JP4534085B2 - Magnetic powder for coating type magnetic recording medium corresponding to high density and manufacturing method thereof - Google Patents

Description

  The present invention relates to a magnetic powder for a coated magnetic recording medium and a method for producing the same.

  In order to meet the demands for smaller equipment, improved recording / reproduction signal quality, longer recording time, increased recording capacity, etc., the recording density, reliability, and durability of recording media will be further improved. It has always been desired.

  For example, in audio and video applications, in order to respond to the practical use of digital recording systems that realize improved sound quality and image quality, and the development of recording systems compatible with high-definition TVs, the wavelength is even shorter than conventional systems. There is a demand for magnetic recording media that can record and reproduce signals and that have excellent reliability and durability even when the relative speed between the head and the medium increases. In addition, it is desired that a large-capacity digital recording medium be developed in order to store an increasing amount of data for computer use.

  For future magnetic recording media, to achieve even higher recording density, the wavelength of signals used is strongly reduced, and in order to cope with this, finer particles and higher-performance ferromagnetic powders are required. It is coming. If the size of the magnetic particles used is not much smaller than the length of the area for recording the signal on the short wavelength side, a clear magnetization transition state cannot be created, so that recording becomes virtually impossible.

  Further, unless the variation in size and shape of the fine particles is small, the magnetic particles whose magnetic characteristics are caused by shape anisotropy will have large variations in Hc, creating a clear magnetization transition state for the shortest wavelength used. Cannot be recorded, and this is virtually impossible to record. Therefore, it is necessary to develop magnetic particles that are sufficiently small and have excellent particle size distribution, and such fine particles are being studied.

  However, as the magnetic particles become finer, the particle size distribution greatly widens, and the axial ratio decreases, making it impossible to obtain the desired Hc. In addition, when magnetic particles become smaller than a certain size, thermal fluctuations are generated, and stable magnetic properties are lost (super para), and it is necessary to reduce particles on the fine particle side in the particle size distribution.

  In addition, when the magnetic particles are metal magnetic particles, they have an oxide film with a thickness of several nanometers on the surface, so when they are miniaturized, the internal metal portion disappears due to oxidation and becomes oxide particles. Ultrafine particle components are generated, leading to a significant decrease in magnetic properties. In order to suppress this, it is necessary to reduce the particles on the fine particle side of the particle size distribution.

  Patent Documents 1 to 3 disclose fine particles and a ferromagnetic powder having a small particle size distribution. However, the particle distribution constituting the magnetic powder is such that the proportion of particles larger than the average value is reduced. The distribution is improved, and the ultrafine particle component is present in a considerable proportion, so that it is not sufficient for a magnetic recording medium corresponding to high density.

At present, there are no magnetic particles having a small particle size, a narrow particle size distribution, and desired Hc and SFD corresponding to future high-density magnetic recording media.
JP 2000-149243 A JP 2000-149294 A JP 2001-152212 A

Despite the various proposals as described above, in the field of ferromagnetic powders mainly composed of iron, it has not been possible to meet further demands for higher recording density. It's real. In particular,
(1) In order to achieve a high recording density of magnetic recording media, the wavelength of signals used has been shortened strongly. However, if the particle volume of magnetic particles is reduced to accommodate short wavelength recording, the size of the particles can be reduced. In addition, the variation in shape becomes large, and the particles on the fine particle side of the particle size distribution do not have magnetism due to thermal fluctuation, that is, super para, and as a result, the SFD deteriorates when viewed with the whole powder. As a result, the rise of magnetization becomes steep and the width of the magnetization reversal transition region of the recorded signal becomes large, so that it becomes unsuitable for high-density recording (noise (N) of a short-wavelength recording signal). Increases and resolution (C / N) decreases).
(2) If the particle volume of the magnetic particles is reduced corresponding to the short wavelength recording, the axial ratio of the magnetic metal particles is lowered, and magnetic particles having high Hc cannot be obtained. In addition, as the microparticulation progresses, the fine particle side particles of the particle size distribution are oxidized to the metal portion inside the particle, resulting in a significant decrease in magnetic properties such as Hc. As a result, an output (C) corresponding to high-density recording cannot be obtained, and the C / N is low. Further, it is impossible to obtain stable magnetization of a finer recording unit (magnetization switching unit).

  The present invention aims to solve the above-described problems in obtaining a magnetic recording medium having a high recording density, and in order to achieve this, it is fine and has small variations in size and shape. By reducing the ultrafine particles, the spread of the particle size distribution is reduced, and a ferromagnetic powder having desired magnetic properties such as Hc is obtained.

  In order to solve the above-mentioned problems, the present inventors have conducted various tests and studies. As a result, the inventors have found a method for reducing the amount of ultrafine particles in iron oxyhydroxide and obtaining a good particle size distribution. We have obtained a ferromagnetic powder with few ultrafine particles, good particle size distribution, and desired magnetic properties.

That is, according to the present invention, needle-like particles mainly containing Fe containing Co, Al, and R (R represents at least one kind of rare earth elements including Y), and the average major axis length of the particles L = 10-80 nm, average minor axis length D of particles = 2 nm-20 nm, axial ratio L / D = 1.5-8, major axis length distribution of particles (standard deviation / average value × 100) σL = 25 % Or less, particle short axis length distribution (standard deviation / average value × 100) σD = 25% or less, particle crystallite (crystal grain size) Dx = 50 to 160 Å, and long axis length 1 nm Provided is a ferromagnetic iron alloy powder for coating-type magnetic recording media in which the abundance ratio of ultrafine particles of 10 nm is 15% or less. In this magnetic powder, Co, Al and R are in the range of Co / Fe = 10 to 50 at.%, Al / (Fe + Co) = 2 to 40 at.%, R / (Fe + Co) = 5 to 30 at.%. Can be. Further, the magnetic powder may have an Hc of 1200 or more.

  This magnetic powder is obtained by neutralizing an iron salt solution containing a Co salt with an alkali, adding an oxidizing agent and oxidizing it, adding an Al compound during the oxidation process, and then adding an R compound (R is Y In the method for producing magnetic powder, the obtained slurry is subjected to solid-liquid separation, the powder is subjected to heat oxidation treatment, and then heat reduction treatment. It can be obtained by a production method in which the neutralized product is crushed and stirred for 1 hour or more after the neutralization treatment is completed under the condition that the treatment is maintained at a liquid temperature of less than 55 ° C.

  When the magnetic powder is atomized, the particle distribution is widened and the magnetic powder is inevitably unsuitable as a high recording density medium. However, according to the present invention, the ultrafine particle component of 10 nm or less is reduced. , The fine magnetic powder with narrow major axis length distribution, minor axis length distribution, and axial ratio distribution is obtained, so that the signal waveform at the time of recording on the medium can be sharply recorded and has excellent electromagnetic conversion characteristics Magnetic powder to be a high recording density medium is obtained.

  In order to solve the above-mentioned problems, the present inventors changed the type of iron salt used, the amount, the type of alkali, the amount, the temperature, the process time, the contained substances, etc. as the conditions for producing acicular iron oxyhydroxide. However, many tests were conducted, and research was repeated to find out how to obtain ferromagnetic metal powders suitable for high-density magnetic recording media.

  As a result, in the neutralization production reaction of the raw material, the shape of the neutralized product greatly changes depending on the production conditions such as alkali equivalent, temperature, reaction time, etc. It was found that the shape, size, and variation of iron oxyhydroxide obtained by oxidizing it had a significant effect. In other words, by creating a specific neutralized product, it is possible to reduce the ultrafine particles on the fine particle side of the particle size distribution, which could not be achieved in the past, and to generate fine particles having a uniform particle size. It was.

  As a result, the number of ultrafine particles on the fine particle side of the particle size distribution is reduced, and it is possible to obtain magnetic particles that are fine particles but have uniform particle size, excellent magnetic properties, and improved oxidation resistance. It became. The details will be described below.

  First, in the process of neutralizing alkali and iron sulfate, the neutralized product has a large change in shape, particle size, crystallinity, etc. depending on various conditions such as added alkali equivalent, type, temperature, and time. I know. In the present invention, the neutralization and aging after neutralization are performed at a low temperature, and when the neutralized product is aged, crushing or strong agitation is performed, and the shape of the neutralized product is specified. There is one feature in that it is controlled to a thing (fine and crystalline chain-like thing). Thereby, the iron oxyhydroxide produced | generated by oxidation can maintain a uniform particle size and acicularity, although it is a microparticle. Here, the low temperature neutralization means a temperature of 55 ° C. or less, preferably 45 ° C. or less, more preferably 35 ° C. or less, and most preferably 25 ° C. or less, and thereby fine particles are formed. While maintaining the acicularity, the particles on the fine particle side of the particle size distribution are reduced, and a uniform particle size is easily generated. Conversely, if the temperature is high, the neutralized product becomes coarse, and iron oxyhydroxide obtained by dissolution and precipitation reaction of the neutralized product is not preferable because the particle size distribution is poor and the particles on the fine particle side of the particle size distribution also increase.

  The aging process after neutralization is a process that greatly affects the form of the neutralized product, and here, the crushing must be performed for a long time with a strong crushing and stirring force. It is necessary to maintain the temperature in this step at a low temperature as in neutralization. For the crushing in this step, a homomixer, a line mill, and a homogenizer are most preferable. However, the apparatus is not particularly limited to these apparatuses as long as it has a strong crushing and stirring power.

  As for the neutralization aging temperature, a temperature similar to the neutralization temperature is preferable. In addition, since the reaction rate of the neutralized product is lower at lower temperatures, the lower the temperature, the longer the crushing / stirring time is required to obtain the effect of the present invention. In addition, when the crushing / stirring force is strong, the required aging time is short, and when it is weak, it is long. However, the conditions for easily producing uniform particles with reduced fine particle components, which is the effect of the present invention, are most preferably low temperature and long time conditions.

  As the alkali, sodium hydroxide, potassium hydroxide, alkali carbonate shown below and the like can be used. As the alkali carbonate, sodium carbonate, sodium hydrogen carbonate, ammonium carbonate, ammonium hydrogen carbonate, etc. can be used. If it is necessary to further strengthen the basicity from the balance of acid and base, NaOH or the like is used together with the alkali carbonate. Alkalis can be used.

  As the iron salt, hydrates of iron salts such as sulfates and hydrochlorides are used after being dissolved in water. Preferably, sulfate hydrates are inexpensive and easy to handle. Further, by adding not only Fe but also Co at the same time, the saturation magnetization and Hc of the reduced metal particles are greatly improved, and the physical properties of the tape are improved. The amount of Co added is balanced in terms of magnetic properties when Co / Fe = 10 to 50%. If it is more than that, the growth inhibitory effect of iron oxyhydroxide will increase, and the acicularity will be lost, and when it is reduced to a ferromagnetic metal powder, the magnetic properties will be greatly reduced.

  As for oxidation, generating a large number of more uniform nucleation crystals in the initial stage of oxidation leads to uniform particle size and fine particle formation. Therefore, uniform nucleation and finer nucleation can be generated by performing oxidation at a stretch with a stronger oxidizing power in the initial stage of oxidation. The selection of the oxidizing power can be controlled by the input amount, input time, oxidant type, and the like. As the oxidizing agent, oxygen, aqueous hydrogen peroxide, or the like can be used. Preferably, a large flow rate of oxygen-containing gas, and more preferably, iron oxide oxyhydroxide having a uniform particle size with highly oxidizing hydrogen peroxide. It is preferable in obtaining.

  The iron oxyhydroxide particles obtained in this way reduce the ultrafine particles on the fine particle side of the particle size distribution, and even though they are fine particles, they have a uniform particle size.

  The iron oxyhydroxide particles preferably contain an Al compound or a rare earth element compound as a sintering inhibitor for maintaining the shape during firing and reduction. Al addition is performed by adding a water-soluble aluminum salt to the reaction solution in the middle of the production reaction of iron oxyhydroxide so that Al is present inside the iron oxyhydroxide. As the aluminum salt, sodium aluminate, aluminum sulfate or the like can be used. As for the amount of Al added, a suitable anti-sintering effect can be obtained when the Fe ratio is 2 to 40 at%. If it is less than this, the anti-sintering effect is low and the magnetic properties are greatly reduced. In this case, foreign particles are noticeable around the metal particles after reduction, resulting in a decrease in magnetic properties and wasteful production costs. Preferably, when it is about 5 to 35 at%, the sintering preventing effect appears more effectively. As a method of containing high Al, a method of adding an aqueous solution of Al during the iron oxyhydroxide reaction is used, but in order to contain more Al in iron oxyhydroxide, liquid properties such as alkali equivalent, temperature, You must balance the oxidation rate.

  For the addition of rare earth elements, a sulfuric acid solution of a lanthanoid rare earth element such as Y, La, Nd, Ce, Sm, Gd, Yb or the like is added to an iron oxyhydroxide slurry, or the fired hematite is slurried with water. It is good to make it adhere to the surface by adding it in the inside. The addition amount is preferably 5 to 30 at% in terms of Fe ratio, and this effectively exhibits the effect of preventing sintering. When it is less than this, it does not show a sufficient sintering preventing effect, and when it is more than this, it becomes difficult to contain it uniformly. The amount of change varies depending on the rare earth element selected, and the appropriate amount should be determined and used.

  Further, the obtained iron oxyhydroxide is filtered, washed with water, dried and then fired at 250 to 600 ° C. After calcination, in order to remove soluble components appearing on the surface, the slurry is slurried with water, stirred for 12 hours or longer, washed with filtered water, repeated three times or more, and then dried. By proceeding with the removal of this soluble component, it becomes possible to suppress the sintering of the fine particles during the subsequent reduction. However, in some cases, the following reduction may be performed without firing and cleaning. Next, reduction is performed for 1 hour or more in a hydrogen atmosphere at 300 to 700 ° C., and the reduction is advanced to metal particles. At that time, water vapor may be added to the hydrogen atmosphere. The finer the particles, the better the reduction. Those containing a large amount of Al have a large sintering preventing effect, so that the reduction can be promoted with the reduction temperature raised and the crystallinity raised.

  Thereafter, in order to form an oxide film on the surface, an oxide film is formed on the surface for stabilization while adjusting the oxygen concentration to a small amount, thereby obtaining magnetic metal particles. In addition, during this oxidation, the thickness of the oxide film can be adjusted by adjusting the oxidation temperature.

  The magnetic particles thus obtained can be present as fine particles having a uniform particle size and shape even when they become metal magnetic fine particles in the subsequent firing and reduction. The magnetic powder of the present invention thus obtained can have the following characteristics.

  The average major axis length is 10 to 80 nm, preferably 15 to 60 nm, and more preferably 20 to 50 nm. If the average major axis length is too large, it does not correspond to short wavelength recording, and if it is too small, it is affected by thermal fluctuations, so this range is necessary. The average minor axis diameter is 2 to 20 nm, preferably 5 to 17 nm, more preferably 6 to 15 nm. If the surface is too small, the metal portion at the center of the particle disappears when the surface oxide film is formed, and the magnetic properties However, if it is too large, the axial ratio is lowered, Hc is lowered, and it is not suitable as a high-density medium. The axial ratio is preferably 1.5 to 8, more preferably 2 to 8, and further preferably 2 to 5.

  The dispersion of the major axis length of the particles is preferably distribution (standard deviation / average value × 100) σL = 25% or less, more preferably 20% or less. Further, the minor axis length distribution of particles (standard deviation / average value × 100) σD = 25% or less, more preferably 20% or less. The crystallite (crystal grain size) Dx of the particles should be 50 to 160 angstroms, preferably 70 to 145 angstroms, more preferably 80 to 130 angstroms. If the crystallite is too small, the crystallinity is insufficient and desired magnetic characteristics cannot be obtained. If the crystallite is too large, the electromagnetic conversion characteristics of the tape may be adversely affected.

  Here, the ratio of the ultrafine particles of 1 nm to 10 nm present in the magnetic powder needs to be 15% or less, preferably 10% or less, more preferably 8% or less, with respect to all particles. However, it has excellent electromagnetic conversion characteristics and can be used as a high-density magnetic recording medium. As other characteristics, the magnetic powder according to the present invention has an oxidation resistance Δσs of 10% or less, a water-soluble sulfate group, a water-soluble group 1a element, a group 2a element each of 50 ppm or less, and a magnetic characteristic of Hc 1200 Oe or more. is there.

  Examples are given below. Each measured value in the examples is according to the following measuring method.

[Powder shape]
・ Adjustment of photographic sample Add about 0.005 g of measurement sample to 10 mL of 2% collodion solution, disperse the solution, and drop 1 to 2 drops of the solution in water to form a collodion film on one side of the grid. After depositing and air drying, carbon deposition was performed to strengthen the coating. The transmission electron microscope measurement is performed using the grid.

・ Observation of particles The particle diameter was observed in a bright field using a transmission electron microscope (TEM, JEM-2010 model manufactured by JEOL Ltd., at an acceleration voltage of 200 kV. Average minor axis length, The major axis length is measured by measuring the major axis and minor axis of each of 500 or more particles shown in the photo of an electron micrograph (× 50,000) enlarged three times in the vertical and horizontal directions, and calculating the average value. However, the particles present on the electron micrograph are not only monodispersed particles, but also particles that are bonded (sintered or intergrowth) between particles, and in various states such as overlapping particles. Since it exists in the photograph, it is necessary to make a reasonable and reasonable decision in advance as to which particle is to be measured and how to measure it. The standard was measured. It was as follows.

-Long and short axis diameter measurement position reference The major axis diameter is a value obtained by measuring the longest part in the longitudinal direction of the particle. The minor axis diameter refers to a value obtained by measuring the longest portion in the width direction of the particle. The selection criteria for the measurement particles of the particles obtained in the transmission electron micrograph were as follows.

  [1] Among particles, particles that partly protrude outside the field of view of the photograph are not measured. [2] Measure particles that have a clear outline and exist in isolation. [3] Of the particles, particles that are not needle-shaped but are independent and can be measured as single particles are measured. [4] Among the particles, there is an overlap between the particles, but the boundary is clearly known, and the particle whose shape can be judged is measured as each single particle. [5] Of the particles that overlap, the boundaries between the particles are not clear, and the particles whose total shape is known are considered as sintered or intergranular. Measure as one particle. [6] Of the particles, those that overlap and whose boundaries are not clear, and that do not know the entire shape of the particles, are not measured because the shape of the particles cannot be determined.

  The presence or absence of bonding between the particles, that is, whether the particles are simply overlapping or sintered is determined by the following judgment method. (B) Prepare multiple photos with different focus, and from the photo where fringes (note: the boundary line where the substance changes in the bright field of the electron microscope) often appear, Determine the boundary. (B) In the overlapping particles, observe the corners to be formed in the overlapping part, and when the formed corners are clearly seen, it is judged that the particles are overlapping, and conversely if they are rounded Sintered. (C) If it is not clear whether the boundary exists or not, and it is difficult to judge, it is not judged that inter-particle sintering has occurred. Therefore, consideration was given to prevent the geometric standard deviation from increasing due to misjudgment. This is because if the particle is considered to be sintered, the particle size is measured as a large particle size. If the particle size variation is large, the geometric standard deviation indicating the particle size variation. This is because it is necessary to prevent an increase in the standard deviation due to a particle judgment error.

[Variation of major axis length and minor axis length]
The dispersion of the major axis length and minor axis diameter was calculated by standard deviation / average value × 100.
[Abundance of fine particles with a major axis length of 10 nm or less]
The presence ratio of fine particles having a major axis length of 10 nm or less was calculated as the ratio (%) to the total number of measured particles by calculating the number of particles having a major axis length of 10 nm or less among all the measured particles.

〔composition〕
The amount of Co, Al and amount of rare earth elements in each magnetic particle powder were measured by ICP.
[Powder characteristics]
The specific surface area was determined by measuring the specific surface area (m ² / g) by the BET method.
Dx (crystallite particle size) was determined from the Debye-Scherrer equation using the X-ray diffraction method (unit: angstrom).
[Magnetic properties]
Measured at 10 KOe using VSM.
[Weather resistance of powder]
For weather resistance (Δσs), measure σs when stored for 1 week in an environment of temperature 60 ° C and humidity 90% RH, and save the% decrease in σs of the sample before storage (difference between σs before and after storage) The weather resistance was evaluated by the value divided by the previous σs × 100 = Δσs%).

[Single layer tape, coating properties]
The following materials are blended in a proportion of the following composition with respect to 100 parts by weight of magnetic powder, and dispersed for 1 hour with a centrifugal ball mill to produce a magnetic paint. This magnetic paint is applied to a base film made of polyethylene terephthalate. The magnetic tape was produced by applying the magnetic tape, the coercive force Hcx was measured, and the SFD value was calculated from the hysteresis loop.

Magnetic powder 100 parts by weight Polyurethane resin 30 parts by weight Methyl ethyl ketone 190 parts by weight Cyclohexanone 80 parts by weight Toluene 110 parts by weight Stearic acid 1 part by weight Acetylacetone 1 part by weight Alumina 3 parts by weight Carbon black 2 parts by weight

[Multilayer tape]
Ferromagnetic iron alloy powder was subjected to a production test of a magnetic tape having a multilayer structure of a magnetic layer and a nonmagnetic layer, and an electromagnetic conversion measurement and storage stability evaluation were performed. In the preparation of the magnetic coating material, the following materials were blended at a ratio of the following composition to 100 parts by weight of the ferromagnetic iron alloy powder. In preparation of the non-magnetic coating material, the following materials were blended at a ratio of the following composition with respect to 80 parts by weight of the non-magnetic powder. All the blends were kneaded and dispersed using a kneader and a sand grinder. The obtained coating liquid for forming a magnetic layer and the coating liquid for forming a specific magnetic layer (lower layer) are each formed on a base film made of an aramid support with a target layer thickness of 2.0 μm and a magnetic layer thickness of 0.20 μm. While the magnetic layer was in a wet state, it was oriented by applying a magnetic field, dried, and calendered to produce a multilayered magnetic tape.

[Composition of magnetic paint]
Ferromagnetic iron alloy powder 100 parts by weight Carbon black 5 parts by weight Alumina 3 parts by weight Vinyl chloride resin (MR110) 15 parts by weight Polyurethane resin (UR8200) 15 parts by weight Stearic acid 1 part by weight Acetylacetone 1 part by weight Methyl ethyl ketone 190 parts by weight Cyclohexanone 80 parts by weight 110 parts by weight of toluene

[Composition of non-magnetic paint]
Nonmagnetic powder α-Fe ₂ O ₃ 85 parts carbon black 20 parts alumina 3 parts vinyl chloride resin (MR110) 15 parts polyurethane resin (UR8200) 15 parts methyl ethyl ketone 190 parts cyclohexanone 80 parts toluene 110 parts by weight

[Surface smoothness]
The surface roughness was evaluated by measuring the Ra (roughness) of the surface of the lower layer tape using a three-dimensional fine shape measuring machine (ET-30HK) manufactured by Kosaka Laboratory. The smaller the Ra, the smaller the surface roughness and the smoother the surface properties.

[Electromagnetic conversion characteristics]
The magnetic characteristics and electromagnetic conversion characteristics (C / N, output) of the obtained magnetic tape were measured. Of these, the C / N ratio was recorded by attaching a recording head to a drum tester and recording a digital signal at a recording wavelength of 0.35 μm. At that time, an MR head was used to measure the reproduction signal, and the noise was measured as modulation noise. In the evaluation, the output when the ferromagnetic iron alloy powder obtained in Comparative Example 1 was used, and C / N were displayed as 0 dB. Further, the storage stability of the magnetic tape was evaluated as ΔBm, which represents the change in saturation magnetization before and after storage in% at 60 ° C. and 90% RH atmosphere in%.

[Example 1]
[Neutralization treatment, aging treatment after neutralization]
Under a nitrogen atmosphere, a solution of FeSO ₄ + CoSO ₄ (a solution containing Co at a ratio of Co / Fe × 100 = 24 at.%) Was added to a solution concentration of 0.2 mol / L so that the liquid volume became 30 L. Place in the reactor and stir while maintaining at 40 ° C. Therefore, an aqueous solution of Na ₂ CO ₃ is added in an amount equivalent to 2.6 equivalents to Fe, and further an aqueous solution of NaOH is added in an amount equivalent to 0.3 equivalents for neutralization.

[Aging treatment after neutralization]
Thereafter, pure water is added so that the amount of the solution in the container becomes 40 L. While stirring the solution, the solution is circulated, and a ripening treatment is performed while performing a wet crushing treatment at 7500 rpm for 3 hours with a homomixer.

[Oxidation treatment and Al input treatment]
Next, with the temperature kept at 40 ° C., air was blown into the reaction vessel at a flow rate of 3000 mL / min, and during the oxidation, the Al ₂ (SO ₄ ) ₃ solution was Al / (Fe + Co) × 100 = 20.1 at.%. Add over time. Subsequently, the air is continuously blown for 24 hours to oxidize.

[Rare earth element coating]
After completion of the oxidation treatment, a sulfuric acid solution of Y is added in an amount of Y / (Fe + Co) × 100 = 13 at.%, And the reaction is terminated after stirring for a while. Then, it is filtered and washed with water and dried at 100 ° C. for 12 hours.

[Heat oxidation treatment, cleaning treatment]
The obtained powder is baked in the atmosphere at 300 ° C. for 30 minutes to obtain iron oxide powder. This iron oxide powder is mixed with pure to make a slurry and stirred for 12 hours. Thereafter, filtration and washing with pure water are repeated three times, followed by drying to remove soluble components such as K, Na, and Ca. When this treatment with pure water was carried out three or more times with water washing, it was confirmed later that the periodic table group 1a elements in the powder were 50 ppm or less in total and the periodic table group 2a elements were also 50 ppm or less in total. Become.

[Heat reduction treatment]
Next, it is reduced to metal at 550 ° C. while flowing hydrogen gas at a flow rate of 10 L / min.

[Stabilization treatment (surface oxidation)]
After the reduction is completed, the mixture is cooled to 80 ° C., switched to nitrogen gas containing 0.1 vol.% Oxygen, oxidized at that temperature for 12 hours, cooled to room temperature, and the treatment is completed to obtain a magnetic powder. Tables 1 and 2 show the composition, powder characteristics, and tape characteristics of the obtained magnetic powder.

[Examples 2 to 9]
Example 1 was repeated except that the manufacturing conditions were the same as those described in Table 1 for each example. Tables 1 and 2 show the composition, powder characteristics, and tape characteristics of the obtained magnetic powder.

[Comparative Examples 1-3]
Example 1 was repeated except that the manufacturing conditions were the same as those described in Table 1 for each comparative example. Tables 1 and 2 show the composition, powder characteristics, and tape characteristics of the obtained magnetic powder.

  As can be seen from the results in Tables 1 and 2, in the crushing / stirring treatment during the aging of the neutralized product in the wet reaction for iron oxyhydroxide formation, the homogenizer or homogenizer is strongly crushed / stirred. Iron oxyhydroxide in which the ultrafine particle component of iron hydroxide is reduced is obtained, and the magnetic powder obtained by reducing it is reduced in the ultrafine particle component to obtain a magnetic powder having an improved particle size distribution. Further, the SFD of the tape using the magnetic powder is greatly improved, and a magnetic recording medium having excellent tape electromagnetic conversion characteristics can be obtained. In addition, it can be seen that these crushing and stirring processes cannot be effective unless they are performed at low temperatures for a long time. This indicates that when the neutralized product is refined in the aging step of the neutralized product, the particle size distribution of iron oxyhydroxide obtained therefrom is improved and the number of ultrafine particles is reduced.

Claims (6)

Co as Co / Fe, 10 to 50 at. % , Al as Al / (Fe + Co), 2 to 40 at. % , R (R represents at least one kind of rare earth element including Y) as R / (Fe + Co). % Acicular particles mainly containing Fe,
Average major axis length L of particles = 10 to 80 nm,
Average minor axis length D of particles = 2 nm to 20 nm,
Particle axial ratio L / D = 1.5-8,
Long axis length distribution of particles (standard deviation / average value × 100) σL = 25% or less,
Particle minor axis length distribution (standard deviation / average value × 100) σD = 25% or less,
Particle crystallite (crystal grain size) Dx = 50 to 160 angstrom,
Consisting of acicular particles in the range of
Furthermore, the fine particle magnetic powder for coating-type magnetic recording media, wherein the abundance ratio of ultrafine particles having a major axis length of 1 nm to 10 nm is 15% or less. After the iron salt solution containing Co salt is neutralized with alkali, an oxidizing agent is added and oxidized, and an Al compound is added in the course of this oxidation treatment, and then an R compound (R is a rare earth element containing Y). In the method for producing magnetic powder in which the obtained slurry is subjected to solid-liquid separation after the obtained slurry is solid-liquid separated, and then subjected to heat reduction treatment, the neutralization treatment is performed at a liquid temperature of 40 Particle size distribution with a small amount of ultrafine particles, characterized by maintaining the temperature below ℃ and holding the neutralized product for 1 hour or more after completion of the neutralization treatment in a nitrogen atmosphere. Manufacturing method of excellent fine particle magnetic powder. The Co salt has a Co / Fe atomic ratio of 10 to 50 at. %, The Al compound is 2 to 40 at.% In atomic ratio percentage of Al / (Fe + Co). %, R is an atomic ratio percentage of R / (Fe + Co) of 5 to 30 at. The method for producing fine particle magnetic powder according to claim 2 , which is added at a ratio of%. Preparation of microparticulate magnetic powder according to claim 2 or 3 carried with H ₂ O ₂ as an oxidizing agent for oxidation treatment. Fine particle magnetic powder for coating-type magnetic recording media obtained by using the production method according to claim 2 . A coated magnetic recording medium using the magnetic fine particles according to claim 1 .