JPH01119516A - 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 element in the amts. equiv. to the constituent ratio of the targeted substance, is mixed with the aq. alkali soln. of hydroxide, carbonate, etc., of alkali metal and adjusted to >=5pH value, and the obtd. 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 Mg, Ti, Mn, Co, Ni, Cu, Sb, (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, which has a hexagonal crystal system and uniaxial magnetization anisotropy, such as BaFe, lite (BaFe+zO+), is a hexagonal plate-shaped crystal with an axis of easy magnetization perpendicular to the plate surface, and the coating film This type of magnetic material for perpendicular magnetic recording must satisfy the following requirements. The magnetic material has a moderate coercive force (Ilc, 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 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 in terms of noise, and more preferably 0.1 μm or less.

(Problem to be solved by the invention) Ba ferrite (BaPe+zOt,) 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 Pe 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 being able to mix very well with various metals added in small amounts, resulting in uniform ferrite, and being able to form ferrite at relatively low temperatures because the coprecipitate is a microcrystalline powder. There is.

However, in general, the particle size of magnetic powder obtained by the coprecipitation method is as thick as 0.15 μm at the minimum ((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 inventors have discovered that the object can be achieved by producing substituted hexagonal ferrite magnetic powder using 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 MII is Mg+ Ti, Mn, Co, N
i+ represents at least one metal element selected from Cu, Zn and Sb, a, b, c, d
, e and f are Fe, Zr, Si, M respectively
", M" and the number of atoms of 0, 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 take values of 0.01 to 3.0, and f is the number of oxygen atoms satisfying the valences of other elements. ) 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 size 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 a magnetic powder 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 valence of other elements. In some cases, particles whose crystals do not necessarily have a normal hexagonal plate shape are mixed, but as long as the number of atoms is within the range of the present invention, 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+ NazCOi +NaHCO3,
KOH + KzCOs + NH4OH, (NH4)z
cOz etc. are used, and the combination 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 separated after washing with water. 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 macrogonal 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, a water-soluble flux (for example, an alkali metal halide such as sodium chloride or potassium chloride, or a halogen such as barium chloride or strontium chloride) is added to the washed coprecipitate. Add appropriate amounts 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 a metal ion aqueous solution and an alkaline aqueous solution with water. After drying this by evaporating the water without doing anything,
After high-temperature firing at 600 to 1100"C for 10 minutes to 30 hours, the water-soluble flux is washed and separated with water or acid aqueous solution, and if necessary, after further washing with water, it is dried to obtain the corresponding hexagonal ferrite magnetic powder. obtain.

(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 μm 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 the sake of brevity.

Example I BaCl z' 2820 0.55 mol, Zr0
(N(h)z ・28g00.45mol, Cu(NO
i) z' 3HzOO, 35 mol and FeC1,.5
ozo 5.2 moles to 101! , in this order, to prepare Solution A. NaOH 17.5 mol, Na
, C014,72 mol and NazSi03.9H200
, 3 moles were dissolved in 152 room temperature distilled water to prepare Solution B. After gradually adding liquid B to liquid A heated to 50°C,
Stirred at 50'C for 16 hours. The coprecipitate thus obtained was separated, thoroughly washed with water, dried at 150°C, and heated to 900°C.
It was fired in an electric furnace at °C for 2 hours. Ba obtained in this way
-Ferrite is Bad, +Fe+ o, aZro,
Indicated by qcuo, , sio, b.

This fine particle powder has a plate shape with an average particle size of 0.083 μm, a coercive force (Hc) of 8490e, and a saturation magnetization (σ, ).
was 55.2 emu/g.

Comparative Example 1 Same as Example 1 except that copper nitrate was removed (Ba-
Manufactured ferrite. The obtained Ba-ferrite is B
a1. Indicated by +Fe+o, aZro, ++Sio, b. This fine particle powder has a plate shape with an average particle size of 0.30 μm, Hc is 9570e, σ is 3B, and 2emu
/g.

Example 2 BaCl2 z' 2H! OO, 55 mol, Zr0
(NO+)z ・2HzOO025 mol, N1(NOs
)z・68z0 0.5 mol and FeCj! 3.61
10 of 1zO5.25 moles! were dissolved in distilled water in this order to obtain Solution A. 17.5 mol NaOH, NazCO+
4.72 mol and NazSiOs' 911zO0,
Liquid B was obtained by dissolving 15 mol in distilled water at room temperature.

After gradually adding liquid B to liquid A heated to 50°C,
The mixture was stirred at C for 16 hours. The thus obtained coprecipitate was separated and washed with water. 400 g of NaCl was added as a flux to the cake-like coprecipitate slurry obtained. After thorough mixing, water was evaporated to dryness, and this was heated at 900°C. It was baked in an electric furnace for 2 hours. The fired product was washed with water until all soluble materials were removed, separated, and dried. The Ba-ferrite thus obtained contains Ba, 1Felo, 5Zr
o, sNi 1. osio, denoted by s.

This fine particle powder has a plate shape with an average particle size of 0.060 μm, Hc of 6510e, and as of 55. Oemu/
It was g.

Examples 3 to 6 Ba-
Manufactured ferrite.

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 am or less and has coercive force and saturation magnetization suitable for perpendicular magnetic recording.

Examples 7 to 25 Magnetic powders shown in Table 2 were prepared in exactly the same manner as in Example 2, except that the M1 component and the composition ratio were changed. Note that chloride was used as the raw material for the M1 component, nitrates were used for Mn, Ni, and Cu as raw materials for the MII component, and chlorides were used for the other components.

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 Mg, Ti, Mn, Co, Ni, Cu, Z
represents at least one metal element selected from n and Sb, and a, b, c, d, e and f are Fe, Z, respectively.
is the number of atoms of r, Si, M^I, M^II and O, and a
is 8-12, b is 0.01-3.0, c is 0.05-2
．． 0 and d take values of 0.5 to 3.0, e takes values of 0.01 to 3.0, and f is the number of oxygen atoms satisfying the valences of other elements. ) Magnetic powder for magnetic recording having an average particle diameter of 0.1 μm or less.