JPH04236404A - Ferrite magnetic powder and magnetic recording medium using same - Google Patents

Abstract

PURPOSE:To realize the reduction of the temperature coefficient of coercive force, without decreasing the rectangularity ratio of ferrite magnetic powder of compound type hexagonal system. CONSTITUTION:Hexagonal system ferrite and spinel ferrite are compounded to obtain the title magnetic powder. The compound type magnetic powder contains 0.02-0.95 of Li element in 1mol of alkaline earth ions (one kind selected out of Ba, Sr, Pb and Ca) which are constituent elements of the hexagonal system ferrite. Further it is a characteristic that the ratio of the spinel ferrite phase to the hexagonal system ferrite phase is less than 0.1-2.0mols to hexagonal system ferrite of 1mol. The compound type magnetic powder is dispersed and contained in a magnetic layer to obtain magnetic recording medium. As the result of the above compounding, the rectangularity ratio of magnetic powder can be restrained, and the temperature stability of coercive force also is increased, so that highly reliable magnetic recording function is exhibited.

Description

[Detailed description of the invention]

0001

[Purpose of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite type ferrite magnetic powder of hexagonal ferrite and spinel ferrite suitable for constructing high-density magnetic recording media, and a magnetic recording medium using the same.

0003

2. Description of the Related Art A perpendicular magnetic recording system that uses magnetization in a direction perpendicular to the medium surface, instead of a magnetic recording system that uses magnetization in the in-plane longitudinal direction, is attracting attention as a next-generation high-density magnetic recording system. Such perpendicular magnetic recording media include a Co-Cr metal thin film with an easy axis of magnetization perpendicular to the medium surface, and a hexagonal ferrite magnetic powder that is a plate-shaped crystal with an easy axis of magnetization perpendicular to the plate surface. , recording media coated on a supporting substrate and vertically oriented have been mainly studied.

By the way, in the medium using the above-mentioned hexagonal ferrite magnetic powder, the coercive force (H
It shows a characteristic temperature characteristic in that the value of c) increases as the temperature rises, making it a relatively stable medium against temperature changes.However, from a practical point of view, this magnetic powder also requires further temperature stability. was desired.

[0005]

[Problems to be Solved by the Invention] As a method for improving the temperature stability of the coercive force of the above-mentioned hexagonal ferrite magnetic powder, in addition to the solution of partially replacing Fe with atoms such as Sn, A ferrite magnetic powder has been proposed that is a composite of hexagonal ferrite having a positive temperature coefficient of magnetic force and spinel ferrite having a negative temperature coefficient of coercive force. However, according to the studies of the present inventors, in magnetic powder that is a composite of hexagonal ferrite and spinel ferrite,
Although it is possible to control the temperature coefficient of coercive force to almost zero, increasing the proportion of spinel ferrite tends to decrease the squareness ratio of the magnetic powder and deteriorate the electromagnetic conversion characteristics.

The present invention was made in view of the above circumstances, and by incorporating a predetermined amount of Li element into the above-mentioned composite hexagonal ferrite magnetic powder, it is possible to obtain a magnetic powder without reducing the squareness ratio of the magnetic powder. It was discovered that the temperature coefficient of coercive force can be reduced.

[0007]

[Structure of the invention]

[0008]

[Means for Solving the Problems] The magnetic powder for high-density magnetic recording according to the present invention is a magnetic powder that is a composite of hexagonal ferrite and spinel ferrite, and the composite magnetic powder contains the Li element in a hexagonal manner. Contains 0.02 to 0.95 alkaline earth ions (one selected from Ba, Sr, Pb, and Ca) per mole, which is a constituent element of crystalline ferrite, and has a hexagonal system with a spinel ferrite phase. The ratio to the ferrite phase is 0.1 to less than 2.0 mol per 1 mol of hexagonal ferrite,
Further, the magnetic recording medium according to the present invention is characterized in that the composite magnetic powder is dispersed and contained in the magnetic layer.

[0009] Here, the ratio of the spinel ferrite phase to the hexagonal ferrite phase is defined as the composition of the composite hexagonal ferrite of interest as follows: basic formula of hexagonal ferrite phase + αM1 Fe2 O4 (basic formula of spinel phase) M1 is the value of α when expressed as (one or more elements with an average valence of 2), and in the present invention, α is
It means 0.1 or more and less than 2.0. Also,
The basic formula of the hexagonal ferrite phase is BaO・nFe2O3 in the case of magnetoplumbite ferrite.
(n=5 to 6.0), in the case of M type, BaO・2
It is represented by M2 O.8 Fe2 O3 (M2 is one or more elements having an average valence of 2), but some of these may be substituted with other elements.

[0010] A feature of the present invention is that the squareness ratio of the magnetic powder is improved by incorporating Li into the above-mentioned composite hexagonal ferrite. The alkaline earth ion is selected in a range of 0.02 to 0.95 mol per mol. When the Li content is less than 0.02 mol, the effect of improving the squareness ratio is not so pronounced, and when it is more than 0.95 mol, the particle size distribution deteriorates and the desired function is not exhibited.

On the other hand, in the present invention, the ratio of the spinel ferrite phase to the hexagonal ferrite phase in the magnetic powder is selected within the range of 0.1 or more and less than 2.0. This is because if this ratio is less than 0.1, the temperature coefficient of coercive force will not be sufficiently improved, and if it is more than 2.0, the particle size distribution of the magnetic powder will deteriorate.

0012

[Operation] The magnetic powder for high-density magnetic recording according to the present invention is a magnetic powder that is a composite of hexagonal ferrite and spinel ferrite, and the composite magnetic powder contains a predetermined amount of Li.
By controlling the ratio of the spinel ferrite phase to the hexagonal ferrite phase within a predetermined range while containing the elements, we can suppress the decrease in the squareness ratio of the magnetic powder due to compounding, and at the same time improve the temperature stability of the coercive force. Exhibits enhanced and reliable functionality.

[0013]

[Examples] Examples of the present invention will be described below. Prior to describing specific embodiments, general matters regarding the configuration of the present invention will be described. First, by containing Zn at the same time as Li in the Li-containing composite ferrite magnetic powder, saturation magnetization can be further improved. The Zn content is from 0.1 to Zn/Li molar ratio.
A range of 3.0 is preferred. This is because if the Zn/Li ratio is less than 0.1, the effect of improving saturation magnetization becomes less noticeable, and if it exceeds 3.0, saturation magnetization tends to decrease significantly.

[0014] Furthermore, the Li-containing composite ferrite magnetic powder according to the present invention has an average particle size of 0.02 to 0.2.
μm, preferably 0.04 to 0.1 μm. In other words, when the average particle size is less than 0.02 μm, magnetization is difficult to remain due to the influence of thermal fluctuations, and 0.2 μm
This is because, if it exceeds , there is a tendency for the recording resolution in the short wavelength region to decrease. On the other hand, regarding coercive force,
200-2000 Oe, preferably 400-15
Selected and set to 00 Oe. In other words, the coercive force is 2
Below 00 Oe, magnetization is difficult to remain, and below 2000 Oe
This is because writing with a magnetic head becomes difficult if the value exceeds .

In the present invention, when spinel ferrite is composited, magnetoplumbite ferrite or W-type ferrite is used as the base hexagonal ferrite, as described above. A simple substance or a substituted substance of ferrite is preferable. Specifically, the general formula AO・n(Fe2-x-y M1xM2yO3) (A
:Ba, Sr, Pb, Ca, M1 :Co, Ni, Cu
, Zn, Mn, M2: Ti, Sn, Nb, Sb, Zr
, X: 0 ~ 0.3, Y: 0 ~ 0.3, n=
5 to 6.0).

[0016] Further, as a method for producing the Li-containing composite ferrite magnetic powder, for example,
- Glass crystallization method described in No. 67904 and JP-A-61-
The hydrothermal synthesis-calcination method described in No. 168532 is suitable.

Next, specific examples of the present invention will be described.

[0018] BaCo3, Fe2O3, CoO,
Raw material powders of ZnO, Li2O, and TiO2 were mixed with Ba
:Fe:Co:Zn:Li:Ti molar ratios are as shown in Table 1. Nine types of mixtures including a comparative example were prepared, and each of these mixed powder raw materials was placed in a crucible together with BaO/B2O3 glass. It melted at 1350°C. This melt was rapidly cooled by rolling with twin metal rolls rotating at high speed to form an amorphous material. This amorphous flake is heated to 800℃ in an electric furnace.
The magnetic powder was crystallized in BaO/B2O3 glass at a temperature of . Next, each of these crystallized products was washed with a 10% acetic acid solution to remove the BaO/B2 O3 glass, and then washed with water to produce magnetic powder. As a result of X-ray diffraction, these magnetic powders had peaks corresponding to Ba ferrite and spinel ferrite. Next, the temperature dependence of the saturation magnetization σs, coercive force Hc, and Hc of these magnetic powders was measured using a vibrating sample magnetization measuring device (VSM) with a maximum magnetic field of 10 KOe.
Measured at The temperature measurement of Hc is carried out in the range of 0 to 60℃, and the temperature coefficient dHc/dT is dHc/dT=
It was defined as Hc (60°C) - Hc (0°C)/dT.

[0019] Also, the average particle diameter (Dm) of these magnetic powders
The maximum particle diameter (Dmax) was determined for 400 particles on a transmission electron micrograph taken at a magnification of 100,000 times. The composition and properties of these magnetic powders are summarized in Table 2.

[0020]
Table 1 Ba:Fe:Co
:Li:Zn:Ti Li/Ba
Zn/Li α*
(molar ratio)
(Mole ratio) (Mole ratio) Real 1 1:
10,55:0,85:0.05:0:0.85
0.05 0
0.1 2 1:13,00:0
．． 75:0.50:0:0.750.
50 0 1.0
3 1:14, 31:0.72:0.75
: 0 :0.72 0.75
0 1.5 4
1:15, 35:0.70:0.95:0:0.
70 0.95 0
1.9 Example 5 1:12,80
:0.75:0.30:0.40:0.75
0.30 1.1 1
．． 0 6 1:12,90:0.75:0
．． 40:0.20:0.75 0.40
0.5 1.0 ratio
1 1:10.30:0.85: 0: 0:0
．． 85 0 -
0 comparison 2 1:
16.10:0.70:1.10:0:0.70
1.10 0
2.2 Example 3 1:13.60:
1.90: 0 :0.30:0.70 0
-1.5
α* is the molar ratio of spinel ferrite to hexagonal ferrite.

Table 2
Saturation magnetization Coercive force Squareness ratio Temperature coefficient of Hc Average grain size Maximum grain size
σs (emu/g) Hc (Oe)
(Oe/℃)
Dm (nm) Dmax (nm) Actual 1
57 850 0
．． 49 3.8 50
122 2 58
860 0.49
1.5 52
122 3 59
830 0.50 1.
0 51 131
4 60 86
0 0.50 0.4
55 150 Example 5
65 850
0.49 1.1
51 122 6
63 840 0.4
9 1.3 52
125 ratio 1 57
760 0.47
4.9 50 1
22 comparison 2 61
870 0.50 0.3
68 370 Example 3 58 840
0.42 1.2
52 136 A magnetic paint having the following composition was prepared using each of the magnetic powders obtained above, and after filtering through a 1 μm filter, it was applied onto a polyethylene terephthalate film. That is, 100 parts by weight of magnetic powder, 10 parts by weight of vinyl chloride vinyl acetate copolymer, 10 parts by weight of polyurethane, 4 parts by weight of lecithin, 93 parts by weight of methyl isobutyl ketone, 93 parts by weight of toluene, and Coronate L (trade name, Nippon Polyurethane Co., Ltd.) A magnetic coating material was prepared using 3 parts by weight of a polyisocyanate compound (manufactured by Polyisocyanate Compound) according to a conventional method.

Next, the coated surface of the polyethylene terephthalate film coated with the magnetic paint is coated with four
The magnetic powder was dried while being applied with a magnetic field of 000 Oe to orient it in the magnetic field, and the surface was smoothed by calendering. Each of these pieces was cut into 1/2 inch width pieces to serve as media samples. After performing magnetic recording on each of these media samples, the reproduction output was measured to examine the characteristics of the tape. The magnetic head used at this time was a ring-type ferrite head with a gap width of 0.3 μm and a track width of 35 mm.
μm, and the relative speed of the head and tape is 3.75 m.
/sec, and the recording frequency was 5 MHz. Table 3 summarizes the magnetic properties and reproduction output values of these media.

[0023]
Table 3 Media saturation magnetization
Media coercive force Temperature coefficient of Hc Squareness ratio Media output Ms (emu/g) H
c(Oe) (Oe/℃) (Vertical) (dB) 1 13
0 880 3
．． 0 0.75 +0.1
Real 2 132 8
70 0.8 0.
75 +0.2 3 1
35 830
0.3 0.76 +0.3
Example 4 137
840 -0.3 0
．． 78 +0.5 5
150 850
0.6 0.75 +1.
2 6 140
850 0.7
0.76 +0.7 ratio 1
128 860
4.5 0.73
0 comparison 2 134
840 -0.5
0.82 -3.4 Example 3
132 850
0.6 0.63
-1.5 In Table 3, the numbers of Examples and Comparative Examples correspond to the numbers in Tables 1 and 2 above.

As shown in Table 1, the magnetic powder of the present invention is
By combining hexagonal ferrite and spinel ferrite, not only the temperature dependence of coercive force is improved compared to single-phase hexagonal ferrite (see magnetic powder in Comparative Example 1), but also the hexagonal By controlling the ratio α of crystalline ferrite and spinel ferrite within a predetermined range,
The spread of particle size distribution due to compositing (see magnetic powder of Comparative Example 2) is suppressed. Furthermore, the magnetic powder according to the present invention is
By containing Li, the decrease in squareness ratio due to compositing (see magnetic powder of Comparative Example 3) is also suppressed. Due to these characteristics, the medium using the magnetic powder of the present invention is
This medium not only has a small temperature dependence of coercive force, but also has excellent high-density characteristics.

[0025]

As explained above, according to the present invention, in a composite magnetic powder of hexagonal ferrite and spinel ferrite, by containing a predetermined amount of Li in the magnetic powder, the square shape of the magnetic powder can be improved. By improving the ratio and controlling the composite ratio of the hexagonal ferrite phase and the spinel ferrite phase, deterioration of the particle size distribution of the magnetic powder due to composite is also suppressed. By improving the squareness ratio and suppressing deterioration of the particle size distribution, it is possible to provide a magnetic recording medium with small temperature dependence of coercive force and excellent high-density recording characteristics.

Claims (2)

[Claims] 1. A composite magnetic powder of hexagonal ferrite and spinel ferrite, wherein the magnetic powder contains 0.02 to 0.0.0. A composite hexagonal crystal for high-density magnetic recording, which contains 95 moles of Li element and has a content of spinel ferrite in the range of 0.1 to less than 2.0 moles per mole of hexagonal ferrite. ferrite magnetic powder. 2. A composite magnetic powder of hexagonal ferrite and spinel ferrite, wherein the magnetic powder contains 0.02 to 0.0.0. A composite hexagonal ferrite magnetic powder for high-density magnetic recording containing 95 mol of Li element and having a spinel ferrite content in the range of 0.1 to less than 2.0 mol per 1 mol of hexagonal ferrite. 1. A magnetic recording medium comprising: a magnetic layer comprising a magnetic layer on a non-magnetic substrate surface.