阅读说明：本技术 MnAl合金及其制造方法 (MnAl alloy and method for producing same ) 是由 佐藤卓 于 2019-06-27 设计创作，主要内容包括：本发明提供在宽幅的温度内显示变磁性的Mn系合金。本发明的MnAl合金具有变磁性,且具有包含τ－MnAl相的结晶颗粒和包含γ2－MnAl相及β－MnAl相的结晶颗粒。优选的是,在将τ－MnAl相的比率设为A的情况下,满足75％≤A≤99％,在将γ2－MnAl相的比率设为B,将β－MnAl相的比率设为C的情况下,满足B＜C。由此,能够在宽幅的温度、特别是－100℃～200℃的温度范围内得到变磁性,并且能够得到高的饱和磁化。(The invention provides a Mn-based alloy exhibiting metamagnetism over a wide range of temperatures. The MnAl alloy of the present invention has metamagnetism, and has crystal grains containing a tau-MnAl phase and crystal grains containing a gamma 2-MnAl phase and a beta-MnAl phase. Preferably, the composition satisfies 75% or more and 99% or less of A when the ratio of the τ -MnAl phase is defined as A, and satisfies B < C when the ratio of the γ 2-MnAl phase is defined as B and the ratio of the β -MnAl phase is defined as C. Thereby, metamagnetism can be obtained in a wide temperature range, particularly in a temperature range of-100 ℃ to 200 ℃, and high saturation magnetization can be obtained.)

1. A MnAl alloy is characterized in that,

it has metamagnetism and has crystalline particles containing a tau-MnAl phase and crystalline particles containing a gamma 2-MnAl phase and a beta-MnAl phase.

2. The MnAl alloy according to claim 1,

when the ratio of the tau-MnAl phase is A, it is 75% to 99% of A.

3. The MnAl alloy according to claim 2,

a is more than or equal to 95 percent and less than or equal to 99 percent.

4. The MnAl alloy according to claim 2 or 3,

b < C is satisfied where B represents the ratio of the gamma 2-MnAl phase and C represents the ratio of the beta-MnAl phase.

5. The MnAl alloy according to claim 4,

B/C is more than or equal to 0.01 and less than or equal to 0.17.

6. A method for producing a MnAl alloy, comprising:

a step of electrolyzing a molten salt containing a Mn compound and an Al compound at a temperature of 350 ℃ to 450 ℃ to precipitate a MnAl alloy;

and a step of heat-treating the MnAl alloy at a temperature of 400 ℃ or higher but lower than 600 ℃.

Technical Field

The present invention relates to a MnAl alloy and a method for producing the same, and particularly to a MnAl alloy having metamagnetism and a method for producing the same.

Background

MnAl alloys have been known as magnetic materials since a long time ago. For example, patent document 1 discloses a MnAl alloy having a tetragonal structure, in which the atomic ratio of Mn to Al is 5: 4, showing magnetism. Patent document 2 discloses a method of producing a first phase of a MnAl alloy having a tetragonal structure and Al₈Mn₅The second phase composed of crystal grains is present in a mixed state, and the MnAl alloy can be used as a permanent magnet having a high coercive force.

Further, as shown in patent document 3, it is known that a part of a magnetic material containing Mn as a main constituent element exhibits metamagnetism. Metamagnetism is the property of being transferred from paramagnetic or antiferromagnetic to ferromagnetic by a magnetic field. Metamagnetic materials exhibiting metamagnetism are expected to find applications in magnetic refrigerators, actuators, and current limiters.

Disclosure of Invention

Technical problem to be solved by the invention

However, the metamagnetic materials described in patent document 3 all utilize primary phase transition from paramagnetic to ferromagnetic by a magnetic field, and therefore exhibit metamagnetism only in the vicinity of the curie temperature. Therefore, it is practically difficult to apply to a flow restrictor or the like.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an Mn-based alloy that exhibits metamagnetism over a wide range of temperatures.

Technical solution for solving technical problem

In order to achieve the object of solving the above-described problems, the present inventors focused on metamagnetic materials of the type that are ferromagnetic to antiferromagnetic transfer by a magnetic field (hereinafter referred to as "AFM-FM transfer type metamagnetic materials"). This is because the AFM-FM transfer metamagnetic material exhibits metamagnetism at a temperature not higher than the denier temperature at which the antiferromagnetic order is not present, and therefore, there is no need to maintain a narrow temperature band around the curie temperature as in the metamagnetic material of a type in which paramagnetism is transferred to ferromagnetism (hereinafter referred to as "PM-FM transfer metamagnetic material").

In order to realize AFM-FM transfer type metamagnetism, it is necessary to maintain high magnetocrystalline anisotropy and to have antiferromagnetic properties. Therefore, as an AFM-FM transfer type metamagnetic material, various alloys and compounds have been studied focusing on Mn-based magnetic materials using a single Mn which exhibits antiferromagnetic properties. As a result, it has been found that in Mn-based alloys, by providing an antiferromagnetic element to a relatively rare MnAl alloy which exhibits ferromagnetism, metamagnetism can be exhibited over a wide temperature range. The present invention has been completed based on this finding, and is characterized in that the MnAl alloy of the present invention has metamagnetism, and has crystal grains containing a τ -MnAl phase and crystal grains containing a γ 2-MnAl phase and a β -MnAl phase.

That is, in the monomer, crystal grains of the τ -MnAl phase exhibit ferromagnetism, and crystal grains containing the γ 2-MnAl phase and the β -MnAl phase exhibit non-magnetism, but when they are mixed, they impart antiferromagnetism to the τ -MnAl phase, and exhibit AFM-FM transfer type metamagnetism.

When the ratio of the τ -MnAl phase is A, a high saturation magnetization can be obtained by satisfying 75% or more and 99% or less of A, and a higher saturation magnetization can be obtained by satisfying 95% or more and 99% or less of A. Further, when the ratio of the γ 2-MnAl phase is B and the ratio of the β -MnAl phase is C, a high saturation magnetization can be obtained by satisfying B < C, and a higher saturation magnetization can be obtained by satisfying B/C of 0.01. ltoreq. B/C. ltoreq.0.17.

In the MnAl alloy of the present invention, it is preferable that the magnetic structure of the τ -MnAl phase has an antiferromagnetic structure. In a non-magnetic field before phase transfer, an AFM-FM transfer type metamagnetic material is realized by using an antiferromagnetically stable Mn-based alloy. If the stability of the antiferromagnetic state is too high, a phase transition to ferromagnetic state cannot be generated by a magnetic field. On the other hand, if the stability of the antiferromagnetic property is too low, the ferromagnetic property may be obtained even in the case of no magnetic field or a very weak magnetic field. Further, since the stability of the antiferromagnetic state of the MnAl alloy is appropriate, if the AFM-FM transfer type metamagnetism is given, the metamagnetism can be exhibited in a wide temperature range.

As a result of studying the mechanism of making τ -MnAl phase antiferromagnetic by adjusting the Mn amount of Al sites through first principle calculation, it was found that Mn of Mn sites via p orbital valence electrons in Al atoms of Al sites are due to super exchange interaction with each other. Superexchange interaction is one of the mechanisms of exchange interaction in which the 3d orbital valence electron of a transition metal atom acts through mixing with the orbital of the p orbital valence electron in an atom having a p orbital valence electron called a ligand. Here, when the angle formed by the transition metal atom, the ligand, and the transition metal atom causing bonding is close to 180 °, antiferromagnetic bonding is caused. That is, it was found that the reason for this is that an angle formed by Mn at the Mn site in the τ -MnAl phase, Al at the Al site as a ligand, and Mn in the (1,1,0) and (1,1,1) directions from the Mn site is close to 180 °, and antiferromagnetic bonding is caused. Further, it was found that when the Al site is replaced with an Mn atom, Mn in the Mn site does not produce a super exchange interaction with each other, and it is difficult to form an antiferromagnetic magnetic structure. From these results, it was found that the stability of antiferromagnetic property can be adjusted by adjusting the Mn amount of Al sites in the τ -MnAl phase.

The method for producing a MnAl alloy of the present invention is characterized by comprising: a step of electrolyzing a molten salt containing a Mn compound and an Al compound at a temperature of 350 ℃ to 450 ℃ to precipitate a MnAl alloy; and a step of heat-treating the MnAl alloy at a temperature of 400 ℃ or higher but lower than 600 ℃. Thus, by heat-treating the MnAl alloy formed by the molten salt electrolysis method at a predetermined temperature, metamagnetism can be imparted to the MnAl alloy and high saturation magnetization can be obtained.

Effects of the invention

Thus, according to the present invention, a MnAl alloy exhibiting metamagnetism over a wide temperature range can be provided.

Drawings

Fig. 1 is a schematic view showing crystal grains of the MnAl alloy of the present embodiment.

Fig. 2 is a graph showing the magnetic characteristics of various magnetic materials.

Fig. 3 is a graph showing the magnetic properties of the MnAl alloy having metamagnetism, showing only the first quadrant (I).

Fig. 4 is another graph showing the magnetic properties of the MnAl alloy having metamagnetism.

Fig. 5 is a graph showing the derivative of the characteristic shown in fig. 4.

Fig. 6 is a graph showing the second derivative of the characteristic shown in fig. 4.

Fig. 7 is a schematic view of an electrowinning apparatus for producing MnAl alloy.

Fig. 8 is a schematic phase diagram of the MnAl alloy.

FIG. 9 is a first table showing the evaluation results of examples.

FIG. 10 is a graph showing XRD measurement results of comparative example 2, examples 5 to 8 and comparative example 9.

FIG. 11 is a graph showing XRD measurement results of comparative example 6, examples 21 to 24 and comparative example 13.

Fig. 12 is an enlarged view of XRD measurement results of comparative example 6 and example 23.

Fig. 13(a) to (c) are tables obtained by restacking the maximum magnetization, the τ phase ratio, and the γ 2 phase/β phase intensity ratio shown in fig. 9 in accordance with the electrodeposition temperature and the heat treatment temperature.

FIG. 14 is a second table showing the evaluation results of examples.

Detailed Description

Preferred embodiments of the present invention will be described below. The present invention is not limited to the following embodiments and examples. The constituent elements shown in the embodiments and examples described below may be appropriately combined or selected.

Metamagnetism refers to the property of phase transfer from Paramagnetic (PM: Paramagnetic) or antiferromagnetic (AFM: Anti-Ferromagnetic) to Ferromagnetic (FM: Ferromagnetic) once by a magnetic field. A phase transition caused by a magnetic field refers to a point where the change in magnetization with respect to the magnetic field is discontinuous. Metamagnetic materials are classified into PM-FM transfer type metamagnetic materials that are transferred from paramagnetic to ferromagnetic due to a magnetic field and AFM-FM transfer type metamagnetic materials that are transferred from antiferromagnetic to ferromagnetic due to a magnetic field. The PM-FM transition metamagnetic material undergoes a primary phase transition only in the vicinity of the Curie temperature, whereas the AFM-FM transition metamagnetic material undergoes a primary phase transition if the amorphous state is not more than the denier temperature at which the antiferromagnetic state disappears. In addition, the MnAl alloy of the present embodiment is an AFM-FM transfer type metamagnetic material, and therefore exhibits metamagnetism in a wide temperature range.

Fig. 1 is a schematic view showing crystal grains of the MnAl alloy of the present embodiment.

As shown in fig. 1, the MnAl alloy of the present embodiment has crystal grains 10 including a τ -MnAl phase and crystal grains 20 including a γ 2-MnAl phase and a β -MnAl phase. The crystalline particles 10 containing the tau-MnAl phase are phases having ferromagnetism themselves, and the crystalline particles 20 containing the gamma 2-MnAl phase and the beta-MnAl phase are phases having no ferromagnetism themselves. The crystalline particles 10 containing the tau-MnAl phase may also be twinned. Further, by mixing crystal grains 10 containing a τ -MnAl phase and crystal grains 20 containing a γ 2-MnAl phase and a β -MnAl phase, it is possible to realize AFM-FM transfer type metamagnetism, and it is possible to obtain metamagnetism in a wide temperature range. The τ -MnAl phase is a crystal phase having a tetragonal structure and has ferromagnetism in a single body, but by mixing the γ 2-MnAl phase and the β -MnAl phase, the τ -MnAl phase is given opposite ferromagnetism and exhibits metamagnetism.

The gamma 2-MnAl phase is also called Al₈Mn₅Phase, Mn₁₁Al₁₅The phases r-MnAl and gamma-MnAl are crystal phases having a prismatic crystal structure, and having lattice constants of a and b of 1.26nm, c of about 0.79nm, and a Mn/Al ratio of about 31 to 47 at%.

The beta-MnAl phase has a cubic structure and has a crystal phase with a lattice constant of about 0.64nm and a Mn/Al ratio of about 60 to 98 atomic%.

In the present embodiment, the magnetic structure of the τ -MnAl phase contained in the MnAl alloy has an antiferromagnetic structure. The antiferromagnetic structure is a structure in which spins, which are sources of magnetization of a magnetic body, have periodicity in space, and a structure in which the magnetization of the entire magnetic body is not present (i.e., spontaneous magnetization), and is different from a paramagnetic structure in which spins have no periodicity in space and have no order, and do not have magnetization of the entire magnetic body. In a non-magnetic field before phase transfer, an AFM-FM transfer type metamagnetic material is realized by using an antiferromagnetic stabilized MnAl alloy. If the stability of the antiferromagnetic state is too high, the magnetic field required for the magnetic phase transition for ferromagnetism is too large, and the magnetic phase transition cannot be caused by the magnetic field. On the other hand, if the stability of the antiferromagnetic property is too low, the ferromagnetic property may be obtained even in a non-magnetic field or a very weak magnetic field. Further, if the stability of the antiferromagnetic state of the MnAl alloy is adjusted and AFM-FM transfer type metamagnetism is given, metamagnetism can be exhibited in a wide temperature range.

The crystalline particles 10 containing the tau-MnAl phase are preferably composed of only the tau-MnAl phase having an antiferromagnetic structure, but may also contain a ferromagnetic or paramagnetic, ferrite magnetic structure in a part. Further, as long as it has metamagnetism, the antiferromagnetic structure of the τ -MnAl phase in the MnAl alloy may be a collinear antiferromagnetic structure in which the rotation axis is constant or a non-collinear antiferromagnetic structure in which the rotation axis is not constant, but the antiferromagnetic structure having a magnetic structure with a long period is preferable in terms of application because the magnetic field required for the antiferromagnetic transfer to ferromagnetism is small.

In order for the crystal grains 10 containing the τ -MnAl phase to have an antiferromagnetic structure, it is preferable that the Al site in the τ -MnAl phase is occupied by Al, but the atom occupying the Al site may be any atom as long as it has a p-orbital valence electron. Specifically, B, Ga, In, Tl, C, Si, Ge, Sn, Pb, N, P, As, Sb, Bi, O, S, Se, Te, Po, F, Cl, Br, I, At having P orbital valence electrons can be candidates thereof.

Mn for the MnAl alloy of the present embodiment_aAl_100－aWhen the composition formula of the T-MnAl phase is expressed, it is preferable that 48. ltoreq. a < 55 be satisfied. The amount of Mn in the Al site of the tau-MnAl phase a < 48 is small, the stability of the antiferromagnetic state is very high, and the magnetic field required for the magnetic phase transition is large, which is not preferable in terms of application. Since the τ -MnAl phase of a ≧ 55 contains more Mn than Al, it is easily substituted with Mn at the Al site. Mn substituted at the Al site is antiferromagnetically bonded to Mn at the Mn site, whereby ferrite is carried out as a whole in a τ -MnAl phase by causing ferromagnetic bonding between Mn at the Mn siteThe bulk magnetization makes it difficult to obtain metamagnetism. By setting the proportion of Mn of the tau-MnAl phase to be more than or equal to 48 and less than 55 and adjusting the stability of an antiferromagnetic state in a non-magnetic field, the AFM-FM transfer type metamagnetism can be realized, and the metamagnetism in a large temperature range can be obtained.

The MnAl alloy of the present embodiment is preferably composed of only the crystal grains 10 including the τ -MnAl phase and the crystal grains 20 including the γ 2-MnAl phase and the β -MnAl phase, but may include an amorphous phase as long as it has metamagnetism. Further, if the alloy has metamagnetism, the alloy may be a multicomponent MnAl alloy in which Mn sites or Al sites are partially substituted with elements such as Fe, Co, Cr, and Ni.

The composition ratio of Mn and Al in the MnAl alloy is not particularly limited, but Mn is preferably 45 at% or more and less than 55 at%, Al is more than 45 at% and 55 at% or less, and Mn is particularly preferably 45 at% or more and 52 at% or less. Namely, in the presence of Mn_bAl_100－bWhen the MnAl alloy has a composition formula, it preferably satisfies 45. ltoreq. b < 55, and particularly preferably satisfies 45. ltoreq. b.ltoreq.52. If the composition ratio of Mn and Al is set in this range, crystal grains 10 containing the τ -MnAl phase and crystal grains 20 containing the γ 2-MnAl phase and the β -MnAl phase are easily mixed.

The ratio of Mn in the MnAl alloy can be controlled by the temperature at the time of electrodeposition described later. Specifically, the higher the electrodeposition temperature, the higher the ratio of Mn in the τ -MnAl phase tends to be.

Here, when the ratio of the τ -MnAl phase is A, it is preferable that A is 75% or more and 99% or less. Accordingly, the saturation magnetization of the MnAl alloy can be improved. Particularly, the saturation magnetization of the MnAl alloy can be further improved by satisfying that A is more than or equal to 95% and less than or equal to 99%. When the ratio of the γ 2-MnAl phase is B and the ratio of the β -MnAl phase is C, B < C is preferably satisfied. Accordingly, the saturation magnetization of the MnAl alloy can be improved. In particular, the saturation magnetization of the MnAl alloy can be further improved by satisfying 0.01. ltoreq. B/C. ltoreq.0.17. This indicates that the saturation magnetization of MnAl alloy having metamagnetism is not only determined by the ratio A of the τ -MnAl phase but also depends on the ratio B/C of the γ 2-MnAl phase and the β -MnAl phase.

Fig. 2 is a graph showing magnetic characteristics of various magnetic materials, in which the horizontal axis (X axis) as the first axis shows a magnetic field H, and the vertical axis (Y axis) as the second axis shows magnetization M. In fig. 2, the reference numeral AFM-FM represents the magnetic properties of the MnAl alloy of the present embodiment, the reference numeral SM represents the magnetic properties of a normal soft magnetic material, and the reference numeral HM represents the magnetic properties of a normal hard magnetic material.

As shown by reference sign SM in fig. 2, a typical soft magnetic material has a high magnetic permeability in a low magnetic field region and is easily magnetized, and when the magnetic field strength exceeds a predetermined value, magnetic saturation occurs, and the above characteristic shows that the material is hardly magnetized. In other words, in a magnetic field region where there is no magnetic saturation, the derivative of the magnetization M with respect to the magnetic field H is large, and in a magnetic field region where there is magnetic saturation, the derivative of the magnetization M with respect to the magnetic field H is reduced. In addition, since a typical soft magnetic material has no hysteresis or very small hysteresis, a characteristic curve indicated by the symbol SM passes through the origin of the graph or its vicinity. Therefore, the characteristic curve denoted by the symbol SM appears in the first quadrant (I) and the third quadrant (III) of the graph, and does not actually appear in the second quadrant (II) and the fourth quadrant (IV).

As shown by the symbol HM in fig. 2, a normal hard magnetic material has large hysteresis, and can maintain a magnetized state even if the magnetic field is zero. Therefore, the characteristic curve shown by the symbol HM appears in all of the first quadrant (I) to the fourth quadrant (IV) of the graph.

As for these general ferromagnetic materials, the MnAl alloy of the present embodiment shows a characteristic that the MnAl alloy is hardly magnetized in the low magnetic field region because of its low magnetic permeability, and is easily magnetized in the medium magnetic field region because of its high magnetic permeability, as shown by the symbol AFM-FM in the first quadrant (I) and the third quadrant (III) of the graph, and further hardly further magnetized because of its magnetic saturation when it is in the high magnetic field region. In accordance with the later-described electrodeposition conditions and heat treatment conditions, although hysteresis is extremely small in the first quadrant (I) and the third quadrant (III), the residual magnetization is zero or extremely small, and therefore the characteristic curve indicated by the symbol AFM-FM actually passes through the origin of the graph. Even when the characteristic curve represented by the symbol AFM-FM does not pass through the origin of the graph exactly, it passes through the vicinity of the origin of the horizontal axis or the vertical axis. This means that the same magnetic properties can be obtained regardless of whether the MnAl alloy of the present embodiment is in the initial state or in the state after the magnetic field is repeatedly applied.

Fig. 3 is a graph showing the magnetic properties of the MnAl alloy of the present embodiment, and shows only the first quadrant (I).

To describe the magnetic properties of the MnAl alloy of the present embodiment more specifically with reference to fig. 3, when the magnetic field is increased from the state of no magnetic field H, the increase in magnetization M is very small because the magnetic permeability is low in the region up to the first magnetic field strength H1 (first magnetic field region MF 1). The slope of the graph, i.e. the derivative of the magnetization M with respect to the magnetic field H, is linked to the magnetic permeability. The magnetic permeability in first magnetic field region MF1 is the same as the magnetic permeability of the nonmagnetic material, and therefore, it actually appears as a nonmagnetic material in first magnetic field region MF 1.

On the other hand, in the region from the first magnetic field strength H1 to the second magnetic field strength H2 (second magnetic field region MF2), the magnetic permeability sharply increases, and the value of the magnetization M greatly increases. That is, when the magnetic field is increased, the magnetic permeability sharply increases at the first magnetic field strength H1. The magnetic permeability in second magnetic field region MF2 is close to the magnetic permeability of the soft magnetic material, and therefore, it behaves as if it is soft magnetic in second magnetic field region MF 2.

When the magnetic field is increased to exceed the second magnetic field strength H2 (third magnetic field region MF3), magnetic saturation occurs, and the slope of the graph, that is, the magnetic permeability decreases again.

In contrast, when the magnetic field is weakened from the third magnetic field region MF3 and is lower than the third magnetic field strength H3, the magnetic permeability becomes high again in the region up to the fourth magnetic field strength H4. When the magnetic field strength is lower than the fourth magnetic field strength H4, the magnetic permeability decreases, and the magnetic field strength becomes nonmagnetic again. Thus, although hysteresis is present in the first quadrant (I), since there is almost no residual magnetization, once the magnetic field H returns to near zero, the same characteristics as those described above are obtained again.

The vertical axis of the graphs shown in fig. 2 and 3 is the magnetization M, but the same relationship holds true with the vertical axis replaced by the magnetic flux density B.

Fig. 4 is another graph showing the magnetic properties of the MnAl alloy of the present embodiment, in which the horizontal axis as the first axis represents the magnetic field H and the vertical axis as the second axis represents the magnetic flux density B.

As shown in fig. 4, even when the vertical axis is replaced with the magnetic flux density B, the magnetic properties of the MnAl alloy of the present embodiment draw the same property curve in the first quadrant (I) of the graph. That is, the gradient is small in the first magnetic field region MF1 which is a low magnetic field, the gradient is rapidly large in the second magnetic field region MF2 which is a medium magnetic field, and the gradient is again small in the third magnetic field region MF3 which is a high magnetic field. In the graph shown in fig. 4, the characteristic curve showing the magnetic characteristics of the MnAl alloy of the present embodiment actually passes through the origin, and even when the characteristic curve does not pass through the origin of the graph strictly, the characteristic curve passes through the vicinity of the origin of the horizontal axis or the vertical axis.

Fig. 5 is a graph showing the derivative of the characteristic shown in fig. 4, and fig. 6 is a graph showing the second derivative of the characteristic shown in fig. 4. The characteristic shown in fig. 5 corresponds to the derivative of the magnetic permeability of the MnAl alloy of the present embodiment.

As shown in fig. 5, when the first derivative is made to the characteristic shown in fig. 4, the derivative reaches a maximum in the second magnetic field region MF 2. In the first magnetic field region MF1 and the third magnetic field region MF3, the derivatives are still small values. Also, as shown in fig. 6, when the second derivative is made to the characteristic shown in fig. 4, the second derivative is inverted from a positive value to a negative value in the second magnetic field region MF 2. In the first magnetic field region MF1 and the third magnetic field region MF3, the second derivative is approximately zero. As described above, the MnAl alloy of the present embodiment has a characteristic that when the second derivative of the magnetic flux density B with respect to the magnetic field H is made, the second derivative is inverted from a positive value to a negative value.

After a MnAl alloy is precipitated by electrolyzing a molten salt in which a Mn compound and an Al compound are mixed and melted, the MnAl alloy is heat-treated at a predetermined temperature, thereby obtaining the MnAl alloy of the present embodiment.

Fig. 7 is a schematic view of an electrowinning apparatus for making MnAl alloy.

The electroanalysis apparatus shown in FIG. 7 comprises an alumina crucible 2 disposed inside a sealed vessel 1 made of stainless steel. The alumina crucible 2 is a crucible for holding the molten salt 3, and the molten salt 3 in the alumina crucible 2 is heated by an electric furnace 4 disposed outside the sealed container 1. A cathode 5 and an anode 6 immersed in the molten salt 3 are provided in the alumina crucible 2, and a current is supplied to the cathode 5 and the anode 6 via a constant current power supply device 7. The cathode 5 is a plate-like body made of Cu, and the anode 6 is a plate-like body made of Al. The molten salt 3 in the alumina crucible 2 can be stirred by the stirrer 8. N supplied via gas path 9 into sealed container 1₂And filling with inert gas.

The molten salt 3 contains at least a Mn compound and an Al compound. Can use MnCl₂As Mn compound, AlCl can be used₃、AlF₃、AlBr₃Or AlNa₃F₆As an Al compound. The Al compound can be AlCl alone₃Alternatively, AlF may be used₃、AlBr₃Or AlNa₃F₆Replacing a portion thereof.

The molten salt 3 may contain a halide other than the Mn compound and the Al compound. As another halide, a metal halide such as NaCl, LiCl or KCl is preferably selected, and LaCl may be added to the alkali metal halide₃、DyCl₃、MgCl₂、CaCl₂、GaCl₃、InCl₃、GeCl₄、SnCl₄、NiCl₂、CoCl₂、FeCl₂Rare earth halides, alkaline earth halides, typical element halides, transition metal halides, and the like.

The molten salt 3 can be obtained by charging such a Mn compound, an Al compound, and another halide compound into the alumina crucible 2 and heating and melting them in the electric furnace 4. After the melting, the molten salt 3 is preferably sufficiently stirred by the stirrer 8 so that the composition distribution of the molten salt 3 becomes uniform.

Electrolysis of the molten salt 3 is performed by passing a current between the cathode 5 and the anode 6 by a constant current power supply device 7. This enables the MnAl alloy to be precipitated on the cathode 5.The heating temperature of the molten salt 3 during electrolysis is preferably 200 ℃ to 500 ℃, and the amount of electricity may be set to 1cm per electrode area²The amount of electricity of (c) is 15mAh or more, preferably 150 mAh. In electrolysis, preference is given to passing N₂Etc. fills the inside of the hermetic container 1 with the inert gas.

Further, by controlling the concentration of the Mn compound in the molten salt 3 per 1 mass% and the area of the electrode per 1cm²The electric energy of (a) is 50mAh or more, and the cathode 5 can deposit powdery MnAl alloy by the current flowing between the cathode 5 and the anode 6. This is because the precipitation is promoted as the concentration of the Mn compound in the molten salt 3 is higher, and the precipitation is promoted as the amount of electricity per unit electrode area is larger, and as a result, the precipitated MnAl alloy is likely to be in a powder form by satisfying the above numerical value range (50mAh or more). If the MnAl alloy precipitated in the cathode 5 is in the form of powder, the precipitation of the MnAl alloy does not stop even if electrolysis is performed for a long time, and therefore, the productivity of the MnAl alloy can be improved. Further, by compression molding the obtained powder-like MnAl alloy, an arbitrary product shape can be obtained.

The initial concentration of the Mn compound in the molten salt 3 is preferably 0.2% by mass or more, and more preferably 0.2% by mass or more and 3% by mass or less. Further, it is preferable to maintain the concentration of the Mn compound in the molten salt 3 by additionally charging the Mn compound during electrolysis. The Mn compound to be added is in the form of powder or particles formed from powder, and may be continuously or periodically added to the molten salt 3. Thus, if the Mn compound is additionally charged in the electrolysis of the molten salt 3, the concentration of the Mn compound in the molten salt 3 can be maintained at a predetermined value or more while suppressing the decrease in the concentration of the Mn compound with the progress of the electrolysis. This can suppress the change in the composition of the precipitated MnAl alloy.

The composition of the MnAl alloy deposited by electrolysis is such that substantially all of the alloy is deposited in the form of a τ -MnAl phase when Mn is 45 at% or more and less than 55 at%, and Al is more than 45 at% and 55 at% or less. When the heat treatment is performed at 400 ℃ or higher and lower than 600 ℃ with respect to the MnAl alloy of the tau-MnAl phase, part of the tau-MnAl phase is changed to the gamma 2-MnAl phase or the beta-MnAl phase. This is considered to be because the movement of Al occurs by the heat treatment, and as a result, the Al-rich region where the Al concentration increases changes to the γ 2 — MnAl phase, and the region where the Al concentration decreases becomes the τ — MnAl phase. Further, it is considered that the movement of Mn occurs by the heat treatment, and as a result, the Mn-rich region where the Mn concentration increases changes to the β -MnAl phase, and the region where the Mn concentration decreases becomes the τ -MnAl phase. Further, the proportions of the tau-MnAl phase, the gamma 2-MnAl phase and the beta-MnAl phase are changed depending on the temperature of the electroprecipitation and the temperature of the heat treatment.

Further, the ratio (B/C) of the γ 2-MnAl phase and the β -MnAl phase after the heat treatment depends on the Mn concentration of the τ -MnAl phase, and the lower the Mn concentration in the τ -MnAl phase, the more the ratio (B) of the γ 2-MnAl phase, the higher the Mn concentration in the τ -MnAl phase, and the more the ratio (C) of the β -MnAl phase. Here, the τ -MnAl phase having a high Mn concentration tends to have a large maximum magnetization value.

Fig. 8 is a schematic phase diagram of the MnAl alloy, with the horizontal axis representing the Mn ratio and the vertical axis representing the temperature. However, the phase diagram shown in fig. 8 is a diagram partially predicted, and is not a diagram based on all the actual measurement results.

As shown in fig. 8, when a MnAl alloy having an atomic ratio of Mn of 50% is produced by an electrodeposition method, the alloy becomes a τ phase substantially as a whole, but the atomic ratio of Mn has a predetermined distribution. That is, there are a portion having a high Mn atomic ratio, a portion having a low Mn atomic ratio, and the like. When the MnAl alloy is heat-treated, a part of the tau-MnAl phase is changed into a gamma 2-MnAl phase or a beta-MnAl phase by the movement of Al and Mn. The dots shown by the black dots in fig. 8 indicate phases existing at respective temperatures, and there are a region a in which the higher the temperature, the higher the Mn ratio of the τ -MnAl phase, and a region B in which the lower the temperature, the higher the Mn ratio of the τ -MnAl phase. In the region A, the Mn ratio of the γ 2-MnAl phase hardly changes even if the temperature becomes high, and in the region B, the Mn ratio of the β -MnAl phase hardly changes even if the temperature becomes low. Thus, when Al is moved by heat treatment, the region where Al is trapped is changed to γ 2 — MnAl phase, while the Mn concentration is considered to be gradually increased in the region where Al is lost, and when Mn is moved by heat treatment, the region where Mn is trapped is changed to β — MnAl phase, while the Mn concentration is considered to be gradually decreased in the region where Mn is lost.

However, when the heat treatment temperature exceeds a predetermined value, the τ -MnAl phase cannot exist and the γ 2-MnAl phase and the β -MnAl phase are mixed. In this state, the magnetic properties are lost because the τ -MnAl phase is not present.

By this mechanism, it is expected that the heat treatment temperature changes the proportions of the τ -MnAl phase, γ 2-MnAl phase and β -MnAl phase, and changes the Mn concentration in the τ -MnAl phase. Then, when the ratio of the τ -MnAl phase is A, the ratio of the γ 2-MnAl phase is B, and the ratio of the β -MnAl phase is C, the A content is 75% or more and 99% or less, preferably 95% or more and 99% or less, and the B < C content is preferably 0.01% or more and B/C0.17, whereby the saturation magnetization of the MnAl alloy having metamagnetism can be improved.

The MnAl alloy of the present embodiment can be applied to various electronic components. For example, if the MnAl alloy of the present embodiment is used as a magnetic core, the alloy can be applied to a reactor, an inductor, a current limiter, an electromagnetic actuator, a motor, and the like. In addition, if the MnAl alloy of the present embodiment is used as a magnetic refrigeration working substance, it can be applied to a magnetic refrigerator.

While the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.