JPH0580729B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to magnetic powder for magnetic recording, and more particularly to hexagonal ferrite magnetic powder comprising 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 having a hexagonal crystal system and uniaxial magnetization anisotropy, such as Ba ferrite (BaFe ₁₂ O ₁₉ ), is a hexagonal plate-shaped crystal with an axis of easy magnetization perpendicular to the plate surface. This material satisfies the above requirements as a type of magnetic material for perpendicular magnetic recording. The magnetic material should have an appropriate coercive force (Hc, usually about 300 to 2000 Oe) and as large a saturation magnetization (σs) as possible, and in relation to the recording wavelength, the average particle diameter of the magnetic powder is 0.3 μm or less. It is necessary that By the way, Ba ferrite has a coercive force of 5000 Oe or more, which is too large to be used as a magnetic material for magnetic recording as it is, so a method has been proposed to reduce the coercive force by replacing part of Fe with Co and Ti. (For example, JP-A-55-86103, JP-A-59-
Publication No. 175707, IEEE Trans. on Magn., MAG
-18, 16 (1982) P.1122, etc.). (Problems to be Solved by the Invention) By the way, in known magnetic powders in which a part of Fe is replaced with Co and Ti, even if the composition ratio of the constituent elements is almost the same, the manufacturing method and manufacturing conditions of the magnetic powder are different. As shown in Table 1, the coercive force and saturation magnetization will vary if the values are different. This means that a part of Fe is Co
This shows that the control of coercive force is still insufficient just by replacing with Ti and Ti.

[Table] (Means for solving the problems) As a result of intensive study to develop magnetic powder for perpendicular magnetic recording that does not have these conventional drawbacks, the present inventors found that in addition to the conventional Co and Ti Furthermore, they discovered that it is effective to add a specific metal, leading to the completion of the present invention. That is, according to the present invention, the general compositional formula Fe _a Co _b Ti _c M〓 _d M〓 _{e Of}
Represents at least one metal element selected from Mo, W, Ru, Rh, Pd and Re, a, b, c,
d, e and f are Fe, Co, Ti, M〓, M〓 respectively
and the number of atoms of O, a is 8 to 11.8, b is 0.05
~2.0, c is 0.05~2.0, d is 0.5~3.0 and e is 0.01
It takes a value of ~2.0, and f represents the number of oxygen atoms satisfying the valences of other elements. ) and has an average particle diameter of 0.01 to 0.3 μm. In the present invention, it is necessary that the number of atoms a to e of each component element of the magnetic powder is within the above numerical range, and outside this range, the magnetic powder has coercive force and saturation magnetization suitable for magnetic recording. Magnetic powder is difficult to obtain. The preferable ratio of each component of the magnetic powder is a of 8 to
11.8, b is 0.1-1.5, c is 0.1-1.5, d is 0.8-2.0
and e takes a value of 0.02 to 1.0, and f is the number of oxygen atoms satisfying the valences of other elements. The magnetic powder of the present invention may contain particles whose crystals do not have a normal hexagonal plate shape depending on the manufacturing method or manufacturing conditions. As long as it is within the scope of the invention, the object of the invention can be fully achieved. According to the magnetic powder of the present invention, even if the manufacturing method and manufacturing conditions are different, it has the coercive force and saturation magnetization that must be possessed as a magnetic powder for magnetic recording. This is considered to be because the magnetic powder according to the present invention has a completely different function from the conventional magnetic powder containing Co and Ti. The magnetic powder according to the present invention can be prepared by various methods known in this field, such as glass crystallization method, coprecipitation method,
It can be produced by a flux method, a hydrothermal synthesis method, etc. The raw materials for each element used include oxides, ammonium salts, nitrates, carbonates,
Examples include organic acid salts, salts such as halides, free acids, acid anhydrides, and condensed acids. The magnetic powder according to the present invention is a plate-shaped particle having an axis of easy magnetization in a hexagonal C-plane, and is suitable as a magnetic material for perpendicular magnetic recording. Among the magnetic powders according to the present invention, especially coercive force 300~
Those with 2000 Oe and saturation magnetization of 40 emu/g or more are prized. 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 by filling a glass test tube with an inner diameter of 5 mm and a length of 5 cm with the obtained magnetic powder, and using a DC magnetization characteristic measuring device at a maximum applied magnetic field of 3500 Oe. 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. X-ray diffraction was performed on the Examples listed here, and in all cases the crystal phase of the magnetic powder was hexagonal ferrite having a magnetoblanbite structure. Further, the experimental formula for magnetic powder shown in the examples uses the atomic ratio of each metal 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 BaCl ₂ 2H ₂ O 0.55 mol, TiCl ₄ 0.375 mol,
0.375 mol of CoCl ₂ .6H ₂ O, 0.075 mol of Rh(NO ₃ ) ₃ and 5.25 mol of FeCl ₃ .6H ₂ O were dissolved in this order in 10 distilled water, and this was used as liquid A. 17.5 moles of NaOH and 4.72 moles of Na ₂ CO ₃ were dissolved in distilled water at room temperature, 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 pH after stirring was 10.35. 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 for 2 hours. thus obtained
Ba-ferrite is represented by Ba _1.1 Fe _10.5 Co _0.75 Ti _0.75 Rh _0.15 . This fine particle powder had a plate shape with an average particle size of 0.08 μm, a coercive force of 7650 Oe, and a saturation magnetization of 56 emu/g. Comparative Example 1 Ba-ferrite was produced in exactly the same manner as in Example 1 except that rhodium nitrate was removed. obtained
Ba-ferrite is indicated by Ba _1.1 Fe _10.5 Co _0.75 Ti _0.75 . This fine particle powder was plate-shaped with an average particle size of 0.25 μm, Hc was 444 Oe, and σs was 35 emu/g. Example 2 BaCl ₂ 2H ₂ O 0.55 mol, TiCl ₄ 0.375 mol,
0.375 mol of CaCl ₂ .6H ₂ O, 0.075 mol of Rh(NO ₃ ) ₃ and 5.25 mol of FeCl ₃ .6H ₂ O were dissolved in this order in 10 distilled water, and this was used as liquid A. Dissolve 17.5 moles of NaOH and 4.72 moles of Na ₂ CO ₃ in 15 ml of distilled water,
This was designated as liquid B. After adding liquid A and liquid B heated to 50°C to an autoclave and stirring at 300°C for 4 hours,
This was cooled to room temperature. The pH at this time was 10.44. After washing the precipitate thus obtained thoroughly with water,
It was dried at 150°C and heat treated in an electric furnace at 750°C for 8 hours. The Ba-ferrite thus obtained has Ba _1.1
Fe _10.5 Co _0.75 Ti _0.75 Rh _0.15 . This fine particle powder was plate-shaped with an average particle size of 0.10 μm, Hc was 780 Oe, and σs was 54 emu/g.
From this result, it can be seen that magnetic powders having almost the same magnetic properties can be obtained whether the hydrothermal synthesis method of this example is used or the coprecipitation method of Example 1 is used. Comparative Example 2 Ba-ferrite was produced in exactly the same manner as in Example 2, except that rhodium nitrate was removed. The Ba-ferrite obtained is indicated by Ba _1.1 Fe _10.5 Co _0.75 Ti _0.75 . The average particle size of this fine powder is 0.33μ
m plate shape, Hc is 225Oe, σs is 21emu/g
It was hot. Example 3 Ba-ferrite was produced in exactly the same manner as in Example 1, except that the amount of NaOH in liquid B was changed to 25.0 mol. This fine particle powder was plate-shaped with an average particle size of 0.10 μm, Hc was 754 Oe, and σs was 55 emu/g. Comparative Example 3 Ba-ferrite was produced in exactly the same manner as in Comparative Example 1, except that the amount of NaOH in liquid B was changed to 25.0 mol. This fine particle powder had a plate shape with an average particle size of 0.13 μm, Hc of 920 Oe, and σs of 23 emu/g. From the results of Examples 1 to 3, it can be seen that the magnetic powder according to the present invention has almost the same performance even if the manufacturing conditions are different. Examples 4 to 18 M〓Component M〓Magnetic powders shown in Table 2 were prepared in the same manner as in Example 1, except that the components and composition ratio were changed. In addition, the raw material for the M〓 component is chloride,
The raw materials for the M component are Mo and W, which are oxides.
In other cases, chloride was used. However, MoO ₃ and
WO ₃ was dissolved in liquid B.

【table】

Claims (1)

[Claims] 1. Represented by the following general compositional formula, and having an average particle size of
Magnetic powder for magnetic recording characterized by having a particle size of 0.01 to 0.3 μm Fe _a Co _b Ti _c M〓 _d M〓 _{e Of} (here, M〓 is at least one kind selected from Ba, Sr, Ca, and Pb) represents a metal element; M represents at least one metal element selected from Mo, W, Ru, Rh, Pd, and Re;
b, c, d, e and f are Fe, Co, Ti, respectively
M〓, M〓 and the number of atoms of O, a is 8 to 11.8,
b takes a value of 0.05 to 2.0, c takes a value of 0.05 to 2.0, d takes a value of 0.5 to 3.0, and e takes a value of 0.01 to 2.0, and f is the number of oxygen atoms satisfying the valences of other elements. ). 2 a is 8-11.8, b is 0.1-1.5, c is 0.1-1.5,
2. The magnetic powder for magnetic recording according to claim 1, wherein d takes a value of 0.8 to 2.0, e takes a value of 0.02 to 1.0, and f is the number of oxygen atoms satisfying the valences of other elements. 3 Coercive force is 300 to 2000 Oe and saturation magnetization is
The magnetic powder for magnetic recording according to claim 1, which has an amount of 40 emu/g or more.