shows a STEM image of the cross section of the sample in Example 1. [Figure 16] Graph showing hydrogen pressure change during hydrogen exposure test using the sample of Example 1 [Figure 17] Graph showing hydrogen pressure change during hydrogen exposure test using the sample of Example 2 [Figure 18] Graph showing hydrogen pressure change during hydrogen exposure test using the sample of Example 3 [Figure 19] FIG. 1 shows an SEM image of a cross section of the sample in Example 1 after a hydrogen exposure test. [Figure 20] FIG. 1 is an enlarged SEM image of a cross section of the sample in Example 1 after a hydrogen exposure test. [Figure 21] FIG. 1 shows a STEM image of the cross section of the sample in Example 1 after hydrogen exposure test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that like elements are given like reference numerals and their description will be omitted. (Embodiment 1) In the first embodiment, a magnetic refrigeration material and a manufacturing method thereof according to the present invention will be described.

[0012] FIG. 1 is a schematic diagram showing a magnetic refrigeration material according to the present invention. FIG. 2 is a schematic diagram showing the crystal structure of ErCo2.

[0013] The magnetic refrigeration material 100 of the present invention is mainly composed of Laves phase compound 110 represented by general formula RT2 (wherein R is at least one rare earth element, and T is at least one element selected from the group consisting of cobalt (Co), nickel (Ni), aluminum (Al), and iron (Fe)), and has a barrier layer 140 including a Cu layer 120 made of copper (Cu) that covers the Laves phase compound 110, and a Ni layer 130 made of nickel (Ni) located on the Cu layer 120. For ease of understanding, FIG. 1 shows a cross section of the magnetic refrigeration material 100 in the form of particles.

[0014] FIG. 2 shows the crystal structure of ErCo2, a Laves phase compound 110 in which R is erbium (Er) and T is cobalt (Co). The structure is MgCu2 type of Laves phase, and the lattice parameters are a=b=c=7.153 Å and α=β=γ=90°. In such a Laves phase, R and T metal elements with an atomic radius ratio of approximately 1.2:1 are bonded in a composition ratio of RT2 to form a compound. The crystal structure consisting of a large atom R and a small atom T is considered to be a packed structure of large and small spheres, and occupies specific lattice positions, R site and T site. The R site has four R and 12 T atoms as neighboring atoms, and the T site is surrounded by six R atoms and six T atoms. In a realistic Laves phase crystal, atomic packing is performed so that the RR atoms and TT atoms are in contact with each other, and there is no contact between the RT atoms. In such a case, the atomic radius ratio of both atoms is R. R / R T =√(3 / 2)=1.225. Generally, atoms arranged at the R site are arranged in a similar manner to the diamond structure, and atoms at the T site form tetrahedra around the R site. Since Laves phase compounds are a type of close-packed structure, there are three types of crystal structures due to differences in the stacking of atoms, similar to the difference between a face-centered cubic lattice and a hexagonal close-packed lattice: cubic MgCu2 type (C15), hexagonal MgZn2 type (C14), and MgNi2 type (C36).

[0015] In RAl2 (R = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu), where T is aluminum (Al), there is clearly a ferromagnetic exchange interaction between the magnetic moments of the rare earth metals in RAl2, but as in HoAl2, the obtained magnetic moment is lower than the theoretical moment value gI of the trivalent Ho ion.

[0016] For example, in RT2 (R = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb), the magnetic data of RNi2 (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm), RCo2 (R = Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu), and RFe2 (R = Ce, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu, Y) have already been investigated.

[0017] Thus, it is clear that ErCo2, ErNi2, ErAl2, ErFe2, etc. are not only MgCu2 type Laves phase intermetallic compounds, but also function as magnetic refrigeration materials. In addition, the laminated film of the Cu layer and Ni layer on the surface of these can have hydrogen barrier properties. In the following, ErCo2 will be particularly described, but it will be understood by those skilled in the art that the same applies to any of these Laves phase intermetallic compounds.

[0018] In this way, since the magnetic refrigeration material 100 of the present invention is mainly composed of the Laves phase compound 110, it exhibits the maximum entropy change and has a desirable Curie temperature T C and has a huge magnetocaloric effect for hydrogen liquefaction. Furthermore, by having the barrier layer 140 consisting of a laminate of the Cu layer 120 and the Ni layer 130, hydrides are not generated, pulverization is suppressed, and hydrogen barrier resistance can be improved. Furthermore, since the barrier layer 140 is made of metal, the thermal conductivity performance is not impaired.

[0019] As shown in Fig. 1, the magnetic refrigeration material 100 of the present invention preferably has a particle shape. This allows for increased heat exchange with gas or liquid when applied to a magnetic refrigeration device, which will be described later. Note that while Fig. 1 shows the magnetic refrigeration material 100 as a perfect sphere, it should be understood that this is a schematic diagram for ease of understanding, and that in reality the material is a sphere having various aspect ratios.

[0020] When the magnetic refrigeration material 100 of the present invention is in the form of particles, it is preferable that the particle size (average particle size) is in the range of 10 μm to 3000 μm. This makes it suitable for magnetic refrigeration devices. For example, the particle size may be 50 μm or more, 100 μm or more, or 200 μm or more, or 2000 μm or less, 1000 μm or less, or 500 μm or less, in a spherical approximation. In particular, when the magnetic refrigeration material 100 of the present invention has a particle size in the range of 200 μm to 400 μm, it is preferable because heat exchange can be maximized.

[0021] The average particle size is determined by measuring the particle sizes of 100 randomly selected particles in an image observed by a scanning electron microscope (SEM) using image analysis software. In this specification, Image J (ver. 1.51n; an open source, public domain image processing software) was used as the image analysis software.

[0022] Of course, in order to obtain high hydrogen barrier resistance, it is desirable for the barrier layer 140 to cover the entire surface of the Laves phase compound 110, but it is sufficient that the barrier layer 140 covers at least 80% of the surface area of ​​the Laves phase compound 110. This can improve the hydrogen barrier resistance.

[0023] The present inventors have discovered that hydrogen barrier resistance can be achieved by combining and laminating a Cu layer that does not have hydrogen barrier resistance with a Ni layer that has not been reported to have hydrogen barrier resistance.

[0024] The thickness of the Cu layer 120 may preferably satisfy the range of 1 μm or more and 20 μm or less. In this range, the adhesion to the Laves phase compound 110 is excellent, and the hydrogen barrier resistance can be improved. The thickness of the Cu layer 120 may more preferably satisfy the range of 1 μm or more and 10 μm or less. In this range, the adhesion to the Ni layer 130 is excellent, and the hydrogen barrier resistance can be further improved. The thickness of the Cu layer 120 may even more preferably satisfy the range of 3 μm or more and 7 μm or less. In this range, the adhesion to the Ni layer 130 is particularly excellent, and the hydrogen barrier resistance can be further improved.

[0025] The thickness of the Ni layer 130 may preferably satisfy the range of 0.2 μm or more and 20 μm or less. In this range, the adhesion to the Cu layer 120 is excellent and the hydrogen barrier resistance can be improved. The thickness of the Ni layer 130 may more preferably satisfy the range of 1 μm or more and 10 μm or less. In this range, the adhesion to the Cu layer 120 is excellent and the hydrogen barrier resistance can be further improved. The thickness of the Ni layer 130 may even more preferably satisfy the range of 1.5 μm or more and 4 μm or less. In this range, the adhesion to the Cu layer 120 is particularly excellent and the hydrogen barrier resistance can be further improved.

[0026] FIG. 3 is a schematic diagram showing another magnetic refrigeration material according to the present invention.

[0027] 3, the magnetic refrigeration material 300 of the present invention may further include an interface layer 310 between the Cu layer 120 and the Ni layer 130. The interface layer 310 can improve the adhesion between the Cu layer 120 and the Ni layer 130. The interface layer 310 preferably contains palladium (Pd) and tin (Sn). The presence of these materials on the Cu layer 120 promotes the generation of the Ni layer 130, and can improve the adhesion between the Cu layer 120 and the Ni layer 130.

[0028] From this viewpoint, in the present specification, "a Ni layer located on a Cu layer" refers not only to the case where a Ni layer is located directly on a Cu layer as shown in FIG. 1, but also to the case where a layered structure in which a Cu layer and a Ni layer are stacked in this order, but where an interface layer is provided between the Cu layer and the Ni layer as shown in FIG. 3.

[0029] The thickness of the interface layer 310 may preferably be in the range of 30 nm to 200 nm. This range may contribute to the adhesion between the Cu layer 120 and the Ni layer 130. The thickness of the interface layer 310 may more preferably be in the range of 50 nm to 150 nm. This range maintains the adhesion between the Cu layer 120 and the Ni layer 130 while exhibiting excellent hydrogen barrier resistance. The thickness of the interface layer 310 may even more preferably be in the range of 100 nm to 150 nm. This range maintains the adhesion between the Cu layer 120 and the Ni layer 130 while exhibiting even more excellent hydrogen barrier resistance.

[0030] In this specification, the thickness of the interface layer 310 is defined as the average value of thicknesses measured at any four points in an electron microscope image observed at an accelerating voltage of 200 kV and a magnification of 80,000.

[0031] FIG. 4 is a schematic diagram showing another magnetic refrigeration material according to the present invention.

[0032] 4, the magnetic refrigeration material 400 of the present invention may further include an oxygen-rich layer 410 between the Laves phase compound 110 and the barrier layer 140 (more specifically, the Cu layer 120). This allows organic contaminants and natural oxide films on the surface of the Laves phase compound 110 to be removed in the process of generating the oxygen-rich layer 410, making it easier to exhibit the original magnetic refrigeration characteristics. In addition, the oxygen-rich layer 410 improves the adhesion between the Laves phase compound 110 and the Cu layer 120, and improves the hydrogen barrier resistance.

[0033] More specifically, the oxygen-rich layer 410 is made of a material containing an R element, a T element, and an oxygen (O) element, and may be an oxide of the R element and the T element. Here, the R element and the T element are the same elements as those of the Laves phase compound 110.

[0034] In this specification, the oxygen-rich layer refers to a layer in which the concentration of oxygen atoms is 20 atomic % or more when the total of R element, T element and oxygen element is taken as 100 atomic % as measured by energy dispersive X-ray spectroscopy. If the oxygen atomic concentration is 20 atomic % or more, the crystal structure of the Laves phase compound cannot be maintained, so 20 atomic % is set as the lower limit.

[0035] The thickness of the oxygen-rich layer 410 may preferably satisfy the range of 3 μm or more and 20 μm or less. In this range, the adhesion between the Laves phase compound 110 and the Cu layer 120 can be further improved. The thickness of the oxygen-rich layer 410 may more preferably satisfy the range of 3 μm or more and 10 nm or less. In this range, the adhesion between the Laves phase compound 110 and the Cu layer 120 is maintained while the deterioration of the magnetic properties is suppressed. The thickness of the oxygen-rich layer 410 may even more preferably satisfy the range of 5 μm or more and 10 μm or less. In this range, the adhesion between the Laves phase compound 110 and the Cu layer 120 is maintained while the deterioration of the magnetic properties is further suppressed.

[0036] In this specification, the thicknesses of Cu layer 120, Ni layer 130, and oxygen-rich layer 410 are defined as the average values ​​of thicknesses measured at any four points in an electron microscope image observed at an accelerating voltage of 15 kV and a magnification of 2000 times.

[0037] Of course, the magnetic refrigeration material of the present invention may have both the interface layer 310 and the oxygen-rich layer 410 in addition to the barrier layer 140 made of the Cu layer 120 and the Ni layer 130, so as to have both excellent magnetic properties and hydrogen barrier resistance.

[0038] The thicknesses of the barrier layer 140, the interface layer 310 and the oxygen-rich layer 410 are preferably set so that the ratio of the volume of the barrier layer 140, the interface layer 310 and the oxygen-rich layer 410, if necessary, to the volume of the entire particles of the magnetic refrigeration materials 100, 300 and 400 is 3 / 4 or less. This makes it possible to suppress the deterioration of the magnetic properties while maintaining the hydrogen barrier properties.

[0039] Next, a method for producing the magnetic refrigeration material according to the present invention will be described. FIG. 5 is a flow chart showing the steps of producing the magnetic refrigeration material according to the present invention.

[0040] The process for producing the magnetic refrigeration material of the present invention includes the following steps. Step S510: A Cu layer 120 (FIG. 1) made of copper (Cu) is formed on the surface of a Laves phase compound 110 (FIG. 1) represented by a general formula RT2 (wherein R is at least one rare earth element, and T is at least one element selected from the group consisting of cobalt (Co), nickel (Ni), aluminum (Al), and iron (Fe)). Step S520: A Ni layer 130 (FIG. 1) made of nickel (Ni) is formed on the Cu layer.

[0041] The present inventors focused on the Laves phase compound represented by RT2 as a magnetic refrigeration material, and selected Cu, which has excellent electrical conductivity among many metals, as a coating. They were able to coat the Laves phase compound with a Cu layer with good adhesion. Furthermore, they found that when they coated the Cu layer with a Ni layer, which also has excellent electrical conductivity, the laminate of the Cu layer and the Ni layer functions as a barrier layer 140 (Fig. 1) that prevents hydrogen from penetrating, and they succeeded in manufacturing a magnetic refrigeration material with improved hydrogen barrier resistance. Each process will be described in detail.

[0042] The Laves phase compound represented by formula RT2 used in step S510 may be prepared by applying a gas atomization method, a mechanical method, or the like to an ingot obtained by a melting method, etc. Among them, the gas atomization method is preferable because it can obtain a particulate Laves phase compound having the above-mentioned particle size.

[0043] In steps S510 and S520, the method of forming the Cu layer and Ni layer is not particularly limited, but the Cu layer and Ni layer are preferably formed by electroless plating. This allows uniform Cu layer and Ni layer to be formed regardless of the shape of the Laves phase compound. In particular, even if there are defects such as gaps or unevenness on the surface of the Laves phase compound, the electroless plating method allows the Cu layer and Ni layer to be formed so as to fill the defects, resulting in a dense barrier layer.

[0044] The Cu layer is preferably formed to have a thickness in the range of 1 μm or more and 20 μm or less, more preferably 1 μm or more and 10 μm or less, and even more preferably 3 μm or more and 7 μm or less.

[0045] The Ni layer is preferably formed to have a thickness in the range of 0.2 μm or more and 20 μm or less, more preferably 1 μm or more and 10 μm or less, and even more preferably 1.5 μm or more and 5 μm or less.

[0046] If the Cu layer and Ni layer are within the above ranges, the above-mentioned barrier layer 140 (FIGS. 1, 2, and 3) can be formed. Those skilled in the art will understand that a Cu layer and Ni layer having a desired thickness can be formed by controlling conditions such as the plating time of the electroless plating method.

[0047] Prior to step S520, the surface of the Cu layer obtained in step S510 may be activated. Such activation promotes the formation of a Ni layer in the following step S520. A catalyst containing tin (Sn) and palladium (Pd) may be used for surface activation. For example, a two-liquid type catalysis method is known that uses a sensitizing solution containing tin chloride as Sn and an activating solution containing palladium chloride as Pd. This forms catalyst nuclei on the surface of the Cu layer, promotes the formation of the Ni layer, and allows the Cu layer and the Ni layer to adhere to each other via an interface layer 310 (FIG. 3) containing Pd and Sn.

[0048] Prior to step S510, the surface of the Laves phase compound may be treated with an acid solution. This removes organic contaminants and a natural acid film on the surface of the Laves phase compound, and also forms an oxygen-rich layer 410 (FIG. 4). If a Cu layer is formed on such an oxygen-rich layer 410, a dense Cu layer is formed.

[0049] The surface treatment is preferably an etching treatment using an aqueous acid solution such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, or hydrofluoric acid. This allows easy removal of organic contaminants and natural oxide films on the surface. Specifically, the Laves phase compound is immersed in an aqueous solution with a concentration in the range of 1% by volume to 10% by volume and held for 10 seconds or more. There is no particular upper limit, but the longer the holding time, the more the Laves phase compound itself is removed, so the upper limit may be 15 minutes, and more preferably, the time may be 10 seconds to 30 seconds. After the surface treatment, it is preferable to wash the compound with distilled water or the like.

[0050] Prior to the above-mentioned surface treatment, it is preferable to perform a homogenization treatment on the Laves phase compound, which can improve the magnetic properties of the Laves phase compound. For example, the Laves phase compound may be heat-treated in an inert atmosphere such as argon gas or in a vacuum at a temperature range of 700°C to 900°C for a period of 1 day to 10 days.

[0051] (Embodiment 2) In the second embodiment, a magnetic refrigeration device using the magnetic refrigeration material of the present invention described in the first embodiment will be described.

[0052] FIG. 6 is a schematic diagram showing a magnetic refrigeration apparatus according to the second embodiment.

[0053] The magnetic refrigeration device 600 of the present invention, which includes the magnetic refrigeration material 100 of the present invention described in the first embodiment, can be used to generate ultra-low temperatures, for example, liquefy hydrogen. The magnetic refrigeration device 600 of the present invention further includes an AMR bed 620 filled with the magnetic refrigeration material 100, a magnetic field application means 630 for applying a magnetic field thereto, a cooling stage 690 for cooling an object to be cooled by cold and hot, and a heat exchanger 640 for discharging heat generated by the magnetic refrigeration material in the AMR bed 620. Here, the magnetic refrigeration material 100 is the magnetic refrigeration material described in the first embodiment.

[0054] The magnetic field application means 630 can be any means for applying a magnetic field to the AMR bed 620, and it is practical to use a magnetic field with a strength of about 1 to 10 T (tesla), for example. A superconducting magnet, a permanent magnet, or the like can be adopted as the magnetic field application means 630. In addition, the relative position between the magnetic field application means 630 and the AMR bed 620 can be changed by a driving mechanism (not shown) to change the magnitude of the magnetic field applied to the AMR bed 620.

[0055] A pre-cooling stage 660 is provided on the high temperature side of the AMR bed 620, an 80K shield 670 is connected to the low temperature side of the pre-cooling stage 660, and a 300K shield 680 is connected to the high temperature side of the pre-cooling stage 660. Furthermore, a cooling stage 690 is provided on the low temperature side of the AMR bed 620, and a liquefaction vessel 650 is provided and thermally connected to the cooling stage 690. In other words, the liquefaction vessel 650 is the object to be cooled. In addition, an inlet and outlet for the heat transport refrigerant are provided in the AMR bed 620, and the heat transport refrigerant can flow back and forth inside the AMR bed 620 through the gaps in the magnetic refrigeration material 100.

[0056] A gas 610 to be liquefied (eg, hydrogen, helium (He), etc.) is supplied to the liquefaction vessel 650 from a tank (not shown).

[0057] The magnetic refrigeration device 600 of the present invention operates as follows, and can produce liquid hydrogen or gas-cool it.

[0058] First, a magnetic field is applied by the magnetic field application means 630 to the AMR bed 620 filled with the magnetic refrigeration material 100, thereby increasing the temperature of the magnetic refrigeration material 100.

[0059] Next, the heat transport refrigerant is caused to flow in a direction 600A from the low temperature end side to the high temperature end side of the AMR bed 620. The heat transport refrigerant exchanges heat with the magnetic refrigeration material 100 filled inside the AMR bed 620 and receives hot heat, while flowing through the gaps between the magnetic refrigeration material 100, and flows out from the high temperature end of the AMR bed 620. The heat transport refrigerant flowing out from the high temperature end of the AMR bed 620 flows through the pre-cooling stage 660 into the heat exchanger 640 that dissipates the hot heat, and excess heat is dissipated to the outside.

[0060] Then, the magnetic field of the AMR bed 620 filled with the magnetic refrigeration material 100 is removed (reduced), causing the temperature of the magnetic refrigeration material 100 to drop.

[0061] Next, the heat transport refrigerant is caused to flow in a direction 600B from the high temperature end side to the low temperature end side of the AMR bed 620. The heat transport refrigerant flows into the high temperature end of the AMR bed 620 through the pre-cooling stage 660, and while being cooled by heat exchange with the magnetic refrigeration material 100 filled inside, it flows through the gaps between the magnetic refrigeration material 100 and reaches the low temperature end of the AMR bed 620. The flow of the heat transport refrigerant is driven by a refrigerant driving means (not shown). The refrigerant driving means is not particularly limited as long as it can drive an oscillating flow that reciprocates the heat transport refrigerant in synchronization with the AMR cycle, and examples of the refrigerant driving means include a system that combines a piston, a blower and a valve.

[0062] When the temperature of the low-temperature end of the AMR bed 620 drops below the boiling point of liquid hydrogen (20 K at atmospheric pressure), the hydrogen gas supplied to the liquefaction vessel 650 is cooled by heat exchange with a cooling stage 690 provided on the low-temperature end side of the AMR bed 620, and is concentrated and liquefied.

[0063] This process is repeated to periodically liquefy and / or cool the gas within liquefying vessel 650 .

[0064] In FIG. 6, the magnetic refrigeration material 100 filled in the AMR bed 620 has been described as being a single magnetic refrigeration material 100 of the present invention. However, it goes without saying that the magnetic refrigeration material 300 and the magnetic refrigeration material 400 described in embodiment 1 may be provided in place of or together with the magnetic refrigeration material 100, and other magnetic refrigeration materials may be provided in addition to the magnetic refrigeration materials 100, 300, and 400 of the present invention.

[0065] FIG. 7 is a schematic diagram showing an AMR bed including multiple magnetic refrigeration materials.

[0066] As shown in Fig. 7, a plurality of different magnetic refrigeration materials 710, 720, 730, 740, and 750, including the magnetic refrigeration material of the present invention, can be filled in an AMR bed 620. The magnetic refrigeration materials 710, 720, 730, 740, and 750 are arranged in a space separated by a partition 760. The partition 760 may have any shape as long as it does not mix different materials and does not impede the flow of the heat transport refrigerants 600A and 600B (Fig. 6), and specific shapes include a mesh or a partition plate having fine holes.

[0067] By selecting the magnetic refrigeration materials 710-750 having different peak temperatures of magnetic entropy change, it is possible to achieve high magnetic refrigeration performance in a wider temperature range than when a single magnetic refrigeration material 100, 300, or 400 is used. When the AMR bed 620 is incorporated into the magnetic refrigeration device 600 and operated, it is effective to increase the refrigeration performance by sequentially arranging and filling the magnetic refrigeration materials 710-750 on the side corresponding to the high temperature side of the AMR bed 620 so that the peak temperature of the magnetic entropy change is high. The number of types of magnetic refrigeration materials having different peak temperatures to be combined is not particularly limited to the number shown in the schematic diagram of FIG. 7, and multiple appropriate materials can be combined in consideration of the characteristics of the temperature dependence of each magnetic entropy change. By sequentially arranging multiple magnetic refrigeration materials having different peak temperatures, i.e., multiple magnetic refrigeration materials having different optimal operating temperature ranges, in the order of the operating temperature ranges, multiple highly efficient thermal cycles are combined, making it possible to efficiently cool from high temperatures to extremely low temperatures of 20K or less.

[0068] There are no particular limitations on the other magnetic refrigeration materials to be combined with the magnetic refrigeration material 100 of the present invention, and by referring to the magnetic entropy change and Curie temperature of the other magnetic refrigeration materials, they can be appropriately combined with the magnetic refrigeration material 100 of the present invention. For example, when R in the magnetic refrigeration material 100 of the present invention is Er or Ho, it has a large magnetic entropy change at 15 K to 20 K, so that it is particularly effective for the purpose of hydrogen liquefaction to place this material in a position in the AMR bed that operates at about 20 K and combine it with other materials.

[0069] The present invention will now be described in detail with reference to specific examples, but it should be noted that the present invention is not limited to these examples. EXAMPLES

[0070] [Synthesis of ErCo2 particles] As raw materials, lump Er (3N, purity 99.9%) manufactured by Fujian Changting Golden Dragon Rare-Earth Co., Ltd. and lump Co (3N, purity 99.9%) manufactured by Sumitomo Metal Mining Co., Ltd. were weighed out to a molar ratio of Er:Co=1:2, and melted in a high-frequency melting furnace in argon to synthesize ErCo2. The obtained ErCo2 was identified by powder X-ray diffraction.

[0071] A cast ingot rod was made from the synthesized ErCo2. Using a free-fall type gas atomizing device manufactured by Nisshin Giken Co., Ltd., this cast ingot rod was used as an electrode and the tip was melted at high frequency up to about 1400℃. Argon pressurized to 1-5MPa was blown through a gas jet nozzle into the resulting falling molten metal flow, stirring and atomizing the molten metal flow. This resulted in the production of ErCo2 particles.

[0072] The obtained ErCo2 particles were wrapped in tantalum foil and placed in a stainless steel tube, and argon gas was sealed in the stainless steel tube at about 0.5 atmospheres. The sealed tube was placed in a muffle furnace and heated from room temperature at a rate of about 5°C / min. After reaching 850°C, the temperature was maintained for one week. After that, the power to the furnace was turned off and the tube was cooled to room temperature (homogenization treatment).

[0073] The ErCo2 particles thus obtained were observed under a scanning electron microscope (SEM, manufactured by JEOL Ltd., JSM-7000F) and found to be spherical with a diameter of several hundred μm. The average diameter was calculated using Image J and found to be 300 μm.

[0074] The ErCo2 particles thus obtained were subjected to a hydrogen exposure test. FIG. 8 is a schematic diagram showing a measurement device for the hydrogen exposure test.

[0075] A sample (approximately 0.5 g) is sealed in a sample cell and immersed in a hot water bath or kept at room temperature. Figure 8 shows the sample cell immersed in a hot water bath, but a hot water bath is not necessary for measurements at room temperature. The air in the sample cell was evacuated using a vacuum pump, and high-pressure hydrogen (H2, 12 atm) was introduced and sealed, and the pressure and temperature of the high-pressure hydrogen in the sample cell were examined over time. The pressure was measured by a pressure sensor in the piping between the sample cell and the high-pressure hydrogen inlet. The temperature was measured at three points: the upper (T1) and lower (T2) of the piping, and the sample cell (T3). Note that T1 and T2 were equal to room temperature. The results of the hydrogen exposure test measured in this way are shown in Figure 9.

[0076] FIG. 9 is a diagram showing the change in hydrogen pressure in a hydrogen exposure test when ErCo2 particles are used.

[0077] According to Fig. 9, the hydrogen pressure after injection (1.268 MPa) decreased to 1.17 MPa within a few minutes and then remained almost constant, reaching 1.007 MPa after 27 hours. This indicated that the ErCo2 particles themselves did not have hydrogen barrier properties and hydrogenation proceeded rapidly.

[0078] [Example 1: Magnetic refrigeration material with barrier layer (Cu layer / Ni layer)] In Example 1, a magnetic refrigeration material having a barrier layer in which a Cu layer and a Ni layer were laminated on the surface of an ErCo2 particle was produced according to the flow chart shown in FIG.

[0079] The homogenized ErCo2 particles were immersed in a 4% by volume aqueous hydrochloric acid solution (25°C) for 20 seconds to acid-treat the surface. After the acid treatment, the particles were washed with distilled water, placed in a dryer at 70°C, and left in an air atmosphere for 6 hours or more to dry. The cross-section of the ErCo2 particles after the acid treatment was cut and observed with a scanning electron microscope (SEM, JEOL Ltd., JSM-7000F) equipped with an energy dispersive spectroscopy (EDS) device to perform composition analysis. The results are shown in Figure 10.

[0080] FIG. 10 is a diagram showing an SEM image of a cross section of an ErCo2 particle after the acid aqueous solution treatment.

[0081] FIG. 10(B) shows an enlarged view of the rectangular region in FIG. 10(A). In FIG. 10(A), a dark region was observed outside the lightly-illustrated region of the ErCo2 particle. A composition analysis of the lightly-illustrated region (1) showed Er: 60.06 atomic %, Co: 31.56 atomic %, and oxygen: 8.38 atomic %, which matched ErCo2. The small amount of oxygen detected was thought to be due to a natural oxide film generated by an oxidation reaction between oxygen in the air and the Er and Co on the surface when the cut surface was exposed to air. On the other hand, a composition analysis of the darkly-illustrated region (2) showed Er: 34.86 atomic %, Co: 22.69 atomic %, and oxygen: 42.45 atomic %, which did not match ErCo2 and was found to be an oxygen-rich layer. The average thickness of the oxygen-rich layer was 7.0 μm.

[0082] Next, the electroless Cu plating solution shown in Table 1 was prepared, and the ErCo2 particles after the surface acid treatment were immersed for 90 minutes to form a Cu layer made of Cu (step S510 in FIG. 5). Next, the surface of the ErCo2 particles on which the Cu layer was formed was activated using a two-liquid type catalysis method. In detail, the ErCo2 particles on which the Cu layer was formed were first immersed in a sensitizing solution (tin chloride (SnCl2): 1.0 g / L + hydrochloric acid 1 mL / L) for 60 seconds. Next, after washing with distilled water, they were immersed in an activating solution (palladium chloride (PdCl2): 0.1 g / L + hydrochloric acid 1 mL / L) for 60 seconds. This allowed the surface to support catalytic nuclei for nickel plating.

[0083] Next, the electroless Ni plating solution shown in Table 2 was prepared, and the ErCo2 particles carrying the catalytic cores were immersed in the solution for 90 minutes to form a Ni layer (Step S520 in FIG. 5). The sample thus obtained is referred to as the sample of Example 1.

[0084] A cross section of the sample of Example 1 was cut and observed by SEM, and a composition analysis was performed by EDS. The details of the sample of Example 1 were observed by a scanning transmission electron microscope (STEM, manufactured by JEOL Ltd., JEM-2100F). A hydrogen exposure test was performed on the sample of Example 1 in a warm water bath (35°C). A cross section of the sample of Example 1 after the hydrogen exposure test was cut and observed by SEM, and STEM observation and EDS analysis were performed. These results are shown in Figures 11, 12, 15, 16, 19 to 21, and Table 3.

[0085] [Example 2: Magnetic refrigeration material with barrier layer (Cu layer / Ni layer)] In Example 2, another magnetic refrigeration material having a barrier layer in which a Cu layer and a Ni layer are laminated on the surface of an ErCo2 particle was manufactured according to the flow chart shown in FIG. 5. Example 2 was the same as Example 1 except that the activation treatment using tin / palladium was not performed before the formation of the Ni layer. The sample obtained in this manner is referred to as the sample of Example 2. For the sample of Example 2, surface observation, elemental analysis, and hydrogen exposure test were performed in the same manner as in Example 1. The results are shown in FIG. 17 and Table 3.

[0086] [Example 3: Magnetic refrigeration material with a Cu layer] In Example 3, a magnetic refrigeration material having a Cu layer on the surface of ErCo2 particles was produced. Example 3 was the same as Example 1, except that the activation treatment using tin / palladium and the subsequent formation of a Ni layer were not performed. The sample obtained in this manner is referred to as the sample of Example 3. For the sample of Example 3, surface observation, elemental analysis, and hydrogen exposure test were performed in the same manner as in Example 1. These results are shown in Figures 13, 14, 18, and Table 3.

[0087] [Table 1]

[0088] [Table 2]

[0089] [Table 3]

[0090] The above results will be summarized. FIG. 11 is a diagram showing an SEM image of a cross section of the sample of Example 1. FIG. 12 is an enlarged SEM image of a cross section of the sample of Example 1. FIG. 13 is a diagram showing an SEM image of a cross section of the sample of Example 3. FIG. 14 is an enlarged SEM image of a cross section of the sample of Example 3.

[0091] According to Fig. 11, it was confirmed that the sample of Example 1 was a particle having a coating of several tens of micrometers on the outermost surface, and that the coating covered 80% or more of the particle surface area. According to Fig. 12 and EDS, it was confirmed that the coating was an oxygen-rich layer, a Cu layer, and a Ni layer from the inside of the particle. Although not shown, the sample of Example 2 had a similar appearance.

[0092] The thicknesses of the oxygen-rich layer, Cu layer, and Ni layer of the sample of Example 1 were 7.0 μm, 3.95 μm, and 2.68 μm, respectively. The thicknesses of the oxygen-rich layer, Cu layer, and Ni layer of the sample of Example 2 were estimated to be 7.0 μm, 5.9 μm, and 2.0 μm, respectively, based on the plating conditions of the sample of Example 1. It was confirmed that the volume ratio of the Cu layer / Ni layer and the oxygen-rich layer to the total volume of the particle was 3 / 4 or less.

[0093] According to Fig. 13, it was confirmed that the sample of Example 3 was a particle having a coating of about 10 μm thickness on the outermost surface. According to Fig. 14 and EDS, it was confirmed that the coating was an oxygen-rich layer and a Cu layer from the inside of the particle. The thicknesses of the oxygen-rich layer and the Cu layer of the sample of Example 3 were 7.0 μm and 4.0 μm, respectively.

[0094] This shows that by carrying out the method of the present invention according to the flowchart in Figure 5, a magnetic refrigeration material can be produced which comprises a Laves phase compound represented by the general formula RT2 (wherein R is at least one rare earth element, and T is at least one element selected from the group consisting of cobalt (Co), nickel (Ni), aluminum (Al), and iron (Fe)), such as ErCo2, and a barrier layer covering the surface of the compound, which is made of a Cu layer and a Ni layer located on the Cu layer.

[0095] FIG. 15 is a diagram showing a STEM image of a cross section of the sample of Example 1.

[0096] Figure 15(B) shows an enlarged view of the rectangular area shown in Figure 15(A). Figures 15(A) and (B) show that in the sample of Example 1, the Cu layer and the Ni layer are in close contact with each other via an interface layer. EDS also shows that the interface layer contains Pd and Sn as main components. The thickness of the interface layer is 135 nm.

[0097] On the other hand, according to the STEM image (not shown) of the cross section of the sample of Example 2, the Cu layer and the Ni layer were in close contact, but there was no interface layer. This indicates that the interface layer was formed by surface activation using the Pd / Sn catalyst. In addition, the thickness of the Ni layer in Table 3 indicates that the presence of the interface layer promotes the formation of the Ni layer.

[0098] FIG. 16 is a diagram showing the change in hydrogen pressure in a hydrogen exposure test when the sample of Example 1 was used. FIG. 17 is a diagram showing the change in hydrogen pressure in a hydrogen exposure test when the sample of Example 2 was used. FIG. 18 is a diagram showing the change in hydrogen pressure in a hydrogen exposure test when the sample of Example 3 was used.

[0099] According to Fig. 16, when the sample of Example 1 having a Cu / Ni barrier layer and a PdSn interface layer was used, the hydrogen pressure after sealing (1.28 MPa) decreased slightly over time, but was maintained at 1.257 MPa even after 144 hours, indicating excellent hydrogen barrier properties. The amount of reacted hydrogen in the sample of Example 1 was only 11.6% of that in the ErCo2 particles used as the raw material that had only been homogenized before the barrier layer coating.

[0100] According to Fig. 17, when the sample of Example 2 having a Cu / Ni barrier layer was used, the hydrogen pressure after sealing (1.281 MPa) increased and decreased corresponding to the change in the outside air temperature at T1 and T2, but was maintained at 1.277 MPa even after 151 hours, indicating excellent hydrogen barrier properties. The amount of reacted hydrogen in the sample of Example 2 was only 2.1% of that in the ErCo2 particles used as the raw material that had only been homogenized before being coated with the barrier layer. The results of Fig. 16 and Fig. 17 show that the PdSn interface layer between the Cu and Ni layers is not essential, but is effective in promoting the formation of the Ni layer.

[0101] According to Fig. 18, when the sample of Example 3 having a Cu layer was used, the hydrogen pressure after sealing (1.271 MPa) decreased to 1.12 MPa within a few hours and then became almost constant, and did not show hydrogen barrier resistance. The amount of reacted hydrogen in the sample of Example 3 was 81% of that in the ErCo2 particles that were homogenized only before being coated with Cu, which was used as the raw material.

[0102] The results of FIG. 9 and FIG. 16 to FIG. 18 show that hydrogen barrier resistance is dramatically improved by covering a Laves phase compound such as ErCo2 with a barrier layer in which a Cu layer and a Ni layer located on the Cu layer are laminated. From the results of the hydrogen exposure test of the sample of Example 3 having a Cu layer, it is clear that the Cu layer does not have hydrogen barrier resistance. Furthermore, there has been no report to date that Ni metal has hydrogen barrier resistance. In this way, the inventors of the present application have succeeded in expressing hydrogen barrier resistance by intentionally combining and laminating metal materials that do not have hydrogen barrier resistance.

[0103] FIG. 19 is a diagram showing an SEM image of a cross section of the sample of Example 1 after the hydrogen exposure test. FIG. 20 is an enlarged SEM image of the cross section of the sample of Example 1 after the hydrogen exposure test. FIG. 21 is a diagram showing a STEM image of a cross section of the sample of Example 1 after the hydrogen exposure test.

[0104] 19 and 20 and Fig. 11 and 12, the state of the sample of Example 1 did not change even after the hydrogen exposure test, and the laminated structure of the barrier layer of the Cu layer and the Ni layer was maintained. Although not shown, the sample of Example 2 also did not change before and after the hydrogen exposure test.

[0105] According to FIG. 21, even after the hydrogen exposure test, the Cu layer and the Ni layer in the sample of Example 1 were well adhered to each other through the interface layer. Furthermore, according to EDS, the interface layer contained Pd and Sn as main components, and did not change even after the hydrogen exposure test. From this, the barrier layer between the Cu layer and the Ni layer of the magnetic refrigeration material of the present invention maintains a metallic state even after the hydrogen exposure test, and unlike an oxide layer, can have high thermal conductivity. If such a magnetic refrigeration material is used in a magnetic refrigeration device, the heat exchange efficiency can be improved. [Industrial Applicability]

[0106] The magnetic refrigeration material of the present invention is resistant to hydrogenation and can withstand long-term use. Such a magnetic refrigeration material is used in magnetic refrigeration devices and effectively functions for liquefying hydrogen, etc. This can contribute to the widespread use of hydrogen, which is a promising energy carrier. [Explanation of symbols]

[0107] 100, 300, 400, 710, 720, 730, 740, 750 Magnetic refrigeration materials 110 Laves phase compound 120 Cu layer 130 Ni layer 140 Barrier Layer 310 Interface layer 410 Oxygen-rich layer 600 Magnetic Refrigeration Unit 610 Gas 620 AMR Bed 630 Magnetic field application means 640 heat exchanger 650 Liquefaction vessel 660 Pre-cooling stage 670 80K Shield 680 300K Shield 690 Cooling Stage 760 Partition

Claims

1. General formula RT ２ A Raves phase compound represented by (wherein R is at least one rare earth element, and T is at least one element selected from the group consisting of cobalt (Co), nickel (Ni), aluminum (Al), and iron (Fe), A barrier layer comprising a Cu layer made of copper (Cu) and a Ni layer made of nickel (Ni) located on the Cu layer, which coats the Laves phase compound. A magnetic refrigeration material equipped with the following features.

2. The magnetic refrigeration material according to claim 1, wherein the thickness of the Cu layer is in the range of 1 μm or more and 20 μm or less.

3. The magnetic refrigeration material according to claim 2, wherein the thickness of the Cu layer is in the range of 3 μm or more and 7 μm or less.

4. The magnetic refrigeration material according to claim 1, wherein the thickness of the Ni layer is in the range of 0.2 μm or more and 20 μm or less.

5. The magnetic refrigeration material according to claim 4, wherein the thickness of the Ni layer is in the range of 1.5 μm or more and 4 μm or less.

6. The magnetic refrigeration material according to claim 1, further comprising an oxygen-rich layer between the Laves phase compound and the barrier layer.

7. The magnetic refrigeration material according to claim 6, wherein the thickness of the oxygen-rich layer is in the range of 3 μm to 20 μm.

8. The magnetic refrigeration material according to claim 7, wherein the thickness of the oxygen-rich layer is in the range of 5 μm or more and 10 μm or less.

9. The magnetic refrigeration material according to claim 1, further comprising an interface layer containing palladium (Pd) and tin (Sn) at the interface between the Cu layer and the Ni layer.

10. The magnetic refrigeration material according to claim 9, wherein the thickness of the interface layer is in the range of 30 nm to 200 nm.

11. The magnetic refrigeration material according to claim 10, wherein the thickness of the interface layer is in the range of 50 nm to 150 nm.

12. The magnetic refrigeration material according to claim 1, wherein the particles have a particle size in the range of 10 μm to 3000 μm.

13. General formula RT ２ Forming a Cu layer made of copper (Cu) on the surface of a Laves phase compound represented by (wherein R is at least one rare earth element, and T is at least one element selected from the group consisting of cobalt (Co), nickel (Ni), aluminum (Al), and iron (Fe)), A nickel (Ni) layer is formed on the Cu layer. A method for producing a magnetic refrigeration material according to any one of claims 1 to 12, comprising:

14. The method according to claim 13, wherein the Cu layer and the Ni layer are formed by an electroless plating method.

15. The method according to claim 13, further comprising activating the surface of the Cu layer prior to forming the Ni layer.

16. The method according to claim 15, wherein the activation is performed using a catalyst containing tin (Sn) and palladium (Pd).

17. The method according to claim 13, further comprising treating the surface of the Laves phase compound with an acidic aqueous solution prior to forming the Cu layer.

18. The method according to claim 17, further comprising homogenizing the Raves phase compound prior to treating the surface.

19. An AMR bed comprising a magnetic refrigeration material according to any one of claims 1 to 12.

20. A magnetic refrigeration system equipped with an AMR bed, The AMR bed is the AMR bed described in claim 19, in a magnetic refrigeration apparatus.

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