Compound, magnetic material, module, heat source, and magnetic refrigeration device

Abstract

In the present invention, in a Heusler structure, a compound contains four or more elements, and a structural first-order phase transition and a magnetic second-order phase transition occur continuously. A magnetic material includes a first compound and a second compound. A heat source comprises: the magnetic material; and an application unit that applies a magnetic field to the magnetic material. This magnetic refrigeration device comprises: the heat source; and a moving unit that moves a fluid that exchanges heat with the magnetic material.

Description

Compound, magnetic material, module, heat source and magnetic refrigerator

[0001] The present invention relates to a compound, a magnetic material, a module, a heat source, and a magnetic refrigerator.

[0002] Conventionally, as an environmentally friendly refrigeration technology, magnetic refrigeration using magnetic entropy change has been researched and developed. For example, Patent Document 1 (JP 2008-150695 A) describes a magnetic material used for such magnetic refrigeration. Patent Document 1 describes a NaZn alloy containing 4 atomic % to 15 atomic % of La, 3 atomic % to 25 atomic % of Si, 1.5 atomic % to 10 atomic % of Co, and 50 atomic % to 91.5 atomic % of Fe. 13 The magnetic refrigeration material is disclosed as an alloy having a crystal structure of the type as a main phase, and characterized in that the alloy contains 0.29 atomic % to 2.8 atomic % of C.

[0003] As described in the above-mentioned patent document, materials that exhibit large magnetic entropy changes are desired.

[0004] The compound according to the first aspect contains four or more elements in a Heusler structure, and a first-order structural phase transition and a second-order magnetic phase transition occur successively.

[0005] According to the compound of the first aspect, since the Heusler structure contains four or more elements, it is possible to increase the amount of entropy change accompanying a magnetic second-order phase transition. Furthermore, since a structural first-order phase transition occurs consecutively with a magnetic second-order phase transition, it is possible to increase the amount of entropy change accompanying a first-order phase transition. Therefore, the compound of the first aspect can exhibit a large magnetic entropy change.

[0006] The compound according to the second aspect is the compound according to the first aspect, and contains all of the elements chromium (Cr), cobalt (Co), iron (Fe), and phosphorus (P).

[0007] In the compound of the second aspect, by including Cr, Co, Fe and P as the four or more elements, it is possible to easily realize a large magnetic entropy change.

[0008] The compound according to the third aspect is the compound according to the second aspect, further including a fifth element.

[0009] Like the compounds of the third aspect, compounds of the present disclosure may contain five or more elements.

[0010] A magnetic material according to a fourth aspect includes a first compound and a second compound. The first compound is a compound according to any one of the first aspect to the third aspect. The second compound has a different composition from the first compound.

[0011] Like the magnetic material of the fourth aspect, it may contain two or more compounds.

[0012] A magnetic material according to a fifth aspect is the magnetic material according to the fourth aspect, wherein the second-order phase transition temperature of the first compound is different from the second-order phase transition temperature of the second compound.

[0013] In the magnetic material of the fifth aspect, by using compounds with different phase transition temperatures, heat exchange using the magnetic material can be carried out efficiently.

[0014] In the module according to the sixth aspect, a first compound according to the fourth or fifth aspect and a second compound according to the fourth or fifth aspect are linked together.

[0015] In the magnetic material of the sixth aspect, a fluid that has undergone heat exchange with one of the first compound and the second compound can be further subjected to heat exchange with the other of the first compound and the second compound.

[0016] A heat source according to a seventh aspect includes a magnetic material and an application unit. The magnetic material is the magnetic material according to the fourth or fifth aspect. The application unit applies a magnetic field to the magnetic material.

[0017] In the heat source of the seventh aspect, heat exchange with the fluid can be performed by utilizing heat released from the magnetic material to which the magnetic field is applied from the application unit.

[0018] A magnetic refrigeration apparatus according to an eighth aspect includes a heat source and a moving unit. The heat source is the heat source according to the seventh aspect. The moving unit moves a fluid that exchanges heat with the magnetic material.

[0019] In the magnetic refrigeration device of the eighth aspect, a fluid that has been heated by heat exchange with a magnetic material can be moved by a moving unit to extract hot heat, and a fluid that has absorbed heat by heat exchange with a magnetic material can be moved by a moving unit to extract cold heat.

[0020] FIG. 1 is a diagram showing an image of successive occurrence of a first-order phase transition and a second-order phase transition in a compound according to an embodiment of the present disclosure. FIG. 2 is an external configuration diagram of a module according to an embodiment of the present disclosure. FIG. 3 is an external configuration diagram of a module according to another embodiment of the present disclosure. FIG. 4 is a schematic configuration diagram of a heat source according to an embodiment of the present disclosure. FIG. 5 is a schematic configuration diagram of a magnetic refrigeration device according to an embodiment of the present disclosure. FIG. 6 is a graph showing the temperature and performance index of a second-order phase transition in a Heusler compound. FIG. 7 is a graph showing the temperature and entropy change of a second-order phase transition in a Heusler compound extracted from FIG. 6. FIG. 8 is a graph showing the entropy change with respect to temperature in a compound consisting of four elements, Cr, Co, Fe, and P, in a Heusler structure. La(Fe ０．８５ Si ０．１５ ) １３ 1 is a graph showing the entropy change with respect to the temperature of a compound having a Heusler structure, the temperature of a second-order phase transition, and the lattice size of the compound having a four-element structure of Cr, Co, Fe, and P.

[0021] Hereinafter, a compound, a magnetic material, a module, and a magnetic refrigeration device according to an embodiment of the present disclosure will be described with reference to examples.

[0022] (1) Compound (1-1) Overview The compound of this embodiment contains four or more elements in a Heusler structure. Therefore, unlike conventional Heusler compounds consisting of three elements, the compound of this embodiment contains four or more elements in a Heusler structure, which may enhance the magnetocaloric effect.

[0023] The four or more elements are, for example, selected from Cr, Co, Fe, P, metal elements of the second period, the third period, and the fourth period, and non-metallic elements, and in this case, it is preferable to include all of the elements Cr, Co, Fe, and P. When the compound is composed of Cr, Co, Fe, and P, the composition ratio of Cr, Co, Fe, and P is more preferably Cr:Co:Fe:P=(0.5 to 1.5):(0.5 to 1.5):(0.5 to 1.5):(0.5 to 1.5).

[0024] The compound may also contain five or more elements. In this case, the compound preferably contains Cr, Co, Fe, P, and a fifth element. Examples of the fifth element include, but are not limited to, silicon (Si), aluminum (Al), germanium (Ge), tin (Sn), and hydrogen (H). In this case, when the composition ratio of Cr, Co, Fe, P, and the fifth element is expressed as Cr:Co:Fe:P:fifth element, the composition ratio of the fifth element is smaller than the composition ratios of the other four elements.

[0025] The fifth element may be introduced, for example, between the crystal lattice or may substitute for some of the lattice sites.

[0026] Furthermore, compounds undergo successive first-order structural phase transitions and second-order magnetic phase transitions. The first-order phase transition is a transformation that changes the crystal structure, such as martensitic transformation. The first-order phase transition occurs when the temperature drops to the martensitic transformation temperature. The second-order phase transition is a magnetic phase transition, such as a change from a paramagnetic material to a ferromagnetic material. The second-order phase transition occurs at the Curie temperature.

[0027] Here, in a compound, the temperature at which a first-order phase transition occurs (hereinafter also referred to as the "temperature of first-order phase transition") and the temperature at which a second-order phase transition occurs (hereinafter also referred to as the "temperature of second-order phase transition") are substantially the same. "Substantially the same" means that the temperature difference is within about 2 K. Note that either the first-order phase transition or the second-order phase transition may occur first.

[0028] The temperature of the first-order phase transition and the temperature of the second-order phase transition can be set according to the application of the object to be heat exchanged, and is preferably, for example, 270K or higher and 310K or lower.

[0029] FIG. 1 illustrates an image of a compound undergoing successive first-order and second-order phase transitions. In FIG. 1, the horizontal axis represents temperature, and the vertical axis represents energy within the compound. Here, the energy within the compound is entropy. Furthermore, Tc represents the temperature at which a first-order phase transition occurs and the temperature at which a second-order phase transition occurs. As shown in FIG. 1, when the temperature of the compound drops from Ta at point A to Tc at point B, a magnetic second-order phase transition occurs, releasing energy up to point C. Subsequently, a structural first-order phase transition occurs from point C, releasing energy up to point D. Thus, the compound of this embodiment undergoes successive first-order and second-order phase transitions at temperature Tc, releasing energy from point B to point D. Here, the compound has a martensitic transformation temperature, which is the temperature of a first-order phase transition, near the Curie temperature, which is the temperature of a second-order phase transition. Therefore, a first-order phase transition accompanying the martensitic transformation occurs along with a magnetic second-order phase transition, resulting in a large entropy change.

[0030] Such compounds constitute magnetic materials and are used in magnetic refrigerators of the active magnetic refrigeration (AMR) type.

[0031] (1-2) Manufacturing Method The compound of this embodiment is manufactured by selecting four or more elements that cause a first-order structural phase transition and a second-order magnetic phase transition to occur successively, and introducing the selected four or more elements into a Heusler structure.

[0032] Alternatively, after the four elements are introduced into the Heusler structure, a part of them may be replaced with a fifth element.

[0033] The temperature of the second-order phase transition can be controlled by adjusting the lattice size, and therefore, the lattice size is further selected so that the temperature of the second-order phase transition is substantially the same as the temperature of the first-order phase transition for the four or more selected elements.

[0034] (2) Magnetic Material (2-1) Overview The magnetic material includes a first compound and a second compound. The second compound has a different composition from the first compound. The first compound is the compound (1) above. The second compound does not have to be the compound (1) above, but in this embodiment, it is the compound (1) above. The Curie temperature, which is the temperature of the second-order phase transition of the first compound, is preferably different from the Curie temperature, which is the temperature of the second-order phase transition of the second compound. The second-order phase transition temperature of the first compound may be higher or lower than the second-order phase transition temperature of the second compound.

[0035] The magnetic material, for example, changes the entropy of the first compound and the second compound to obtain the magnetocaloric effect and exchange heat with the fluid. In other words, the magnetic material can be used to cool or heat the fluid. The first compound and the second compound generate heat when a magnetic field is applied, and absorb heat when the application of the magnetic field is stopped and removed.

[0036] The magnetic material is not limited as long as it contains at least two types of compounds.

[0037] (2-2) Method for Identifying Compounds in Magnetic Materials The method for identifying compounds in magnetic materials is to measure the interstitial distance by XRD (X-ray Diffraction), thereby identifying the crystalline phase.

[0038] Furthermore, by observing the backscattered electron image of the surface of the compound using a scanning electron microscope (SEM), it is possible to distinguish between portions with different crystalline phases.

[0039] Furthermore, the distribution of elements on a surface or cross section can be analyzed by electron beam methods such as EPMA (Electron Probe Micro Analyzer) or EDX (Energy Dispersive X-ray spectroscopy).

[0040] (3) Module (3-1) Overview A module is a module in which at least two types of compounds are arranged side by side. The shape and arrangement of the module are not particularly limited. The first compound and the second compound constituting the module are preferably arranged side by side, more preferably arranged in thermal contact with each other, and even more preferably arranged in direct physical contact with each other. This makes it possible to increase the efficiency when used as an AMR module.

[0041] 2 , module 10 of this embodiment includes a first compound 11 and a second compound 12 connected together. Specifically, module 10 includes first compound 11 having a stripe-shaped recess on the top thereof and second compound 12 having a stripe-shaped recess on the top thereof, and first compound 11 and second compound 12 are arranged so that the recesses are continuous with each other.

[0042] 3, the module 10 may have three or more compounds arranged in parallel, or may have three or more compounds arranged so as to overlap one another in the vertical direction.

[0043] (3-2) Manufacturing Method An example of a manufacturing method for the module 10 shown in FIG. 2 will be described. First, as described in (1-2) above, the first compound and the second compound are manufactured. Next, the first compound and the second compound are each placed in a mold with a partition, and then the partition is removed and the mixture is pressed. This makes it possible to manufacture the module 10 in which the first compound 11 and the second compound 12 are connected.

[0044] (4) Heat Source The heat source of this embodiment exchanges heat with a fluid by utilizing heat emitted from a magnetic material. The heat source includes the magnetic material described above in (2) and an application unit. Here, the heat source includes the module described above in (3) and an application unit.

[0045] The application unit applies a magnetic field to the magnetic material. Specifically, the application unit is capable of changing the magnetic field applied to the magnetic material. The application unit has a magnetic circuit or the like, and has a portion located on one side and a portion located on the other side of the magnetic material containing the first compound and the second compound.

[0046] The application unit can switch between a state in which a magnetic field is applied to the magnetic material and a state in which a magnetic field is not applied. The application unit may also be capable of performing a process of strengthening the magnetic field applied to the magnetic material and a process of weakening the magnetic field without reducing it to zero.

[0047] Such a heat source can be configured, for example, as a heat source 1 shown in Fig. 4. This heat source 1 includes a module 10 made of a magnetic material and an application unit 30.

[0048] The first compound 11 and the second compound 12 that make up the module 10 (magnetic material) are provided, for example, so as to be in contact with each other. The application unit 30 has a portion located on one side of the module 10 and a portion located on the other side, and can apply a magnetic field to the module 10, and can also stop applying the magnetic field to remove the magnetic field.

[0049] (5) Magnetic Refrigeration Apparatus The magnetic refrigeration apparatus of this embodiment is an AMR type, and includes the heat source described in (4) above and a moving unit.

[0050] The moving part moves a fluid that exchanges heat with the magnetic material. The fluid is in thermal contact with the magnetic material. The fluid is, for example, a heat medium such as a refrigerant or water.

[0051] Specifically, the moving unit moves the fluid relative to the magnetic material provided in the module. The moving unit is not particularly limited, and may be configured by pistons provided on both sides of the magnetic material, or may be configured by a pump provided in a closed circuit.

[0052] Such a magnetic refrigeration apparatus can be configured, for example, as a magnetic refrigeration apparatus 100 shown in Fig. 5. The magnetic refrigeration apparatus 100 here is a temperature control apparatus. The magnetic refrigeration apparatus 100 includes a heat source 1, a transfer circuit 60, a high-temperature side circuit 40, and a low-temperature side circuit 50.

[0053] As described above, the heat source 1 includes a module 10 made of a magnetic material and an application unit 30. The magnetic material constituting the module 10 in FIG. 5 includes, for example, a first compound 11, a second compound 12, a third compound 13, and a fourth compound 14. Here, the first compound 11, the second compound 12, the third compound 13, and the fourth compound 14 are the compounds (1) described above and have different compositions. The first compound 11, the second compound 12, the third compound 13, and the fourth compound 14 are composed of compounds having increasing second-order phase transition temperatures in this order. The first compound 11, the second compound 12, the third compound 13, and the fourth compound 14 are arranged in descending order of second-order phase transition temperatures. The application unit 30 can apply a magnetic field to all of the first compound 11, the second compound 12, the third compound 13, and the fourth compound 14 contained in the magnetic material (module 10), and can weaken or stop the applied magnetic field to remove the magnetic field.

[0054] The movement circuit 60 includes a tank 62, a pump 63, and a flow path 61 connecting these, and is filled with a fluid. The magnetic material constituting the module 10 may be disposed inside the tank 62, or may be disposed outside the tank 62 so that the fluid inside the tank 62 and the magnetic material are in thermal contact. The tank 62 includes a high-temperature reservoir 62a on the high-temperature side relative to the module 10 and a low-temperature reservoir 62b on the low-temperature side relative to the module 10. In the module 10, compounds with high second-order phase transition temperatures are located in the high-temperature reservoir 62a, and compounds with low second-order phase transition temperatures are located in the low-temperature reservoir 62b. When a magnetic field is applied to the module 10 from the application unit 30 and the fluid is heated by heat radiated from the module 10, the pump 63 is driven to move the fluid to the high-temperature side relative to the module 10. As a result, the high-temperature fluid is stored in the high-temperature reservoir 62a. Furthermore, when the application unit 30 stops applying the magnetic field to the module 10 and removes the magnetic field, the module 10 absorbs heat from the fluid, and when the temperature of the fluid drops, the pump 63 is driven to move the fluid to the low-temperature side of the module 10. As a result, the low-temperature fluid is stored in the low-temperature storage unit 62b. By repeating the above-described movement of the fluid and the application and removal of the magnetic field, the high-temperature fluid is collected in the high-temperature storage unit 62a, and the low-temperature fluid is collected in the low-temperature storage unit 62b.

[0055] The high-temperature side circuit 40 includes a high-temperature side first heat exchanger 41, a high-temperature side pump 44, a high-temperature side second heat exchanger 42, and a high-temperature side flow path 43 connecting these elements. A high-temperature side heat medium, such as a refrigerant or water, circulates through the circuit. The high-temperature side first heat exchanger 41 is disposed within the high-temperature reservoir 62a and performs heat exchange between the high-temperature side heat medium flowing through the high-temperature side first heat exchanger 41 and the high-temperature fluid in the high-temperature reservoir 62a. The high-temperature side second heat exchanger 42 uses the high temperature of the high-temperature side heat medium flowing through it to heat an object to be temperature-controlled. The object to be temperature-controlled may be air, a fluid such as water, or a solid to be heated. The high-temperature side flow path 43 connects the high-temperature side first heat exchanger 41, the high-temperature side pump 44, and the high-temperature side second heat exchanger 42 so that the high-temperature side heat medium can circulate between them. When driven, the high-temperature side pump 44 circulates the high-temperature side heat medium within the high-temperature side circuit 40 .

[0056] The low-temperature side circuit 50 includes a first low-temperature side heat exchanger 51, a low-temperature side pump 54, a second low-temperature side heat exchanger 52, and a low-temperature side flow path 53 connecting these components. A low-temperature side heat medium, such as a refrigerant or water, circulates through the circuit. The first low-temperature side heat exchanger 51 is provided in the low-temperature reservoir 62b and performs heat exchange between the low-temperature side heat medium flowing through the first low-temperature side heat exchanger 51 and the low-temperature fluid in the low-temperature reservoir 62b. The second low-temperature side heat exchanger 52 uses the low temperature of the low-temperature side heat medium flowing through it to cool a temperature-adjusted object. The temperature-adjusted object may be air, a fluid such as water, or a solid to be cooled. The low-temperature side flow path 53 connects the first low-temperature side heat exchanger 51, the low-temperature side pump 54, and the second low-temperature side heat exchanger 52 so that the low-temperature side heat medium can circulate between them. When driven, the low-temperature side pump 54 circulates the low-temperature side heat medium within the low-temperature side circuit 50 .

[0057] (6) Characteristics (6-1) Compounds 11 and 12 according to this embodiment contain four or more elements in a Heusler structure, and a first-order structural phase transition and a second-order magnetic phase transition occur successively.

[0058] According to Compounds 11 and 12 of this embodiment, since the Heusler structure contains four or more elements, the entropy change amount accompanying the magnetic second-order phase transition can be increased. Furthermore, since the structural first-order phase transition occurs continuously with the magnetic second-order phase transition, the entropy change amount accompanying the first-order phase transition can be increased. Therefore, Compounds 11 and 12 of this embodiment have a higher entropy change amount than conventional NaZn. 13 Compared to materials with a structure (La—Fe—Si-based materials), they can exhibit a large magnetic entropy change.

[0059] Furthermore, since compounds 11 and 12 of this embodiment exhibit large magnetic entropy without the application of pressure other than a magnetic field, a pressure generator can be omitted, thereby enabling the miniaturization and weight reduction of devices including compounds 11 and 12.

[0060] Furthermore, since Compounds 11 and 12 of this embodiment exhibit a large magnetocaloric effect near room temperature, they can be cooled or heated near room temperature. Therefore, Compounds 11 and 12 of this embodiment can be suitably used in refrigerators, heating devices, cooling devices, etc., and are more suitably used in air conditioning and heating equipment that replaces vapor compression systems.

[0061] (6-2) Compounds 11 and 12 according to this embodiment contain all of the elements Cr, Co, Fe and P in the compound according to (6-1) above.

[0062] Here, by including Cr, Co, Fe, and P as the four or more elements, it is possible to easily realize a large magnetic entropy change.

[0063] (6-3) Compounds 11 and 12 according to this embodiment are the compounds according to (6-2) above, which further contain a fifth element.

[0064] Thus, compounds 11 and 12 may contain five or more elements. The compound containing five elements is preferably a Heusler compound in which a fifth element is introduced between lattices to adjust the lattice size and change the temperature of the second-order phase transition, or a Heusler compound in which a part of the lattice sites is substituted with the fifth element to adjust the lattice size and change the temperature of the second-order phase transition.

[0065] (6-4) The magnetic material according to this embodiment includes a first compound 11 and a second compound 12. The first compound 11 is a compound according to any one of the above (6-1) to (6-3). The second compound 12 has a different composition from that of the first compound 11.

[0066] In this way, the magnetic material may contain two or more types of compounds 11 and 12. The second compound 12 may be a compound according to any one of the above (6-1) to (6-3), or may not be a compound according to any one of the above (6-1) to (6-3).

[0067] (6-5) In the magnetic material according to this embodiment, the first compound 11 and the second compound 12 in the magnetic material according to (6-4) above have different second-order phase transition temperatures.

[0068] Here, by using compounds 11 and 12 with different phase transition temperatures, heat exchange with a fluid using a magnetic material can be efficiently performed.

[0069] (6-6) In the module 10 according to this embodiment, the first compound 11 and the second compound 12 are linked together in the magnetic material according to (6-4) or (6-5) above.

[0070] Here, the fluid that has undergone heat exchange with one of the first compound 11 and the second compound 12 can be further subjected to heat exchange with the other of the first compound 11 and the second compound 12 .

[0071] (6-7) The heat source 1 according to this embodiment includes a magnetic material (a module 10 in this embodiment) and an application unit 30. The magnetic material is the magnetic material according to either (6-4) or (6-5) above. The application unit 30 applies a magnetic field to the magnetic material.

[0072] Here, heat exchange with the fluid can be performed by utilizing the heat released from the magnetic material to which a magnetic field is applied from the application unit 30. Therefore, by repeatedly applying and removing a magnetic field to the compounds 11 and 12, it is possible to at least cool and heat the fluid.

[0073] (6-8) The magnetic refrigeration device 100 according to this embodiment includes a heat source 1 and a pump 63 as a moving unit. The heat source 1 is the heat source according to (6-7) above. The pump 63 as a moving unit moves a fluid that exchanges heat with the magnetic material (the module 10 in this embodiment).

[0074] Here, the fluid heated by heat exchange with the magnetic material can be moved by the pump 63 as a moving part to extract hot heat, and the fluid that has absorbed heat by heat exchange with the magnetic material can be moved by the pump 63 as a moving part to extract cold heat.

[0075] (7) Modification The heat source 1 and the magnetic refrigeration device 100 described above include, but are not limited to, two or more types of compounds 11 and 12. The module and the magnetic refrigeration device of this modification include one type of compound.

[0076] (Simulation Method) In this example, the following three methods (a) to (c) were used as the simulation method.

[0077] (a) AkaiKKR AkaiKKR is a method for first-principles electronic structure calculations based on density functional theory using Green's functions, and is also known as Machikaneyama (see "Introduction to Computational Materials Design", Osaka University Press).

[0078] Specifically, AkaiKKR is a program package for first-principles electronic structure calculations based on the local density approximation (LDA) or generalized gradient approximation (GGA) of density functional theory. AkaiKKR can easily calculate the electronic structures of metals, semiconductors, compounds, etc., and is particularly useful as a first-principles calculation method that can handle alloys. AkaiKKR incorporates the coherent potential approximation (CPA), making it possible to handle not only conventional ordered crystals, but also disordered systems such as impurity systems, disordered substitutional alloys, and mixed crystals.

[0079] (b) HiLAPW HiLAPW uses the FLAPW method, which is one of the first-principles electronic structure calculation methods based on density functional theory (see "Band Theory" by Oguchi Tamio, Uchida Rokakuho Publishing).

[0080] Specifically, HiLAPW is an application that implements a first-principles calculation method based on the all-electron calculation method and full-potential method known as the FLAPW method. Because the FLAPW method uses the full potential, it is known as a method that can accurately calculate energies, and is particularly suitable for comparing energies within a lattice.

[0081] (c) Monte Carlo Simulation Method The Monte Carlo simulation method is a common one, but it uses values ​​calculated using Akai KKR for the magnetic interactions between magnetic atoms and the Potts model for the spin model. The entropy is estimated from this Monte Carlo simulation method.

[0082] Example 1 In Example 1, the performance index as a magnetic material and the temperature of second-order phase transition of a Heusler compound were calculated by exhaustive calculation. The results are shown in Fig. 6. In Fig. 6, the vertical axis represents the temperature of second-order phase transition, and the horizontal axis represents the performance index as a magnetic material. The performance evaluation (performance index) is a value based on the state of electron spin, and the higher the value, the better the performance.

[0083] In Figure 6, systems S that exhibit second-order and first-order phase transitions were extracted, centering on compositions present in the target temperature range. The results are shown in Figure 7. In Figure 7, the vertical axis represents the entropy change, and the horizontal axis represents the temperature of the second-order phase transition. The entropy change is a negative value. In Figure 7, the entropy change of MnAs is shown as a reference line L.

[0084] From FIG. 7 , six points (candidate materials extracted in FIG. 7 ) with performance higher than the reference line L were extracted, and the temperature of the second-order phase transition and the entropy change due to electron spin were determined using a Monte Carlo simulation. As a result, in the Heusler structure, a compound containing Cr, Co, Fe, and P elements with the same content ratio (composition ratio) showed the best results. The results are shown in FIG. 8 . In FIG. 8 , the vertical axis represents the entropy change due to electron spin when no magnetic field is applied (0.0 [T]) and when a magnetic field of 1.0 [T] is applied, and the horizontal axis represents temperature. As shown in FIG. 8 , a quaternary compound containing all of the elements Cr, Co, Fe, and P exhibits an entropy change of approximately 23 [J / kgK] due to the second-order phase transition at 520 [K], which is the temperature of the second-order phase transition.

[0085] It should be noted that FIG. 8 shows calculated values, and the calculated values ​​are approximately 200K to 300K larger than the actual values, so FIG. 8 shows that approximately 500K is preferable.

[0086] The inventors have also determined that the martensitic transformation temperature of a quaternary compound containing all of the elements Cr, Co, Fe, and P in a Heusler structure is 520 K. This indicates that a first-order structural phase transition and a second-order magnetic phase transition occur consecutively in this compound. Furthermore, the inventors have found that a first-order phase transition exhibits an entropy change equivalent to that of a second-order phase transition. This indicates that this compound exhibits an entropy change of approximately 46 [J / kgK] due to the successive occurrence of a first-order phase transition and a second-order phase transition.

[0087] (Comparative Example 1) As Comparative Example 1, La(Fe ０．８５ Si ０．１５ ) １３ The temperature of the second-order phase transition and the entropy change due to electron spin were calculated. The results are shown in FIG. 9. FIG. 9 corresponds to FIG. 8, and the vertical axis shows the entropy change due to electron spin when no magnetic field is applied (0.0 [T]) and when a magnetic field of 1.0 [T] is applied, and the horizontal axis shows the temperature when a magnetic field of 1.0 [T] is applied. As shown in FIG. 9, ０．８５ Si ０．１５ )１３ It can be seen that the second-order phase transition of La(Fe) in Comparative Example 1 shows an entropy change of about 14 [J / kgK]. Therefore, when only the second-order phase transition is taken into consideration, the entropy change amount in the second-order phase transition of the quaternary Heusler compound of Cr, Co, Fe and P, which showed the best results in Example 1, is about 14 [J / kgK]. ０．８５ Si ０．１５ ) １３ It can be seen that the entropy change is higher than that in the second-order phase transition of

[0088] Furthermore, La(Fe ０．８５ Si ０．１５ ) １３ The calculation result is the result of only the entropy change of the second-order phase transition. However, the entropy change (about 46 [J / kgK]) of the quaternary Heusler compound of Cr, Co, Fe and P, which showed the best result in Example 1, was about 46 [J / kgK]. ０．８５ Si ０．１５ ) １３ It can be seen that this is more than three times the entropy change (approximately 14 [J / kgK]) of

[0089] Example 2 In Example 2, the relationship between lattice size and the temperature of the second-order phase transition was investigated. Specifically, the temperatures of the second-order phase transition were determined for a compound consisting of the elements Cr, Co, Fe, and P in a Heusler structure at various lattice sizes. The results are shown in Figure 10. In Figure 10, the vertical axis represents the temperature of the second-order phase transition, and the horizontal axis represents the expansion rate of the lattice size, with the lattice constants a and b set at 3.905 [Å] and c set at 5.756 [Å] as the reference (0).

[0090] 10, it can be seen that in a Heusler structure, the compound consisting of the elements Cr, Co, Fe, and P has a higher second-order phase transition temperature as the lattice size increases. This shows that by adjusting the lattice size, the second-order phase transition temperature can be controlled to be substantially the same as the first-order phase transition temperature.

[0091] It is also clear that by introducing a fifth element into the interstitial spaces or substituting a portion of the lattice sites of the compound with the fifth element, adjusting the lattice size, and changing the temperature of the second-order phase transition, it is possible to realize a compound in which a first-order structural phase transition and a second-order magnetic phase transition occur successively.

[0092] Although the embodiments and examples of the present disclosure have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the present disclosure as defined in the claims.

[0093] 1: Heat source 10: Module 11, 12, 13, 14: Compound 30: Applicator 63: Pump (moving part) 100: Magnetic refrigerator

[0094] Japanese Patent Application Laid-Open No. 2008-150695

Claims

1. A compound (11) containing four or more elements in a Heusler structure, in which a first-order structural phase transition and a second-order magnetic phase transition occur successively.

2. The compound according to claim 1, containing all of the elements Cr, Co, Fe and P.

3. The compound of claim 2, further comprising a fifth element.

4. A magnetic material comprising: a first compound (11) according to any one of claims 1 to 3; and a second compound (12) having a composition different from that of the first compound.

5. The magnetic material according to claim 4, wherein a temperature of a second-order phase transition of the first compound and a temperature of a second-order phase transition of the second compound are different.

6. The module (10) according to claim 4 or 5, wherein the first compound and the second compound are linked together.

7. A heat source (1) comprising: a magnetic material according to claim 4 or 5; and an application unit (30) that applies a magnetic field to the magnetic material.

8. A magnetic refrigeration device (100) comprising: the heat source according to claim 7; and a moving part (63) that moves a fluid that exchanges heat with the magnetic material.

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