JP2003193102A - Iron-rhodium magnetic powder and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide iron-rhodium magnetic powder whose magnetic properties can be controlled to develop its use by applying peculiar magnetic properties of the conventional iron-rhodium magnetic powder, and to provide a synthesis method therefor. <P>SOLUTION: The iron-rhodium magnetic powder consists of iron and rhodium. When the iron-rhodium alloy components are expressed as Fe<SB>1-x</SB>Rh<SB>x</SB>, x is 0.4 to <0.8, and the grain sizes lie within the range of 20 nm to 200 μm, and also, a reduction temperature is changed within the range from 300 to 1,200°C, so that its magnetic properties can be controlled. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an iron-rhodium alloy powder containing iron and rhodium as at least constituent elements and a method for producing the same, and more specifically to various magnetic sensors utilizing temperature dependence of magnetic characteristics. The present invention relates to alloy powders most suitable for magnetic media, magneto-optical media, magnetic cards and the like.

[0002]

2. Description of the Related Art The present inventors have been conducting research on iron-rhodium magnetic powders to date, and show that the saturation magnetization of iron-rhodium magnetic powders shows a sharp change with respect to temperature, and It has been shown to have temperature hysteresis.
This sharp change in saturation magnetization is called magnetic transition, and the temperature at which magnetic transition occurs is called magnetic transition temperature. The magnetic transition temperature of the iron-rhodium magnetic powder produced by the conventional production method was about 120 ° C.

Further, the present inventors have found that the above-mentioned magnetic characteristics peculiar to the iron-rhodium magnetic powder can be variously controlled during the manufacturing process. For example, by adding raw materials other than iron and rhodium,
The magnetic transition temperature can be controlled. In addition, although it has been found that the magnetic characteristics are changed by changing the conditions such as the temperature and the atmosphere also in the reduction process and the heat treatment process, it has not been controlled.

[0004]

From the above, iron-
Details of the control of the magnetic properties depending on the reducing conditions during the manufacturing process of the rhodium-based magnetic powder are still unknown.

The present invention has been made in view of such a situation, and in the manufacturing process of iron-rhodium magnetic powder, magnetic characteristics are controlled by reducing conditions to obtain iron-rhodium magnetic powders having different temperature hysteresis. Aimed to make.

[0006]

The present inventors have prepared a precipitate containing iron and rhodium by mixing an aqueous solution containing iron and rhodium ions with an alkaline aqueous solution, and heat treating the precipitate to produce iron. And an oxide containing rhodium are prepared, and the oxide is heated and reduced to form an iron-rhodium magnetic powder. In the iron-rhodium magnetic powder, when the iron-rhodium alloy component is represented by Fe _1-x Rh _x , x is 0.4 or more and less than 0.8, and the particle size is in the range of 20 nm to 200 μm. The present invention provides an iron-rhodium-based magnetic powder capable of controlling magnetic characteristics by changing the reduction temperature and a method for producing the same.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below. In the manufacturing method of the present invention, iron as a raw material,
It is said that a compound containing at least rhodium and an additional element is dissolved in an aqueous solution and neutralized with an alkali to obtain a precipitate containing these components, and these are heated in a reducing atmosphere to obtain an alloy powder. A process was used. Hereinafter, the manufacturing method will be described step by step.

(Preparation of Precipitate) At least an iron salt, a rhodium salt and an additional element are dissolved in water to prepare a solution containing at least iron ions and rhodium ions. The iron salts used at that time include iron nitrate, iron sulfate, iron chloride,
Examples of rhodium salts such as iron acetate include rhodium nitrate, rhodium chloride, and rhodium acetate. As the additive element, palladium, ruthenium, iridium, platinum, gold,
It may contain silver, osmium, aluminum, titanium, silicon, boron, rare earth elements and their compounds.

There are two types of additives: a component that forms a solid solution with iron and rhodium by reduction in a hydrogen stream, and a component that is not reduced by reduction in a hydrogen stream and remains in an oxide state.

Examples of the solid solution component include palladium, ruthenium, iridium, platinum, gold, silver and osmium. These solid solution components are preferable as additional elements for controlling the transition temperature.

As a component which does not form a solid solution, aluminum,
Examples include titanium, silicon, boron, and rare earths. These impede particle growth during reduction and in the subsequent heat treatment step, and are therefore effective mainly for atomization.

In the present invention, first, the composition of iron, rhodium, and additional elements was examined. As a result, when the iron-rhodium alloy component in the iron-rhodium alloy powder is represented by Fe _1-x Rh _x , x is preferably 0.4 or more and less than 0.8. This is because when x is less than 0.4, the abundance ratio of iron exhibiting ferromagnetism becomes large, and thus it becomes difficult to observe magnetic transition, and when x is 0.8 or more, it has no magnetism. This is because the ratio of rhodium in the reaction becomes relatively large and the saturation magnetization does not show a significant change.

An aqueous ammonia solution is added to the solution to form a coprecipitate, and the coprecipitate is heated, washed with water, filtered and dried to obtain an oxide. As the alkali, sodium hydroxide, potassium hydroxide or the like may be used.

(Reduction Step) The oxide is heated and reduced in a hydrogen stream to produce an iron-rhodium alloy powder. Next, after flowing hydrogen gas, it was cooled to room temperature, then switched to nitrogen gas and taken out into the air. The reduction temperature is preferably in the range of 300 ° C to 600 ° C. If it is lower than this temperature, it is difficult to obtain a uniform iron-rhodium alloy, and if it is too high, the particle size increases due to sintering. Reduction temperature is 3
When the temperature is lower than 00 ° C., reduction does not proceed sufficiently and magnetic transition is not observed. Temperature hysteresis is observed even at 600 ° C. or higher, but at 1200 ° C. or higher, sintering occurs and the temperature hysteresis disappears.

(Heat Treatment Step) In the present invention, the iron-rhodium alloy powder after the reduction of the oxide may be subjected to a heat treatment so as not to be oxidized. The heat treatment temperature is preferably in the range of 300 ° C to 600 ° C. If it is lower than this temperature, it is difficult to obtain the effect of heat treatment, and if it is too high, the particle size increases due to sintering. Heat treatment temperature is 300 ℃
Below, no change in temperature characteristics is observed, and at 1200 ° C. or higher, sintering of the particles occurs, temperature hysteresis disappears, and the temperature characteristics become equivalent to those in bulk.

Further, the temperature in the reduction and heat treatment steps was examined. As a result, the reduction and heat treatment temperatures are
300-1200 degreeC is preferable. The temperature dependence of the magnetic properties, particularly the width of the temperature hysteresis, changes depending on the reduction or heat treatment temperature.

Next, the magnetic characteristics will be described. Iron-rhodium alloys are known to exhibit temperature dependence of unique magnetic properties. That is, at temperatures below about 150 ° C,
Although it exhibits almost no spontaneous magnetization and the saturation magnetization is almost zero, the saturation magnetization sharply increases to about 100 to 130 emu / g in the temperature range of about 150 to 200 ° C. The temperature at which the saturation magnetization changes sharply is called the magnetic transition temperature.

When an iron-rhodium alloy that exhibits ferromagnetism due to magnetic transition is cooled to a temperature below the magnetic transition temperature, it returns to antiferromagnetism while following the original curve in the case of bulk,
The saturation magnetization becomes zero. In the case of iron-rhodium magnetic powder, the saturation magnetization remains even when the magnetic transition temperature is reached or lower, and the saturation magnetization shows temperature hysteresis.

Further, it has been found that this magnetic property changes depending on the reducing conditions. That is, the reduction temperature is 300 ° C
If it is below, no magnetic transition is observed and the reduction temperature is 300
Magnetic transition and temperature hysteresis are observed in the range of ℃ to 600 ℃. Also, magnetic transition is observed at 600 ° C. or higher, but at 1200 ° C. or higher, sintering of particles progresses and temperature hysteresis disappears.

[0020]

EXAMPLES The present invention will be described below with reference to examples. (Example 1) 0.00092 mol of iron (III) nitrate and 0.
001 mol of rhodium (III) nitrate was dissolved in 50 cc of water. Separately from this aqueous nitrate solution, an aqueous 0.0054 mol ammonia solution was adjusted to 50 cc. After adding a nitrate aqueous solution to this aqueous ammonia aqueous solution to generate a nitrate coprecipitate, the precipitate was heated at 100 ° C. to form a precipitate of iron and rhodium oxide. The suspension of this precipitate was washed with water until the pH became 8 or less, and then filtered to take out the precipitate.

Next, the precipitate is spread on a vat and 60
It was dried at ℃ for 4 hours, and the oxides of iron and rhodium were taken out.

This surface-treated oxide was heated at 400 ° C. in a hydrogen stream.
Was heated and reduced for 2 hours to prepare an iron-rhodium alloy powder. Next, while flowing hydrogen gas, the mixture was cooled to room temperature and then taken out into the air to obtain an iron-rhodium alloy magnetic powder.

As a result of investigating the contents of iron and rhodium by fluorescent X-ray, when expressed by Fe _{1- x} Rh _x , x is 0.521.
Met.

FIG. 1 shows the temperature dependence of the saturation magnetization of this iron-rhodium magnetic powder. Table 1 shows the results of a summary of the main magnetic characteristics such as the magnetic transition temperature and the saturation magnetization changing with the magnetic transition.

Example 2 A coprecipitate containing iron and rhodium was prepared in the same manner as in Example 1 except that the reduction temperature was 500 ° C. in the preparation of the iron-rhodium magnetic powder of Example 1. Generate, wash with water, filter, dry, heat reduce,
An iron-rhodium alloy was prepared.

As a result of examining the contents of iron and rhodium by fluorescent X-ray, when expressed by Fe _{1- x} Rh _x , x was 0.518.
Met.

FIG. 2 shows the temperature dependence of the saturation magnetization of the iron-rhodium magnetic powder. Table 1 shows the results of a summary of the main magnetic characteristics such as the magnetic transition temperature and the saturation magnetization changing with the magnetic transition.

(Example 3) A coprecipitate containing iron and rhodium was prepared in the same manner as in Example 1 except that the reduction temperature was changed to 600 ° C in the preparation of the iron-rhodium magnetic powder of Example 1. Generate, wash with water, filter, dry, heat reduce,
An iron-rhodium alloy was prepared.

As a result of investigating the contents of iron and rhodium by fluorescent X-ray, when expressed by Fe _{1- x} Rh _x , x is 0.520.
Met.

FIG. 3 shows the temperature dependence of the saturation magnetization of this iron-rhodium magnetic powder. Table 1 shows the results of a summary of the main magnetic characteristics such as the magnetic transition temperature and the saturation magnetization changing with the magnetic transition.

Comparative Example 1 A coprecipitate containing iron and rhodium was prepared in the same manner as in Example 1 except that the reduction temperature was 290 ° C. in the production of the iron-rhodium magnetic powder of Example 1. Generate, wash with water, filter, dry, heat reduce,
An iron-rhodium alloy was prepared.

As a result of investigating the contents of iron and rhodium by fluorescent X-ray, when expressed by Fe _{1- x} Rh _x , x is 0.515
Met.

FIG. 4 shows the temperature dependence of the saturation magnetization of this iron-rhodium magnetic powder. Table 1 shows the results of a summary of the main magnetic characteristics such as the magnetic transition temperature and the saturation magnetization changing with the magnetic transition.

Comparative Example 2 A coprecipitate containing iron and rhodium was prepared in the same manner as in Example 1 except that the reduction temperature was 1250 ° C. in the preparation of the iron-rhodium magnetic powder of Example 1. After being produced, washed with water, filtered, dried, and heated and reduced, an iron-rhodium alloy was produced.

As a result of investigating the contents of iron and rhodium by fluorescent X-ray, when expressed by Fe _{1- x} Rh _x , x is 0.51
It was 9.

FIG. 5 shows the temperature dependence of the saturation magnetization of this iron-rhodium magnetic powder. Table 1 shows the results of a summary of the main magnetic characteristics such as the magnetic transition temperature and the saturation magnetization changing with the magnetic transition.

<Measurement Results of Temperature Dependence of Saturation Magnetization Amount of Iron-Rhodium Alloy Magnetic Powder> FIGS. 1 to 3 show Example 1
4 to 5 show the temperature dependence of the saturation magnetization of the iron-rhodium alloy magnetic powder produced in Example 3 and the iron-rhodium alloy magnetic powders produced in Comparative Examples 1 and 2.

Iron of Example 1 having a reduction temperature of 400 ° C.
Rhodium alloy magnetic powder is approximately 100% as shown in FIG.
At a temperature of 0 ° C. or lower, a saturation magnetization of about 50 emu / g is exhibited. It is considered that this saturation magnetization amount is due to the saturation magnetization amount of iron existing in addition to the iron-rhodium alloy magnetic powder.

On the other hand, when the temperature of this magnetic powder is raised to 100 ° C. or higher, the iron-rhodium alloy magnetic powder is transformed from antiferromagnetic to ferromagnetic by magnetic transition at a temperature of 100 to 120 ° C., and the saturation magnetization is about 120 emu. Sharply increases to / g. When the temperature is further raised to 300 ° C., the saturation magnetization amount is slightly reduced.

Next, when the temperature is lowered from 300 ° C., the original magnetization curve is followed up to about 120 ° C. at which magnetic transition occurs, but 1
Below 20 ° C., it does not follow the original curve and exhibits hysteresis. That is, for example, at 120 ° C where the magnetic transition starts, about 120
It exhibits a saturation magnetization of emu / g, and shows a saturation magnetization of about 70 emu / g even when the temperature is lowered to room temperature of 20 ° C.
When the temperature is further lowered to about −100 ° C., the initial saturation magnetization amount becomes about 50 emu / g, which indicates that the iron-rhodium alloy magnetic powder returns to the state before the temperature rise.

FIG. 2 shows the temperature dependence of the saturation magnetization of the iron-rhodium alloy magnetic powder of Example 2 having a reduction temperature of 500 ° C. The saturation magnetization before magnetic transition is about 20 emu /
g, and the magnetic saturation at 100 to 120 ° C. increases the saturation magnetization to 120 emu / g. The saturation magnetization before the magnetic transition is smaller than that of the magnetic powder of Example 1,
It is considered that because of the high reduction temperature, the generation of the iron-rhodium alloy proceeded, and the relative amount of the saturation magnetization due to iron existing in addition to the iron-rhodium alloy magnetic powder decreased. Even in this magnetic powder, remarkable hysteresis is still observed due to magnetic transition.

FIG. 3 shows the temperature dependence of the saturation magnetization of the iron-rhodium alloy magnetic powder of Example 3 having a reduction temperature of 600 ° C. The saturation magnetization before magnetic transition is about 10 emu /
g, and the magnetic saturation at 100 to 120 ° C. increases the saturation magnetization to 120 emu / g. For the same reason as in Example 2, the saturation magnetization amount before the magnetic transition takes a larger value, and in this magnetic powder, a remarkable hysteresis is observed due to the magnetic transition.

FIG. 4 shows the temperature dependence of the saturation magnetization of the iron-rhodium magnetic powder of Comparative Example 1. The reduction temperature of this magnetic powder was 290 ° C. Since the reduction temperature is low, the formation of iron-rhodium alloy does not proceed, it does not exhibit the magnetic transition peculiar to iron-rhodium magnetic powder, and the saturation magnetization monotonically decreases as the temperature increases.

FIG. 5 shows the temperature dependence of the saturation magnetization of the iron-rhodium magnetic powder having a reduction temperature of 1250 ° C. in Comparative Example 2. This iron-rhodium magnetic powder has a magnetic transition temperature of 120 ° C, but no temperature hysteresis is observed. It is considered that this is because the particles were sintered due to the high reduction temperature and exhibited the same characteristics as the bulk.

FIG. 6 shows an X-ray diffraction pattern of the iron-rhodium alloy magnetic powder of Example 2. A sharp diffraction peak due to the iron-rhodium alloy is observed. Further, in addition to the iron-rhodium alloy, a minute diffraction peak based on the slightly present unreacted metal rhodium is also observed. In the iron-rhodium magnetic powder of the present invention, it is unclear how the metal rhodium is distributed, but when temperature hysteresis is observed in the magnetic properties, iron- It is known that peaks corresponding to the metal rhodium are observed in addition to the rhodium alloy. On the other hand, FIG. 7 is an X-ray diffraction diagram of the iron-rhodium magnetic powder of Comparative Example 1. Also in this figure, as in FIG. 6, peaks corresponding to the iron-rhodium alloy are observed.
From these, it can be seen that even if the reduction temperature is less than 300 ° C., the iron-rhodium alloy is produced, but if the reduction temperature is low, the magnetic characteristics showing the magnetic transition peculiar to iron-rhodium are not exhibited.

Compositions of the iron-rhodium alloy magnetic powders prepared in Examples 1 to 3 and the iron-rhodium alloy magnetic powders of Comparative Examples 1 and 2, magnetic transition temperature (Ttrs), and saturation magnetization due to magnetic transition. Change amount (ΔMtrs), saturation magnetization amount before magnetic transition (Mint), saturation magnetization amount after magnetic transition (Mt)
ras), and the saturation magnetization (Mrmt) at 20 ° C. when the temperature rises above the magnetic transition temperature and drops below the temperature at which the magnetic transition occurs, and ΔMd which is the difference between Mrmt and Mint.
The if values are summarized in Table 1.

The magnetic transition temperature is defined as an intermediate temperature between the temperature at which the magnetic transition starts and the temperature at which the magnetic transition ends. Further, since the saturation magnetization amount decreases with further temperature increase after the magnetic transition, the maximum saturation magnetization amount after the transition is shown as the saturation magnetization amount after the magnetic transition.

[0048]

[Table 1]

As is clear from Table 1, the temperature hysteresis of the iron-rhodium magnetic powders shown in the examples increased with increasing temperature in the range up to the warming reduction temperature of 600 ° C. In addition, iron having a low reduction temperature shown in Comparative Example 1
-No magnetic transition temperature was observed in the rhodium-based magnetic powder. On the contrary, in the iron-rhodium magnetic powder having a high reduction temperature shown in Comparative Example 2, the magnetic transition was observed, but the temperature hysteresis was not observed. Further, the iron-rhodium-based magnetic powders shown in Examples and Comparative Examples 2 have a change amount of saturation magnetization due to magnetic transition (ΔMtrs), a saturation magnetization amount before magnetic transition (Mint), and a saturation magnetization amount after magnetic transition. (Mt
ras) and the saturation magnetization (Mrmt) at 20 ° C. when the temperature is raised above the magnetic transition temperature and dropped below the temperature at which the magnetic transition occurs, but the reduction temperature shown in Comparative Example 1 is low. 20 ° C for iron-rhodium magnetic powder
The saturation magnetization amount (Mrmt) is observed, and other characteristics are not observed.

The amount of change in saturation magnetization (ΔMtrs) due to magnetic transition is 63 emu / g to 106 emu in this embodiment.
/ G, but it is 10 emu / g to 200 emu by changing the additive element and the heat treatment condition similarly to the reduction temperature.
It is possible to prepare in the range of / g.

Iron used in Examples and Comparative Examples
When the X-ray diffraction spectrum of the rhodium-based alloy powder was measured, an X-ray diffraction spectrum unique to the iron-rhodium ordered alloy was observed. It is known that the crystal structure of an iron-rhodium ordered alloy having a composition ratio of 1: 1 is a cesium chloride type structure, but in the iron-rhodium alloy powder of the present invention, at least the iron-rhodium ordered alloy described above is used. A unique X-ray diffraction spectrum was observed.

[0052]

As described above, the iron-rhodium alloy powder of the present invention can control the magnetic characteristics by changing the reduction temperature, and the unique magnetic characteristics of conventional iron-rhodium alloys can be controlled. In addition, it can be seen that it is a new alloy powder with new performance. Therefore, the alloy powder of the present invention is an alloy powder particularly suitable for a medium that requires temperature control, and its industrial utility value is extremely large.

[Brief description of drawings]

FIG. 1 is a diagram showing the temperature dependence of the saturation magnetization of the iron-rhodium magnetic powder of Example 1.

FIG. 2 is a diagram showing the temperature dependence of the saturation magnetization of the iron-rhodium magnetic powder of Example 2.

FIG. 3 is a diagram showing the temperature dependence of the saturation magnetization of the iron-rhodium magnetic powder of Example 3.

FIG. 4 is a diagram showing the temperature dependence of the saturation magnetization of the iron-rhodium magnetic powder of Comparative Example 1.

5 is a diagram showing the temperature dependence of the saturation magnetization of the iron-rhodium-based magnetic powder of Comparative Example 2. FIG.

6 is an X-ray diffraction diagram of iron-rhodium magnetic powder of Example 2. FIG.

7 is an X-ray diffraction diagram of iron-rhodium-based magnetic powder of Comparative Example 1. FIG.

Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G11B 11/105 506 G11B 11/105 506Z (72) Inventor Shinichi Kitahata 1-88, Torora, Ibaraki-shi, Osaka Hitachima F-Term in Kucsel Co., Ltd. (reference) 4K017 AA04 BA02 BB06 CA07 DA03 EH18 FB06 4K018 BA16 BA20 BB04 BD02 5D006 BA04 BA08 5D075 FF02 GG16 5D112 BB02 BB06

Claims (2)

[Claims] 1. An iron-rhodium magnetic powder containing iron and rhodium as at least constituent elements, wherein when the iron-rhodium alloy component is represented by Fe _1-x Rh _x , x is 0.4 or more and 0. Less than 8 and a particle size of 20 nm to 200
It is in the range of μm and the reduction temperature is 300 ° C. or higher 12
An iron-rhodium-based magnetic powder characterized in that its magnetic properties can be controlled by changing within a range of less than 00 ° C. 2. An aqueous solution containing at least iron and rhodium ions is mixed with an alkaline aqueous solution to form a precipitate containing at least iron and rhodium, and the precipitate is heat-treated to obtain at least iron and rhodium. An iron-rhodium-based magnetic powder is produced by producing an oxide containing a metal oxide and heating and reducing the oxide.