JPH05326237A - Composite ferrite magnetic powder and production thereof - Google Patents

Abstract

PURPOSE:To produce magnetic recording material suitable for high density recording in which saturation magnetization is enhanced drastically as compared with conventional one, temperature fluctuation of coercive force is suppressed, electric resistance of powder is lowered, and dispersion performance is improved. CONSTITUTION:The composite ferrite magnetic powder is composed by forming spinel ferrite layer shown by general formula a(M'O).Fe2O3 (where, M' represents one or more kind of metallic element selected from Co, Ni, Zn, Cu, Mg, Mn, and Fe (II), and 0<a<=1) on the surface of hexagonal system ferrite particle exhibiting hexagonal plate shape wherein all peaks in X-ray diffraction spectrum employing Kalpha ray of Cu have broad crystal structure except those on (110) and (220) faces.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel composite ferrite magnetic powder and a method for producing the same. 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 of The present invention relates to a composite ferrite magnetic powder having a small temperature change and a low electric resistance, and a method for producing the same.

In recent years, with the demand for higher density of magnetic recording,
A perpendicular magnetic recording system using magnetoplumbite type ferrite magnetic powder as a magnetic recording medium is under development, and applications such as DAT tape, 8 mm tape, and high-definition tape are considered. As the magnetoplumbite type ferrite magnetic powder used for the perpendicular magnetic recording method, one having an appropriate coercive force (200 to 2000 Oe), a saturation magnetization as high as possible, a small coercive force temperature change, and a good orientation. Is desired.

[0003]

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 a method for producing a magnetoplumbite type ferrite magnetic powder. About the chemical method, Japanese Patent Publication Sho 60-155
Japanese Patent Application Laid-Open No. 59-175, which is disclosed in JP-A-75-175
It is proposed in Japanese Patent Publication No. 707, Japanese Patent Publication No. 60-12973, Japanese Patent Publication No. 60-15576, Japanese Patent Publication No. 60-137002, and the like.

However, the magnetoplumbite type ferrite magnetic powders obtained by any of the above methods have drawbacks such as a low saturation magnetization of 60 emu / g or less and a large change in coercive force with temperature. On the other hand, the magnetoplumbite type ferrite magnetic powder is a conventional Co-γ-Fe
_Since the electric resistance of powder is higher than that of ₂ O ₃ , it is necessary to add a large amount of a conductive substance when forming a coating medium.
Therefore, there is a problem that the electromagnetic conversion characteristics deteriorate.

As a method for solving these problems, Japanese Patent Laid-Open Nos. 62-139122, 62-139124, and 62-26 have been proposed.
In Japanese Patent Nos. 5122, 63-144118, and 63-144119, it is proposed to coat the surface of ferrite magnetic powder with spinel-type ferrite. Although the ferrite magnetic powder obtained by this is actually improved in the above various characteristics, since the surface of the ferrite magnetic powder is coated with a large amount of spinel-type ferrite, the orientation of the particles is deteriorated and a coating film is formed. In this case, the squareness ratio becomes small, and the easy axis of magnetization deviates from the C axis.

[0006]

The object of the present invention is to solve the above problems,
To provide a composite ferrite magnetic powder having fine particles, 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, and a method for producing the same. It is in.

[0007]

The present invention relates to Cu Kα
X-ray diffraction spectrum using X-rays has a hexagonal plate-like hexagonal ferrite particle surface having a crystal structure in which all peaks are broad except for the (110) plane and (220) plane peaks. Formula a (M ′ O) ・ Fe ₂ O
₃ (where M ′ is one or more metal elements selected from Co, Ni, Zn, Cu, Mg, Mn and Fe (II), and 0 <a ≦ 1). The present invention relates to a composite ferrite magnetic powder characterized in that

In the composite ferrite magnetic powder of the present invention,
As shown in Fig. 1, the core ferrite particles are K of Cu.
Crystal structure in which only two peaks of (110) plane (2Θ = 30.3 °) and (220) plane (2Θ = 63.0 °) are sharp and all other peaks are broad in the X-ray diffraction spectrum using α rays Have. As shown in FIG. 2, these peak positions substantially match the peak positions of the X-ray diffraction spectrum of the conventionally known magnetoplumbite type ferrite.

In the present invention, by changing the crystal structure as described above, the saturation magnetization is improved as compared with the conventional magnetoplumbite type ferrite, and ferrite magnetic powder having a small change in coercive force with temperature is obtained. Be done. Further, in order to increase the density of magnetic recording, the particle size is preferably 50 nm 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 alkali hydroxide concentration 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 preferably 8 to 12 gram atoms per 1 gram atom of A. If the amount of Fe is too small, the amount of ferrite magnetic powder produced is small,
Crystallinity also deteriorates. If the amount of Fe is too large, hematite is by-produced, and the ferrite magnetic powder particles become large, resulting in poor magnetic properties.

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 the 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 the range of 4 to 8 M is preferable. If the amount of alkali hydroxide is too small, the particles become large, the particle size distribution becomes broad, and hematite is formed. In addition, it is not economical to increase the amount of alkali hydroxide excessively.

The method of 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 hydrothermal treatment to produce and precipitate fine crystals. The temperature of hydrothermal treatment is 120 to 300 ° C. If the temperature is too low, the formation of crystals is not sufficient, and if the temperature is too high, the grain size of the finally obtained ferrite powder becomes large, which is not preferable. Hydrothermal treatment time is usually
It takes about 0.5 to 20 hours, and an autoclave is usually adopted 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 diameter 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,
Acidify the slurry containing the precipitate. For acid treatment, nitric acid,
An inorganic acid such as hydrochloric acid or an organic acid such as acetic acid or propionic acid can be used. By the acid treatment, mainly the component A in the fine particles is partially eluted. The ratio can be controlled by the conditions such as the acid addition amount of the acid treatment, temperature, time and the like.

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 is no advantage due to the large amount, and it is not 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 10 minutes to 30 hours is suitable. The composite ferrite magnetic powder of the present invention, on the ferrite particle surface,
General formula a (M ′ O) · Fe ₂ O ₃ (where M ′ is Co, Ni, Zn, Cu, Mg, Mn
And one or more metal elements selected from Fe (II), 0
<A ≦ 1. The spinel ferrite layer represented by () is formed.

The composite ferrite magnetic powder of the present invention is prepared by suspending the ferrite particles in water, and adding Co, Ni, Zn, Mg, Mn to the suspension.
And an aqueous solution containing one or more metal ions selected from Cu and Fe ²⁺ and an alkaline aqueous solution are added, and the resulting mixed suspension is heated at 50 to 200 ° C. in a non-oxidizing atmosphere, and then washed, Filtered, then 1 in a non-oxidizing atmosphere
It is obtained by heat treatment at 00 to 500 ° C.

To form a spinel ferrite layer, first, ferrite particles are sufficiently dispersed in water to prepare a suspension solution, to which an aqueous solution of the metal ion is added in a non-oxidizing atmosphere, and then an aqueous alkaline solution is added. 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. C
The molar ratio of one or more metal ions selected from o, Ni, Zn, Mg, Mn and Cu to Fe ²⁺ is 1: 2 to 20, particularly 1:
3-12 are preferable.

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% by weight, based on the ferrite particles.
Is about 20% by weight. 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, the saturation magnetization is high, the change in coercive force with temperature is small,
A composite ferrite magnetic powder having a low electric resistance and excellent orientation can be obtained. Further, by heat-treating this magnetic powder in a non-oxidizing atmosphere, it is possible to prevent the improved various characteristics from deteriorating with time.

[0024]

EXAMPLES The present invention will be described in more detail with reference to the following 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 is added to 20
After aging at ℃ for 6 hours, 0.092 mol of bismuth nitrate was added to 2N-HNO
_A solution dissolved in 50 ml of ₃ solutions 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, 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 thoroughly washed with water, filtered and dried, and a mixture of NaCl and BaCl ₂ .2H ₂ O in a weight ratio of 1: 1 was added to the precipitate as 100% by weight. % Was added and mixed. The mixture was calcined at 860 ° C for 2 hours under a nitrogen atmosphere. 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.
Only the two peaks at 2Θ = 30.3 ° and 2Θ = 63.0 ° 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 Coercive force temperature change 0.2 Oe / ° C Electric resistance of powder compact 1.2 × 10 It was ⁷ Ω · cm.

100 g of this ferrite magnetic powder was suspended in 1000 ml of water, and a solution of 0.027 mol of cobalt chloride and 0.162 mol of ferrous chloride was added to 200 ml of water and mixed thoroughly, and 1.7 mol of caustic soda was added to water. A solution dissolved in 300 ml was added and aged at 120 ° C. in a nitrogen atmosphere to form a spinel ferrite layer on the surface of the fine ferrite particles in an amount of 15 wt%. Then, the obtained slurry was washed and filtered, and the powder was heat-treated at 400 ° C. for 1 hour in a nitrogen atmosphere.

The characteristics of the obtained composite ferrite magnetic powder are coercive force 660 Oe, saturation magnetization 68.8 emu / g, change in coercive force with temperature, -0.6 Oe / ° C, electric resistance of powder compact 6.2 × 10 ⁴ Ω · cm. It was

Example 2 Ferrous nitrate (3.251 mol), cobalt nitrate (0.368 mol) and titanium chloride (0.061 mol) were dissolved in deionized water (1800 ml). Separately, barium hydroxide (0.460 mol) and caustic soda (37 mol) were dissolved in deionized water (2000 ml). 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 of 0.092 mol of bismuth nitrate dissolved 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 precipitate obtained was thoroughly washed with water, and nitric acid was added to the precipitate to give 0.1N.
The solution was prepared and treated at 70 ° C. for 3 hours. The precipitate obtained is washed thoroughly with water, filtered and dried.
And a mixture of BaCl ₂ .2H ₂ O in a weight ratio of 1: 1 was added to the precipitate in an amount of 100% by weight 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 = 63.0 ° 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 Temperature change of coercive force 0.3 Oe / ° C Electric resistance of powder compact 1.4 × 10 ⁷ Ω ・It was cm.

Using this ferrite magnetic powder, Example 1
A spinel ferrite layer was formed on the surface of the ferrite fine particles in the same manner as in. The characteristics of the obtained composite ferrite magnetic powder were coercive force 670 Oe, saturation magnetization 67.8 emu / g, temperature change of coercive force -0.6 Oe / ° C, electric resistance of the powder compact was 7.1 × 10 ⁴ Ω · cm.

Example 3 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 = 63.0 ° are sharp,
All other peaks were broad.

The characteristics of this ferrite magnetic powder are as follows: particle size 0.062 μm, plate ratio 7.5 coercive force 450 Oe saturation magnetization 64.2 emu / g coercive force temperature change 0.2 Oe / ° C electric resistance of powder compact 1.4 × 10 It was ⁷ Ω · cm.

Using this ferrite magnetic powder, Example 1
A spinel ferrite layer was formed on the surface of the ferrite fine particles in the same manner as in. The properties 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 7.1 × 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 = 63.0 ° 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 It was ⁷ Ω · cm.

Using this ferrite magnetic powder, Example 1
A spinel ferrite layer was formed on the surface of the ferrite fine particles in the same manner as in. 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 6.9 × 10 ⁴ Ω · cm.

Comparative Example 1 A 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 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, Example 1
A spinel ferrite layer was formed on the surface of the ferrite fine particles in the same manner as in. The properties of the obtained composite ferrite magnetic powder were coercive force 570 Oe, saturation magnetization 60.1 emu / g, coercive force temperature change 1.6 Oe / ° C, and 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 performed. 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, Example 1
A spinel ferrite layer was formed on the surface of the ferrite fine particles in the same manner as in. 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.

[0044]

EFFECTS 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 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 (4)

[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. the crystal system ferrite particle surface, the general formula a (M 'O) · Fe 2 O 3 ( however, M' is Co, Ni, Zn, Cu, Mg, Mn
And one or more metal elements selected from Fe (II),
0 <a ≦ 1. ) A composite ferrite magnetic powder characterized in that a spinel ferrite layer represented by (4) is formed. 2. The composite ferrite magnetic powder according to claim 1, wherein the ferrite particles have a particle size of 50 nm or less and a plate ratio of 5 or less. 3. A solution containing each element constituting the ferrite magnetic powder and an alkali hydroxide are mixed so that the alkali hydroxide concentration in the solution after mixing is 3 M or more to form a precipitate, The precipitate-containing slurry is hydrothermally treated at 120 to 300 ° C., the precipitate-containing slurry is washed, and then treated with an acid to obtain a precipitate at 700 to 950 ° C.
By firing, the resulting ferrite fine particles suspended in water,
To this, an aqueous solution and an alkaline aqueous solution containing one or more metal ions selected from Co, Ni, Zn, Mg, Mn, and Cu and Fe ²⁺ were added, and the resulting mixed suspension was placed in a non-oxidizing atmosphere. 5
The method for producing a composite ferrite magnetic powder according to claim 1, wherein the composite ferrite magnetic powder is heat-treated at 0 to 200 ° C., washed, filtered, and then heat treated at 100 to 500 ° C. in a non-oxidizing atmosphere. 4. A solution containing each element constituting the ferrite magnetic powder and an alkali hydroxide are mixed so that the alkali hydroxide concentration in the solution after mixing is 3 M or more to form a precipitate, followed by aging. After that, a solution containing Bi was added, and the slurry containing the precipitate was hydrothermally treated at 120 to 300 ° C.
The slurry containing the precipitate is washed, then treated with an acid,
The obtained precipitate was calcined at 700 to 950 ° C., and the obtained ferrite fine particles were suspended in water. Co, Ni, Zn, M
Fe ²⁺ and one or more metal ions selected from g, Mn and Cu
Aqueous solution containing the above and an aqueous alkali solution are added, and the obtained mixed suspension is heat-treated at 50 to 200 ° C. in a non-oxidizing atmosphere, washed, filtered, and then 100 to 500 in a non-oxidizing atmosphere. The method for producing a composite ferrite magnetic powder according to claim 2, wherein the heat treatment is performed at ℃.