JPS61234506A - Magnetic material and manufacture thereof - Google Patents

Abstract

PURPOSE:To enable the remarkable reduction of noise while restraining the decline of output of the electromagnetic conversion characteristics to the possible minimum by forming the material out of the ferromagnetic minute particles including the iron carbide having a needle-form property. CONSTITUTION:The surface of alpha-oxy-iron hydroxide or that in which an element selected from Al, Si and etc. was coprecipitated is coated with the element selected from B, Al, Si and etc. for avoidance of sintering, maintenance of shape, control of coersive force, improvement in erosion resistance, and etc. Then the dried surface-modified alpha-oxy-iron hydroxide is milled and calcined into a surface-modified alpha-oxy-iron hydroxide. Next, the surface-modified powder is dilluted by a mixed gas of a reducable gas and a carbonizable gas. If necessary by an inert gas, to cause a gas-phase contact reaction and accordingly, needle-form minute particles including iron carbide showing ferromagnetic property are manufactured.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a magnetic material and a manufacturing method thereof.

This material can be suitably used as a magnetic material in a magnetic recording medium suitable for high-density recording mainly for audio and video.

<Prior Art> Magnetic powders useful as magnetic tapes and magnetic recording media were once mainly composed of γ iron monoxide. In recent years, demand has increased for high-density recording media for VTRs and high-end audio, and metallic iron or cobalt, which is obtained by gas-phase catalytic reduction reaction of iron oxyhydroxide or iron oxide powder with a reducing gas, has recently become desirable. Alternatively, magnetic powders having a high coercive force and mainly composed of an alloy of nickel and iron have come to be used. The coercive force of metal magnetic fine particles has strong shape anisotropy, so it depends on the particle size, acicularity, etc., but for tape recording, an appropriate coercive force is required in consideration of the capabilities of the playback head and erase head. It is. Magnetic recording media, whether used for audio or video, are required to have high output and low noise over a wide recording frequency band. In other words, the shape of magnetic powder tends to become finer.In addition, it is desired to further improve the affinity and dispersibility with paint resins, as well as the orientation and filling properties of coating films, and binder resins and various additives. Research is being carried out to improve the paint dispersion and media processing technology.
= For example, Akashi Okabe, "Advances in magnetic tape," Journal of the Japan Society of Applied Magnetics, 7(3), 185 (1983), ).

Therefore, increasing the Hc value as much as possible within the permissible range of magnetic powder and making it finer are extremely rate-limiting elemental technologies for realizing high-density recording.

In the case of acicular metal powder particles whose main component is iron, the thickness may vary depending on the manufacturing method (although there is room for change).
Overall, the He- value mentioned above is almost determined by the values of the major axis diameter (L) and minor axis diameter (=D) or their axial ratio (L/D'), for example, L/D: For acicular fine particle systems of around 10 or more, L: around 1μ and Hc-value: 500 to 70
About 00e, L: around 0.5μ, Hc-value: 1000
From about 12000e to about 1400 at L: 0.1μ
A value of about 16,000e to 16,000e is normally achieved.

Conventionally, the techniques for reducing the particle size while maintaining the shape of magnetic powder and having an appropriate coercive force include (1) a method of designing an extremely low axial ratio (2) a method of designing a large amount of Ni-component. Further, (3) a method for producing semimetallic alloyed particles based on the introduction of Si, B, P, C, N, etc. is also known.

In (1), by reducing the shape anisotropy,
The principle is to suppress the ferromagnetic expression mechanism, and (2)
This is a method that actively utilizes the fact that the magnetic anisotropy decreases due to the magnetic dilution caused by the lattice substitution of the body-centered cubic crystal (:bcc) formed by the Fe-component due to Ni. However, when processed into a tape medium, sufficient orientation cannot be achieved, and the residual magnetic flux density (:Br) and maximum magnetic flux density (
:Bm): There is a drawback that the Br/Bm value, that is, the squareness ratio thereof is greatly reduced.

In (3), the starting material is various iron oxyhydroxides, and even if a compound containing B, Si, and P is surface-modified, the oxides can be stopped by a gas phase catalytic reaction mainly using hydrogen gas. Therefore, their introduction is impossible. A gas phase catalytic reaction using expensive borane gas, silane gas, and phosphine gas will be performed. Only the remaining N and C can be introduced into the iron by gas phase catalytic reaction because their raw material gases are inexpensive, but since ammonia is used as a nitriding agent to introduce N, the production equipment It was necessary to take special anti-corrosion measures, which was impractical when considering industrial production.

[Problems to be Solved by the Present Invention] Regarding acicular magnetic powder as a magnetic material for high-density magnetic recording media mainly intended for audio and video, its particle size and magnetic properties, especially coercive force Hc - The design technology that independently controls the value is one of the ultimate elemental technologies regarding magnetic powder. This can be positioned as one of the most awaited industrial technologies for increasing density.

The present inventors have already published a method for producing iron carbide fine particles by a gas phase catalytic reaction of reduced iron with a carbonizing gas and a method for producing iron carbide fine particles by a gas phase catalytic reaction of reduced iron with a reducing gas and a carbonizing gas. A manufacturing method has been proposed. However, in these techniques, a carbonization reaction is performed after producing reduced iron, which makes the process complicated and the productivity low (which is extremely undesirable).

In the production of iron carbide fine particles, the present invention aims to simultaneously reduce and carbonize the raw material iron oxyhydroxide or iron oxide, and to minimize the amount of iron oxide and carbon produced as by-products.

Basic Idea> In order to solve the above problems, the inventors of the present invention have conducted various studies, and while continuing to research improvements in their properties, they have discovered that reducing gas can coexist with carbonizing gas. It has been discovered that iron carbide, which is suitable as a magnetic material and produces less iron oxide and carbon, can be produced by simultaneously carrying out a reduction reaction and a carbonization reaction. With this method, the carbonization reaction proceeds efficiently, so compared to the coercive force (Hc) of reduced iron powder, it can be lowered to about 8000e depending on the degree of carbonization, and it is also possible to maintain a high saturation magnetization (σS). .

In other words, even if finer particles are controlled to be reduced to an appropriate level of He, this is an epoch-making technology that can dramatically reduce noise while minimizing the decrease in the output of the electromagnetic conversion characteristics of the media tape. This is what we found.

<Disclosure of the Invention> Raw material for acicular metal powder fine particles containing gamma iron monoxide or iron as a main component for magnetic recording, i.e., iron oxyhydroxide or oxidized iron oxide whose surface has been modified to avoid sintering, maintain shape, etc. It is also possible to use iron as it is as a raw material for producing iron carbide.

For example, α-iron oxyhydroxide or AI with a specific surface area of 20 to 150 rf/gr! , S i, p, 'ri,
At least one element selected from elements such as Cr, Mn, Co, Ni, and Zn is co-precipitated into α-iron oxyhydroxide to avoid sintering, maintain shape, control coercive force, improve corrosion resistance, etc. , B, Al1%S i, p, T i, Zn,
Cr.

Mn5Co, Ni, Cu, Zr, Sn, Pb, Ca, B
The surface of the dried surface-modified α-iron oxyhydroxide is coated with at least one element selected from the elements such as a, and the dried surface-modified α-iron oxyhydroxide is crushed and calcined at 300 to 800°C as necessary to form the surface-modified α-iron oxyhydroxide.
Use iron monoxide.

Next, the surface-modified powder is subjected to a gas phase contact reaction (hereinafter simply referred to as carbonization reaction) with a mixed gas of a reducing gas and a carbonizing gas, diluted with an inert gas if necessary, to produce carbonization that exhibits ferromagnetism. Iron-containing acicular fine particles can be produced.

The appropriate temperature for carrying out the carbonization reaction is 200 to 700°C. If the reaction temperature is lower than 200° C., carbonization will not substantially proceed and the object of the present invention will not be met. If the temperature exceeds 700°C, although the carbonization reaction itself will proceed, the acicular fine particles will be severely sintered, making the powder unsuitable as a magnetic powder for magnetic recording. Moreover, the time of the carbonization reaction is 5 to 600
min, the degree is appropriate. If it is less than this, the carbonization reaction cannot be controlled with good reproducibility, and if it exceeds this, it is economically unsuitable.

The supply amount and speed of the reaction gas are determined by the gas hourly space velocity (:G
H8V) is 0.1 to 100, preferably 10 to
A range of 30 N1-m1x gas/gr-Fe/Hr is suitable. If it is less than this range, the carbonization reaction will proceed but at a slow rate, which is not practical, and if it exceeds this range, the pressure drop in the reaction system will increase, which is not preferable as a reaction operation.

The composition of the product varies depending on the contact conditions in the gas phase catalytic reaction and the raw material conditions for the raw material powder. becomes an iron oxide-iron carbide-carbon based product. When the product was subjected to powder X-ray diffraction measurement and identified from the diffraction angle of the crystalline diffraction peak group, the iron carbide was found to be so-called cementite species (F'e3C,
ASTM-23-1113) was detected, and as iron oxide, magnetite species (Fe50<, ASTM 19
629) is detected. On the other hand, when the carbonization reaction is performed with a gas composition containing a reducing gas such as hydrogen gas, the amount of iron oxide and carbon produced is small, and depending on the conditions, the α-Fe phase may be detected at the same time.

Although it is possible to use mainly hydrogen gas as the reducing gas and a hydrocarbon gas such as methane or propane as the carbonizing gas, carbon monoxide gas, which can be carbonized at a relatively low temperature, is most preferred. Moreover, an inert gas can be entrained. Volume ratio of hydrogen gas and carbon monoxide gas (co:H
z) is preferably between 10:1 and 1:1000. If the carbon monoxide concentration is small, it is difficult for the carbonization reaction to proceed, and conversely, if the carbon monoxide concentration is large, the amount of iron oxide and carbon produced as described above increases.

Although it is possible to use helium gas, argon gas, carbon dioxide gas, etc. as the inert gas to be entrained in the mixed gas, nitrogen gas is most preferable since it is relatively inexpensive. The volume ratio (CO:N2) in this case is, for example, 1:1
~1: About 500 is appropriate, and by changing this amount, the reaction rate of the carbonization reaction can be mainly controlled.

In the carbonization reaction, the only noticeable difference between the presence and absence of hydrogen gas is the amount of iron oxide phase produced from a crystallographic point of view, but when positioned as a magnetic material, its saturation increases with the production of iron oxide phase and carbon. A large difference appears in the magnetization (σS) or the residual magnetic flux density (Br) of the tape after media processing, which affects the recording density, which is one of the most important factors in a magnetic recording medium.

When the obtained composition is expressed as FeCxOy, the value of X is 0.05 to 0.5 and the value of y is 0.01 to 1.0.
It is appropriate that the value be within the range of .

When the X-value is less than 0.05, the desired ferromagnetic properties, especially the Hc-value, are reduced to less than 2000e. In addition, when the X-value exceeds 0.5, the decrease in the Hc-value is thicker than that of metallic iron fine particles produced by gas-phase contact reaction with a reducing gas (although Saturation magnetization, which is one of the factors that regulates the residual magnetic flux density 2Br- value in the case of Even if y≦1.0, the formation of antiferromagnetic wustite species (FeO) is not observed, and magnetite species are confirmed, so a value as small as possible is desirable, but the above range is practical. I can say that.

When the particle shape of the carbonized powder is observed under an electron microscope with a magnification of 30,000 to 90,000 times, the image shows that the shape closely follows the shape of the iron oxyhydroxide fine particles used as the primary raw material, and has a shape of approximately 100 to 300 times. A large number of spherical ultrafine particles (referred to as crystallites, microcrystals, crystallites, grains, etc.) are assembled to form each needle-shaped carbonized powder skeleton particle. Incidentally, there is hardly any damage, destruction, or interparticle bonding, that is, sintering.

(Then, acicular iron oxyhydroxide fine particles are used as the primary raw material, and carbonization is carried out by a gas phase catalytic carbonization reaction in the coexistence of hydrogen gas.
It can be manufactured in powder form. Since the gas phase catalytic carbonization reaction uses carbon monoxide as the carbonization agent, problems such as corrosion of reaction equipment do not occur, and it is extremely convenient.

The magnetic properties of the acicular iron carbide powder have an Hc-value of 50
00e or more, σS-value is F30 emu/gr
1 or more is appropriate. If the value is less than this value, the desired high-output, high-density magnetic recording cannot be achieved. This magnetic property is −
It is possible to control the morphology of the next raw material, iron oxyhydroxide fine particles, its modification recipe, and the conditions of the subsequent carbonization reaction.

Summary 1> The function of the present invention will be explained by comparing it with that of the prior art and clarifying its position.

Iron carbide itself is a well-known chemical species, and it is also known that it can be obtained by carbonizing α-Fe with carbon monoxide gas.
For example: H. A. Bahr et al. “Die Kohl
en-oxyd-Spaltung an Eise
Noxyd und Eisen J, Bericht.
e, 66, 1238 (1933)). Although there are many well-known facts about its carbonization mechanism, most of its uses have so far been for the so-called carburizing treatment for designing the phase structure of steel plates and improving their mechanical hardness.

Very little is known about synthesizing iron carbide as fine particles and utilizing its ferromagnetic properties as magnetic material powder for magnetic recording media, and only a few US patents are available: USP 3,572,9.
93 (Mar, 1971: D, B, Roge
rs). According to the patent specification, a fine particle type χ-phase is obtained by thermally decomposing an iron carbonyl compound (=especially Fe(Co)) at a temperature of 280 to 340°C in an atmosphere of hydrogen and carbon monoxide gas. As,
This material is called magnetic powder. The χ-phase is the so-called H'a g
It is a species called iron carbide of g, and is written as Fe2C. Also, according to the description in the patent specification, the particle shape is 0.
．． They are spherical ultrafine particles with a size of 0.005 to 0.1μ, and their magnetic properties include Hc-values of 200 to 10,000e.

The σS value is approximately 85 to 100 emu/gr.

There are almost no known examples of using bulk iron carbide as a magnetic material in the field of magnetic recording, and this is only found in JP-A-53-26218. In the Japanese Patent Application Laid-open No. 2003-120023, an iron-based alloy containing 0.5 to 5.0% carbon is melted, and the melt is rapidly cooled by centrifugation to form a ribbon-shaped sample with a thickness of about 3 μm. Then, the quenched sample was heated to 100'C/
The sample is heated to 800° C. at a heating rate of H, and thereafter cooled to room temperature at the same rate. It has been shown that this heat treatment increases the saturation magnetization of the ribbon-shaped sample.

As a method for synthesizing iron carbide fine particles, the thermal decomposition method of iron-cyanide compounds in a non-oxidizing atmosphere (= JP-A-50-2
2000), a method by evaporation of iron metal in a low-pressure active gas (Japanese Patent Laid-Open No. 52-84179), a method by gas spraying of a melt (Japanese Patent Laid-Open No. 54-29305), and the like.

In the method of the present invention, acicular iron oxyhydroxide fine particles are prepared, subjected to a modification treatment and calcination process to which a shape-retaining component is adhered, and then subjected to a carbonization process (and a reduction process) to reduce the molecular species to F.
It is characterized by e5C needle-like ferromagnetic iron carbide fine particles.

In the method of USP 3,572,993, ferromagnetic spherical ultrafine particles are formed by thermal decomposition of iron carbonyl bodies in a reducing atmosphere, and the molecular species thereof is Fe2C. Therefore, the present invention can be said to be completely different from the patented technology system. In the method of the present invention, one of the key points is to use specific acicular fine particles, and there are no defects due to the characteristics of the magnetic medium. Can not.

The technique described in JP-A-53-26218 is a manufacturing recipe for improving the ferromagnetic properties of iron carbide, and is completely different from the present invention in terms of purpose and effect.

Furthermore, JP-A-50-22000.52-84179.5
No. 4-29305 and the like are methods for producing spherical particles, and it can be said that the technical idea is different from the present invention.

A technique for subjecting acicular iron oxyhydroxide or iron oxide to a gas phase contact reaction with carbon monoxide is disclosed in Japanese Patent Publication No. 39-500.
9, Japanese Unexamined Patent Publication No. 59-199533, etc. However, the former undergoes an oxidation reaction after coming into contact with carbon monoxide gas.
This is a method for producing so-called r-iron monoxide, and its purpose is different from the present invention. The iron carbide mainly produced in the latter case is Fe5C2, which is different from the cementite species (Fe, C) of the main product of the present invention in terms of composition and crystallography. Furthermore, since carbon monoxide gas that does not contain hydrogen gas, which is a reducing gas, is used in the gas phase catalytic carbonization reaction, as mentioned above, the amount of iron oxide and carbon produced is large, making it impractical. This can be said to be the least preferable method in terms of the concept of the present invention.

As seen above, the method of the present invention is completely different in purpose from conventional related technology systems, and provides a novel magnetic material powder that has not been seen before in the field of magnetic recording technology. I understand that it is something.

The effect of acicular ferromagnetic fine particles whose molecular species is expressed as Fe5C is that the particle size that exhibits the same He value can be designed to be sufficiently small when compared with α-Fe powder fine particles. This is something that can be done. Moreover, even if more than the stoichiometric amount of carbon is contained, as long as the present invention is applicable, Fe5C will be formed as a molecular species, so unlike the case of Fe2C mentioned above, the saturation magnetization will be large. There is no decline, which is extremely convenient.

As a result, when media processing is performed, it is possible to create a system in which the magnetic properties remain almost the same, while using finer particles as the raw material powder. As a direct result of this, the magnetic recording characteristics that are strongly controlled by the particle size of the magnetic powder, that is, the electromagnetic conversion characteristics (=sensitivity/output) and noise in high frequencies, are greatly improved.

<Example> Hereinafter, the method and effects of the present invention will be described in detail with reference to Examples and Comparative Examples. The carbonization reaction was mainly carried out using a thermogravimetric measuring device TG-30 manufactured by Shimadzu Corporation.

[Examples 1 to 3] This example describes a case in which a gas phase catalytic carbonization reaction is performed on a raw material adhering powder for so-called audio metal position iron powder using a mixed gas of carbon monoxide gas and hydrogen gas. This is an example showing an overview of the method of the invention and its effects.

Production of surface-modified iron oxyhydroxide powder> By the method described in JP-A-57-106527 and JP-A-57-96504, P4Si and a Ni-component as a coprecipitated component were mixed in a weight ratio of P/Fe:=0.2/ 100,
Si/Fe = 1.8/100 and Ni/
Acicular iron oxyhydroxide fine particles containing Fe = 1.5/100 were synthesized.

The shape of the fine particles has a specific surface area (SA) of 38.6 mgr calculated from the adsorption characteristics of nitrogen gas, and a major axis diameter (L) calculated from a transmission electron microscope image of 60,000 to 90,000 times. The ratio to the short axis diameter (:D), that is, the axial ratio (:L/D) was 20.

Next, after passing through a drying and pulverizing process, calcining (temperature = 700
℃).

<Carbonization reaction> Gas phase catalytic carbonization reaction (gas hourly space velocity = 20 Nm) at the specified temperature, time and mixed gas composition under the conditions listed in Table 1.
-m1x gas/kgr -Fe/Hr, ) was carried out for a long time.

Results> Table 1 shows the results of carbon and iron analysis of the product and specific surface area measurement using the nitrogen gas method. In addition, the magnetic properties of the product were measured using a vibrating magnetic property measuring device VSM-I manufactured by Toei Kogyo Co., Ltd.
The results measured by type II are also shown in Table 1. Furthermore, the X-ray diffraction pattern (target: Cr, filter: v) of the product of Example-3 is shown in FIG.

[Comparative Examples-1 to 2] When the raw material powder used in the above examples was subjected to a so-called gas phase catalytic reduction reaction using hydrogen gas (Comparative Example-1), and when carbon monoxide gas containing no hydrogen gas Table 1 shows the results of the gas phase catalytic carbonization reaction (Comparative Example 2) with a nitrogen gas composition.

[Example-4] P/Fe = 0.3 / under similar conditions as Example-1
100%Si/Fe = 3.0/Zoo, N
Acicular iron oxyhydroxide fine particles containing i/Fe = 2.8/100 were synthesized.

The shape of the fine particles has a specific surface area (SA) of 68.7r
rt/gr.

Also, the axial ratio (: L/D) calculated from the transmission electron microscope image
was 14. Next, Table 1 shows the conditions and results of the gas phase catalytic carbonization reaction of the raw material powder that has undergone the drying and pulverization process.

[Example-5] This example is an example showing an overview of the method of the present invention and its effects on acicular ferromagnetic fine particles containing iron carbide as a main component for high-position audio applications. .

Production of iron carbide powder> The same surface-modified powder as in Example 1 was charged into a steel pipe reactor equipped with a preheater for the raw material gas for reaction and whose temperature could be controlled from the outside, and then heated under the conditions listed in Table 1. It was subjected to gas phase catalytic carbonization reaction. The results are shown in Table-1.

Next, after thoroughly immersing the fine particles in toluene, the fine particle slurry was transferred onto an enamel vat to a thickness of approximately 1 cIIL Ω, and subjected to toluene scattering treatment in the atmosphere. When the solvent odor disappeared, the magnetic powder was collected and used as air-dried iron carbide powder.

<Evaluation of air-dried iron carbide powder into paint, coating, and tape properties>
10 grams of the air-dried iron carbide powder was collected and put into a pot with an internal volume of 550 ml together with the following materials, and mixed and dispersed for 5 hours using a paint shaker manufactured by Red Devil Co., Ltd., USA. As the dispersion media, 2nφ α-alumina beads were used.

- UCC salt vinyl acetate poly? -VAGH: 1. Og
r.Polyurethane NL-2448 manufactured by Mitsui Toatsu Chemical Co., Ltd.: 1. Ogr ・Phosphate ester AP-13 manufactured by Otona Kagaku Co., Ltd.: 0.2g
r・α-Alumina AKP-30 manufactured by Sumitomo Chemical Co., Ltd.: 0.
2gr/solvent toluene: 14gr, MEK: 14
Then, the dispersion media was separated to obtain a magnetic paint, which was coated onto a 12μ thick polyester film manufactured by Toshi Co., Ltd. (Lumirror 128-LIO) using a precision coater equipped with magnetic tape and an applicator. After that, the coating surface was smoothed by calender roll treatment, and
The polyurethane curing reaction was completed by heat treatment at ℃ for 2 days. The sheet was cut to 3.81 inches to produce a magnetic tape of the current cassette specification size.

The magnetic properties of the magnetic tape are measured using the measuring device described above.
As a result of evaluation, Hc=7300e, Br=2660 Gauss
, Br/Bm=0.75, showing sufficient characteristic values.

<Evaluation of audio characteristics> Tape tester manufactured by Nippon Columbia: DENON-031
Audio characteristics were measured and evaluated using IDC standard Type-U tape as a standard, using the R (equipped with an IEC-specified standard head) and in accordance with the measurement method described in Japan Magnetic Tape Standard: MTS-0101 ('72). .

As a result, the low frequency sensitivity (333Hz sensitivity) was +3.
6dB, high frequency sensitivity (12.5kHz sensitivity) +3.
5dB1 maximum output (=3%MOL) is +7.6dB,
Saturation output (=10 kHz, sOL) is -2.5 dB
, and AC bias noise after auditory correction (: Nac
) is -57.8 dB, which shows sufficient high-frequency sensitivity and saturation output, and gives a uniquely low noise.

mouth of mouth
> The effects and effects of the present invention can be summarized as follows based on the results of Examples and Comparative Examples.

That is, in the case of acicular ferromagnetic fine particles as a magnetic recording material suitable for high-density magnetic recording, the fine particles are mainly iron-based fine particles containing a predetermined amount of carbon, and the acicular ferromagnetic fine particles are coated with modified acicular ferromagnetic particles. By subjecting iron hydroxide fine particles to a gas phase catalytic carbonization reaction with a mixed gas of a reducing gas and a carbonizing gas to form ferromagnetic iron carbide-containing iron fine particles, (1) As for the iron carbide fine particles themselves, While exhibiting acicular properties well inheriting the shape of iron oxyhydroxide, (2) it is possible to control the magnetic property values, especially the coercive force Hc value, in a wide range according to the degree of carbonization, and (3) magnetic powder The particles are fine and have suitable magnetic properties (coercive force,
(4) As for manufacturing equipment, ferromagnetism made from iron oxyhydroxide is used as a raw material. It has been found that the metal powder manufacturing equipment can be used as is.

As described above, the substance of the present invention is a magnetic material with remarkable characteristics for use in audio and video applications, and provides a method for producing the same.

[Brief explanation of drawings]

FIG. 1 is an X-ray diffraction pattern diagram of the product in Example-3.

Claims (8)

[Claims] (1) A magnetic material for magnetic recording media consisting of ferromagnetic fine particles containing acicular iron carbide. (2) The value of x in iron carbide composition FeC_xO_y is
The magnetic material according to claim 1, wherein the value of y is in the range of 0.05 to 0.5 and 0.01 to 1.0. (3) The magnetic material according to claim 1, wherein the fine particles have a long axis diameter of 1 μm or less, a short axis diameter of 0.1 μm or less, and an axial ratio of 10 to 30. (4) Magnetic property values are 500 Oe or more as coercive force and 80 emu/gr as saturation magnetization. A magnetic material according to claim 1 containing iron carbide which shows the above. (5) Acicular iron carbide-containing steel for magnetic recording in which acicular iron oxyhydroxide fine particles that have been adhered and modified with a shape-retaining component are subjected to a vapor phase catalytic carbonization reaction using a mixed gas of a carbonizing gas and a reducing gas. Method for producing magnetic fine particles. (6) The method according to claim 5, wherein the reducing gas is a gas mainly composed of hydrogen, and the carbonizing gas is a gas mainly composed of carbon monoxide. (7) The volume ratio of carbon monoxide and hydrogen (CO:H_2) is 1
7. The method according to claim 6, wherein the composition ratio is between 1000 and 10:1, and the gas phase catalytic carbonization reaction is carried out at 200 to 700°C. (8) The method according to claim 7, wherein the gas phase catalytic carbonization reaction is carried out by diluting a mixed gas of carbon monoxide and hydrogen with an inert gas.