JPS63179001A - Production of hyper-fine particle of magnetic material - Google Patents

Abstract

PURPOSE:To produce hyper-fine particle of a magnetic material having a uniform particle shape and distribution, high saturation magnetization and low coercive force by subjecting a base material consisting of the hyper-fine particle of the magnetic material contg. Fe and Zn elements to a heat treatment at a high temp. in an atmosphere below atm. pressure. CONSTITUTION:A base material consisting of the hyper-fine particle of the magnetic material contg. the Fe and Zn elements is subjected to the heat treatment for 1 - several hours at >=800 deg.C in the atmosphere of the atm. pressure or reduced pressure. The above-mentioned base material is preferably obtd. by a co-deposition method such as, for example, method of adding NaOH to an aq. soln. contg. FeCl2 and ZnCl2 and has about several - tens and some nm grain size. The above-mentioned heat treatment is adequately executed in the atm. atmosphere or inert gaseous atmosphere such as N2. The hyper-fine particle of the magnetic material of the single compsn. having the high saturation magnetization, low coercive force and uniform particle shape and distribution is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of application of the present invention)
The present invention relates to a method for producing ultrafine magnetic particles having

(Problems raised by the prior art and the invention as a final step) Conventionally, the magnetic ultrafine particles of this woodcutter have been used for magnetic recording.

It is used in many directions for magnetic fluids. For example, γ-Fe is one of the most widely used materials for magnetic recording particles, and its production process uses acicular α-Fe00H as a starting material, (1-Fe0OH+ a -Fe2O-+FB, 0.→
γ-Fe2O3 is produced through the following steps. All of these steps are oxidation or reduction reactions accompanied by heat treatment. In this case, especially in the initial process, the uniformity of the shape (acicular, branched shape distribution) is seriously impaired due to the formation of bores (holes) due to dehydration and sintering. Therefore, when producing a medium for recording hunting trips, there was a problem in that the particles were not sufficiently dispersed and the magnetic properties were rarely uniform.

In response to this, a sealing treatment is performed to prevent the formation of bores, but in this case as well, although some improvement in coercive force is generally recognized, the result is that impurities are contained, so it is chaotic. The problem of lowering the level of 50% is rare.
There was a problem that the number of processes would increase.

In addition, magnetic shielding materials generally have high saturation magnetization;
It is desired to have a low coercive force, low cost, and high productivity. Conventionally, Zn-ferrite has been mainly used, but its saturation magnetization is as small as emu/l at most, and it has not been possible to obtain a material with good characteristics. On the other hand, there are other high saturation magnetization materials, such as sendust, but this material suffers from the problems of being difficult to process, expensive, and lacking in productivity due to its tendency to become fine particles. That is, in the technical field of conventional magnetic shielding materials, there has been no material that satisfies both <&) productivity and (b) high saturation magnetization.

(Objective of the Invention) The present invention has been proposed to improve the above-mentioned drawbacks, and an object of the present invention is to provide a method for producing ultrafine particles having uniform particle shapes and high saturation magnetization. .

(Friendly means to resolve the problem) In order to achieve the above object, the present invention provides a base material made of ultrafine magnetic particles containing Fe and Zn elements at a temperature of 800°C or higher in an atmosphere of normal pressure or reduced pressure. The gist of the invention is a method for producing ultrafine magnetic particles characterized by heat treatment.

The feature of the present invention is that it can be obtained by using the coprecipitation method.
The starting material (base material) is ultrafine magnetic particles with several 1O planes, and the 1- The manufacturing method of magnetic ultrafine particles obtained by heat treatment for several hours is different from conventional technology because (a) the starting material is different, (b) the process is simple with only one, and (c) the range of heat treatment conditions. They are different in that they are different.

Next, the present invention will be explained in detail. It should be noted that the embodiments are merely illustrative, and it goes without saying that various changes and improvements may be made without departing from the scope of the present invention.

The method for producing ultrafine magnetic particles as a starting base material is disclosed in Japanese Patent Publication No. 36-18284, Japanese Patent Application No. 59-200298, etc., and examples thereof will be described here. . The magnetic ultrafine particles that will serve as the starting base material thereafter can be produced in the same manner.

[Implementation f/+J 1: Fe0o, @Zn06,4・
In the case of Fetol] (1) 0.2 mol/l FeCL
g water bath & 0.1 mol/l FeCL* at 50 mA
Add 50 mt of an aqueous solution of ZnCtl and ZnCtl at a ratio of 6:4 to make a ferrite aqueous solution, and then suddenly add 3N NaOH at room temperature. 3N Na
The OH violet was adjusted so that the pH of the mixed solution was alkaline, around 13. The mixed bath solution was heated while stirring, and the w% composition of the precipitate was heated at ℃ for 1 hour. After that, it is thoroughly cleaned, dehydrated in a centrifuge, and heated at a lower temperature.
For example, drying is carried out under reduced pressure at 60°C r O-I Torr. In this way, P″eo@,s Zn0 as the starting base material
6,4 @ got 'etos (# A O) 7
to get jL 7j Fe0o, @ Zn0o, a ”
For Fe101 particles, the semi-uniform particle diameter was determined from the half-width of the xm (b) fold spectrum using the 7-error formula (Sherrer, ).

In addition, hunting characteristics were measured using an excitation magnetometer (manufactured by Toei Kogyo) at a maximum magnetic field of 12KOe, and this was determined by 1/H (H = fBJa
)→0(H→■) Find the saturation magnetization σB as the limit.

In addition, chemical analysis confirmed that although the water was contained in several layers, it was found to have a consistent composition.

Fe06 of the above starting base material #A-〇. @*Zn06. a・
The semi-uniform grain size of Fe, 03 is about 10 nm, the saturation magnetization is about 70 emu/f + the coercive force Hc is less than 100 e, making it a good choice.

(2) This Fe0(,,@* Zn0o, 4-Fe*
03e (A 1 ) In the atmosphere.

(A-2) In Nt gas, specifically in a furnace of about 10 tons,
Flow N and gas in a mud wave for 1 mL, (A-3) 1 to 3
Heat treatment was performed for 1 hour at temperature T'C in reduced pressure air of In air, heat treatment was further performed at 100°C for 2 hours (A-3)' and 3 hours (A-31). Too soo
The value of the starting base material increased by 9 when the heat treatment temperature exceeded 'c. In particular, in a reduced pressure atmosphere at 1000°C for 1 hour (D
(A-3) and 1000 CX 2 hours.

For those heat-treated at 1000°C for 3 hours, '3 = 110
emu/l was 57% larger than the starting base material, 70 emu/f.

At this time, the coercive force was a small value of 200e or less.

In addition, the particle size varies from about 10 nm of the starting base material to about 400 nm.
The particle size has grown to about 1.0 m and the particle size has increased while maintaining the shape (size ratio) of 1 particle.However, no bores are seen.Figure 2 shows Fe06.@ as the starting base material. Zn
06.4" FetO1 particles (Fig. 2a) and particles obtained by heat-treating the FetO1 particles at 1000°C for 1 hour under reduced pressure (Fig. 2a)
Transmission electron microscope showing the shape of wJ2 figure b) 〇 [Implementation?] 1J2) (1) FeC1HfA degree f 0.4 m in implementation PI l
ol/l* FeC4 and ZnCtt 5lft 0.
2 mol/l each k 2 times Kj Is everything else done? +1
Fe06. @ Zn0a, 4 Fet
Obtained US. This sample was designated as #B. In this case, the average particle size was approximately 12 nm, which was slightly larger than that of the starting base material #A-0 of Example 1.

(2) In Example 1, FeC4 concentration 1 jtl t 1 mol
/l, FeCt, and ZnCt total concentration 5 mol
F in the same manner as in Example 1, except that /l and each are multiplied by 5.
e0(1,@znoO,4Fetus) was obtained. This sample was designated as #C, and the average particle size of $C was 14 nm, which was larger than that of #A-0.

The above starting base materials #B and #C were heated in the same way as in the test sample 1 in a reduced pressure atmosphere, specifically at 1 to 3 x 10-” Torr.
Heat treatment was carried out at temperature TC in an atmosphere of 1 hour, and the saturation magnetization values were plotted in FIG.

In Figure 3, (A-3) in Figure 1 is also reproduced.

As shown in Figure 3, heat treatment exceeds 900℃! A starting base material with a large saturation magnetization was obtained at a temperature of 1. The coercive force is also 300
It was small at 0e.

[Example 3] (1) In Example 1, the ratio of the valley FeCtt and ZnC4 mixture with a concentration of 0.1 mol/l was changed to (3-1) 30
Near 0° (3-2) 50:50. (3-3) 70:3
The starting base material F was prepared in the same manner as in Example 1 except that
e0xZn01-xeFet03 (However, (3-1
) is x=0.3. (3-2) is x=0.5. (3
-3) creates x=o, 7]. These starting base materials are heated in a reduced pressure air atmosphere, specifically 1 to 3
Heat treatment was performed for 1 hour at a temperature of TC in an atmosphere of 0.25 mm, and the resulting saturation magnetization was plotted in Figure 4. The same figure shows the 11th
The curve (A-3) is also reproduced.

As can be seen from the figure, large saturation magnetization of the starting base material was obtained at heat treatment temperatures exceeding 900 Ct. Coercive force H
C is also small and friendly, less than 300e. Mayu Koto! ! Similar to Disaster 1, the shape is cubic, and there is no sintering or bore formation.

[Comparative Example 1] In Implementation NJ 1, FeC at a concentration of 0.1 mol/
t150 ml t 0.2 mol/1 (Ik) eO・FelOl particles were obtained in the same manner as in Example 1, except for mixing and stirring with FeC450mt.
In a reduced pressure air atmosphere of 1 to 3 X 10-” Torr @
The dependence of the saturation magnetization on the heat treatment temperature for this sample is also shown in Figure 4 (thick solid line in Figure 4).

That is, in the comparative example, the saturation magnetization of the starting base material was 77 ernu/f.
At 100 degrees Celsius, the temperature increases slightly at a heat treatment temperature of 100 degrees Celsius, but rapidly decreases as the heat treatment temperature rises above 100 degrees Celsius.
At 000°C, the value decreased to 26 emu/7, 3H% and 28%, respectively, compared to the starting base material and bulk values (92 emu/f).

From the above, we can understand the following.

(υ When the starting material is Fe-Zn-based magnetic ultrafine particles, heat treatment at 800 C or higher for 1 hour in reduced pressure air, atmospheric pressure, or inert gas increases the TO magnetization. Particularly, Fed@, @ZnO@, 4 Fetus
When the starting base material was heat-treated for more than 1 hour in reduced pressure air, aB = 110 emu/f, which was a large value of 57% increase compared to the starting base material (70% mu/?), was obtained. Ta.

Also, the coercive force Hc is small, less than 4.20 Q6. Moreover, as shown in FIG. 2, the particles have grown to a large size while maintaining their shape, and no sintering between particles is observed.

(2) The tendency for the saturation magnetization to increase due to the heat treatment described above was similarly obtained even if the concentration of the bath solution during the production of ultrafine magnetic particles was changed.

(3) Even if the chemical formula Fe0z Zn01-1* Fe1O1 is changed over a wide range of x = 0.3, 0.5°, 0.6, 0.7, the saturation magnetization value of the starting base material is still high with the same heat treatment. Obtained7'CQ (4) On the other hand, in the chemical formula in section (3) above, x=1
In the comparative example, it was found that under similar heat treatment conditions, the saturation magnetization decreased with increasing temperature.

(Results from 1 to (3) are groundbreaking, and that's the point) tt'l The saturation magnetization of ultrafine magnetic particles containing Fe and Zn elements is higher than that of the bulk of the starting base material. is obtained, the coercive force is as small as 4 to 300 e, and the particle morphology is largely preserved, with no or almost no sintering occurring. Moreover, it can be said that the process is simple and industrial. These can be said to have solved the conventional drawbacks.

Incidentally, in the uninvented embodiment, the monomorphic Fe is used as the starting material.
x = 0 in 0z ZnO1-X @Fet03
．． 3 *0.5, 0.6, 0.7 are used, but the present invention is not limited to these
Any n-based magnetic ultrafine particles may be used.

Furthermore, the coprecipitation method has the advantage of being able to obtain ultrafine particles with less variation in particle size distribution.

Furthermore, N as an inert gas! Although it is possible to use M gas, it is not limited to this. Furthermore, the reaction time is not limited to the embodiments of the present invention, and if slow and efficient crystal growth can be performed, for example, 0.5 hours to several hours can be used without any effort (effects of the invention). In accordance with the present invention, the magnetic ultrafine particles produced by heat-treating the magnetic ultrafine particles of the starting base material at a temperature of 800°C or higher in air, an inert gas, or a reduced pressure atmosphere thereof are It not only has the characteristics of high saturation magnetization Φ and low coercive force, but also has the advantage that it becomes particles of a single composition with no bores and almost no sintering, and a uniform particle shape and distribution.

Moreover, since the explosion method of the present invention can be carried out in one process without pretreatment, it has the advantage of high productivity.

The magnetic ultrafine particles of the present invention have been actively researched and developed in recent years. ! ! As a magnetic recording memory, for example, the shape is cubic (cubic J).
Since it has an excellent orientation n1 and a small coercive force of 200e or less, it can be used as an underlayer for perpendicular recording.

Further, by utilizing the small coercive force and high saturation magnetization, it can be used as various magnetic shielding materials by mixing with other binders such as binders. It is clear that it can also be used as a magnetic fluid.

[Brief explanation of the drawing]

Figures 1, 3 and 4 show the chemical formula FeO2Zn01-
Using 20 g of 8.Fe as a starting material, the dependence of saturation magnetization on heat treatment temperature was determined by heat treatment atmosphere and heat treatment time (Fig. 1),
Solution concentration at the time of starting material preparation (Figure 3) and composition of starting material (in the case of x = 0.3, 0.5, 0.6, 0.7, 1 in the above chemical formula) (section 4)
is shown in the parameters. Figure 2 td Fete, @ Zn0o, 4・Fe10g
ic Tite I) A An electron micrograph of ultrafine magnetic particles heat-treated at 1000° C. for 1 hour in pressurized air is shown. Patent applicant: Nippon Telegraph and Telephone Corporation No. 1 Figure 0 200 ge℃ 6■ &wa 1σka
Merit recognition processing room (°C) Fig. 2 (0) Fig. 3 Hou l and private (°C) Fig. 4 Netsumari Unfriend ('C)

Claims (3)

[Claims] (1) A method for producing ultrafine magnetic particles, which comprises heat-treating a base material made of ultrafine magnetic particles containing Fe and Zn elements at a temperature of 800° C. or higher in an atmosphere of normal pressure or reduced pressure. (2) The method for producing ultrafine magnetic particles according to claim 1, wherein the base material is obtained by a coprecipitation method. (3) The method for producing ultrafine magnetic particles according to claim 1, wherein the heat treatment is performed in an inert gas atmosphere or an air atmosphere.