JPH01119517A - Magnetic powder for magnetic recording - Google Patents

Abstract

PURPOSE:To obtain the title hexagonal magnetic fine powder suitable as magnetic material for perpendicular magnetic recording, by subjecting to composing specified amts. of each metal element as showing in the formula and to having well-regulated particle size. CONSTITUTION:The aq. soln. obtd. by dissolving the material compds. such as (hydro)oxide, nitrate, carbonate, halogenide of each metal element in the amts. equiv. to the constituent ratio of the targeted substance, in water, is mixed with the aq. alkali soln. of hydroxide, carbonate, etc., of alkali metal and adjusted to >=5pH value, and the produced coprecipitate is washed, filtered and dried. Then, the coprecipitate is high temp. calcined at 600-1,100 deg.C for 10min-30hr, as occasion demands, in the presence of the flux such as NaCl, BaCl2, KNO3 to obtain the magnetic powder having <=1mu mean particle diameter and the axis of easy magnetization in the face (c) of hexagonal system, of formula (where, MI is Ba, Sr, Ca, Pb, MII is V, Cr, Mo, W, Ag, Cd, Ge, Sn, P, Bi, Te, (a) is 8-12, (b) and (e) are 0.01-3.0, (c) is 0.05-2.0, (d) is 0.5-3.0 and (f) is the number of oxygen atom satisfying the valence of the other elements).

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, 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 (BaFe+zO+v), is a hexagonal plate-shaped crystal with an axis of easy magnetization in the direction perpendicular to the plate surface. A magnetic material for magnetic recording must satisfy the following requirements. The magnetic material should have a moderate coercive force (Hc, usually about 200 to 20,000 e) and as large a saturation magnetization (σ5, as small as 40 em).
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 the second range, the average particle diameter is preferably smaller in terms of noise, and more preferably 0.1 μm or less.

(Problem to be solved by the invention) Ba ferrite (BaFe+zOtq) 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, and various methods have been proposed to reduce the coercive force by substituting a part of Fe with various other metals.

Incidentally, the glass crystallization method, hydrothermal synthesis method, and coprecipitation method have traditionally been used as methods for producing Ba ferrite, but among these methods, the coprecipitation method is used for coercive force control and other purposes. It has many advantages, such as the ability to mix very well with various metals added in small amounts, resulting in uniform ferrite, and the fact that the coprecipitate is a microcrystalline powder, so it can be turned into ferrite at relatively low temperatures. .

However, in general, the particle size of magnetic powder obtained by the coprecipitation method is large, at least 0.15 μm (Japanese Patent Laid-Open No. 61-17
4118), it tends to produce agglomerated powder, contains particles with a particle size of about 0.5 μm, and has a low uniformity of shape (see JP-A-58-2223). It cannot be said that it is a manufacturing method.

(Means for Solving the Problems) As a result of intensive studies aimed at developing magnetic powder for perpendicular magnetic recording with a smaller average particle size than ever before, the inventors of the present invention discovered that a part of Fe could be replaced with a specific metal element. The present inventors have discovered that the object can be achieved by producing substituted hexagonal ferrite magnetic powder by a coprecipitation method, and have completed the present invention.

Thus, according to the present invention, the general compositional formula % represents at least one metal element selected from Ca and Pb, and MI is V, Cr, Mo, W, Ag,
C+L Ge.

Represents at least one metal element selected from Sn, P, Bi and Te, a, b, c,
d, e and f are Fe, Zr, St, respectively
The number of atoms of M", M" 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 to 3.0 and e takes a value of 0.01 to 3.0, r
is the number of oxygen atoms that satisfies the valences of other elements. )
A magnetic powder for magnetic recording having an average particle diameter of 0.1 μm or less is provided.

The magnetic powder of the present invention has an average particle diameter of 0.1 μm or less, and has the coercive force and saturation magnetization required for a magnetic powder for magnetic recording, so it is suitable for perpendicular magnetic recording.

In the present invention, the number of atoms a-e of each component element of the magnetic powder is
must be within the above numerical range; outside this range, not only will the average particle diameter be 0.1 μm or more, but magnetic powder with coercive force and saturation magnetization suitable for magnetic recording magnetic powder will not be obtained. It's hard to get caught.

The preferred proportions of each component in the magnetic powder are a: 8 to 12 degrees, b: 0
．． 02-2.4. c is 0.1 to 1.0. d 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 is manufactured by a conventional coprecipitation method, and includes raw material compounds of each metal element constituting the magnetic powder, an aqueous alkali solution, and a flux (added as necessary when firing the coprecipitate). Conventionally used fluxes and the like are also used.

Raw material compounds for each metal element include oxides, oxyhydroxides, hydroxides, ammonium salts, nitrates, sulfates, carbonates, organic acid salts, halides, salts such as alkali metal salts, free acids, and acid anhydrides. Examples include esters, condensed acids, and the like.

Particularly preferred are water-soluble compounds. The raw material compounds of each metal element are preferably mixed and dissolved in water to form an aqueous solution. 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.

The alkaline component used in the partially alkaline aqueous solution may be any water-soluble one, and examples thereof include alkali metal hydroxides, carbonates, ammonia, ammonium carbonate, and the like.

For example, NaOH* NatCOz + NaHCOs
I KOH, KzCQz + NH4OH, (NHi)
tcQs etc. are used, and the combined use of hydroxide and carbonate is particularly preferred.

Next, 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 washed with water and then separated in a furnace. The cake-like or slurry-like coprecipitate obtained in this way is dried at 600-1100°C for 10 minutes to 3 minutes.
The corresponding hexagonal ferrite magnetic powder is obtained by firing at a high temperature for 0 hours. In addition, when the coprecipitate is calcined in the presence of flux, water-soluble flux (for example, alkali metal halides such as sodium chloride and potassium chloride, halogen salts such as barium chloride and strontium chloride) is added to the washed coprecipitate. Add an appropriate amount of alkaline earth metal salts, sodium sulfate, potassium sulfate, sodium nitrate, potassium nitrate, mixtures thereof, etc.) or wash the coprecipitate obtained from a mixture of an aqueous metal ion solution and an aqueous alkali solution. (After evaporating the water and drying it,
After high-temperature firing at 600 to 1100°C for 10 minutes to 30 hours, the water-soluble flux is washed with water or an acid aqueous solution, separated in a furnace, further washed with water if necessary, and dried to produce the corresponding hexagonal ferrite magnetic powder. get.

(Effects 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 as small as 0.1 am or less, but also has the same particle size as the original particle size. Since it is manufactured by a precipitation method, the manufacturing process is simple and economical, and it is suitable as a magnetic material for perpendicular magnetic recording.

The present invention will be explained in more detail with reference to Examples below. The coercive force and saturation magnetization in the examples were measured using a VSM (vibrating magnetometer) at a maximum applied magnetic field of 10 kOe and 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 l BaC1z ・2Hz0 0.55 mol, ZrO(N
Os) g ・2Hz00.2mol, 5nCffi z
'2HzOO, 5mol and FeCj'+'6uto
A solution A was prepared by dissolving 5.3 moles in 101 distilled water in this order. NaOH17.5 mol, Na2CO34,
72 mol and 0.15 mol of NatSiOs.9Hz0 were dissolved in 151 room temperature distilled water to obtain Solution B. 50
Solution B was gradually added to solution A heated to 0.degree. C., and then stirred at 50.degree. C. for 16 hours. The coprecipitate thus obtained was separated, thoroughly washed with water, dried at 150°C, and heated to 870°C for 2.5
Fired in an electric furnace for an hour. The Ba-ferrite thus obtained has a Ba1. +Fet o, b'lro, as
Indicated by nl, osio, s.

This fine particle powder has a plate shape with an average grain size of 0.064 μm, a coercive force (Hc) of 6750e, and a saturation magnetization (C3
) was 54.8 emu/g.

Comparative Example 1 Ba was prepared in exactly the same manner as in Example 1 except for tin chloride.
-Produced ferrite. The obtained Ba-ferrite is Bat, +Fe+a, hZro, 4sia, 3
It is indicated by.

This fine particle powder has a plate shape with an average particle size of 0.33 μm,
Hc was 10840e and a was 38.6 emu/g.

Example 2 BaCl z ・21zOQ, 55 mol, Zr0(N
(h) z ・2Hz80.4 mol, GeCl1a
0.35 mol and FeCj! x ・6Hz05.25
A solution A was obtained by dissolving the moles in 10 f of distilled water in this order.

17.5 mol of NaOH, 4.72 mol of NatCOx and 0.15 mol of NazSiO:+98z8 at 151
Solution B was obtained by dissolving in distilled water at room temperature. 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 and washed with water, and Na was added as a flux to the cake-like coprecipitate slurry obtained.
After adding 400 g of Cl and thoroughly mixing, water was evaporated to dryness, and the mixture was fired in an electric furnace at 880°C for 2.5 hours. The fired product was washed with water until all soluble materials were removed, separated, and dried.

The Ba-ferrite thus obtained is Ba1.1Fe
Lo, 5Zro, 5Geo, tsia, s.

This fine particle powder has a plate shape with an average particle size of 0.069 μm, Hc is 4410e, and σS is 56.4 emu/
It was 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 M1 component, composition ratio, and type and amount of flux were changed.

From the results of Examples 1 to 6, it can be seen that the magnetic powder of the present invention has an average particle size of 0.1 μm or less and has coercive force and saturation magnetization suitable for perpendicular magnetic recording.

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 component and the composition ratio were changed. Note that the raw material for the MI component is chloride, the raw material for the M1 component is sodium salt for Cr and Te, and V,
Ammonium salts were used for Mo, W and P, nitrates were used for Ag and Bi, and chlorides were used for the other components. Cr, Te, V, Mo.

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

Claims (1)

[Claims] General composition formula Fe_aZr_bSi_cM^ I_dM
^II_eO_f (here, M^I represents at least one metal element selected from Ba, Sr, Ca, and Pb, and M^II represents V, Cr, Mo, W, Ag, Cd, Ge,
Represents at least one metal element selected from Sn, P, Bi, and Te, and a, b, c, d, e, and f are the number of atoms of Fe, Zr, Si, M^I, M^II, and O, respectively. , a is 8 to 12, b is 0.01 to 3.0, c is 0.05 to 2.0, d is 0.5 to 3.0, and e is 0.0
It takes a value of 1 to 3.0, and f is the number of oxygen atoms that satisfies the valences of other elements. ) is 0.
．． Magnetic powder for magnetic recording of 1 μm or less.