Nonvolatile magnetic thermal switch material, nonvolatile magnetic thermal switching element, and method for controlling nonvolatile magnetic thermal switch

Abstract

To provide a nonvolatile magnetic thermal switch material which shows thermal conductivity different from thermal conductivity before an external field is applied even after the external field is applied, and a nonvolatile magnetic thermal switching element having the nonvolatile magnetic thermal switch material.SOLUTION: In a magnetic thermal switching material, a thermal conductivity when an external magnetic field is not applied is defined as an initial value, the thermal conductivity changes from the initial value when a predetermined external magnetic field is applied, and the thermal conductivity when the predetermined external magnetic field is set to zero is different from the initial value.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a nonvolatile magnetocaloric switching material, a nonvolatile magnetic thermal switching element, and a method for controlling a nonvolatile magnetocaloric switching material.

Background Art

[0002] A heat flow switch in which the flow of heat is controlled by an external field such as an external magnetic field is a device capable of controlling the heat flow in a solid without mechanical movement. This heat flow switch is being studied worldwide as an important technology for device thermal control and efficiency improvement (for example, Patent Document 1, Patent Document 2, Non-Patent Document 1).

[0003] The heat flow switch of Patent Document 1 includes a transition body represented by the general formula A x D y O z (wherein A is at least one element selected from alkali metals, alkaline earth metals, Sc, Y, and rare earth elements, and D is at least one transition element selected from Group IIIa, Group IVa, Group Va, Group VIa, Group VIIa, Group VIII, and Group Ib). In the heat flow switch of Patent Document 1, it is disclosed that by applying an external field to the transition body, the transition body undergoes an electronic phase transition and the electronic thermal conductivity is changed.

[0004] The heat flow switch of Patent Document 2 includes a temperature-changing body formed of silicon oxide, hafnium oxide, silicon nitride, etc., and a phase transition body represented by the general formula A 2+δ M laminated on the temperature-changing body (wherein A is at least one of Ag and Cu, and M is at least one of S, Se, and Te).

[0005] In the heat flow switch of Patent Document 2, it is disclosed that the temperature-changing body is Joule-heated to generate heat, and the thermal conductivity of the phase transition body in contact with the temperature-changing body is also changed.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in the thermal switches disclosed in the above Patent Document 1 and Patent Document 2, when an external field such as an external magnetic field is removed, the thermal conductivity of the temperature - varying body becomes equal to the thermal conductivity before the application of the external magnetic field. That is, the magnetic thermal switches described in Patent Document 1 and Patent Document 2 are volatile thermal switches in which the thermal conductivity changes only in an external magnetic field - applied environment and returns to the magnitude before the external magnetic field is stopped after the external magnetic field is stopped.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a non - volatile magnetic thermal switch material that exhibits a thermal conductivity different from the thermal conductivity before applying an external field even after applying the external field, a non - volatile magnetic thermal switching element including the non - volatile magnetic thermal switch material, and a control method for the non - volatile magnetic thermal switch material.

Means for Solving the Problems

[0009] The present invention provides the following means to solve the above problems. (1) The non - volatile magnetic thermal switch material according to one aspect of the present invention uses the thermal conductivity when no external magnetic field is applied as an initial value, the thermal conductivity changes from the initial value when a predetermined external magnetic field is applied, and the thermal conductivity when the predetermined external magnetic field is set to zero is different from the initial value.

[0010] (2) The non - volatile magnetic thermal switch material of (1) above may contain at least one superconductor containing Pb as a main component, and the content rate of components other than Pb may be 0.05 mass% or more.

[0011] (3) The non-volatile magnetocaloric switching material described in (1) or (2) above is composed of the at least one superconductor and the component other than Pb, and the at least one superconductor may be made of Pb.

[0012] (4) In the non-volatile magnetocaloric switching material according to any one of (1) to (3) above, the at least one superconductor includes a first superconductor and a second superconductor, and the critical magnetic field of the first superconductor and the critical magnetic field of the second superconductor may be different from each other.

[0013] (5) The non-volatile magnetocaloric switching material according to any one of (1) to (4) above may be a phase-separated alloy.

[0014] (6) The non-volatile magnetocaloric switching material according to any one of (1) to (5) above may have a non-volatile magnetocaloric switching ratio (MTSR) represented by the following formula (1) of 10% or more in a zero magnetic field environment. 100×{k(0, demagnetization) - k(0, initial value)} / k(0, initial value) ··· (1) (In formula (1), k(0, demagnetization) is the thermal conductivity when the predetermined external magnetic field is made zero, k(0, initial value) is the thermal conductivity when the external magnetic field is not applied)

[0015] (7) In the non-volatile magnetocaloric switching material according to any one of (1) to (6) above, the difference in the magnitudes of the critical magnetic fields of the first superconductor and the second superconductor may be 350 Oe or more in an absolute zero environment.

[0016] (8) In the non-volatile magnetocaloric switching material according to any one of (1) to (7) above, the difference in the superconducting transition temperatures of the first superconductor and the second superconductor may be 3.0 K or more in a zero magnetic field environment.

[0017] (9) In the non-volatile magnetocaloric switching material according to any one of (1) to (8) above, the at least one superconductor includes a first superconductor, a second superconductor, and a third superconductor, The critical magnetic field of the first superconductor, the critical magnetic field of the second superconductor, and the critical magnetic field of the third superconductor may be different from each other.

[0018] (10) In any of the non-volatile magnetothermal switching material according to (1) to (9) above, among the critical magnetic fields of the first, second, and third superconductors, the difference between the smallest critical magnetic field and the next smallest critical magnetic field may be 350 Oe or more.

[0019] (11) In any of the non-volatile magnetothermal switching material according to (1) to (10) above, among the superconducting transition temperatures of the first, second, and third superconductors, the difference between the smallest superconducting transition temperature and the next smallest superconducting transition temperature may be 3.0 K or more.

[0020] (12) In any of the non-volatile magnetothermal switching material according to (1) to (11) above, the first superconductor may be Sn and the second superconductor may be Pb.

[0021] (13) In any of the non-volatile magnetothermal switching material according to (1) to (12) above, the content of Sn may be 5% by mass or more and 95% by mass or less, and the content of Pb may be 5% by mass or more and 95% by mass or less.

[0022] (14) The non-volatile magnetic thermal switching element according to one aspect of the present invention includes any of the non-volatile magnetothermal switching materials according to (1) to (13) above.

[0023] (15) The method for controlling a non-volatile magnetothermal switching material according to one aspect of the present invention includes at least one of a setting step of applying and demagnetizing an external magnetic field to any of the non-volatile magnetothermal switching materials according to (1) to (13) above to make the thermal conductivity higher than before the application of the external magnetic field, and a reset step of heating or applying a current to the non-volatile magnetothermal switching material to make the thermal conductivity lower.

Effect of the Invention

[0024] According to the present invention, it is possible to provide a nonvolatile magnetothermal switch material that exhibits a thermal conductivity different from that before the application of an external magnetic field even after the external magnetic field is removed, a nonvolatile magnetic thermal switching element including the nonvolatile magnetothermal switch material, and a method for controlling the nonvolatile magnetothermal switch material.

Brief Description of Drawings

[0025]

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Mode for Carrying Out the Invention

[0026] Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. Note that the drawings used in the following description may show the characteristic parts enlarged for the sake of easy understanding of the features of the present invention. For this reason, the dimensional ratios of the respective components may be different from the actual ones.

[0027] [Nonvolatile Magnetocaloric Switch Material] The magnetocaloric switch material of the present invention uses the thermal conductivity when no external magnetic field is applied as the initial value, the thermal conductivity changes from the initial value when a predetermined external magnetic field is applied, and the thermal conductivity when the predetermined external magnetic field is set to zero is different from the initial value. Figs. 1 to 3 are conceptual diagrams for explaining the operation of the magnetocaloric switch material according to an embodiment of the present invention. Fig. 1 shows the magnetocaloric switch material before the external magnetic field H is applied. Fig. 2 shows the magnetocaloric switch material when an external magnetic field H exceeding the critical magnetic field Hc of the contained superconductor is applied. Fig. 3 shows the magnetocaloric switch material after the external magnetic field H is removed.

[0028] The magneto-thermal switching material 10 shown in FIGS. 1 to 3 contains, for example, at least one superconductor containing Pb as a main component and a component other than Pb, and the content of the component other than Pb is 0.05% by mass or more. In the present embodiment, the main component of the magneto-thermal switching material 10 means that the content rate in the magneto-thermal switching material 10 is 50% by mass or more. The content rate of the at least one superconductor in the magneto-thermal switching material 10 is preferably 80% or more, more preferably 90% or more, still more preferably 95% or more, and may be 99% or more. The content rate of a predetermined element in the magneto-thermal switching material can be measured by fluorescent X-ray analysis (XRF) or energy-dispersive X-ray spectroscopy (EDX). As the superconductor, a metal element whose single substance exhibits superconductivity in an atmospheric pressure environment can be used.

[0029] The magneto-thermal switching material 10 includes, for example, a first superconductor and a second superconductor as the at least one superconductor. The critical magnetic field of the first superconductor and the critical magnetic field of the second superconductor are different from each other. That is, the magneto-thermal switching material 10 has, for example, a plurality of types of superconductors as main components. Hereinafter, among the plurality of types of superconductors included in the magneto-thermal switching material 10, the superconductor with the lowest critical magnetic field (H c ) is referred to as the first superconductor, and the superconductor with the second lowest critical magnetic field (H c ) is referred to as the second superconductor. More specifically, the first superconductor and the second superconductor are the superconductor with the lowest critical magnetic field at extremely low temperatures and the superconductor with the second lowest critical magnetic field at extremely low temperatures among the superconductors having a content rate of 5% by mass or more in the magneto-thermal switching material 10. Here, in the present embodiment, the extremely low temperature means a temperature of 4.0 K or lower, such as a temperature of 2.5 K or 0 K (absolute zero). That is, in the present embodiment, the first superconductor is more likely to break the superconducting state and become a normal conducting state than the second superconductor. Here, the magnetothermal switch material 10 may include a third superconductor having a critical magnetic field different from that of the first superconductor and the second superconductor. Further, the sum of the content rates of the first superconductor and the second superconductor in the magnetothermal switch material 10 is preferably, for example, 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more, and may be 95% by mass or more. The magnetothermal switch material 10 preferably consists of the first superconductor and the second superconductor.

[0030] Here, the critical magnetic field of the superconductor at extremely low temperatures refers to the maximum magnetic field that can maintain the superconducting state under an atmospheric pressure environment, zero-field cooled, and at each temperature environment, and is the magnetic field defined in JIS C5600:2006.

[0031] The difference between the magnitude of the critical magnetic field of the second superconductor in an extremely low temperature environment and the magnitude of the critical magnetic field of the first superconductor at extremely low temperatures is, for example, 350 Oe or more, preferably 450 Oe or more, more preferably 500 Oe or more, and even more preferably 700 Oe or more. When the magnetothermal switch material further includes a third superconductor, among the critical magnetic fields of the first, second, and third superconductors in an extremely low temperature environment, the difference between the smallest critical magnetic field and the next smallest critical magnetic field is, for example, 350 Oe or more, preferably 450 Oe or more, and more preferably 500 Oe or more. Further, the upper limit value of the critical magnetic field of the superconductor included in the magnetothermal switch material 10 is not particularly limited, but from the viewpoint of control, the critical magnetic field of the superconductor having the second smallest critical magnetic field is preferably 350 Oe or less. Considering this, the difference between the smallest critical magnetic field and the next smallest critical magnetic field is preferably, for example, 100 Oe or less.

[0032] In a zero magnetic field environment, the difference between the superconducting transition temperature of the second superconductor and that of the first superconductor is, for example, 3.0 K or more, preferably 3.5 K or more, and more preferably 4.0 K or more. When the magnetocaloric switching material further includes a third superconductor, among the superconducting transition temperatures of the first, second, and third superconductors in a zero magnetic field environment, the difference between the lowest superconducting transition temperature and the second lowest superconducting transition temperature is, for example, 3.0 K or more, preferably 3.5 K or more, and more preferably 4.0 K or more. A large difference between the lowest superconducting transition temperature and the second lowest superconducting transition temperature enables a stable non-volatile magnetocaloric switching material. Here, the transition temperature of the superconductor means the temperature at which the superconductor exhibits superconductivity below it when the magnetic field strength and current are zero, and is the temperature defined in JISH7005 815-01-09.

[0033] From the viewpoint of use at a temperature close to room temperature, the transition temperature of the second superconductor is preferably 7.0 K or more, and more preferably 9.0 K or more.

[0034] Superconductors other than Pb (superconducting transition temperature 7.2 K in a zero magnetic field environment, critical magnetic field 803 Oe at 0 K (absolute zero)) included in the magnetocaloric switching material 10 are, for example, one or more metal elements selected from the group consisting of Sn (superconducting transition temperature 3.7 K in a zero magnetic field environment, critical magnetic field 306 Oe at 0 K (absolute zero)), Nb (same 9.2 K, 1980 Oe), In (same 3.4 K, 293 Oe), V (same 5.3 K, 1020 Oe), and Ta (same 4.4 K, 780 Oe). As the combination of the first superconductor and the second superconductor, it is preferable that (the first superconductor, the second superconductor) is any one of (Sn, Pb), (In, Pb), (Ta, Pb), (V, Pb), (Pb, Nb). In such a combination of the first superconductor and the second superconductor, the magnetocaloric switching material 10 exhibits a high non-volatile MTSR. Also, from the viewpoint of obtaining the magnetocaloric switching material 10 which is a complete phase separation type alloy, as the combination of the first superconductor and the second superconductor, it is preferable that (the first superconductor, the second superconductor) is any one of (Sn, Pb), (In, Pb), (Ta, Pb), (V, Pb), (Pb, Nb). By selecting the combination of these metal elements as the first superconductor and the second superconductor, the critical magnetic field of the superconductor with a low superconducting transition temperature is low, and it is considered that the magnetocaloric switching material 10 becomes a complete phase separation type alloy.

[0035] The magnetocaloric switching material 10 shown in FIGS. 1 to 3 includes a first phase 1 and a second phase 2. The first phase 1 and the second phase 2 are phases composed of different elements. The magnetocaloric switching material 10 is a phase separation type alloy in which a plurality of phases are phase-separated. FIGS. 1 to 3 show an example in which the magnetocaloric switching material 10 is composed of the first phase 1 and the second phase 2, but the number of phases corresponds to the types of superconductors included in the magnetocaloric switching material. That is, a phase separation type alloy composed of two types of superconductors and inevitable impurities becomes a binary phase separation type alloy. In the magnetocaloric switching material 10 composed of the first superconductor and the second superconductor, the first phase 1 preferably contains the first superconductor as a main component and is composed of the first superconductor. The second phase 2 preferably contains the second superconductor as a main component and is composed of the second superconductor. The element content ratio of each phase in the phase separation type alloy can be analyzed by fluorescent X-ray analysis (XRF) or energy dispersive X-ray spectroscopy (EDX). The first phase 1 is a region where the content ratio of the first superconductor is higher than the content ratios of other elements, and the second phase 2 is a region where the content ratio of the second superconductor is higher than the content ratios of other elements.

[0036] In the magnetocaloric switching material 10, the content of the first superconductor is, for example, 5% by mass or more and 95% by mass or less, preferably 7% by mass or more and 90% by mass or less, more preferably 8% by mass or more and 60% by mass or less, and may be 50% by mass or less or 30% by mass or less. Also, in the magnetocaloric switching material 10, the content of the second superconductor is, for example, 5% by mass or more and 95% by mass or less, preferably 10% by mass or more and 93% by mass or less, more preferably 40% by mass or more and 92% by mass or less, and may be 50% by mass or more or 70% by mass or more. It is considered that the magnetocaloric switching material 10 having a superconductor at such a content exhibits high non-volatile magnetocaloric switching characteristics.

[0037] Next, the operation of the magnetocaloric switching material 10 will be described. As shown in FIG. 1, before the external magnetic field H is applied, in an extremely low temperature environment, the first superconductor and the second superconductor contained in the magnetocaloric switching material 10 are in a superconducting state. Therefore, in the magnetocaloric switching material 10, Cooper pairs 5 exist in both the regions of the first phase 1 and the second phase 2. The thermal conductivity of a substance consists of the sum of the component in which carriers carry heat and the component in which lattice vibrations (phonons) carry heat. In the state shown in FIG. 1, both the first superconductor and the second superconductor are in a superconducting state, Cooper pairs are formed and aggregated, and since the component in which carriers carry heat is low, the thermal conductivity of the magnetocaloric switching material 10 is low. The state in which the thermal conductivity of the magnetocaloric switching material 10 is the thermal conductivity before the application of the external magnetic field H as shown in FIG. 1 is referred to as the OFF state. That is, the magnetocaloric switching material 10 has a low thermal conductivity in the OFF state.

[0038] When an external magnetic field H is applied to the magnetothermal switch material 10 shown in FIG. 1 and the magnitude of the external magnetic field H is gradually increased, the magnetothermal switch material 10 assumes the state shown in FIG. 2. That is, an external magnetic field H exceeding the critical magnetic fields Hc of the first superconductor and the second superconductor contained in the magnetothermal switch material 10 shown in FIG. 2 is applied. FIG. 2 shows the state when a magnetic field larger than the critical magnetic fields of the first superconductor and the second superconductor is applied. When an external magnetic field H exceeding the critical magnetic field Hc is applied to the magnetothermal switch material 10, both the first superconductor and the second superconductor become normal conducting states, the component of the carrier 6 that transports heat increases, and the thermal conductivity increases. A state in which the thermal conductivity is higher than that in the OFF state due to the application of an external magnetic field H exceeding the critical magnetic field Hc of the superconductor contained in the magnetothermal switch material 10 as shown in FIG. 2 is referred to as the ON state. That is, the magnetothermal switch material 10 has a higher thermal conductivity in the ON state than in the OFF state.

[0039] FIG. 3 shows the magnetothermal switch material after the external magnetic field H has been removed. When the external magnetic field H applied to the magnetothermal switch material 10 is gradually decreased from a magnitude exceeding the critical magnetic field Hc as shown in FIG. 2, under the condition that the magnitude of the external magnetic field H is higher than the critical magnetic field Hc (first) of the first superconductor and lower than the critical magnetic field Hc (second) of the second superconductor (Hc (first) < H < Hc (second)), the second superconductor becomes a superconducting state, and Cooper pairs 5 are formed in the second phase 2. On the other hand, at this time, magnetic flux is trapped in the first superconductor, which is in a state close to the normal conducting state. Further, this state is maintained even when the external magnetic field H is further decreased to an external magnetic field H = 0 (Oe), that is, in an environment where the external magnetic field H has been removed. This is achieved by the magnetic flux trapped in the first phase 1 while being protected by the superconducting current generated in the second phase 2.

[0040] As shown in FIG. 3, the magnetocaloric switch material 10 maintains an ON state higher than the OFF state even after the external magnetic field H is removed. In this way, even when the application of the external magnetic field H is removed, the magnetocaloric switch material 10 traps magnetic flux in the first phase 1, so that the whole does not become a uniform superconducting state and a part becomes a state close to the normal conducting state, and thus it can be said that it has non-volatile magnetocaloric switching characteristics.

[0041] That is, the magnetocaloric switch material 10 is a non-volatile magnetocaloric switch material that exhibits different thermal conductivities in an environment of external magnetic field H = 0 before the application of the external magnetic field H and in an environment of external magnetic field H = 0 after the application of the external magnetic field H. The non-volatility of the magnetocaloric switch material 10 is caused by magnetic flux being trapped in the first phase 1 where the first superconductor with a small critical magnetic field is distributed. The non-volatility of the magnetocaloric switch material 10 means that due to the trapping of magnetic flux, the first superconductor distributed in the first phase 1 loses the bulk property of superconductivity and becomes a state close to the normal conducting state. In this way, even after the external magnetic field is removed, the fact that magnetic flux is trapped in the first phase 1 and the component of heat conduction by charge carriers remains is a matter first discovered in the present invention. That is, after the external magnetic field is removed, it exhibits a high thermal conductivity.

[0042] The magnetocaloric switch ratio (MTSR) of the magnetocaloric switch material is generally expressed by the following formula (2) when the thermal conductivity is k (kappa). k(high) represents the thermal conductivity of the magnetocaloric switch material in a high state, that is, the ON state, and k(low) represents the thermal conductivity of the magnetocaloric switch material in a low state, that is, the OFF state. 100×{k(high)-k(low)} / k(high)···(2)

[0043] The non-volatile magneto-thermal switching ratio (MTSR) of the magneto-thermal switch material 10 is represented by the following formula (1). In formula (1), k(0, initial) represents the thermal conductivity in the ultra-low temperature and zero magnetic field environment in the initial state (before applying an external magnetic field), and k(0, demagnetized) represents the thermal conductivity after applying and demagnetizing an external magnetic field exceeding the critical magnetic field of the superconductor contained in the magneto-thermal switch material in the ultra-low temperature and zero magnetic field environment. 100×{k(0, demagnetized) - k(0, initial)} / k(0, initial) ··· (1)

[0044] The non-volatile MTSR of the magneto-thermal switch material 10 in the present embodiment is, for example, 10% or more, preferably 40% or more, more preferably 100% or more, still more preferably 150% or more, and particularly preferably 300% or more. Here, the thermal conductivity k in the above non-volatile MTSR is the thermal conductivity measured by the four-probe method, and k(0, demagnetized) is the thermal conductivity after applying and demagnetizing an external magnetic field having a magnitude exceeding the critical magnetic field of the superconductor contained as a main component in the non-volatile magneto-thermal switch material 10, for example, an external magnetic field of 1500 Oe or more.

[0045] Although the magneto-thermal switch material 10 having a plurality of types of superconductors as main components has been described above, the magneto-thermal switch material according to the present embodiment may not have a plurality of types of superconductors as main components. Specifically, the magneto-thermal switch material according to the present embodiment may have Pb as a main component. For example, the magneto-thermal switch material may contain Pb as a main component and contain impurities other than Pb.

[0046] Hereinafter, a magnetocaloric switching material containing impurities other than Pb with Pb as the main component will be described. Such a magnetocaloric switching material may sometimes be referred to as the magnetocaloric switching material according to a modified example. In the magnetocaloric switching material according to the modified example, the content of components (impurities) other than Pb is, for example, 0.05% by mass or more, and preferably 0.06% by mass or more. When a superconductor such as Sn is included as an impurity other than Pb, the upper limit is considered to be the same as that of the magnetocaloric switching material according to the above embodiment. The content of components (impurities) other than Pb can also be, for example, 1% by mass or less. The components other than Pb are, for example, metal elements such as Cu, and preferably metal elements that are superconductors. In the magnetocaloric switching material according to the modified example, impurity particles are ubiquitous inside. Also, there is weak intergranular coupling between the particles contained inside.

[0047] When an external magnetic field is applied and demagnetized to the magnetocaloric switching material according to the modified example, magnetic flux is trapped between the Pb region and the impurity particles or in the impurity particles. As a result, a part of the superconducting state of Pb disappears, and the magnetocaloric switching material according to the modified example also exhibits non-volatile magnetocaloric switching characteristics. Incidentally, this is a phenomenon peculiar to the non-volatile magnetocaloric switching material mainly composed of Pb. When any one of Ta, Nb, and V is used as the main component and contains impurities of about 0.1% or 0.2% in the same amount as the impurity content at which Pb exhibits non-volatile magnetocaloric switching characteristics, the non-volatile magnetocaloric switching characteristics in zero magnetic field are not confirmed. The reason why the magnetocaloric switching material according to the modified example exhibits non-volatile magnetocaloric switching characteristics is considered to be that since the main component is Pb, the influence of impurities is likely to occur from its superconducting transition temperature and critical magnetic field. For example, it is considered that a part of Pb is solid-solved with impurities to create a minute region with a low superconducting transition temperature.

[0048] The magnetocaloric switching material according to the modified example contains a sufficient amount of components other than Pb, so that a sufficient amount of magnetic flux is trapped between the Pb region and the impurity particles or in the impurity particles to exhibit non-volatile magnetocaloric switching characteristics. As a result, the thermal conductivity in zero magnetic field becomes higher than that in the initial state during zero-field cooling.

[0049] It is considered that the non-volatile magnetic thermal switching characteristics change according to the amount of the impurity content.

[0050] [Non-volatile magnetic thermal switching element] FIG. 4 is a cross-sectional view showing an example of the configuration of a non-volatile magnetic thermal switching element according to an embodiment of the present invention. The non-volatile magnetic thermal switching element 100 shown in FIG. 4 includes the magnetocaloric switching material 10 according to the above embodiment. The non-volatile magnetic thermal switching element 100 includes, for example, a magnetocaloric switching material 10, a fixing member 20 capable of fixing the magnetocaloric switching material 10, a magnetic field application coil 30 capable of applying an external magnetic field to the magnetocaloric switching material 10, and an adjusting member 40 capable of adjusting the fixing method by the fixing member 20.

[0051] The fixing member 20 is composed of, for example, a pair of members 20a and 20b having the same configuration. The members 20a and 20b have, for example, pedestals 21 and 24 arranged to face each other, upright connecting portions 22 and 25 extending upright from the pedestals 21 and 24, and clamping portions 23 and 26 that are orthogonal to the upright connecting portions 22 and 25 and clamp the magnetocaloric switching material 10. The pedestals 21 and 24 are, for example, circular in plan view. For example, screw holes H are formed in the pedestals 21 and 24. In the pedestals 21 and 24, the screw holes H are arranged, for example, along the circumferential direction of the pedestals 21 and 24.

[0052] The distance between the pair of members 20a and 20b and the interval between the clamping portions 23 and 26 in the fixing member 20 are adjusted by, for example, the adjusting member 40. The adjusting member 40 is provided, for example, so as to be grounded to the pedestals 21 and 24, and has grounding portions 42 and 44 formed with holes at positions corresponding to the screw holes H of the pedestals 21 and 24, and a joint member 41 extending in a direction orthogonal to the grounding portions 42 and 44 and connecting the grounding portions 42 and 44 to each other. The adjusting member 40 includes screws 45 and 46 that pass through the holes provided in the joint member 41 and the screw holes H provided in the fixing member 20 and are tightened. By tightening the screws 45 and 46 that pass through the holes of the joint member 41 into the screw holes H, the fixing member 20 is fixed. Further, the clamping portions 23 and 26 may be configured to be able to apply a current to the magnetocaloric switching material 10.

[0053] The magnetic field applying coil 30 is composed of, for example, a pair of coils 31 and 32. The coils 31 and 32 are arranged, for example, between the pedestal 21 of the member 20a and the magnetocaloric switching material 10 and between the pedestal 24 of the member 20b and the magnetocaloric switching material 10, respectively. The magnetic field applying coil 30 is connected to, for example, a power source (not shown), and is configured such that the external magnetic field H applied to the magnetocaloric switching material 10 can be adjusted by adjusting the current flowing through the magnetic field applying coil 30 by the power source.

[0054] According to the magnetocaloric switching element 100 according to the present embodiment, before applying an external magnetic field to the magnetocaloric switching material 10, and after applying and demagnetizing an external magnetic field H having a magnitude exceeding the critical magnetic field Hc of the first superconductor, since the magnetocaloric switching material 10 exhibits different thermal conductivities, it can be utilized as a nonvolatile magnetocaloric switching element.

[0055] According to the above embodiment, even after removing the external magnetic field, a magnetocaloric switching material that exhibits a thermal conductivity different from the thermal conductivity (initial value) before applying the external magnetic field in a zero magnetic field environment and a nonvolatile magnetic thermoswitching element including the magnetocaloric switching material can be provided.

[0056] Alternatively, the magnetocaloric switch material 10 according to the present embodiment may be formed on a member composed of other raw materials. For example, the magnetocaloric switch material 10 may be formed on a flux core. Even if the magnetocaloric switch material 10 is formed on a member composed of such other raw materials, non-volatile magnetocaloric switching characteristics are exhibited.

[0057] [Method for Controlling Magnetocaloric Switch Material] The magnetocaloric switch material according to the above embodiment can be controlled, for example, by the following method. The method for controlling the magnetocaloric switch material changes the thermal conductivity of the magnetocaloric switch material 10 by performing at least one of a set process of setting the magnetocaloric switch material 10 to an ON state with high thermal conductivity and a reset process of setting the magnetocaloric switch material 10 to an OFF state with low thermal conductivity.

[0058] In the set process, for example, a predetermined external magnetic field is applied to the magnetocaloric switch material 10 that is not controlled to the ON state to set it to the ON state with high thermal conductivity. The predetermined external magnetic field is a magnetic field having a magnitude exceeding the critical magnetic field of the superconductor contained in the magnetocaloric switch material 10. When the magnetocaloric switch material 10 contains a plurality of superconductors, the critical magnetic field is preferably a magnetic field having a magnitude equal to or greater than the critical magnetic field of the second superconductor and a magnetic field having a magnitude equal to or greater than the critical magnetic fields of all the contained superconductors.

[0059] The reset process is performed, for example, by heating the magnetocaloric switch material 10 or applying an electric current to the magnetocaloric switch material 10. When resetting the magnetocaloric switch material 10 by heating, it is heated to a temperature equal to or higher than the superconducting transition temperature of the superconductor contained in the magnetocaloric switch material 10. When the magnetocaloric switch material 10 contains a plurality of superconductors, the heating temperature is preferably a temperature equal to or higher than the superconducting transition temperature of the second superconductor and a temperature equal to or higher than the superconducting transition temperatures of all the contained superconductors. When resetting the magnetocaloric switch material 10 by applying a current, a current equal to or higher than the critical current of the superconductor contained in the magnetocaloric switch material 10 is passed through the magnetocaloric switch material 10. When a plurality of superconductors are contained in the magnetocaloric switch material 10, the current is preferably a current having a magnitude equal to or higher than the critical current of the second superconductor and a current equal to or higher than the critical currents of all the contained superconductors.

Example

[0060] Hereinafter, embodiments of the present invention will be described. The present invention is not limited only to the following embodiments.

[0061] [Example 1] As the magnetocaloric switch material of Example 1, a Pb wire with a purity of 3N (99.9%) was prepared. The cross-sectional area of this Pb wire is 0.196 mm 2 . Pb is a type-I superconductor and is known to have a critical temperature (superconducting transition temperature) Tc of about 7.2 K and a critical magnetic field Hc of about 803 Oe at 0 K (absolute zero) in a zero magnetic field environment. Fluorescent X-ray analysis was performed on the magnetocaloric switch material of Example 1 using an energy dispersive fluorescent X-ray analyzer JSX-1000S (manufactured by JEOL) (measurement conditions: tube voltage 50 kV, collimator 0.9 mm). As a result, it was confirmed that 0.07 mass% of Cu was contained as an impurity.

[0062] First, an external magnetic field of 200 Oe, 400 Oe, 600 Oe, and 800 Oe was applied to the magnetocaloric switch material of Example 1 by the Thermal Transport Option (TTO) of a Physical Property Measurement System (Physical Property Measurement System (PPMS) manufactured by Quantum Design), and the change in thermal conductivity when the temperature was changed from 2 K to 8 K in each external magnetic field was examined. The measurement of thermal conductivity was performed by the four-probe method of TTO.

[0063] FIG. 5 shows the measurement results and is a graph representing the temperature dependence of the thermal conductivity of the magnetocaloric switching material according to Example 1 in each external magnetic field. From FIG. 5, it was confirmed that the material exhibits a higher thermal conductivity in an external magnetic field application environment compared to when there is no magnetic field. Also, when the magnitude of the external magnetic field applied to the magnetocaloric switching material is less than 800 Oe, it was confirmed that as the magnitude increases, the temperature (superconducting transition temperature) at which the thermal conductivity significantly improves shifts to a lower temperature side as the magnitude of the applied external magnetic field becomes larger.

[0064] Next, with respect to the magnetocaloric switching material of Example 1, the thermal conductivity was measured by the four-probe method while changing the magnitude of the external magnetic field applied in an environment at a temperature of 2.5 K. Specifically, for the magnetocaloric switching material in the initial state without an applied external magnetic field, the external magnetic field was first gradually increased from 0 Oe to 1500 Oe (first step), and then the external magnetic field was gradually decreased from 1500 Oe to 0 Oe (second step).

[0065] FIG. 6 is a graph showing the external magnetic field dependence of the thermal conductivity when the external magnetic field applied to the magnetocaloric switching material of Example 1 is changed. From FIG. 6, it was confirmed that the thermal conductivity is different between the initial value of the thermal conductivity before increasing the external magnetic field from the zero magnetic field environment to the high external magnetic field environment as the first step and the thermal conductivity after demagnetization after reducing the external magnetic field from the high external magnetic field environment to the zero magnetic field environment as the second step, indicating non-volatile magnetocaloric switching characteristics. When the non-volatile MTSR was calculated for the magnetocaloric switching material of Example 1 by the following formula (1), it was 14%, and it was quantitatively confirmed that the material exhibits non-volatile MTSR. 100×{k(0, demagnetization) - k(0, initial)} / k(0, initial) ··· (1) (In formula (1), k(0, initial) represents the thermal conductivity in the initial state (before applying the external magnetic field in the first step), and k(0, demagnetization) represents the thermal conductivity when the zero magnetic field environment is achieved at the end of the second step.)

[0066] [Example 2] As a magnetocaloric switch material of Example 2, a wire made of a composition (Sn45-Pb55) containing 45 mass% of Sn and 55 mass% of Pb was prepared. As described above, Pb is known to be a type-I superconductor with a critical temperature Tc of about 7.2 K and a critical magnetic field Hc at zero degree of about 803 Oe. Also, Sn is known to be a type-I superconductor with a critical temperature (superconducting transition temperature) Tc of about 3.7 K in a zero magnetic field environment and a critical magnetic field Hc at 0 K (absolute zero) of about 306 Oe. That is, the magnetocaloric switch material of Example 2 is a magnetocaloric switch material having Sn as the first superconductor and Pb as the second superconductor. The cross-sectional area of this wire is 0.88×1.10 mm 2 is. For the magnetocaloric switch material of Example 2, impurities were measured in the same manner as in Example 1. As a result, it was confirmed that the magnetocaloric switch material of Example 2 contains 0.2 mass% of Cu as an impurity.

[0067] In order to confirm the distribution of the Sn element, which is the first superconductor, and the Pb element, which is the second superconductor, in the magnetocaloric switch material of Example 2, observation was carried out using a scanning electron microscope (device model number: Carl Zeiss Cross-Beam 1540ESB). The conditions for quantitative mapping by energy-dispersive X-ray spectroscopy were as follows.

[0068] Figure 7 shows the analysis results using a scanning electron microscope of the magnetocaloric switch material of Example 2. Figure 7(a) is a scanning electron microscope image, Figure 7(b) is an element mapping by energy-dispersive X-ray spectroscopy (SEM-EDX), Figure 7(c) is an enlarged view of Figure 7(b), and Figure 7(d) is a line profile along the arrow in Figure 7(c) obtained by quantitative mapping. From the analysis results shown in Figure 7, it can be seen that the magnetocaloric switch material of Example 2 is a completely phase-separated alloy.

[0069] Next, for the magnetocaloric switch material of Example 2, the thermal conductivity was measured by the four-probe method while changing the magnitude of the external magnetic field applied in a predetermined temperature environment.

[0070] Specifically, for a magnetocaloric switching material in an initial state where no external magnetic field is applied, first, an external magnetic field is increased from 0 Oe to 1700 Oe gradually (the first step), and then the external magnetic field is gradually reduced from 1700 Oe to -1700 Oe (the second step).

[0071] FIG. 8 is a graph showing the external magnetic field dependence of the thermal conductivity when the magnitude of the external magnetic field of the magnetocaloric switching material according to Example 2 is changed. FIG. 8(a) is a graph in an environment at a temperature of 2.5 K, FIG. 8(b) is a graph in an environment at 3.0 K, FIG. 8(c) is a graph in an environment at 4.2 K, and FIG. 8(d) is a graph in an environment at 8.0 K.

[0072] In FIGS. 8(a) to 8(c) which are the measurement results at temperatures from 2.5 K to 4.2 K, it was confirmed that the thermal conductivity in the initial state before the application of the external magnetic field and the thermal conductivity in the zero magnetic field environment after demagnetization in the second and third steps after the application of the external magnetic field were significantly different. That is, it was confirmed that the magnetocaloric switching material of Example 2 exhibits non-volatile magnetocaloric switching characteristics at least at temperatures below the superconducting transition temperature of the second superconductor. The non-volatile MTSR represented by the above formula (1) was about 150% in an environment at a temperature of 2.5 K, about 70% in an environment at 3.0 K, and about 15% in an environment at 4.2 K. That is, it can be said that the non-volatile MTSR of the magnetocaloric switching material of Example 2 in an extremely low temperature environment (2.5 K or lower) is 150% or more.

[0073] The thermal conductivity of the magnetocaloric switching material in the environment at a temperature of 8.0 K shown in FIG. 8(d) was substantially constant regardless of the magnitude of the external magnetic field. This is because neither superconductor became superconducting since the environment was at a temperature higher than the superconducting transition temperature of both the first superconductor and the second superconductor.

[0074] Also, the magnetocaloric switching material of Example 2 was subjected to zero-field cooling (ZFC) and field cooling (FC) at 1500 Oe, and the temperature dependence of the thermal conductivity in a zero-field environment (ZFC, FC) and the temperature dependence of the thermal conductivity in a 1500 Oe environment (FC) were measured.

[0075] FIG. 9 is a graph showing the temperature dependence of the thermal conductivity at 0 Oe when the magnetocaloric switching material of Example 2 was zero-field cooled (ZFC), and the temperature dependence of the thermal conductivity at 0 Oe and 1500 Oe when field cooled (FC) at 1500 Oe. As shown in FIG. 9, below a temperature of 7 K, differences appear in each k-T graph, and a correlation with the results shown in FIG. 8 was confirmed. Also, in the sample field cooled (FC) at 1500 Oe, a higher thermal conductivity is shown compared to the sample zero-field cooled (ZFC), which is considered to be due to the superconducting state being destroyed by applying an external magnetic field exceeding the critical magnetic field of the second superconductor. Also, even for samples that were field cooled (FC) under the same magnetic field, it was confirmed that the measurement results of the thermal conductivity in a low magnetic field environment (0 Oe) take an intermediate thermal conductivity between the measurement results of the thermal conductivity in a high magnetic field environment (1500 Oe) and the measurement results with ZFC. For samples after field cooling (FC) at a high magnetic field, it can be seen that the thermal conductivity takes a value higher than that of ZFC because magnetic flux is trapped in the magnetocaloric switching material even after demagnetization.

[0076] The temperature dependence of the magnetization of the magnetocaloric switching material of Example 2 was measured in an environment of approximately 10 Oe using a Magnetic Property Measurement System (MPMS-3, manufactured by Quantum Design). Fig. 10(a) is a graph showing the temperature dependence of the magnetization of the zero-field-cooled (ZFC) sample, and Fig. 10(b) is a graph showing the temperature dependence of the magnetization of the sample field-cooled (FC) at 1500 Oe. Similar to the previous results, the zero-field-cooled (ZFC) sample and the field-cooled (FC) sample show clearly different characteristics. The zero-field-cooled (ZFC) sample shows diamagnetism associated with a (one-step) superconducting transition at approximately 7 K, which is the superconducting transition temperature of Pb. In contrast, the field-cooled (FC) sample shows characteristics close to ferromagnetism below approximately 7 K. From these results, it is considered that in the field-cooled (FC) sample, magnetic flux is trapped in the magnetocaloric switching material, specifically in the first phase composed of Sn, at temperatures below the superconducting transition temperature of Pb, which is the second superconductor. It is considered that the trapping of magnetic flux in this first phase leads to the exhibition of non-volatile magnetocaloric switching characteristics.

[0077] To further evaluate the magnetic properties of the magnetocaloric switching material of Example 2, the external magnetic field dependence of the magnetization was examined using a Magnetic Property Measurement System (MPMS-3). Fig. 10(c) is a graph showing the external magnetic field dependence of the magnetization of the magnetocaloric switching material of Example 2 at 2.5 K under zero-field cooling, and Fig. 10(d) is a graph showing the external magnetic field dependence of the magnetization at 3.0 K and 4.2 K. The external magnetic field was increased from zero to 1200 Oe (first step), then decreased to -1200 Oe (second step), and finally increased to 1200 Oe (third step). Fig. 10(e) is a graph showing the external magnetic field dependence of the internal magnetic flux density represented by B = H + 4πM at 2.5 K confirmed in Fig. 10(c).

[0078] Similar trends can be observed at any temperature from FIGS. 10(c) and 10(d). From FIG. 10(e), it shows perfect diamagnetism (Meissner state) up to about 500 Oe in the first step, and then, the internal magnetic flux density and the external magnetic field take equal values up to about 700 Oe, which is the critical magnetic field of Pb, the second superconductor in the magnetocaloric switching material of Example 2. In the second step, the superconducting state of Pb appears at H < 700 Oe, magnetic flux is trapped, and the internal magnetic flux density also takes a high value even at H = 0 Oe. Thus, it is considered that by applying an external magnetic field higher than the critical magnetic field of the second superconductor to the magnetocaloric switching material of Example 2, magnetic flux is trapped in the magnetocaloric switching material, leading to the exhibition of non-volatile magnetocaloric switching characteristics.

[0079] FIG. 11 is a graph showing the temperature dependence of the residual specific heat. The residual specific heat shown in FIG. 11 was obtained from the difference between the specific heat C(0 Oe) in a zero magnetic field environment and the specific heat C(1500 Oe) in a high magnetic field environment of 1500 Oe, using the specific heat C of the zero-field-cooled (ZFC) sample and the field-cooled (FC) sample at 1500 Oe shown in FIG. 9. The specific heat C was measured with the specific heat option of PPMS.

[0080] From FIG. 11, since the specific heat jump near the superconducting transition temperature of Sn, which corresponds to the onset of the superconducting state of Sn, was confirmed only in the zero-field-cooled (ZFC) sample, it is considered that in the field-cooled (FC) sample, no bulk superconducting transition accompanied by a large entropy change occurs in the first phase where Sn is distributed.

[0081] [Example 3] A magnetocaloric switching material similar to that of Example 2 was prepared, except that the composition was changed to a composition containing 10 mass% Sn and 90 mass% Pb (Sn10-Pb90).

[0082] [Example 4] A magnetocaloric switching material similar to that of Example 2 was prepared, except that the composition was changed to a composition containing 20 mass% Sn and 80 mass% Pb (Sn20-Pb80).

[0083] [Example 5] A magnetothermal switch material similar to that of Example 2 was prepared, except that the composition was changed to a composition containing 90% by mass of Sn and 10% by mass of Pb (Sn90-Pb10).

[0084] For the magnetothermal switch materials of Examples 3 to 5, the external magnetic field dependence of the thermal conductivity of the magnetothermal switch materials in a zero magnetic field environment and a 1500 Oe external magnetic field environment was evaluated. The evaluation was performed by the four-terminal method in the same manner as in Examples 1 and 2.

[0085] Figs. 12(a), 12(b) and 12(c) are graphs showing the temperature dependence of the thermal conductivity of the magnetothermal switch materials of Example 3, Example 4 and Example 5, respectively, in a zero magnetic field environment and a 1500 Oe external magnetic field environment. As shown in Fig. 12, it was confirmed that in any of the magnetothermal switch materials, the thermal conductivity was lower at lower temperatures, and the thermal conductivity was higher in the external magnetic field applied environment than in the zero magnetic field environment.

[0086] In addition, for the magnetothermal switch materials of Examples 3 to 5, except that the magnitude of the applied external magnetic field was adjusted to a maximum of 1500 Oe and the external magnetic field in a predetermined direction was demagnetized to zero magnetic field and then no external magnetic field was applied in the reverse direction, the magnetothermal switch material in the initial state was zero-field cooled in the same manner as in Adjusted Example 2, and the external magnetic field was changed to evaluate the external magnetic field dependence of the thermal conductivity. Figs. 13(a), 13(b) and 13(c) are graphs showing the external magnetic field dependence of the thermal conductivity of the magnetothermal switch materials of Example 3, Example 4 and Example 5, respectively. As shown in Figs. 13(a), 13(b) and 13(c), in any of the magnetothermal switch materials of Examples 3 to 5, it was confirmed that the thermal conductivity when a 1500 Oe external magnetic field was applied and demagnetized to zero was higher than the thermal conductivity (initial value) when no external magnetic field was applied.

[0087] For the magnetocaloric switch materials of Examples 2 to 5, the nonvolatile MTSR (NMTSR) calculated by the above formula (1) was calculated. FIG. 14 is a graph summarizing the compositions and nonvolatile MTSRs of the magnetocaloric switch materials of Examples 2 to 5.

[0088] [Example 6] A sample similar to Example 2 was prepared except that a magnetocaloric switch material in which a composition (Sn40-Pb60) containing 40% by mass of Sn and 60% by mass of Pb was formed so as to coat the flux core was used. For this sample, the magnetocaloric switch material in the initial state was zero-field cooled in the same manner as in Example 2, and the external magnetic field dependence of the thermal conductivity was evaluated by changing the external magnetic field.

[0089] FIG. 15 is a graph of the thermal conductivity dependence when the external magnetic field of the magnetocaloric switch material of Example 6 was changed in a 2.5 K environment. As shown in FIG. 15, it was confirmed that the magnetocaloric switch material of Example 6 also exhibits nonvolatile magnetocaloric switching characteristics. The nonvolatile MTSR represented by the formula (1) of the magnetocaloric switch material of Example 6 was 55%.

[0090] [Comparative Example 1] Wires similar to those in Example 1 were prepared except for the different purity. In Comparative Example 1, a 5N (99.999%) Pb wire was prepared. Fluorescent X-ray analysis was performed with a JSX-1000S (JEOL) under the same conditions as in Example 1, but no impurities were detected.

[0091] [Comparative Example 2] Wires similar to those in Example 1 were prepared except for the different composition. In Comparative Example 2, an Nb wire with a purity of 3N (99.9%) was prepared. Fluorescent X-ray analysis was performed with a JSX-1000S (JEOL) under the same conditions as in Example 1, but no impurities were detected.

[0092] [Comparative Example 3] Except for the difference in composition, a wire material similar to that in Example 1 was prepared. In Comparative Example 3, a V wire material with a purity of 3N (99.9%) was prepared. When fluorescence X-ray analysis was performed using JSX-1000S (JEOL) under the same conditions as in Example 1, 0.02 mass% of Ca and 0.09 mass% of W were detected.

[0093] [Comparative Example 4] Except for the differences in purity and composition, a wire material similar to that in Example 1 was prepared. In Comparative Example 4, a Ta wire material with a purity of 99.95% was prepared. When fluorescence X-ray analysis was performed using JSX-1000S (JEOL) under the same conditions as in Example 1, 0.1 mass% of Fe was detected.

[0094] [Comparative Example 5] Except for the difference in composition, a wire material similar to that in Example 1 was prepared. In Comparative Example 5, an Sn wire material with a purity of 3N (99.9%) was prepared. When fluorescence X-ray analysis was performed using JSX-1000S (JEOL) under the same conditions as in Example 1, 0.2 mass% of Pb was detected.

[0095] The samples of Examples 3 to 6 and Comparative Examples 1 to 5 were zero-field cooled, the external magnetic field applied from zero magnetic field was increased, and then the non-volatile magnetic thermal switching ratio was evaluated by the following formula (1) using the thermal conductivity when demagnetized to zero magnetic field. The maximum value of the external magnetic field was set to be greater than the critical magnetic field of the superconductor contained in the sample in principle. The results are summarized in Table 1. 100×{k(0, demagnetization) - k(0, initial value)} / k(0, initial value) ··· (1) (In formula (1), k(0, demagnetization) is the thermal conductivity when the predetermined external magnetic field is set to zero, k(0, initial value) is the thermal conductivity when the external magnetic field is not applied).

[0096] Also, FIGS. 16, 17, 18, and 19 are graphs showing the external magnetic field dependence of the thermal conductivity of Comparative Example 1 (5N-Pb), Comparative Example 2 (3N-Nb), Comparative Example 3 (3N-V), and Comparative Example 4 (Ta99.95%), respectively.

[0097]

Table 1

[0098] In Table 1, for the samples with ○ in the column of the complete phase separation alloy system, they are the samples for which it was confirmed that they are complete phase separation alloy systems, and for those with -, they are the samples that are not complete phase separation alloy systems. In Table 1, the zero magnetic field environment non-volatile magnetic thermal switching ratio (MTSR) is the value represented by Equation (1), and "-" indicates that clear non-volatility was not confirmed in the zero magnetic field environment. That is, among these, they are samples with a magnetic thermal switching ratio (MTSR) of less than about 10% for which discrimination is possible in the zero magnetic field environment. Regarding Comparative Example 1 (5N (99.999%) Pb wire), as shown in FIG. 16, when an external magnetic field of 500 to 600 Oe was applied, the superconducting state was destroyed, and the thermal conductivity became a high value of about 2000 W / mK. Therefore, further measurement of higher thermal conductivity is difficult due to the specifications of the apparatus, and the magnitude of the external magnetic field applied was set to 600 Oe. Also, an attempt was made to measure the zero magnetic field environment non-volatile magnetic thermal switching ratio (MTSR) at this time.

[0099] [Control of the Magnetic Thermal Switching Material of Example 2] The magnetic thermal switching material of Example 2 was zero-field cooled to 2.5 K, and then as a setting process, (i) application of an external magnetic field of 1500 Oe and (ii) demagnetization of the external magnetic field were performed in sequence, and as a reset process, (iii) heating and (iv) cooling of the magnetic thermal switching material in a zero magnetic field environment were performed in sequence.

[0100] Figure 20 is a graph showing the correlation between the thermal conductivity, temperature, and external magnetic field when the set process and the reset process are sequentially performed on the magnetocaloric switching material of Example 2. As shown in Figure 20, by applying and demagnetizing an external magnetic field of 1500 Oe above the critical magnetic field of the superconductors Sn and Pb contained in the magnetocaloric switching material (Sn45-Pb55) of Example 2, it was confirmed that the thermal conductivity of the magnetocaloric switching material takes a value (k(0, demagnetization)) different from the initial value (k(0, initial value)). Also, by heating the magnetocaloric switching material up to a temperature of 8 K above the superconducting transition temperature of the superconductors Sn and Pb, it was confirmed that after cooling, the thermal conductivity of the magnetocaloric switching material becomes the initial value (k(0, initial value)) and can be reset.

Explanation of symbols

[0101] 1 First phase 2 Second phase 5 Cooper pair 6 Carrier 10 Magnetocaloric switching material 20 Fixing member 20a, 20b Members 21, 24 Pedestals 22, 25 Direct connection parts 23, 26 Clamping parts 30 Magnetic field application coil 31, 32 Coils 40 Adjusting member 41 Joint member 42, 44 Grounding parts 43 Joint part 100 Non-volatile magnetic switching element

Claims

1. Using the thermal conductivity when no external magnetic field is applied as the initial value, the thermal conductivity changes from the initial value when a predetermined external magnetic field is applied, and the thermal conductivity when the predetermined external magnetic field is set to zero is different from the initial value, a non-volatile magnetic thermal switch material.

2. At least one superconductor containing Pb as a main component, components other than Pb, are contained, the content rate of the components other than Pb is 0.05 mass% or more, the non-volatile magnetic thermal switch material according to Claim 1.

3. consisting of the at least one superconductor and the components other than Pb, the non-volatile magnetic thermal switch material according to Claim 2, wherein the at least one superconductor consists of Pb.

4. the at least one superconductor includes a first superconductor and a second superconductor, the non-volatile magnetic thermal switch material according to Claim 2, wherein the critical magnetic field of the first superconductor and the critical magnetic field of the second superconductor are different from each other.

5. the non-volatile magnetic thermal switch material according to Claim 4, which is a phase-separated alloy.

6. The non-volatile magnetic thermal switching ratio (MTSR) represented by the following formula (1) in a zero magnetic field environment is 10% or more, the non-volatile magnetic thermal switch material according to Claim 1 or 2. 100×{k(0, demagnetization) - k(0, initial value)} / k(0, initial value) ··· (1) (In formula (1), k(0, demagnetization) is the thermal conductivity when the predetermined external magnetic field is set to zero, k(0, initial value) is the thermal conductivity when no external magnetic field is applied).

7. In an absolute zero environment, the difference in the magnitudes of the critical magnetic field of the first superconductor and the critical magnetic field of the second superconductor is 350 Oe or more, the non-volatile magnetic thermal switch material according to Claim 4.

8. In a zero magnetic field environment, the difference in the magnitudes of the superconducting transition temperature of the first superconductor and the superconducting transition temperature of the second superconductor is 3.0 K or more, the non-volatile magnetic thermal switch material according to Claim 4.

9. the at least one superconductor includes a first superconductor, a second superconductor, and a third superconductor, the non-volatile magnetic thermal switch material according to Claim 2, wherein the critical magnetic field of the first superconductor, the critical magnetic field of the second superconductor, and the critical magnetic field of the third superconductor are different from each other.

10. The non-volatile magnetic thermal switch material according to claim 9, wherein the difference between the smallest critical magnetic field and the second smallest critical magnetic field among the critical magnetic fields of the first, second, and third superconductors is 350 Oe or more.

11. The non-volatile magnetic thermal switch material according to claim 9, wherein the difference between the smallest superconducting transition temperature and the second smallest superconducting transition temperature among the superconducting transition temperatures of the first, second, and third superconductors is 3.0 K or more.

12. The non-volatile magnetic thermal switch material according to claim 4 or 9, wherein the first superconductor is Sn and the second superconductor is Pb.

13. The content rate of Sn is 5 mass% or more and 95 mass% or less, The non-volatile magnetic thermal switch material according to claim 7, wherein the content rate of Pb is 5 mass% or more and 95 mass% or less.

14. A non-volatile magnetic thermal switching element comprising the non-volatile magnetic thermal switch material according to any one of claims 1 to 13.

15. A setting step of applying and demagnetizing an external magnetic field to the non-volatile magnetic thermal switch material according to any one of claims 1 to 13 to make the thermal conductivity higher than before the application of the external magnetic field; A reset step of heating or applying a current to the non-volatile magnetic thermal switch material to make the thermal conductivity lower; A control method for a non-volatile magnetic thermal switch material having at least one of the above.

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