JPS63260104A - Magnetic powder for magnetic recording - Google Patents

Abstract

PURPOSE:To obtain magnetic powder for vertical magnetic recording having a small average grain size, by preparing the magnetic powder, whose general composition formula is expressed by FeaCobSicMIdMIIeOf, and specifying the amounts of (a)-(f), which are the numbers of atoms of component elements. CONSTITUTION:This magnetic powder is expressed by a general composition formula FeaCobSicMIdMIIeOf. In this formula, MI represents one kind of a metal element, which is selected among Ba, Sr, Ca and Pb. MII represents at least one kind of a metal element, which is selected among Mg, Al, Cd, In, Tl, Sn and Bi. (a)-(f) are the number of atoms of Fe, Co, Si, MI, MII and O. (a) has a value of 8-12, (b) has a value of 0.01-3.0, (c) has a value of 0.05-2.0, (d) has a value of 0.5-3.0 and (e) has a value of 0.01-3.0. (f) represents the number of the oxygen atoms, which satisfies the valence of the other element. In this way, the powder for vertical magnetic recording having an average grain size of 0.1 mum or less and aligned grain sizes is obtained.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to magnetic powder for magnetic recording, and more specifically to hexagonal ferrite magnetic powder consisting of fine particles suitable for high-density magnetic recording media. be.

(Prior Art) In recent years, with the demand for higher density magnetic recording, a perpendicular magnetic recording method that records a magnetic field in the thickness direction of a magnetic recording medium has been attracting attention. The magnetic material used in such perpendicular magnetic recording systems needs to have an axis of easy magnetization in a direction perpendicular to the surface of the recording medium.

Ferrite with hexagonal crystal system and uniaxial magnetization anisotropy, such as Ba ferrite (BaFe+zO+w), is a hexagonal plate-shaped crystal with an axis of easy magnetization in the direction perpendicular to the plate surface. This material satisfies the above requirements as a magnetic material for magnetic recording. The magnetic material should have an appropriate coercive force (He, usually about 200 to 20,000e) and as large a saturation magnetization as possible (σ8, at least 40 emu/
g or more), and the average particle size of the magnetic powder must be 0.3 μm or less in terms of recording wavelength, and 0.01 μm or more in terms of superparamagnetism.

In this range, the average particle diameter is preferably smaller in terms of noise, and more preferably 081 μm or less.

(Problems to be Solved by the Invention) By the way, Ba-ferrite has a coercive force of 50,000e or more, which is too large to be used as a magnetic material for magnetic recording as it is, so some of the Fe is replaced with various other metals. ,
A method of lowering the coercive force has been proposed (for example, Japanese Patent Application Laid-Open No. 61-40823).

However, known magnetic powders in which only a portion of Fe is replaced with various other metals have relatively large average particle diameters of 0.1 μm or more, and are still insufficient as magnetic powders for perpendicular magnetic recording. In addition, glass crystallization, hydrothermal synthesis, coprecipitation, and other methods are used to manufacture barium ferrite, but the coprecipitation method uses various metals added in small amounts for coercive force control and other purposes. It has many advantages, such as being able to mix very well so that uniform ferrite can be obtained, and since the coprecipitate is a microcrystalline powder, it can be turned into ferrite at a relatively low temperature. However, magnetic powder obtained by the coprecipitation method generally has a particle size as thick as 0.15 μm at the minimum
1-174118), agglomerated powder is likely to be produced, and the particle size is around 0.5 μm, and the uniformity of shape is low (see JP-A-58-2223). A magnetic powder satisfactory for magnetic recording by coprecipitation method has not yet been obtained.

In view of this background, the present inventors conducted intensive studies to develop a magnetic powder for perpendicular magnetic recording with a smaller average particle diameter than ever before, and as a result, they were able to develop a new magnetic powder in the present invention. It was.

(Means for Solving the Problems) That is, according to the present invention, the general composition formula % (where MI represents at least one metal element selected from Ba, Sr, Ca and PB, and Ml represents Mg
.

Represents at least one metal element selected from Al, Cd, In, Tl, Sn and Bi, a, b,
c, d.

e and f are respectively Fe, Co+ St+ MI1M”
and the number of atoms of 0, a is 8 to 12, and b is 0.01 to
3.0, C is 0.05-2.0, d is 0.5-3.0 and e is 0. A magnetic powder for magnetic recording is provided, which has a value of O1 to 3.0, and f represents the number of oxygen atoms satisfying the valences of other elements.

In the present invention, the number of atoms of each component element of the magnetic powder a ”
-e must be within the above numerical range; outside this range, the average particle diameter will not only be 0.1 μm or more, but also the magnetic powder will have a coercive force and saturation magnetization suitable for magnetic recording magnetic powder. is difficult to obtain.

The preferable ratio of each component of magnetic powder is a: 8 to 12, b: 0
．． 02-2.4, C is 0.1-1.0. b is 0.8-2
．． 0 and e take values of 0.02 to 2.4, and f is the number of oxygen atoms that satisfies the valences of other elements. In the magnetic powder of the present invention, depending on the manufacturing conditions, the crystals of the magnetic powder particles obtained may not necessarily have a normal hexagonal plate shape, but the number of atoms is within the range of the present invention. Within this range, the object of the present invention can be fully achieved.

The magnetic powder of the present invention has an average particle diameter of 0.1 μm or less, and has a predetermined coercive force and saturation magnetization required as a magnetic powder for magnetic recording.

The magnetic powder of the present invention can also be produced by a glass crystallization method or a hydrothermal synthesis method, but when produced by a coprecipitation method or a coprecipitation flux method, the particle size and magnetic properties are significantly improved. The production of the magnetic powder of the present invention by the coprecipitation method will be explained below.

The raw material compounds for each metal element constituting the magnetic powder of the present invention include oxides, oxyhydroxides, hydroxides, ammonium salts, nitrates, sulfates, carbonates, organic acid salts, halides, alkali metal salts, etc. Examples include salts, free acids, acid anhydrides, and condensed acids. Particularly preferred are water-soluble compounds. The raw material compounds of each metal element are mixed and dissolved in water so that the number of atoms of each metal element becomes the above-mentioned values. Further, if it is convenient to mix and dissolve in an alkaline aqueous solution, it can be mixed and dissolved in an alkaline aqueous solution, which will be described later.

On the other hand, the alkaline component used in the alkaline aqueous solution is not particularly limited as long as it is water-soluble, and examples thereof include alkali metal hydroxides, carbonates, ammonia, ammonium carbonate, and the like. For example, NaOH.

Na2CO3, NaHCO+, KOH+ KzCOz
, Nn4. all (NH4)zcOs etc. are used, and the combined use of hydroxide and carbonate is particularly preferred.

Then, the metal ion aqueous solution and the alkaline aqueous solution are mixed to produce a coprecipitate at a pH of 5 or more, preferably ptts or more. The obtained coprecipitate is separated after washing with water. When using the coprecipitation method, the cake-like or slurry-like coprecipitate obtained in this way is dried at 600° C.
The corresponding hexagonal ferrite magnetic powder is obtained by high-temperature firing at ~1ioo°C for 1θ minutes ~30 hours. In addition, when using the coprecipitation flux method, a water-soluble flux (for example, an alkali metal halide such as sodium chloride or potassium chloride, or an alkaline earth metal halide such as barium chloride or strontium chloride) is added to the washed coprecipitate. , sodium sulfate, potassium sulfate, sodium nitrate, potassium nitrate, and mixtures thereof are commonly used).
Alternatively, the coprecipitate obtained from the mixture of the metal ion aqueous solution and the alkaline aqueous solution is directly evaporated without washing with water, dried, and then I
After firing at a high temperature for 0 minutes to 30 hours, the water-soluble flux is washed with water or an acid aqueous solution, if necessary, further washed with water, and then dried to obtain the corresponding hexagonal ferrite magnetic powder.

(Effect of the invention) The magnetic powder according to the present invention is a plate-shaped particle having an axis of easy magnetization in the hexagonal C plane, and not only has an average particle size of 0.1 μm or less, but also has a particle size that is the same as the original size. Since it has the coercive force and saturation magnetization required for magnetic recording, it is suitable as a magnetic material for perpendicular magnetic recording.

(Example) The present invention will be described in more detail with reference to Examples below. The coercive force and saturation magnetization in the examples were measured using a VSM (vibrating magnetometer), with a maximum applied magnetic field of 10 koe,
The measurement was performed at a measurement temperature of 28°C. The average particle diameter was calculated by measuring the maximum diameter of 400 particles from a photograph taken with a transmission electron microscope and calculating the arithmetic average.

Further, the compositional formula of the magnetic powder shown in the examples uses the atomic ratio of each element at the time of raw material preparation. The display of oxygen in the magnetic powder components has been omitted for brevity.

Example I Bace z ・2th0 0.55 mol, CoC1z
-6Hz00.35mol, 81 (NO3h・9Hz
0 0.35 mol and FeCj! z' 68z0
5.3 moles were dissolved in 1 (l) of distilled water in this order, and this was used as liquid A. 17.5 moles of NaOH, NazCOz
4.72 mol and NazSi(1+ + 9820 0
．． 25 mol was dissolved in 151 room temperature distilled water, and this was
It was made into a liquid. After gradually adding Solution B to Solution A heated to 50°C, the mixture was stirred at 50°C for 16 hours. The coprecipitate thus obtained was separated, thoroughly washed with water, dried at 150°C, and fired in an electric furnace at 900°C for 2 hours. The Ba-ferrite thus obtained has Ba11Fe+ o,6CO(1,?A1o,
tsia, denoted by s.

This fine particle powder has a plate shape with an average particle size of 0.069 μm, a coercive force of 7260e, and a saturation magnetization of 54.3ea+u.
/g Comparative Example 1 Ba-ferrite was produced in exactly the same manner as in Example 1 except that aluminum nitrate was removed. The obtained Ba-ferrite is Bad, lFe1(1, &C011,ts
io, denoted by s. This fine particle powder has an average particle size of 0.
It is a 21μm police paper, Hc is 8920e, ty,
was 42.8 emu/g.

Example 2 BaC1!・2820 0.55 mol, CoC1z
・61hOO045mol, MgC/! 15 moles of g O and 5.4 moles of FeC13.68z0 were dissolved in 101 distilled water in this order, and this was used as liquid A. NaOH17
, 5 mol, NazCoz 4.722 mol, and Na2
0.2 mol of SiO3.9HtQ was dissolved in 15ff of distilled water at room temperature, and this was used as liquid B. A heated to 50℃
After gradually adding Solution B to the solution, the mixture was stirred at 50° C. for 16 hours. The coprecipitate thus obtained was separated and washed with water, and NaC14 was added as a flux to the cake-like coprecipitate slurry obtained.
00g was added and thoroughly mixed, the moisture was evaporated to dryness, and the mixture was fired in an electric furnace at 860°C for 1.5 hours. After washing this fired product with water until all soluble materials are removed,
Furnace separated and dried. The Ba-ferrite thus obtained has the following properties: Bad, +Fe1o, 5coo, Jgo, 5
sio, denoted by a.

This fine particle powder was plate-shaped with an average particle size of 0.073 μ-, Hc was 7120e, and σ was 55.5 emu/g.

Examples 3 to 6 Ba-ferrite shown in Table 1 was produced in exactly the same manner as in Example 2, except that the Ml component, composition ratio, and type and amount of flux were changed.

From the results of Examples 1 to 6, the magnetic powder according to the present invention has a 0.
It can be seen that magnetic powder having an average particle size of 1 μm or less can be obtained.

Examples 7 to 23 Magnetic powders shown in Table 2 were prepared in exactly the same manner as in Example 2, except that the Mx component, Ml component, and composition ratio were changed. Furthermore, M! The acid component raw material uses chloride, and M! As acid component raw materials, chlorides were used for Mg, Cd, In, and Sn, and nitrates were used for the other components.

Claims (1)

[Claims] General composition formula Fe_aCo_bSi_cM^I_dM^I^I_eO
_f (here, M^I represents at least one metal element selected from Ba, Br, Ca, and Pb, and M^I^
I represents at least one metal element selected from Mg, Al, Cd, In, Tl, Sn and Bi;
, c, d, e and f are respectively Fe, Co, Si, M^
The number of atoms of I, M^I^I and o, a is 8 to 12,
b is 0.01-3.0, c is 0.05-2.0, d is 0
．． 5 to 3.0 and e takes a value of 0.01 to 3.0, f
is the number of oxygen atoms that satisfies the valence of other elements.) Magnetic powder for magnetic recording.