JP2018031047A - Method for producing magnetic compound - Google Patents

Abstract

A method for producing a magnetic compound having a high anisotropic magnetic field is provided. Rx (Fe (1-a) Coa) (12-y) Moy (wherein R is Y, Zr, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, One or more elements selected from the group consisting of Ho and Lu, represented by 1 ≦ x ≦ 1.5, 0.5 ≦ y ≦ 1, and 0 ≦ a ≦ 0.7. A method comprising preparing an alloy having a crystal structure and nitriding the alloy at 525 ° C. to 625 ° C. in an N 2 -containing gas. [Selection figure] None

Description

The present invention relates to a method for producing a magnetic compound having a ThMn ₁₂ type crystal structure with a high anisotropic magnetic field.

  The application of permanent magnets extends to a wide range of fields such as electronics, information communication, medical care, machine tool fields, industrial and automotive motors, and the demand for suppression of carbon dioxide emissions is increasing. In recent years, there are increasing expectations for the development of permanent magnets with even higher characteristics due to energy savings and improved power generation efficiency in the industrial field.

  At present, Nd—Fe—B magnets, which are dominating the market as high-performance magnets, are also used in drive motor magnets for HV / EHV. Recently, new permanent magnet materials are being developed in response to the demand for further miniaturization and higher output of motors (increase in residual magnetization of magnets).

As one of the developments of materials having performance exceeding Nd—Fe—B type magnets, research on rare earth-iron type magnetic compounds having a ThMn ₁₂ type crystal structure is underway. For example, Patent Document 1 proposes a nitrided magnetic composition having a ThMn ₁₂ type crystal structure containing Nd as a rare earth element.

JP 2004-265907 A

Conventionally known compounds having a composition of NdFe ₁₁ TiN _x having a ThMn ₁₂ type crystal structure exhibit uniaxial magnetic anisotropy when N atoms enter a predetermined position in the NdFe ₁₁ Ti crystal lattice. Therefore, the anisotropic magnetic field is high. However, since N is desorbed at a high temperature of 600 ° C. or higher and the anisotropy magnetic field is lowered, it has been difficult to achieve high performance by full fluence such as sintering. In addition, when nitriding using N ₂ gas, only the outside of the particles is nitrided, the inside is not easily nitrided, and the distribution of N is non-uniform, leading to a decrease in magnetic anisotropy. is there.

  An object of the present invention is to provide a method for producing a magnetic compound having a high anisotropic magnetic field in which N is uniformly distributed and which can solve the above-described problems of the prior art.

In order to solve the above problems, according to the present invention, the following formula R _x (Fe _(1-a) Co _a ) _(12-y) Mo _y
(In the above formula, R is one or more elements selected from the group consisting of Y, Zr, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, and Lu;
1 ≦ x ≦ 1.5,
0.5 ≦ y ≦ 1,
0 ≦ a ≦ 0.7)
And a step of preparing an alloy having a ThMn ₁₂ type crystal structure represented by:
There is provided a method for producing a magnetic compound, comprising a step of nitriding the alloy at 525 ° C. to 625 ° C. in an N ₂ -containing gas.

According to the present invention, by nitriding an alloy having a ThMn ₁₂ type crystal structure containing Mo as a stabilizing element at 525 ° C. to 625 ° C. in an N ₂ -containing gas, not only the surface of the magnetic compound, A magnetic compound with improved magnetic anisotropy that is nitrided to the inside and uniformly nitrided as a whole can be obtained.

2 is a graph showing the XRD result of the particles of Example 1. 6 is a graph showing XRD results of particles of Comparative Example 1. 3 is an image showing the EPMA measurement result of the particles of Example 1. FIG. 6 is an image showing an EPMA measurement result of particles of Comparative Example 1. 2 is a mapping image of N distribution by EPMA measurement of the particles of Example 1. FIG. 3 is a mapping image of N distribution by EPMA measurement of particles of Comparative Example 1. 4 is a graph showing the results of DSC measurement of the particles of Example 1. 6 is a graph showing a DSC measurement result of particles of Comparative Example 3. 2 is a perspective view schematically showing a crystal structure of a particle of Example 1. FIG. 3 is a perspective view schematically showing a crystal structure of a particle of Comparative Example 1. FIG. It is a graph which shows the relationship between nitriding temperature and an anisotropic magnetic field. It is a graph which shows a stabilization element and a stabilization area | region.

Hereinafter, the manufacturing method of the magnetic compound which concerns on this invention is demonstrated in detail. Method for producing a magnetic compound of the present invention, first the formula _{R x (Fe (1-a} ) Co a) (12-y) Mo y
(In the above formula, R is one or more elements selected from the group consisting of Y, Zr, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, and Lu;
1 ≦ x ≦ 1.5,
0.5 ≦ y ≦ 1,
0 ≦ a ≦ 0.7)
An alloy having a ThMn ₁₂ type crystal structure is prepared by a conventional method, for example, a strip casting method, a casting method, or the like. Each component of this alloy will be described below.

(R)
R is one or more elements selected from the group consisting of Y, Zr, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, and Lu, and is used in the present invention to exhibit permanent magnet characteristics. It is an essential component of the magnetic compound. The blending amount x of R is 1 ≦ x ≦ 1.5. This is because if x is less than 1, soft magnetic α-Fe is generated in addition to the predetermined ThMn ₁₂ phase, and the magnetic properties, particularly the anisotropic magnetic field, are reduced. On the other hand, when x exceeds 1.5, similarly, a lot of soft magnetic Nd ₂ Fe ₁₇ phase or Nd ₃ Fe ₂₉ phase is generated, and the anisotropic magnetic field and saturation magnetization are lowered. Preferably, the blending amount x of R is 1 ≦ x ≦ 1.2.

(Mo)
When Mo is added to the R—Fe binary alloy, it contributes to stabilizing the ThMn ₁₂ type crystal structure and providing excellent magnetic properties. FIG. 5 shows the stabilization region of the T element in the RFe _12-x T _x compound (source: KHJ Buschow, Rep. Prog. Phys. 54, 1123 (1991)). It is known that the addition of Ti, V, Mo, and W as the third element stabilizes the ThMn ₁₂ type crystal structure and exhibits excellent magnetic properties.

Conventionally, when Mo is used as a stabilizing element, it has been said that at least 1.5 Mo per unit is required for stabilizing the crystal structure. However, in the present invention, by using Mo as the stabilizing element and nitriding under the predetermined conditions described below, the ThMn ₁₂ type crystal structure can be stabilized even with one Mo amount per unit cell. Became possible. Therefore, the compounding amount y of Mo is 0.5 ≦ y ≦ 1.

(Fe and Co)
The alloy used in the present invention is Fe other than the above elements, but a part of Fe may be substituted with Co. When Co is replaced with Fe, the spontaneous magnetization is increased by the Slater poling rule, and both the anisotropic magnetic field and the saturation magnetization can be improved. Here, the substitution amount a of Co is 0 ≦ a ≦ 0.7. However, when the substitution amount of Co exceeds 0.7, the effect cannot be exhibited. Moreover, since the Curie point of the compound is increased by substituting Fe with Co, there is an effect of suppressing a decrease in magnetization at a high temperature. Preferably, the substitution amount a of Co is 0 ≦ a ≦ 0.4.

In the method of the present invention, the magnetic compound includes a step of nitriding an alloy having a ThMn ₁₂ type crystal structure represented by the above formula in an N ₂ -containing gas at 525 ° C. to 625 ° C. As the N ₂ -containing gas, N ₂ alone gas or N ₂ + H ₂ mixed gas can be used, and the N ₂ concentration in this mixed gas is preferably 20% to 80%. The nitriding temperature is more preferably 550 ° C. to 600 ° C., and the nitriding time is preferably 0.5 h to 24 h.

By nitriding at 525 ° C. to 625 ° C. in such N ₂ -containing gas, the resulting magnetic compound is uniformly nitrogenated, that is, there is little distribution of nitrogen concentration, and there is no need for other than the 2b site of the crystal structure. Intrusion of nitrogen atoms into the site is suppressed, and approximately one nitrogen atom can be present in the unit cell. As a result, the anisotropic magnetic field can be improved.

Examples 1-5 and Comparative Examples 1-3
Alloy flakes having the compositions shown in Table 1 below were produced by strip casting, and heat treatment was performed at 1100 ° C. for 4 hours in an Ar atmosphere. Next, the flakes were pulverized using a cutter mill in an Ar atmosphere, and particles having a particle size of 30 μm or less were collected. The obtained particles were nitrided in a flow of N ₂ gas (N ₂ gas concentration 100%) at 450 ° C. to 600 ° C. for 4 hours. The magnetic properties of the particles thus obtained (vibration sample type magnetometer, VSM), structure observation (electron beam microanalyzer, EPMA) and crystal structure analysis (X-ray diffraction, XRD) were performed. Table 1 below shows measurement results of nitriding conditions and magnetic properties.

  From the results shown in Table 1, in the comparative example using Ti as the stabilizing element, one or more nitrogen atoms tend to penetrate per unit cell, while in the examples using Mo as the stabilizing element, It was found that the amount of nitriding was stabilized at about one. It was also found that the anisotropic magnetic field of the magnetic characteristics is larger when Mo is used than when Ti is used.

  The XRD result of Example 1 is shown in FIG. 1, and the XRD result of Comparative Example 1 is shown in FIG. It can be seen that as the amount of nitrogen increases, the peak shifts to the lower angle side and the crystal lattice expands. Further, it is clear from the clarity of the peak that the crystallized Mo-based sample (Example 1) after nitriding is better than the Ti-based sample (Comparative Example 1).

  The EPMA result of Example 1 is shown in FIG. 3, and the EPMA result of Comparative Example 1 is shown in FIG. It was found that the Ti-based sample (Comparative Example 1) was non-uniformly nitrided, concentrated on the outer periphery of the particles, and the central portion was thin, whereas the Mo-based sample (Example 1) was uniformly nitrided. .

  FIG. 5 shows a mapping image of N distribution by EPMA of Example 1, and FIG. 6 shows a mapping image of N distribution by EPMA of Comparative Example 1. As shown in FIG. 6, the nitrogen distribution in the center of the particle in Comparative Example 1 is 34% of the nitrogen concentration in the surface layer of the particle, whereas the nitrogen distribution in the center of the particle in Example 1 as shown in FIG. Is 100% of the nitrogen concentration of the particle surface layer. Therefore, it can be seen that the Mo-based sample of Example 1 has nitrogen infiltrated uniformly to the center of the particles. The nitrogen concentration in the center of the particle is preferably 50% or more of the nitrogen concentration in the particle surface layer.

  Moreover, the DSC measurement result of Example 1 is shown in FIG. 7, and the DSC measurement result of Comparative Example 3 is shown in FIG. The exothermic peak that first appears on the temperature rise side is the nitrogen dissociation (decomposition) temperature. The Ti-based sample of Comparative Example 3 started to decompose at about 500 ° C. and reached a peak at 591 ° C. (FIG. 8), whereas the Mo-based sample of Example 1 started to decompose from about 700 ° C. It peaked at 778 ° C. (FIG. 7). From this result, it can be seen that the Mo-based sample of Example 1 has a higher nitrogen separation temperature. Therefore, it was found that the material is hardly thermally decomposed and has high heat resistance.

  From the above, it is estimated that the Mo-based sample is uniformly nitrided and nitrogen is preferentially occupied in the 2b site (FIG. 9). On the other hand, the amount of nitriding at the outer periphery of the Ti-based sample particles is much larger than one, and there is a possibility that nitrogen atoms have penetrated into sites other than the 2b site (FIG. 10). It was also found that nitriding was not completed at the center. This is considered to be a cause of a low anisotropic magnetic field in the Ti-based sample. A portion where nitriding is incomplete (insufficient) does not have uniaxial anisotropy but has in-plane anisotropy, and is not suitable for a permanent magnet.

Examples 1 and 7 and Comparative Examples 4-7
In the same manner as in the above examples, alloy flakes having the compositions shown in Table 2 below were prepared by strip casting, and heat treatment was performed at 1100 ° C. for 4 hours in an Ar atmosphere. Next, the flakes were pulverized using a cutter mill in an Ar atmosphere, and particles having a particle size of 30 μm or less were collected. The obtained particles were nitrided at 450 ° C. to 600 ° C. for 4 hours in a flow of N ₂ gas and N ₂ gas (N ₂ gas concentration 100%). Table 2 below shows measurement results of nitriding conditions and magnetic properties. FIG. 11 shows the relationship between the nitriding temperature and the anisotropic magnetic field.

From the results shown in Table 2 and FIG. 11, the nitriding amount increased as the nitriding temperature increased. At 550 ° C. and 600 ° C., the amount of nitriding became approximately one. Regarding the magnetic characteristics, it was found that the nitriding amount was maximized around one. From the XRD results, the amount of nitriding was increased to 1.5 at 650 ° C., which is thought to be because the ThMn ₁₂ type crystal structure became unstable and phase-divided into α-Fe.

From this result, it was said that when Mo is used as a stabilizing element in the prior art, 1.5 or more per unit cell is required as shown in FIG. Even in the amount, the ThMn ₁₂ type crystal structure could be stabilized. This is considered to be because one nitrogen per unit cell is stabilized and the crystallinity is also improved.

Claims (1)

A method for producing a magnetic compound comprising the following formula: R _x (Fe _(1-a) Co _a ) _(12-y) Mo _y
(In the above formula, R is one or more elements selected from the group consisting of Y, Zr, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, and Lu;
1 ≦ x ≦ 1.5,
0.5 ≦ y ≦ 1,
0 ≦ a ≦ 0.7)
And a step of preparing an alloy having a ThMn ₁₂ type crystal structure represented by:
A method comprising nitriding the alloy at 525 ° C. to 625 ° C. in an N ₂ containing gas.