JPH06267721A - M-type ferrite magnetic powder and anisotropic magnet - Google Patents

Abstract

PURPOSE:To provide M-type ferrite magnetic powder and an anisotropic magnet having high coercive force. CONSTITUTION:M-type ferrite magnetic powder is represented by a general formula of XO.nFe2O3 (in the formula, X is a mixture of Sr and Ba, and n is a real number of 5.6-6.1), wherein Sr/Ba is 8/2-5/5. An anisotropic magnet uses the powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel M-type ferrite magnetic powder and magnet, more specifically having a high coercive force,
The present invention relates to an M-type ferrite magnetic powder that can be used for magnetic recording and the like and an anisotropic magnet using the same.

[0002]

2. Description of the Related Art M-type ferrites are represented by the above general formula XO.n.
Fe ₂ O ₃ and X is Sr, Ba, Ca and P
It is said that it represents at least one metal selected from b, but in the past, only Ba or Sr alone has been used in practice.

The Ba-based materials are so-called isotropic magnetic powders which are manufactured without magnetic field shaping (to improve the magnetic properties by aligning the easy axis of magnetization) during the manufacturing process because of the low cost of the raw materials. Being manufactured. Further, since the Sr system has a larger crystal magnetic anisotropy constant than the Ba system, a high coercive force can be obtained, and the raw material is relatively expensive as compared with the Ba system, but the magnetic characteristics are Ba by the magnetic field molding.
It is manufactured as a so-called anisotropic magnetic powder which is 2 to 4 times as much as the isotropic magnetic powder. Further, it is also used as magnetic powder for magnetic cards by utilizing the high coercive force of these magnetic powders.

[0004]

With the recent downsizing trend, there is an increasing demand for high performance and space saving permanent magnet materials used in motors and speakers incorporated in such electronic devices. Sm-Co based materials and Nd-F as materials that meet those requirements
So-called rare earth magnets such as e-B series are used. However, these materials are expensive, and are not used in large quantities for consumer use because they use raw materials that are unstable in terms of supply and use a special manufacturing method such as a quenching method.

Therefore, by studying additives, particle diameters, molding methods, etc. with Sr-based materials, which are cheaper than these raw materials, a high coercive force is achieved and magnetic characteristics are improved. However, even if these methods are used, it has reached the limit level industrially.

[0006]

As described above, X of the general formula is used.
Is at least one metal selected from Sr, Ba, Ca, and Pb, but Sr and Ba are mainly contained, and Sr / Ba
There is no description about the ratio of M type ferrite, and actually there is no M type ferrite having X as a mixture of Sr and Ba.

The present inventor has found that a high coercive force can be obtained by a completely new method, instead of the high coercive force obtained by the conventional extension methods such as additives, particle diameters and molding methods. That is, in order to explain the coercive force of M-type ferrite, three magnetic anisotropies of strain, shape, and crystal are taken up, and theoretical formulas are presented for each. Focusing on the strain magnetic anisotropy among them, the divalent metals Sr and Ba, which are largely different in ionic radius and can enter into the M-type ferrite crystal lattice, are added at the same time, so that the strain is generated in the M-type ferrite. As a result of repeated studies based on the idea that they may occur, they have found that the coercive force is increased in the region of a specific Sr / Ba ratio, compared with the case where they are added alone, and arrived at the present invention.

That is, the present invention relates to the general formula XO.nFe
₂ o ₃ (wherein X: a mixture of Sr and Ba, n: 5.6 to
An M-type ferrite magnetic powder having a Sr / Ba ratio of 8/2 to 5/5. It is a sex magnet.

The present invention will be described in detail below. Since Sr and Ba used in the present invention are finally used in the form of oxides, there are raw materials such as hydroxides, nitrates, sulfates, organometallic compounds and carbonates which become oxides when heated. However, industrially, carbonate (SrCO ₃ and BaCO
₃ ) is most desirable because it is easy to handle, inexpensive, and high-purity raw material can be obtained. Further, since Fe is finally used as an oxide in the form of red iron oxide (α-Fe ₂ O ₃ ), a raw material such as metallic iron, Fe ₃ O ₄ , which becomes an oxide in this form when heated, FeOOH, iron carbonate,
There are iron sulfate, iron chloride, organic metal iron, etc., but industrially, red iron oxide is the most desirable because it is easy to handle, inexpensive and a high-purity raw material can be obtained.

The raw material having a particle size of about 0.1 to 2 μm is easy to handle when mixing these raw materials. M according to the present invention
SrO and BaO are used in the production of die-type ferrite.
So that the molar ratio of SrCO ₃ is from 8/2 to 5/5.
And BaCO ₃ were weighed, and Fe ₂ O ₃ / (SrCO ₃
Fe ₂ O ₃ is weighed so that the molar ratio of + BaCO ₃ ) is in the range of 5.6 to 6.1, and the powders are mixed by a wet or dry method using a mixer such as a ball mill. The desired M by firing in a heating device such as an electric furnace at various temperatures.
The method of obtaining type ferrite is the most widely used method industrially called the powder method. At that time, a melting method is also possible in which the mixed powder is mixed with a salt such as salt or glass and heated and dissolved to cause a reaction to obtain ferrite. Further, an aqueous solution containing salts of Sr, Ba and Fe is prepared so as to become the above ferrite, and the precipitate obtained by coprecipitating it with an organic acid such as alkali or oxalic acid is calcined at an appropriate temperature. (Coprecipitation method), or by heating and decomposing the aqueous solution at an appropriate temperature (pyrolysis method),
Alternatively, the ferrite can be obtained by reacting the salts in the aqueous solution under an appropriate pressurized steam (hydrothermal synthesis method).

[0011]

EXAMPLES The present invention will be described below with reference to examples. Example 1 In M-type ferrite XO.nFe ₂ O ₃ , X is B
When a or Sr is a single product, the value of n is usually 5.6 to
Although it is in the range of 6.1, as the value of n becomes smaller, the sintering temperature at the time of sintering the magnetic powder as a magnet only decreases, and the magnetic characteristics do not significantly change. Therefore, for the case of n = 6, which is the stoichiometrically optimum value, Sr
The characteristics of the magnetic powder were comparatively examined by changing the ratio of Ba and Ba. That is, when weighed so that the total weight of iron oxide (α-Fe ₂ O ₃ ), strontium carbonate and barium carbonate was 1000 g, and wet-mixed (Sr / Ba = 7/3), SrCO ₃ = 94.7 g. , BaCO
₃ = 26.8 g, α-Fe ₂ O ₃ = 878.5 g were weighed, and 1500 g of pure water and zirconia balls 3000 were weighed.
g and wet mixed for 20 hours. ), After drying 1125
Calcination was performed for 1 hour.

Next, this fired product was roughly crushed by an atomizer and then S was added as a grain growth inhibitor in a batch type dry vibration mill.
0.6 wt% of iO ₂ was added, and finely pulverized so as to have a specific surface area of 2.7 to 3.0 m ² / g by BET method. To the powder thus obtained, add 10 wt% of PVA solution at 10 wt% (1 wt% as PVA) to 15 mm.
Molding was performed using a φ mold at a molding pressure of 1500 kg / cm ² .

This molded body is heated in the atmosphere at a heating rate of 200 ° C. /
It heated up at h and baked at 1180 degreeC for 1 hour. After cooling, the magnetic characteristic was measured using a direct current magnetization characteristic automatic recorder (manufactured by Riken Denshi Co., Ltd.) with an applied magnetic field of 10 kOe.

Table 1 shows the results of the remanent magnetization (Br), the magnetic flux density coercive force (bHc), the magnetic coercive force (iHc), and the maximum energy product BH (max) obtained from the above.

[0015]

[Table 1]

As a result, the Sr / Ba ratio is from 8/2 to 5
It was found that in the range of / 5, the coercive force is improved as compared with the case of Ba alone or Sr alone.

Example 2 Next, as magnetic powder for anisotropy, Fe ₂ O ₃ / (SrO +
The molar ratio of BaO) is 6.0 and the ratio of Sr / Ba is the magnetic powder for isotropicity, and iHc was the maximum at 7/3 composition, so for comparison, 10/0, 7/3, 6/4 composition. Was tested. The method is iron oxide (α-F
e ₂ O ₃ ), strontium carbonate, and barium carbonate were weighed and wet-mixed to a total weight of 1000 g, dried, and then baked at 1300 ° C. for 1 hour. Next, after roughly crushing this fired product with an atomizer, 0.36 wt% of SiO ₂ was used as a grain growth inhibitor during sintering with a planetary wet ball mill.
0.45 wt% of CaO was added and finely pulverized so that the specific surface area measured by the BET method was 3.6 to 4.0 m ² / g. The slurry thus obtained was subjected to magnetic field molding in a magnetic field of 5000 G using a mold of 15 mmφ at a molding pressure of 350 kg / cm ² . This molded body is heated in the atmosphere at a heating rate of 2
The temperature was raised at 00 ° C./h and firing was performed at 1225 ° C. for 1 hour. After cooling, the magnetic characteristics were measured with an applied magnetic field of 10 kOe using a DC magnetization characteristic automatic recording device. Table 2 shows the measurement results.

[0018]

[Table 2]

From this, remanent magnetization (Br), magnetic flux density coercive force (bHc), magnetization coercive force (iHc), and maximum energy product BH (max) were obtained. As a result, it was confirmed that the magnetic properties were improved as compared with the Sr single product, which is said to have the best properties.

[0020]

EFFECT OF THE INVENTION Sr / in M-type ferrite according to the present invention
The ratio of Ba is between 8/2 and 5/5, and high coercive force can be obtained by using Sr and Ba alone. Therefore, by using this, a magnetic card having higher coercive force can be produced. It is also possible to use it as a high-performance sintered magnetic material. In addition, since it is possible to improve the performance by using a part of inexpensive Ba without producing the expensive Sr alone and to produce it by the usual industrial ceramics production method, it is also advantageous in terms of cost.

Claims (2)

[Claims] 1. The general formula XO.nFe ₂ O ₃ (wherein X: S
In a magnetoplumbite type ferrite (hereinafter referred to as M type ferrite) represented by a mixture of r and Ba, n: representing a real number of 5.6 to 6.1, the ratio of Sr / Ba is 8/2 to 5 /. 5. An M-type ferrite magnetic powder characterized by being No. 5. 2. An anisotropic magnet produced by using the M-type ferrite magnetic powder according to claim 1.