JP7134906B2 - magnetic refrigeration material - Google Patents

Description

The present invention relates to a magnetic refrigeration material composed of a magnetic material, and particularly to a magnetic refrigeration material that exhibits a large magnetocaloric effect and adiabatic temperature change in a higher temperature range (for example, room temperature or higher) than conventional magnetic refrigeration materials.

In recent years, a new magnetic refrigeration system has been proposed to replace the conventional gas refrigeration system using Freon-based gas as a refrigerant, which causes environmental problems such as global warming and destruction of the ozone layer. In this magnetic refrigeration system, a certain type of magnetic material is used as a coolant, and the magnetocaloric effect, that is, the amount of change in magnetic entropy that occurs when the magnetic order of the magnetic material is changed by a magnetic field in an isothermal state, and the magnetic field in the adiabatic state. Utilizes the adiabatic temperature change that occurs when the order is changed by a magnetic field.

Magnetic refrigerators and magnetic heat pumps using magnetic materials having such a magnetocaloric effect as refrigerants have been extensively studied. According to this magnetic refrigeration system, it is possible to manufacture a magnetic refrigeration system and a magnetic heat pump system without using Freon gas, and it has the advantage of being more efficient than the conventional gas system.

A magnetic material having such a magnetocaloric effect is particularly called a magnetic refrigeration material (magnetic refrigeration working material).

As magnetic refrigeration materials used in such a magnetic refrigeration system, compound-based magnetic refrigeration materials such as LaFeSi and MnFePSi are known as efficient materials that exhibit a large magnetocaloric effect in a low magnetic field. are 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 transitions from ferromagnetism to paramagnetism), and a large magnetocaloric effect can be obtained. As a result, a temperature change occurs in the magnetic refrigeration material.

In relation to the Curie temperature, the difference between the Curie temperature when the magnetic refrigeration material is heated while being heated and the Curie temperature when the temperature is being lowered while being cooled is called hysteresis. A disadvantage is that the larger the hysteresis, the smaller the adiabatic temperature change.

So far known substances exhibiting a magnetocaloric effect (for example, LaFeSi-based and MnFePSi-based compounds) have a magnetocaloric effect in a relatively wide temperature range from the freezing range to the room temperature range. For example, the magnetocaloric effect is small at room temperature or higher, particularly at 60°C or higher, and in order to achieve practical performance as a magnetic heat pump device, a very strong magnetic field that can only be realized with a superconducting magnet or the like is applied. There is a need.

Under such circumstances, in order to improve the magnetocaloric effect, a magnetic refrigeration material has been proposed in which an element is added to a substance exhibiting the conventional magnetocaloric effect.

For example, MnFeRuPSi-based and MnFePSiB-based magnetic refrigeration materials have been proposed as conventional magnetic refrigeration materials. For example, as a conventional magnetic refrigeration material, there is a magnetic refrigeration 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 a method for producing a magnetic refrigeration material, which includes a cooling step of cooling a manganese-based compound containing manganese to a Curie temperature specific to the manganese-based compound or lower. (Patent Document 2).

JP 2014-15678 A International publication WO2016/104739

However, conventional magnetic refrigerating materials, such as MnFeRuPSi-based magnetic refrigerating materials, having a Curie temperature above room temperature, particularly above 60° C., have a large hysteresis, and as a result, the adiabatic temperature change is small. , there was a problem that practical ability could not be realized.

Thus, a magnetic refrigeration material that can operate at room temperature or higher, particularly 60° C. or higher, has a small hysteresis, exhibits a giant magnetocaloric effect, and has a large adiabatic temperature change value. However, such magnetic refrigeration materials are currently absent.

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

As a result of intensive research, the present inventors have found that a material having an Fe ₂ P-type structure and containing both Si and Ge and having a composition that has not been known in the past has been found to operate at room temperature or higher, particularly at 330 K (approximately 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. Found it.

MnFePSi-based and MnFeRuPSi-based magnetic refrigeration materials have a Curie temperature (Tc) of 60° C. or higher by decreasing the ratio of Mn to Fe, that is, by increasing the ratio of Fe. When trying to do so, the hysteresis generally becomes very large, resulting in a small adiabatic temperature change. It was found that the frozen material can increase the Curie temperature (Tc) and suppress the increase in hysteresis, exhibiting a large adiabatic temperature change.

Furthermore, the Curie temperature (Tc) can be controlled within 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 refrigerating materials with different Curie temperatures (Tc) and combining them, it is possible to realize a magnetic refrigerating device and a magnetic heat pump device that can operate in a wide temperature range including near room temperature. .

1 shows X-ray diffraction (XRD) measurement results of the magnetic refrigeration material according to the present invention. FIG. 4 shows X-ray diffraction (XRD) measurement results of a magnetic refrigeration material according to a comparative example; FIG. 1 shows measurement results of a magnetic refrigeration material according to the present invention with a differential scanning calorimeter (DSC) (Examples 1 to 10). Measurement results of the magnetic refrigeration material according to the present invention with a differential scanning calorimeter (DSC) (scanning speed 2 ° C./min result (a) and 10 ° C./min result (b)) are shown (Examples 11 to 14 , Comparative Examples 4 and 5). 1 shows the measurement results of the magnetic refrigeration material according to the present invention with a differential scanning calorimeter (DSC) (Examples 17 to 19). 2 shows the measurement results of the magnetic refrigeration material according to the present invention with a differential scanning calorimeter (DSC) (Examples 6, 20 to 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, wherein the sum of the compounding molar ratios of Si and Ge is 0.5. 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 Although it is not limited, it is more preferable that the ratio is near the stoichiometric ratio where the Fe ₂ P type structure is formed, so the sum of the blending molar ratios of Mn _, Fe and Ru is the blending molar ratio of P _, Si _and Ge is preferably 1.9 or more and 2.1 or less with respect to the sum of .
(Mn _, Fe _, Ru) _A (P _, Si _, Ge) (I)
(In the above formula, 1.9 ≤ A ≤ 2.1)

Among these, the compounding molar ratio of each of the constituent elements Mn _, Fe, and Ru, and the compounding molar ratio of each of P _, Si _, and Ge are not particularly limited, but the point is that a better magnetocaloric effect is exhibited. Therefore, it is more preferable to use a magnetic refrigeration material comprising a compound represented by the following general formula (I-1).
_{MnAxyFexRuyP1 - zwSizGew ( 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)

In addition, 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 hysteresis value increases. It is possible to suppress the deterioration of the properties caused by this, and to stably exhibit the magnetocaloric effect.

In addition, as described above, the sum of the blending molar ratios of Mn _, Fe and Ru is preferably 1.9 or more and 2.1 or less with respect to the sum of the blending molar ratios of P _, Si _and Ge. , More preferably, it is less than the stoichiometric ratio, that is, the blending molar ratio of Mn _, Fe and Ru is 1.9 or more and 2.0 or less with respect to the sum of the blending molar ratios of P _, Si _and Ge is more preferable. With this configuration, a distorted crystalline state is formed due to partial defects in the crystal, and this distorted crystalline state can produce a large magnetocaloric effect.

Further, the present magnetic refrigeration material preferably has a hexagonal crystal structure, and has a lattice constant a at room temperature of 6.20 Å≦a≦6.32 Å and a lattice constant c of 3.26 Å≦c≦3. 34 Å is preferred. Such a crystal structure makes it possible to stably exhibit a large magnetocaloric effect.

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

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

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, maintained at the temperature for 5 hours, and then naturally cooled to room temperature. The obtained sintered body was pulverized to 53 microns or less to obtain a sample.

According to the mixing and firing method described above, the target composition is _{MnAxyFexRuyP1 - zwSizGew} represented by the general _formula (I-1) above ( _{wherein 1} . 9≦A≦2.1, 0<x<A, 0<y<1, 0.40≦w+z≦0.65, 0<w, 0<z), Table 1 Magnetic refrigeration materials of Examples 1 to 16 and Comparative Examples 1 to 8 shown in were produced. Magnetic refrigeration materials not substituted with Ge were designated as Comparative Examples 1-3. Comparative Examples 4, 6, and 8 were magnetic refrigeration materials in which the sum of the compounding molar ratios of Si and Ge exceeded 0.65. Comparative Examples 5 and 7 were magnetic refrigeration materials containing no Si.

In order to identify the crystal phase structure of the magnetic refrigeration material according to each example, X-ray diffraction (XRD) measurement was performed. A powder obtained by pulverizing each magnetic refrigeration material to a size of 53 μm or less was used as an XRD sample. Cu was used as the target. An X-ray diffraction (XRD) measurement was similarly performed for the comparative example.

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

In any composition, the magnetic refrigeration material according to each example was in a ferromagnetic phase (FM-phase) at room temperature, and a material with an Fe ₂ P type structure was obtained. On the other hand, in the magnetic refrigeration materials according to the respective comparative examples, as is clear from the results of FIG. 2, many heterogeneous phases existed, and they could not be obtained as materials with an Fe ₂ P type structure.

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

Further, the adiabatic temperature changes (ΔT _ad ) of Examples 1 to 10 and Comparative Examples 1 to 3 were measured with an adiabatic temperature measuring device. The applied magnetic field was 1 T, the temperature before magnetic field application and the temperature after magnetic field application 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 values and hysteresis (ΔT _hys ) for each example.

The adiabatic temperature change (K) of Examples 11 to 14 is a region that could not be measured due to the Curie temperature in the high temperature range exceeding the measurement limit of the measuring device used, but it is based on the measured hysteresis value. For example, it was confirmed to have a very small hysteresis similar to that of Examples 1-10.

From the obtained results, in Examples 1 to 10, a large adiabatic temperature change was observed near the Curie temperature. , y=0.01, z=0.55, w=0.023) and the smallest is 1.7K. This value is 1.5 times or more that of Comparative Examples 1 to 3 (Comparative Examples 4 and 5 have DSC spectrum This is the level at which no peak was detected, and since this peak was not detected, it is considered that a good magnetocaloric effect is not achieved). In addition, adiabatic temperature change equal to or greater than that of a material without Ge substitution (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 replacement (in the presence of Si) of a magnetic refrigeration material having a Curie temperature near room temperature, the target composition was obtained by the above general formula (I-1) according to the above-described mixing and firing method. Mn Axy Fe _x Ru _y P _{1- zw} Si _z Ge _w (where 1.9≦A≦2.1, 0<x<A, 0<y<1, 0 . 40≦w+z≦0.65, 0<w, 0<z), the magnetic refrigeration materials of Examples 17 to 19 and Comparative Examples 9 to 11 shown in the table below were produced. did. Comparative Examples 9-11 are magnetic refrigeration materials that do not contain Ge.

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

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

From the obtained results, in Examples 17 to 19, a large adiabatic temperature change was observed near the Curie temperature, and the maximum adiabatic temperature change value in a magnetic field of 1 T was 1.9 K (A = 2, x = 0.68 , y=0.08, z=0.54, w=0.01) and the smallest is 1.8K. This value is about 1.2 times that of the comparative example, and it was confirmed that the adiabatic temperature change value was improved by replacing Ge (in the presence of Si) even in magnetic refrigeration materials with a Curie temperature between room temperature and about 50°C. did.

In addition, Comparative Example 8, Example 14, and Example 16, which are cases in which P and Si are increased or decreased under the constant condition that the molar ratio of Ge is 0.30 among the above Examples, were obtained by the same method as described above. , Curie temperature, hysteresis, DSC peak, and structural analysis results by XRD were obtained and arranged in the following table (listed in the following table in ascending order of the blending molar ratio of P).

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 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 desired compound was synthesized. Further, from the results of Example 16, it was confirmed that even if the molar ratio of P was increased from 0.45, which is the value of Example 14, to 0.60, good characteristics could be obtained without fail. .

Next, Comparative Example 4, Comparative Example 6, Comparative Example 7, and Example, which are cases in which the compounding molar ratio of P and Si were increased or decreased under the constant condition that the compounding molar ratio of Ge was 0.20 among the above Examples. For 15, the Curie temperature, hysteresis, DSC peak, and structural analysis results by XRD were obtained by the same method as above, and are summarized in the following table (in the following table, the 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 mixing 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 molar ratio of P is increased from 0.5, which is the value of Example 15, to 0.60 as described above, good characteristics can be reliably obtained. However, it was confirmed that the Curie temperature decreased significantly when the ratio was increased to 0.80.

Next, the results of measuring the lattice constant a and the lattice constant c of the crystal structure of the magnetic refrigeration material according to each example are shown below. In Comparative Examples 6 and 8, there is no data because no crystals were formed. Moreover, since the Curie temperature of Comparative Example 7 was too low, it was excluded from the target and no data was obtained.

From the above results, regarding the crystal structure of the magnetic refrigeration material according to each example, the magnetic refrigeration material of this embodiment preferably has a hexagonal crystal structure, and furthermore, the lattice constant a at room temperature is 6.20 Å ≤ a ≤ 6.32 Å, and it was confirmed that the lattice constant c is preferably 3.26 Å≦c≦3.34 Å. A crystal structure having such characteristics can stably exhibit a large magnetocaloric effect.

Next, magnetic refrigeration materials of Examples 20 to 22 were obtained with the following molar ratios of Fe, which were based on the molar ratio of the magnetic refrigeration material of Example 6. That is, in Examples 20 to 22, the general formula (I- ₁ ) was _{MnAxyFexRuyP1 - zwSizGew} ( _{where 1.9≤A≤2.1} , 0<x<A, 0<y<1, 0.40≦w+z≦0.65, 0<w, 0<z), particularly 1.9≦A ≦2.0.

The results of the obtained DSC spectrum are shown in FIG. From the obtained results, it was confirmed that when the sum of the blending molar ratios of Mn, Fe, and Ru was 1.9 or more and 2.0 or less, a steeper DSC spectrum peak was obtained. Therefore, it was confirmed to have an excellent magnetocaloric effect.

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

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

From the above results, the magnetic refrigeration material according to this example exhibits a large magnetocaloric effect not only in the vicinity of room temperature, but also in a particularly high temperature range (60 ° C. or higher), and a large adiabatic temperature change value can be obtained. was confirmed.

Claims (3)

A magnetic refrigeration material comprising a compound represented by the following general formula (I-1).
_{MnAxyFexRuyP1 - zwSizGew ( I -} 1)
(In the above formula, 1.9≦A≦2.1, 0<x<A, 0.01≦ y ≦0.08 , 0.40≦w+z≦0.65, 0<w, 0<z ) 2. The magnetic refrigeration material according to claim 1 , wherein the compounding molar ratio of Mn is larger than the compounding molar ratio of Fe. 3. The magnetic refrigeration material according to claim 1, wherein the sum of molar ratios of Mn, Fe, and Ru is 1.9 or more and 2.0 or less.

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