Cold storage medium, cold storage apparatus, and cryogenic refrigerator

Abstract

Provided is a cold storage medium for a cryogenic refrigerator, wherein, in order to reduce the amount of use of rare earth metals such as Ho and Er, a cold storage medium (15) for a cryogenic refrigerator contains a crystal of CuFe1-xMxO2 (M is a metal element other than Fe), and, in a temperature region of 10 K or less, CuFe1-xMxO2 is antiferromagnetic and has higher volume specific heat than lead.

Description

Cool storage material, cool storage unit, and cryogenic refrigerator

[0001] The present invention relates to a regenerator material, a regenerator, and a cryogenic refrigerator.

[0002] A Gifford-McMahon (GM) refrigerator is known as an example of a cryogenic refrigerator capable of cooling an object to a low temperature (e.g., 4.2 K, the temperature of liquid helium). The GM refrigerator includes a compressor that compresses helium gas and a regenerator material that exchanges heat with the compressed helium gas, and realizes the low-temperature environment described above by expanding the helium gas cooled by the regenerator material. Other examples of cryogenic refrigerators that can use the same regenerator material as the GM refrigerator include a Stirling refrigerator and a pulse tube refrigerator. These cryogenic refrigerators are classified as regenerator refrigerators. These cryogenic refrigerators are also sometimes simply referred to as low-temperature refrigerators or low-temperature regenerator refrigerators.

[0003] A material used as a regenerator for generating low temperatures is required to have a relatively large specific heat even in a low temperature range (for example, a temperature range of 4.2 K or more and 10 K or less).

[0004] For example, lead is known as a material with a relatively large specific heat in the low temperature range. However, because the specific heat of lead is due to lattice vibration, the lower the temperature (the closer to 4.2 K), the lower the specific heat of lead. In addition, the use of lead in electrical appliances is now prohibited in principle. Therefore, bismuth alloys are used as a substitute for lead in current regenerator materials. The specific heat of bismuth alloys, like that of lead, is due to lattice vibration, so the lower the temperature, the lower the specific heat. In addition, the specific heat of bismuth alloys is lower than that of lead. Note that the specific heat used in this specification refers to volumetric specific heat, which is the specific heat per volume.

[0005] Therefore, in order to obtain the specific heat in the above-mentioned low temperature range, the specific heat caused by the magnetic phase transition (hereinafter referred to as magnetic specific heat) is utilized in the regenerator material. Materials that exhibit the magnetic phase transition in the above-mentioned low temperature range include HoCu ２ Ya, Er ３For example, the problem to be solved by the invention of Patent Document 1 is that of the rare earth intermetallic compounds such as HoCu ２ and Er ３ Patent Document 1 also mentions a regenerator material filled with a laminate of R １－ｘ (Ge １－ｙ M ｙ ) ｘ (wherein R represents at least one rare earth element selected from Y, La, Ce, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, M represents at least one element selected from Ag, Au, Al, Ga, In, Sn, Bi, Pd, Pt, Zn, Rh, Ir, Ru, Mn, Cr, Mo, W, V, Nb, Ta, Ti, Zr and Hf, and x and y respectively satisfy the atomic ratios of 0.1≦x≦0.8 and 0≦y≦0.5.) Patent Document 2 also describes a cold storage material using a magnetic substance represented by the formula: (wherein R represents at least one rare earth element selected from Y, La, Ce, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, M represents at least one element selected from Ag, Au, Al, Ga, In, Sn, Bi, Pd, Pt, Zn, Rh, Ir, Ru, Mn, Cr, Mo, W, V, Nb, Ta, Ti, Zr and Hf, and x and y respectively satisfy the atomic ratios of 0.1≦x≦0.8 and 0≦y≦0.5.) Patent Document 2 also describes a cold storage material using ErIn as a material for a cold storage material that utilizes magnetic specific heat. ３ is exemplified.

[0006] The magnetic phase transition temperatures of these rare earth intermetallic compounds exist in the low temperature region described above. Therefore, in these rare earth intermetallic compounds, the magnetic specific heat remains even in the low temperature region. Furthermore, the magnetism in these rare earth intermetallic compounds is mediated by the spin of the 4f electrons that constitute the rare earth metals, such as Ho and Er. The 4f electrons of rare earth metals can have a large magnetic moment due to the number of unpaired electrons in their outermost shells. Therefore, in rare earth intermetallic compounds, by appropriately selecting the combination of rare earth metals and transition metals, it is possible to maintain a large magnetic specific heat even in the low temperature region.

[0007] Japanese Unexamined Patent Publication No. 2004-143341 Japanese Unexamined Patent Publication No. 11-108479

[0008] However, since the rare earth metals contained in the rare earth intermetallic compounds are rare, they tend to be more expensive than transition metals, and the use of rare earth intermetallic compounds as regenerator materials is one factor that increases the manufacturing costs of GM refrigerators.

[0009] One aspect of the present invention has been made in consideration of the above-mentioned problems, and its object is to reduce the amount of rare earth metals, such as Ho and Er, used in a regenerator material for a cryogenic refrigerator, such as a GM refrigerator.

[0010] In order to solve the above problems, a regenerator material according to one aspect of the present invention is a regenerator material containing CuFe １－ｘ M ｘ O ２ (M is a metal element other than Fe) crystals. １－ｘ M ｘ O ２ In the temperature range below 10K, CuFe １－ｘ M ｘ O ２ The material has antiferromagnetic properties and a volumetric specific heat, which is the specific heat per volume, greater than that of lead.

[0011] In order to solve the above-mentioned problems, a regenerator according to one aspect of the present invention includes a regenerator material according to one aspect of the present invention.

[0012] In order to solve the above-mentioned problems, a cryogenic refrigerator according to one aspect of the present invention includes a regenerator according to one aspect of the present invention.

[0013] According to one aspect of the present invention, the amount of rare earth metals such as Ho and Er used in the regenerator material constituting the cryogenic refrigerator can be reduced.

[0014] 1 is a conceptual diagram of a Gifford-McMahon refrigerator according to a first embodiment of the present invention. １－ｘ Al ｘ O ２ Magnetic phase diagram of CuFe １－ｘ Ga ｘ O ２ 1 is a magnetic phase diagram of a CuFe alloy according to a fourth embodiment of the present invention; ０．９８ Al ０．０２ O ２ The pellet-shaped CuFe alloy before the pulverization step shown in FIG. ０．９８ Al ０．０２ O ２ This is an image of the fourth embodiment of the present invention, CuFe０．９８ Al ０．０２ O ２ The powdered CuFe after the pulverization step shown in FIG. ０．９８ Al ０．０２ O ２ 1 is an image of a CuFe pellet according to each example of the present invention. １－ｘ Al ｘ O ２ The bottom row of FIG. 7 shows the X-ray diffraction pattern of CuFeO ２ The calculated X-ray diffraction pattern of the polycrystal of CuFe powder according to each example of the present invention is also shown. １－ｘ Al ｘ O ２ 8 is a graph showing the temperature dependence of the specific heat of lead. The second embodiment and the lead-based regenerator material, the fourth embodiment and the lead-based regenerator material, and the HoCu regenerator material are shown in FIG. 8. ２ 10 is a graph showing the temperature dependence of the cooling capacity of a cold accumulator made of lead and a cold accumulator made of lead. ２ 1 is a graph showing the temperature dependence of the cooling capacity of a regenerator material made of lead and a regenerator material made of lead.

[0015] [First embodiment] <Gifford-McMahon refrigerator> A Gifford-McMahon (GM) refrigerator 10 according to a first embodiment of the present invention will be described with reference to Figs. 1 to 3. The GM refrigerator 10 has the same configuration as existing Gifford-McMahon refrigerators, except for a regenerator material 15, which will be described later. Therefore, in this embodiment, only a brief description of the GM refrigerator 10 will be given. Fig. 1 is a conceptual diagram of the GM refrigerator 10. Figs. 2 and 3 each show a CuFe １－ｘ Al ｘ O ２ and CuFe １－ｘ Ga ｘ O ２ Magnetic phase diagram of multiferroic delafossite CuFe 1-y Ga yO2N. Terada, T. Nakajima, S. Mitsuda and H. Kitazawa, J. Phys. Conference Series 145 012071 (2009)). The Gifford-McMahon refrigerator is an example of a cryogenic refrigerator. Other examples of cryogenic refrigerators include a Stirling refrigerator and a pulse tube refrigerator. These cryogenic refrigerators are classified as regenerative refrigerators. These cryogenic refrigerators are also sometimes simply called low-temperature refrigerators or low-temperature regenerative refrigerators.

[0016] As shown in FIG. 1 , the GM refrigerator 10 includes a compressor 11 and a regenerator 12. The regenerator 12 includes a pair of stoppers 13 and 14 and a regenerator material 15. Since FIG. 1 is a conceptual diagram, only the final-stage regenerator 12 is shown. However, the GM refrigerator 10 may include one or more additional regenerators disposed before the regenerator 12. The specific configuration of the GM refrigerator is described in, for example, Patent Document 2 (e.g., FIG. 1 ). Therefore, a detailed description of the GM refrigerator will be omitted here. The regenerator material 15 of the GM refrigerator 10 corresponds to the regenerator material 24 of the GM refrigerator described in Patent Document 2.

[0017] The compressor 11 has a pair of ports P1 and P2. The port P1 is a port for discharging compressed helium (He) gas. The port P2 is a port to which the He gas to be compressed is supplied.

[0018] Ports P1 and P2 are both connected to the regenerator 12. The two cylinders shown in Fig. 1 represent the relationship in pressure between the He gas upstream and downstream of the regenerator 12. The cylinder on the left side in Fig. 1 represents the image of He gas compressed by the compressor 11 being supplied. The cylinder on the right side in Fig. 1 represents the image of He gas expanded in the downstream of the regenerator 12 returning to the compressor 11. In other words, compressed high-pressure He gas is supplied to the regenerator 12, and the He gas expands in the downstream of the regenerator 12, reducing its pressure.

[0019] The regenerator 12 is a cylindrical member having openings at both ends. Each of the openings at both ends is provided with a pair of stoppers 13, 14. Each of the pair of stoppers 13, 14 is configured to block the regenerator material 15 while allowing He gas to pass through.

[0020] The inside of the regenerator 12 is filled with powdered regenerator material 15. The GM refrigerator 10 is designed so that the diameter of each hole provided in the pair of stoppers 13, 14 is smaller than the particle diameter of the material composing the regenerator material 15. Therefore, the regenerator material 15 is confined inside the regenerator 12. In this way, the regenerator 12, together with the pair of stoppers 13, 14, functions as a housing that houses the regenerator material 15.

[0021] <Regenerator Material> The regenerator material 15 is a regenerator material for a cryogenic refrigerator. In this embodiment, a Gifford-McMahon refrigerator is used as an example of a cryogenic refrigerator. However, the regenerator material 15 can also be applied to other examples of cryogenic refrigerators, such as a Stirling refrigerator and a pulse tube refrigerator. The regenerator material 15 is made of CuFe １－ｘ M ｘ O ２ (M is a metal element other than Fe) crystals. In the temperature range below 10K, CuFe １－ｘ M ｘ O ２ exhibits antiferromagnetism and is configured so that its specific heat is greater than that of lead. Note that the specific heat used below is volumetric specific heat, which is the specific heat per volume. Furthermore, the term "crystal" includes both single crystal and polycrystal. Therefore, CuFe １－ｘ M ｘ O ２ The regenerator material 15 may be either single crystal or polycrystalline. The regenerator material 15 is an aspect of the present invention, similar to the GM refrigerator 10.

[0022] In the cold storage material 15, M is preferably at least one of Al, Ga, Mn, and Rh. More preferably, in the cold storage material 15, M is Al, and the amount x of Fe substituted by M satisfies 0≦x≦0.2.

[0023] In this embodiment, CuFe １－ｘ M ｘ O ２ The particle diameter is measured by optically observing the appearance of the particles to obtain an image of the particles, and then calculating the particle diameter by image analysis of the image. An example of such a particle diameter measurement device is the dynamic imaging particle size distribution analyzer (QICPIC). QICPIC randomly selects particles to be observed from a group of particles, obtains an image of the selected particles, and performs image analysis. In this image analysis, the volume of the particle is calculated, a sphere having the calculated volume is assumed, and the diameter of the sphere is calculated. In other words, QICPIC derives the diameter by converting the shape of an amorphous particle into a roughly spherical shape by volume. Note that CuFe １－ｘ M ｘ O ２ The shape and diameter of the particles vary. Therefore, it is preferable to perform the above-described image analysis on a plurality of particles and use a representative value (average value) of the obtained diameters as the particle diameter. The number of particles to be subjected to image analysis is not limited, but in this embodiment, 100 or more particles are used. １－ｘ M ｘ O ２ When measured using this measurement method, the particle diameter of the powder is preferably 180 μm or more and 500 μm or less.

[0024] In the regenerator material 15, the substitution amount x may be x = 0. That is, in one embodiment of the present invention, the general formula CuFe １－ｘ M ｘ O ２ The compound represented by the formula: CuFeO ２ Alternatively, CuFeO ２ CuFe containing １－ｘ M ｘ O ２ It may be a single crystal or a polycrystal.

[0025] The regenerator material 15 is made of the above-mentioned CuFe １－ｘ M ｘ O ２As will be described in the examples below, CuFe in one embodiment of the present invention may further contain a second compound having a Neel temperature in the temperature range of 5 K or more and 10 K or less. １－ｘ M ｘ O ２ The specific heat of CuFe is larger than that of lead in the temperature range below 10K, but in the temperature range around 5K, １－ｘ M ｘ O ２ Therefore, in order to obtain a specific heat in the temperature range around 5 K, the second compound is changed to CuFe １－ｘ M ｘ O ２ It is preferable to combine the first and second compounds. Furthermore, when the cold storage material 15 contains a first compound and a second compound, the first compound and the second compound may be filled together in a single cold storage unit, or each may be filled in a separate cold storage unit. In other words, the cold storage unit 12 containing the cold storage material 15 may be a single cold storage unit, or multiple cold storage units each containing a different compound. Furthermore, when the cold storage material 15 contains a first compound and a second compound, the cold storage material containing the first compound is an example of a first cold storage material, and the cold storage material containing the second compound is an example of a second cold storage material. In this case, it is preferable that the second cold storage material be arranged at a lower temperature than the first cold storage material. By arranging the first and second cold storage materials in this order, the He gas discharged from the compressor 11 is first heat-exchanged by the first cold storage material, and then heat-exchanged by the second cold storage material.

[0026] An example of the second compound is Gd ２ O ２ Examples include S.

[0027] As described above, the cold storage material 15 may contain the second compound, but may also contain a third compound or a metal equivalent thereto. The third compound or the metal equivalent thereto preferably does not contain a rare earth metal. A cold storage material containing the third compound or a metal equivalent thereto is an example of a third cold storage material. In this case, the third cold storage material is preferably arranged on a higher temperature side than the first cold storage material, and the second cold storage material is preferably arranged on a lower temperature side than the first cold storage material. That is, the first cold storage material, the second cold storage material, and the third cold storage material are preferably arranged in this order from the higher temperature side to the lower temperature side: the third cold storage material, the first cold storage material, and the second cold storage material. Examples of the third compound or a metal equivalent thereto include lead (Pb), bismuth (Bi), and a bismuth alloy. The composition of the bismuth alloy is not limited, but examples of metals other than bismuth contained in the bismuth alloy include antimony and tin. The amount of metals other than bismuth contained in the bismuth alloy is not limited, but an example of the content of antimony relative to the entire bismuth alloy is 5% or more and 10% or less. The bismuth alloy may also contain trace amounts of additive elements in addition to the antimony and tin described above. A bismuth alloy constructed in this way can have a higher hardness than bismuth, but on the other hand, it is thought that the specific heat will be lower.

[0028] (Regarding Metal Elements) FIGS. 2 and 3 show CuFe, １－ｘ Al ｘ O ２ and CuFe １－ｘ Ga ｘ O ２ 2 and 3, the magnetic phase diagram of CuFeO where x=0 is a function of the amount of Fe substituted by M and temperature. ２has a magnetic phase with a low specific heat capacity called the 4SL phase (4-sublattice antiferromagnetic phase) in the temperature range below 11 K. When Al is used as M and the substitution amount x is 0.005≦x≦0.027, a phase transition from the 4SL phase to the FEIC (ferroelectric incommensurate) phase with a high specific heat capacity occurs at temperatures between 4.2 K and 10 K, depending on the amount of x (see Figure 2). By utilizing the increase in specific heat capacity below 10 K due to this small amount of Al substitution, the regenerator material 15 ensures its performance as a regenerator material. However, as described below, a specific heat gain due to magnetic specific heat can be obtained even if the substitution amount x is 0.027<x. Therefore, the substitution amount x may be 0.027<x. In the examples described with reference to Fig. 5 to Fig. 10, when the substitution amount x is gradually increased from x = 0 to x = 0.2, the peak value of the specific heat decreases as x increases, but the base of the specific heat peak spreads toward the low temperature side (see Fig. 8). According to Fig. 8, when the specific heat when x = 0 is used as the reference, if emphasis is placed on the specific heat gain near 8 K or 9 K, x = 0.01 should be adopted, and when emphasis is placed on the specific heat gain near 7 K, x = 0.02 should be adopted. In addition, in the regenerator material 15, multiple types of CuFe alloys with different substitution amounts x, such as x = 0.01 and x = 0.02, are used. １－ｘ M ｘ O ２ 2, when x is in the vicinity of 0.015, the 4SL phase disappears, while the phase transition temperature from the PD phase (partially disordered phase) to the FEIC phase remains relatively high at approximately 8.8 K. Therefore, it is more preferable that the substitution amount x satisfies 0.01≦x≦0.02.

[0029] Even when Ga is used as M, a phase transition from the 4SL phase to the FEIC phase is observed as the substitution amount x increases. However, compared to when M = Al, the substitution amount x required to cause the phase transition from the 4SL phase to the FEIC phase is larger when M = Ga. For example, when Ga is used as M and the substitution amount x is set to 0.013≦x≦0.056, the phase transition from the 4SL phase to the FEIC phase occurs in the low temperature range of 4.2 K to 9 K, depending on the amount of x (see Figure 3). However, as will be described later, even if the substitution amount x is 0.056<x, a specific heat gain due to magnetic specific heat can be obtained. Therefore, the substitution amount x may be 0.056<x. Furthermore, as in the case of using Al as M, when Ga is used as M, the substitution amount x can be appropriately determined, and multiple types of CuFe alloys with different substitution amounts x can be used. １－ｘ M ｘ O ２ 3, when x is in the vicinity of 0.018, the 4SL phase disappears, while the phase transition temperature from the PD phase to the FEIC phase remains relatively high at approximately 8.7 K. Therefore, it is more preferable that the substitution amount x satisfies 0.015≦x≦0.035.

[0030] As mentioned above, M may be Mn or Rh. When Mn is used as M, the magnetic phase diagram is, for example, as shown in Structural, magnetic, and ferroelectric properties of CuFe 1-x Mn x O2, K. Hayashi, R. Fukatsu, T. Nozaki, Y. Miyazaki, and T. Kajitani, PHYSICAL REVIEW B 87, 064418 (2013), and Impact of Mn3+ substitution on magnetization and electric polarization behavior in geometry frustrated CuFe 1-x Mn xO2, Guiling Xiao, Zhengcai Xia, Xiaoxing Zhang, Yujie Song, Sha Huang, Feng Yang1, Dequan Jiang, Han Deng, Zhongwen Ouyang, Liran Shi, Journal of Materials Science: Materials in Electronics (2019) 30:9531-9539. The magnetic phase diagram when Rh is used as M is shown in Spin-driven ferroelectricity in the delafossite CuFe 1-x Rh x O2(0 < x <0.15), E. Pachoud, C. Martin, B. Kundys 1, Ch. Simon, A. Maignan, Journal of Solid State Chemistry 183 (2010) 344-349.

[0031] In one aspect of the present invention, a compound having a magnetic specific heat in a temperature range of 10 K or less is used as at least a part of the regenerator material to improve the cooling efficiency of He gas and replace at least a part of the rare earth metals such as Ho and Er contained in conventional regenerator materials. Therefore, it is preferable to select the substitution amount x according to each M within the following range so that the FEIC phase exists at any temperature included in the temperature range of 10 K or less. When M = Al: 0.005 ≦ x When M = Ga: 0.013 ≦ x When M = Mn: 0.02 ≦ x When M = Rh: 0.02 ≦ x Furthermore, even when a metal element other than Al, Ga, Mn, or Rh is used as M, a material having a magnetic specific heat in a temperature range of 10 K or less is possible. CuFe １－ｘ M ｘ O ２ CuFeO ２ ABO ２It is a delafossite-type oxide, and it is thought that any element that occupies the B site can partially substitute the Fe site. According to "Hydrothermal Synthesis of Delafossite-Type Oxides," William C. Sheets, Emmanuelle Mugnier, Antoine Barnabe, Tobin J. Marks, Kenneth R. Poeppelmeier, Chem. Mater. 2006, 18, 7-20, in addition to the four elements mentioned above, Sc, Cr, and Co can also partially substitute the Fe site. CuFe when M is Sc, Cr, or Co １－ｘ M ｘ O ２ Regarding x, the substitution amount x can be appropriately selected to produce a satisfactory magnetization specific heat.

[0032] Regarding the upper limit of the substitution amount x, when the substitution amount x is further increased from the FEIC phase, which has a large specific heat, there is a change in the magnetic phase to the OPD phase (Oblique Partially Disordered Phase), but there is no dramatic change in the magnitude of the specific heat. However, as the substitution amount x increases, the substituted Fe atoms are diluted, and the absolute value of the specific heat decreases as the Fe composition ratio decreases. Thus, the upper limit of the substitution amount x is preferably 0.1 or less, and more preferably 0.05 or less.

[0033] Second Embodiment A manufacturing method M10 according to a second embodiment of the present invention will be described with reference to Fig. 4. Fig. 4 is a flowchart of the manufacturing method M10. The manufacturing method M10 is a method for manufacturing a regenerator using CuFe contained in the regenerator material 15 described in the first embodiment. １－ｘ M ｘ O ２ This is a manufacturing method.

[0034] As shown in FIG. 4, the manufacturing method M10 includes a weighing step S11, a mixing step S12, a molding step S13, a firing step S14, and a pulverizing step S15.

[0035] The weighing step S11 is carried out by weighing the CuFe after production. １－ｘ M ｘCopper oxide (e.g., Cu) is added so that the composition ratio of Cu, Fe, and M in the alloy becomes the desired 1:1-x:x. ２ O), iron oxide (e.g., α-Fe ２ O ３ ), and oxides of M (for example, when M=Al, α-Al ２ O ３ These oxides are commercially available and therefore readily available.

[0036] The mixing step S12 is a step of mixing the copper oxide, iron oxide, and oxide of M weighed in the weighing step S11. The mixing method is not limited, but for example, in the case of not mass production, mixing can be performed using a mortar and pestle. When mixing these oxides, an appropriate amount of alcohol (e.g., ethanol) may be dropped into the mortar and the oxides may be mixed in the alcohol. When mixing these oxides in alcohol, it is preferable to volatilize the alcohol after mixing.

[0037] The molding step S13 is a step of pressure molding the mixture of oxides obtained in the mixing step S12. The shape of the pressure molded product is not limited and can be determined appropriately, and one example is pellets. Note that spray drying can also be used instead of pressure molding in the molding step S13. However, when spray drying is used instead of pressure molding, the produced CuFe １－ｘ M ｘ O ２ Therefore, the density of the produced CuFe １－ｘ M ｘ O ２ From the viewpoint of increasing the density, it is preferable to use a pressure molding method in the molding step S13.

[0038] The firing step S14 is a step of firing the mixture of oxides obtained in the molding step S13. The firing temperature, firing time, and atmosphere in the firing step S14 can be appropriately selected according to the knowledge obtained so far. For example, when M=Al, the firing temperature can be set to 1100°C, the firing time can be set to 48 hours, and the atmosphere can be set to Ar. By performing the firing step S14, the following chemical reaction proceeds, and CuFe １－ｘ M ｘ O ２ In the following chemical reactions, M=Al is used as an example of M. Cu ２ O+(1-x)Fe ２ O ３ + xAl ２ O ３ -> 2CuFe １－ｘ Al ｘ O ２ The pulverization step S15 is a step of pulverizing the pellets fired in the firing step S14. The pulverization method is not limited, but for example, in the case of non-mass production, the pellets can be pulverized using a mortar and pestle. １－ｘ M ｘ O ２ In the １－ｘ M ｘ O ２ The particle size is preferably 180 μm or more and 500 μm or less.

[0039] [Additional Notes] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0040] [Summary] The regenerator material according to the first aspect of the present invention is CuFe １－ｘ M ｘ O ２ (M is a metal element other than Fe) crystals. １－ｘ M ｘ O ２ In the temperature range below 10K, CuFe１－ｘ M ｘ O ２ The material has antiferromagnetic properties and a volumetric specific heat, which is the specific heat per volume, greater than that of lead.

[0041] Lead is known as a material that has a relatively large specific heat in the low temperature range. The specific heat of lead is due to lattice vibration, so the lower the temperature (approaching 4.2 K), the smaller the specific heat of lead. On the other hand, CuFe １－ｘ M ｘ O ２ The crystal exhibits antiferromagnetism in the temperature range of 10 K or less, and has a specific heat due to magnetic order (hereinafter also referred to as magnetic specific heat) in addition to the specific heat due to lattice vibration. １－ｘ M ｘ O ２ The specific heat of the crystal of CuFe exceeds that of lead in the temperature range below 10 K. In addition, the specific heat of bismuth alloys, which replace lead, is smaller than that of lead. １－ｘ M ｘ O ２ The specific heat of the crystal of CuFe exceeds that of the bismuth alloy in the temperature range of 10 K or less. １－ｘ M ｘ O ２ The crystal of CuFe can cool He gas more efficiently than lead and bismuth alloy regenerator materials in the temperature range of 10 K or less. Therefore, this regenerator material can replace at least a part of the bismuth alloy contained in conventional regenerator materials while improving the cooling capacity. １－ｘ M ｘ O ２ does not contain rare earth metals. Therefore, at least a part of the compounds containing rare earth metals such as Ho and Er contained in the regenerator material is replaced with CuFe １－ｘ M ｘ O ２ By replacing it with rare earth metal, the amount of rare earth metal used in the regenerator material can be reduced.

[0042] In addition, in the cold storage material according to the second aspect of the present invention, in addition to the configuration of the cold storage material according to the first aspect described above, a configuration is adopted in which M is at least one of Al, Ga, Mn, and Rh.

[0043] CuFeO ２ The single crystal and polycrystal of the above have a Neel temperature of, for example, about 14 K, and have a very large specific heat in the temperature range near the Neel temperature (typically, in the case of a single crystal, the peak value is about 1 J / ccK, and in the case of a polycrystal, the peak value is about 1.3 J / ccK). However, in such single crystals and polycrystals, the antiferromagnetic magnetic interaction tends to saturate in a relatively high temperature range (for example, 10 K or higher or in a temperature range near 10 K), so that the specific heat gain due to the magnetic specific heat tends to decrease rapidly in a temperature range near 10 K. According to the above configuration, M, which is at least one of Al, Ga, Mn, and Rh, is CuFe. １－ｘ M ｘ O ２ Therefore, the Néel temperature is lowered and the peak value of the specific heat is reduced, but the base of the specific heat peak is broadened to the low temperature side. Therefore, this regenerator material can cool He gas more efficiently in the temperature range of 10 K or less.

[0044] Furthermore, in the cold storage material according to the third aspect of the present invention, in addition to the configuration of the cold storage material according to the second aspect described above, a configuration is adopted in which M is Al and the substitution amount x satisfies 0≦x≦0.2.

[0045] According to the above configuration, it is possible to obtain a specific heat gain resulting from magnetic specific heat in a temperature range of 10K or less.

[0046] In addition, in the cold storage material according to the fourth aspect of the present invention, in addition to the configuration of the cold storage material according to any one of the first to third aspects described above, CuFe １－ｘ M ｘ O ２ The particle diameter of the powder is 180 μm or more and 500 μm or less.

[0047] In order to improve the heat exchange efficiency with He gas, CuFe １－ｘ M ｘO ２ It is preferable to increase the surface area of ​​CuFe. １－ｘ M ｘ O ２ However, the particle size of CuFe １－ｘ M ｘ O ２ If the particle size is reduced, the size of the voids through which the helium gas passes becomes smaller, resulting in an increase in pressure loss.

[0048] According to the above configuration, CuFe １－ｘ M ｘ O ２ The surface area of ​​the gas and the pressure loss of the He gas can be optimized in a well-balanced manner.

[0049] Also, CuFe １－ｘ M ｘ O ２ The particle size of CuFe １－ｘ M ｘ O ２ If the particle size is 180 μm or more, CuFe １－ｘ M ｘ O ２ Since the antiferromagnetism of the alloy is not too weak, a desired magnetic specific heat can be obtained in the temperature range of 10 K or less.

[0050] In addition, in the cold storage material according to the fifth aspect of the present invention, in addition to the configuration of the cold storage material according to any one of the first to fourth aspects described above, CuFe １－ｘ M ｘ O ２ The composition further includes a second compound having a Neel temperature in the temperature range of 5K or more and 10K or less.

[0051] According to the above configuration, the specific heat of the regenerator material can be further increased in the temperature range of 5 K to 10 K. Therefore, the regenerator material can more efficiently cool He gas in the temperature range of around 4.2 K within the temperature range of 10 K or less.

[0052] In addition to the configuration of the cold accumulating material according to the fifth aspect of the present invention, the second compound is Gd ２ O２ The configuration adopted is S.

[0053] An example of the second compound is Gd ２ O ２ S. Gd ２ O ２ S has a very large specific heat (typically 0.35 J / ccK) in the vicinity of 5 K, and is therefore suitable as the second compound. In addition, according to this configuration, while the specific heat in the temperature range of around 5 K is secured, the specific heat in the temperature range of 10 K or less is reduced to that of CuFe. １－ｘ M ｘ O ２ Since it can be secured using CuFe １－ｘ M ｘ O ２ Without using Gd ２ O ２ Compared to the case where only S is used to ensure the specific heat in the low temperature range, the amount of rare earth metal used can be reduced.

[0054] A regenerator according to a seventh aspect of the present invention includes the regenerator material according to any one of the first to sixth aspects of the present invention.

[0055] One aspect of the present invention also includes a regenerator including the regenerator material according to the above-described aspect of the present invention.

[0056] In addition, in the cold storage device according to the eighth aspect of the present invention, in addition to the configuration of the cold storage device according to the seventh aspect described above, a configuration is adopted in which the cold storage material is used as a first cold storage material and further includes a second cold storage material containing a second compound having a Neel temperature in the temperature range of 5K or more and 10K or less, and the second cold storage material is arranged on the lower temperature side than the first cold storage material.

[0057] According to the above configuration, the He gas cooled by the first regenerator material is cooled by the second regenerator material, so that the He gas can be cooled more efficiently.

[0058] A cryogenic refrigerator according to one aspect of the present invention includes the regenerator according to the seventh or eighth aspect of the present invention.

[0059] One aspect of the present invention also includes a cryogenic refrigerator equipped with the regenerator according to the aspect of the present invention described above. Example group

[0060] CuFe constituting a part of the regenerator material 15 １－ｘ Al ｘ O ２ 5 to 10, in this example group, the substitution amount x is x=0, and CuFeO ２ Single crystals and powder-like polycrystals of CuFeO were prepared, as well as powder-like polycrystals with x = 0.01, 0.02, 0.05, 0.10, and 0.20. ２ The single crystal of CuFeO is called the first example. ２ The polycrystal of CuFe where x=0.01, 0.02, 0.05, 0.10, 0.20 is called the second example. １－ｘ Al ｘ O ２ The polycrystals are referred to as the third to seventh examples, respectively. FIG. 5 is an image of the pellet-shaped fourth example before the pulverization step S15 shown in FIG. 4 is carried out. FIG. 6 is an image of the powder-shaped fourth example after the pulverization step S15 is carried out. FIG. 7 shows the X-ray diffraction patterns of the second to seventh examples. The bottom row of FIG. 7 shows the X-ray diffraction patterns of CuFeO ２ Calculated values ​​of the X-ray diffraction pattern of the polycrystal of the above are also shown. FIG. 8 is a graph showing the temperature dependence of the specific heat in the first to seventh examples. Note that FIG. 8 also shows the temperature dependence of the specific heat of lead and bismuth. FIG. 9 is a graph showing the temperature dependence of the specific heat of the cold storage material 15 made of lead in the second example, the cold storage material 15 made of lead in the fourth example, and the first reference example, HoCu. ２ 10 is a graph showing the temperature dependence of the cooling capacity of the cold storage material 15 made of lead and the cold storage material made of lead. ２ 9 is a graph showing the temperature dependence of the cooling capacity of a regenerator material made of lead and a regenerator material made of lead. Note that the performance of the refrigerator used in the test is different between the measurement results shown in FIG. 9 and the measurement results shown in FIG. 10. Therefore, the measurement results shown in FIG. 10 tend to have lower cooling capacity than the measurement results shown in FIG. 9.

[0061] CuFeO in the first embodiment ２ The single crystal of CuFeO in the second example was produced using the floating-zone method (see T.R. Zhao, M. Hasegawa, and H. Takei, J. Cryst. Growth 166, 408 (1996)). ２ The polycrystal of CuFeO was manufactured by two methods: a manufacturing method based on the manufacturing method M10 shown in FIG. 4, but using a spray-drying method instead of a pressure molding method in the molding step S13, and the manufacturing method M10. Below, the CuFeO manufactured by the former manufacturing method will be described. ２ The polycrystal of CuFeO manufactured by manufacturing method M10 is simply referred to as the second example. ２ The polycrystal of CuFe in the third to seventh embodiments is called the second embodiment. １－ｘ Al ｘ O ２ The second to seventh examples were manufactured using manufacturing method M10. The starting material was Cu with a purity of 99.9% manufactured by Furuuchi Chemical. ２ O and 99.9% pure α-Fe produced by Kojundo Chemical ２ O ３ and α-Al with 99.99% purity manufactured by Kojundo Chemical. ２ O ３ In the firing step S14, the firing temperature was 1100°C, the firing time was 48 hours, and the atmosphere was Ar. In the manufacturing method M10, when the second example where x = 0 was manufactured, α-Al ２ O ３ You should not use it.

[0062] Referring to FIG. 7, the pellets obtained in the second to seventh examples were CuFe １－ｘ Al ｘ O ２ It was found to be polycrystalline.

[0063] The second example, which was manufactured using the spray drying method as a step performed before the firing step S14, had a lower density than the second example', which was manufactured using the molding step S13 as a step performed before the firing step S14, and the third to seventh examples. ２ Even when producing polycrystals of CuFeO, by using the molding step S13 as a step performed before the firing step S14, ２ The density of the polycrystal of CuFeO ２ The polycrystals were also produced by using the production method M10 as described above.

[0064] FIG. 8 also shows the temperature dependence of the specific heat measured in Examples 1 to 7. FIG. 8 also shows the temperature dependence of the specific heat of lead and bismuth. Referring to FIG. 8, it can be seen that the specific heat of bismuth is lower than that of lead. Furthermore, the specific heat of a bismuth alloy, in which bismuth is mixed with another metal (e.g., antimony), is thought to be lower than that of bismuth. Therefore, the specific heat of a bismuth alloy is thought to be lower than that of lead. Thus, although bismuth and bismuth alloys are used as alternatives to lead, they have a problem of low cooling capacity in low-temperature regions due to their lower specific heat than lead. Referring to FIG. 8, it can be seen that the specific heats of Examples 1 to 7 are higher than those of lead and bismuth in the temperature range below 10 K. Furthermore, when comparing the specific heats of these examples with those of bismuth, it can be seen that the specific heats of Examples 1 to 6 are higher than that of bismuth in the temperature range below 15 K. Therefore, by using each of the present examples instead of bismuth or a bismuth alloy, it is possible to improve the cooling capacity in the low temperature range. Also, referring to Figure 8, the first to seventh examples exhibit magnetic specific heat in the temperature range of 10 K or less. Therefore, it was found that the first to seventh examples are antiferromagnetic.

[0065] The fourth example (CuFe ０．９８ Al ０．０２ O２ The regenerator material 15 was made of polycrystalline silicon (24 g) and lead (58 g). The ratio of the fourth embodiment to lead in the regenerator material 15 was 1:1 in terms of the volume ratio of the filled space. Here, lead, which constitutes the regenerator material 15 together with the fourth embodiment, is an example of the third compound.

[0066] The third example (CuFe ０．９９ Al ０．０１ O ２ The regenerator material 15 was made of polycrystalline silicon (24 g) and lead (58 g). The ratio of the third embodiment to lead in the regenerator material 15 was 1:1 in terms of the volume ratio of the filled space. Here, the lead constituting the regenerator material 15 together with the third embodiment is an example of the third compound.

[0067] Also, the second example' (CuFeO ２ The regenerator material 15 was made of polycrystalline (24 g) of ZnO and lead (58 g). The ratio of the second embodiment' to lead in the regenerator material 15 was 1:1 in terms of the volume ratio of the filled space. Here, the lead constituting the regenerator material 15 together with the second embodiment' is an example of the third compound.

[0068] In addition, the second example (CuFeO ２ The cold storage material 15 was constructed using polycrystalline (14 g) of lead (58 g) and lead. The ratio of lead to lead in the cold storage material 15 of the second example was 1:1 in terms of the volume ratio of the filled space. Here, the lead constituting the cold storage material 15 together with the second example is an example of a third compound. As described above, the second example, in which the spray drying method was performed before performing the firing step S14, had a lower density than the second example', third example, and fourth example obtained by manufacturing method M10. Due to this lower density, the second example', third example, and fourth example, which had the same volume as 58 g of lead, all had a weight of 24 g, whereas the second example, which had the same volume as 58 g of lead, had a weight of 14 g.

[0069] In addition, as a cold storage material for comparison with these cold storage materials 15, HoCu ２The cold storage material used was a mixture of copper (51 g) and lead (58 g), and a cold storage material made of lead (116 g). ２ (51g) and lead (58g) in the regenerator material ２ The ratio of lead to silicon is 1:1 in terms of the volume ratio of the filled space.

[0070] The cold storage material 15 including the second embodiment, the cold storage material 15 including the fourth embodiment, HoCu ２ The cooling capacity of the cold storage unit including the cold storage material 15 of the fourth embodiment was measured in the temperature range of 10 K or less, and the cooling capacity of the cold storage unit including the cold storage material 15 of the fourth embodiment was measured in the temperature range of 10 K or less. ２ It was found that the cooling capacity of this material approaches that of ice packs containing

[0071] Also, the cold storage material 15 including the second embodiment, the cold storage material 15 including the second embodiment', the cold storage material 15 including the third embodiment, the cold storage material 15 including the fourth embodiment, HoCu ２ The cooling accumulators including the cold storage material containing HoCu and the cold storage material containing lead were fabricated and mounted on the GM refrigerator 10, and the cooling capacities were measured again. The results are shown in Figure 10. Referring to Figure 10, the cooling capacities of the cold storage material 15 including the second embodiment, the cold storage material 15 including the third embodiment, and the cold storage material 15 including the fourth embodiment all exceed the cooling capacity of the cold storage material containing lead in the temperature range of 10K or less. ２ It was found that the cooling capacity of this material approaches that of ice packs containing

[0072] 9 and 10, the cooling capacity of the regenerator material 15 including the second embodiment is lower than that of a regenerator material made of lead in the temperature range of 10 K or less. However, the low cooling capacity of the regenerator material 15 including the second embodiment is due to the low density of the second embodiment. ２ When the polycrystal of CuFeO is produced by the production method M10, ２ The density of the polycrystal of CuFeO is approximately the same as that of the third and fourth embodiments. ２The cooling capacity of the regenerator material 15 including the polycrystal of HoCu is considered to be about 24 / 14 times that of the regenerator material 15 including the second embodiment. In fact, as shown in FIG. 10, the cooling capacity of the regenerator material 15 including the second embodiment' exceeds that of the regenerator material made of lead in the temperature range of 10 K or less, similar to the cooling capacity of the regenerator material 15 including the third and fourth embodiments. ２ It was found that the cooling capacity of this material approaches that of ice packs containing

[0073] From the above results, it can be seen that the CuFe contained in the regenerator material 15 １－ｘ Al ｘ O ２ In the temperature range of 10 K or less, the CuFe contained in the regenerator material 15 can cool He gas more efficiently than the regenerator material made of lead. １－ｘ Al ｘ O ２ In the temperature range of 10 K or less, the CuFe contained in the regenerator material 15 can cool He gas more efficiently than the regenerator material made of a bismuth alloy. １－ｘ Al ｘ O ２ does not contain rare earth metals. Therefore, at least a part of the compounds containing rare earth metals such as Ho and Er contained in the regenerator material is replaced with CuFe １－ｘ M ｘ O ２ Therefore, it has been found that the amount of rare earth metals such as Ho and Er used in the regenerator material 15 can be reduced in the regenerator material constituting a cryogenic refrigerator, such as a Gifford-McMahon refrigerator.

[0074] 10 Gifford McMahon (GM) refrigerator 11 Compressor 12 Regenerator 13, 14 Pair of stoppers 15 Regenerator material

Claims

1. CuFe １－ｘ M ｘ O ２ (M is a metal element other than Fe) crystals, in a temperature range of 10K or less, １－ｘ M ｘ O ２ A heat storage material characterized in that said material exhibits antiferromagnetism and has a volumetric specific heat that is a specific heat per volume greater than that of lead.

2. The regenerator material according to claim 1, wherein M is at least one of Al, Ga, Mn, and Rh.

3. The regenerator material according to claim 2, wherein M is Al, and the amount x of Fe substituted with M satisfies 0≦x≦0.

2.

4. CuFe １－ｘ M ｘ O ２ The cold storage material according to any one of claims 1 to 3, characterized in that the particle diameter of said powder is 180 µm or more and 500 µm or less.

5. CuFe １－ｘ M ｘ O ２ The regenerator material according to any one of claims 1 to 3, further comprising a second compound having a Neel temperature in a temperature range of 5K or more and 10K or less.

6. The second compound is Gd ２ O ２ The regenerator material according to claim 5, wherein the regenerator material is S.

7. A regenerator comprising the regenerator material according to claim 1.

8. The regenerator according to claim 7, further comprising a second regenerator material containing a second compound having a Neel temperature in the temperature range of 5K or more and 10K or less, the second regenerator material being disposed on the lower temperature side than the first regenerator material.

9. A cryogenic refrigerator comprising the regenerator according to claim 7 or 8.

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