JP7378773B2 - Magnetic refrigeration materials, magnetic refrigeration systems using them, cold storage materials - Google Patents

Description

The present invention relates to a magnetic refrigeration material that contributes to hydrogen liquefaction, and particularly to a magnetic refrigeration material that causes a large entropy change near 20 Kelvin (K), where hydrogen liquefies.
The present invention also relates to a magnetic refrigeration system using the above magnetic refrigeration material.

To popularize hydrogen, which holds promise as an energy carrier, it is desirable to use it in a "liquid" state that can be stored and transported at high density. At this time, the liquefaction temperature of hydrogen is approximately 20 Kelvin (minus 253 degrees Celsius), which is the second lowest after helium, so it is essential to develop and improve the efficiency of hydrogen liquefaction technology. In conventional liquefaction methods that utilize gas compression and expansion, the cost of hydrogen liquefaction remains high due to the theoretical upper limit (approximately 40%) of liquefaction efficiency. On the other hand, magnetic refrigeration technology based on the magnetocaloric effect, which utilizes the entropy change caused by magnetizing (heating) and demagnetizing (absorbing heat) a magnetic material using a magnetic field, has a liquefaction efficiency of up to 90% in theory, and hydrogen It is expected that it will contribute to its widespread use (for example, see Patent Document 1).

In the development of magnetic refrigeration materials that are directly linked to hydrogen liquefaction efficiency, it is first important to bring about a large entropy change when the magnetic field is turned on and off in the magnetic material near 20 Kelvin, where hydrogen liquefies. Therefore, materials such as room temperature magnetic refrigeration material (La(FeSi) ₁₃ ) have been developed (see Non-Patent Document 1). Further, even near the hydrogen liquefaction temperature, for example, Patent Document 2 proposes Er ₅ Pd ₂ , and Patent Document 3 proposes Ho _x Er _1-x Ni _y (0≦x<1, 0.8<y≦1). has been proposed, and Patent Document 4 proposes a holmium copper-based heat storage material (HoCu _2-x M _x ). Further, Non-Patent Document 2 reports magnetic refrigeration materials such as Laves phase (ErCo ₂ ) as a regenerator material, and Non-Patent Document 3 reports erbium silicide (Er ₅ Si ₃ ).

Special Publication No. 2003-532861 (especially Figures 5 and 6, paragraph numbers 0031-0039) JP 2017-39993 A (especially claim 1) CN103572097A (especially claim 1, Tables 3 to 9) WO2018/199278 publication

S. Fujida et al. , Appl. Phys. Lett. 89, 062504 (2006) Hirofumi Wada, Masayuki Shiga, "Magnetocaloric Effect - Aiming for Highly Efficient Magnetic Refrigeration", Materia Vol. 39, No. 11, p. 909-915 (2000) N. Mohapatra et al. , AIP Conference Proceedings 1447, 1165 (2012)

In the room temperature magnetic refrigeration material (La(FeSi) ₁₃ ), attempts have been made to lower the magnetic transition temperature and the entropy change associated with it by element substitution. Residual magnetization associated with this has become an issue.
Furthermore, in the Laves phase (ErCo ₂ ), damage to the material is a problem due to the large magnetovolume effect (rapid change in the crystal lattice due to magnetic transition caused by a magnetic field) accompanying the first-order transition. Furthermore, it is a decomposition and melting material, which poses hurdles to making it a practical material.
Regarding erbium silicide (Er ₅ Si ₃ ), although there are some paper reports, the current situation is that no systematic research, such as engineering studies, has been conducted with an eye toward practical materials.

The present invention solves the problems of existing magnetic refrigeration materials mentioned above, and provides a high-performance magnetic refrigeration material that efficiently cools in a temperature range from liquid nitrogen temperature (77K) to hydrogen liquefaction temperature (20K). The purpose is to

The present inventor discovered that holmium silicide (Ho ₅ Si ₃ ) has magnetism induced by the magnetic moment of holmium (Ho), and the entropy change brought about by this induced magnetism is combined with Si, which has a high Clark number. Considering that Ho 5 Si 3 is an optimal material candidate for hydrogen liquefaction, we synthesized Ho ₅ Si ₃ and evaluated its physical properties as a magnetic refrigeration material. At this time, we took into account the fact that holmium silicide (Ho ₅ Si ₃ ) is a molten substance and can be obtained by arc melting, and that the material is stable even after synthesis, with the aim of making it a practical material in the future. ing.
Furthermore, regarding Er ₅ Ge ₃ and Er ₅ Ga ₃ , which are compounds with similar composition to holmium silicide (Ho ₅ Si ₃ ), the entropy change due to the total angular momentum (J) of erbium (Er) and the Si site It was found that by replacing the material with an element with a different atomic radius and controlling the magnetic order temperature, it could become an optimal material candidate for hydrogen liquefaction.

[1] The magnetic refrigeration material of the present invention is a magnetic refrigeration material containing at least one compound from the group of Ho ₅ Si ₃ , Er ₅ Ge ₃ , and Er ₅ Ga ₃ .
[2] In the magnetic refrigeration material of the present invention, Ho ₅ Si ₃ has a magnetic field greater than 0.08 [J/cm ³ K] under conditions of 22 to 32 Kelvin and an applied magnetic field of 0 to 5 Tesla. Has an entropy change. Here, the magnetic entropy change refers to a change in absolute value.

[3] The magnetic refrigeration system of the present invention uses the magnetic refrigeration material according to claim 1 or 2 as a magnetic refrigeration material exhibiting a magnetocaloric effect.
[4] The cold storage material of the present invention is a cold storage material containing at least one compound from the group of Ho ₅ Si ₃ , Er ₅ Ge ₃ , and Er ₅ Ga ₃ .

[5] The magnetic refrigeration system of the present invention is a refrigeration system that includes a magnetic container, an excitation/demagnetization mechanism for applying and removing a magnetic field to and from the magnetic container, and a cryopump stage inside a vacuum container equipped with a cryopump. ,
The magnetic container has a magnetic member on at least one end surface, and has a heat insulating material on at least one end surface,
The excitation/demagnetization mechanism has a thermal switch and a permanent magnet, is movable within the vacuum container, and has a superconducting magnet together with the permanent magnet,
The cryopump stage and the magnetic container are in contact with each other at an end surface provided with the heat insulating material,
The excitation/demagnetization mechanism may be in contact with the magnetic member and the cryopump stage through a thermal switch.

[6] In the magnetic refrigeration system of the present invention, preferably, as the magnetic member, a magnetic refrigeration material containing at least one of the compounds from the group of Ho ₅ Si ₃ , Er ₅ Ge ₃ and Er ₅ Ga ₃ is used. good.

According to the magnetic refrigeration material of the present invention, for Ho ₅ Si ₃ , Er ₅ Ge ₃ , and Er ₅ Ga ₃ , the temperature is 20 to 30 Kelvin, which is around the boiling point of liquid hydrogen, and the applied magnetic field is 0 to 5 Tesla. Since it has a magnetic entropy change larger than 0.08 [J/cm ³ K], it is a magnetic refrigeration material suitable for producing liquid hydrogen, for example.
According to the magnetic refrigeration system using the magnetic refrigeration material of the present invention, since the magnetic refrigeration material that has a large magnetic entropy change at 20 to 30 Kelvin, which is around the boiling point of liquid hydrogen, is used, it is possible to produce liquid hydrogen. It can be done energy-efficiently.
According to the cold storage material of the present invention, Ho ₅ Si ₃ , Er ₅ Ge ₃ , and Er ₅ Ga ₃ can be stored at temperatures of 20 to 30 Kelvin, which is near the boiling point of liquid hydrogen, and under the conditions of an applied magnetic field of 0 to 5 Tesla. , 0.08 [J/cm ³ K], so it is a suitable cold storage material for use near the boiling point temperature of liquid hydrogen, for example.

1 is a diagram showing a crystal structure of Ho ₅ Si ₃ showing an example of the present invention. It has a space group P63/mcm. FIG. 2 is a diagram showing powder X-ray structural diffraction of arc-fused Ho ₅ Si ₃ at room temperature, illustrating an example of the present invention. FIG. 3 is a diagram showing the temperature dependence (low temperature part) of the entropy change of Ho ₅ Si ₃ . FIG. 3 is a diagram showing the temperature dependence of the entropy change of Ho ₅ Si ₃ (up to room temperature). FIG. 3 is a diagram showing the temperature dependence (up to room temperature) of the entropy change of Er ₅ Ge ₃ showing another example of the present invention. FIG. 7 is a diagram showing the temperature dependence (up to room temperature) of the entropy change of Er ₅ Ga ₃ showing another example of the present invention. This is a diagram showing the magnetization of Er ₅ Ga ₃ at 2, 20, and 40 Kelvin, where the vertical axis is the magnetization M and the horizontal axis is the magnetic field H. FIG. 1 is a conceptual diagram of a refrigeration system that uses the magnetic refrigeration material of the present invention to generate extremely low temperatures without using liquid helium.

Definition of terms ``Magnetocaloric effect'' Temperature change is induced by changing the magnetic field applied to a magnetic material. When the magnetic field applied to a magnetic material is removed, magnetic entropy increases and heat absorption occurs. The amount of heat absorbed at this time is given by the product of magnetic entropy change and absolute temperature, so if a larger magnetic entropy change is obtained, a larger amount of heat will be absorbed. This process of cutting off the magnetic field applied to the magnetic material corresponds to the process of gas expansion in gas refrigeration.

``Ferromagnetic material'' A magnetic material that exhibits a magnetic structure in which adjacent electron spins point in the same direction. Magnetization exists under zero magnetic field and has the property of attracting magnets. The temperature at which a ferromagnetic structure appears is called the Curie temperature.
"Antiferromagnetic material" A magnetic material that exhibits a magnetic structure in which adjacent electron spins are oriented in opposite directions. Under zero magnetic field, there is no magnetization and it does not have the property of attracting a magnet. The temperature at which an antiferromagnetic magnetic structure appears is called the Neel temperature.

"Magnetic entropy" A quantitative state quantity that expresses the randomness of spin states. In ferromagnetic and antiferromagnetic structures that appear at low temperatures, adjacent electron spins are aligned in the same or opposite directions, so the magnetic entropy is small. On the other hand, large magnetic entropy is observed in paramagnetic structures in which the electron spins that appear at high temperatures are oriented in random directions.

"n-order phase transition" refers to a phase transition in which the (n-1) order differential of Gibbs free energy G with respect to temperature T is continuous and the n order differential is discontinuous.
"First-order phase transition" Discontinuities occur in the entropy, volume, polarization, etc. of a crystal, including (a) transition between gas and liquid, (b) transition between liquid and solid, (c) polymorphic transition of crystal, (e) There are transitions between metals and insulators (Mott transition), etc.
"Secondary phase transition" The entropy, volume, polarization, etc. of a crystal are continuous, and the temperature differential of these changes discontinuously, resulting in (a) rotational transition in molecular crystals, and (b) order/disorder transition in alloys. , (c) phase transition of ferroelectrics, (d) magnetic phase transitions such as ferromagnetism and antiferromagnetism, (v) λ-transition of liquid helium, and (c) phase transition of superconductors. A common feature of second-order phase transitions is that, although there is no change in the crystal structure at the transition temperature Tc, a λ-type anomalous specific heat is observed, and a certain macroscopic ordering occurs in the low-temperature phase that does not exist at high temperatures. This is the point where it appears as an observable physical quantity.

``Clark number'' The proportion of elements present near the earth's surface is estimated based on the results of chemical analysis of igneous rocks, and is expressed as abundance ratio (mass percent concentration). The most abundant element is oxygen, followed by silicon, aluminum, and iron.

The magnetic refrigeration materials Ho ₅ Si ₃ , Er ₅ Ge ₃ , Er ₅ Ga ₃ of the present invention are obtained by melting the raw materials so as to have a predetermined composition. Specifically, it can be obtained by melting the rare earth metal holmium (Ho) or erbium (Er) and silicon (Si), germanium (Ge), or gallium (Ga) as raw materials in an arc furnace in an argon gas atmosphere. I can do it. It is desirable to measure the diffraction pattern of the obtained substance using an X-ray powder diffractometer and confirm that it has a Mn ₅ Si ₃ type hexagonal crystal structure.

The magnitude of the magnetocaloric effect is expressed by the isothermal magnetic entropy change amount ΔSM or the adiabatic temperature change amount ΔTad. ΔSM is approximately calculated from the isothermal magnetization curve using the following Maxwell relation.
(M in the formula represents magnetization)

ΔSM can also be calculated by measuring the temperature change in molar specific heat while varying the external magnetic field and applying it to the following thermodynamic formula.
(In the formula, H ₀ represents the case where there is no external magnetic field, and H ₁ represents that the external magnetic field H = H _1. )

The adiabatic temperature change amount ΔTad is calculated using the magnetic field dependence C(T, H) of the measured molar specific heat. That is, C (T, H) is determined by measuring the specific heat with a magnetic field applied, and the entropy at zero magnetic field and at each magnetic field is determined by integrating the experimental value with respect to temperature. Draw the obtained entropy in each magnetic field on a curve as an entropy-temperature graph. At this time, the temperature at the intersection of the entropy curve of the external magnetic field H1 and a horizontal line representing a constant entropy value S is defined as T(S)H1. Similarly, the temperature T(S)H ₀ is determined from the intersection of the entropy curve in the case of zero magnetic field and the horizontal line representing the entropy value S. By applying these values to the following thermodynamic formula, the adiabatic temperature change amount ΔTad can be calculated.

(In the formula, H ₀ represents the case where there is no external magnetic field, and H ₁ represents that the external magnetic field H = H _1. )

Another aspect of the present invention, the cold storage material, utilizes the fact that Ho ₅ Si ₃ , Er ₅ Ge ₃ , and Er ₅ Ga ₃ still have large specific heats even at temperatures below 25K. The material can therefore be used as a cold storage material in systems that use liquid helium, for example.

A refrigeration system that combines a cryopump and a magnetic refrigeration device using the magnetic refrigeration material of the present invention will be described using FIG. 8.
The refrigeration system of the present invention includes a magnetic container and an excitation/demagnetization mechanism provided inside a vacuum container 11 equipped with a cryopump.

The magnetic container has a magnetic member 31 on at least one end surface and a heat insulating material 33 on at least one end surface. The magnetic container is in contact with the cryopump stage 23 via a heat insulating material 33. Moreover, a magnetic refrigeration material is used for the magnetic member 31.

The excitation/demagnetization mechanism is provided to apply or remove a magnetic field to the magnetic container, includes a permanent magnet 41 and a mechanical heat switch 42, and is made so as to be movable within the vacuum container. For example, in the example of FIG. 8, movement is performed by a movable rod 44. Furthermore, the excitation/demagnetization mechanism can perform excitation/demagnetization in an extremely low temperature environment of about 20 K by using a cryogen and a superconducting magnet. Further, examples of permanent magnets that can generate a strong magnetic field of about 1 Tesla at such extremely low temperatures include neodymium-based rare earth permanent magnets. By using a superconducting magnet in combination, it is possible to generate a strong magnetic field, for example 5 to 10 Tesla, which is difficult to achieve with permanent magnets alone. As the cryogen, liquid hydrogen (20 Kelvin) or liquid helium can be used.

The sample is cooled by performing an adiabatic cooling process after the excitation cooling process. FIG. 8(a) is a conceptual diagram during the excitation cooling process. First, a sample is placed in the internal space 32 of the magnetic container and placed inside the vacuum container 11 . The inside of the vacuum container 11 is roughly pumped using the rough pump 13 to the extent that the cryopump can be started. When the cryopump can be started, the movable rod 44 is moved to adjust the position of the excitation/demagnetization device so that the magnetic field by the permanent magnet 41 is applied to the magnetic member 31. At this time, the thermal switch 42 of the excitation/demagnetization device is brought into contact with the magnetic member 31 and the cryopump stage 23. Since the magnetic member 31 generates heat due to the application of the magnetic field, the cryopump is activated by the heat switch 42. If a gas with high vapor pressure that does not condense at a temperature of about 10 to 20K, such as helium, is used for the cryopump, cooling progresses and the cryopump stage 23 is cooled to about 10K. Furthermore, if a gas with high vapor pressure that does not condense at a temperature of about 22 to 50K, such as hydrogen, is used for the cryopump, cooling progresses and the cryopump stage 23 is cooled to about 25K.

Once the excitation cooling process has stopped cooling the sample, an adiabatic cooling process is performed next. As shown in FIG. 8(b), by moving the movable rod 44, the position of the excitation/demagnetization mechanism is moved. At this time, the excitation/demagnetization mechanism and the magnetic container are spaced apart so that the magnetic field applied to the magnetic member 31 from the permanent magnet 41 is as small as possible. This operation causes a magnetic cooling effect, which further cools the sample since the magnetic container is thermally insulated from the cryopump stage by the insulation material 33.

This magnetic refrigeration system uses superconducting electromagnets and can generate strong magnetic fields that are difficult to achieve with permanent magnets alone. Therefore, by using Ho ₅ Si ₃ , Er ₅ Ge ₃ , and Er ₅ Ga ₃ for the magnetic member 31 and attaching a superconducting electromagnet to the permanent magnet 41, a strong magnetic field of 5 to 10 Tesla can be generated. Liquid hydrogen can be produced with energy efficiency. This is because Ho ₅ Si ₃ , Er ₅ Ge ₃ , and Er ₅ Ga ₃ used in the magnetic member 31 are magnetic refrigeration materials that have a large magnetic entropy change at 20 to 30 Kelvin, which is near the boiling point of liquid hydrogen. Additionally, using liquid helium makes it easy to create superconducting electromagnets. Even with liquid hydrogen, superconducting electromagnets can be realized by appropriately selecting superconducting materials.

The present invention will be explained below using Examples, but the present invention is not limited thereto.

The magnetic refrigeration material of the present invention is manufactured, for example, through the following manufacturing steps (a) to (k), and inspected through the following testing steps (k) to (k).
(A) Regarding the target material (Ho ₅ Si ₃ ), weigh out a total of approximately 5 g of each element (Ho, Si) in stoichiometric ratio (mole ratio).
(i) Place the raw materials in (a) into the copper hearth in the arc melting furnace.
(c) Evacuate the inside of the arc melting furnace and exhaust the atmosphere inside the chamber.
(E) After exhausting the atmosphere in the chamber, introduce argon gas and close the chamber.
(E) Arc melting the material.
(i) Repeat melting approximately 5 times for the material to ensure homogeneous melting.
(i) Take out the finished material and cut it.

(h) Part of the cut material is powdered in a mortar, and the material is evaluated by a powder X-ray diffraction experiment at room temperature.
(k) Measure the temperature dependence of magnetization of a part of the cut material using a magnetization measuring device. The measurement range is temperature: 2 to 300 Kelvin, magnetic field: 0.01 to 5 Tesla. Analyze the measurement data and find the entropy change.

As the powder X-ray diffraction device, for example, a MiniFlex600 X-ray powder diffraction device manufactured by Rigaku Corporation is used. A superconducting quantum interference device (SQUID) manufactured by Quantum Design, MPMS-5, was used to measure magnetization. Specific heat can be measured, for example, by a thermal relaxation method using a PPMS-9 physical properties measurement system manufactured by Quantum Design.

FIG. 1 is a diagram showing the crystal structure of Ho ₅ Si ₃ showing an example of the present invention. Holmium silicide (Ho ₅ Si ₃ ) has a hexagonal crystal structure, and the crystal structure has a space group P63/mcm.
FIG. 2 is a diagram showing the powder X-ray structure diffraction results of arc-melted Ho ₅ Si ₃ at room temperature. As a result, the desired Ho ₅ Si ₃ was created, and based on this data, the lattice constants were determined to be a = 0.8284 (a) nm, c = 0 in the sample obtained after arc melting. It was evaluated to be .6222(5) nm. Since the sample has just been arc melted and has not been annealed yet, the literature values (https://materialsproject.org/materials/mp-13236/) are a = 0.8401 nm, b = 0.8401 nm, c=0.6326 nm, which does not strictly match.

FIG. 3 is a diagram showing the temperature dependence (low temperature part) of the entropy change of Ho ₅ Si ₃ . It has a large peak near 25 Kelvin, and has a peak value of 0.095 [J/cm ³ K] when evaluating entropy changes from 0 to 5 Tesla. Ho ₅ Si ₃ has a magnetic entropy change greater than 0.08 [J/cm ³ K] at 22 to 32 Kelvin and under the conditions of an applied magnetic field of 0 to 5 Tesla.
In the first-order transition material (ErCo ₂ ), the temperature range that causes a large entropy change is not wide due to the nature of the first-order phase transition, but in Ho ₅ Si ₃ , the entropy change is gradual, which is considered to be advantageous for hydrogen liquefaction.

FIG. 4 is a diagram showing the temperature dependence of the entropy change of Ho ₅ Si ₃ (up to room temperature). Regarding the temperature dependence of entropy change, in addition to a large peak near 25 Kelvin, there is a sub-peak near 70 Kelvin. Ho ₅ Si ₃ has a magnetic entropy change larger than 0.04 [J/cm ³ K] under conditions of 12 to 54 Kelvin and an applied magnetic field of 0 to 5 Tesla. Further, Ho ₅ Si ₃ has a magnetic entropy change larger than 0.02 [J/cm ³ K] under conditions of 8 to 94 Kelvin and an applied magnetic field of 0 to 5 Tesla.
Note that by measuring the specific heat of Ho ₅ Si ₃ , the adiabatic temperature change amount ΔTad can be evaluated.

FIG. 5 is a diagram showing the temperature dependence (up to room temperature) of the entropy change of Er ₅ Ge ₃ showing another example of the present invention. The entropy change from 0 to 5 Tesla is evaluated. Er ₅ Ge ₃ has a magnetic entropy change larger than 0.06 [J/cm ³ K] under the conditions of 16 to 46 Kelvin and an applied magnetic field of 0 to 5 Tesla, and has a peak near 34 Kelvin. It has a value of 0.082 [J/cm ³ K]. Furthermore, when comparing Er ₅ Ge ₃ with Ho ₅ Si ₃ , the peak temperature of magnetic entropy has shifted to a higher temperature side by about 10 Kelvin.

FIG. 6 is a diagram showing the temperature dependence of entropy change (up to room temperature) of Er ₅ Ga ₃ showing another embodiment of the present invention. The magnetic entropy change from 0 to 5 Tesla is evaluated. Er ₅ Ga ₃ has a magnetic entropy change larger than 0.08 [J/cm ³ K] under conditions of 6 to 15 Kelvin and an applied magnetic field of 0 to 5 Tesla, and has a peak near 10 Kelvin. It has a value of 0.095 [J/cm ³ K]. Furthermore, when comparing Er ₅ Ga ₃ with Ho ₅ Si ₃ , the peak temperature of magnetic entropy has shifted to a lower temperature side by about 12 Kelvin, indicating that the transition point can be controlled by changing the elements. .
FIG. 7 is a diagram showing the magnetization of Er ₅ Ga ₃ at 2, 20, and 40 Kelvin, where the vertical axis is the magnetization M and the horizontal axis is the magnetic field H. Although residual magnetization remains at 2 Kelvin, almost no residual magnetization, which is disadvantageous to magnetic refrigeration, is observed at 20 Kelvin, which is essentially important for hydrogen liquefaction, and at temperatures higher than that, 40 Kelvin. .

The magnetic refrigeration materials of the _present invention, _{Ho5Si3 , Er5Ge3} , and _Er5Ga3 , are suitable in the temperature range from liquid nitrogen temperature ( _77K ) to hydrogen liquefaction temperature (20K), and have large adiabatic temperature changes. shows. Additionally, this material can be used in refrigeration systems and cold storage materials.
According to the magnetic refrigeration system using the magnetic refrigeration material of the present invention, liquid hydrogen can be produced with energy efficiency.

11 Vacuum vessel 12 Compressor unit 13 Rough quota pump 21 Cryopanel (condensation panel)
22 Cryopanel (adsorption panel)
23 Cryopump stage 31 Magnetic material 32 Inside of magnetic container 33 Insulating material 41 Magnet 42 Heat switch 44 Movable rod

Claims (5)

A magnetic refrigeration material made of any one of the compounds from the group of Ho ₅ Si ₃ , Er ₅ Ge ₃ and Er ₅ Ga ₃ . A claim characterized in that Ho ₅ Si ₃ has an entropy change larger than 0.08 [J/cm ³ K] under conditions of a temperature of 22 to 32 Kelvin and an applied magnetic field of 0 to 5 Tesla. The magnetic refrigeration material according to item 1. A magnetic refrigeration system characterized in that the magnetic refrigeration material according to claim 1 or 2 is used as a magnetic refrigeration material exhibiting a magnetocaloric effect. A cold storage material made of any one of the compounds from the group of Ho ₅ Si ₃ , Er ₅ Ge ₃ , and Er ₅ Ga ₃ . A refrigeration system including a magnetic container, an excitation/demagnetization mechanism that applies and removes a magnetic field to and from the magnetic container, and a cryopump stage inside a vacuum container equipped with a cryopump,
The magnetic container has a magnetic member on at least one end surface, and has a heat insulating material on at least one end surface,
The excitation/demagnetization mechanism has a thermal switch and a permanent magnet, is movable within the vacuum container, and has a superconducting magnet together with the permanent magnet,
The cryopump stage and the magnetic container are in contact with each other at an end surface provided with the heat insulating material,
The excitation/demagnetization mechanism can be in contact with the magnetic member and the cryopump stage through a thermal switch , and
A refrigeration system characterized in that, as the magnetic member, a magnetic refrigeration material made of any one of compounds from the group of Ho ₅ Si ₃ , Er ₅ Ge ₃ , and Er ₅ Ga ₃ is used.