JP2018110167A - Composite magnetic particle, electromagnetic wave absorber, and method of producing composite magnetic particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a composite magnetic particle which is capable of controlling magnetic characteristics and which contains crystal phases of ε-FeOand barium ferrite; an electromagnetic wave absorber; and a method of producing a composite magnetic particle.SOLUTION: A composite magnetic particle of the present invention contains an epsilon-type iron oxide phase and a barium ferrite phase, the content of barium being 7-20 mol%.SELECTED DRAWING: None

Description

  The present invention relates to composite magnetic particles, radio wave absorbers, and methods for producing composite magnetic particles.

  In recent years, technological innovation has rapidly progressed in the information and communication field. For example, cellular phones, wireless LANs, power line communications, non-stop automatic toll collection systems (ETC), etc. Electromagnetic waves have been used (for example, see Non-Patent Document 1).

  As the usage of radio waves in the high frequency range increases in this way, the risk of malfunction and malfunction due to interference between electronic components provided in the device increases, so the importance of radio wave management is expected to increase. Is done. As one of the management methods, there is a method of absorbing unnecessary radio waves and preventing radio waves from entering by using a radio wave absorber.

  A typical radio wave absorbing sheet is a mechanism that converts radio waves into heat by magnetic loss of magnetic powder. The magnetic loss mainly consists of three of a hysteresis loss, an eddy current loss, and a residual loss, and the residual loss is mainly due to magnetic resonance. As a material used for absorbing radio waves by magnetic loss, for example, there is a radio wave absorber using particles of magnetoplumbite type hexagonal ferrite (see, for example, Patent Document 1).

Patent Document 1 describes that, when a radio wave absorber using a BaFe _12-x Al _x O ₁₉ system magnetoplumbite type hexagonal ferrite is used, the ferromagnetic resonance frequency can be set to about 50 to 100 GHz. For example, it is described that it has an absorption peak around 53 GHz.

In addition to magnetoplumbite-type hexagonal ferrite, for example, iron oxide having an epsilon crystal structure (epsilon-type iron oxide (ε-Fe ₂ O ₃ )) has been proposed as a material used for the radio wave absorption sheet. (For example, refer to Patent Document 2). ε-Fe ₂ O ₃ is an extremely rare phase among iron oxides, and ε-Fe ₂ O ₃ can be obtained as a single phase by a chemical nanoparticle synthesis method using a reverse micelle method and a sol-gel method. The obtained ε-Fe ₂ O ₃ phase is known to exhibit a large coercive force of, for example, 20 kOe (1.59 × 10 ⁶ A / m) at room temperature. Since the frequency of absorbed electromagnetic waves increases as the coercive force increases, the ε-Fe ₂ O ₃ phase exhibiting a large coercive force can absorb electromagnetic waves with a very high frequency of 182 GHz. Patent Document 2 describes that the absorption frequency is controlled by doping ε-Fe ₂ O ₃ with Al or Ga to control the coercive force.

  In order to cope with absorption of a wide range of frequencies, a method of mixing a plurality of magnetic materials corresponding to absorption of each frequency has been proposed (see, for example, Patent Documents 3 and 4). As a radio wave absorbing sheet combining such a plurality of types of magnetic materials, Patent Document 3 describes a magnetic loss body in which a plurality of types of soft magnetic powders are mixed, and Patent Document 4 includes a hexagonal ferrite material. A radio wave absorber is described in which the surface of the center material is coated with a magnetic material having a saturation magnetization of 0.5 T or more. Patent Document 1 also describes a magnetoplumbite type hexagonal ferrite in which a part of iron element of ferrite is substituted with at least one metal.

Further, there is a method of manufacturing a nanocomposite magnet by combining a plurality of magnetic materials (see, for example, Patent Document 6). In Patent Document 6, a nanocomposite magnetic material having a hard magnetic phase core portion containing ε-Fe ₂ O ₃ and a soft magnetic phase shell portion containing Fe and covering at least a part of the core portion. Is described.

JP 11-354972 A JP 2009-224414 A JP 2004-111956 A JP 2001-060791 A JP 2011-35006 A

Surface technology Vol. 62, (2011), no. 5, p244-p250

  However, as in the techniques disclosed in Patent Documents 3 to 5, when different types of magnetic materials, particularly magnetic particles, are mixed, the magnetic particles tend to aggregate due to magnetic energy, and a plurality of different types of particles are It may be difficult to mix and stably absorb a wide range of frequencies.

  In addition, the technique disclosed in Patent Document 6 is a magnetic material in which a magnetic material that forms a soft magnetic phase is coated with a magnetic material that forms a hard magnetic phase and is combined, and is sufficiently capable of absorbing a wide range of frequencies. It may not be possible.

In addition to the crystalline phase containing ε-Fe ₂ O ₃ , the magnetic phase contains a different phase from different types of crystalline particles so that the magnetic particles can be applied to the electromagnetic wave absorber to exhibit a wider range of electromagnetic wave absorption performance. However, magnetic particles capable of adjusting magnetic properties such as coercive force are desired.

One embodiment of the present invention provides a composite magnetic particle containing a crystalline phase of ε-Fe ₂ O ₃ and barium ferrite, a radio wave absorber, and a method for producing the composite magnetic particle, which can control magnetic properties. Make it the purpose.

  The composite magnetic particle in one embodiment of the present invention includes an epsilon-type iron oxide phase and a barium ferrite phase, and the barium content is 7 to 20 mol%.

  The radio wave absorber in one embodiment of the present invention includes the above composite magnetic particles.

  The manufacturing method of the composite magnetic particle in 1 aspect of this invention makes the 1st compound containing an iron element react with the 2nd compound containing a barium element, and contains the iron oxide of a spinel structure, and the said barium element. A step of forming iron compound particles, a step of forming a coating layer containing silica on the surface of the iron compound particles using a silicon compound, and the iron compound particles having the coating layer formed thereon at a temperature higher than 900 ° C. Heat-treating at a high temperature of 1100 ° C. or lower to produce a composite magnetic particle including an epsilon-type iron oxide phase containing epsilon-type iron oxide and a barium ferrite phase containing barium ferrite. The barium content is 7 to 20 mol%.

According to one aspect of the present invention, there are provided composite magnetic particles containing a crystalline phase of ε-Fe ₂ O ₃ and barium ferrite, a radio wave absorber, and a method for producing the composite magnetic particles, capable of controlling magnetic properties. be able to.

FIG. 1 is an X-ray diffraction spectrum of the composite magnetic powders of Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2. FIG. 2 is a transmission electron micrograph of the composite magnetic powder of Example 1-1. FIG. 3 is a transmission electron micrograph of the composite magnetic powder of Example 1-2. FIG. 4 shows the magnetic properties of the composite magnetic powders of Examples 1-1 and 1-2 and Comparative Examples 1-2 and 1-3. FIG. 5 is an X-ray diffraction spectrum of the composite magnetic powders of Examples 2-1 and 2-1, and Comparative Example 2. FIG. 6 is an X-ray diffraction spectrum of the composite magnetic powder of Comparative Examples 3-1 to 3-4. FIG. 7 is an X-ray diffraction spectrum of the composite magnetic powder of Comparative Examples 4-1 to 4-4.

  Embodiments according to the present invention will be described below. The embodiment is not limited to the following description, and can be appropriately changed without departing from the gist of the present invention.

<Composite magnetic particles>
The composite magnetic particle according to the embodiment has an epsilon-type iron oxide phase (ε-Fe ₂ O ₃ phase) and a barium ferrite phase (Ba ferrite phase).

ε-Fe ₂ O ₃ phase is a crystalline phase of ε-Fe ₂ O _3, composed of crystal grains of the ε-Fe ₂ O _3. As described later, ε-Fe ₂ O ₃ is obtained by heat-treating iron oxide particles (spinel-type iron oxide particles) having a spinel structure obtained using a compound containing Fe element.

Whether or not ε-Fe ₂ O ₃ is formed on the composite magnetic particle is obtained by measuring the X-ray diffraction (XRD) of the composite magnetic particle using an X-ray diffractometer. It can be confirmed from the X-ray diffraction spectrum. For example, the lattice constant and the crystallite size are determined from the obtained X-ray diffraction spectrum using the powder X-ray diffraction pattern comprehensive analysis software JADE (MDI, automatically calculated by Scherrer's formula) attached to the powder X-ray diffractometer. It can be confirmed by calculating the area of the peak and calculating the proportion of the crystalline part. The calculation process by the software is performed based on, for example, an instruction manual (Jade (Ver. 5) software). The XRD peak of ε-Fe ₂ O ₃ is 27.7 °, 30.1 °. 33 °, 34.9 °, 35.2 °, 36.6 °, 40.3 °, 41.5 °.

The Ba ferrite phase is a crystal phase of Ba ferrite, is composed of Ba ferrite crystal particles, and is represented by BaO.6Fe ₂ O ₃ . The XRD peaks of Ba ferrite are 30.3 °, 31.0 °, 32.3 °, 34.2 °, 37.1 °, 40.4 ° and 42.5 °.

The content of the barium (Ba) element is 7 to 20 atomic% and preferably 7 to 15 atomic% with respect to the iron element. When the content of the Ba element is less than 7 atomic%, the effect of the Ba element may not be exhibited. Therefore, the Ba ferrite phase is not generated in the composite magnetic particle according to the embodiment, and alpha-type iron oxide (α-Fe ₂ O ₃ ) is generated. The composite magnetic particle according to the embodiment has magnetic characteristics such as coercive force HcJ. It may not be possible to adjust. On the other hand, when the content of Ba element exceeds 20 atomic%, the proportion of non-magnetic substance such as Ba element increases. Therefore, the composite magnetic particle according to the embodiment may not have excellent magnetic properties such as exhibiting a high coercive force HcJ.

The average particle diameter of the crystal grains of the ε-Fe ₂ O ₃ phase is preferably 10 nm or more, and more preferably 20 nm or more. The upper limit varies depending on the use of the composite magnetic particle according to the embodiment and is not particularly limited. If the average particle diameter of the ε-Fe ₂ O ₃ phase crystal grains is 10 nm or more, for example, an increase in the proportion of composite magnetic particles that do not contribute to improvement of magnetic properties such as amorphous iron oxide can be suppressed. A decrease in magnetic properties per unit weight can be suppressed.

  The average particle diameter of the Ba ferrite phase crystal grains is preferably 3 nm or more. If the average particle diameter of the Ba ferrite phase crystal grains is 3 nm or more, the effect of the Ba ferrite phase being generated in the composite magnetic particles can be exerted, so the magnetic properties of the composite magnetic particles can be easily controlled. Can be.

Incidentally, ε-Fe ₂ average particle diameter of the crystal grains of the O ₃ phase and Ba ferrite phase, ε-Fe ₂ O ₃ phase and the Ba ferrite phase grain transmission electron microscope (TEM) at an arbitrary number ( for example, 100) observed, the average particle diameter of the ε-Fe ₂ O ₃ phase and Ba ferrite phase of the crystal grains of the major axis and the average value of the minor axis ε-Fe ₂ O ₃ phase and Ba ferrite phase .

The content of the Ba element is 7 to 20 atomic% and preferably 7 to 15 atomic% with respect to the iron element. When the content of the Ba element is less than 7 atomic%, the effect of the Ba element may not be exhibited. Therefore, the Ba ferrite phase is not generated in the composite magnetic particle according to the embodiment, and alpha-type iron oxide (α-Fe ₂ O ₃ ) is generated. The composite magnetic particle according to the embodiment has magnetic characteristics such as coercive force HcJ. It may not be possible to adjust. On the other hand, when the content of Ba element exceeds 20 atomic%, the proportion of non-magnetic substance such as Ba element increases. Therefore, the composite magnetic particle according to the embodiment may not have excellent magnetic properties such as exhibiting a high coercive force HcJ.

  The magnetic properties of the composite magnetic particles according to the embodiment can be confirmed using, for example, a physical property measurement device (PPMS), an automatic magnetization property measurement device (BH curve tracer), or the like.

The composite magnetic particle according to the embodiment has an ε-Fe ₂ O ₃ phase and a Ba ferrite phase, and the Ba ferrite phase is dispersed almost uniformly in the composite magnetic particle, so that the ε-Fe ₂ O ₃ phase and the Ba ferrite phase are dispersed. And in a compounded state. Thereby, magnetic characteristics can be controlled, for example, by adjusting the coercive force HcJ within a range of 1000 Oe to 10000 Oe.

<Method for producing composite magnetic particles>
One aspect of the method for producing composite magnetic particles according to the embodiment will be described. In the method for producing composite magnetic particles according to the embodiment, spinel iron oxide particles obtained using a compound containing Fe element are heat-treated to produce composite magnetic particles containing an ε-Fe ₂ O ₃ phase and a Ba ferrite phase. It is a method to do.

  A solution in which the first compound containing the iron element is dissolved and a solution in which the second compound containing the Ba element is dissolved are mixed, and the first compound containing the iron element, and the second compound containing the Ba element, React. Thereby, iron compound particles containing spinel-type iron oxide particles and Ba element are generated. These iron compound particles are used as starting material particles.

  As the solution containing the first compound or the second compound, for example, an aqueous solution in which an iron element and a Ba element are dissolved in water can be used.

  The iron element only needs to be included in the iron compound particles as spinel-type iron oxide particles, and a part of the iron element may be included as amorphous iron compound particles that do not constitute the spinel-type iron oxide particles. .

The first compound is a compound containing an iron element. Examples of the compound containing an iron element include iron nitrate (Fe (NO ₃ ) ₃ ), iron chloride (FeCl ₂ , FeCl ₃ ), and iron acetate (Fe (CH ₃ CO ₂ ) ₂ ) or iron sulfate (FeSO ₄ ) can be used. The first compound can include any one or more of iron nitrate, iron chloride, iron acetate, or iron sulfate. As the first compound, a hydrate of a compound containing these iron elements can be used.

  The second compound is a compound containing a Ba element, and as the compound containing a Ba element, a nitrate, chloride, acetate, sulfate, or the like containing Ba can be used. The second compound includes one or more compounds containing a Ba element. As the second compound, a hydrate of a compound containing a Ba element can be used.

The content of the Ba element is 7 to 20 atomic% and preferably 7 to 15 atomic% with respect to the iron element. The content of the Ba element in the iron compound particle corresponds to the content of the Ba element contained in the composite magnetic particle according to the embodiment, and the content of the Ba element in the iron compound particle corresponds to the Ba of the composite magnetic particle according to the embodiment. Element content. When the content of Ba element is less than 7 atomic%, the effect of Ba element is not exerted. Therefore, a Ba ferrite phase is not generated in the composite magnetic particle according to the embodiment, and α-Fe ₂ O ₃ is generated. The composite magnetic particles according to the form may not be able to adjust magnetic properties such as coercive force HcJ. On the other hand, when the content of the Ba element exceeds 20 atomic%, the proportion of the non-magnetic substance such as the Ba element increases. Therefore, the composite magnetic particles according to the embodiment exhibit excellent magnetic force such as high coercive force HcJ. It may not be possible to have characteristics.

  Ba element should just be contained with the spinel type iron oxide particle in the iron compound particle, and may be contained with the form of the oxide.

Examples of the iron oxide having a spinel structure include magnetite (Fe ₃ O ₄ ) and gamma-type iron oxide (γ-Fe ₂ O ₃ ).

  When producing spinel type iron oxide particles, hydrothermal method, coprecipitation method, etc. can be used. When spinel type iron oxide particles described later are coated with silica, dispersion of spinel type iron oxide particles in the solution is performed. It is preferable to use a hydrothermal method because it is preferable to improve the property. In particular, among hydrothermal methods, a solvothermal method in which the first compound is crystallized in a high-temperature, high-pressure solvent to produce iron oxide having a spinel structure is preferable.

  An example of a method for producing spinel iron oxide particles using a hydrothermal method will be described. First, the first compound and the second compound are dissolved in water, ethylene glycol is added to an aqueous solution containing the first compound and the second compound, the aqueous solution is stirred, the first compound and the second compound, Mix with ethylene glycol. Next, an alkaline aqueous solution containing sodium hydroxide, potassium hydroxide, ammonia or the like is added to the obtained aqueous solution to precipitate a hydroxide containing an iron element in the aqueous solution. Next, after the aqueous solution containing hydroxide is transferred to a pressure vessel made of Teflon (registered trademark), the reaction is carried out at 50 to 200 ° C. using a Teflon (registered trademark) pressure vessel, and spinel iron oxide Generate particles. Thereafter, the spinel-type iron oxide particles and the solution in the aqueous solution are subjected to solid-liquid separation using a centrifuge, and then the solution is discarded to recover the spinel-type iron oxide particles. Next, spinel-type iron oxide particles are dispersed in water using an ultrasonic cleaner, and solid-liquid separation is performed again. By repeating this operation, the spinel-type iron oxide particles are washed, and the iron compound particle-containing slurry is prepared so that the spinel-type iron oxide particles are dispersed in water.

  The iron compound particles are preferably prepared as a solution dispersed in water. When the iron compound particles are dispersed in water, the iron compound particles are less aggregated than the dried state of the iron compound particles, and the surface of the spinel-type iron oxide particles is covered with a layer containing silica in the solution. be able to.

  Next, after obtaining the iron compound particles, the iron compound particles are mixed with water glass, silicon compound, etc., and silica is generated on the surface of the spinel type iron oxide particles contained in the spinel type iron oxide particles, and the spinel type A coating layer containing silica is formed on the surface of the iron oxide particles. Thereby, core-shell type spinel iron oxide particles can be produced.

  Examples of silicon compounds include trimethylmethoxysilane, trimethylethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, methyltrimethoxysilane, tetramethoxysilane, methyltriethoxysilane, tetraethoxysilane, methyldimethoxysilane, dimethylethoxysilane, and dimethylvinyl. Methoxysilane, dimethylvinylethoxysilane, methylvinyldimethoxysilane, methylvinyldiethoxysilane, diphenyldimethoxysilane, phenyltrimethoxysilane, diphenyldiethoxysilane, phenyltriethoxysilane, vinyltriethoxysilane, γ-chloropropyltrimethoxysilane , Γ-chloropropylmethyldichlorosilane, γ-chloropropylmethyldimethoxysilane, γ-aminopropylto Ethoxysilane, N- (β-aminoethyl) -γ-aminopropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ- Methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane and the like are preferably used. Among these, methyltriethoxysilane or tetraethoxysilane is preferable from the viewpoint of the reactivity between the iron element and the Ba element and the dispersibility of the iron element and the Ba element. These silicon compounds may be used alone or in combination of two or more.

  When silicic acid is produced using water glass, it is preferable to hydrolyze the water glass using an acid such as hydrochloric acid.

  When producing silicic acid using a silicon compound, it is preferable to produce silicic acid by hydrolyzing water and a silicon compound, for example, by a Stover method or the like. The Stover method is disclosed in, for example, “W. Stober, A. Fink and E. Bohn, Journal of Colloid and Interface Science, Volume 26, Issue 1, p. 62-69, January, 1968.” .

  Silica is generated after the spinel-type iron oxide particles are dispersed in water using an ultrasonic cleaner or simultaneously with the dispersion of the spinel-type iron oxide particles in water. A dispersion containing spinel-type iron oxide particles coated with is obtained.

  Specifically, a spinel-type iron oxide particle, a surfactant, an acid solution or an alkali solution, ethanol or propanol, and water are mixed to prepare a metal oxide-containing aqueous solution. The metal oxide-containing aqueous solution is irradiated with ultrasonic waves having a frequency of, for example, 25 kHz to 1 MHz, for example, for 1 to 60 minutes using an ultrasonic irradiator. Thereafter, the aqueous solution after irradiation with ultrasonic waves is dropped into a mixed solution containing a silicon compound and a dispersion solvent to cause a reaction. Thereafter, by removing the dispersion solvent, spinel iron oxide particles whose surface is coated with a coating layer containing silica can be obtained.

Next, the spinel-type iron oxide particles coated with the coating layer and the iron compound particles containing the Ba element are used, for example, in an atmosphere using an electric furnace or the like at a temperature higher than 900 ° C. and lower than 1100 ° C. By performing heat treatment for ˜6 hours, composite magnetic particles containing an ε-Fe ₂ O ₃ phase and a Ba ferrite phase are produced.

If the heat treatment temperature is less than 900 ° C., the ε-Fe ₂ O ₃ phase and the Ba ferrite phase cannot be sufficiently generated, and the magnetic properties of the composite magnetic particles may not be controlled. When the heat treatment temperature exceeds 1100 ° C., the amount of α-Fe ₂ O ₃ phase generated increases, and the coercive force HcJ of the composite magnetic particles may decrease.

If the heat treatment time is less than 4 hours, there is a possibility that the ε-Fe ₂ O ₃ phase that can exhibit excellent magnetic properties is not sufficiently generated in the composite magnetic particles according to the embodiment. Even if the heat treatment time exceeds 6 hours, the amount of ε-Fe ₂ O ₃ phase produced does not change so much and is not effective.

  In order to remove or reduce the coating layer, silica contained in the coating layer using an alkaline aqueous solution containing sodium hydroxide, potassium hydroxide, etc., an alkaline aqueous solution containing alkali metal and tetraalkylammonium hydroxide, etc. May be dissolved to remove the coating layer.

Thus, after spinel iron oxide particles obtained using a compound containing Fe element are coated with a coating layer containing silica, heat treatment is performed, whereby Ba ferrite is generated in the composite magnetic particles, and ε-Fe Composite magnetic particles containing a ₂ O ₃ phase and a Ba ferrite phase can be produced. Exemplary are substantially uniformly dispersed within the surface layer and the Ba ferrite phase ε-Fe ₂ O ₃ phase in the composite magnetic particles according, composite magnetic particles according to embodiments, ε-Fe ₂ O ₃ phase and the Ba ferrite It contains the phases in a compounded state. Thereby, control of magnetic characteristics such as coercive force HcJ can be performed.

As described above, the composite magnetic particle according to the embodiment has the ε-Fe ₂ O ₃ phase and the Ba ferrite phase, and includes the ε-Fe ₂ O ₃ phase and the Ba ferrite phase in a composite state. Since magnetic characteristics such as coercive force HcJ can be controlled, it can be suitably used for a radio wave absorber or a high-density magnetic recording medium. The radio wave absorber to which the composite magnetic particle according to the embodiment is applied is configured to adjust the coercive force HcJ of the composite magnetic particle according to the embodiment over a wide range of, for example, 1000 Oe to 10000 Oe, and control the magnetic characteristics, thereby achieving a wider range of radio wave absorption performance. Can be achieved.

  Hereinafter, although an example and a comparative example are shown and an embodiment is explained still more concretely, an embodiment is not limited by these examples.

<Examples 1-1 to 1-3, Comparative Examples 1-1 to 1-3>
[Production of composite magnetic particles]
As the second compound, 0.78 g (3.2 mmol) of barium (II) chloride tetrahydrate (BaCl ₂ .4H ₂ O) was dissolved in 20 mL of water so that the barium content was 10 mol%. . Thereafter, this aqueous solution was used as a first compound, 1.3 g (6.4 mmol) of iron chloride (II) tetrahydrate (FeCl ₂ .4H ₂ O) and iron chloride (III) hexahydrate (FeCl _3. 6H ₂ O) (6.05 g, 22.4 mmol) was mixed in a solution of 20 mL of water. Then, the liquid mixture was stirred with the magnetic stirrer. Thereafter, water and ethylene glycol were added to the mixed solution to make a 70 mL solution, and the solution was further stirred. Next, a solution in which 20 g of sodium hydroxide was dissolved in 20 mL of water was added to precipitate barium, iron (II) and iron (III) hydroxides. Furthermore, after this solution was transferred to a Teflon (registered trademark) container, it was reacted at 180 ° C. for 4 hours by a solvothermal method using a Teflon (registered trademark) pressure container to obtain spinel-type iron oxide particles and Iron compound particles containing barium were produced. Thereafter, the iron compound particles and the solution were separated into solid and liquid by a centrifuge, and then the solution was discarded. Then, using an ultrasonic cleaner, the iron compound particles were dispersed in water and again solid-liquid separated. By repeating this operation, the iron compound particles were washed to prepare an iron compound particle-containing slurry in which the iron compound particles were dispersed in water.

  Thereafter, iron compound particles were coated with a silicon compound. Specifically, 900 g of ethanol and 280 g of water were mixed in a beaker, and 106 g of an iron compound particle-containing slurry having a solid-liquid concentration of 2.45% was added thereto. To this was added 0.1 g of a surfactant (A6114, manufactured by Toagosei Co., Ltd.) and ammonia water as an alkaline solution, and then an iron compound particle-containing slurry was further added. Thereafter, spinel iron oxide particles in the iron compound particle-containing slurry were dispersed using an ultrasonic irradiator. The solid content in the iron compound particle-containing slurry obtained by drying the iron compound particle-containing slurry was determined as the weight of the iron compound particles. Thereafter, the iron compound particle-containing slurry was dropped into an ethanol solution containing 5.2 g of tetraethyl orthosilicate (TEOS), and the mixture was stirred and reacted. The resulting solution was washed with ethanol and dried. The obtained iron compound particles were heat-treated at any of 850 ° C., 900 ° C., 920 ° C., 950 ° C., and 1000 ° C. to produce composite magnetic particles. Then, after putting the obtained composite magnetic particles in a 5N aqueous sodium hydroxide solution, the aqueous sodium hydroxide solution was heated to 70 ° C. and allowed to stand for 24 hours to remove silica.

[Evaluation]
The crystallinity of the obtained composite magnetic particles, the average particle diameter of the ε-Fe ₂ O ₃ phase and the Ba ferrite phase of the composite magnetic particles, and the magnetic properties of the composite magnetic particles were evaluated.
(Confirmation of crystallinity)
The obtained composite magnetic particles were subjected to XRD using an XRD apparatus (RINT2000, manufactured by Rigaku Corporation). FIG. 1 shows the XRD measurement results of the composite magnetic particles obtained at the respective heat treatment temperatures. From the X-ray diffraction spectrum obtained by the measurement, confirm the crystallinity of the composite magnetic particles using the powder X-ray diffraction pattern comprehensive analysis software JADE (MDI, automatically calculated by Scherrer's formula) attached to the powder X-ray diffractometer did. In X-ray diffraction, Cu-Kα ray was used as an X-ray source. The measurement conditions were a voltage of 40 kV and a current of 400 mA, and a range of 2θ = 25 ° to 50 ° with a scanning speed of 1 deg / sec. The XRD peaks of ε-Fe ₂ O ₃ are 27.7 °, 30.1 °, 33 °, 34.9 °, 35.2 °, 36.6 °, 40.3 °, 41.5 °. is there. The XRD peaks of Ba ferrite are 30.3 °, 31.0 °, 32.3 °, 34.2 °, 37.1 °, 40.4 ° and 42.5 °.
(Measurement of average particle size)
Among the examples and comparative examples, the composite magnetic particles obtained in Example 1-2 were observed with a TEM, and the average particle diameters of the ε-Fe ₂ O ₃ phase and the Ba ferrite phase constituting the composite magnetic particles were measured. did. As for the average particle diameter of the ε-Fe ₂ O ₃ phase and the Ba ferrite phase, the average value of the major axis and the short axis was defined as the average particle diameter of the ε-Fe ₂ O ₃ phase and the Ba ferrite phase. The observation result by TEM of the composite magnetic particle obtained in Example 1-1 is shown in FIG. 2, and the observation result by TEM of the composite magnetic particle obtained in Example 1-2 is shown in FIG.
(Confirmation of magnetic properties)
Among the examples and comparative examples, the magnetic properties of the composite magnetic particles obtained in Examples 1-1 and 1-2 and Comparative Examples 1-2 and 1-3 were measured using PPMS. As magnetic characteristics, coercive force HcJ, saturation magnetization (saturation magnetic flux density) Js, and residual magnetization (residual magnetic flux density) Br were measured. The measurement results of the magnetic properties of the composite magnetic particles are shown in FIG. FIG. 4 shows the measurement results of the magnetic properties of the composite magnetic particles obtained at the respective heat treatment temperatures.

As shown in FIG. 1, when the heat treatment temperature was 920 ° C., the majority was ε-Fe ₂ O ₃ , but it was confirmed that Ba ferrite was slightly formed (Example 1-1). reference). When the heat treatment temperature was 950 ° C., it was confirmed that the proportion of Ba ferrite produced increased and that ε-Fe ₂ O ₃ was produced (see Example 1-2). Furthermore, when the heat treatment temperature was 1000 ° C., it was confirmed that most of Ba ferrite was formed and α-Fe ₂ O ₃ and ε-Fe ₂ O _{3 were} slightly formed (Example 1). -3). On the other hand, when heat treatment was not performed, it was confirmed that Fe ₃ O ₄ having a spectrum similar to that of γ-Fe ₂ O ₃ was generated (see Comparative Example 1-1). When the heat treatment temperature is 850 ° C., γ-Fe ₂ O ₃ is formed, and the peak of ε-Fe ₂ O ₃ is slightly observed at 33 °, and ε-Fe ₂ O _{3 is} slightly formed. (See Comparative Example 1-2). When the heat treatment temperature was 900 ° C., it was confirmed that ε-Fe ₂ O ₃ was generated, but Ba ferrite was not generated (see Comparative Example 1-3).

As shown in FIG. 2, when the heat treatment temperature is 920 ° C., about 3 nm of Ba ferrite phase crystal particles are dispersed around the surface of the ε-Fe ₂ O ₃ phase crystal particles having an average particle diameter of 60 nm or more. It was confirmed that Further, as shown in FIG. 3, when the heat treatment temperature is 950 ° C., Ba ferrite phase crystal particles of 100 nm or more are dispersed around the ε-Fe ₂ O ₃ phase crystal particles having an average particle diameter of about 50 nm. Thus, it was confirmed that the ε-Fe ₂ O ₃ phase crystal particles and the Ba ferrite phase crystal particles did not agglomerate and existed in contact with each other.

  As shown in FIG. 4, when the heat treatment temperature was 920 ° C., it was confirmed that the saturation magnetization Js was 19.1 emu / g and the coercive force HcJ was 6068 Oe (see Example 1-1). When the heat treatment temperature was 950 ° C., it was confirmed that the saturation magnetization Js was 45.9 emu / g and the coercive force HcJ was 2008 Oe (see Example 1-2). When the heat treatment temperature was 1000 ° C., it was confirmed that the saturation magnetization Js was 46.0 emu / g and the coercive force HcJ was 1874 Oe (see Example 1-3). The composite magnetic particles obtained when the heat treatment temperature was 950 ° C. had higher saturation magnetization Js and the coercive force HcJ was lower than the composite magnetic particles obtained when the heat treatment temperature was 920 ° C. . Therefore, as the heat treatment temperature rises, the saturation magnetization Js increases and the coercive force HcJ tends to decrease. Therefore, it can be said that the magnetic characteristics can be changed by changing the heat treatment temperature.

On the other hand, when the heat treatment temperature was 850 ° C., the saturation magnetization Js was 38.5 emu / g, and the coercive force HcJ was 20 Oe (see Comparative Example 1-2). This can be attributed to the fact that the saturation magnetization Js produced by γ-Fe ₂ O ₃ is large and the coercive force HcJ is small. When the heat treatment temperature was 900 ° C., the saturation magnetization Js was 17.5 emu / g, and the coercive force HcJ was 14924 Oe (see Comparative Example 1-3).

<Examples 2-1, 2-2, and Comparative Example 2>
As the second compound, the addition amount of barium (II) chloride tetrahydrate (BaCl ₂ .4H ₂ O) of Examples 1-1 to 1-3 was changed from 0.78 g to 1.17 g (4.8 mmol). As the first compound, the amount of iron (II) chloride tetrahydrate (FeCl ₂ .4H ₂ O) added in Examples 1-1 to 1-3 was changed from 1.3 g to 0.96 g (4.8 mmol). The addition amount of iron (III) chloride hexahydrate (FeCl ₃ .6H ₂ O) remains 6.05 g and the barium content in the obtained iron compound particles is 15 mol%. It changed so that it might become. The obtained iron compound particles were heat-treated at any temperature of 850 ° C., 900 ° C., and 950 ° C. to produce composite magnetic particles, and the same as in Examples 1-1 to 1-3. I went. The X-ray diffraction result of the obtained composite magnetic particle is shown in FIG.

As shown in FIG. 5, when the heat treatment temperature was 900 ° C., most of the heat treatment was ε-Fe ₂ O ₃ , but it was confirmed that Ba ferrite was slightly formed (Example 2-1). reference). When the heat treatment temperature is 950 ° C., both ε-Fe ₂ O ₃ and Ba ferrite are produced, but the proportion of Ba ferrite produced increases, and it is confirmed that the majority is Ba ferrite. (See Example 2-2). On the other hand, when the heat treatment temperature was 850 ° C., it was confirmed that both α-Fe ₂ O ₃ and γ-Fe ₂ O ₃ were produced (see Comparative Example 2).

When the heat treatment temperature was 900 ° C., the coercive force HcJ of the composite magnetic particles was 4108 Oe, and the saturation magnetization was 19.2 emu / g (see Example 2-1). Further, the average particle size of the composite magnetic particles is, as in Example 1-1, particles derived from the ε-Fe ₂ O ₃ phase having an average particle size of about 50 nm and particles derived from the Ba ferrite phase of 100 nm or more. It was confirmed that the particles attributed to the ε-Fe ₂ O ₃ phase and the particles attributed to the Ba ferrite phase existed without being aggregated.

<Comparative Examples 3-1 to 3-3>
As the second compound, the amount of barium (II) chloride tetrahydrate (BaCl ₂ .4H ₂ O) added in Examples 1-1 to 1-3 was changed from 0.78 g to 0.39 g (1.6 mmol). As the first compound, the amount of iron (II) chloride tetrahydrate (FeCl ₂ .4H ₂ O) added in Examples 1-1 to 1-3 was changed from 1.3 g to 1.19 g (8.0 mmol). The addition amount of iron (III) chloride hexahydrate (FeCl ₃ .6H ₂ O) remains 6.05 g and the barium content in the obtained iron compound particles is 5 mol%. It changed so that it might become. The obtained iron compound particles were heat-treated at any one of 160 ° C., 850 ° C., 900 ° C., and 950 ° C. to produce composite magnetic particles. Examples 1-1 to 1-3 And performed in the same manner. The X-ray diffraction result of the obtained composite magnetic particle is shown in FIG.

As shown in FIG. 6, even when the heat treatment temperature is 160 ° C., 850 ° C., 900 ° C., or 950 ° C., no peak is observed at 32 or 34 ° where the maximum peak of barium ferrite is present, It was not confirmed that both the ε-Fe ₂ O ₃ phase and the Ba ferrite phase were generated in the composite magnetic particles (see Comparative Examples 3-1 to 3-4).

<Comparative Examples 4-1 to 4-4>
As the second compound, barium (II) chloride tetrahydrate (BaCl ₂ .4H ₂ O) of Examples 1-1 to 1-3 was replaced with strontium chloride hexahydrate (SrCl ₂ .6H ₂ O). The amount of iron (II) chloride tetrahydrate (FeCl ₂ .4H ₂ O) added in Examples 1-1 to 1-3 was 1 as the first compound. The amount of iron (III) chloride hexahydrate (FeCl ₃ .6H ₂ O) remains unchanged at 6.05 g, and the barium content in the resulting iron compound particles remains unchanged. It was made to become 10 mol%. The obtained iron compound particles were heat-treated at any temperature of 800 ° C., 850 ° C., 900 ° C., and 950 ° C. to produce composite magnetic particles. Examples 1-1 to 1-3 And performed in the same manner. The XRD peaks of strontium silicate are 24.5 °, 26.5 °, 30.5 °, 35.5 °, and 44 °. The X-ray diffraction result of the obtained composite magnetic particle is shown in FIG.

As shown in FIG. 7, when the heat treatment temperatures are 800 ° C., 850 ° C., and 900 ° C., only γ-Fe ₂ O ₃ or ε-Fe ₂ O ₃ is produced in the composite magnetic particles. Was confirmed (see Comparative Examples 4-1 to 4-3). When the heat treatment temperature is 950 ° C., it is confirmed that strontium silicate is produced in addition to γ-Fe ₂ O _{3 in} the composite magnetic particles, and a small amount of α-Fe ₂ O ₃ is also produced. It was confirmed that However, no peaks were observed at 32 ° and 34 ° where the maximum peak of strontium ferrite (Sr ferrite) was present, and it was not confirmed that Sr ferrite was generated in the composite magnetic particles (Comparative Example 4- 3).

The type of the first compound, the type of the second compound, the amount of barium added, the heat treatment temperature, the presence or absence of ε-Fe ₂ O ₃ phase and Ba ferrite phase, and the composite used in each of the above Examples and Comparative Examples Table 1 shows the coercivity HcJ of the magnetic particles. Incidentally, for the presence of the production of ε-Fe ₂ O ₃ and Ba ferrite phase, if both ε-Fe ₂ O ₃ and Ba ferrite phase is generated, and circles, and the other was crosses.

  As described above, the composite magnetic particles and the manufacturing method thereof according to the embodiments are useful for high-density magnetic recording medium applications, and from the stability of the substance that is an oxide and excellent magnetic properties, from gigahertz to terahertz. It can be applied to radio wave absorbers corresponding to frequencies, nanoscale electronics materials, biomolecule labeling agents, drug carriers, etc.

Claims (6)

An epsilon-type iron oxide phase;
A barium ferrite phase;
Including
A composite magnetic particle having a barium content of 7 to 20 mol%.   The composite magnetic particle according to claim 1, further comprising a coating layer containing silica on a surface of the composite magnetic particle.   A radio wave absorber comprising the composite magnetic particles according to claim 1. Reacting a first compound containing an iron element and a second compound containing a barium element to produce iron compound particles containing spinel-type iron oxide and the barium element;
Forming a coating layer containing silica on the surface of the iron compound particles using a silicon compound;
The iron compound particles on which the coating layer is formed are heat-treated at a temperature higher than 900 ° C. and not higher than 1100 ° C., and a composite containing an epsilon iron oxide phase containing epsilon iron oxide and a barium ferrite phase containing barium ferrite Producing magnetic particles;
Including
Content of barium in the said composite magnetic particle is 7-20 mol%, The manufacturing method of the composite magnetic particle characterized by the above-mentioned.   The manufacturing method of the composite magnetic particle of Claim 4 which produces | generates the said iron compound particle | grain using the said 1st compound and the said 2nd compound using a hydrothermal method.   The method for producing composite magnetic particles according to claim 4, further comprising a step of removing the silica using an alkaline aqueous solution after the composite magnetic particles are generated.