JP2006303321A - Zinc-contained iron-nitride powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a magnetic characteristic by which a progress of nitriding is promoted in an iron-nitride magnetic powder to effectively prevent a sintering by using a Goethite resulting from dissolving Al. <P>SOLUTION: The iron-nitride powder mainly comprised of Fe<SB>16</SB>N<SB>2</SB>contains the dissolved Al, and is obtained by applying a nitriding treatment to an α-Fe powder obtained by reducing the Goethite coated by Zn. An average particle diameter of a long diameter can be 20 nm or smaller. It is desirable that Zn content to Fe is 0.05 to 5% in atomic ratio. Particularly, when an X-ray diffraction is conducted by Co-Kα-ray, it is a favorable object that the powder has a relation of equation (1): I<SB>50</SB>/I<SB>52</SB>≥1.5 between a peak height I<SB>50</SB>in a range of 2θ: 49.5 to 50.5° of the X-ray diffraction pattern and the peak height I<SB>52</SB>of the range of 2θ: 51.5 to 53.0°. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an iron nitride-based magnetic powder suitable for a high recording density magnetic recording medium.

  In recent years, higher recording density has been desired for magnetic recording media, and in order to achieve this, recording wavelengths have been shortened. If the size of the magnetic particle is not much smaller than the length of the region for recording a signal with a short wavelength, a clear magnetization transition state cannot be created, and recording becomes impossible. Therefore, the magnetic powder is required to have a particle size sufficiently smaller than the recording wavelength.

  In order to increase the density, it is necessary to increase the resolution of the recording signal. For this reason, it is important to reduce the noise of the magnetic recording medium. Noise is greatly influenced by the size of the particles, and the smaller the particles, the more the noise is reduced. Therefore, the magnetic powder for high recording density is required to have a sufficiently small particle size from this point.

  However, as the particles become finer, it becomes difficult for each particle to exist independently, and even in the case of metal magnetic powders commonly used for data storage, if the particles become significantly finer, the manufacturing process There is a problem that it is easy to sinter during reduction. If the sintering occurs, the volume of the particles becomes large, so that it becomes a source of noise, and when taped, it has adverse effects such as deterioration of dispersibility and loss of surface smoothness. Magnetic powder suitable for high-density recording media needs to have good magnetic properties as a magnetic material, but powder properties when taped to more than that, that is, particle size, particle size distribution, specific surface area, TAP density, dispersibility, etc. are important.

So far, an iron nitride-based magnetic powder having an Fe ₁₆ N ₂ phase as a main phase is known as a magnetic powder suitable for a high-density recording medium having excellent magnetic properties, and is disclosed in Patent Document 1. For example, Patent Document 1 discloses an iron nitride-based magnetic material having a large specific surface area as a magnetic material that exhibits a high coercive force (Hc) and a high saturation magnetization (σs), and crystal magnetic anisotropy of the Fe ₁₆ N ₂ phase. As a synergistic effect of increasing the specific surface area of the magnetic powder, it is taught that high magnetic properties can be obtained regardless of the shape.

Patent Document 2 describes an essentially spherical or elliptical rare earth-iron-boron-based, rare-earth-iron-based, or rare-earth-iron nitride-based magnetic powder as an improved magnetic powder from Patent Document 1. It is taught that excellent properties can be obtained when they are used to make tape media. Among them, the rare earth-iron nitride magnetic powder mainly composed of Fe ₁₆ N ₂ phase has a high coercive force of 200 kA / m (2512 Oe) or more in spite of being fine particles of about 20 nm, and the ratio by BET method. It is said that since the surface area is small, the saturation magnetization is also high and the storage stability is good. By using this rare earth-iron nitride magnetic powder, the recording density of the coating type magnetic recording medium can be dramatically increased. Has been. Moreover, the Example of patent document 2 has description of the particle | grains excellent in the magnetic characteristic of a particle size level of 20 nm or less.

This rare earth-iron nitride magnetic powder is produced by reducing magnetite with rare earth elements and one or two of Al and Si deposited on the surface of the particles to reduce the magnetite to a rare earth-iron magnetic powder. This is an ammonia nitriding method that performs nitriding with _three gases. Due to the large magnetocrystalline anisotropy of the Fe ₁₆ N ₂ phase produced by this nitriding, magnetic powder suitable for high recording density media, that is, fine particles, high Hc, and high Magnetic powder having characteristics such as σs can be obtained.

JP 2000-277311 A International Publication No. 03/079333 Pamphlet

  When the average particle size is 20 nm or less, the effect of reducing the particle volume is very large even if the particle size is reduced by 1 nm. For example, when the size is reduced from 40 nm to 39 nm, the particle volume is only reduced to 93%, but when the size is reduced from 20 nm to 19 nm, the particle volume is reduced to 86%. In addition, as the volume reduction effect increases, the effect of increasing the specific surface area also increases. However, there is a problem that sintering is likely to occur during the production process when the particle size is reduced. Even if the magnetic properties have a high potential, when sintering occurs, the original excellent magnetic properties are not fully exhibited, but also the particle size distribution and dispersibility are hindered. It becomes difficult to apply to a recording medium.

In Patent Document 2, when an Fe ₁₆ N ₂ phase having a large magnetocrystalline anisotropy is generated, Si, Al, rare earth elements (including Y), etc. are deposited on the particle surface as a sintering inhibitor. , Producing fine particles without sintering. However, the method of preventing sintering by this deposition is that when the deposition conditions are insufficient, the degree of deposition of the sintering inhibitor varies from particle to particle. While it can be prevented, it will sinter in places that are not so much deposited. As a result, there is a problem that the particle size distribution of the obtained powder is deteriorated. In particular, in the case of fine particles, the particles tend to aggregate and behave as aggregates, so that uneven deposition tends to occur. The deterioration of the particle size distribution causes the surface properties of the tape to deteriorate, and consequently the electromagnetic conversion characteristics of the tape.

  In addition, even if the particles are uniformly dispersed without being agglomerated, in the method of preventing sintering by deposition, if the specific surface area increases as the particles become finer, the entire surface is coated according to the increase in specific surface area. The amount of sintering inhibitor must also be increased. Furthermore, when Si is used as an anti-sintering agent, Si has a strong adsorptive power and a high anti-sintering effect can be obtained, but on the other hand, the bonding between Si is also strong, so that the dispersibility of the particles tends to be hindered.

  Therefore, after various studies to solve such problems, the present applicant uses a goethite containing Al as a starting material for the production of iron nitride-based magnetic powder. It has been found that an iron nitride magnetic powder having a diameter of 20 nm or less can be obtained and proposed as Japanese Patent Application No. 2004-76080. This iron nitride magnetic powder exhibits good dispersibility when taped.

However, when goethite containing Al is used as a solid solution, sintering can be prevented without impairing dispersibility, but there are cases where nitriding to Fe ₁₆ N ₂ does not proceed well. If nitriding is insufficient, a large amount of α-Fe phase remains and causes a decrease in magnetic properties, particularly coercive force Hc.

In view of such a current situation, the present invention provides a Fe ₁₆ N ₂ phase-based iron nitride-based magnetic powder that uses a goethite in which Al is dissolved to prevent sintering and ensure dispersibility. It is about providing something that improves progress.

We result of various studies, the goethite was deposited with Zn to alpha-Fe powder produced through the reduction treatment as a raw material, when subjected to a nitriding treatment, Fe ₁₆ N ₂ phase mainly having excellent magnetic properties It was found that an iron nitride-based powder was obtained. As the goethite, it is particularly preferable to apply a material that prevents sintering by dissolving Al in solid solution. The preferable Fe ₁₆ N ₂ phase-based iron nitride-based powder with improved nitriding progress contains, for example, 0.05 to 5% of Zn in terms of atomic ratio to Fe (ie, Zn / Fe atomic ratio) after nitriding. .
Here, the Zn / Fe atomic ratio was measured by measuring the Zn content (atomic%) and Fe content (atomic%) in the powder,
Zn content (atomic%) / Fe content (atomic%) × 100
It can ask for.

Al is preferably contained in an atomic ratio of 0.1 to 20% with respect to Fe. In such a thing, the outstanding sintering prevention effect is exhibited. The content of Al contained in the powder is mainly Al dissolved in goethite, but in order to enhance the sintering prevention effect, it is also effective to perform Al deposition treatment, In that case, the particles are designed by including the deposited Al in the Al content. As such an iron nitride-based powder mainly composed of the Fe ₁₆ N ₂ phase of the present invention, the average particle diameter of the long diameter (the length obtained by measuring the longest diameter among the respective particles) was reduced to 20 nm or less. Things are provided.

Here, “Fe ₁₆ N ₂ phase-based iron nitride-based powder” means that when a powder to be evaluated is subjected to X-ray diffraction by Co—Kα rays, the diffraction angle 2θ is 10 in the X-ray diffraction pattern. The highest peak among the diffraction peaks in the range of ˜120 ° appears at the position of 49.5-50.5 °. In particular, in the X-ray diffraction pattern, the peak height I _{50 in} the range of 2θ: 49.5 to 50.5 ° and the peak height I ₅₂ in the range of 2θ: 51.5 to 53.0 ° Those satisfying the relationship of the following expression (1) are suitable targets.
I ₅₀ / I ₅₂ ≧ 1.5 (1)
However, the value of the ratio is calculated by adopting a value determined as an amount proportional to the X-ray diffraction intensity (cps) as the peak height.

According to the present invention, by using a goethite coated with Zn, it is possible to provide an iron nitride-based powder mainly composed of an Fe ₁₆ N ₂ phase having a sufficiently advanced nitriding and excellent magnetic properties. In particular, since the goethite on which Zn or Al is further deposited can be subjected to the reduction treatment after the Al is solid-dissolved, the excellent anti-sintering effect due to the Al solid solution + Al deposition and the Zn deposition. Both of the nitriding promotion effects can be enjoyed simultaneously. For this reason, it is not necessary to employ the conventional means for preventing sintering by Si deposition, and the disadvantage of the decrease in dispersibility that has become a problem with Si deposition can be avoided. Therefore, the present invention provides a magnetic powder suitable for a coating type magnetic recording medium in terms of magnetic characteristics and powder characteristics.

In the present invention, iron nitride magnetic powder mainly composed of Fe ₁₆ N ₂ phase obtained by nitriding α-Fe derived from goethite (iron oxyhydroxide) is an object. In order to obtain α-Fe from goethite, it is necessary to perform a reduction treatment in an atmosphere such as hydrogen. Α-Fe can be obtained directly from goethite, or a process of generating iron oxide as an intermediate substance may be taken. In either case, the heat treatment is generally performed in a reducing atmosphere such as hydrogen. In this reduction heat treatment, it is important to prevent sintering of the particles. As the sintering preventing means, there are a method of depositing Si as described above and a method of using raw material powder that dissolves Al, but considering the application to a coating type magnetic recording medium, the latter Al solidification method. It can be said that the method using dissolution is advantageous in terms of dispersibility. However, in the latter case, there is a negative factor that the progress of nitriding is suppressed, and the establishment of a method for overcoming this has been awaited.

  As a result of detailed researches by the inventors, even if it is a goethite in which Al is dissolved, by further depositing Zn, the easiness of nitriding is remarkably improved and the coercive force is excellent. It was found that fine iron nitride powder was obtained. At this time, it is desirable to ensure that the abundance of Zn in the powder is 0.05% or more in terms of the atomic ratio to Fe (Zn / Fe atomic ratio). If Zn is less than that, a sufficient nitriding promotion effect cannot be obtained. The upper limit of the Zn / Fe atomic ratio is not particularly limited as long as the effect of promoting nitriding is sufficiently obtained and other characteristics (magnetic characteristics and powder characteristics) are not impaired, but the Zn / Fe atomic ratio is 5%. If it exceeds, σs decreases due to a decrease in the Fe content, and it becomes difficult to obtain a recording signal necessary for the magnetic recording medium. Usually, good results are obtained when the Zn / Fe atomic ratio is in the range of 0.1 to 3%.

Easily nitriding means that an Fe ₁₆ N ₂ phase is easily generated. Specifically, when nitriding is performed under the same conditions, the abundance of Fe ₁₆ N ₂ phase is higher after nitriding and α This means that the abundance of -Fe is lower. According to the X-ray diffraction irradiated with characteristic X-rays, the diffraction peak with the highest intensity of the Fe ₁₆ N ₂ phase and the diffraction peak with the highest intensity of α-Fe appear at very close positions. For example, in X-ray diffraction using Co—Kα rays, the peak of the Fe ₁₆ N ₂ phase appears when the diffraction angle 2θ is between 49.5 and 50.5 °, and that of α-Fe is 2θ of 51.5. Appears between -53.0 °. By examining the relative ratio of these two peak heights (plotted as a value proportional to the diffraction intensity (cps)), the ease of nitriding can be evaluated.

According to the study by the inventors, in an iron nitride-based powder manufactured under practical nitriding conditions, 2θ: 49.5-50 on the X-ray diffraction pattern measured using Co—Kα rays. Between the peak height I _{50 in} the range of 0.5 ° and the peak height I ₅₂ in the range of 2θ: 51.5 to 53.0 °, the following formula (1):
I ₅₀ / I ₅₂ ≧ 1.5 (1)
It was found that powders satisfying the above relationship are sufficiently nitrided and exhibit excellent magnetic properties in applications corresponding to the respective particle sizes when compared with those having the same average particle size. In particular, iron nitride powders having an average major axis of 20 nm or less that satisfy the above formula (1) exhibit magnetic characteristics suitable as magnetic powders for coating-type magnetic recording media having a high recording density.

  The mechanism by which the progress of nitriding is improved when using a goethite coated with Zn has not been clarified at this time. However, as can be seen from FIG. 1 described later, in the iron nitride magnetic powder of the present invention, an oxide film enriched with Zn is formed on the outermost layer of the particles. This Zn-concentrated oxide film is presumed to have a structure in which nitrogen is more likely to enter the inside than an oxide film not containing Zn.

The iron nitride-based powder of the present invention can be obtained, for example, by the following production method.
As a starting material, it is desirable to prepare a goethite in which Al is dissolved in order to provide an excellent sintering preventing effect. In order to obtain such a goethite, Al is accompanied when the goethite is synthesized by a wet method. For example, a method in which a ferrous salt aqueous solution (aqueous solution of FeSO ₄ , FeCl _2, etc.) is neutralized with an alkali hydroxide (NaOH or KOH aqueous solution) and then oxidized with air to generate goethite. The production reaction may be performed in an environment in which an Al-containing salt is present. Further, in the method of neutralizing the ferrous salt aqueous solution with alkali carbonate and then oxidizing it with air or the like to generate goethite, this goethite formation reaction may be performed in the presence of an Al-containing salt. Alternatively, the reaction of neutralizing an aqueous ferric salt solution (aqueous solution of FeCl ₃ ) with NaOH or the like to generate goethite may also be performed in the presence of an Al-containing salt.

  Next, Zn is deposited on this goethite. For example, after dispersing the above Al solid solution goethite in water, adding a water-soluble Zn-containing salt such as zinc nitrate or zinc sulfate and neutralizing with alkali, or evaporating water from the dispersion Zn can be deposited on the particle surface by a method or the like. It is desirable to adjust the Zn deposition amount so that the desired Zn / Fe atomic ratio is obtained. The Zn / Fe atomic ratio at this stage is directly reflected in the Fe / Zn atomic ratio after nitriding. The amount of deposition can be adjusted by changing the concentration of the Zn-containing salt.

  The goethite coated with only Zn can be subjected to reduction treatment as it is, but in order to obtain a higher sintering prevention effect, one or more of Al, rare earth elements (including Y), etc. are deposited. Is desirable. These can be performed simultaneously with the above Zn deposition. In that case, a solution obtained by adding a water-soluble salt containing a necessary deposition element together with the Zn-containing salt may be used. Examples of the salt serving as the Al source and the rare earth element (including Y) source include sodium aluminate, lanthanum nitrate, and yttrium nitrate, respectively. In addition, depositing Zr, Mo, W, P, B, etc. is also effective in enhancing the sintering prevention effect.

  The total amount of Al to be dissolved in goethite and the amount of Al to be deposited may be about 0.1 to 14%, preferably about 1 to 10% in terms of the Al / Fe atomic ratio with respect to Fe. When the Al / Fe atomic ratio is less than 0.1%, the σs of the magnetic powder increases, but a sufficient sintering preventing effect cannot be obtained. Conversely, if it exceeds 14%, the sintering preventing effect is sufficient, but even if the Zn deposition method is employed, the effect of promoting the progress of nitriding is insufficient. The amount of sintering inhibitor excluding Al (total amount X of rare earth elements including Y, etc.) deposited on goethite is 0.1 to 10%, preferably 0.1 to 5% in terms of the atomic ratio X / Fe to Fe. do it.

  The goethite thus obtained can be subjected to a reduction treatment after being filtered and washed with water and then dried at a temperature of 200 ° C. or lower. Alternatively, the goethite may be subjected to a treatment of dehydrating at 200 to 600 ° C. or a treatment of reducing in a hydrogen atmosphere having a moisture concentration of 5 to 20% to temporarily form an intermediate substance, which may be further reduced. The intermediate substance is not particularly limited as long as it is a compound of iron and oxygen, and examples thereof include goethite (an initial one is modified), hematite, maghemite, magnetite, and wustite. These average particle diameters are desirably 35 nm or less. If it is larger than 35 nm, the particle diameter of the finally obtained iron nitride-based magnetic powder is also increased. As a result, the particle volume is increased, which is not suitable for short wavelength recording, and the surface smoothness of the magnetic tape is also reduced. Unfortunately, the noise becomes high, so it is not suitable for magnetic powders for high recording density magnetic recording media.

Next, the goethite or the intermediate substance is reduced to α-Fe. In general, a reduction method using hydrogen (H ₂ ) is suitable for the reduction treatment, and the temperature is preferably 300 to 600 ° C. If the temperature is lower than 300 ° C., the reduction may be insufficient. In this case, oxygen may remain and the nitriding speed may be significantly reduced. When the reduction temperature exceeds 600 ° C., sintering between particles is likely to occur even if a measure to contain a sintering inhibitor such as Al is taken, which causes an increase in average particle diameter and deterioration of dispersibility.

For the nitriding treatment itself, the ammonia method described in Japanese Patent Application Laid-Open No. 11-340023 published by the same applicant can be applied. That is, an iron nitride powder mainly composed of an Fe ₁₆ N ₂ phase can be obtained by holding a nitrogen-containing gas typified by ammonia at 200 ° C. or lower and holding it for several hours to several tens of hours. The amount of oxygen in the gas used for the nitriding treatment is preferably several ppm or less.

  After the nitriding treatment, it is preferable to gradually oxidize the particle surface with a mixed gas containing about 0.01 to 2% by volume of oxygen in nitrogen to obtain an iron nitride-based magnetic powder that can be stably handled in the air.

  In order to apply to a high recording density magnetic recording medium, it is desirable to use a fine iron nitride-based powder having a major axis having an average diameter of 20 nm or less. It can be performed by controlling the rate, time, and temperature of air oxidation.

  Examples of the present invention will be described below, but before that, methods for measuring characteristic values obtained in the respective examples will be described in advance.

[Composition analysis]
The amount of Fe in the magnetic powder was determined using a Hiranuma automatic titrator (COMTIME-980) manufactured by Hiranuma Sangyo Co., Ltd.

[Magnetic properties in powder bulk]
Measurement of magnetic properties (coercive force Hc, saturation magnetization σs): Measurement was performed with an externally applied magnetic field of 796 kA / m at maximum using VSM (manufactured by Digital Measurement Systems Co., Ltd.).

[Average particle size]
1000 particles capable of discriminating the boundary between particles except for particles displayed as 300,000 times transmission electron micrographs, in which it is not possible to determine whether two or more particles overlap or are sintered. The average value of the lengths obtained by measuring the longest diameter among the particles was used.

[Measurement of concentration distribution of each element by ESCA]
In order to investigate the depth profile of the element concentration in the vicinity of the surface of the iron nitride-based particles, measurement was performed using ESCA. Measurement is made by ULVAC-PHI Co., Ltd. 5800, X-ray source: Al anode source, 150 W, analysis area: 800 μmφ, neutralizing gun: used, sample adjustment: set on sample holder, take-off angle: 45 °, Ar sputtering rate: 8.7 nm / min (SiO ₂ conversion value)

  In ESCA measurement, the element concentrated on the particle surface is detected at the highest concentration immediately after the start of measurement, and then the detected concentration decreases and becomes constant at a certain concentration. From this, for example, when the change in the concentration of Zn and oxygen shows the above change, it can be said that Zn is mainly present in the oxide film layer of the outer particle layer.

[Example 1]
After adding 0.5 L of 12 mol / L NaOH aqueous solution and sodium aluminate aqueous solution to 4 L of FeSO ₄ aqueous solution of 0.2 mol / L (L represents liter), the liquid temperature at 40 ° C. is maintained. Then, air was blown at a flow rate of 300 mL / min for 2.5 hours to obtain a starch (goethite) in which Al was dissolved.

  The goethite starch was filtered, washed with water and dispersed again in water. A zinc nitrate aqueous solution and an yttrium nitrate aqueous solution were added to the dispersion, and a sodium aluminate aqueous solution and an NaOH aqueous solution were added at 40 ° C. to adjust the pH to 7 to 8, and Zn, Y and Al were deposited on the particle surfaces. . Thereafter, the solid content obtained by filtering the liquid was washed with water and then dried at 110 ° C. in air.

As a result of X-ray diffraction, the obtained powder was confirmed to be a compound mainly composed of goethite. The average particle size of the major axis of this goethite powder was 30 nm. Using this powder as a starting material, reduction treatment with hydrogen gas at 500 ° C. for 3 hours and cooling to 100 ° C., at this temperature, the hydrogen gas was switched to ammonia gas, the temperature was raised again, and when it reached 140 ° C., Nitriding treatment was performed for 20 hours. After the nitriding treatment, it was cooled to 80 ° C. and switched to nitrogen gas. Then, the nitrogen gas of air so that the O ₂ concentration of 0.01% to 2% of the particle surface and gradual oxidation treatment was added, and the obtained powder was taken out into the atmosphere.

From the electron micrograph, the obtained powder was found to be composed of spherical or elliptical particles having an average particle diameter of 17 nm. As a result of X-ray diffraction, this was an iron nitride-based powder mainly composed of Fe ₁₆ N ₂ phase, and I ₅₀ / I ₅₂ = 1.69. Table 1 shows the composition and characteristics of the iron nitride powder. FIG. 1 shows a profile of element concentration near the surface by ESCA. FIG. 1B is an enlarged view of the Zn curve of FIG.

[Comparative Example 1]
An iron nitride-based powder was produced in the same manner as in Example 1 except that Zn was not deposited (no zinc nitrate was added to the solution as a Zn source).

From the electron micrograph, the obtained powder was found to be composed of spherical or elliptical particles having an average particle diameter of 18 nm. As a result of X-ray diffraction, this was an iron nitride-based powder mainly composed of Fe ₁₆ N ₂ phase, and I ₅₀ / I ₅₂ = 1.39. Table 1 shows the composition and characteristics of the iron nitride powder. Further, a profile of the element concentration near the surface by ESCA is shown in FIG. FIG. 2B is an enlarged view of the Zn curve of FIG.

[Comparative Example 2]
An iron nitride-based powder was produced in the same manner as in Comparative Example 1, except that the amount of Al added to the goethite was increased as compared with Comparative Example 1.

From the electron micrograph, the obtained powder was found to be composed of spherical or elliptical particles having an average particle diameter of 17 nm. As a result of X-ray diffraction, I ₅₀ / I ₅₂ = 0.86. The composition and characteristics of this powder are shown in Table 1.

As shown in Table 1, even in Comparative Example 1, a magnetic powder having a very small diameter such as an average particle diameter of 20 nm is obtained. However, in order to further improve the magnetic recording density, further finer particles are necessary, and it is necessary to examine how to suppress the sintering of the particles. In Comparative Example 2, the amount of goethite solute Al is increased, so that the sintering preventing effect is larger than that of Comparative Example 1, and fine particles are obtained (that is, the average particle diameter of the long diameter is small). However, the I ₅₀ / I ₅₂ value, which is an index for determining how much nitriding has progressed, is very low, and it can be seen that nitriding is difficult to proceed by increasing the amount of Al dissolved. On the other hand, in Example 1 in which Zn was deposited instead of increasing the amount of Al solid solution, fine particles were obtained in the same manner as in Comparative Example 2, and the anti-sintering effect reduced the amount of Al solid solution. It turns out that it became as high as what we increased. Further, I ₅₀ / I ₅₂ is higher than 1.5, and nitriding is sufficiently advanced. Therefore, the coercive force Hc is improved, and a product exhibiting a high coercive force exceeding 200 kA / m is obtained. . In contrast, the saturation magnetization σs tends to slightly decrease, but in the comparative example, I ₅₀ / I ₅₂ <1.5, so that there is a large amount of Fe phase, and therefore the saturation magnetization of the Fe phase has an effect. It is higher than the example. From this, it can be seen that in the comparative example, there are _two phases of Fe ₁₆ N ₂ phase and Fe phase, and the mixed state adversely affects the magnetic characteristics, so it is preferable as the magnetic material of the magnetic recording medium. Absent.

FIG. 1 shows that Zn is concentrated in the oxide film near the surface of the iron nitride powder of the present invention.
For reference, FIGS. 3, 4, and 5 show transmission electron micrographs of the iron nitride powders obtained in Example 1, Comparative Example 1, and Comparative Example 2, respectively. In each photograph, the distance between both ends in the horizontal direction of the field of view corresponds to about 580 nm.

The graph which shows the depth direction profile of the element concentration by ESCA about the iron nitride system powder of Example 1. FIG. The graph which shows the depth direction profile of the element concentration by ESCA about the iron nitride type powder of the comparative example 1. 2 is a transmission electron micrograph of the iron nitride powder obtained in Example 1. FIG. 2 is a transmission electron micrograph of the iron nitride-based powder obtained in Comparative Example 1. FIG. 6 is a transmission electron micrograph of the iron nitride-based powder obtained in Comparative Example 2. FIG.

Claims (6)

An iron nitride-based powder mainly composed of Fe ₁₆ N ₂ phase obtained by nitriding α-Fe powder obtained by reducing goethite coated with Zn.   The iron nitride-based powder according to claim 1, wherein the goethite contains solute Al. An iron nitride-based powder mainly composed of Fe ₁₆ N ₂ phase containing 0.05 to 5% of Zn with respect to Fe. The iron nitride-based powder mainly comprising an Fe ₁₆ N ₂ phase according to claim 3, further comprising Al in an atomic ratio of 0.1 to 20% with respect to Fe.   The iron nitride-based powder according to claim 1, having an average particle size of 20 nm or less. When X-ray diffraction was performed using Co-Kα rays, the peak height I ₅₀ in the range of 2θ: 49.5 to 50.5 ° of the X-ray diffraction pattern and 2θ: 51.5 to 53.0 ° The iron nitride-based powder according to any one of claims 1 to 5, wherein a relationship of the following formula (1) is established between the peak height I ₅₂ in the range.
I ₅₀ / I ₅₂ ≧ 1.5 (1)