WO2008065537A2

WO2008065537A2 - PRODUCTION METHOD FOR FePT-Fe-NANOCOMPOSITE METAL MAGNETIC

Info

Publication number: WO2008065537A2
Application number: PCT/IB2007/004282
Authority: WO
Inventors: Tetsuya Shoji; Noritsugu Sakuma
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2006-11-28
Filing date: 2007-11-27
Publication date: 2008-06-05
Also published as: JP4232817B2; WO2008065537A3; JP2008133504A

Abstract

In a production method for a nanocomposite metal magnetic particle containing an FePt particle and an Fe particle, a salt of Fe and a salt of Pt are dissolved in a solvent containing a surface-active agent, and a reducing agent is added at a temperature that is higher than or equal to a reduction temperature of an Fe ion that constitutes the salt of Fe. Thereby, FePt particles are synthesized, and at the same time, Fe particles are deposited on a portion of the FePt articles serving as a core.

Description

PRODUCTION METHOD FOR FePt-Fe-NANOCOMPOSITE METAL MAGNETIC

PARTICLE

FIELD OF THE INVENTION [0001] The invention relates to a production method for a nanocomposite metal magnetic particle that can be used as a high-density magnetic recording medium, a permanent magnet, etc.

BACKGROUND OF THE INVENTION [0002] Magnetic recording medium materials are required to have high coercive force for stable record retention. As a metal magnetic material having such a high coercive force, an FePt-based metal magnetic particle is known.

[0003] The FePt-based metal magnetic particle is disclosed in Japanese Patent Application Publication No. 2005-48250 (JP-A-2005-48250). This FePt-based metal magnetic particle can be obtained as follows. Firstly, iron acetylacetonate and platinum acetylacetonate are added to tetraethylene glycol, and are reacted at high temperature by blowing in a nitrogen gas. After that, oleic acid and oleylamine are added as dispersants into a suspension containing aggregated FePt particles, and furthermore, a mixture of cyclohexane, oleic acid and oleylamine is added, and then the suspension is shaken. In this manner, FePt-based metal magnetic particles are obtained as monodispersed FePt nanoparticles.

[0004] Magnetic particles as described above are used in a wide variety of fields, including electronics, information and communications, industrial and automotive electric motors, etc. With regard to the magnetic particles, further enhancement in performance and further reduction in size and weight are demanded. One approach that has been made for such performance enhancement is the development of a nanocomposite magnet in which a soft magnetic phase with high magnetization and a hard magnetic phase with high coercive force are uniformly distributed in the same metallic structure and the soft and hard magnetic phases are magnetically coupled due to an exchange interaction.

[0005] However, although the foregoing method provides minute FePt nanoparticles, the method does not provide nanocomposite particles. That is, after FePt hard magnetism particles are produced, Fe soft magnetism particles need to be mixed in and be supported on the surfaces of the FePt hard magnetism particles. This gives rise to a problem of performance degradation being caused by the oxidation or the like of either kind of particles at the time of the mixture.

DISCLOSURE OF THE INVENTION [0006] It is an object of the invention to provide a method of producing a nanocomposite metal magnetic particle that contains an FePt particle and an Fe particle by performing a synthetic reaction once.

[0007] A first aspect of the invention relates to a method of producing a nanocomposite metal magnetic particle. In this production method, a salt of Fe and a salt of Pt are dissolved in a solvent containing a surface-active agent, and a reducing agent is added at a temperature that is higher than or equal to a reduction temperature of an Fe ion that constitutes the salt of Fe, and the FePt particle is synthesized and at the same time the Fe particle is deposited.

[0008] A second aspect of the invention relates to a method of producing a nanocomposite metal magnetic particle. In this production method, a salt of Fe and a salt of Pt are dissolved in a solvent, and a reducing agent is added at a temperature that is higher than or equal to a reduction temperature of an Fe ion that constitutes the salt of Fe, and then a surface-active agent is added, and the FePt particle is synthesized and at the same time the Fe particle is deposited. [0009] In the foregoing aspects of the invention, the salt of Fe may be iron acetylacetonate, and the salt of Pt may be platinum acetylacetonate.

[0010] In the aspects of the invention, the reducing agent may be a polyol. [0011] In the aspects of the invention, the polyol may be at least one of 1,2-octanediol, 1,2-dodecanediol, 1,2-tetradecanediol, and 1,2-hexadecanediol. [0012] In the aspects of the invention, the reducing agent may be added at a temperature higher than or equal to 230⁰C.

[0013] In the aspects of the invention, a ratio between the salt of Fe and the salt of Pt may be set so that a molar ratio of Fe to Pt becomes excessively large. [0014] In the aspects of the invention, a ratio between the salt of Fe and the salt of Pt may be the salt of Fe:the salt of Pt is 7:3 to 9:1 in molar ratio.

[0015] In the aspects of the invention, the solvent may be at least one of octyl ether, octadecene, squalene, tetraethylene glycol, and triphenyl methane.

[0016] In the aspects of th& invention, the surface-active agent may be at least one of oleylamine, oleic acid, tetraethylene glycol, sodium dodecylbenzenesulfonate, phenylphosphonic acid, myristylic acid, dodecanethiol, and dodecylamine.

[0017] In the aspects of the invention, an amount of the surface-active agent added may be 10 to 100% of the solvent in mass ratio.

[0018] Furthermore, an amount of the reducing agent added may be 1.5 to 2 times as large in molar ratio as the amount of the salt of Fe and the amount of the salt of Pt.

[0019] According to the aspects of the invention, FePt hard magnetism particles and Fe soft magnetism particles can be simultaneously synthesized and composited in the order of nanometer by performing a reaction once. Thus, the FePt-Fe-based nanocomposite metal magnetic particle can easily be produced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The foregoing and further features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIGS. IA to ID are photographs of FePt particles and Fe particles used in working examples which were under a transmission electron microscope (hereinafter, referred to as "TEM"); and

FIGS. 2A and 2B are graphs showing volume fraction data and particle diameter distribution of FePt particles and Fe particles obtained in working examples.

DETAILED DESCRIPTION OF EMBODIMENTS

[0021] Hereinafter, a production method for a nanocomposite metal magnetic particle in accordance with the invention will be described in detail. In the production method for a nanocomposite metal magnetic particle in accordance with the invention, firstly, a salt of Fe and a salt of Pt are dissolved in a solvent. It is preferable that the salt of Fe and the salt of Pt each be a metal complex that has an organic ligand. Examples of the salt of Fe usable herein include iron (II) acetylacetonate, iron (III) acetylacetonate, etc. Examples of the salt of Pt usable herein include platinum (II) acetylacetonate, dichloro-l,10-platinum phenanthroline, 2,2-bipyridine dichloroplatinum. The ratio between the salt of Fe and the salt of Pt is set so that the molar ratio of Fe to Pt becomes excessive in magnitude. For example, the ratio may be the salt of Fe:the salt of Pt = 7:3 to 9:1 in molar ratio. [0022] It is preferable that the solvent have high boiling point and be stable, since the solvent is heated in the deposition reaction of the FePt particles and the Fe particles. Examples of the solvent usable herein include octyl ether, octadecene, squalene, tetraethylene glycol, triphenyl methane, etc.

[0023] In a first embodiment of the invention, the salt of Fe and the salt of Pt are dissolved in the solvent after a surface-active agent has been added into the solvent. Examples of the surface-active agent usable herein include oleylamine, oleic acid, tetraethylene glycol, sodium dodecylbenzenesulfonate, phenylphosphonic acid, myristylic acid, dodecanethiol, dodecylamine, etc. It is preferable that the amount of the surface-active agent added be 10% to 100% of the solvent in mass ratio. [0024] After the salt of Fe and the salt of Pt are added to the solvent, the mixture may be heated to dissolve the salts into the solvent if needed. Then, the solution is further heated. After a fixed temperature is reached or exceeded, a reducing agent is added. The temperature at which the salts are dissolved is normally about 160⁰C, although it varies depending on the salts and the solvent that are used. Besides, the temperature at which the reducing agent is added is a temperature that allows the Fe ions constituting the salt of Fe to be reduced to Fe, and is normally about 230⁰C. As for the reducing agent, it is preferable to use a polyol (polyhydric alcohol). The polyol is not particularly limited. For example, 1,2-octanediol, 1,2-dodecanediol, 1,2-tetradecanediol, 1,2-hexadecanediol, etc., can be used. The polyols having a boiling temperature higher than the aforementioned reaction temperature are preferable. It is also preferable that the amount of the reducing agent added be 1.5 to 2 times as large in molar ratio as the total amount of the salt of Fe and the salt of Pt.

[0025] In a second embodiment of the invention, the surface-active agent is added after the reducing agent has been added, instead of being added in the solvent beforehand as in the first embodiment.

[0026] Thus, by the Fe and the Pt are reduced through the use of a polyol as a reducing agent, nanoparticles of FePt are obtained. Furthermore, the reduction at high temperature raises the activity of Fe, and allows the reduction of only Fe, so that the synthesis of FePt and the deposition of Fe can be simultaneously performed.

[0027] In the polyol reduction, in general, the reduction reaction instantly occurs, and hardly involves the process of core growth, so that the size control of the particles obtained is difficult. In the first embodiment of the invention, the addition of a surface-active agent with polarity into a non-polar solvent, such as octyl ether or the like provides polarity. This polarity promotes the re-formation of complex irons having_a metal ion as a core in the solvent, so that the free energy declines. Therefore, the critical core radius during the core generation increases, and therefore the growth of particles is promoted. As a result, large FePt particles can be obtained. Furthermore, since a surface-active agent with polarity is contained from the beginning, the degree of activity rises, and it becomes easier to generate Fe.

[0028] In the second embodiment of the invention, after the reducing agent is added, the surface-active agent is added. Therefore, the volume fraction of the Fe nanoparticles can be lowered. This is considered to be because the activity (amount of activity) of the salt of Fe in octyl ether is low. [0029] By simultaneously depositing FePt particles and Fe particles as described above, nanocomposite metal magnetic particles containing FePt particles and Fe particles can be obtained. The metal magnetic particles can be used as a material for magnetic recording media, a permanent magnet material, etc. [0030] (EXAMPLE 1) 0.8 mL of oleic acid and 0.85 mL of oleylamine were added into 50 mL of octyl ether to prepare a mixed solvent. 1.236 g of iron (III) acetylacetonate and 0.59 g of platinum (II) acetylacetonate were added to the mixed solvent, and the solvent was kept at 160⁰C (for about 30 minutes) until the added salts dissolved. Next, after the solvent was heated to 230⁰C, 1.94 g of hexadecanediol, that is, a reducing agent, was added and the solvent was kept at 230⁰C for 60 minutes. After that, the mixture was cooled, and the particles were collected.

[0031] (EXAMPLE 2) 1.236 g of iron (III) acetylacetonate and 0.59 g of platinum (II) acetylacetonate were added into 50 mL of octyl ether, and the mixture was heated to 160⁰C and was kept (for about 30 minutes) until the added salts dissolved. Next, after the mixture was heated to 230⁰C, 1.94 g of hexadecanediol, that is, a reducing agent, was added. After 30 minutes, 0.8 mL of oleic acid and 0.85 mL of oleylamine were added as a surface-active agent, the mixture was kept at 230⁰C for 30 minutes. After the mixture was cooled, the obtained particles were collected.

[0032] Results of the TEM observation of obtained particles are shown in FIGS. IA to ID. The volume fraction data and the particle diameter distribution of the obtained FePt particles and the obtained Fe particles are shown in FIGS. 2 A and 2B. From these results, it can be understood that the volume fraction of FePt /Fe can be changed by changing the amount of the surface-active agent added into the reaction solvent and the timing of adding the surface-reactive agent. The particle diameter of the nanoparticle at that time did not depend on the concentration of the surface-active agent, and the particle diameter of FePt was 2 to 3 nm and the particle diameter of Fe was about 10 to 15 nm.

[0033] While the invention has been described with reference to example embodiments thereof, it is to be understood that the invention is not limited to the described embodiments or constructions. On the other hand, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the disclosed invention are shown in various example combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the scope of the appended claims.

Claims

CLAIMS:

1. A production method for a nanocomposite metal magnetic particle containing an FePt particle and an Fe particle, comprising: dissolving a salt of Fe and a salt of Pt in a solvent containing a surface-active agent; adding a reducing agent at a temperature that is higher than or equal to a reduction temperature of an Fe ion that constitutes the salt of Fe; and thereby synthesizing the FePt particle and depositing the Fe particle on a surface of the FePt particle.

2. A production method for a nanocomposite metal magnetic particle containing an FePt particle and an Fe particle, comprising: dissolving a salt of Fe and a salt of Pt in a solvent; adding a reducing agent at a temperature that is higher than or equal to a reduction temperature of an Fe ion that constitutes the salt of Fe; then adding a surface-active agent; and thereby synthesizing the FePt particle and depositing the Fe particle on a surface of the FePt particle.

3. The production method according to claim 1 or 2, wherein the salt of Fe is iron acetylacetonate, and the salt of Pt is platinum acetylacetonate.

4. The production method according to any one of claims 1 to 3, wherein the reducing agent is a polyol.

5. The production method according to claim 4, wherein the polyol is at least one of 1,2-octanediol, 1,2-dodecanediol, 1,2-tetradecanediol, and 1,2-hexadecanediol.

6. The production method according to any one of claims 1 to 5, wherein the reducing agent is added at a temperature higher than or equal to 23O⁰C.

7. The production method according to any one of claims 1 to 6, wherein a ratio between the salt of Fe and the salt of Pt is set so that a molar ratio of Fe to Pt becomes excessively large.

8. The production method according to any one of claims 1 to 7, wherein a ratio between the salt of Fe and the salt of Pt is the salt of Fe:the salt of Pt is 7:3 to 9:1 in molar ratio.

9. The production method according to any one of claims 1 to 8, wherein the solvent is at least one of octyl ether, octadecene, squalene, tetraethylene glycol, and triphenyl methane.

10. The production method according to any one oi claims 1 to 9, wherein the surface-active agent is at least one of oleylamine, oleic acid, tetraethylene glycol, sodium dodecylbenzenesulfonate, phenylphosphonic acid, myristylic acid, dodecanethiol, and dodecylamine.

11. The production method according to any one of claims 1 to 10, wherein an amount of the surface-active agent added is 10 to 100% of the solvent in mass ratio.

12. The production method according to any one of claims 1 to 11, wherein an amount of the reducing agent added is 1.5 to 2 times as large in molar ratio as the total amount of the salt of Fe and the salt of Pt.