Magnetic refrigeration material and magnetic refrigeration device using the same

Abstract

To provide a magnetic refrigeration material consisting of only a rock forming element, such as iron, manganese, chlorine, hydrogen and oxygen and showing a large magnetocaloric effect in a temperature of 20-30K.SOLUTION: A magnetic refrigeration material may includes: (Fe1-xMnx)Cl2(0≤x≤0.14) having a trigonal system (R-3m) cadmium chloride anhydrate type structure as a main component; and (Fe1-xMnx)2H2O(0≤x≤0.14) having a monoclinic system (C12 / m1) cadmium chloride dihydrate type structure or (Fe1-xMnx)Cl2 H2O having an ortho rhombic system (Pnma) cadmium chloride monohydrate type structure as a hydrous sub-component. The ratio of one of the (110) plane X diffraction intensity of the (Fe1-xMnx)2H2O as a hydrous sub-component and the (101) plane X diffraction intensity of the (Fe1-xMnx)H2O as a hydrous sub-component to the (003) plane X diffraction intensity of the main component is 4:1 or less.SELECTED DRAWING: Figure 18

Description

[Technical Field]

[0001] The present invention relates to a magnetic refrigeration material suitable for use in producing liquid hydrogen and a magnetic refrigeration device using the same. [Background technology]

[0002] Hydrogen is a storable, next-generation energy source that can replace fossil fuels in a carbon-neutral society, and liquid hydrogen is preferable for efficient storage and transportation. Until now, gas refrigeration technology, which exploits the entropy change that accompanies the compression and expansion of gases, has been used for cooling, both in industrial and residential applications. However, the efficiency of gas refrigeration declines significantly at extremely low temperatures (see Non-Patent Document 1), and its use in the production of liquid hydrogen consumes a large amount of energy. For this reason, attempts have been made to use magnetic refrigeration, which can provide efficient cooling even at extremely low temperatures. Because the boiling point of hydrogen is between 20 K (1 atm) and 30 K (8 atm), and the efficiency of gas refrigeration declines with decreasing temperature, magnetic refrigeration is particularly promising in the temperature range between 20 K and 30 K, where gas refrigeration performance is at its lowest.

[0003] Magnetic refrigeration is a refrigeration technology that uses the magnetocaloric effect of magnetic materials. The magnetocaloric effect refers to the phenomenon whereby the magnetic entropy of a magnetic material changes when the strength or direction of the magnetic field applied to the magnetic material is changed, inducing a temperature change. For magnetic refrigeration technology to be put into practical use, it is necessary to use magnetic materials that exhibit a large magnetocaloric effect, and various types of magnetic materials are being explored. In this case, the magnetic entropy change ΔS obtained when the magnetic field is changed is M is mainly used as an index of magnetic refrigeration performance.

[0004] First, materials that exhibit a large magnetocaloric effect in the temperature range of 20K to 30K when the magnetic field strength is increased or decreased from zero to a finite magnetic field include the boride LnB2 containing the rare earth element Ln, the nitride LnN, the cobalt alloy LnCo2, the aluminum alloy LnAl2, and the nickel alloy LnNi2. Table 1 shows the temperature T at which the largest magnetic entropy change is obtained when a magnetic field ranging from zero to 5T is applied to these materials. M Table 1 shows the magnitude of the large magnetocaloric effect (entropy change of approximately 15 J kg) between no magnetic field and a magnetic field of 5 T at around 20-30 K. -1 ·K -1 All known materials that have a large magnetocaloric effect around 20-30K contain rare earth elements. [Table 1] Such large (approximately 15 J·kg -1 ·K -1 As for materials that exhibit the magnetocaloric effect (above), examples have already been reported in which they have been incorporated into magnetic refrigerators that can change the strength of the magnetic field (LnN: see Non-Patent Document 2, LnAl2: see Non-Patent Document 3, LnNi2: see Non-Patent Document 4, where Ln is a rare earth element). However, all of these materials that exhibit a large magnetocaloric effect when the magnetic field strength is changed from no magnetic field to 5 T all contain large amounts of rare elements such as rare earth elements, and there have been problems with the resource supply that would prevent liquid hydrogen from being widely used as the foundation for a carbon-neutral society.

[0005] Furthermore, the increase or decrease in the magnetic field strength may be a finite magnetic field of a different magnitude from a non-zero finite magnetic field. In the case of a method that changes the current flowing through a superconducting electromagnet, the magnetic field strength can be easily set to zero by stopping the current (see Non-Patent Document 4), but a large amount of power is required to change the magnetic field throughout the entire space inside the magnet. On the other hand, in the method of extracting the magnetic refrigeration material from the superconducting electromagnet rather than changing the current (see, for example, Patent Documents 1 and 2), it is only necessary to input mechanical energy equivalent to the magnetic energy of only the magnetic refrigeration material, resulting in high power efficiency. However, with a conventional solenoid coil-type superconducting magnet, it is difficult to reduce the magnetic field strength to zero when the material is extracted due to the leakage magnetic field (see Non-Patent Document 3). This has led to the need for a magnetic refrigeration material that can operate between a non-zero finite magnetic field and a finite magnetic field of different magnitude. However, with previous magnetic refrigeration materials that utilize ferromagnetism, the magnetic entropy change is greatest near zero magnetic field (see Non-Patent Document 5), making it difficult to efficiently utilize the magnetocaloric effect, as in the example of LnN (Ln = Dy) in Table 2. Table 2 shows that a somewhat large magnetocaloric effect (entropy change of approximately 5 J·kg) is observed between a finite magnetic field and a different finite magnetic field around 20-30 K. -1 ·K -1 The magnetic refrigeration material and the present example show the above. [Table 2] As a method for shifting the magnetic field range where such a large magnetic entropy change occurs from near zero magnetic field, the use of spin reorientation from an antiferromagnetic state has been theoretically proposed (see Non-Patent Document 6), and it has been shown that this can be achieved with pure holmium metal. However, the total amount of magnetic entropy change is not as large as other methods, as shown in Table 2. Furthermore, when the magnetic field strength is changed from a finite magnetic field to a finite magnetic field, a somewhat large entropy change (approximately 5 J kg -1 ·K -1 All of the materials that exhibit the magnetocaloric effect contain large amounts of rare elements such as rare earth elements, and there are problems with resource supply when it comes to widely using liquid hydrogen as the foundation for a carbon-neutral society.

[0006] On the other hand, in addition to the method of changing the magnetic field strength described above, there is also a known method of obtaining the magnetocaloric effect by changing the direction of the magnetic field or the orientation of the magnetic refrigeration material relative to the magnetic field, without changing the current in the superconducting electromagnet (see, for example, Figure 2 in Non-Patent Document 7). Table 3 shows magnetic refrigeration materials that exhibit a large magnetocaloric effect (entropy change) when a magnetic field rotates around 20-30 K, as well as examples of these materials. All known materials that exhibit a large rotational magnetocaloric effect around 20-30 K contain rare earth elements. These materials also contain large amounts of rare elements such as rare earth elements, and there have been problems with resource supply when using liquid hydrogen widely as the foundation for a carbon-neutral society. [Table 3]

[0007] Among materials composed of the twelve major elements (rock-forming elements) that make up the Earth's crust, namely oxygen, silicon, aluminum, iron, calcium, sodium, potassium, magnesium, hydrogen, titanium, chlorine, and manganese, alloys, intermetallic compounds, and oxides exhibit strong magnetic coupling between magnetic ions such as iron, titanium, and manganese, resulting in a large magnetocaloric effect at high temperatures, including room temperature. Therefore, their use in room-temperature magnetic refrigeration is being considered. Meanwhile, in the case of paramagnetic salts, in which water molecules are intercalated between the magnetic ions, the magnetic coupling between the magnetic ions is extremely weak, resulting in a large magnetocaloric effect at temperatures below 4 K. Therefore, iron alum (NH4Fe(SO4)2·12H2O) and chrome alum (KCr(SO4)2·12(H2O)) are used in ultralow-temperature adiabatic demagnetization refrigerators. However, in the intermediate temperature range of 20 to 30 K used for hydrogen liquefaction, although MnSi exhibits a certain magnetocaloric effect, no other materials have been reported that are primarily composed of rock-forming elements that do not pose a problem in terms of resource supply, even when including rare transition metal elements (Table 4). Table 4 shows the transition metal alloys and compounds that have been reported to have a magnetocaloric effect (entropy change) in the temperature range of around 20-30 K, as well as the examples used in this study. -1 ·K -1 There are no known transition metal alloys or compounds that exhibit these properties. [Table 4] [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2015 / 199139 [Patent Document 2] International Publication No. 2016 / 204294 [Non-patent literature]

[0009] [Non-Patent Document 1] J.Phys.: Condens. Matter 21 (2009) 164219 [Non-patent document 2] Cryocoolers 16, (2010) 531-535, [Non-patent document 3] Superconductivity and Cryogenics 15, (2013), 1-8 [Non-patent document 4] Cryogenics 57 (2013) 113-121 [Non-Patent Document 5] Acta Phys. Polonica A 127, 815-817 (2015). [Non-patent document 6] Appl. Phys. Lett. 104, 052415 (2014) [Non-Patent Document 7] Nature Communications volume 12, Article number 1212 (2021) Summary of the Invention [Problem to be solved by the invention]

[0010] In conventional technology, materials composed of the twelve major elements (rock-forming elements) were sought to obtain a large magnetocaloric effect in the temperature range of 20 K to 30 K, which is the boiling point of liquid hydrogen. However, there was a problem in that the temperatures at which alloys, intermetallic compounds, and oxides composed of the twelve major elements (rock-forming elements: O, Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, H, and Cl) exhibit a large magnetocaloric effect were too high, while the temperatures at which paramagnetic salts with hydration water exhibit a large magnetocaloric effect were too low.

[0011] As mentioned above, even in the prior art, the thermal conductivity is 15 J kg in the temperature range of 20-30 K. -1 ·K -1 Materials with such large magnetocaloric effects have been developed, and methods have been proposed for incorporating them into magnetic refrigerators that produce liquid hydrogen. However, all of the materials developed using conventional background technology contain rare metal elements, and because liquid hydrogen is widely used throughout society, there have been practical issues with resource supply when incorporating them into a large number of magnetic refrigerators around the world.

[0012] Furthermore, in the method of extracting the magnetic refrigeration material from the superconducting electromagnet, it is difficult to reduce the magnetic field strength to zero due to the leakage magnetic field. Therefore, the magnetic refrigeration material incorporated into the magnetic refrigerator in the background art had the problem of being unable to utilize the magnetic field range with the greatest magnetocaloric effect. The object of the present invention is to provide a magnetic refrigeration material that uses transition metal chlorides from which water molecules have been removed and that exhibits a large magnetocaloric effect in the temperature range of 20-30K, using only rock-forming elements such as iron, manganese, chlorine, hydrogen, and oxygen. Another object of the present invention is to provide a magnetic refrigeration device using the above magnetic refrigeration material. [Means for solving the problem]

[0013] [1] The magnetic refrigeration material of the present invention has a trigonal (R-3m) cadmium chloride anhydrate structure (Fe 1-x Mn x ) Cl2 (0≦x≦0.14) as the main component, Monoclinic (C12 / m1) cadmium chloride dihydrate type structure (Fe 1-x Mn x )·2H2O (0≦x≦0.14) or orthorhombic (Pnma) cadmium chloride monohydrate type structure (Fe 1-x Mn x ) Cl₂·H₂O may be included as a water-containing minor component, Water-containing subcomponents (Fe 1-x Mn x )·2H2O (110) plane X-ray diffraction intensity or hydrous subcomponent (Fe 1-x Mn x The ratio of the (101) X-ray diffraction intensity of )·H2O to the (003) X-ray diffraction intensity of the main component is 4:1 or less. [2] In the magnetic refrigeration material [1] of the present invention, preferably, the main component is used alone, and the water-containing subcomponent is below the detection limit of X-ray diffraction intensity. [3] In the magnetic refrigeration material [1] or [2] of the present invention, preferably, Cadmium chloride anhydrate structure (Fe 1-x Mn x )Cl2 (0≦x≦0.14) with the c-axis, which is the easy axis of magnetization, aligned, and the remanent magnetization M at 2 K extrapolated from the magnetization curve in the ferromagnetic state. r and saturation magnetization M s Ratio (squareness ratio M r / M s ) should be greater than 0.5. [4] In the magnetic refrigeration materials [1] to [3] of the present invention, preferably, It is preferable to show a large magnetocaloric effect by changing the strength of the applied magnetic field from a range of 1 to 2 T to a range of 5 to 6 T.

[0014] [5] The magnetic refrigeration device of the present invention is configured such that the direction of application of a magnetic field to the magnetic refrigeration material [3] is changed to a cadmium chloride anhydrate structure (Fe 1-x Mn x This magnetic refrigeration device exhibits a large magnetocaloric effect when rotated from a direction parallel to the c-axis, which is the axis of easy magnetization of ZnO (0≦x≦0.14), to a direction perpendicular to the c-axis. [Effects of the Invention]

[0015] The magnetic refrigeration material of the present invention uses only the rock-forming elements iron, manganese, chlorine, hydrogen, and oxygen to provide a material that exhibits a large magnetocaloric effect through low-power consumption, i.e., through changes in magnetic field strength or direction without completely eliminating the magnetic field, in the temperature range of 20 K to 30 K, the boiling point of liquid hydrogen.The magnetic refrigeration material of the present invention, which exhibits a large magnetocaloric effect through efficient magnetic field changes, can be used in magnetic refrigerators for hydrogen liquefaction, without considering resource depletion.

[0016] Furthermore, the magnetic refrigeration device of the present invention takes advantage of the antiferromagnetic properties of anhydrous iron chloride to obtain a large magnetocaloric effect even when a magnetic field from a finite magnetic field is applied. Therefore, even in a magnetic refrigeration device that extracts magnetic refrigeration material from a low-power superconducting magnet, there is no need to completely eliminate the magnetic field, which simplifies the design of the magnetic refrigeration device and improves the performance of the magnetic refrigerator. [Brief explanation of the drawings]

[0017] [Figure 1A] FIG. 1 is a schematic structural diagram of iron (II) chloride hydrate used in a comparative example of the present invention, showing the monoclinic P121 / c1 iron (II) chloride tetrahydrate structure. [Figure 1B] Schematic structural diagram of iron (II) chloride hydrate used in one embodiment of the present invention, in which the monoclinic system (C12 / m1) shows a cadmium chloride dihydrate structure. [Figure 1C] In the structural diagram of iron (II) chloride hydrate used in one embodiment of the present invention, the orthorhombic system (Pnma) shows a cadmium chloride monohydrate type structure. [Figure 1D] FIG. 1 is a schematic structural diagram of iron (II) chloride hydrate used in one embodiment of the present invention, showing a trigonal (R-3m) anhydrous cadmium chloride structure. [Figure 2] FIG. 1 shows an X-ray diffraction pattern for Cr characteristic X-rays of iron (II) chloride tetrahydrate powder that is stable in a humid atmosphere. [Figure 3]FIG. 1 shows the temperature dependence of magnetization of iron (II) chloride tetrahydrate powder, which is stable in a humid atmosphere, in a magnetic field of 0.1 T. [Figure 4] FIG. 1 shows the magnetic field dependence of magnetization of iron(II) chloride tetrahydrate powder, which is stable in a humid atmosphere, at low temperatures and near the boiling point of hydrogen. [Figure 5] This figure shows the entropy change when the magnetic field of iron (II) chloride tetrahydrate powder, which is stable in a humid atmosphere, is changed from no magnetic field to 1 T, 2 T, or 5 T. [Figure 6] FIG. 1 shows the X-ray diffraction pattern of partially dehydrated iron (II) chloride powder for Cr characteristic X-rays. [Figure 7] FIG. 1 shows the temperature dependence of magnetization of partially dehydrated iron(II) chloride powder in a magnetic field of 0.1 T. [Figure 8] FIG. 1 shows the magnetic field dependence of magnetization of partially dehydrated iron(II) chloride powder at low temperatures and near the hydrogen boiling point. [Figure 9] This figure shows the entropy change when the magnetic field of partially dehydrated iron (II) chloride powder is changed from no magnetic field to 1 T, 2 T, or 5 T. [Figure 10] FIG. 1 shows an X-ray diffraction pattern for Cr characteristic X-rays of completely dehydrated anhydrous iron (II) chloride powder. [Figure 11] FIG. 1 shows the temperature dependence of magnetization of completely dehydrated anhydrous iron (II) chloride powder in a magnetic field of 0.1 T. [Figure 12] FIG. 1 shows the magnetic field dependence of magnetization of completely dehydrated anhydrous iron (II) chloride powder at low temperatures and near the hydrogen boiling point. [Figure 13] This figure shows the entropy change when the magnetic field of completely dehydrated anhydrous iron (II) chloride powder is changed from no magnetic field to 1 T, 2 T, or 5 T. [Figure 14] FIG. 1 shows an X-ray diffraction pattern for Cr characteristic X-rays of a powder of oriented completely dehydrated anhydrous iron (II) chloride. [Figure 15]This figure shows the temperature dependence of magnetization when a 0.1 T magnetic field is applied parallel or perpendicular to the compression axis (orientation axis) direction (c) to anhydrous iron (II) chloride powder obtained by aligning completely dehydrated anhydrous iron (II) chloride. [Figure 16] This shows the magnetic field dependence of magnetization when a magnetic field is applied parallel or perpendicular to the compression axis (orientation axis) direction (c) of anhydrous iron (II) chloride powder, which is an oriented powder of completely dehydrated anhydrous iron (II) chloride, at low temperatures and near the hydrogen boiling point. [Figure 17] This figure shows the entropy change when a magnetic field is applied from no magnetic field to 1 T, 2 T, or 5 T in the direction of the compression axis (orientation axis) (c) of iron (II) chloride tetrahydrate powder, which is an oriented powder of completely dehydrated anhydrous iron (II) chloride. [Figure 18] This figure shows the entropy change when a magnetic field is applied from no magnetic field to 5 T parallel or perpendicular to the compression axis (orientation axis) direction (c) of iron (II) chloride tetrahydrate powder, which is an oriented powder of completely dehydrated anhydrous iron (II) chloride. [Figure 19] FIG. 1 shows the X-ray diffraction pattern for Cr characteristic X-rays of a mixed oriented powder of 14% manganese-doped iron (II) chloride anhydrate / monohydrate. [Figure 20] FIG. 1 shows the temperature dependence of magnetization of anhydrous iron (II) chloride powders with various manganese doping amounts in a magnetic field of 0.1 T. [Figure 21] This shows the magnetic field dependence of magnetization when a magnetic field is applied parallel or perpendicular to the compression axis direction (c) of a mixed oriented powder of 14% manganese-doped iron (II) chloride anhydrate / monohydrate at low temperatures and near the hydrogen boiling point. [Figure 22] This figure shows the entropy change when the magnetic field applied to a mixed oriented powder of 14% manganese-doped iron (II) chloride anhydrate / monohydrate is changed from no magnetic field to 1 T, 2 T, or 5 T. [Figure 23] 1 is a schematic diagram illustrating each step of a magnetic refrigeration cycle in which the magnetic refrigeration material of the present invention is used. FIG. [Figure 24] FIG. 1 is a schematic diagram illustrating an active magnetic regenerator (AMR) cycle. [Figure 25] Schematic diagrams 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. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be described below with reference to the drawings. 1A to 1D are structural diagrams of iron(II) chloride hydrates used in the examples and comparative examples of the present invention, where (a) is a monoclinic P121 / c1 iron(II) chloride tetrahydrate structure, (b) is a monoclinic (C12 / m1) cadmium chloride dihydrate structure, (c) is an orthorhombic (Pnma) cadmium chloride monohydrate structure, and (d) is a trigonal (R-3m) cadmium chloride anhydrate structure.

[0019] <Comparative Example 1> X-ray diffraction was measured for iron(II) chloride tetrahydrate (FeCl2·4H2O) (99%) powder, which is stable in humid atmosphere. Figure 2 shows the X-ray diffraction pattern for Cr characteristic X-rays of iron(II) chloride tetrahydrate powder, which is stable in humid atmosphere. The plane indices and calculated diffraction line positions indicated by vertical bar markers at the bottom of the figure are for the iron(II) chloride tetrahydrate structure in Figure 1(a). The known monoclinic P121 / c1 iron(II) chloride tetrahydrate structure (Figure 1(a)) was confirmed. The temperature and magnetic field dependence of magnetization of this sample was measured. Figure 3 shows the temperature dependence of magnetization in a magnetic field of 0.1 T for iron(II) chloride tetrahydrate powder, which is stable in a humid atmosphere. Figure 4 shows the magnetic field dependence of magnetization at low temperatures and near the boiling point of hydrogen for iron(II) chloride tetrahydrate powder, which is stable in a humid atmosphere. The magnetization in a magnetic field μH = 0.1 T monotonically increased from 60 K to 2 K as the temperature T decreased. Furthermore, within this temperature range, the magnetization increased as the magnetic field was increased from zero. In other words, the sample was paramagnetic, with no magnetic order.

[0020] Next, we use the measured temperature and magnetic field dependence of the magnetization to obtain Maxwell's equation

number

[0021] Example 1 X-ray diffraction was measured on iron(II) chloride powder, which was prepared by partially removing water molecules from iron(II) chloride tetrahydrate. Figure 6 shows the X-ray diffraction pattern of partially dehydrated iron(II) chloride powder for Cr characteristic X-rays. The plane indices and calculated diffraction line positions indicated by vertical bar markers at the bottom of the figure correspond to the anhydrous iron(II) chloride structure shown in Figure 1(d) in the upper row and the iron(II) chloride dihydrate structure shown in Figure 1(b) in the lower row. The partially dehydrated iron(II) chloride powder was shown to be a mixture of FeCl2 (Fig. 1(d)), which has the known trigonal (R-3m) cadmium chloride anhydrate structure, and FeCl2·2H2O (Fig. 1(b)), which has the monoclinic (C12 / m1) cadmium chloride dihydrate structure. The ratio of the X-ray diffraction intensity of the (110) plane of the dihydrate to the X-ray diffraction intensity of the (003) plane of the anhydrate was used as an indicator of the mixture ratio, which was 1:4.

[0022] The temperature and magnetic field dependence of magnetization of this sample was measured. Figure 7 shows the temperature dependence of magnetization of partially dehydrated iron (II) chloride powder in a magnetic field of 0.1 T. Figure 8 shows the magnetic field dependence of magnetization of partially dehydrated iron (II) chloride powder at low temperatures and near the hydrogen boiling point. When the temperature is lowered from 60 K, the magnetization at a magnetic field μ0H = 0.1 T increases once and then decreases at the antiferromagnetic transition temperature T of the anhydrate. N It shows a maximum value at 24K, and then decreases. N At a higher temperature of 26K, when the magnetic field is increased from zero, the magnetization increases at a gradually decreasing rate. On the other hand, this T N When the magnetic field is increased from zero at lower temperatures, 18 K or 22 K, the rate of increase in magnetization increases from around 0.5 T to 1 T at 18 K and from around 1 T to 1.5 T at 22 K due to spin reorientation from the antiferromagnetic state to the ferromagnetic state.

[0023] From the measured temperature and magnetic field dependence of the magnetization, we used Maxwell's equation to calculate the change in magnetic entropy ΔS when a magnetic field of H1=0 is applied to each temperature, from zero to H2=1T, 2T, or 5T. M Figure 9 shows the entropy change when the magnetic field of partially dehydrated iron (II) chloride powder is changed from no magnetic field to 1 T or 5 T. ΔS M The magnitude of is -15 J kg when a magnetic field of 5 T is applied from no magnetic field at 25 K. -1 ·K -1 This is the ΔS of the transition metal alloys / compounds shown in Table 4. M The ΔS at 20 K of existing magnetic refrigeration materials containing rare elements shown in Table 1, such as Ln5Pd2 (Ln = Er), is much larger than the M It was the same size as

[0024] <Example 2> X-ray diffraction was measured on anhydrous iron(II) chloride powder, in which water molecules were completely removed from iron(II) chloride tetrahydrate. Figure 10 shows the X-ray diffraction pattern for Cr characteristic X-rays of completely dehydrated anhydrous iron(II) chloride powder. The plane indices and calculated diffraction line positions indicated by vertical bar markers at the bottom of the figure correspond to the anhydrous iron(II) chloride structure in Figure 1(d). The anhydrous iron(II) chloride powder, in which water molecules were completely removed from the tetrahydrate, was confirmed to be a simple substance, FeCl2 (Figure 1(d)), with the known trigonal (R-3m) anhydrous cadmium chloride structure. The temperature and magnetic field dependence of magnetization of this sample was measured. Figure 11 shows the temperature dependence of magnetization of completely dehydrated anhydrous iron (II) chloride powder in a magnetic field of 0.1 T. Figure 12 shows the magnetic field dependence of magnetization of completely dehydrated anhydrous iron (II) chloride powder at low temperatures and near the hydrogen boiling point. The magnetization at a magnetic field μ0H=0.1 T increases once when the temperature is lowered from 60 K, and then decreases at the antiferromagnetic transition temperature T N It shows a maximum value at 24K, and then decreases. N At a higher temperature of 26K, when the magnetic field is increased from zero, the magnetization increases at a gradually decreasing rate. N When the magnetic field is increased from zero at lower temperatures, 18 K or 22 K, the rate of increase in magnetization increases from around 0.5 T to 1 T at 18 K and from around 1 T to 1.5 T at 22 K due to spin reorientation from the antiferromagnetic state to the ferromagnetic state.

[0025] From the measured temperature and magnetic field dependence of the magnetization, we used Maxwell's equation to calculate the change in magnetic entropy ΔS when a magnetic field of H1=0 is applied to each temperature, from zero to H2=1T, 2T, or 5T. M 13 is a graph showing the entropy change when the magnetic field applied to a completely dehydrated anhydrous iron (II) chloride powder is changed from no magnetic field to 1 T or 5 T. Change in magnetic entropy ΔS M The magnitude of is -19 J kg when a magnetic field of 5 T is applied from no magnetic field at 25 K. -1 ·K -1This is the ΔS of the transition metal alloys / compounds shown in Table 4. M The ΔS at 23 K of existing magnetic refrigeration materials containing rare elements shown in Table 1, such as LnMn2 (Ln = Ho), is much larger than the M It was the same size as

[0026] Example 3 X-ray diffraction measurements were performed on anhydrous iron(II) chloride (FeCl2), a powder prepared by completely removing water molecules from iron(II) chloride tetrahydrate, when pressure was applied to the powder and oriented. X-rays were irradiated in a plane perpendicular to the compression axis (c). Figure 14 shows the X-ray diffraction pattern for Cr-characteristic X-rays of an oriented powder of completely dehydrated anhydrous iron(II) chloride. The plane indices and calculated diffraction line positions indicated by vertical bar markers at the bottom of the figure correspond to the anhydrous iron(II) chloride structure shown in Figure 1(d). Anhydrous iron(II) chloride (FeCl2), prepared by completely removing water molecules from iron(II) chloride tetrahydrate, has the known trigonal (R-3m) cadmium chloride anhydrate structure (Figure 1(d)). The X-ray diffraction pattern shows the predominant diffraction intensity of the (003) plane, confirming that the c-axis of the crystal is preferentially oriented along the compression axis.

[0027] We also measured the temperature and magnetic field dependence of magnetization when a magnetic field was applied parallel or perpendicular to the compression axis for powders oriented by applying pressure. Figure 15 shows the temperature dependence of magnetization when a 0.1 T magnetic field was applied parallel or perpendicular to the compression axis direction (c) to anhydrous iron (II) chloride powder obtained by aligning completely dehydrated anhydrous iron (II) chloride. Figure 16 shows the magnetic field dependence of magnetization when a magnetic field was applied parallel or perpendicular to the compression axis direction (c) to anhydrous iron (II) chloride powder obtained by aligning completely dehydrated anhydrous iron (II) chloride at low temperatures and near the hydrogen boiling point. When a magnetic field μH = 0.1 T was applied, the magnetization initially increased when the temperature was lowered from 60 K, whether parallel or perpendicular to the compression axis, and then decreased at the antiferromagnetic transition temperature T N It shows a maximum value at 24K, and then decreases, but the degree of change is larger when the compression axis is parallel. NWhen the magnetic field is increased from zero at lower temperatures, such as 18K or 22K, the rate of increase in magnetization becomes significantly larger at around 0.5T to 1T at 18K and around 1T to 1.5T at 22K when the magnetic field is parallel to the compression axis.

[0028] On the other hand, when a magnetic field is applied perpendicular to the compression axis, such a sudden increase is not clearly observed. This is because ferromagnetic spin reorientation occurs in the direction of the easy axis of magnetization, which is parallel to the c-axis. Generally, the remanent magnetization M r and saturation magnetization M s Ratio (squareness ratio M r / M s ) is used, and approaches 1 as the degree of orientation increases from 0.5 in the non-oriented state. Following this, the remanent magnetization M r The squareness ratio M r / M s The squareness ratio M r / M s (0.5) From the temperature and magnetic field dependence of the magnetization measured for this oriented powder, Maxwell's equation was used to calculate the change in magnetic entropy ΔS when a magnetic field of H1 = 0 to H2 = 1 T, 2 T, or 5 T was applied at each temperature. M Figure 17 shows the entropy change when a magnetic field ranging from no magnetic field to 1 T or 5 T is applied in the direction of the compression axis (c) to an anhydrous iron (II) chloride powder, which is an iron (II) chloride tetrahydrate powder prepared by aligning completely dehydrated anhydrous iron (II) chloride.

[0029] Change in magnetic entropy ΔS M The magnitude of is -24 J kg when a magnetic field of 5 T is applied from no magnetic field at 24 K. -1 ·K -1 This is the ΔS of the transition metal alloys / compounds shown in Table 4. M The rare elements shown in Table 1 are much larger than the ΔS MThis is equivalent to the size of existing magnetic refrigeration materials. Furthermore, the ΔS M The change in magnetic entropy ΔS when the magnetic field obtained from the difference between H1 and H2 is reversed from H1=1T to H2=5T M The magnitude of is -22 J kg at 24 K. -1 ·K -1 This is the same size as the existing magnetic refrigeration materials containing rare elements shown in Table 2. Figure 18 shows the entropy change when a magnetic field is applied from no magnetic field to 5 T parallel or perpendicular to the compression axis direction (c) to iron (II) chloride tetrahydrate powder, which is an iron (II) chloride anhydrate powder obtained by aligning completely dehydrated iron (II) chloride anhydrate. The change in magnetic entropy ΔS M This difference is due to the change in magnetic entropy ΔS when rotating between these orientations in this magnetic field. M In this example, this change is -18 J kg -1 ·K -1 This is equivalent to the rotational magnetocaloric effect of existing magnetic refrigeration materials containing rare elements, as shown in Table 3.

[0030] Example 4 FeCl2·4H2O and MnCl2·4H2O, which has the same structure, were mixed in a molar ratio of 1-x:x (x≦0.14), dissolved in pure water, and reprecipitated (Fe 1-x Mn xX-ray diffraction measurements were performed on a manganese-doped iron chloride powder prepared by dehydrating most of the water molecules from )Cl₂·4H₂O. The powder was oriented by applying pressure, and X-rays were irradiated in a plane perpendicular to the compression axis (c). Figure 19 shows the X-ray diffraction pattern for the 14% manganese-doped iron(II) chloride anhydrate / monohydrate mixed oriented powder, measured using characteristic Cr X-rays. The calculated diffraction positions indicated by the vertical bar markers at the bottom of the figure correspond to the iron(II) chloride anhydrate structure shown in Figure 1(d) (top row) and the iron(II) chloride monohydrate structure shown in Figure 1(c) (bottom row). This X-ray diffraction pattern indicates a mixture of the anhydrate (Figure 1(d)) with the known trigonal (R-3m) cadmium chloride anhydrate structure and the monohydrate (Figure 1(c)) with the orthorhombic (Pnma) cadmium chloride monohydrate structure. In the example of x=0.14 shown in FIG. 17, the ratio of the X-ray diffraction intensity of the (101) plane of the monohydrate to the X-ray diffraction intensity of the (003) plane of the anhydrate was approximately 1:10 as an index of the mixing ratio.

[0031] The temperature dependence of magnetization was measured for these manganese-doped iron chloride powders when a magnetic field was applied parallel to the compression axis. Figure 20 shows the temperature dependence of magnetization for anhydrous iron (II) chloride powders with various manganese doping amounts in a magnetic field of 0.1 T. The temperature T at which a peak associated with the antiferromagnetic transition appears in the temperature dependence of magnetization when a magnetic field μH = 0.1 T is applied is shown. N decreased with increasing manganese doping amount x.

[0032] The magnetization curve for the example of x=0.14 shown in FIG. 21 shows the same T N At lower temperatures, such as 14K or 18K, when the magnetic field is increased from zero, the magnetization increases sharply, indicating that spin reorientation occurs in the ferromagnetic configuration. r The squareness ratio M r / M s The result was 0.69. Now, from the measured temperature and magnetic field dependence of the magnetization, we use the Coswell's relation to calculate the change in magnetic entropy ΔS when a magnetic field of H1=0 is applied to H2=1T, 2T, or 5T at each temperature. M Fig. 22 shows the change in entropy when the magnetic field of the oriented mixed powder of 14% manganese-doped iron (II) chloride anhydrate / monohydrate is changed from no magnetic field to 1 T or 5 T. The change in magnetic entropy ΔS M The magnitude of is -19 J kg when a 5 T magnetic field is applied at 20 K. -1 ·K -1 This is the ΔS of the transition metal alloys / compounds shown in Table 4. M The rare elements shown in Table 1 are also included, and the maximum ΔS M The size was comparable to that of the existing magnetic refrigeration material Er5Pd2, which has a

[0033] Next, a magnetic refrigeration device using the magnetic refrigeration material of the present invention will be described. FIG. 23 is a schematic diagram illustrating each step of the magnetic refrigeration cycle. In a magnetic refrigeration cycle, a thermal cycle similar to a vapor compression cycle is constructed based on a repeated cycle of temperature rise due to a decrease in entropy caused by excitation in an adiabatic state, heat release due to thermal contact (insulation release) with one end (top end in the diagram), temperature drop due to an increase in entropy caused by demagnetization in a re-adiabatic state, and heat absorption due to thermal contact (insulation release) with the opposite end (bottom end in the diagram).

[0034] Fig. 24 is a schematic diagram illustrating an active regenerative magnetic refrigeration (AMR) cycle. In Fig. 24, the dashed line indicates the temperature distribution before the process operation, and the solid line indicates the temperature distribution after the process operation. A magnetic refrigerator for the AMR cycle consists of an AMR bed, which doubles as a packed bed of magnetic refrigeration material and a heat exchanger, a magnet, a drive unit (displacer), and a heat transfer medium (hydrogen, helium, etc.). The drive unit is a control device that adjusts the relative positions of the magnetic refrigeration material and the AMR bed.

[0035] 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). In adiabatic excitation, the magnetic refrigeration material is magnetized and its temperature rises due to the magnetic refrigeration effect (entropy reduction), which causes the temperature of the entire AMR bed to rise. 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 drive device. The heat transfer medium inside the AMR bed is heated by the magnetization of the magnetic refrigeration material and is transferred to the high-temperature side, while the inflow of heat transfer medium from the low-temperature side changes the temperature distribution inside the AMR bed. In adiabatic demagnetization, the magnetic refrigeration material is demagnetized and its temperature drops due to the magnetic refrigeration effect (entropy increase), so the temperature inside the AMR bed also drops. The temperature drops overall while maintaining the temperature distribution inside the AMR bed. When transferring heat from the high-temperature end to the low-temperature end, the heat transfer medium is moved to the low-temperature side by a drive unit. The heat transfer medium, which is cooled by the magnetization of the magnetic refrigeration material inside the AMR bed, is transferred to the low-temperature side, while the inflow of the heat transfer medium from the high-temperature side changes the temperature distribution inside the AMR bed.

[0036] If these four steps are considered one cycle, after one cycle the temperature distribution within 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 within the AMR bed becomes almost constant. The temperature within the AMR bed is determined by the properties of the magnetic refrigeration material that makes up the AMR bed.

[0037] FIG. 25 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 the AMR shown in Figure 25, 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 temperature differences by magnetization and demagnetization. Curie temperature T C or antiferromagnetic transition temperature T Nare the temperatures at which the phase transition from the paramagnetic state to the ferromagnetic or antiferromagnetic state occurs, respectively, and often coincide with the temperature at which the maximum magnetocaloric effect occurs. Therefore, in the AMR shown in Figure 25, multiple temperature zones (T C1 ~T C4 ) magnetic refrigeration material that exhibits a large magnetocaloric effect is arranged according to the expected temperature gradient, so performance is unlikely to deteriorate even if a temperature gradient occurs in the magnetic refrigeration material packed layer. In the embodiment of the present invention, as can be seen by comparing FIGS. 7 and 9, 11 and 13, 15 and 17, and 20 and 22, the temperature T N The temperature at which the maximum magnetocaloric effect occurs is almost the same as that at which the maximum magnetocaloric effect occurs. N Several magnetic refrigeration materials (Fe 1-x Mn x By appropriately arranging Cl2, it is possible to realize an AMR that can efficiently cool and liquefy hydrogen in the temperature range of 20K to 30K, where gas refrigeration performance is at its lowest. [Industrial Applicability]

[0038] The magnetic refrigeration material of the present invention is composed only of rock-forming elements, namely iron, manganese, chlorine, hydrogen, and oxygen. Therefore, the magnetic refrigeration material exhibits a large magnetocaloric effect due to efficient magnetic field changes and can be used in magnetic refrigerators for hydrogen liquefaction without having to consider resource depletion. Furthermore, according to the magnetic refrigeration device of the present invention, even in a magnetic refrigeration device that extracts magnetic refrigeration material from a superconducting magnet with low power consumption, there is no need to completely eliminate the magnetic field, which simplifies the design of the magnetic refrigeration device and improves the performance of the magnetic refrigerator.

Claims

1. It has a trigonal (R-3m) anhydrous cadmium chloride structure (Fe １－ｘ Mn ｘ ) Cl ２ (0≦x≦0.14) as the main component, Monoclinic (C12 / m1) cadmium chloride dihydrate structure (Fe １－ｘ Mn ｘ ) 2H ２ O (0≦x≦0.14) or orthorhombic (Pnma) cadmium chloride monohydrate type structure (Fe １－ｘ Mn ｘ ) Cl ２ ・H ２ O may be included as a water-containing subcomponent, As the water-containing subcomponent (Fe １－ｘ Mn ｘ ) 2H ２ The (110) plane X-ray diffraction intensity of O, or the hydrous subcomponent (Fe １－ｘ Mn ｘ ) H ２ A magnetic refrigeration material characterized in that the ratio of any one of the (101) plane X-ray diffraction intensities of O to the (003) plane X-ray diffraction intensity of said main component is 4:1 or less.

2. 2. The magnetic refrigeration material according to claim 1, wherein the X-ray diffraction intensity of the water-containing minor component is below the detection limit and the magnetic refrigeration material consists solely of the main component.

3. Cadmium chloride anhydrate structure (Fe １－ｘ Mn ｘ ) Cl ２ Align the c-axis, which is the axis of easy magnetization, of (0≦x≦0.14), The remanent magnetization M at 2 K extrapolated from the magnetization curve in the ferromagnetic state ｒ and saturation magnetization M ｓ The ratio (squareness ratio M ｒ / M ｓ 3. The magnetic refrigeration material according to claim 1, wherein the value of σ is greater than 0.

5.

4. By changing the applied magnetic field strength from 1 to 2 T to 5 to 6 T, the entropy change was 15 J kg －１ ・K －１ 4. A magnetic refrigeration material according to claim 1, which exhibits the above-mentioned large magnetocaloric effect.

5. Using the magnetic refrigeration material of claim 3, the direction of application of a magnetic field is changed to a cadmium chloride anhydrate structure (Fe １－ｘ Mn ｘ ) Cl ２ By rotating the magnet from a direction parallel to the c-axis, which is the axis of easy magnetization (0≦x≦0.14), to a direction perpendicular to the c-axis, the entropy change is 15 J kg －１ ・K －１ A magnetic refrigeration device characterized by exhibiting the above-mentioned large magnetocaloric effect.

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