JPH0677034A - Method of manufacturing compound ferrite magnetic particles - Google Patents

Abstract

PURPOSE:To obtain the title compound ferrite magnetic particles having excellent orientation, high saturated magnetization as well as minor temperature fluctuation in coercive force and low electric resistance of the particles by forming a specific spinel ferrite layer on the surface of specific particles. CONSTITUTION:A hexagonal system ferrite particles displaying hexagonal platy shape in the crystalline structure having the whole broad peak excluding those on 110 and 220 surfaces in X-ray diffraction spectrum using Kalpha rays of Cu are heat-treated in non-oxidative atmosphere at 100 deg.C-500 deg.C. Next, a spinel ferrite layer represented by a general formula of (M'O) Fe2O3 (where M' represents exceeding one kind of metallic elements selected out of Co, Ni, Zn, Cu, Mg, Mn and Fe(II) while 0<a<=1) is formed on the surface of the ferrite particles. Through these procedures, high saturated magnetization as well as minor temperature in coercive force and low electric resistance of the particles can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a new composite ferrite magnetic powder. More specifically, the present invention has a coercive force of 200 to 2000 Oe, which is suitable for use in a magnetic recording medium for high density recording, has improved saturation magnetization as compared with the conventional one, and has a coercive force The present invention relates to a method for producing a composite ferrite magnetic powder having a small temperature change and a low electric resistance of the powder. recent years,
Along with the demand for higher density magnetic recording, a perpendicular magnetic recording system using magnetoplumbite type ferrite magnetic powder as a magnetic recording medium is under development.
Applications such as 8 mm tape and high-definition tape are considered. As magnetoplumbite-type ferrite magnetic powder used in the perpendicular magnetic recording method, one having an appropriate coercive force (200 to 2000 Oe), high saturation magnetization, small temperature change of coercive force, and good orientation Is desired.

[0002]

2. Description of the Related Art Conventionally, various methods such as a coprecipitation method, a glass crystallization method, and a hydrothermal synthesis method are known as methods for producing magnetoplumbite type ferrite magnetic powder. About the chemical method, Japanese Patent Publication Sho 60-155
Japanese Patent Laid-Open No. 59-175, which is disclosed in JP-A-75-175
It is proposed in Japanese Patent No. 707, Japanese Patent Publication No. 60-12973, Japanese Patent Publication No. 60-15576, Japanese Patent Laid-Open No. 60-137002, and the like. However, the magnetoplumbite ferrite magnetic powder obtained by any of the above methods has a saturation magnetization of 6
There were drawbacks such as a low value of 0 emu / g or less and a large change in coercive force with temperature. On the other hand, the magnetoplumbite type ferrite magnetic powder has a higher electric resistance than the conventional Co-γ-Fe ₂ O ₃ , so that a large amount of conductive substance must be added when it is used as a coating medium. Therefore, there is a problem that the electromagnetic conversion characteristics are deteriorated. As a method for solving these problems, JP-A-62-139122, JP-A-62-139124, JP-A-62-265122, and JP-A-63-144.
In Japanese Patent No. 118 and Japanese Patent No. 63-144119, it is proposed to coat the surface of ferrite magnetic powder with spinel type ferrite. Ferrite magnetic powder obtained by this,
Although the above various characteristics are actually improved, since a large amount of spinel type ferrite is coated on the surface of the ferrite magnetic powder, the orientation of the particles is deteriorated and the squareness ratio when formed into a coating becomes small. There is also a problem that the easy axis of magnetization deviates from the C axis.

[0003]

The object of the present invention is to solve the above problems,
To provide a method for producing a composite ferrite magnetic powder which is fine particles and has a coercive force of 200 to 2000 Oe, a high saturation magnetization, a small change in coercive force with temperature, a low electric resistance of the powder, and an excellent orientation. is there.

[0004]

The present invention relates to Cu Kα
In the X-ray diffraction spectrum using X-rays, hexagonal ferrite particles having a hexagonal plate shape and having a crystal structure in which all peaks except the (110) plane and (220) plane are broad are suspended in water. Turbid, add reducing agent, C
An aqueous solution containing one or more metal ions selected from o, Ni, Zn, Mg, Mn and Cu and an aqueous solution containing Fe ²⁺ and an alkaline aqueous solution are added, and the resulting mixed suspension is added in an amount of 50 to 2 in a non-oxidizing atmosphere.
After heat treatment at 00 ° C., washing, filtration, and then heat treatment at 100 to 500 ° C. in a non-oxidizing atmosphere, the surface of the ferrite particles is characterized by the general formula a (M′O)
・ Fe ₂ O ₃ (However, M'is Co, Ni, Zn, Cu, Mg, Mn and Fe (II)
One or more metal elements selected from the following, and 0 <a ≦ 1. ) Relates to a method for producing a composite ferrite magnetic powder having a spinel ferrite layer formed therein.

In the composite ferrite magnetic powder of the present invention,
As shown in Fig. 1, the ferrite particles that serve as nuclei are Cu K
Crystal structure in which only two peaks of (110) plane (2Θ = 30.3 °) and (220) plane (2Θ = 62.9 °) are sharp and all other peaks are broad in X-ray diffraction spectrum using α rays Have. As shown in FIG. 2, these peak positions substantially coincide with the peak positions of the X-ray diffraction spectrum of the conventionally known magnetoplumbite ferrite. In the present invention, by changing the crystal structure as described above, the saturation magnetization is improved and the ferrite magnetic powder having a small change in coercive force with temperature is obtained as compared with the conventional magnetoplumbite type ferrite. Also, in order to increase the density of magnetic recording, the particle size is 50n.
It is preferably m or less.

Such ferrite particles are manufactured by the following method. A solution containing A, Fe and M forming the ferrite particles and an alkali hydroxide are mixed so that the concentration of the alkali hydroxide in the solution after mixing is 3 M or more to form a precipitate, and the precipitate is formed. 120 to 3 containing slurry
After hydrothermal treatment at 00 ° C., the slurry containing the precipitate was washed and then treated with an acid to obtain a precipitate having a temperature of 700-700.
By firing at 950 ° C., the ferrite magnetic powder can be obtained. A is one or more elements selected from Ba, Sr, Ca and Pb. As the compound of A, nitrate, chloride, hydroxide and the like are used. The amount of A used is preferably such that the concentration of A is in the range of 0.03 to 0.50 M in order to obtain particles with good crystallinity.

As the Fe compound, nitrates, chlorides and the like are used. The amount of Fe used is 8 for 1 gram atom of A.
~ 12 gram atoms are preferred. If the amount of Fe is too small,
The amount of ferrite magnetic powder produced is small and the crystallinity is poor. If the amount of Fe is too large, hematite may be a byproduct,
In addition, the particles of the ferrite magnetic powder become large, and the magnetic properties become poor. M is Co, Ni, Zn, Cu, Mg, Mn, Fe (II), Bi, Si, T
It is one or more elements selected from i, Zr, Sn, Ta, Nb, Mo, V and W. As the compound of M, chloride, nitrate, ammonium salt and the like are used. As alkali hydroxide,
Sodium hydroxide, potassium hydroxide or the like is used. The amount of alkali hydroxide used is required to be such that the alkali hydroxide concentration in the solution after mixing the alkali hydroxide is 3 M or more, and preferably in the range of 4 to 8 M. If the amount of alkali hydroxide is too small, the particles become large, the particle size distribution becomes broad, and hematite is formed. Also, it is not economical to increase the amount of alkali hydroxide excessively.

The method for mixing the solution containing A, Fe and M with the alkali hydroxide is not particularly limited,
For example, there is a method of adding an aqueous solution of alkali hydroxide to a solution containing A, Fe and M. Then, the slurry containing the obtained precipitate is subjected to a hydrothermal treatment to generate and precipitate fine crystals. The temperature of hydrothermal treatment is 120 to 300 ° C. If the temperature is too low, the formation of crystals will not be sufficient, and if the temperature is too high, the particle size of the ferrite powder finally obtained will be large, such being undesirable. Hydrothermal treatment time is normal,
It takes about 0.5 to 20 hours, and an autoclave is usually used for hydrothermal treatment.

In the present invention, before the hydrothermal treatment,
The slurry containing the precipitate may be aged at a temperature of 50 ° C. or lower for 0.5 to 48 hours, and then the solution containing Bi may be added. The amount of Bi added is 1 to 5 mol%, preferably 2 to 4 mol%, based on the total amount of Fe and M. By adding Bi,
The particle size of the ferrite magnetic powder can be 50 nm or less, and the plate ratio can be 5 or less. Next, the precipitate of fine crystals produced by the hydrothermal treatment is washed with water to remove free alkali components, and then the slurry containing the precipitate is treated with an acid. For the acid treatment, inorganic acids such as nitric acid and hydrochloric acid and organic acids such as acetic acid and propionic acid can be used. Due to the acid treatment, the component A mainly in the fine particles is partially eluted. The ratio can be controlled by the conditions such as the addition amount of acid in the acid treatment, temperature and time.

Then, the obtained precipitate is washed with water and then fired to obtain a ferrite magnetic powder. In the calcination, it is preferable to mix a flux with the precipitate obtained in advance. As the flux, sodium chloride, barium chloride,
At least one of potassium chloride, strontium chloride and sodium fluoride is used. The amount of the flux used is preferably 10 to 180% by weight, more preferably 30 to 120% by weight, based on the precipitate (dry matter basis). If the amount of the flux is too small, the particles will sinter, and if the amount is too large, there will be no advantage due to the increased amount and it will not be economical. The method of mixing the precipitate and the flux is not particularly limited, and for example, the flux may be added to the slurry of the precipitate and wet-mixed, and then the slurry may be dried, or the precipitate may be dried and then the flux is added. You may dry-mix. The firing temperature is 700 to 950 ° C, preferably 800 to 930 ° C. If the temperature is too low, crystallization does not proceed and the saturation magnetization becomes low. On the other hand, if the temperature is too high, particles become large and sintering occurs, which is not preferable.
A firing time of about 10 minutes to 30 hours is suitable.

The composite ferrite magnetic powder of the present invention comprises
General formula a (M'O) ・ Fe on the surface of the elite particles₂O₃(However
M'is one selected from Co, Ni, Zn, Cu, Mg, Mn and Fe (II).
It is a metal element of at least one kind, and 0 <a ≦ 1. )
A spinel ferrite layer is formed. Of the present invention
The composite ferrite magnetic powder suspends the ferrite particles in water.
It was made turbid by adding reducing agent and Co, Ni, Zn, Mg, Mn and Cu.
One or more selected metal ions and Fe ²⁺Water containing
Solution and alkaline aqueous solution are added, and the resulting mixed suspension is
After heat treatment at 50 to 200 ° C in an oxidizing atmosphere, wash
Clean, filter, then 100-50 in non-oxidizing atmosphere
Obtained by heat treatment at 0 ° C.

To form the spinel ferrite layer, first, ferrite particles are sufficiently dispersed in water to prepare a suspension solution, and a reducing agent is added to the suspension solution in a non-oxidizing atmosphere. An aqueous solution is added and then an alkaline aqueous solution is added to deposit the hydroxide on the surface of the fine particles. Alternatively, the order of adding the metal ion aqueous solution and the alkaline aqueous solution may be reversed. The molar ratio of one or more metal ions selected from Co, Ni, Zn, Mg, Mn and Cu to Fe ²⁺ is preferably 1: 2 to 20, and particularly preferably 1: 3 to 12. As the reducing agent, aldehydes, hydroquinone, hydrazine,
An organic reducing agent such as formic acid or an inorganic reducing agent such as H ₂ or CO is used.

Next, the obtained mixed suspension is heat-treated at 50 to 200 ° C. in a non-oxidizing atmosphere. The heat treatment forms a spinel ferrite layer on the surface of the fine particles.
The heat treatment is performed at 50 to 200 ° C., especially 50 to 1
By carrying out at a low temperature of 20 ° C., the orientation of the obtained particles in the coating film is improved and the squareness ratio is improved. If the heat treatment is insufficient, the amount of spinel ferrite produced will be small, and if it is excessively performed, the characteristics will not be improved. The proportion of the spinel ferrite layer is 5 to 30% by weight, preferably 10 to 20% by weight, based on the ferrite particles. If it is less than this range, the saturation magnetization is high, the change in coercive force with temperature is small, and the electric resistance of the powder cannot be obtained, and if it is more than this range, the orientation of the particles deteriorates, Perpendicular magnetic anisotropy deteriorates.

Further, in the present invention, the spinel ferrite layer may partially contain an oxide of a metal element constituting the spinel ferrite. Then, the obtained powder is heated to 100 to 500 ° C., preferably 1 in a non-oxidizing atmosphere.
Heat treatment is performed at 50 to 400 ° C. The non-oxidizing atmosphere is preferably an inert gas such as nitrogen or helium, or in vacuum. In the present invention, by using the ferrite particles, a spinel ferrite layer is formed on the surface of the ferrite particles with a three-dimensional regularity. As a result, a composite ferrite magnetic powder having a high saturation magnetization, a small change in coercive force with temperature, a small electric resistance, and an excellent orientation can be obtained. Furthermore, by subjecting this magnetic powder to a heat treatment in a non-oxidizing atmosphere, In addition, it is possible to prevent deterioration of various improved characteristics over time.

[0015]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples. Example 1 Ferric nitrate 3.251 mol, cobalt nitrate 0.184 mol, titanium tetrachloride 0.061 mol and zinc nitrate 0.184 mol, deionized water 1800
Then, 0.460 mol of barium hydroxide and 37 mol of caustic soda were dissolved in 2000 ml of deionized water, and both solutions were mixed to form a precipitate. Next, the slurry containing the formed precipitate was aged at 20 ° C. for 6 hours, and then bismuth nitrate was adjusted to 0.
A solution of 092 mol dissolved in 50 ml of 2N-HNO ₃ solution was added.
The slurry containing the obtained precipitate was placed in an autoclave,
Hydrothermal treatment was performed at 140 ° C. for 6 hours. Then, the obtained precipitate was thoroughly washed with water, 100 ml of acetic acid was added to make a 0.2N solution, and the mixture was treated at 80 ° C for 2 hours. The precipitate obtained was washed thoroughly with water, filtered and dried. NaCl and BaCl were used as fluxing agents.
The weight ratio of ₂ · 2H ₂ O is 1: 100 relative to the mixture the precipitate of 1
% By weight was added and mixed. This mixture was added under a nitrogen atmosphere to 86
It was baked at 0 ° C. for 2 hours. The obtained fired product was thoroughly washed with water, filtered and dried to obtain ferrite magnetic powder.

The X-ray diffraction spectrum of the obtained ferrite magnetic powder is, as shown in FIG. 1, 2Θ = 30.3 ° and 2Θ = 6.
Only two peaks at 2.9 ° were sharp and all other peaks were broad. The characteristics of this ferrite magnetic powder are as follows: particle size 0.042 μm Plate ratio 3.5 Coercive force 460 Oe Saturation magnetization 64.4 emu / g Temperature change of coercive force 0.2 Oe / ° C Electric resistance of powder compact 1.2 × 10 ⁷ Ω ・It was cm.

100 g of this ferrite magnetic powder was suspended in 1000 ml of water, and 0.0189 mol of hydrazine was added, to which 200 ml of water was separately added 0.027 mol of cobalt chloride and 0.162 mol of ferrous chloride.
After adding a solution in which and were dissolved and thoroughly mixed, a solution in which 1.7 mol of caustic soda was dissolved in 300 ml of water was added and aged in a nitrogen atmosphere at 120 ° C to form a spinel ferrite layer of 15% by weight on the surface of the ferrite fine particles. . Then, the obtained slurry is washed and filtered, and the powder is heated to 400 ° C. in a nitrogen atmosphere.
And heat treated for 1 hour. The characteristics of the obtained composite ferrite magnetic powder were coercive force 660 Oe, saturation magnetization 68.8 emu / g, temperature change of coercive force -0.6 Oe / ° C, and electric resistance of the powder compact was 1.2 × 10 ⁴ Ω · cm.

Example 2 3.251 mol of ferric nitrate, 0.368 mol of cobalt nitrate and 0.061 mol of titanium chloride were dissolved in 1800 ml of deionized water, and separately, 0.460 mol of barium hydroxide and 37 mol of caustic soda were dissolved in 2000 ml of deionized water. The two solutions were mixed to form a precipitate. Next, the slurry containing the formed precipitate was aged at 20 ° C. for 6 hours, and then a solution prepared by dissolving 0.092 mol of bismuth nitrate in 50 ml of 2N-HNO ₃ solution was added. The slurry containing the obtained precipitate was placed in an autoclave and hydrothermally treated at 140 ° C. for 6 hours. Then, the obtained precipitate was thoroughly washed with water, nitric acid was added to make a 0.1 N solution, and the mixture was treated at 70 ° C. for 3 hours. The precipitate obtained was washed thoroughly with water, filtered and dried, and the weight ratio of NaCl to BaCl ₂ .2H ₂ O as a flux was 1: 1.
100% by weight of the mixture of 1 was added and mixed. The mixture was calcined under a nitrogen atmosphere at 870 ° C. for 2 hours. The obtained fired product was thoroughly washed with water, filtered and dried to obtain ferrite magnetic powder.

In the X-ray diffraction spectrum of the obtained ferrite magnetic powder, only two peaks at 2Θ = 30.3 ° and 2Θ = 62.9 ° were sharp, and all other peaks were broad.
The characteristics of this ferrite magnetic powder are as follows: particle size 0.040 μm Plate ratio 3.7 Coercive force 450 Oe Saturation magnetization 62.6 emu / g Coercive force temperature change 0.3 Oe / ° C Electric resistance of powder compact 1.4 × 10 ⁷ Ω ・It was cm. Using this ferrite magnetic powder, a spinel ferrite layer was formed on the surface of ferrite fine particles in the same manner as in Example 1. The properties of the obtained composite ferrite magnetic powder were coercive force 670 Oe, saturation magnetization 67.8 emu / g, coercive force temperature change -0.6 Oe / ° C, and electric resistance of the powder compact was 1.1 × 10 ⁴ Ω · cm.

Example 3 A ferrite magnetic powder was obtained in the same manner as in Example 1 except that bismuth nitrate was not added. The X-ray diffraction spectrum of the obtained ferrite magnetic powder is 2θ.
= Only two peaks at 30.3 ° and 2Θ = 62.9 ° are sharp,
All other peaks were broad. The characteristics of this ferrite magnetic powder are as follows: particle size 0.062 μm Plate-like ratio 7.5 Coercive force 450 Oe Saturation magnetization 64.2 emu / g Temperature change of coercive force 0.2 Oe / ° C Electric resistance of powder compact 1.4 × 10 ⁷ Ω ・It was cm. Using this ferrite magnetic powder, a spinel ferrite layer was formed on the surface of ferrite fine particles in the same manner as in Example 1. The characteristics of the obtained composite ferrite magnetic powder were coercive force 670 Oe, saturation magnetization 68.1 emu / g, coercive force temperature change -0.6 Oe / ° C, and the electric resistance of the powder compact was 1.1 × 10 ⁴ Ω · cm.

Example 4 Ferrite magnetic powder was obtained in the same manner as in Example 2 except that bismuth nitrate was not added. The X-ray diffraction spectrum of the obtained ferrite magnetic powder is 2θ.
= Only two peaks at 30.3 ° and 2Θ = 62.9 ° are sharp,
All other peaks were broad. The characteristics of this ferrite magnetic powder are as follows: particle size 0.070 μm Plate ratio 6.7 Coercive force 440 Oe Saturation magnetization 62.2 emu / g Coercive force temperature change 0.3 Oe / ° C Electric resistance of powder compact 1.4 × 10 ⁷ Ω ・It was cm. Using this ferrite magnetic powder, a spinel ferrite layer was formed on the surface of ferrite fine particles in the same manner as in Example 1. The properties of the obtained composite ferrite magnetic powder were a coercive force of 670 Oe, a saturation magnetization of 67.6 emu / g, and a change of coercive force with temperature of -0.6 Oe / ° C. The electric resistance of the powder compact was 1.9 × 10 ⁴ Ω · cm.

Comparative Example 1 Ferrite magnetic powder was obtained in the same manner as in Example 3, except that the acid treatment was not performed. The X-ray diffraction spectrum of the obtained ferrite magnetic powder is shown in FIG. The characteristics of this ferrite magnetic powder are as follows: particle size 0.061 μm Plate-like ratio 7.7 Coercive force 460 Oe Saturation magnetization 58.2 emu / g Coercive force temperature change 2.9 Oe / ° C Electric resistance of powder compact 1.4 × 10 ⁷ Ω ・It was cm. Using this ferrite magnetic powder, a spinel ferrite layer was formed on the surface of ferrite fine particles in the same manner as in Example 1 except that no reducing agent was added. The characteristics of the obtained composite ferrite magnetic powder were a coercive force of 570 Oe, a saturation magnetization of 60.1 emu / g, and a change of coercive force with temperature of 1.6 Oe / ° C. The electric resistance of the powder compact was 6.1 × 10 ⁶ Ω · cm.

Comparative Example 2 A ferrite magnetic powder was obtained in the same manner as in Example 4, except that the acid treatment was not carried out. The characteristics of the obtained ferrite magnetic powder are as follows: particle size 0.072 μm Plate-like ratio 6.5 Coercive force 410 Oe Saturation magnetization 56.1 emu / g Temperature change of coercive force 3.2 Oe / ° C Electric resistance of powder compact 1.4 × 10 ⁷ Ω ・It was cm. Using this ferrite magnetic powder, a spinel ferrite layer was formed on the surface of ferrite fine particles in the same manner as in Example 1 except that no reducing agent was added. The characteristics of the obtained composite ferrite magnetic powder were coercive force 530 Oe, saturation magnetization 58.1 emu / g, coercive force temperature change 1.6 Oe / ° C, and the electric resistance of the powder compact was 5.8 × 10 ⁶ Ω · cm.

[0024]

EFFECT OF THE INVENTION The composite ferrite magnetic powder obtained by the present invention has dramatically improved saturation magnetization as compared with the conventional one, and further has a small change in coercive force with temperature and a small electric resistance of the powder. It has excellent dispersibility and is suitable for use as a magnetic recording material for high density recording.

[Brief description of drawings]

FIG. 1 is a diagram showing an X-ray diffraction spectrum of a ferrite magnetic powder obtained in Example 1 of the present invention.

FIG. 2 is a diagram showing an X-ray diffraction spectrum of the ferrite magnetic powder obtained in Comparative Example 1 of the present invention.

Claims (2)

[Claims] 1. A hexagonal plate having a hexagonal plate-like structure having a crystal structure in which all peaks except broad peaks of (110) plane and (220) plane in an X-ray diffraction spectrum using Kα ray of Cu are broad. Crystalline ferrite particles are suspended in water, to which a reducing agent and an aqueous solution containing at least one metal ion selected from Co, Ni, Zn, Mg, Mn and Cu and Fe ²⁺ and an alkaline aqueous solution are added. The obtained mixed suspension is heat-treated at 50 to 200 ° C. in a non-oxidizing atmosphere and then washed,
Filter, then 100-500 ° C in non-oxidizing atmosphere
The surface of the ferrite particles is characterized by being heat-treated with the general formula a (M'O) .Fe ₂ O ₃ (where M'is Co, Ni, Z
One or more metal elements selected from n, Cu, Mg, Mn and Fe (II), and 0 <a ≦ 1. The manufacturing method of the composite ferrite magnetic powder in which the spinel ferrite layer represented by this is formed. 2. The method for producing a composite ferrite magnetic powder according to claim 1, wherein the ferrite particles have a particle diameter of 50 nm or less and a plate ratio of 5 or less.