Magnetic refrigeration material and magnetic refrigeration device using the same

Abstract

To provide a refrigerant material that exhibits a large MCE |▵Sm|>20 [J / (kg K)] without thermal hysteresis in the temperature range around 77 K of the liquid nitrogen temperature required for gas liquefaction.SOLUTION: A magnetic refrigeration material consists of Gd (gadolinium), Ge (germanium), Sn (tin) and unavoidable impurities, and has the following composition: Gd5Ge4-xSnx: 1.6<x<2.4.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a magnetic refrigeration material and a magnetic refrigeration device using the same. [Background technology]

[0002] In recent years, there has been an increasing demand for gas consumption and production in all market segments, including natural gas, oxygen, nitrogen and hydrogen. However, gases in the gaseous state are bulky and require liquefaction for storage and transportation. Traditional liquefaction methods require energy-intensive gas compression processes at cryogenic temperatures, which are very inefficient at temperatures below 150 K. Magnetic refrigeration (MR) technology based on the magnetocaloric effect (MCE) can be a radically different alternative to conventional gas compression cooling technology because it is ideally highly efficient and environmentally friendly. To achieve this, magnetic refrigerant materials with large MCE in the temperature region of interest from 20 to 150 K are required to liquefy gases such as hydrogen, nitrogen, oxygen, and natural gas. However, as shown in Figure 6, in the wide temperature range from 60 K to 150 K required for gas liquefaction, the entropy change △S of currently known MR materials in this wide temperature range is 10 to 20 [J / (kg K)]. Therefore, the fact that no MR materials with a huge MCE, with a △S of about 30 to 40 [J / (kg K)] required for gas liquefaction, are known is a bottleneck in the practical application of MR cooling systems.

[0003] In Patent Document 1, a magnetic refrigeration working material is sought that utilizes a large magnetic entropy change caused by an external magnetic field near the Curie temperature of the ferromagnetic-paramagnetic transition in a temperature range of 20 to 300 K. The publication states that an amorphous alloy or a multi-phase microcrystal aggregate alloy produced by quenching a melt consisting of rare earth elements Gd, Tb, Dy, Ho, and Er with large magnetic moments, one or more of Zr, Hf, Al, Si, and Ge as amorphous elements, and Cu, Ni, and Ag as elements that increase affinity with the cooling bodies Cu and Ag in a vacuum or in an inert gas atmosphere with a Cu or Ag cooling body controlled at a temperature of room temperature to 850 K, provides a working material with large magnetic entropy over a wide temperature range and excellent magnetic refrigeration performance. However, the magnetic refrigeration material having the composition disclosed in the examples of the elemental composition disclosed in Patent Document 1 has a small magnetic entropy change and is not suitable for practical use in commercial hydrogen liquefaction devices using magnetic refrigeration. In other words, it was necessary to further search for a magnetic refrigeration material having an optimal elemental composition from the abstract elemental composition disclosed in Patent Document 1.

[0004] In Patent Document 2, the following thermomagnetic material is described as a thermomagnetic material for a heat exchanger: Gd5(Si x Ge 1-x )4, (0.2≦x≦1) (V), Tb5(Si 4-x Ge x ), (x=0, 1, 2, 3, 4) (VI), XTiGe, (X=Dy, Ho, Tm) (VII) has been proposed, but examples are limited to MnFePGe and MnFePGeSb systems. In addition, the thermomagnetic materials in the examples disclosed in Patent Document 2 have Curie temperatures of 240 to 340 K, and no magnetic refrigerant material is disclosed that has a large MCE in the temperature range of interest of 15 to 150 K, which is required for a hydrogen liquefaction device using magnetic refrigeration.

[0005] Second-order magnetic phase transition (SOMT) materials, which have essentially no thermal hysteresis, are expected to be good candidates for this application due to their reversible MCE and excellent mechanical stability during cycling. Ho-based SOMT compounds, such as HoB2, HoN, and HoNi2, exhibit giant MCE (-△S m >20[J / (kg·K)]) has been achieved, but it is impossible to maintain such a huge MCE down to 60K. For example, in ErAl2 and HoN compounds, |△Sm| decreases to 37 [J / (kg·K)] and 29 [J / (kg·K)] at temperatures below 20 K, and to 18 [J / (kg·K)] and 11 [J / (kg·K)] at 60 K. Furthermore, in TbAl2, it deteriorates to 14 [J / (kg·K)] at 90 K, and in (Gd,Tb)Al2 compounds, it deteriorates to 11 [J / (kg·K)] at 140 K. Therefore, there are very few refrigerant materials that show a huge MCE |△Sm|>20 [J / (kg·K)] without thermal hysteresis at temperatures of 60 to 150 K required for gas liquefaction.

[0006] In addition, Patent Documents 3 and 4 propose ErCo2-based magnetocaloric compounds as second order magnetic phase transition (SOMT) materials. 2-y (Fe, Mn) y (0.02≦y≦0.07) is proposed. 2-x-y Ai x Ni y (0 <x≦0.1、0≦y≦0.2)、ErCo 2-x-y Fe x Ni y (0.035≦x≦0.1, 0≦y≦0.2) has been proposed. In these ErCo2-based magnetocaloric compounds, for example, ErCo 1.96 Fe 0.04 At 50K, |△Sm| is about 0.2 J / (cm -3 ·K), and the specific gravity of ErCo2 is about 10g / cm 3If so, it corresponds to approximately 20 [J / (kg·K)]. However, in the temperature range near the liquid nitrogen temperature of 77 K required for gas liquefaction, as a refrigerant material that does not cause thermal hysteresis and exhibits a large MCE with |ΔSm| > 20 [J / (kg·K)], there is a shortage in the bandwidth, and it is necessary to search for new magnetocaloric compounds in the temperature range near the liquid nitrogen temperature of 77 K.

[0007] In contrast, first-order magnetic phase transition (FOMT) materials exhibit a large MCE, and their large MCE can be maintained over a wide temperature range. For example, Gd5(Si x Ge 1-x )4 (0 < x < 0.5) exhibits a large MCE (-ΔS m > 20 [J / (kg·K)]) in a wide temperature range from 20 K to 290 K. However, the Gd5(Si x Ge 1-x )4 compounds related to FOMT suffer from irreversible MCE due to thermal hysteresis and mechanical instability, which hinders their practical application. So far, great efforts have been made to reduce the hysteresis of Gd5(Si x Ge 1-x )4 compounds, and it has been found that the reduction of hysteresis in SOMT materials is achieved at the expense of |ΔSm|. For example, the |ΔSm| of Gd5Si2Ge2 decreases to that of Gd5Si2Ge 1.9 Fe 0.1 which is 7 J / cm 3 K under a magnetic field change of 5 T that minimizes hysteresis. Therefore, there is an issue that Gd5Si2Ge2-based compounds are not very attractive for practical applications.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

[0009] As explained above, our goal is to discover refrigerant materials that exhibit a giant MCE |△Sm|>20 [J / (kg K)] without thermal hysteresis in the temperature range around 77 K, the liquid nitrogen temperature required for gas liquefaction, and to provide new giant magnetocaloric effect materials. [Means for solving the problem]

[0010] The inventors considered that Gd5Ge4 could be a promising candidate for low-temperature gas liquefaction due to its huge MCE (|△Sm|=25[J / (kg·K)]) at 50 K and large refrigeration capacity. However, the large thermal hysteresis up to 5 K (Fig. 1(c)) due to the nature of FOMT prevents its practical use in gas liquefaction. We therefore thought that by searching for Gd5Ge4-based compounds to which a third element had been added, it might be possible to achieve both a huge MCE at 50 K, which is close to the liquid nitrogen temperature, and a material that exhibits second-order magnetic phase transition (SOMT).As a result of searching for a third element to be added to Gd5Ge4-based compounds, we came up with the present invention.

[0011] [1] The giant magnetocaloric effect material of the present invention is composed of Gd (gadolinium), Ge (germanium), Sn (tin) and unavoidable impurities as shown in Table 2, and has the following composition formula: Gd5Ge 4-x Sn x :1.6 <x<2.4 It has the composition: [2] In the giant magnetocaloric effect material of the present invention [1], preferably, Gd5Ge 4-x Sn x : It is preferable that 2.0≦x≦2.3.

[0012] [3] In the embodiment of the present invention, in the magnetic refrigeration material [1] or [2], the transition temperature T tr is in the temperature range of 65K to 85K, and the transition temperature T tr It may exhibit a second-order magnetic phase transition in the range of 20 K around the [4] In the embodiment of the present invention, in the magnetic refrigeration material [3], the second-order magnetic phase transition occurs at a transition temperature T tr The volume change rate (dV / V) may be −0.4% or more and 0.4% or less in the range around 20K. If the volume change rate (dV / V) is between -0.4% and 0.4%, the transition temperature T tr It can be evaluated as a second-order magnetic phase transition (SOMT) in the range of 20K around this temperature. It is believed that the collapse of the crystal structure will be substantially reduced even if the phase transition is repeated. It is suitable for long-term stable use. [5] In the embodiment of the present invention, in the magnetic refrigeration materials [1] to [4], the transition temperature T tr In the range of 20 K around the magnetic field, the magnetic entropy change △Sm may be 15 [J / (kg K)] or more and 50 [J / (kg K)] or less in a 5 T magnetic field. [6] In an embodiment of the present invention, in the magnetic refrigeration material [5], the entropy change may be such that a magnetic entropy change ΔSm is 20 [J / (kg K)] or more and 50 [J / (kg K)] or less under a 5 T magnetic field. [7] In the embodiment of the present invention, in the magnetic refrigeration materials [1] to [4], the transition temperature T tr It is preferable that the hysteresis loss obtained by measuring the MH loop in the vicinity is 1 J / kg or less. [8] In the embodiment of the present invention, the magnetic refrigeration device may use the magnetic refrigeration materials [1] to [7] above. [9] In an embodiment of the present invention, the hydrogen liquefaction device or the helium liquefaction device may use a magnetic refrigeration device [8]. Effect of the Invention

[0013] The giant magnetocaloric effect material of the present invention exhibits both a giant MCE of approximately △Sm>30 [J / (kg K)] under a 5 T magnetic field within the temperature range of 70 K to 85 K, which is close to the liquid nitrogen temperature, and a second-order magnetic phase transition (SOMT) material, making it suitable for use in, for example, hydrogen gas liquefaction. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is an explanatory diagram of the magnetic properties of the Gd5Ge4 compound as a comparative example of the present invention; (a) is the MT curve measured at 2 T, (b) is the magnetic entropy change with a magnetic field change between 2 T and 5 T, and (c) is an allotment plot of the Gd5Ge4 compound. [Diagram 2] 1A and 1B are diagrams for explaining the magnetic properties of Gd5Ge4-based compounds according to examples and comparative examples of the present invention, where (a) is a measurement example of the MT curve of a Gd5Ge3.5M0.5 compound and (b) is a measurement example of the MT curve of a Gd5RE0.5Ge4 compound at 2 T. [Diagram 3] This is an example of the MT curve measurement at 2 T for the Gd5(GeSn)4 compound. [Figure 4] The MH loops of the Gd5Ge4-based compounds showing an example of the present invention and a comparative example were measured at the transition temperature. [Diagram 5] 1 shows an example of the change in magnetic entropy measured at 2 T and 5 T for Gd5Ge4, which is a comparative example of the present invention, and a Gd5Ge2Sn2 compound, which is an embodiment of the present invention. [Figure 6] This is an example of measurement of the magnetic entropy change under a 5 T magnetic field for the most studied material in gas liquefaction at cryogenic temperatures, Gd5Ge2Sn2 compound. [Figure 7] FIG. 2 is a schematic diagram illustrating each step of a magnetic refrigeration cycle in which a magnetic refrigeration material is used in an embodiment of the present invention. [Figure 8] FIG. 1 is a schematic diagram illustrating an active regenerative magnetic refrigeration (AMR) cycle. [Figure 9] 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 10]FIG. 1 is a diagram illustrating a magnetic refrigeration device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The best mode for carrying out the present invention will now be described in detail. As the third element to be added to the Gd5Ge4-based compound, RE considered Yb, Ho, and Mg as the third element to be added to Gd, and M considered Co, Si, Ni, Sn, Fe, V, Mn, and Cu as the third element to be added to Ge. Gd, Yb, and Ho can be obtained from Nippon Yttrium Co., Ltd. (Omuta City, Fukuoka Prefecture), and the material is in the form of a block with a purity of 99.9%. Mg, Ge, Si, Fe, and Mn can be obtained from Kojundo Kagaku Kenkyusho Co., Ltd. (Sakado City, Saitama Prefecture), and the material is in the form of a granule with a purity of 99.99%, while Si is 99.999% and Mn is 99.9%. Co can be obtained from Rare Metallic Co., Ltd. (Chiyoda Ward, Tokyo), and the material is in the form of a granule with a purity of 99.97%. Ni, Sn, V, and Cu are available from Furuuchi Chemical Co., Ltd. (Shinagawa, Tokyo) in granular form with a purity of 99.9%, except for Ni, which is in sheet form.

[0016] The raw materials were lump Gd (purity 99.9%) manufactured by Nippon Yttrium Co., Ltd., lump Ge (purity 99.99%) manufactured by Kojundo Chemical Laboratory, and the above sample was weighed as the third element to obtain Gd5Ge 4-x M x Compounds (where M is Co, Si, Ni, Sn, Fe, V, Mn, or Cu) and Gd 5-y RE yPure constituent elements of Ge4 compounds (RE is either Yb, Ho, or Mg) were prepared by arc melting the pure constituent elements in an atmosphere-controlled arc furnace manufactured by Nissin Giken Co., Ltd. under an argon atmosphere. 1-7 wt% extra Gd was charged to compensate for the evaporation of Gd. The ingots were homogenized by turning them over and remelting them five times during the arc melting process. The magnetic properties were measured using a SQUID-VSM manufactured by Quantum Design Co., Ltd. Furthermore, polycrystalline samples of Gd5Ge2Sn2-based compounds were also prepared by arc melting the pure constituent elements in an argon atmosphere in a Nissin Giken atmosphere-controlled arc furnace. To compensate for the evaporation of Gd, 1-7 wt% of extra Gd was added. The ingots were homogenized by turning them over and remelting them five times during the arc melting process. The magnetic properties were measured using a SQUID-VSM (Quantum Design). Tables 1 and 2 show the composition elements of Gd5Ge4-based compounds to which a third element has been added.

[0017] Tables 1 and 2 show the composition elements of Gd5Ge4-based compounds with added third elements. Table 1 shows Gd5Ge 3.5 M 0.5 The composition (at.%) of the compound is shown (M is Co, Si, Ni, Sn, Fe, V, Mn, or Cu) (sample numbers 1-5 and 9-12). However, for Sn, Gd5Ge 4-x Sn x The composition ratio is varied from x=0.5, 1, 2, and 3 (sample numbers 5-8). 4.5 RE 0.5 The composition (at.%) of Ge4 compound is shown (RE is either Yb, Ho, or Mg) (sample numbers 1, 13-15). [Table 1]

[0018] [Table 2]

[0019] FIG. 1 is an explanatory diagram of the magnetic properties of the Gd5Ge4 compound, which is a comparative example of the present invention. (a) is the MT curve measured at 2 T, (b) is the magnetic entropy change in the magnetic field change between 2 T and 5 T, and (c) is the Arrott plot of the Gd5Ge4 compound. The vertical axis of FIG. 1(a) is the magnetization M (Am 2 / kg), the horizontal axis is temperature in K, and an external magnetic field of 2 T is applied as μ0H. In Fig. 1(b), the vertical axis is the magnetic entropy change △Sm [J / (kg K)], the horizontal axis is the temperature in K, and an external magnetic field μ0H of 2 T and 5 T is applied. In the case of 2 T, the maximum magnetic entropy change obtained is 13-14 [J / (kg K)] in the range of 25-38 K. In the case of 5 T, the maximum magnetic entropy change obtained is 24-26 [J / (kg K)] in the range of 48-44 K. The vertical axis of Fig. 1(c) is the magnetization M 2 (Am 2 / kg) 2 The horizontal axis is the external magnetic field μH and the magnetization M(Am 2 / kg) divided by μH / M(T kg / Am 2 )K, with allocation plots at 3K intervals from 6K to 81K. Here, the allotment plot is a graph in condensed matter physics showing the square of the magnetization of a certain material, M 2 A plot of the magnetization versus the ratio of applied magnetic field to magnetization at a fixed temperature (or temperatures) provides a convenient way to determine the presence of ferromagnetic order in a material.

[0020] Table 3 shows the Gd5Ge 3.5 M 0.5 The magnetic properties of the compounds are shown (M is Co, Si, Ni, Sn, Fe, V, Mn, or Cu) (sample numbers 1-12). Table 4 shows the magnetic properties of Gd 4.5 RE 0.5 The magnetic properties of Ge4 compounds are shown (RE is either Yb, Ho, or Mg) (samples Nos. 1, 13-15). Regarding the Curie temperature Tc (K), Gd5Ge4 (sample number 1) is 38 K at 2 T. The other magnetocaloric effect materials of sample numbers 2-15 are as shown in the respective columns of Tables 3 and 4. The rate of change of magnetization M per temperature dM / dT(Am 2 / kg·K) is 22.1 for Gd5Ge4 (sample number 1). For magnetocaloric effect materials, the rate of change of magnetization M per temperature dM / dT(Am 2 / kg·K) is preferably 10 or more, more preferably 12 or more, and even more preferably 15 or more. The rate of change of magnetization M per temperature dM / dT(Am 2 / kg·K) is 10 or more. 3.5 S 0.5 (Sample No. 3) 19, Gd5Ge 3.5 Sn 0.5 (Sample No. 5) 12.9, Gd5Ge3Sn1 (Sample No. 6) 19.6, and Gd5Ge2Sn2 (Sample No. 7) 14 are sufficient. On the other hand, Gd5Ge 3.5 Co 0.5 (Sample No. 2) 5, Gd5Ge 3.5 Ni 0.5 (Sample No. 4) 4, Gd5Ge1Sn3 (Sample No. 8) 1.37, Gd5Ge 3.5 Fe 0.5 (Sample No. 9) 3.5, Gd5Ge 3.5 V 0.5 (Sample No. 10) 3.37, Gd5Ge 3.5 Mn 0.5 (Sample No. 11) 5, Gd5Ge 3.5 Cu 0.5 (Sample No. 12) 2.54 is Gd 4.5 Yb 0.5 Ge4 (sample number 13) 5, Gd 4.5 Ho 0.5 Ge4 (sample no. 14) 0.5, Gd 4.5 Mg 0.5 The 5 in Ge4 (sample number 15) is not sufficient.

[0021] Figures 2(a) and (b) show the magnetic hysteresis of Gd5Ge4-based compounds in which Ge is replaced by M (see Table 1) and Gd is replaced by rare earth elements (see Table 2). The vertical axis of Figures 2(a) and (b) shows the magnetization M (Am 2 / kg), the horizontal axis is temperature in K, and an external magnetic field of 2 T is applied as μ0H. Thermal hysteresis ΔThys(K) appears in the first-order magnetic phase transition but does not appear in the second-order magnetic phase transition. hys (K) appears in the range of 4K. For magnetocaloric effect materials, thermal hysteresis △T hys (K) is preferably 5K or less, more preferably 3K or less, and even more preferably 2K or less. Thermal hysteresis △T hys An example of a measurement below 5K (K) is Gd5Ge 3.5 S 0.5 (Sample No. 3) 5K, Gd5Ge2Sn2 (Sample No. 7) <1, Gd5Ge1Sn3 (Sample No. 8) 0K, Gd5Ge 3.5 V 0.5 (Sample No. 10) 5K, Gd5Ge 3.5 Mn 0.5 (Sample No. 11) 2K, Gd5Ge 3.5 Cu 0.5 (Sample No. 12) 5K, Gd 4.5 Yb 0.5 Ge4 (sample number 13) 4K, Gd 4.5 Ho 0.5 Ge4 (sample number 14) 0K, Gd 4.5 Mg 0.5 The 4K content of Ge4 (sample number 15) is sufficient. On the other hand, Gd5Ge 3.5 Co 0.5 (Sample No. 2) 6K, Gd5Ge 3.5 Ni 0.5 (Sample No. 4) 9K, Gd5Ge 3.5 Sn 0.5 (Sample No. 5) 13K, Gd5Ge3Sn1 (Sample No. 6) 10K, and Gd5Ge2Sn2 (Sample No. 7) 14K are insufficient.

[0022] Magnetization M(Am 2 / kg) for Gd5Ge4 (sample number 1) is 22.1 at a temperature of 5 K and a magnetic field of 2 T. 2 / kg) is preferably 100 or more, more preferably 120 or more, and even more preferably 150 or more. Magnetization M(Am 2 / kg) is 100 or more. 3.5 Co 0.5 (Sample No. 2) 103, Gd5Ge 3.5 S 0.5 (Sample No. 3) 190, Gd5Ge 3.5 Ni 0.5 (Sample No. 4) 151, Gd5Ge 3.5 Sn 0.5 (Sample No. 5) 150, Gd5Ge3Sn1 (Sample No. 6) 165, Gd5Ge2Sn2 (Sample No. 7) 185, Gd5Ge 3.5 Fe 0.5 (Sample No. 9) 105, Gd5Ge 3.5 V 0.5 (Sample No. 10) 105, Gd5Ge 3.5 Mn 0.5 (Sample No. 11) 130, Gd 4.5 Yb 0.5 Ge4 (sample number 13) 110, Gd 4.5 Mg 0.5 Ge4 (sample number 15) is sufficient at 120. On the other hand, Gd 4.5 Ho 0.5 0.5 for Ge4 (sample number 14), 83 for Gd5Ge1Sn3 (sample number 8), Gd5Ge 3.5 Cu 0.5 (Sample No. 12) 83, Gd 4.5 Ho 0.5 The 40 in Ge4 (sample number 14) is insufficient.

[0023] Regarding the distinction between first order magnetic phase transition (FOMT) and second order magnetic phase transition (SOMT) materials, Gd5Ge1Sn3 (sample number 8) and Gd 4.5 Ho 0.5Ge4 (sample number 14) was a second-order magnetic phase transition (SOMT) material. Gd5Ge2Sn2 (sample number 7) showed properties that were on the border between first-order magnetic phase transition (FOMT) and second-order magnetic phase transition (SOMT) materials. The remaining samples 1-6, 9-13, and 15 were first-order magnetic phase transition (FOMT) materials.

[0024] The change in magnetic entropy, △S [J / (kg·K)], was measured at 0-5 T and was 25 [J / (kg·K)] for Gd5Ge4 (sample number 1). Another sample for which the change in magnetic entropy, △S [J / (kg·K)], was measured was Gd5Ge 3.5 S 0.5 (sample number 3) is 40, Gd5Ge3Sn1 (sample number 6) is 28, and Gd5Ge2Sn2 (sample number 7) is 32. That is, as can be seen from Tables 3 and 4, when searching for a third element M to be added to a Gd5Ge4-based compound that eliminates hysteresis without lowering the MCE (|△Sm|), 4-x M x Among the third elements M in the compounds (M = Co, Si, Ni, Sn, Fe, V, Mn, Cu), it was found that the optimal element was Sn. The other third elements M (M = Co, Ni, Fe, V, Mn, Cu) and Gd 5-y RE y The third element RE in Ge4 (RE=Yb, Ho, Mg) compounds has a rate of change of magnetization M per temperature dM / dT(Am 2 / kg·K) is 10 or more, thermal hysteresis △T hys (K) is 5K or less, or magnetization M(Am 2 / kg) was 100 or more.

[0025] [Table 3] [Table 4]

[0026] Figure 3 shows the M-T curve including the heating branch and the cooling branch measured in a magnetic field of 2 T for Gd5Ge 4-x Sn x -based compounds (sample numbers 5-8). The vertical axis in Figure 3 is magnetization M (A m 2 / kg), and the horizontal axis is temperature K. As x increases from 0 to 1, the thermal hysteresis increases from 4 K to 10 K, and the transition temperature rises from 38 K to 49 K. When x increases to 2, the thermal hysteresis disappears, and the transition temperature rises to 78 K. When x increases to 2.2, there is no thermal hysteresis, and the transition temperature rises to 82 K. When x increases to 2.4, there is no thermal hysteresis, and the transition temperature rises to 85 K, but the magnetization decreases significantly. Further, when x increases to 3, the transition temperature rises to 94 K, and due to the antiferromagnetism of Gd5Ge1Sn3, the transition is blunted and the magnetization decreases significantly. Figure 3 shows that the hysteresis can be eliminated by replacing Ge with Sn in an appropriate ratio. Here, focusing on the composition of Gd5Ge 4-x Sn x : 1 ≤ x ≤ 3, the transition temperature can be adjusted from, for example, 38 K to 94 K. Particularly preferably, 1.6 < x < 2.4, and most preferably, 2.0 ≤ x ≤ 2.3. When x is 1.6 or less, the transition temperature becomes 69 K, and the thermal hysteresis is estimated to be about 4 K, which is not preferable as it is comparable to Gd5Ge4. When x is 2.4 or more, the transition temperature becomes 85 K, and there is no thermal hysteresis, but the decrease in magnetization is significant, which is not preferable.

[0027] For the magnetic refrigeration material having the composition of Gd5Ge 4-x Sn x : 1 ≤ x ≤ 3, the transition without hysteresis spreads from 38 K to 94 K. In particular, considering that liquid nitrogen can be obtained in large quantities at a relatively low cost, it has been demonstrated that a magnetic material suitable for use in the range from liquid nitrogen temperature to liquid nitrogen temperature can be obtained. Further, the hysteresis near the transition temperature of the magnetic refrigeration material is qualitatively evaluated by measuring the M-H loop at that transition temperature. The hysteresis loop of the magnetic refrigeration material near the transition temperature is measured using a magnetic property measurement system, model MPMSR3, manufactured by Quantum Design, Inc., USA, and sold by Quantum Design, Inc. of Japan. The hysteresis loop of the magnetic refrigeration material is measured under an external magnetization of 2 T, and then the temperature is changed at 2 K / min, and another hysteresis loop is measured.

[0028] FIG. 4 shows the MH loop of a Gd5Ge4-based compound according to an embodiment of the present invention, measured at the transition temperature. (a) shows Gd5Ge4, and (b) shows Gd5Ge2Sn2. The vertical axis shows the magnetization M (Am 2 / kg), and the horizontal axis is the magnetic flux density μ0H(T). In Figure 4(a), MH loops for Gd5Ge4 were measured at 3K intervals from 6K to 81K. The hysteresis loss energy is evaluated from the maximum opening of the loop near the transition temperature. For example, for the Gd5Ge4 compound shown in Figure 4(a), the measured value at 45K is the maximum shaded area, and the hysteresis loss is measured to be 80J / kg. In Fig. 4(b), MH loops for Gd5Ge4Sn2 were measured at 3 K intervals from 51 K to 108 K. For the Gd5Ge2Sn2 compound shown in Fig. 4(b), the measured value at 81 K is the maximum shaded area, and is significantly reduced to 8 J / kg. That is, the Gd5Ge2Sn2 compound realizes a hysteresis loss that is one order of magnitude smaller than that of the Gd5Ge4 compound.

[0029] Figure 5 shows the change in magnetic entropy measured at 2 T and 5 T for the Gd5Ge4 and Gd5Ge2Sn2 based compounds, with the vertical axis representing the magnetic entropy change △Sm [J / (kg·K)] and the horizontal axis representing the temperature in K. For Gd5Ge4 (sample number 1), the transition temperature is 38 K and the change in magnetic entropy |△Sm| is about 15 [J / (kg·K)] when measured at 2 T, and the transition temperature is 38 K and the change in magnetic entropy |△Sm| is about 28 [J / (kg·K)] when measured at 5 T. For the Gd5Ge2Sn2 compound (sample number 7), the transition temperature is 78 K and the change in magnetic entropy |△Sm| is about 24 [J / (kg·K)] when measured at 2 T, and the transition temperature is 38 K and the change in magnetic entropy |△Sm| is about 32 [J / (kg·K)] when measured at 5 T.

[0030] Figure 6 shows the magnetic entropy change under a magnetic field of 5 T for the most studied materials and Gd5Ge2Sn2-based compounds in gas liquefaction at cryogenic temperatures. The vertical axis is the magnetic entropy change △Sm [J / (kg·K)], and the horizontal axis is temperature K. In summary, we demonstrate that it is possible to overcome the trade-off between large MCE and small hysteresis in the conventional first-order phase transition (FOMT) material Gd5Ge4 compound by appropriately substituting a portion of Ge with Sn, thereby simultaneously improving the MCE and minimizing the hysteresis.

[0031] Next, a magnetic refrigeration device in which the magnetic refrigeration material of the present invention is used will be described. FIG. 7 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.

[0032] Fig. 8 is a schematic diagram for explaining an active regenerative magnetic refrigeration (AMR) cycle. In Fig. 8, 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.

[0033] 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.

[0034] If these four steps are considered as one cycle, after one cycle, the temperature distribution in 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 will increase, and eventually the temperature distribution in the AMR bed will become almost constant. The temperature distribution in the AMR bed is determined by the properties of the magnetic refrigeration material that makes up the AMR bed.

[0035] FIG. 9 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 9, 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 9, 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.

[0036] FIG. 10 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 particle diameter may be 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, the 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 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 diameter is determined by the volume-based median diameter (d 50 ) 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 used. In the former, a large number of particle images (SEM images, etc.) are taken, and the particle diameter converted into a circle can be calculated from the area of ​​each particle using image analysis software.

[0037] 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 for applying a magnetic field to the AMR bed 220, a cooling stage 290 for cooling an object to be cooled by applying cold and hot, and a heat exchanger 240 for discharging 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 Gd5Ge 4-x Sn x The magnetocaloric compounds of the series can provide magnetic refrigeration materials useful for hydrogen liquefaction systems using the AMR cycle. [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 consists of Gd (gadolinium), Ge (germanium), Sn (tin), and unavoidable impurities, and has the following compositional formula: G$ ５ Yes ４－ｘ Sn ｘ :1.6<8<2.4 A magnetic refrigeration material having the following composition.

2. Gd ５ Ge ４－ｘ Sn ｘ A magnetic refrigeration material according to claim 1, having a composition of 2.0 ≤ x ≤ 2.

3.

3. In the magnetic refrigeration material according to claim 1, Magnetic phase transition transition temperature T ｔｒ The temperature range is 70K to 85K. The transition temperature T ｔｒ A magnetic refrigeration material characterized by exhibiting a secondary magnetic phase transition in a range of 20K before and after a certain temperature.

4. In the magnetic refrigeration material according to claim 3, the secondary magnetic phase transition has a volume change rate (dV / V) of -0.4% or more and 0.4% or less in the range of 20 K before and after the transition temperature T ｔｒ The magnetic refrigeration material is characterized in that

5. In the magnetic refrigeration material according to claim 3, The transition temperature T ｔｒ A magnetic refrigeration material characterized in that, within a range of 20K before and after a certain temperature, the change in magnetic entropy is between 15 [J / (kg·K)] and 50 [J / (kg·K)] under a 5T magnetic field.

6. In the magnetic refrigeration material according to claim 5, The magnetic entropy change is characterized by being between 20 [J / (kg·K)] and 50 [J / (kg·K)] under a 5T magnetic field, making it a material for magnetic refrigeration.

7. In the magnetic refrigeration material according to claim 3, The transition temperature T ｔｒ A magnetic refrigeration material characterized by having a hysteresis loss of 1 J / kg or less, obtained by measuring the M-H loop in the vicinity.

8. A magnetic refrigeration apparatus using the magnetic refrigeration material described in claims 1 to 7.

9. A hydrogen liquefaction apparatus or a helium liquefaction apparatus using a magnetic refrigeration apparatus as described in claim 8.

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