JPH10261514A - Magnetic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extremely reduce the deterioration of the amount of saturated magnetization even after storage for al long period of time under a high temperature and a high humidity by carrying inorganic powder in magnetic power mainly comprising Mn and Bi. SOLUTION: As inorganic powder to be carried in magnetic power mainly comprising Mn and Bi, the oxide powder of silica or alumina or metal powder such s nickel, tin or copper is desired to be used. Mn and Bi are made to alloy ingots by a powder metallurgy method, arc furnace, high frequency melting furnace, melt quenching method and so forth and the ingots are crushed and MnBi powder is synthesized. Thereafter, for example, mixed type mixing machines using such as a ball mill, planetary ball mill and so forth. Or the powder is placed in a dry type mixer such as jet mill or Henschel mixer, is mixed in inert gas atmosphere, and inorganic powder is carried by MnBi powder. Because of this, corrosion by moisture or oxygen is restricted by inorganic powder carried by magnetic powder mainly comprising Mn and Bi, and the deterioration of the amount of saturated magnetization can be reduced even through the powder is stored for a long period of time under high temperature and high moisture atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic material mainly composed of Mn and Bi, and more particularly, to the magnetic material having excellent corrosion resistance.

[0002]

2. Description of the Related Art Magnetic recording media are widely used as video tapes, floppy disks, credit cards, and the like because recording and reproduction are easy. However, since recording and reproduction are easy, in credit cards and the like, accidents and crimes such as data being accidentally erased or intentionally rewritten occur frequently. Particularly, credit cards and prepaid cards are used. Crimes that rewrite data and other data and misuse it frequently occur, and this has become a major social problem.

To prevent this, a magnetic recording medium using a MnBi magnetic powder as a recording element, which has the characteristic that once recorded, it cannot be easily rewritten at room temperature, has been proposed. (Special Publication 57-389
No. 62, Japanese Patent Publication No. 54-33725, Japanese Patent Publication No. 52-46
No. 801, JP-B-59-31764, JP-B-54-1
No. 9244, Japanese Patent Publication No. 57-38963)

[0004]

However, the MnBi magnetic powder used as a recording element of this type of magnetic recording medium has a drawback that its magnetic properties deteriorate due to corrosion and deterioration due to moisture and oxygen. In order to prevent corrosion of such MnBi magnetic powder, various anticorrosives are added,
Attempts have been made to provide a corrosion prevention coating on the particle surface of Bi magnetic powder (Japanese Patent Publication No. 60-57127).
However, these methods still do not have sufficient corrosion resistance under high temperature and high humidity.

The present invention has been made as a result of various studies in view of the present situation. By supporting an inorganic powder on a magnetic powder mainly composed of Mn and Bi, it can be stored for a long time under high temperature and high humidity. Another object of the present invention is to provide a magnetic material mainly composed of Mn and Bi in which deterioration of the saturation magnetization is extremely small.

[0006]

The magnetic material mainly comprising Mn and Bi of the present invention has an inorganic powder supported on a magnetic powder mainly composed of Mn and Bi.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the magnetic material mainly comprising Mn and Bi of the present invention, the inorganic powder is supported on a magnetic powder mainly comprising Mn and Bi.
Suppressed by the inorganic powder supported on the magnetic powder mainly composed of n and Bi, a magnetic material mainly composed of Mn and Bi can be obtained in which the deterioration of the saturation magnetization is extremely small even after long-term storage at high temperature and high humidity. .

Here, the magnetic material mainly composed of Mn and Bi includes a material to which a transition element of Ni, Fe or Co and a rare earth element such as Sm, La or Gd are added for the purpose of improving magnetic properties. .

Inorganic powders supported on magnetic powders mainly composed of Mn and Bi include silica, alumina,
Site, titanium oxide, barium sulfate, calcium carbonate,
Oxide powders such as antimony oxide, zirconia oxide, zinc oxide and tin oxide, metal powders such as nickel, tin and copper are preferably used.In addition, barium ferrite and hexagonal ferrite powders such as strontium ferrite,
Magnetic oxide powders such as gamma iron oxide, magnetite, gamma iron oxide magnetite, chromium dioxide, cobalt-containing iron oxide, alloy magnetic powders such as iron-cobalt and iron-Ni, compound magnetics such as samarium cobalt and neodymium iron boron One or more powders can be used alone or in combination.

The particle diameter of such an inorganic powder is 1/1 / the particle diameter of the magnetic powder mainly composed of Mn and Bi after pulverization.
Particles having a particle diameter of 20 to 1/2 are preferably used, and the particle diameter of the inorganic powder is one of that of the magnetic powder mainly composed of Mn and Bi.
When the ratio is / 20 or more, the aggregation of the inorganic powder is suppressed and the handling becomes easy. When the ratio is 1/2 or less, the surface of the magnetic powder mainly composed of Mn and Bi can be uniformly covered.

The amount of the inorganic powder to be supported is as follows:
The content is preferably 1 to 100% by weight based on the magnetic powder mainly containing Mn and Bi, and when the content is 1% by weight or more, the original characteristics of the magnetic powder mainly containing Mn and Bi can be sufficiently exhibited. By setting the content to not more than the weight%, excellent corrosion resistance due to the support of the inorganic powder can be obtained. This ratio can be determined by XMA analysis from the Mn strength of the magnetic powder mainly composed of Mn and Bi and the strength of other inorganic powders.

The size of the magnetic material in which the inorganic powder is supported on the magnetic powder mainly composed of Mn and Bi is preferably in the range of 0.01 μm to 20 μm. By doing so, the stability of the particles is improved, and when the particle size is 20 μm or less, good surface properties can be obtained when a magnetic recording medium is used.

A magnetic material in which an inorganic powder is supported on such a magnetic powder mainly composed of Mn and Bi is firstly made of Mn and Bi.
Into an alloy ingot by powder metallurgy, an arc furnace, a high-frequency melting furnace, a melting and quenching method, and the like. .

For example, Mn of 100 to 300 mesh
The powder and Bi powder are mixed well in an inert atmosphere. M
The ratio of n to Bi is from 45:55 to 60:40 in molar ratio.
The Bi powder used as a raw material may be one that has been pulverized in advance, or a lump such as flakes or shots may be pulverized and pulverized. In the case of synthesis by a sintering reaction, the reaction is greatly affected by the surface properties of the raw material. Therefore, it is preferable to remove the oxide film on the surface of the raw material. It is preferable to perform a surface treatment performed by powder metallurgy, such as degreasing with a solvent. The mixing can be performed by any means such as an automatic mortar and a ball mill.

The raw material after mixing is formed into a molded body by using a pressure press, whereby the sintering reaction is promoted, and a uniform MnBi ingot is produced. The pressing force at this time is preferably 1 to 8 t / cm ^{2. If} the pressing force is low, uniformity of the MnBi ingot cannot be obtained.
If the pressure is too high, MnB
The characteristics of the i ingot do not improve.

Further, as another method for producing a molded body, it is preferable to dissolve in an inert atmosphere using a high-frequency melting furnace and uniformly mold the same, and to combine a high-frequency melting furnace and an atomizing spray device to form a spherical MnBi ingot powder. A body may be made.

The obtained molded body is sealed in a glass container or a metal container, and the inside of the container is placed in a vacuum or an inert gas atmosphere to prevent oxidation during the heat treatment. Heat treatment is performed for up to 500 hours. When the temperature of this heat treatment is low, the heat treatment takes a long time, and the amount of magnetization of the obtained MnBi ingot also becomes low. Conversely, if the heat treatment temperature is too high, Bi will melt,
A uniform MnBi ingot cannot be obtained.

The MnBi ingot thus produced is taken out and roughly pulverized in an inert gas atmosphere using an automatic mortar or the like to reduce the particle diameter to 500 μm or less.
Fine particles can be formed by wet pulverization using a ball mill, a planetary ball mill, or the like, or dry pulverization such as a jet mill.
Originally, MnBi has a hexagonal structure, and thus has a property of being cleaved in a flaky shape, so that it is not necessary to pulverize with high energy. As a liquid in the case of wet pulverization, a solvent containing no water such as toluene is used, and in the case of dry pulverization, an inert gas atmosphere is used. The particle size after pulverization is about 0.05 to 10 μm, and the control depends on the pulverization conditions.
Can be If the particle size is smaller than 0.05 μm, the saturation magnetization of the finally obtained magnetic material is reduced, and
If it exceeds m, the coercive force of the magnetic material finally obtained is low, and the surface smoothness of a magnetic recording medium using this magnetic material as a powder is reduced, so that sufficient recording cannot be performed.

The method of supporting the inorganic powder on the MnBi powder thus obtained is not particularly limited, but a method based on mechanical action is preferable in consideration of productivity.
MnB is charged into a wet mixer using a ball mill, a planetary ball mill or the like, or a dry mixer such as a jet mill or a Henschel mixer and mixed in an inert gas atmosphere.
An inorganic powder can be supported on the i-powder.

The same effect can be obtained by simultaneously or continuously performing the step of supporting the inorganic powder on the MnBi powder and the step of pulverizing the MnBi ingot.

The magnetic material obtained by carrying the inorganic powder on the magnetic powder mainly composed of Mn and Bi thus obtained is kept in an atmosphere at a temperature of 60 ° C. and a humidity of 90% for one week, reflecting the excellent corrosion resistance. The deterioration rate of the saturation magnetization at this time is 30% or less.

Further, an inert gas containing a certain amount of oxygen, for example, oxygen is supplied from 100 ppm to 10,000 pp.
It is preferable to perform a stabilizing treatment such as a step of gradually contacting the powder with a nitrogen gas, an argon gas, or air containing about m or heating in air.

[0023]

Next, an embodiment of the present invention will be described. Example 1 Mn flake (Fluuchi Chemical Co .; purity 99.9%), B
The i-shot (Furuuchi Chemical Co., Ltd .; purity 99.9%) was pulverized using a mortar, sieved with 100 mesh, weighed 30.3 parts by weight of Mn powder and 94.0 parts by weight of Bi powder,
Mix well using a mortar.

Next, this was subjected to 4 t /
At a pressure of cm ² , a cylinder was molded into a column having a diameter × length of 6 cm × 10 cm, and the molded body was vacuum-sealed in a Pyrex glass tube and heat-treated at 265 ° C. for 10 days in an electric furnace.
An MnBi ingot was produced.

Next, the obtained MnBi ingot was roughly pulverized using a mortar in an inert atmosphere using a glove box, and further reduced to 500 μm or less by a sieve. This was stirred for 200 r in toluene using a planetary ball mill.
Milled for 2 hours at pm.

Next, the MnBi powder was taken out in a state of being immersed in toluene, transferred to a processing vessel, and vacuum dried at 80 ° C. for about 2 hours. After drying, 80 parts by weight of MnBi powder having a particle diameter of 2.0 μm and TiO ₂ powder having a particle diameter of 0.2 μm in a nitrogen gas atmosphere were used.
Put the parts by weight in a Henschel mixer and add 4 parts in nitrogen gas.
The mixture was taken for a period of time and vacuumed.

Next, the pressure is reduced in vacuum with the container kept in the same container, air is gradually introduced so that the temperature of the powder does not reach 30 ° C. or more, the pressure is returned to the atmospheric pressure, and TiO ₂ is supported on the MnBi powder. Magnetic materials were manufactured.

Example 2 In the step of supporting the inorganic powder in Example 1, TiO 2 was used.
MnBi was prepared in the same manner as in Example 1 except that the same amount of barium ferrite powder having a particle size of 0.3 μm was used instead of the _two powders.
A magnetic material having barium ferrite supported on powder was produced.

Example 3 Mn flake (manufactured by Furuuchi Chemical Co .; purity 99.9%), B
The i-shot (Furuuchi Chemical Co .; purity 99.9%) was pulverized using a mortar, sieved with 100 mesh, and 30.2 parts by weight of Mn powder and 94.0 parts by weight of Bi powder were weighed.
Mix well using a mortar.

Next, this was placed in a crucible made of mullite porcelain, heated and mixed by high-frequency induction heating at a frequency of 3 kHz and an output of 20 kW, and cooled in a furnace to obtain a molded body. The molded body was heat-treated at 280 ° C. for 2 days in an electric furnace in an argon gas atmosphere to produce a MnBi ingot.
Next, the MnBi ingot was pulverized in the same manner as in Example 2, and further an inorganic powder was supported thereon.
A magnetic material having barium ferrite having a particle size of 0.3 μm supported on nBi powder was manufactured.

Example 4 Mn flake (manufactured by Furuuchi Chemical Co .; purity 99.9%), B
The i-shot (Furuuchi Chemical Co., Ltd .; purity 99.9%) was pulverized using a mortar, sieved with 100 mesh, and 30.2 parts by weight of Mn powder and 94.0 parts by weight of Bi powder were weighed.
Mix well using a mortar.

Next, this was put into a crucible made of mullite porcelain and subjected to high-frequency induction heating at a frequency of 3 kHz and an output of 20 kW to melt a Mn-Bi-based molten metal.
Next, the molten metal was allowed to flow down from the lower part of the crucible, and spray quenching was performed by ejecting argon gas toward the molten metal to obtain a spherical molded body. This compact was heat-treated at 280 ° C. for 8 hours in an electric furnace in an argon gas atmosphere to produce a MnBi ingot.

The obtained MnBi ingot was sifted through a sieve.
00 μm or less, then 80 parts by weight of MnBi powder and particle size
20 parts by weight of barium ferrite powder of 0.3 μm is put into a jet mill pulverizer, and a nitrogen gas pressure is applied in a nitrogen gas atmosphere.
Mixing and pulverization were performed simultaneously at a pressure of 6.0 Kg / cm · f, and the mixture was taken out into a container that could be evacuated.

Next, the pressure is reduced in vacuum with the container kept in the same container.
Air was gradually introduced so that the temperature of the powder did not reach 30 ° C. or higher, and the pressure was returned to the atmospheric pressure to produce a magnetic material in which barium ferrite was supported on MnBi powder. The size of the magnetic material of only MnBi powder is about 2.5 μm.
Met.

Example 5 Same as Example 4 except that in the step of supporting the inorganic powder on the surface in Example 4, 60 parts by weight of MnBi powder and 40 parts by weight of barium ferrite powder having a particle size of 0.3 μm were used. Thus, a magnetic material having barium ferrite supported on MnBi powder was produced. In addition, Mn of this magnetic material
The size of the Bi powder alone was about 2.5 μm.

Comparative Example 1 A MnBi ingot was prepared in the same manner as in Example 1, and the MnBi ingot was further pulverized and then taken out into a vacuum vessel. Next, the mixture is dried under reduced pressure at 80 ° C. in the same container and allowed to cool to room temperature.
Air was gradually introduced so that the temperature did not exceed ℃, and the pressure was returned to atmospheric pressure.

With respect to the magnetic materials obtained in each of the examples and comparative examples, the composition, particle size, magnetic characteristics, and temperature
The deterioration rate of the saturation magnetization when kept in an atmosphere at 90 ° C. and a relative humidity of 90% for one week was examined. Table 1 below shows the results.

[0038]

FIG. 1 shows an electron micrograph of the magnetic material obtained in Example 4, and FIG. 2 shows an electron micrograph of the magnetic material obtained in Comparative Example 1. FIG. 1 shows that 0.3 μm barium ferrite is carried around a magnetic powder mainly composed of Mn and Bi, so that corrosion by water or oxygen can be prevented. FIG. 2 shows a magnetic powder mainly composed of MnBi, which has poor corrosion resistance in a bare state.

[0040]

As is clear from Table 1 and FIGS. 1 and 2, the magnetic material obtained by the present invention in which the inorganic powder such as another oxide is supported on the surface of the magnetic powder mainly composed of MnBi is as follows. Even when maintained at high temperature and high humidity while maintaining high saturation magnetization and coercive force, there is little deterioration of saturation magnetization, which indicates that excellent corrosion resistance is exhibited.

[Brief description of the drawings]

FIG. 1 is an electron micrograph of a magnetic material obtained in Example 4.

FIG. 2 is an electron micrograph of the magnetic material obtained in Comparative Example 1.

Claims (3)

[Claims] 1. A magnetic material comprising an inorganic powder supported on a magnetic powder mainly composed of Mn and Bi. 2. The magnetic material according to claim 1, wherein the inorganic powder is at least one of an oxide powder and a metal powder. 3. The magnetic material according to claim 1, wherein the inorganic powder is an inorganic powder having a particle diameter of 1/20 to 1/2 of a particle diameter of a magnetic powder mainly composed of Mn and Bi.