JP2002121027A - Magnetic powder and method for manufacturing magnetic powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide new magnetic powder having high coercive force in a fine particle state so as to obtain further excellent recording and reproducing characteristics compared to a magnetic recording medium which uses conventional magnetic powder. SOLUTION: The magnetic powder consists of granules of 3 to 50 nm particle size containing iron as at least a structural element. The core part of the magnetic powder consists of alloy iron. The outer layer of the magnetic powder contains a compound containing rare earth elements and semimetal elements as at least structural elements, and at least either the rare earth elements or the semimetal elements are present by >=1 atm.% in the layer with 5 nm thickness from the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth-iron-metalloid magnetic powder containing at least rare earth, iron, and metalloid as constituent elements and a method for producing the same. More particularly, the present invention relates to a digital video tape. The present invention relates to a magnetic powder most suitable for a magnetic recording medium requiring high density recording, such as a tape and a backup tape for a computer.

[0002]

2. Description of the Related Art A coating-type magnetic recording medium in which a magnetic powder is dispersed in a binder is required to further improve the recording density as the recording / reproducing method shifts from an analog method to a digital method. In particular, this demand is increasing year by year for high-density video tapes and backup tapes for computers.

[0003] The improvement of the recording density has heretofore been largely realized by improving the magnetic powder and improving the tape manufacturing technique.

With respect to the improvement of magnetic powder, finer particles have been made year by year mainly to cope with short-wavelength recording, and at present, acicular metal magnetic powder having a particle length of about 0.1 μm is being put to practical use. . Further, in order to prevent a decrease in output due to demagnetization at the time of short wavelength recording, a high coercive force has been achieved year by year, and a coercive force of about 2500 Oe has been realized by iron-cobalt alloying (for example, JP-A-3-49026). Gazettes).

[0005]

However, in the current magnetic powder which has a high coercive force and is formed into an anisotropic shape by making it a needle-like shape, it has become more difficult to reduce the particle size more than the current state. . The present invention has been made in view of such a situation, and has found magnetic powder having fine particles and high coercive force, based on a different idea from conventional ones.

[0006]

Means for Solving the Problems The present inventor has proposed a magnetic powder containing high-performance fine particles and a high coercive force, which is a magnetic powder containing iron at least as a constituent element. A granular magnetic powder in a range of 3 to 50 nm, wherein the magnetic powder has a core portion, an outer layer portion of the magnetic powder contains a compound containing at least a rare earth element and a metalloid element as constituent elements, and a thickness of 5 nm from the surface. The magnetic powder in which at least one of the rare earth element and the metalloid element is present in the layer of 1 at% or more is found.

In the process for producing the magnetic powder of the present invention, when adding a rare earth element, an alkali is added to at least one kind of salt selected from rare earth salts, and the temperature is from 50 ° C. to 250 ° C.
It is preferable to carry out heat reduction after maintaining the temperature in a temperature range of 1 ° C. for 1 hour or more.

[0008] Further, when adding the metalloid element, 0 ° C.
It is preferable to use a solution in which a metalloid in a temperature range of １５15 ° C. is dissolved.

The magnetic powder of the present invention is prepared by synthesizing various magnetic powders with the aim of improving the magnetic properties from a viewpoint different from the conventional magnetic powder based on shape magnetic anisotropy, and first examining the magnetic anisotropy. As a result, it has been found that a granular powder having a core portion in a magnetic powder and an outer layer portion made of a compound containing a rare earth element satisfies the requirements.

In general, fine particles having a particle diameter of 100 nm or less have a large ratio of atoms appearing on the surface, so that it is known that unique properties of the surface appear, and this is a very interesting practical material. For example, surface active properties are used in catalyst materials. In the case of composite fine particles in which different kinds of materials are mixed in one fine particle, a portion where the core portion and the outer layer portion are in contact with each other becomes large, which greatly affects the properties of the whole fine particles. That is, in the case of fine particles, the surface structure is a factor that determines the material properties.

Therefore, the present inventors have proposed that the particle size is 3 to 50.
As a result of synthesizing and examining various magnetic powders in the range of nm,
A magnetic powder in which a core portion is present and the outer layer portion is a granular powder made of a compound containing a rare earth element, and the rare earth element is present in a layer having a thickness of 5 nm from the surface in a layer of 1 atomic% or more is a high density magnetic recording material. It has been found that it is a suitable material.

The rare earths to be present include rare earth elements such as yttrium, ytterbium, cesium, praseodymium, samarium, lanthanum, europium and neodymium. Among them, samarium, praseodymium and neodymium have high coercive force.

As a result of further study of the improvement of the coercive force, the present inventor found that the outer layer portion contained at least 1 atomic% of a rare earth element and a metalloid, and the outer layer portion contained at least a rare earth element and a metalloid element as constituent elements. It has been found that in such a case, a high coercive force can be achieved as a whole of the magnetic powder. Examples of the metalloid element include boron, phosphorus, silicon, aluminum, and carbon, but calcium and magnesium are also effective elements. In addition, the content of the rare earth element and the metalloid with respect to the iron is a value measured by atomic absorption analysis with respect to the entire magnetic powder, and a value measured by fluorescent X-ray with respect to the outer layer.

By using the magnetic powder having the structure and composition of the present invention, a high coercive force suitable as a magnetic powder for a magnetic recording medium can be obtained.
The reason why high saturation magnetization can be achieved at the same time is considered as follows. That is, since the core portion of the magnetic powder is made of, for example, metallic iron or ferromagnetic iron, and the outer layer surrounding the core is made of fine magnetic powder of a rare earth-iron-metalloid compound, the rare earth-iron-half of the outer layer portion is formed. Since the metal compound has surface magnetic anisotropy, or interfacial magnetic anisotropy caused by structural defects between the metallic iron or ferromagnetic iron in the core portion and the rare earth-iron-metalloid compound in the outer layer portion, large conservation is caused. It is considered that magnetic force is obtained. The reason that such magnetic anisotropy occurs as a property of the whole magnetic powder is that the particle size is 5 μm.
It is as small as 0 nm or less, and the number of atoms existing on the surface or interface is larger than the number of atoms in the entire magnetic powder. The magnetic powder having such a magnetic structure has been found for the first time in the present invention.

Next, the present inventors examined stable magnetic powder suitable for magnetic recording. The outer layer of the magnetic powder was an oxide containing a rare earth element, and the outer layer of the magnetic powder was a rare earth element. And an oxide containing a metalloid element. Among these, it was also found that the outer layer portion of the magnetic powder was an oxide containing a rare earth element and boron as a stable material in which the production method was easy. The state of the rare earth element and the metalloid element was measured by X-ray fluorescence.

In the present invention, the ratio of the rare earth element contained in the compound present in the outer layer having a thickness of 5 nm to the rare earth element contained in the core is preferably 1.5 or more. When this value is 1.5 or less, the abundance ratio of the rare earth element in the core portion increases, and the saturation magnetization of the core portion decreases. Therefore, the saturation magnetization of the magnetic powder as a whole also decreases. Also, the coercive force is greatly reduced. It is considered that this is because the boundary between the core portion and the outer layer portion is not clear, and the magnetic interaction is reduced. In addition, it is preferable that the metalloid element is contained at 5 atomic% or more with respect to iron in the layer having the outer layer thickness of 5 nm. If this value is 5 atomic% or less, it becomes difficult to form an outer layer portion containing a metalloid element, and the coercive force decreases.

The content of the rare earth element in the magnetic powder as a whole is 0.05 to 20 atomic% with respect to iron, and the content of the metalloid element is 0.1 to 15 atomic% with respect to iron. Is preferred.

When the contents of the rare earth element and the metalloid element are 0.05 atomic% and 0.1 atomic%, respectively, it is difficult to form the outer layer portion, and the coercive force decreases.
In addition, the content of each of the rare earth element and the metalloid element is 2
If the content is 0 atomic% or 15 atomic% or more, the ratio of the rare earth element and the metalloid element to the entire magnetic powder becomes large, so that the saturation magnetization decreases.

The magnetic powder of the present invention may contain other elements in order to improve corrosion resistance and the like.
Also in this case, the core part is an alloy and an intermetallic compound, the outer layer part of the magnetic powder is made of a compound containing a rare earth element, and the rare earth element is present in a layer having a thickness of 5 nm from the surface in an amount of 1% by weight or more. preferable. In this case, the particle size of the magnetic powder may be 30 nm or more.

In the production method of the present invention, at the time of adding the rare earth element, an alkali is added to at least one kind of salt selected from rare earth salts, and after maintaining at a temperature range of 50 ° C. to 250 ° C. for 1 hour or more, It is preferred to reduce. This is for dispersing the rare earth element uniformly and stabilizing the formation of the outer layer portion. In addition, when adding a metalloid element, in order to adsorb the metalloid element efficiently,
It is preferable to use a solution in which a metalloid in a temperature range of 0 ° C. to 15 ° C. is dissolved.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.

Example 1 0.074 mol of iron nitrate (II
600cc of I) and 0.0005 mol of samarium nitrate
Dissolved in water. Apart from this nitrate solution, 0.22
Two moles of sodium hydroxide were dissolved in 300 cc of water. An aqueous solution of iron nitrate was added to the aqueous solution of sodium hydroxide, and the mixture was stirred for 5 minutes to form a coprecipitate of iron. Thereafter, the solution was heated to 80 ° C. and held for 30 minutes. After washing with water, the hydroxide was taken out by filtration.

Next, a coprecipitate of iron and samarium was redispersed in an aqueous solution in which 0.007 mol of boric acid was dissolved in 30 cc of water. After filtering this dispersion, it was dried at 60 ° C. for 4 hours to remove water, thereby producing a coprecipitate of iron and samarium containing boron.

This was heated and reduced in a hydrogen stream at 500 ° C. for 4 hours to produce a samarium-iron-metalloid magnetic powder. Next, in air, the temperature was maintained at 60 ° C., and a stabilization treatment was performed for 8 hours. This samarium-iron-
When the contents of samarium and boron with respect to iron of the boron-based magnetic powder were measured by an atomic absorption spectrometer, they were 2.6 atomic% and 3.1 atomic%, respectively. Observation and analysis with a high-resolution analytical transmission electron microscope revealed that the particles were granular or elliptical with a particle diameter of 20 nm, and that the content of samarium in the layer having a thickness of 5 nm from the core portion and the surface was 0.5 atomic%. Was found to be 4 at%. Further, when samarium and boron in the outer layer portion were analyzed by X-ray fluorescence, 30 atomic% and 45 atomic% were present with respect to the iron content in the outer layer portion, respectively. Was. 16kOe
The saturation magnetization measured by applying a magnetic field of 174 emu /
g and coercive force were 1700 Oe.

Example 2 Example 1 was the same as Example 1 except that samarium nitrate was changed to praseodymium nitrate.
A praseodymium-iron-boron magnetic powder was prepared in the same manner as described above.

The content of praseodymium and boron with respect to iron in the praseodymium-iron-metalloid magnetic powder was measured by atomic absorption spectroscopy.
3.0 atomic%. When the magnetic powder was observed and analyzed with a high-resolution analytical transmission electron microscope in the same manner as in Example 1, it was found to be granular or elliptical particles having a particle diameter of 20 nm, and praseodymium in a layer having a thickness of 5 nm from the core portion and the surface. Was 0.5 atomic% and 4 atomic%, respectively. Furthermore, when praseodymium and boron in the outer layer portion were analyzed by X-ray fluorescence, the content of iron in the outer layer portion was 30 atomic% and 45 atomic%, respectively.
Present, and they were found to be oxides. The saturation magnetization measured by applying a magnetic field of 16 kOe was 173 emu / g, and the coercive force was 1710 Oe.

Comparative Example 1 A samarium-iron-boron magnetic powder was prepared in the same manner as in Example 1, except that the amount of samarium nitrate was changed from 0.0005 mol to 0.0001 mol. Produced.

When the contents of samarium and boron with respect to iron of the samarium-iron-boron magnetic powder were measured by an atomic absorption spectrometer, they were 0.5 atomic%, respectively.
It was 2.5 atomic%. When observed and analyzed with a high-resolution analytical transmission electron microscope, it was found to be granular or elliptical with a particle size of 35 nm and a thickness of 5 nm from the core and the surface.
It was found that the content of samarium in the layer was 0.8 atomic% and 0.5 atomic%, respectively.

Further, when samarium and boron in the outer layer portion were analyzed by X-ray fluorescence, 30 atomic% and 45 atomic% were present with respect to the iron content in the outer layer portion, respectively, and these were oxides. I understood that. 16
The saturation magnetization measured by applying a magnetic field of kOe is 186 em
u / g and the coercive force were 890 Oe.

Example 3 A samarium-iron-boron magnetic powder was prepared in the same manner as in Example 1, except that the amount of boron was changed from 0.007 mol to 0.0025 mol. did.

When the contents of samarium and boron with respect to iron of the samarium-iron-boron magnetic powder were measured by an atomic absorption spectrometer, they were 2.6 atomic%, respectively.
It was 0.7 atomic%. When observed and analyzed with a high-resolution analytical transmission electron microscope, it was found to be granular or elliptical with a particle size of 30 nm and a thickness of 5 nm from the core and the surface.
It was found that the content of samarium in each layer was 0.5 atomic% and 4 atomic%, respectively. Furthermore, fluorescent X
When samarium and boron in the outer layer portion were analyzed by a line, they were found to be 30 atomic% and 12 atomic%, respectively, with respect to the iron content in the outer layer portion, and they were found to be oxides. The saturation magnetization measured by applying a magnetic field of 16 kOe is 163 emu / g, and the coercive force is 1450 Omu.
e.

Example 4 Example 1 was repeated except that an aqueous solution of sodium hydroxide was added with an aqueous solution of iron nitrate and then stirred for 5 minutes, and then the solution was heated to 80 ° C. and held for 6 hours. In the same manner as in Example 1, a samarium-iron-boron magnetic powder was produced.

The contents of samarium and boron with respect to iron in the samarium-iron-semimetallic magnetic powder were measured by atomic absorption spectroscopy.
It was 0 atomic%. When the magnetic powder was observed and analyzed with a high-resolution analytical transmission electron microscope in the same manner as in Example 1, it was found to be granular or elliptical particles having a particle size of 15 nm, and samarium in a layer having a thickness of 5 nm from the core portion and the surface. Was determined to be 0.3 atomic% and 8 atomic%, respectively.
Atomic% was found. The saturation magnetization measured by applying a magnetic field of 16 kOe is 180 emu / g, and the coercive force is 1
It was 900 Oe.

(Example 5) In Example 1, after adding an aqueous solution of sodium hydroxide to an aqueous solution of sodium hydroxide,
A samarium-iron-boron magnetic powder was prepared in the same manner as in Example 1 except that the hydrothermal treatment was performed at 60 ° C. for 1 hour.

The contents of samarium and boron with respect to iron of the samarium-iron-semimetallic magnetic powder were measured by atomic absorption spectroscopy.
It was 0 atomic%. When the magnetic powder was observed and analyzed with a high-resolution analytical transmission electron microscope in the same manner as in Example 1, it was found to be granular or elliptical particles having a particle size of 12 nm, and samarium in a layer having a thickness of 5 nm from the core portion and the surface. Was measured to be 0.1 atomic% and 1 atomic%, respectively.
It was found to be 5 atomic%. The saturation magnetization measured by applying a magnetic field of 16 kOe was 155 emu / g, and the coercive force was 2000 Oe.

(Example 6) In Example 1, 30 cc
Dissolve 0.007 mol of boric acid in water and cool to 5 ° C
A samarium-iron-boron-based magnetic powder was produced in the same manner as in Example 1 except that the boric acid solution held in was used.

The samarium-iron-semimetallic magnetic powder was measured by atomic absorption spectroscopy to determine the contents of samarium and boron with respect to iron.
It was 0 atomic%. When the magnetic powder was observed and analyzed with a high-resolution analytical transmission electron microscope in the same manner as in Example 1, it was found to be granular or elliptical particles having a particle diameter of 20 nm, and samarium in a layer having a thickness of 5 nm from the core portion and the surface. Was determined to be 0.5 atomic% and 4 atomic%, respectively.
Atomic% was found. Further, when samarium and boron in the outer layer portion were analyzed by fluorescent X-rays, 35 atomic% and 48 atomic% were respectively determined with respect to the iron content in the outer layer portion.
At%, and these were found to be oxides. The saturation magnetization measured by applying a magnetic field of 16 kOe was 165 emu / g, and the coercive force was 1850 Oe.

[0038]

As explained above, the rare earth of the present invention
The iron-metalloid magnetic powder has a high coercive force based on magnetic anisotropy generated in the core portion and the outer layer portion while having a granular or elliptical shape, and has a high saturation magnetization despite being extremely fine particles. It can be seen that this is a novel magnetic powder that has a completely different idea from the conventional magnetic powder. Therefore, the magnetic powder of the present invention is a magnetic powder particularly suitable for a magnetic recording medium requiring high-density recording, and its industrial utility value is extremely large.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinichi Kitahata 1-1-88 Ushitora, Ibaraki City, Osaka Prefecture Inside Hitachi Maxell Co., Ltd. (72) Mikio Kishimoto 1-188 Ushitora, Ibaraki City, Osaka Hitachi F-term (reference) in Maxell, Inc. 4G002 AA09 AB02 AC00 AD03 AE03 5D006 BA04 BA08 5E040 AA04 BC01 CA06 HB09 HB14 HB17 NN06 NN17 NN18

Claims (11)

[Claims] 1. A granular magnetic powder having iron as a constituent element and having a particle size in the range of 3 to 50 nm, wherein a core portion is present in the magnetic powder, and an outer layer portion of the magnetic powder is composed of a rare earth element and a metalloid element. And at least one of a rare earth element and a metalloid element is present in a layer having a thickness of 5 nm from the surface in an amount of 1 atomic% or more. 2. The magnetic powder according to claim 1, wherein each of the rare earth element and the metalloid element is present in a layer having a thickness of 5 nm from the surface in an amount of 1 atomic% or more. 3. The magnetic powder according to claim 1, wherein the outer layer portion of the magnetic powder is an oxide containing a rare earth element. 4. The magnetic powder according to claim 1, wherein the outer layer portion of the magnetic powder is an oxide containing a rare earth element and a metalloid element. 5. The magnetic powder according to claim 1, wherein the outer layer portion of the magnetic powder is an oxide containing a rare earth element and boron. 6. The rare earth element contained in the compound existing in the layer having a thickness of 5 nm from the surface and the rare earth element contained in the core portion have an abundance ratio of 1.5 or more. Magnetic powder. 7. The magnetic powder according to claim 1, wherein the metalloid element is contained in the layer having a thickness of 5 nm from the surface in an amount of 5 atomic% or more with respect to iron. 8. The magnetic powder according to claim 1, wherein the content of the rare earth element in the whole magnetic powder is 0.05 to 20 atomic% with respect to iron. 9. The magnetic powder according to claim 1, wherein the content of the metalloid element as a whole of the magnetic powder is 0.1 to 15 atomic% based on iron. 10. A method of adding a rare earth element, comprising adding an alkali to at least one kind of salt selected from rare earth salts, maintaining the temperature in a temperature range of 50 ° C. to 250 ° C. for 1 hour or more, and then reducing by heating. The method for producing a magnetic powder according to any one of claims 1 to 9, wherein 11. The method according to claim 1, wherein the addition of the metalloid element is carried out at 0 ° C.
The method for producing a magnetic powder according to any one of claims 1 to 9, wherein a solution in which a metalloid in a temperature range of 15 ° C is dissolved is used.