JPH0479202A - Permanent magnet consisting of single magnetic domain particle - Google Patents

Abstract

PURPOSE:To improve magnetic properties and enable the application of the powder to a bond magnet by making the grain size of the particles within the range of the single magnetic domain particle diameter, with respect to the magnetic material which has the composition in the line of rare earth-iron- nitrogen-hydrogen-oxygen. CONSTITUTION:Rare earth-iron alloy is composed, and after coarse crushing, nitrification and hydrogenation process is performed under low oxygen partial pressure, and the magnetic powder at this stage is further pulverized into the powder which has the particle diameter equivalent to the single magnetic domain particle diameter of magnetic material. The magnetic material shown by the general formula RealphaFe(1-alpha-beta-gamma-delta)NbetaHgammaOdelta (Re is the rare earth element including yttrium, 5<=alpha<=20 atom %, 10<=beta<=25 atom %, 0.01<=gamma<=5 atom %, 0.01<=delta<=10 atom %) is obtained.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is a permanent magnetic material using a powder having a rare earth-iron-nitrogen-hydrogen-oxygen composition and having a single magnetic domain particle size. Regarding magnets.

[Prior Art] The magnetic expression mechanism of rare earth magnets can be broadly classified into nucleation type (eucreation type) and pinning type based on the behavior of the initial magnetization curve. These are Nd-Fe-B system and Sm
This is a useful way to distinguish between CO5-based and 8 m 2 COt 7-based rare earth magnets.

In nucleation type magnets, as seen in Nd-Fe-B magnets, excess Nd or B excess phases segregated at the grain boundaries in the microstructure of the sintered body tend to occur on the particle surface. It improves magnetic properties by suppressing the generation of "reverse magnetic domain buds." On the other hand, in the pinning type, as observed for example in S m 2 Co t □-based magnets, the excess Sm phase in the microstructure pins the ends of the domain wall of the 2-17 ferromagnetic phase, which affects the magnetic properties. is involved in the expression mechanism.

Research is currently underway to better understand the mechanisms by which the magnetic properties of these rare earth magnets develop.
Apart from these ideas, there is the classical idea of single-domain particles. Single-domain particles are particles with a particle size such that only a single magnetic domain can exist in one particle, and the volume is
, where the magnetic anisotropy energy (constant) is 1, Boltzmann's constant is 1, and T is the absolute temperature. This is a simple formula, or one way to think about the size of the particle.

In cases where single-domain particles can be produced and are completely oriented, at least no deterioration in magnetic properties due to multi-domain particles is observed. Therefore, it is an ideal idea to construct a permanent magnet as an aggregate of single-domain particles.

However, this has not been completely achieved with the conventional Sm--Co and Nd--Fe--B systems. The reason for this is that the mechanisms called pinning type and nucleation type, which are the mechanisms by which magnetic properties are expressed in these materials, depend on the microstructure of the sintered body or heat-treated powder.

That is, a non-magnetic phase exists at the grain boundaries of grains having a much larger grain size than single-domain grains, and this two-phase structure plays an important role in the expression of magnetic properties. Therefore, if you attempt to make the grain size closer to the single magnetic domain grain size by making fine grains, this microstructure will be destroyed, so properties that depend on the microstructure, such as retention, will be more important than the properties of single magnetic domain grains. The magnetic force is significantly reduced, and the properties are also deteriorated due to distortion, introduction of defects, and progress of oxidation into the particles due to crushing.

However, since the rare earth-iron-nitrogen-hydrogen-oxygen magnetic material of the present invention is a rare earth material, it is clear that the coercive force increases and the properties improve as the particles become finer, as predicted by the single domain particle theory. .

This indicates that the mechanism of magnetic property development of this material is new, and that it has great potential for application as a powder magnetic material for bonded magnets and the like.

Note that in this patent, magnetic properties are referred to as saturation magnetization (
4πIs, BM) refers to residual magnetization (B), coercive force (H), and squareness ratio.

[Problems to be Solved by the Invention] The present invention is based on the fact that a magnetic material having a rare earth-iron-nitrogen-hydrogen-oxygen composition exhibits magnetic properties in accordance with the so-called single domain particle theory, unlike conventional rare earth magnets. Having found this, we adjusted the particle size of the powder within the range of the single magnetic domain particle size,
The purpose is to improve the magnetic properties and to provide a method for applying the powder to bonded magnets.

[Means for Solving the Problems] The magnetic material of the present invention for solving the above problems has components of rare earth (Re)-iron (Fe) nitrogen (N)-hydrogen (H
)-oxygen (O), is a powder of a magnetic material characterized by being represented by the following general formula, and whose particle size is:
This corresponds to the single magnetic domain particle diameter of the magnetic material of each composition.

General formula Re a Fe x-a-s-v-a+ Ns H,
OaHowever, Re in the above general formula is yttrium (
5≦α≦20 atom% 10≦β≦25 atom% 0, O1≦γ≦5 atom% 0.01≦δ≦10 atom%.

In the present invention, since particles having the above composition and a particle size of around 2 to 4 μm correspond to single domain particles of the magnetic material,
This is related to the fact that permanent magnets, especially bonded magnets, made of powder with a single magnetic domain particle size exhibit high magnetic properties.

Manufacturing method The magnetic material in the present invention can be manufactured by the following steps.

(1) Synthesis of master alloy: Synthesize a rare earth-iron alloy.

(2) Coarse grinding (3) Nitriding, hydrogenation (4) Fine pulverization: This is mainly a coercive force optimization process.

(4) During pulverization, the amount of oxygen can be controlled, and it is also possible to control the particle size, particle shape, defect concentration inside the particles, etc.

In addition, controlling the particle size to a single magnetic domain particle size is also performed at this stage.

(1) After synthesis of the master alloy, annealing is performed to make the composition uniform, and (3) after nitriding and hydrogenation, to make the composition uniform and remove the mechanical stress generated in the particles. It is effective for These steps will be explained below.

(1) Synthesis of master alloy The raw material alloy can be produced by a high frequency furnace, an arc melting furnace, or by a liquid super-quenching method. Its composition is Re 5~
It is preferable that Fe is in the range of 25 at% and 75 to 95 at%. When Re is less than 5 at%, α-Fe is present in the alloy.
There are many phases and high coercive force cannot be obtained. Furthermore, if Re exceeds 25 atomic %, a high saturation magnetic flux density cannot be obtained.

When a high frequency furnace or an arc melting furnace is used, Fe tends to precipitate when the alloy is solidified from a molten state, which causes a decrease in magnetic properties, particularly coercive force. Therefore, it is effective to perform annealing for the purpose of eliminating the phase of Fe alone, making the alloy composition uniform, and improving crystallinity. This annealing is most effective when performed at 800°C to 1280°C. The alloy produced by this method has better crystallinity and higher saturation magnetization than those produced by the liquid ultra-quenching method.

Alloys with the desired composition can also be produced using alloy production methods such as the liquid super-quenching method and the roll rotation method. Moreover, the crystal grains of the alloys produced by these methods are fine, and submicron particles can be prepared depending on the conditions. However, when the cooling rate is high, the alloy becomes amorphous, and even after nitriding and hydrogenation, the saturation magnetization and coercive force do not increase as much as with other methods. In this case as well, post-treatment such as annealing is required.

The master alloy is 300-5 no matter which method is used to make the alloy.
Contains oxygen of about 00ppH. This level of oxygen content at this stage is introduced through normal operations during the process.

(2) Coarse pulverization The pulverization at this stage may be performed using a method such as a Shaw Crusher stamp mill that prepares only coarse powder, or may be performed using a ball mill or jet mill depending on the conditions. However, this pulverization is for the purpose of uniformly performing the nitriding and hydrogenation in the next step, and it is necessary to prepare a powder state that has sufficient reactivity and does not progress to oxidation. is important.

The amount of oxygen contained in this coarsely pulverized material is not much different from that of the mother alloy, and is 11,000 pp or less.

(3) Nitriding and Hydrogenation A method for combining or impregnating nitrogen and hydrogen into the pulverized raw material master alloy is to pressurize or heat-treat the raw material alloy powder in ammonia gas or a reducing mixed gas containing ammonia gas. The method is valid. The amount of nitrogen and hydrogen contained in the alloy can be controlled by the mixture component ratio of the ammonia gas-containing mixed gas, heating temperature, pressurizing force, and treatment time.

As the mixed gas, a mixture of hydrogen, helium, neon, nitrogen, and argon, or a mixture of two or more of them and ammonia gas is effective. Although the mixing ratio can be changed in relation to the processing conditions, it is particularly effective for the ammonia gas partial pressure to be from 0.02 to 0.75 atm, and for the processing temperature to be preferably in the range of 200 to 650°C. At low temperatures, the penetration rate is low, and at high temperatures of 850° C. or higher, iron nitrides are produced, and the magnetic properties are degraded. In the pressure treatment, the contents of nitrogen and hydrogen can be changed even with a pressure of about 10 ati.

If a gas other than ammonia gas is used as the main component of the nitriding or hydrogenation atmosphere, the reaction efficiency will be significantly reduced. However, it is possible to introduce nitrogen and hydrogen, for example, by carrying out a long reaction using a mixed gas of hydrogen gas and nitrogen gas.

Although the nitriding/hydrogenation process is performed in a low oxygen partial pressure, the amount of oxygen at the end of the process increases somewhat to around 1000 pp11.

(4) Micronization When annealing is performed after nitriding and hydrogenating, N.

The composition of H and O is 3 to 4 wt% of N and 10 wt% of H.
~20ppm SO content is around 11,000pp. The pulverization process further pulverizes the magnetic powder at this stage. In the pulverization step, a vibrating ball mill, a planetary ball mill, a normal pot-type rotary ball mill, a jet mill, etc. can also be used. Regardless of which method is used, the impact and shearing force applied to the powder should be as small as possible.
It is also important that the grinding be carried out sufficiently and that oxidation should not occur particularly violently.

Therefore, in this process, operation in a glove box, control of the oxygen partial pressure in the atmosphere, and selection of solvents such as ethanol, water, cyclohexane, carbon tetrachloride, petroleum benzine, etc. in ball milling are important. be.

The contents of N, H, and O after this atomization step are 3 to 4 wt% for N and 200 to 500 ppm for H, respectively.
, 0 is around 1w15.

It is possible to produce various permanent magnets using the magnetic powder produced at this stage.

This patent was developed by focusing on the characteristic of the magnetic material, which exhibits high magnetic properties after pulverization. This is related to the discovery that the powder has the highest properties, and that a permanent magnet made using the powder exhibits a physical property value of (BH) ax of 1 gMGOe or more.

[Definition of single magnetic domain particles in this patent] Single magnetic domain particles in the present invention essentially refer to particles that contain only one magnetic domain in one particle, but with current technology, 10 magnetic domain particles in powder
Since it is industrially impossible to configure 0% by single-domain particles, particles with a volume fraction equivalent to 50% or more of single-domain particles (in the example shown in Example 2, 2 to 4 μm diameter) are used. Particles that exhibit a behavior in which magnetic properties such as coercive force clearly improve as the single domain diameter approaches the average physical properties of the entire powder, as predicted from single-domain particle theory. The population was expressed as a powder having a particle size corresponding to a single magnetic domain particle size.

Models of a single magnetic domain particle in the present invention and a multi-domain polycrystalline particle, which is the opposite polarity thereof, are shown below.

〔Example] Hereinafter, the present invention will be specifically explained with reference to Examples.

Example I S m 10.5 atomic percent and F e 89.5
An ingot having an S m 2 F e t □ structure, which is recognized as a homogeneous phase by X-ray diffraction using an Sm-Fe alloy having a composition of atomic percent, was ground into a powder having a diameter of 20 to 100 μI. Two batches of such powder were made from different lots of S m 2 Fe 17 alloy and each was heated in a tube furnace at 450° C. with 0.0 ml of ammonia gas.
After processing for 1 hour in a mixed gas flow of 35 atm+c and hydrogen gas at 0.85 atm, annealing was performed for 1 hour in an argon gas atmosphere.

As a result, the composition was Sm Fe N HO (1) and 8.8 75.1 15.5 0.1 0
．． 5S m F e N HO (ii) 208.8 75.0 15.2 0.2
A powder of 0.7 to 100 μm was obtained. Put 1 g of each of these powders into a 50 cc glass container, add 50 g of SUS por, and use cyclohexane as a dispersion solvent to approximately 35 Orl) I! 1 for a predetermined time in the range of 1 to 10 hours to obtain a powder having a predetermined coercive force.

FIG. 1 shows (i) and (11) the coercive force and (BH) value of the powder obtained by grinding for a predetermined time, respectively. The bonded magnet was produced by molding powder using a single-push die in a magnetic field of 15 kOe at 1 ton/cd. The properties of the powder magnet were measured using a vibrating sample magnetometer (VSM).

From these results, it is clear that the maximum value of (BH) exists near H-7000 to 90000e.

Figures 2a-e are scanning electron micrographs of the following samples.

Figure 2a shows the starting mother alloy of each sample in line 11 in Figure 1. Figure 2 shows the powder microstructure of the starting sample which was crushed for about 15 minutes to have a coercive force of about 25,000e. Second
Figures c-e show point A (powder with coercive force 58000e) and point B (coercive force 8400e) in line (11), respectively.
(powder with a coercive force of 89000e) and point C (powder with a coercive force of 89000e).

It can be seen that the particle size gradually becomes smaller.

Example 2 The sample in Example (1) above was crushed and the coercive force was reduced to about 50
A sample of 000e was prepared. Further, a turbid liquid was prepared by mixing submicron magnetite fine particles (Fe304) into oleic acid and ultrasonically dispersing the mixture.

Powder having a coercive force of 50,000 e was dispersed in a magnetite particle dispersion liquid, and was precipitated after ultrasonic dispersion. At this time, the magnetite particle dispersion is a low-concentration dispersion whose transparency is slightly reduced compared to that of unmixed oleic acid, and when the magnetic particles precipitate after mixing, the transparency returns to that of oleic acid itself.

After applying Au vapor deposition to these samples, they were observed using a scanning electron microscope (SEM).

For powder with a coercive force of 50,000e, Fig. 3(a) ~
A representative example is shown in (d).The single magnetic domain particle size obtained by this method is measured to be about 2 to 4 microns along the short axis.

From this, it was revealed that in the sample having a particle size of about 5 to 10 μm used in this experiment, the single magnetic domain particle size was about 2 to 4 μm.

[Effects of the Invention] As explained above, the essential characteristics of the magnetic material used in the present invention are that it can be finely pulverized to a single-domain particle diameter that could not be achieved with conventional rare earth magnets, and that it has high coercive force and magnetization. From the change behavior of , it is possible to create a single domain particle magnet.

This material has excellent properties as a magnetic powder for bonded magnets, so (BH) the tnax value is 18MGO.
e can be reached.

[Brief explanation of the drawing]

FIG. 1 is an ax graph showing the coercive force and (BH) value of the powder obtained by crushing the magnetic alloy of Example 1 for a predetermined period of time. Figures 2a-e are scanning electron micrographs showing the particle structure of the sample explained in Example 1, and Figures 3a-d are scanning electron micrographs showing the particle structure of the sample explained in Example 2. be. Figure 1 Patent applicant Asahi Kasei Industries Co., Ltd. Agent Patent attorney Hide Komatsu

Claims (1)

[Claims] (1) Ingredients are rare earth (Re) - iron (Fe) - nitrogen (N)
- Powder of a magnetic material consisting of hydrogen (H) - oxygen (O) and characterized by being represented by the following general formula, the particle size of which corresponds to the single domain particle size of the magnetic material of each composition. A permanent magnet constructed using General formula Re_αFe_(_1_-_α_-β_-_γ_-_δ
_)N_βH_γO_δ However, R in the above general formula
e is a rare earth element containing yttrium (Y), 5≦α≦20 atom%, 10≦β≦25 atom%, 0.01≦γ≦5 atom%, and 0.01≦δ≦10 atom%.