ErCo2-based magnetocaloric compound and magnetic refrigeration device using same

Abstract

A magnetocaloric material according to the present invention is suitable for liquefying natural gas, H2, He, and the like, enables the Curie temperature TC thereof to be in the temperature range of 25-46 K while maintaining the massive magnetocaloric effect thereof, continuously transitions due to secondary magnetic phase transition, and has a small hysteresis in a temperature cycle. One example is <1> a magnetic refrigeration material comprising Er (erbium), Co (cobalt), Ni (nickel), and Al (aluminum), and incidental impurities, and having a composition represented by composition formula: ErCo2-x-yAlxNiy where 0.0<x≤0.1 and 0≤y≤0.2 are satisfied. Preferably, the composition satisfies 0.01≤x≤0.1 and 0.12≤y≤0.2. <2> A magnetic refrigeration material comprising Er (erbium), Co (cobalt), Ni (nickel), and Fe (iron), and incidental impurities, and having a composition represented by composition formula: ErCo2-x-yFexNiy where 0.035 ≤ x ≤ 0.1 and 0.00 ≤ y ≤ 0.2 are satisfied.

Description

[Technical field]

[0001] The present invention relates to an ErCo2-based magnetocaloric compound and a magnetic refrigeration device using the same. [Background technology]

[0002] In recent years, as the demand for hydrogen energy increases toward a fuel cell society, hydrogen liquefaction has been actively researched due to its high energy efficiency in liquid form (during transportation and storage). Compared with conventional liquefaction systems, magnetic liquefaction, which is similar to the Carnot cycle, has higher energy efficiency. Known examples of hydrogen liquefaction devices include the active magnetic refrigeration (AMR) cycle, which is disclosed in, for example, Patent Documents 1 to 3 and Non-Patent Document 1. For magnetocaloric hydrogen liquefaction, taking into consideration the boiling temperature of hydrogen, the prevention of heat loss during liquid hydrogen storage, and the practical application of magnetocaloric refrigeration systems, a magnetic refrigeration material that has a giant magnetocaloric effect (GMCE) in a wide temperature range from 20 K to 70 K is preferable.

[0003] As a compromise to cover such a large temperature range, it has been proposed to build a magnetocaloric hydrogen liquefaction system using a series of functionally graded materials with different transition temperatures. For example, HoB2, HoN, and HoNi2 have sufficient entropy change (△Sm>0.2 J / cm) in the temperature range below 30 K. 3 K), which is sufficient for this purpose. However, as the temperature increases to 70K, the entropy change drops significantly. For example, in the temperature range of 45-70K, △Sm>0.2J / cm 3 At present, no materials that exhibit K are known, making it difficult to put magnetic cooling technology into practical use for hydrogen liquefaction.

[0004] The Laves phase RM2 compounds, where R = heavy rare earth and M = metal, show great potential for cryogenic applications. For example, the RAl2 compound with R = Dy, Ho has a ΔSm of 0.11 J / cm at 60 K. 3K, 0.17 J / cm at 30 K 3 On the other hand, for the compound RCo2, where R = Dy, Ho, or Er, the Curie temperature T C = 135, 77, 32K and ΔSm = 0.14 J / cm 3 K, 0.2 J / cm 3 K, 0.37 J / cm 3 The first-order ferromagnetic-paramagnetic transition of K is at 5 T. Among these Laves phase compounds, the compounds with the largest entropy change and the desirable Curie temperature T C ErCo2, which exhibits a low Curie temperature, is a promising candidate for the development of giant magnetic refrigeration materials for hydrogen liquefaction.

[0005] However, due to the first-order magnetic phase transition (FOMT) accompanied by a structural phase transition in ErCo2 compounds, the reversibility of the magnetocaloric effect due to thermal hysteresis is low, and the mechanical stability is low, so ErCo2 compounds are not necessarily suitable for practical use in magnetocaloric hydrogen liquefaction. In order to improve the cyclic performance of ErCo2 compounds for practical use, it is desirable to change the phase transition of ErCo2 from a first-order magnetic phase transition to a second-order magnetic phase transition (SOMT) that is substantially unaccompanied by a structural phase transition. The second-order magnetic phase transition of the RCo2 Laves phase can be realized by replacing Er with Gd and Tb, but TbCo2 and GdCo2 have Curie temperatures T C = 235K, 406K, which is far from the temperature range of interest (20-70K). When 6% of Co is replaced by 3d elements, the Curie temperature T C The Curie temperature T C rises above 85K, and the entropy change is 0.03 J / cm 3 Mn has been reported to modulate the phase transition from the first-order magnetic phase transition (FOMT) to the second-order magnetic phase transition (SOMT), but the nonstoichiometric ErCoMn x For compounds, the Curie temperature is 150K and the energy is 0.01 J / cm 3 I could only get a K or less.

[0006] Here, the phase transition from the first-order magnetic phase transition (FOMT) to the second-order magnetic phase transition (SOMT) of ErCo2 is controlled in the range of 25K to 70K, and sufficient magnetic recording characteristics and Curie temperature T C It is preferable to be able to adjust the phase transition temperature of ErCo2 to have a second-order phase transition (SOPT). It is also important to raise the phase transition temperature to 25-70K. In this case, if a magnetic refrigeration material with a phase transition temperature of 45-70K exists, for example, if a magnetic refrigeration material with a phase transition temperature of 25-45K, which is about 20K lower than the phase transition temperature, can be found, it would be suitable for magnetocaloric hydrogen liquefaction applications. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 2003-532861 [Patent Document 2] WO2015-199139 publication [Patent Document 3] JP 2012-37112 A [Non-patent literature]

[0008] [Non-Patent Document 1] Akiko Saito et al. "Basic Research on Active Regenerative Magnetic Refrigeration" Cryogenics, Vol. 50, No. 2, pp. 88-95 (2015) Summary of the Invention [Problem to be solved by the invention]

[0009] ErCo2-based compounds are known to provide giant magnetocaloric effects for cryogenic magnetic refrigeration applications such as hydrogen liquefaction. However, because the magnetocaloric effect of this material is due to a first-order magnetic phase transition, the material exhibits hysteresis, which reduces the giant magnetocaloric effect and mechanical stability during the magnetic refrigeration cycle, making it difficult to put into practical use.

[0010] Therefore, the magnetic phase transition temperature T tr The temperature can be adjusted to a range of 25 to 46 K. In addition, the second-order magnetic phase transition is continuous, and the hysteresis caused by temperature cycles is substantially absent. This provides a magnetic refrigeration material suitable for liquefying natural gas, H2, He, etc. [Means for solving the problem]

[0011] As a result of intensive research into solving the above problems, the inventors of the present invention have concluded that, in order to put a magnetocaloric refrigeration system for hydrogen liquefaction into practical use, a magnetic refrigeration material having a giant magnetocaloric effect (GMCE) in the temperature range of, for example, 20 K to 70 K is preferable. The ErCo2 compound has a desirable Curie temperature T C It is one of the promising materials due to the large entropy change caused by the first-order magnetic phase transition (FOMT) accompanied by a structural phase transition. However, due to the nature of the first-order magnetic phase transition (FOMT), it was predicted that the ErCo2 compound would have low reversibility of magnetocaloric performance and low mechanical stability. On the other hand, replacing Er with Gd or Tb does not result in an ErCo2 compound, and the desirable Curie temperature T C It is difficult to achieve the desired Curie temperature T C In this magnetic refrigeration material, a part of Co can be replaced with a third element M to enhance the reversibility of the magnetocaloric properties. This is believed to have resulted in a material in which the magnetic phase transition is a second-order magnetic phase transition that is not substantially accompanied by a structural phase transition.

[0012] As the third element M, it is considered preferable to have properties similar to those of Co (cobalt) while simultaneously having different properties. However, as described in the background art, it is not easy to find such an element. Under such circumstances, the inventors have found that by adding a predetermined amount of a specific element or combination of elements as a substitution element for Co, a desirable Curie temperature T C is newly found to be obtained. Also, it is newly found that a substantially second-order magnetic phase transition occurs. Specifically, the following can be provided. In an embodiment of the present invention, the magnetic refrigeration material consists of Er (erbium), Co (cobalt), Al (aluminum), Fe (iron), Ni (nickel), and inevitable impurities, and has the following composition formula: ErCo 2-x-y (Al, Fe) x Ni y ; It may also include a compound having a composition of 0 < x ≦ 0.1, 0 ≦ y ≦ 0.2. Here, ErCo 2-x-y (Al,Fe) x Ni y may mean that Al and / or Fe are present in a total amount of x. For example, if x = 0.05 and y = 0.1, then ErCo 2-0.05-0.1 (Al,Fe) 0.05 Ni 0.1 is ErCo 1.85 Al0Fe 0.05 Ni 0.1 (ErCo 1.85 Fe 0.05 Ni 0.1 ), ErCo 1.85 Al 0.02 Fe 0.03 Ni 0.1 , ErCo 1.85 Al 0.03 Fe 0.02 Ni 0.1 , ErCo 1.85 Al 0.05 Fe0Ni 0.1 (ErCo 1.85 Al 0.05 Ni 0.1 ), and may be included. Also, depending on the conditions, x ≦ 0.12 and y ≦ 0.3 may be satisfied. For example, ErCo 2-0.12-0.3Al 0.05 Fe 0.07 Ni 0.3 (i.e., ErCo 1.58 Al 0.05 Fe 0.07 Ni 0.3 ) may also be included. When y = 0, it becomes ErCo 2-x (Al,Fe) x . [1] In the examples of the present invention, the magnetic refrigeration material consists of Er (erbium), Co (cobalt), Ni (nickel), Al (aluminum), and inevitable impurities, and has the following composition formula: ErCo 2-x-y Al x Ni y ; It may have a composition of 0.0 < x ≦ 0.1, 0.0 ≦ y ≦ 0.2. Preferably, it may have a composition of 0.01 ≦ x ≦ 0.1, 0.01 ≦ y ≦ 0.2. [2] In the examples of the present invention, in any of the above-mentioned magnetic refrigeration materials, preferably, ErCo 2-x-y Al x Ni y ; It may have a composition of 0.01 ≦ x ≦ 0.1, 0.12 ≦ y ≦ 0.2. Here, when y exceeds 0.2, the transition temperature T tr may be significantly lower than 20 K. It may not be suitable for magnetic refrigeration in the target temperature range. When y is less than 0.01, the Ni content may be less than the reference amount of inevitable impurities. Therefore, there may be a risk of being indistinguishable from the substantially ternary system ErCo 2-x Al x . When y is less than 0.12, there may be a risk of generating a first-order magnetic phase transition (FOMT) accompanied by a structural phase transition. In this case, it may not always be suitable for long-term use. However, it may be possible to handle it for short-term use. Under the above Ni content, when x exceeds 0.1, the transition temperature T trIf x is less than 0.01, the content of Al may be below the standard amount of unavoidable impurities. Therefore, the ternary ErCo alloy is essentially 2-y Ni y It may be difficult to distinguish between them.

[0013] [3] In an embodiment of the present invention, any of the above-mentioned magnetic refrigeration materials is composed of Er (erbium), Co (cobalt), Ni (nickel), Fe (iron) and inevitable impurities, and has the following composition formula: ErCo 2-x-y Fe x Ni y It may have a composition of 0.035≦x≦0.1, 0.00≦y≦0.2. [4] In an embodiment of the present invention, any of the above-mentioned magnetic refrigeration materials preferably comprises: ErCo 2-x-y Fe x Ni y It may have a composition of 0.035≦x≦0.1, 0.01≦y≦0.2. When x is less than 0.035, the transition temperature T tr In general, repeated phase transitions tend to cause the crystal structure to collapse, and the material may not be suitable for stable long-term use. When x exceeds 0.1, the transition temperature T tr If y exceeds 0.2, the transition temperature T tr If y is less than 0.01, the Ni content may be below the standard amount of unavoidable impurities. 2-x Fe x It may be difficult to distinguish between them.

[0014] [5] In an embodiment of the present invention, in any of the above-mentioned magnetic refrigeration materials, the transition temperature T tris in the temperature range of 25K to 46K, and the transition temperature T tr A second-order magnetic phase transition may be observed in the range of 20 K around the [6] In an embodiment of the present invention, in any of the above-mentioned magnetic refrigeration materials, the second-order magnetic phase transition occurs at a transition temperature T tr The volume change rate (dV / V) may be 0.4% or less within a range of 20K around the temperature. If the volume change rate (dV / V) is 0.4% or less, the transition temperature T tr It can be evaluated as a second-order magnetic phase transition (SOMT) in the range of 20 K around the . For example, even if the phase transition is repeated, the collapse of the crystal structure may be substantially small. And it is suitable for long-term stable use. [7] In an embodiment of the present invention, in any of the above-mentioned magnetic refrigeration materials, the transition temperature T tr Within a range of 20K around the center, the entropy change is △S>0.05J / cm under a 5T magnetic field. 3 ·K may be obtained. [8] In an embodiment of the present invention, in any of the above-mentioned magnetic refrigeration materials, the entropy change is ΔSm>0.1 J / cm under a 5 T magnetic field. 3 ·K may be obtained. [9] In the embodiments of the present invention, the magnetic refrigeration device may use any of the magnetic refrigeration materials described above.

[10] In an embodiment of the present invention, the hydrogen liquefaction device or the helium liquefaction device may use any of the magnetic refrigeration devices described above. Effect of the Invention

[0015] In the embodiment of the present invention, the ErCo2-based magnetocaloric compound can maintain a large magnetocaloric effect. C The temperature range of the magnetic phase transition can be 25 to 46K. The transition can be continuous due to the second-order magnetic phase transition. It can also be said that there is substantially no hysteresis due to temperature cycling. It is therefore considered to be a magnetic refrigeration material suitable for liquefying natural gas, H2, He, etc. [Brief description of the drawings]

[0016] [Figure 1A] 1 illustrates the crystal structure of ErCo2, an example of a Laves phase compound that may constitute a magnetic refrigeration material usable in embodiments of the present invention. [Figure 1B] The composition of compounds that may constitute a usable magnetic refrigeration material is illustrated in a ternary composition diagram of Co, Ni, and Al or Fe (here, Er is excluded from this composition diagram because it is always present in a certain amount). [Diagram 2] The temperature dependence of magnetization M at 1 T is shown for the ErCo2 compound. [Diagram 3] The temperature dependence of the entropy change ΔSm from 0 to 5 T is shown for the ErCo2 compound. [Figure 4] The temperature dependence of magnetization M at 1 T is shown for the ErCo2-xFex compound. [Diagram 5] 1 shows the temperature dependence of magnetization M at 1 T for an ErCo2-x-yAlxNiy compound illustrating one embodiment of the present invention. [Figure 6] 1 shows the temperature dependence of the entropy change ΔSm at 0-5 T for an ErCo2-x-yAlxNiy compound illustrating one embodiment of the present invention. [Figure 7] 1 shows the temperature dependence of magnetization M at 1 T for an ErCo2-x-yFexNiy compound illustrating one embodiment of the present invention. [Figure 8] 1 shows the temperature dependence of the entropy change ΔSm at 0-5 T for the ErCo2-x-yFexNiy compound showing one embodiment of the present invention. [Figure 9] This figure shows the volume change for each chemical formula when cooled from 300K to 5K. The state in which the first-order magnetic phase transition (FOMT) changes to the second-order magnetic phase transition (SOMT) was analyzed by cryogenic X-ray diffraction. [Figure 10] FIG. 2 is a schematic diagram illustrating each step of a magnetic refrigeration cycle in which the magnetic refrigeration material according to the embodiment of the present invention is used. [Figure 11] FIG. 1 is a schematic diagram illustrating an active regenerative magnetic refrigeration (AMR) cycle. [Figure 12] FIG. 1 is a schematic diagram showing an example of an AMR in which magnetic refrigeration materials are arranged in a cascade configuration, where (A) is a schematic diagram of the device, and (B) is an explanatory diagram of the operating temperature range of the magnetic refrigeration materials. [Figure 13] FIG. 1 is a diagram illustrating a magnetic refrigeration device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The definitions of technical terms used in this specification are explained below. A phase transition is a change in an order parameter (e.g., the magnetization of a ferromagnet) across a transition. R The order parameter in a phase transition of a magnetic material (magnetic phase transition (the transition of a solid's magnetic property from paramagnetic to ferromagnetic or antiferromagnetic, or vice versa, from ferromagnetic or antiferromagnetic to paramagnetic, depending on the temperature), for example, the transition between ferromagnetic and paramagnetic) is magnetization. Magnetization is a macroscopic physical quantity, but it is derived from the spin of microscopic electrons present inside a magnetic material. The spin has an intrinsic magnetic moment, and magnetization is defined as the sum of the magnetic moments of the entire system. A first-order magnetic phase transition (FOPT) means that the order parameter changes discontinuously. do . A second-order magnetic phase transition (SOPT) is also called a continuous phase transition, and refers to a continuous change in the order parameter. say . Regarding first- and second-order transitions, it is generally believed that in the first-order transition, discontinuities occur in the entropy, volume, polarization, etc. of the crystal, whereas in the second-order transition, these quantities remain continuous and the temperature derivatives show discontinuous changes. Here, the order parameter is a macroscopic variable that represents the order of the phase. R For example, in crystals, the arrangement of atoms has a certain order, and phase transitions are characterized by changes in the value of the order parameter. can be done.The order parameter behaves as a function of external variables such as temperature and pressure; for example, in the case of a temperature-induced phase transition, it may have a finite value in the low-temperature phase (broken symmetry or ordered phase) below the transition temperature, and may be zero in the high-temperature phase (symmetric or disordered phase).

[0018] A first-order magnetic phase transition (FOMT) in a magnetic refrigeration material refers to a material that has a magnetic phase transition at a transition temperature accompanied by a change in either the crystal structure or the crystal volume. Here, the transition temperature is considered to be substantially equivalent to the Curie temperature. The second-order magnetic phase transition (SOMT) in magnetic refrigeration materials essentially involves only a magnetic phase transition (such as a transition from a ferromagnetic state to a paramagnetic state) at the transition temperature, without any substantial change in the crystal structure or crystal volume. Specifically, the boundary between the first-order magnetic phase transition and the second-order magnetic phase transition may be set to a volume change rate (dV / V) of 0.4% in the range around the transition temperature Ttr (Ttr±20K). If dV / V is 0.4% or less, it is considered to be a second-order magnetic phase transition. do In addition, if dV / V exceeds 0.4%, a first-order magnetic phase transition occurs. Let us assume that.

[0019] Figure 1A illustrates the crystal structure of ErCo2. The structure is MgCu2 type in the Laves phase, with lattice parameters a=b=c=0.71536 nm and α=β=γ=90°. In such a Laves phase, A and B metal elements with an atomic radius ratio of approximately 1.2:1 are bonded in a composition ratio of AB2 to form a compound. The crystal structure consisting of a large atom A and a small atom B is considered to be a packed structure of large and small spheres, and occupies specific lattice positions, the A site and the B site. The A site has four A atoms and 12 B atoms as neighboring atoms, and the B site is surrounded by six A atoms and six B atoms. In a realistic Laves phase crystal, the atomic packing is performed so that the AA atoms and BB atoms are in contact with each other, and there is no contact between the AB atoms. In such a case, the atomic radius ratio of both atoms has the relationship RA / RB=√3 / 2=1.225. In general, atoms arranged at the A site are arranged in a similar manner to the diamond structure, and atoms at the B site form a tetrahedron around the A site. Since Laves phase compounds are a type of close-packed structure, they have three types of crystal structures, cubic MgCu2 type (C15), hexagonal MgZn2 type (C14), and MgNi2 type (C36), due to differences in atomic stacking similar to the difference between face-centered cubic lattice and hexagonal close-packed lattice. In the following description, it is considered that Al, Fe, and / or Ni may enter such a crystal structure to substitute for Co. EXAMPLES

[0020] The raw materials were weighed out: Er block (purity 99.9%) manufactured by Nippon Yttrium Co., Ltd., Co block (purity 99.9%) manufactured by Furuuchi Kagaku Co., Ltd., Al powder (purity 99.99%) manufactured by Rare Metallic Co., Ltd., Fe powder (purity 99.95%) manufactured by Toho Zinc Co., Ltd., and Ni powder (purity 99.95%) manufactured by Furuuchi Kagaku Co., Ltd. 2-x-y (Al,Fe) x Ni yThe pure composition elements of the system compounds were prepared by arc melting under an argon atmosphere in an atmosphere-controlled arc furnace manufactured by Nisshin Giken Co., Ltd. In order to compensate for the evaporation of Er and Mn, 2 wt.% extra Er and 5 wt.% extra Mn were charged. The ingot was homogenized by turning it over four times and remelting it in an arc melting process. It was then sealed in quartz under an argon atmosphere and annealed at 1000°C for 50 hours. In this way, the compounds with the composition shown in Table 1 were synthesized. The obtained compounds were granular with a diameter of about 300 microns. The phase components were examined by X-ray diffraction using Cr-Kα radiation (manufactured by Rigaku Co., Ltd.), and the magnetic properties were measured using a SQUID-VSM (manufactured by Quantum Design Co., Ltd.).

[0021] Table 1 shows the experimental results of the present invention. 2-x-y (Al,Fe) x Ni y 1 is a table showing the elemental composition of the system compounds. Experimental Example 1 shows the elemental composition of a sample using ErCo2, which is the basic form of a binary alloy. Experimental Examples 2 to 4 are the basic form of ternary alloy, ErCo. 2-x Fe x In the elemental composition of the samples, the Fe composition ratio x varies in the range of 1.33 to 2.33%. In Experimental Example 5, the quaternary alloy ErCo 2-x-y Al x Ni y The elemental composition of the system compound is expressed in atomic percent, with the Al composition ratio being 1.67% and the Ni composition ratio being 5.0%. In Experimental Example 8, the Al composition ratio is 1.00% and the Ni composition ratio is 5.67%. In Experimental Examples 6 to 7, the quaternary alloy ErCo 2-x-y Fe x Ni y The elemental composition of the system compound is expressed in atomic percent, with the Fe composition ratio being 1.33% and the Ni composition ratio varying in the range of 2.0% to 3.67%. Figure 1B illustrates the compositions of these experimental examples in a ternary composition diagram of Co, Ni, and Al or Fe (where Er is always present in a constant amount and thus excluded from this composition diagram). As a whole, since it is considered 100%, when including Er to make the whole 100%, the described numerical values should be multiplied by 2 / 3. For example, 95 becomes 63.33, 90 becomes 60, 85 becomes 56.67, 5 becomes 3.33, 10 becomes 6.67, and 15 becomes 10. The thick line represents ErCo 2-x-y (Al,Fe) x Ni y corresponds to x = 0, x = 0.1, y = 0, and y = 0.2. Therefore, excluding the case where x = 0, the range enclosed by this thick line can represent the range of 0 < x ≤ 0.1 and 0 ≤ y ≤ 0.2. In the examples of the invention of this application, it can be said that the range enclosed by the thick line is the target composition range.

[0022]

Table 1

[0023] Table 2 shows the physical property values of the ErCo 2-x-y (Al,Fe) x Ni y series compounds. Note that in Table 1, the composition ratio of Al, Fe was represented in atomic%, while in Table 2, it is represented by a chemical formula.

[0024]

Table 2

[0025] ErCo 2-x-y Al x Ni y Regarding the phase transition temperature T tr of the ErCo 1.8 Ni 0.15 Al 0.05 in Example 5, it is 24K under an external magnetic field of 1 T (Tesla), and for the ErCo 1.8 Ni 0.17 Al0.03 So the result was 19K. The rate of change of magnetization M per temperature dM / dT(Am 2 / kg·K) is the ErCo 1.8 Ni 0.15 Al 0.05 11.7, ErCo in Experimental Example 8 1.8 Ni 0.17 Al 0.03 In this case, the magnetization was 8.5. Here, magnetization refers to the magnetic dipole moment per unit volume of a magnetic material. FIG. 2 shows the temperature dependence of magnetization M at 1 T for the ErCo2 compound. FIG. 2-x-y Al x Ni y The temperature dependence of magnetization M at 1 T from 0 to 80 K is shown for the compound.

[0026] Entropy per unit volume △S (J / cm 3 ·K) was not measured in Experimental Example 5. ErCo in Experimental Example 8 1.8 Ni 0.17 Al 0.03 The figure was 0.32 (Figure 6). FIG. 3 shows the temperature dependence of the entropy change ΔSm for the ErCo2 compound at 0-5 T. FIG. 2-x-y Al x Ni y The figure shows the temperature dependence of the entropy change ΔSm from 0 to 5 T for a compound from 0 to 80 K. As for the magnetic phase transition, SOMT was observed in Experimental Examples 5 and 8 (Examples). Thermal hysteresis ΔT hys Regarding (K), it tends to appear in the first-order magnetic phase transition but not in the second-order magnetic phase transition. hys (K) appears with a width of 1.8K, with Experimental Example 5 being 0.65K and Experimental Example 8 being 0.2K.

[0027] ErCo 2-x-y Fe x Ni yThe phase transition temperature T tr Regarding the ErCo in Experiment 2, under an external magnetic field of 1 T (Tesla), 1.96 Fe 0.04 46K, ErCo in Experiment 3 1.95 Fe 0.05 In Experiment 4, ErCo is 55K. 1.93 Fe 0.07 66K, ErCo in Experiment 6 1.9 Ni 0.06 Fe 0.04 36K, ErCo in Experiment 7 1.85 Ni 0.11 Fe 0.04 So it was 28K. The rate of change of magnetization M per temperature dM / dT(Am 2 / Kg·K) is the ErCo 1.96 Fe 0.04 Then, ErCo in Experiment 3 1.95 Fe 0.05 5.2 ErCo in Experimental Example 4 1.93 Fe 0.07 2.8, ErCo in Experimental Example 6 1.9 Ni 0.06 Fe 0.04 7.1 ErCo in Experiment 7 1.85 Ni 0.11 Fe 0.04 The result was 7.2. Figure 4 shows the ErCo 2-x Fe x The temperature dependence of magnetization M at 1 T for the compound is shown in FIG. 2-x-y Fe x Ni y The temperature dependence of magnetization M at 1 T from 0 to 80 K is shown for the compound.

[0028] Entropy per unit volume △S (J / cm 3 ·K) is the ErCo of Experimental Example 2 1.96 Fe 0.04 In Experiment 3, ErCo is 0.21. 1.95 Fe 0.05 It was 0.17 in Experimental Example 1 and not measured in Experimental Example 2. It was 0.24 in both Experimental Examples 6 and 7. FIG. 8 shows an example of the present invention. 2-x-y Fe x Ni y For a compound, the temperature dependence of the entropy change ΔSm from 0 to 5 T from 0 to 80 K is shown. Regarding the magnetic phase transition, SOMT was observed in Experimental Examples 2 to 4. SOMT was observed in Experimental Examples 6 and 7. Thermal hysteresis ΔT hys Regarding (K), it appears in the first-order magnetic phase transition but does not appear in the second-order magnetic phase transition. hys (K) does not appear, which is preferable. In Experimental Example 6, it appears with a width of 0.2K, and in Experimental Example 7, it appears with a width of 0.2K.

[0029] Figure 9 shows the volume change for each chemical formula when cooled from 300 K to 5 K. The state in which the first-order magnetic phase transition (FOMT) changes toward the second-order magnetic phase transition (SOMT) was analyzed by cryogenic X-ray diffraction. In the ErCo2 compound, a step jump in the volume change was observed near the Curie temperature. ErCo 2-x M x The volume change of the (M=Al, Fe) compounds is significantly smaller than that of the samples not containing M shown in Figure 9. 2-x M x In the compounds (M = Al, Fe), no change in volume per chemical formula due to the crystal structure transition near the transition temperature was observed, suggesting that FOPT was significantly suppressed in these compounds and SOPT was realized.

[0030] In the ErCo2 compound, volume expansion at the Curie temperature TC was observed, as shown in Figure 9. As a result, a sharp MT curve with a narrow temperature span was obtained in the ErCo2 compound in Figure 5. Here, the narrow temperature span means that -dM / dT is 18Am 2 / kg·K. More preferably, 9Am 2 / kg·K. As mentioned above, if the volume change rate (dV / V) is 0.4% or less in the range of about 20K around the transition temperature Ttr, it is a second-order magnetic phase transition, and if it exceeds 0.4%, it is a first-order magnetic phase transition. If such a volume change rate cannot be obtained, a first-order magnetic phase transition can also be determined by using -dM / dT as a secondary method. For example, a second-order phase transition occurs when -dM / dT is 18Am 2 / kg·K or less, preferably 9Am 2 / kg K or less, but this can only be used if no volume change is obtained. When M (M=Al, Fe) is added, ErCo 2-x M x The magnitude of the volume change at the phase transition temperature of the (M=Al, Fe) compounds was much smaller than that of the ErCo2 compound. As shown in FIG. 9, the volume change rate (dV / V) around the Curie temperature was 0.4% or less, and a continuous and gentle volume change was obtained. 2-x M x The phase transition to the magnetically ordered state of the (M=Al,Fe) compound is continuous and closer to a second-order transition, which improves the reversibility of magnetic recording performance. Therefore, a second-order phase transition is defined as a transition in which the volume change rate (dV / V) around the Curie temperature is 0.4% or less. do In addition, when this value is exceeded, it is defined as a first-order phase transition. do .

[0031] As experimental examples of the magnetic refrigeration material of the present invention, the experimental configurations shown in Figs. 2 to 8 are shown. The present invention is not limited to these. Furthermore, various embodiments are conceivable within a scope that is obvious to those skilled in the art. Such obvious scope is also included in the scope of the present invention.

[0032] Next, a magnetic refrigeration device using the magnetic refrigeration material according to the embodiment of the present invention will be described. FIG. 10 is a schematic diagram illustrating each step of the magnetic refrigeration cycle. In the magnetic refrigeration cycle, a thermal cycle similar to the vapor compression cycle is formed by a repeated cycle of entropy change (temperature increase) due to excitation in a constant temperature environment and adiabatic temperature change (temperature decrease) due to demagnetization in an adiabatic state.

[0033] Fig. 11 is a schematic diagram for explaining an active regenerative magnetic refrigeration (AMR) cycle. In Fig. 11, the dashed line indicates the temperature distribution before the process operation, and the solid line indicates the temperature distribution after the process operation. The magnetic refrigerator for the AMR cycle consists of an AMR bed, which doubles as a magnetic refrigeration material packed bed and a heat exchanger, a magnet, a drive unit (displacer), and a heat transfer medium (hydrogen, helium, air, etc.). The drive unit is a control device that adjusts the relative positions of the magnetic refrigeration material and the AMR bed.

[0034] The AMR cycle consists of four steps: adiabatic excitation, movement of the heat transfer medium (movement from the low temperature end to the high temperature end), adiabatic demagnetization, and movement of the heat transfer medium (movement from the high temperature end to the low temperature end). (1) In adiabatic excitation, the magnetic refrigeration material is excited, and the temperature of the entire AMR bed increases. (2) When transferring heat from the low temperature end to the high temperature end, the heat transfer medium is moved to the high temperature side by a driving device. The high temperature heat transfer medium in the AMR bed is transferred to the high temperature side, while the inflow of heat transfer medium from the low temperature side changes the temperature distribution in the AMR bed. (3) In adiabatic demagnetization, the temperature in the AMR bed decreases due to the magnetocaloric effect. The temperature decreases overall while maintaining a temperature distribution in the AMR bed. (4) When transferring heat from the hot end to the cold end, the heat transfer medium is moved to the cold end by a driving device. The cold heat transfer medium in the AMR bed is transferred to the cold side, while the inflow of heat transfer medium from the hot side changes the temperature distribution in the AMR bed.

[0035] If these four steps are considered one cycle, after one cycle the temperature distribution inside the AMR bed will be slightly lower on the low-temperature side than at the start of the cycle, and slightly higher on the high-temperature side than at the start of the cycle. By repeating this heat storage and regeneration cycle, the temperature difference increases, and eventually the temperature distribution inside the AMR bed becomes almost constant. This temperature distribution inside the AMR bed is determined by the properties of the magnetic refrigeration material that makes up the AMR bed.

[0036] FIG. 12 is a schematic diagram showing an example of an AMR in which magnetic refrigeration materials are arranged in a cascade arrangement, where (A) is a schematic diagram of the device, and (B) is an explanatory diagram of the operating temperature range of the magnetic refrigeration materials in this device. In the AMR shown in Figure 12, by selectively arranging magnetic refrigeration materials with different operating temperature ranges, it is possible to realize an AMR mechanism with a hierarchical structure that efficiently generates a temperature difference by magnetization and demagnetization. Curie temperature T C is the temperature at which a ferromagnetic material exhibits paramagnetism and corresponds to the temperature at which the maximum magnetocaloric effect occurs. Therefore, in the AMR shown in Figure 12, multiple temperature zones (T C1 ~T C4 ), a large magnetocaloric effect is observed, so performance degradation is unlikely to occur even if a temperature gradient is generated in the magnetic refrigeration material packed bed. C By selectively arranging magnetic refrigeration materials having this property, it is possible to realize an AMR suitable for hydrogen liquefaction.

[0037] FIG. 13 is a schematic diagram showing the main part of a magnetic refrigeration device. A magnetic refrigeration material including the material of the embodiment described above can be used. One form of the magnetic refrigeration material may be particles having a particle diameter in the range of 50 μm to 1000 μm. For example, the magnetic refrigeration material may be in the form of particles having a diameter of 50 μm or more, 100 μm or more, 200 μm or more, or 2000 μm or less, 1000 μm or less, or 500 μm or less, in a spherical approximation. In addition, these lower and upper limits may be appropriately combined to form a predetermined range. By adopting a particle form, the filling rate in the AMR bed can be increased, and the heat exchange cross-sectional area and pressure loss with the heat transport refrigerant can be changed depending on the particle diameter. The smaller the particle diameter, the larger the heat exchange cross-sectional area, which is effective in improving the refrigeration performance from this point of view, but on the other hand, the smaller the particle diameter, the higher the pressure loss, which reduces the refrigeration performance. The actual magnitude of the pressure loss depends not only on the particle diameter but also on the type of heat transport refrigerant and the operating conditions. Here, the particle size is the volume-based median diameter (d50), and the volume-based average particle size can be measured, for example, by a microtrack or laser scattering method. More specifically, static image analysis and dynamic image analysis can be adopted. In the former, a large number of particle images (SEM images, etc.) are taken, and the particle diameter converted into a circle from the area of ​​each particle can be obtained using image analysis software. A magnetic refrigeration device 200 equipped with such a magnetic refrigeration material can be used to generate ultra-low temperatures, for example, to liquefy hydrogen. The magnetic refrigeration device 200 further includes an AMR bed 220 filled with a magnetic refrigeration material 210, a magnetic field application means 230 that applies a magnetic field to the AMR bed 220, a cooling stage 290 that cools the object to be cooled by cold and hot, and a heat exchanger 240 that exhausts heat generated by the magnetic refrigeration work in the AMR bed 220.

[0038] The magnetic field application means 230 can be any means for applying a magnetic field to the AMR bed 220, 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 230. In addition, the relative positions of the magnetic field application means 230 and the AMR bed 220 can be changed by a driving mechanism (not shown) to change the magnitude of the magnetic field applied to the AMR bed 220.

[0039] A pre-cooling stage 260 is provided on the high temperature side of the AMR bed 220, and an 80K shield 270 is connected to the low temperature side of the pre-cooling stage 260, and a 300K shield 280 is connected to the high temperature side of the pre-cooling stage 260. Furthermore, a cooling stage 290 is provided on the low temperature side of the AMR bed 220, and a liquefying vessel 250 is provided and thermally connected to the cooling stage 290. That is, gas to be cooled is supplied to the liquefying vessel 250 and liquefied. In addition, an inlet and outlet for the heat transport refrigerant are provided in the AMR bed 220, and the heat transport refrigerant can flow back and forth inside the AMR bed 220 through the gaps in the magnetic refrigeration material 210.

[0040] The liquefaction vessel 250 is supplied with a gas 310 (e.g., hydrogen, helium (He), etc.) to be liquefied from a tank (not shown). The magnetic refrigeration device 200 may be operated as follows. A magnetic field is applied to the AMR bed 220 filled with the magnetic refrigeration material 210 by the magnetic field application means 230 to raise the temperature of the magnetic refrigeration material 210. Next, the heat transport refrigerant is caused to flow in a direction 300A from the low-temperature end side to the high-temperature end side of the AMR bed 220. The heat transport refrigerant exchanges heat with the magnetic refrigeration material 210 filled inside the AMR bed 220 and receives hot heat, while flowing through the gaps in the magnetic refrigeration material 210 and flowing out from the high-temperature end of the AMR bed 220. The heat transport refrigerant flowing out from the high-temperature end of the AMR bed 220 flows into the heat exchanger 240 that exhausts hot heat via the pre-cooling stage 260, and excess heat is exhausted to the outside. Next, the magnetic field in which the magnetic refrigeration material 210 is filled is removed (reduced), causing the temperature of the magnetic refrigeration material 210 to drop.

[0041] The heat transport refrigerant is then caused to flow in a direction 300B from the high temperature end side to the low temperature end side of the AMR bed 220. The heat transport refrigerant flows into the high temperature end of the AMR bed 220 via the pre-cooling stage 260, and while being cooled by heat exchange with the magnetic refrigeration material 210 filled inside, flows through the gaps in the magnetic refrigeration material 210, and reaches the low temperature end of the AMR bed 220. 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.

[0042] When the temperature of the low-temperature end of the AMR bed 220 drops below the boiling point of liquid hydrogen (20K at atmospheric pressure), the hydrogen gas supplied to the liquefaction vessel 250 is cooled and concentrated / liquefied by heat exchange with the cooling stage 290 provided on the low-temperature end side of the AMR bed 220. By repeating this process, the gas inside the liquefaction vessel 250 is periodically liquefied or cooled. [Industrial Applicability]

[0043] As described above in detail, the ErCo2-based magnetocaloric compound of the present invention can provide a magnetic refrigeration material useful for a hydrogen liquefaction device using an AMR cycle. The ErCo2-based magnetocaloric compound of the present invention can open up new horizons for the use of RECo2-based materials for ultra-low temperature magnetic refrigeration applications. [Explanation of symbols]

[0044] 200 Magnetic Refrigeration Device 220 AMR Bed 230 Magnetic field application means 240 Heat exchanger 250 Liquefaction vessel 260 Pre-cooling stage 270 80K Shield 280 300K Shield 290 Cooling Stage 300A Heat transport refrigerant flow direction 300B Heat transport refrigerant flow direction

Claims

1. It is composed of Er (erbium), Co (cobalt), Al (aluminum), Fe (iron), Ni (nickel) and unavoidable impurities, and has the following composition formula: ErCo ２－ｘ－ｙ (Al, Fe) ｘ Ni ｙ 0.01≦x≦0.1, 0.01≦y≦0.2; Magnetic phase transition temperature T ｔｒ is in the temperature range of 25K to 46K, The transition temperature T ｔｒ A magnetic refrigeration material characterized by exhibiting a second-order magnetic phase transition in the range of about 20 K.

2. The compound has the following formula: ErCo ２－ｘ－ｙ A ｘ Ni ｙ 2. The magnetic refrigeration material according to claim 1, having a composition satisfying the following formula: 0.01≦x≦0.1, 0.01≦y≦0.

2.

3. The compound has the following formula: ErCo ２－ｘ－ｙ A ｘ Ni ｙ 3. The magnetic refrigeration material according to claim 2, having a composition satisfying the following formula: 0.01≦x≦0.1, 0.12≦y≦0.

2.

4. The compound has the following formula: ErCo ２－ｘ－ｙ Fe ｘ Ni ｙ 2. The magnetic refrigeration material according to claim 1, having a composition satisfying the following formula: 0.035≦x≦0.1, 0.01≦y≦0.

2.

5. In the magnetic refrigeration material according to any one of claims 1 to 4, the second-order magnetic phase transition occurs at a transition temperature T ｔｒ A magnetic refrigeration material having a volume change rate (dV / V) of 0.4% or less within a range of 20K around the temperature.

6. 5. The magnetic refrigeration material according to claim 1, wherein the transition temperature T ｔｒ Within a range of 20 K around the center, the entropy change is ΔS>0.05 J / cm under a 5 T magnetic field. ３ A magnetic refrigeration material characterized in that K is obtained.

7. The magnetic refrigeration material according to claim 6, The entropy change is ΔS>0.1 J / cm under a 5 T magnetic field. ３ A magnetic refrigeration material characterized in that K is obtained.

8. A magnetic refrigeration device using the magnetic refrigeration material according to any one of claims 1 to 7.

9. A hydrogen liquefaction system or a helium liquefaction system using the magnetic refrigeration system according to claim 8.

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