JPS63260107A - 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 FeaTibSicMIdMIIeOf, 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 formula FeaTibSicMIdMIIeOf. In this formula, MI represents at least 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 La, V, Mo, W, Cd, Tl, P, Bi, Ce, Nd and Sm. (a), (b), (c), (d), (e) and (f) are the numbers of the atoms of Fe, Ti, 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 oxygen atoms, which satisfies the valence of the other element. In this way, the magnetic powder for vertical magnetic recording having an average grain size of 0.1mum and the aligned grain sizes is obtained.

Description

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

(Prior Art) In recent years, with the demand for higher density magnetic recording, perpendicular magnetic recording methods that record magnetic fields in the thickness direction of a magnetic recording medium have 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 (BaPe+tO+), is a hexagonal plate-shaped crystal with an axis of easy magnetization perpendicular to the plate surface, and is a coated film type. This material satisfies the above requirements as a magnetic material for perpendicular magnetic recording. The magnetic material should have a moderate coercive force □I C% usually about 200 to 20,000e) and as large a saturation magnetization as possible (σ8, at least 40es+
u/g or more), and the average particle diameter of the magnetic powder must be 0.3 μm or less in relation to the recording wavelength, and in the range of 0.01 μm or more in relation to superparamagnetism. be. In this range, the average particle diameter is preferably smaller from the standpoint of noise, and more preferably 0.1 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 large particle size of 0.15 μm at the minimum (see Japanese Patent Application Laid-Open No. 174118/1983), tends to produce agglomerated powder, and has a large particle size. It contains particles of about 0.5 μm, and the uniformity of the shape is low (see Japanese Patent Laid-Open No. 58-2223), and magnetic powder satisfactory for magnetic recording by the 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 Ml represents at least one metal element selected from Ba, Sr, Ca, and PB; Ml represents L
a.

V+ Not W, Cd, TI, Pt Bt,
Ce+ represents at least one metal element selected from Nd and SLl, and a, b, c, d, e, and f are I'e, Co, and St, respectively.

The number of atoms of Ml, Ml and 0, a is 8 to 12, b is 0.01 to 3.0, C is 0.05 to 2.0, d is 0.5
~3.0 and e takes a value of 0.01 to 3.0, and f represents the number of oxygen atoms satisfying the valence of other elements. Powder provided.

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 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. The magnetic powder of the present invention may contain particles whose crystals do not necessarily have a normal hexagonal plate shape depending on the manufacturing conditions, but the number of atoms is within the range of the present invention. If so, the purpose 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 glass crystallization or hydrothermal synthesis, but when produced by coprecipitation or coprecipitation flux, 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. The raw material compounds of each metal element, which are particularly preferably water-soluble compounds, 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.

NazCOz. Na1lCO+, KOH, KgCO
i, NH40B, (NH*)zcOi, 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 form a coprecipitate at a pH of 5 or higher, preferably at a pH of 8 or higher. 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 and then
The corresponding hexagonal ferrite magnetic powder is obtained by high-temperature firing at 1100° C. for 10 minutes to 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 usually used), or a coprecipitate obtained from a mixture of a metal ion aqueous solution and an alkaline aqueous solution is directly hydrated without washing with water. After drying this by evaporating it, it is fired at a high temperature of 600 to 1100°C for 10 minutes to 30 hours, and then the water-soluble flux is washed with water or an acid aqueous solution and separated in a furnace.If necessary, it is further washed with water and then dried. A corresponding hexagonal ferrite magnetic powder is obtained.

(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 the sake of brevity.

Example 1゜BaCJ1g'2Hz0 0.55 mol, TiCl1a
0.25 mol, CdC12g ・2WHz0 0.
35 moles and PeC1, 6Hz0 5.4 moles to 10
j! were dissolved in distilled water in this order, and this was used as Solution A.
17.5 moles of NaOH, 4.72 moles of NazCOz, and 2 moles of NagSiOs.911tOO were dissolved in 151 room temperature distilled water, and this was used as liquid B.

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 in a furnace, thoroughly washed with water, dried at 150°C, and fired in an electric furnace at 890°C for 2 hours. The Ba-ferrite thus obtained is B
at, +Fe+o, 5Tie, 5cdo, ys
io, denoted by a.

This fine particle powder has a plate shape with an average particle size of 0.073μ, a coercive force of 6440e, and a saturation magnetization of 55.4emu/
It was g.

Comparative Example 1 Ba-ferrite was produced in exactly the same manner as in Example 1 except that cadmium chloride was removed. The obtained Ba-ferrite is Bad, +Fe+o, 5Tio, B51o
, denoted by a. This fine particle powder has an average particle size of 0.28
μth plate shape, Hc is 12380e, σ3 is 40
．． 4 emu/g. Example 2 BaCJ! *・2To0 0.55 mol, Tic Il
a O, 45 mol, La(Not)s・6H*o 0
．． 25 moles of FeCR3.61110 and 5.3 moles of FeCR3.61110 were dissolved in 1O1 of distilled water in this order, and this was used as liquid A. 17.5 moles of NaOH, 4.72 moles of NagCOs, and 2 moles of NagSiOs.9BgOO were dissolved in 151 room temperature distilled water, and this was used as liquid B. 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 in a furnace and washed with water, and Na was added as a flux to the cake-like coprecipitate slurry obtained.
After adding 1,400 g of Cl and thoroughly mixing, water was evaporated to dryness, and the mixture was fired in an electric furnace at 870° C. for 2 hours.

This baked acid product was washed with water until no soluble matter remained, and then separated in a furnace and dried. The Ba-ferrite thus obtained is Ba, 1pel11. bTt@, gLa
Indicated by @, Sst@, a.

This fine particle powder had a plate shape with an average particle size of 0.075μ, Hc of 6160e, and σ3 of 55.6 emu/g.

Examples 3-6 MI! Ba-ferrite shown in Table 1 was produced in exactly the same manner as in Example 2, except that the components, 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 31 Magnetic powders shown in Table 2 were prepared in exactly the same manner as in Example 2, except that the MI acid component and the composition ratio were changed. Note that chloride was used as the MI acid component raw material, chloride was used for Cd, ammonium salt was used for V, Mo, W, and P, and nitrate was used for the other components. . V, Mo.

The raw material compounds of W and P were dissolved in an alkaline aqueous solution.

Claims (1)

[Claims] General composition formula Fe_aTi_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 is La, V, Mo, W, Cd, Tl, P, Bi, Ce
, Nd and Sm, and a, b, c, d, e and f each represent Fe.
, Ti, Si, M^I, M^I^I and O atoms, a is 8 to 12, b is 0.01 to 3.0, c is 0.0
5-2.0, d is 0.5-3.0 and e is 0.01-3
．． The value is 0, and f is the number of oxygen atoms satisfying the valences of other elements. ) magnetic powder for magnetic recording