JP2020152930A - Magnetic refrigerant - Google Patents

Abstract

To provide a magnetic refrigerant operable in a high temperature range (for example, approximately room temperature or above) which has a wide operable temperature range and a small hysteresis, and which offers a giant magnetocaloric effect and has a large adiabatic temperature change value.SOLUTION: A magnetic refrigerant is composed of Mn, Fe, Ru, P, Si and Ge. A sum of blending mole fractions of Si and Ge is 0.40-0.65, and a blending mole fraction of P is 0.35-0.60.SELECTED DRAWING: Figure 1

Description

The present invention relates to a magnetic freezing material composed of a magnetic material, which exhibits a large magnetic heat effect and adiabatic temperature change, particularly in a temperature range higher than the conventional one (for example, a room temperature range or higher).

In recent years, a new magnetic freezing method has been proposed in place of the conventional gas freezing method that uses a fluorocarbon gas as a refrigerant, which causes environmental problems such as global warming and ozone layer depletion. In this magnetic refrigeration method, a certain kind of magnetic material is used as a refrigerant, and the magnetic heat effect, that is, the magnetic entropy change amount generated when the magnetic order of the magnetic material is changed by a magnetic field in an isothermal state, and the magnetism of the magnetic material in an adiabatic state. Utilizes the adiabatic temperature change that occurs when the order is changed by a magnetic field.

A magnetic refrigeration device and a magnetic heat pump device using a magnetic material having such a magnetic calorific value effect as a refrigerant have been widely studied. According to this magnetic freezing method, it becomes possible to manufacture a magnetic freezing device and a magnetic heat pump device without using chlorofluorocarbon gas, and there is an advantage that the efficiency is higher than that of the conventional gas method.

A magnetic material having such a magnetic calorific value effect is particularly called a magnetic freezing material (magnetic freezing work substance).

As the magnetic refrigeration material used in such a magnetic refrigeration method, compound-based magnetic refrigeration materials such as LaFeSi-based and MnFePSi-based are known as efficient materials showing a large magnetic calorific value effect in a low magnetic field, and several kinds of elements. Is mixed and sintered or melted to produce a bulk (block shape).

In such a magnetic refrigeration material, a phase transition occurs by crossing the Curie temperature (Tc) (the temperature at which the magnetism of each substance changes from ferromagnetism to paramagnetism), and a large magnetic calorific value effect is obtained. As a result, the temperature of the magnetic refrigeration material changes.

In relation to the Curie temperature, the difference between the Curie temperature when the temperature is raised while applying heat to the magnetic refrigerating material and the Curie temperature when the temperature is lowered while cooling is called hysteresis. When this hysteresis becomes large, there is a drawback that the change in adiabatic temperature becomes small.

Substances exhibiting a magnetic calorific value effect known so far (for example, compounds such as LaFeSi type and MnFePSi type) have a magnetic calorific value effect in a relatively wide temperature range from a freezing range to a room temperature range, but a higher temperature range. For example, the magnetic heat effect is small in the room temperature range or higher, especially in the range of 60 ° C. or higher, and in order to realize the practical ability as a magnetic heat pump device, a very large strong magnetic field that can be realized only by a superconducting magnet or the like is applied. There is a need.

In such a situation, in order to improve the magnetic calorific value effect, a magnetic freezing material in which an element is added to a substance exhibiting a magnetic calorific value effect has been proposed.

For example, as a conventional magnetic freezing material, MnFeRuPSi-based and MnFePSiB-based magnetic freezing materials have been proposed. For example, as a conventional magnetic freezing material, there is a magnetic freezing material characterized by being composed of a compound represented by the following general formula (1).
_{(Mn 2-x Fe x-} z Ru z) 1 + σ (P 1-y A y) ··· (1)
Here, A represents Ge (germanium) or Si (silicon), −0.1 ≦ σ ≦ + 0.1, 0.6 ≦ x ≦ 1.2, 0.03 ≦ y ≦ 0.7, 0 <. z ≦ 0.7 (Patent Document 1).

Further, for example, there is also a method for producing a magnetic refrigeration material, which comprises a cooling step of cooling a manganese-based compound containing manganese to a Curie temperature or lower peculiar to the manganese-based compound. (Patent Document 2).

Japanese Unexamined Patent Publication No. 2014-15678 International Publication WO2016 / 104739

However, as for the conventional magnetic freezing material, for example, in the MnFeRuPSi-based magnetic freezing material, the material having a Curie temperature in the room temperature range or higher, particularly 60 ° C. or higher, has a large hysteresis described above, and as a result, the adiabatic temperature change becomes small. However, there was a problem that practical ability could not be realized.

As described above, a magnetic freezing material that can operate at around room temperature or higher, particularly at 60 ° C. or higher, has a small hysteresis, exhibits a huge magnetic heat effect, and has a large adiabatic temperature change value. Although coveted, no such magnetic freezing material is currently found.

The present invention has been made to solve the above problems, and is a magnetic freezing material that can operate in a high temperature range (for example, near room temperature or higher), has a small hysteresis, and exhibits a huge magnetic heat effect, and is large. It is an object of the present invention to provide a magnetic freezing material having an adiabatic temperature change value.

The present inventors, as a result of intensive studies, have Fe 2 _P structure, where a material represented by a composition not known in the prior containing both Si and Ge, a room temperature range above, particularly 330K (about A new type of magnetic refrigeration material that undergoes a primary magnetic phase transition from a paramagnetic phase to a ferromagnetic phase without substantial structural transformation by applying a magnetic field with a permanent magnet or the like in a temperature range of 60 ° C.) or higher. I found it.

MnFePSi-based and MnFeRuPSi-based magnetic refrigeration materials produce magnetic refrigeration materials having a Curie temperature (Tc) of 60 ° C. or higher by decreasing the ratio of Mn and Fe, that is, increasing the ratio of Fe. In general, when attempted to do so, the hysteresis becomes very large, and as a result, the adiabatic temperature change becomes small. However, the magnetism obtained by the present inventor by Ge substitution (in the presence of Si) at a specific ratio. It has been found that the frozen material can increase the Curie temperature (Tc) and suppress the increase in hysteresis, and exhibits a large change in adiabatic temperature.

Further, the Curie temperature (Tc) can be controlled in the range of 300K or more and less than 447K by adjusting the ratio of Mn and Fe, the ratio of P and Si, and the substitution amount of Ge. Therefore, by preparing a plurality of magnetic refrigeration materials having different Curie temperatures (Tc) and combining them, it is possible to realize a magnetic refrigeration device and a magnetic heat pump device that can operate in a wide temperature range including near room temperature. ..

The X-ray diffraction (XRD) measurement result of the magnetic refrigerating material which concerns on this invention is shown. The X-ray diffraction (XRD) measurement result of the magnetic refrigerating material which concerns on a comparative example is shown. The measurement result by the differential scanning calorimeter (DSC) of the magnetic refrigerating material which concerns on this invention is shown (Examples 1-10). The measurement results (results of scanning speed 2 ° C./min (a) and 10 ° C./min (b)) of the magnetic frozen material according to the present invention with a differential scanning calorimeter (DSC) are shown (Examples 11 to 14). , Comparative Examples 4, 5). The measurement results of the magnetic freezing material according to the present invention with a differential scanning calorimeter (DSC) are shown (Examples 17 to 19). The measurement result by the differential scanning calorimeter (DSC) of the magnetic refrigerating material which concerns on this invention is shown (Example 6, 20-22).

Thus, the magnetic refrigeration material according to the embodiment of the present invention is a magnetic refrigeration material composed of Mn, Fe, Ru, P, Si, and Ge, and the sum of the blending molar ratios of Si and Ge is 0. It is 40 or more and 0.65 or less, and the compounding molar ratio of P is 0.35 or more and 0.60 or less.

If the magnetic refrigeration material according to the present embodiment is composed of each element of Mn, Fe, Ru, P, Si, and Ge, and if the above conditions are satisfied, the compounding molar ratio of each constituent element is particularly high. Although not limited, it is more preferable that the Fe ₂ P type structure is in the vicinity of the chemical quantitative ratio. Therefore, the sum of the mixed molar ratios of Mn _, Fe and Ru is the mixed molar ratio of P _, Si _, and Ge. It is preferable that the sum is 1.9 or more and 2.1 or less, and a magnetic refrigerating material composed of a compound represented by the following general formula (I) can be used.
(Mn _, Fe _, Ru) _A (P _, Si _, Ge) (I)
(In the above formula, 1.9 ≤ A ≤ 2.1)

Of these, the compounding molar ratios of the constituent elements Mn _, Fe and Ru, and the compounding molar ratios of P _, Si _, and Ge are not particularly limited, but a better magnetic calorific value effect is exhibited. Therefore, it is more preferable to use a magnetic refrigerating material composed of a compound represented by the following general formula (I-1).
_{Mn A-x-y Fe x} Ru y P 1-z-w Si z Ge w (I-1)
(In the above formula, 1.9 ≦ A ≦ 2.1, 0 <x <A, 0 <y <1, 0.40 ≦ w + z ≦ 0.65, 0 <w, 0 <z)

Further, the compounding molar ratio of Mn is preferably larger than the compounding molar ratio of Fe, and the temperature difference at the time when ferromagnetism and paramagnetism change when the temperature rises and falls, that is, the value of hysteresis becomes large. It is possible to suppress the deterioration of the characteristics caused by it, and it is possible to stably exert the magnetic calorific value effect.

As described above, _Mn, the sum of the blending molar ratio of Fe and Ru _is, P, _Si, and with respect to the sum of the blending molar ratio of Ge, which is preferably at least 1.9 less than 2.1 , more preferably, not more than the stoichiometric ratio, i.e., _Mn, blending molar ratio of Fe and Ru _is, P, _Si, and with respect to the sum of the blending molar ratio of Ge, 1.9 to 2.0 Is more preferable. With this configuration, a partial defect occurs in the crystal to form a distorted crystal state, and the distorted crystal state makes it possible to exert a large magnetic calorific value effect.

Further, this magnetic freezing material preferably has a hexagonal crystal structure, and further, the lattice constant a at room temperature is 6.20Å≤a≤6.32Å, and the lattice constant c is 3.26Å≤c≤3. It is preferably 34Å. With such a crystal structure, it is possible to stably exert a large magnetic calorific value effect.

In order to further clarify the features of the present invention, examples are shown below, but the present invention is not limited to these examples.

(Example)
The samples of each example according to the present invention were prepared by the following procedure. That is, each raw material was weighed, and the sample and the ball were placed in a special container in a glove box and mixed with a planetary ball mill for 6 hours. The inside of the container had a nitrogen atmosphere.

60 g of the mixed sample was placed in a carbon container and fired.

The sealed sample was heated from room temperature to about 1100 ° C. over 6 hours, held for 5 hours while maintaining the temperature, and then naturally cooled to room temperature. The obtained sintered body was pulverized to 53 microns or less to obtain a sample.

Accordance mixing and firing method described above, the target composition is, in the formula _Mn indicated by _{(I-1) A-x} -y Fe x Ru y P 1-z-w Si z Ge w ( Formula 1. Among the compounds represented by 9 ≦ A ≦ 2.1, 0 <x <A, 0 <y <1, 0.40 ≦ w + z ≦ 0.65, 0 <w, 0 <z), Table 1 The magnetic refrigeration materials of Examples 1 to 16 and Comparative Examples 1 to 8 shown in the above were prepared. The magnetic freezing materials not substituted with Ge were designated as Comparative Examples 1 to 3. Further, the magnetic freezing materials in which the sum of the compounding molar ratios of Si and Ge exceeds 0.65 were designated as Comparative Examples 4, 6 and 8. Further, the magnetic freezing materials containing no Si were designated as Comparative Examples 5 and 7.

X-ray diffraction (XRD) measurements were performed to identify the crystal phase structure of the magnetically frozen material according to each example. A powder obtained by pulverizing each magnetic freezing material to 53 μm or less was used as a sample for XRD. Cu was used as the target. X-ray diffraction (XRD) measurement was also performed in the comparative example.

Among the obtained X-ray diffraction (XRD) measurement results, FIG. 1A shows A = 2, x = 0.75, y = 0.01, z = 0.55, w = 0.01 (implementation). Example 1), FIG. 1 (b) shows A = 2, x = 0.77, y = 0.01, z = 0.55, w = 0.015 (Example 5), FIG. 1 (c) shows A. = 2, x = 0.79, y = 0.01, z = 0.55, w = 0.023 (Example 9), A = 2, x = 0.79, y = in FIG. 1 (d). The measurement results of 0.01, z = 0.25, and w = 0.30 (Example 14) are shown. Further, as comparative examples, A = 2, x = 0.79, y = 0.01, z = 0.70, w = 0.20 (Comparative Example 6), FIG. 2 (b) in FIG. 2 (a). ) Shows the measurement results of A = 2, x = 0.79, y = 0.01, z = 0.60, w = 0.30 (Comparative Example 8).

In any of the compositions, magnetic refrigeration materials according to each embodiment is a ferromagnetic phase at room temperature (FM-phase), the material of the Fe 2 _P structure is obtained. In contrast, magnetic refrigeration materials according to the comparative example, as is clear from the results of FIG. 2, it heterophase many exist, could not be obtained as a material of Fe 2 _P structure.

FIG. 3 is a graph showing the measurement results of Examples 1 to 10 according to the present invention, and FIG. 4 shows the measurement results of Examples 11 to 14 and Comparative Examples 4 to 5 according to the present invention using a differential scanning calorimeter (DSC). The weight of the measurement sample was about 30 mg, and alumina was used as the standard sample. The Curie temperature of the sample shows a minimum value. The following table shows the Curie temperatures of Examples 1 to 14 and Comparative Examples 1 to 5.

Moreover, the adiabatic temperature change (ΔT _ad ) of Examples 1 to 10 and Comparative Examples 1 to 3 was measured by the adiabatic temperature measuring device. The applied magnetic field was 1 T, and the temperature before the magnetic field was applied and the temperature after the magnetic field was applied were measured at each specified temperature, and the difference was taken as the adiabatic temperature change value. The following table shows the adiabatic temperature change value and the hysteresis ( _ΔThys ) of each example.

The adiabatic temperature change (K) in Examples 11 to 14 is a region that could not be actually measured due to the Curie temperature in a high temperature range exceeding the measurement limit of the measuring device used, but it depends on the measured hysteresis value. For example, it was confirmed that it had a very small hysteresis similar to that of Examples 1 to 10, and as a result, it is considered that an excellent adiabatic temperature change is exhibited as in Examples 1 to 10.

From the obtained results, a large change in adiabatic temperature was observed near the Curie temperature in Examples 1 to 10, and the adiabatic temperature change value in a magnetic field of 1 T was the largest at 1.8 K (A = 2, x = 0.77). , Y = 0.01, z = 0.55, w = 0.023), and even a small one is 1.7K. This is a value 1.5 times or more that of Comparative Examples 1 to 3 (Note that Comparative Examples 4 and 5 have DSC spectra based on the scanning speed in FIG. 4, as is particularly clear from the results of FIG. 4 (b). The peak is not detected, and since the peak was not detected, it is considered that a good magnetic calorie effect is not exhibited). In addition, a large change in adiabatic temperature equal to or greater than that of a non-Ge-substituted material (in the presence of Si) having a Curie temperature in the room temperature range (40 ° C. or lower) was confirmed.

Next, in order to confirm the effect of Ge substitution (in the presence of Si) of the magnetic refrigerating material having a Curie temperature near room temperature, the target composition is represented by the above general formula (I-1) according to the above-mentioned mixing and firing method. been _{Mn A-x-y Fe x} Ru y P 1-z-w Si z Ge w ( where, 1.9 ≦ A ≦ 2.1,0 <x <A, 0 <y <1,0. Among the compounds represented by 40 ≦ w + z ≦ 0.65, 0 <w, 0 <z), the magnetic refrigerated materials of Examples 17 to 19 and Comparative Examples 9 to 11 shown in the following table were prepared. did. Comparative Examples 9 to 11 are Ge-free magnetic freezing materials.

FIG. 5 is a graph showing the measurement results of the differential scanning calorimetry (DSC) of Examples 17 to 19 according to the present invention. The weight of the measurement sample was about 30 mg, and alumina was used as the standard sample. The Curie temperature of the sample shows a minimum value.

The table below shows the Curie temperatures of Examples 17-19 and Comparative Examples 9-11. Further, the adiabatic temperature change (ΔT _ad ) of Examples 17 to 19 and Comparative Examples 9 to 11 was measured by an adiabatic temperature measuring device. The applied magnetic field was 1 T, and the temperature before the magnetic field was applied and the temperature after the magnetic field was applied were measured at each specified temperature, and the difference was taken as the adiabatic temperature change value. Each adiabatic temperature change value and hysteresis ( _ΔThys ) are also shown in the table below.

From the obtained results, a large change in adiabatic temperature was observed near the Curie temperature in Examples 17 to 19, and the adiabatic temperature change value in a magnetic field of 1 T was the largest at 1.9 K (A = 2, x = 0.68). , Y = 0.08, z = 0.54, w = 0.01), and even a small one is 1.8K. This is about 1.2 times the value of the comparative example, and it was confirmed that the adiabatic temperature change value is improved by Ge substitution (in the presence of Si) even in the magnetic freezing material having a Curie temperature of about 50 ° C. from the room temperature range. did.

Further, in Comparative Example 8, Example 14, and Example 16, in which P and Si were increased or decreased under a constant condition that the compounding molar ratio of Ge was 0.30 among the above Examples, the same method as described above was applied. , Curie temperature, hysteresis, DSC peak, and XRD structural analysis results were obtained and organized in the table below (in the table below, the molar ratios of P are listed in ascending order).

From the obtained results, it was confirmed that the target compound could not be synthesized in Comparative Example 8 in which the sum of the compounding molar ratios of Ge and Si was 0.90. On the other hand, in Example 14 in which the sum of the compounding molar ratios of Ge and Si was 0.55, the target compound was synthesized. Further, from the results of Example 16, it was confirmed that even if the compounding molar ratio of P was increased from the value of Example 14 of 0.45, good characteristics were surely obtained up to 0.60. ..

Next, in each of the above examples, Comparative Example 4, Comparative Example 6, Comparative Example 7, and Examples, in which the compounding molar ratio of P and Si was increased or decreased under a constant condition that the compounding molar ratio of Ge was 0.20. Regarding No. 15, structural analysis results by Curie temperature, hysteresis, DSC peak, and XRD were obtained by the same method as above, and arranged in the following table (in the table below, the compounding molar ratio of P is in ascending order). Described).

From the obtained results, it was confirmed that the target compound could not be synthesized in Comparative Example 6 in which the sum of the compounding molar ratios of Ge and Si was 0.80. It was also confirmed that the target compound could not be synthesized even in Comparative Example 4 in which the sum of the compounding molar ratios of Ge and Si was 0.75. On the other hand, in Example 15 in which the sum of the compounding molar ratios of Ge and Si was 0.50 (that is, 0.40 or more and 0.65 or less), the target compound was synthesized.
Further, from the results of Comparative Example 7, even if the compounding molar ratio of P is increased from 0.5, which is the value of Example 15, good characteristics are surely obtained up to 0.60 as described above. However, it was confirmed that when the temperature was increased to 0.80, the Curie temperature decreased significantly.

Next, the results of measuring the lattice constant a and the lattice constant c for the crystal structure of the magnetic freezing material according to each example are shown below. In Comparative Example 6 and Comparative Example 8, there is no data because no crystals were generated. Further, in Comparative Example 7, since the Curie temperature is too low, the data is not acquired because it is excluded from the target.

From the above results, regarding the crystal structure of the magnetic refrigeration material according to each example, it is preferable that the magnetic refrigeration material in this embodiment has a hexagonal crystal structure, and the lattice constant a at room temperature is 6.20Å≤a≤a≤. It was confirmed that it was 6.32Å and that the lattice constant c was preferably 3.26Å≤c≤3.34Å. The crystal structure having such characteristics makes it possible to stably exert a large magnetic calorific value effect.

Next, based on the compounding molar ratio of the magnetic freezing material of Example 6, the magnetic refrigerating materials of Examples 20 to 22 were obtained with the following compounding molar ratio in which the compounding molar ratio of Fe was reduced. That is, embodiments in 20-22, in the general formula (I-1) as the _{Mn A-x-y Fe x} Ru y P 1-z-w Si z Ge w ( Formula, 1.9 ≦ A ≦ 2.1 , 0 <x <A, 0 <y <1, 0.40 ≦ w + z ≦ 0.65, 0 <w, 0 <z), especially 1.9 ≦ A ≦ 2.0.

The result of the obtained DSC spectrum is shown in FIG. From the obtained results, it was confirmed that a steeper DSC spectrum peak was obtained when the sum of the blended molar ratios of Mn, Fe, and Ru was 1.9 or more and 2.0 or less. Therefore, it was confirmed that it has an excellent magnetic calorific value effect.

The table below shows the Curie temperatures of Examples 20-22. Further, the adiabatic temperature change (ΔT _ad ) of Examples 20 to 22 was measured by the adiabatic temperature measuring device. The applied magnetic field was 1 T, and the temperature before the magnetic field was applied and the temperature after the magnetic field was applied were measured at each specified temperature, and the difference was taken as the adiabatic temperature change value. Each adiabatic temperature change value and hysteresis ( _ΔThys ) are also shown in the table below.

From the obtained results, a large adiabatic temperature change was observed in the vicinity of the Curie temperature in Examples 20 to 22, and the adiabatic temperature change value in the magnetic field 1T was 1.7K. It was confirmed that the adiabatic temperature change value was improved by Ge substitution (in the presence of Si) even in the magnetic refrigerated material in which the sum of the mixed molar ratios of Mn, Fe, and Ru was 1.9 or more and 2.0 or less.

From the above results, the magnetic freezing material according to the present embodiment shows a large magnetic calorific value effect not only in the Curie temperature near room temperature but also in a particularly high temperature region (60 ° C. or higher), and a large adiabatic temperature change value can be obtained. It was confirmed that.

Claims (5)

A magnetic refrigeration material composed of Mn, Fe, Ru, P, Si, and Ge, wherein the sum of the compounding molar ratios of Si and Ge is 0.40 or more and 0.65 or less, and the compounding molar ratio of P is However, the magnetic refrigerating material is characterized by having a value of 0.35 or more and 0.60 or less. The magnetic freezing material according to claim 1, which comprises a compound represented by the following general formula (I).
(Mn _, Fe _, Ru) _A (P _, Si _, Ge) (I)
(In the above formula, 1.9 ≤ A ≤ 2.1) The magnetic freezing material according to claim 1 or 2, characterized in that it comprises a compound represented by the following general formula (I-1).
_{Mn A-x-y Fe x} Ru y P 1-z-w Si z Ge w (I-1)
(In the above formula, 1.9 ≦ A ≦ 2.1, 0 <x <A, 0 <y <1, 0.40 ≦ w + z ≦ 0.65, 0 <w, 0 <z) The magnetic freezing material according to any one of claims 1 to 3, wherein the compounding molar ratio of Mn is larger than the compounding molar ratio of Fe. The magnetic freezing material according to any one of claims 1 to 4, wherein the sum of the blending molar ratios of Mn, Fe, and Ru is 1.9 or more and 2.0 or less.

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