JP2008057037A - METHOD FOR PRODUCING FePt NANOPARTICLE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing FePt nanoparticles capable of directly synthesizing L1<SB>0</SB>-phase FePt nanoparticles having high regularization degree and coercivity with ease. <P>SOLUTION: The method for producing the FePt nanoparticles comprises: a solution preparing step for preparing a solution containing iron (Fe) acetylacetonate, platinum (Pt) acetylacetonate, and a reducing agent in a mixed solvent made by mixing a first solvent consisting of triphenylbenzene or triphenylene and a second solvent consisting of at least one kind of a straight-chain hydrocarbon represented as C<SB>n</SB>H<SB>2n+2</SB>(n=22 to 30) or a branched hydrocarbon; and a reacting step for obtaining the L1<SB>0</SB>-phase FePt nanoparticles by heating the solution to no less than 360°C and reducing the same. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for synthesizing FePt nanoparticles containing Fe and Pt.

A magnetic recording medium material is required to have a high coercive force for stable recording and holding. As the metal magnetic material having a high coercive force, a large L1 ₀ phase FePt nanoparticle magnetic anisotropy is known.

For example, Non-Patent Document 1 reports a method for producing FePt nanoparticles having a diameter in the range of 3 to 10 nm. The FePt nanoparticles in the as-synthesized a face centered cubic (fcc) structure of non-magnetic, it is necessary to transfer to the L1 ₀ phase by heat treatment above 550 ° C..
Further, Non-Patent Documents 2 to 4, tetracosane is a high boiling point, tetraethylene glycol, with hexadecylamine etc. as a solvent, a method for direct synthesis of L1 ₀ phase FePt nanoparticles have been reported.

However, in the method of Non-Patent Document 1, since particle growth / aggregation of nanoparticles occurs due to the heat treatment, the dispersibility deteriorates and is not suitable as a material for a magnetic recording medium. Further, as a method of lowering the phase transition temperature to L1 ₀ phase from fcc structures, Cu, Ag, there is a method of heat treatment by adding Sb or the like in the magnetic particles, reduction in magnetic properties that the addition of these metals There are things to do. As another method for lowering the phase transition temperature, a method of heat treatment under a hydrogen atmosphere is known, but synthesis in an organic solvent under a hydrogen atmosphere is difficult in terms of management.
Further, in Non-Patent Documents 2 to 4 of method, although it is possible to directly synthesize the L1 ₀ phase FePt nanoparticles, magnetic properties such as coercive force is still insufficient.

For these reasons, the synthesis method of FePt nanoparticles can be easily synthesized directly L1 ₀ phase FePt nanoparticles having excellent magnetic characteristics such as coercive force is desired.

S. Sun et al, Science, 287 (2000) 1989-1992 Luciano E.M.Howard et al, J. Am. Chem. Soc., 127 (2005) 10140-10141 Seiichi Kuno et al., Journal of Japan Society of Applied Magnetics, 29 (2005) 814-819 Z. Jia et al, IEEE Trans. Magn., 41 (2005) 3385-3387

The present invention, such conventional been made in view of the problems, and to provide a method of synthesizing FePt nanoparticles can be easily synthesized directly high L1 ₀ phase FePt nanoparticles regularity degree-coercivity To do.

The first invention includes a first solvent consisting of triphenyl benzene or _{triphenylene, C n H 2n + 2 (} n = 22~30) with at least one or more of the linear hydrocarbon or branched hydrocarbon represented A solution preparation step of preparing a solution containing iron (Fe) acetylacetonate, platinum (Pt) acetylacetonate and a reducing agent in a mixed solvent obtained by mixing a second solvent comprising:
By reduction by heating the solution to above 360 ° C., in the synthesis method of FePt nanoparticles; and a reaction step of obtaining an L1 ₀ phase FePt nanoparticles (claim 1).

  In the synthesis method of the present invention, in the solution preparation step, a metal complex (iron acetylacetonate, platinum acetylacetonate) and a reducing agent are added in the mixed solvent obtained by mixing the first solvent and the second solvent. In the reaction step, the solution is heated to 360 ° C. or higher, and the metal complex is reduced with a reducing agent.

That is, in this invention, the said mixed solvent which mixed the said 1st solvent and the said 2nd solvent from which a property differs, and has the characteristic which canceled each other's strong point was used. This mixed solvent has a low melting point and a high boiling point, and has a characteristic that the solubility of the metal complex is high. This makes it possible to easily direct synthesis of high L1 ₀ phase FePt nanoparticles regularity degree-coercivity. This will be described below.

As the first solvent, triphenylbenzene (melting point: 172 to 174 ° C., boiling point: 460 ° C.) or triphenylene (melting point: 195 to 198 ° C., boiling point: 438 ° C.) is used. The first solvent has a boiling point as high as 400 ° C. or higher. Moreover, since it has a benzene ring, its polarity is high. That is, the solubility of the metal complex is high.
However, the first solvent has a characteristic that it has a high melting point and is easily sublimated. Therefore, when the synthesis is carried out using the first solvent alone, in the solution preparation step, a temperature higher than the melting point (180 ° C. or more) is required to prepare a uniform solution, and an unstable metal before the synthesis. The complex will decompose. In the reaction step, the sublimed first solvent may adhere to the reflux tube, and the reflux tube may be clogged.

Further, Examples of the second _{solvent, C n H 2n + 2 (} n = 22~30) with use those containing at least one or more of the linear hydrocarbon or branched hydrocarbon represented. The second solvent has a low melting point of 60 ° C. or lower and a high boiling point of 360 ° C. or higher.
However, hydrocarbon compounds such as the second solvent are nonpolar, and the solubility of the metal complex is low. Therefore, when synthesis is performed using the second solvent alone, it is difficult to prepare a uniform solution in the solution preparation step.

  Therefore, in the present invention, the mixed solvent obtained by mixing the first solvent and the second solvent having different properties, which is difficult to use alone, is used. The mixed solvent has the characteristics of maintaining the advantages of the first solvent and the second solvent and canceling the disadvantages. That is, it has a low melting point and a high boiling point and a high solubility of the metal complex. And the following effects are acquired by synthesize | combining using such a mixed solvent.

Since the mixed solvent has a high boiling point, synthesis at a high temperature is possible. Since the FePt nanoparticles undergo a phase transition from the fcc structure to the L1 ₀ phase at a high temperature, as a result, the L1 ₀ phase can be directly synthesized and the degree of ordering is increased.
Further, since the mixed solvent has high solubility, the number of nucleation during synthesis is reduced, and relatively large nanoparticles can be synthesized. According to thermodynamic calculations, it has been found that easily phase transition in L1 ₀ phase the larger the particle diameter. Further, since the high temperature nucleation occurs, the nucleus of the first from the L1 ₀ phase is generated. As a result, the L1 ₀ phase is easily generated.

In addition, since the mixed solvent has a low melting point, a uniform solution can be stably prepared at a low temperature in the solution preparation step.
Furthermore, in the reaction step, the second solvent having a low melting point is refluxed, and the first solvent having a high melting point attached to the reflux tube is washed away.

As described above, in the present invention, the mixed solvent having the characteristics that the first solvent and the second solvent having different properties are mixed, has a low melting point and a high boiling point, and has a high solubility of the metal complex is used. Te, by performing synthesis at temperatures as high as 360 ° C. or higher, can be easily synthesized directly with high regularity degree L1 ₀ phase FePt nanoparticles. Also, L1 ₀ phase has a magnetic anisotropy, the characteristics becomes greater the higher ordering degree. Therefore, a high coercive force can be obtained.

Note that the L1 ₀ phase FePt nanoparticles here do not necessarily mean that the entire crystal structure is a complete L1 ₀ phase. That is, there is a state in which a complete L1 ₀ phase in which atoms are regularly arranged and an incomplete L1 ₀ phase in which atoms are irregularly arranged or the arrangement is shifted are mixed. Including. Usually, it is in a mixed state.

The degree of ordering is a parameter indicating the degree of regular arrangement of atoms. In the present invention, it is used as a parameter indicating the percentage of full L1 ₀ phase. That is, the higher ordering degree, the proportion of full L1 ₀ phase is meant high. This degree of ordering can be obtained from intensity measurements of reflections called regular gratings or superlattice reflections that appear as weak diffraction spots in the X-ray diffraction pattern.

The second invention is a solution preparation for preparing a solution containing iron (Fe) acetylacetonate, platinum (Pt) acetylacetonate and a reducing agent in a solvent comprising 4-benzoylbiphenyl and / or 2-naphthylphenylketone. Process,
By reduction by heating the solution to above 360 ° C., in the synthesis method of FePt nanoparticles; and a reaction step of obtaining an L1 ₀ phase FePt nanoparticles (claim 5).

  In the synthesis method of the present invention, in the solution preparation step, a solution containing a metal complex (iron acetylacetonate, platinum acetylacetonate) and a reducing agent in the solvent is prepared. It heats above and reduces the said metal complex with a reducing agent.

  That is, in the present invention, 4-benzoylbiphenyl (melting point: 99 to 101 ° C., boiling point: 419 to 420 ° C.), 2-naphthylphenyl ketone (melting point: 82 ° C., boiling point: 225 ° C./8 mmHg (390 ° C./390)/ 1 atmosphere equivalent))) or a mixture of both. The solvent has a melting point as low as about 100 ° C. or lower and a boiling point as high as 390 ° C. or higher. Moreover, since it has a benzene ring, its polarity is high. That is, the solubility of the metal complex is high.

By using the above-mentioned solvent having such a low melting point and high boiling point and high solubility of the metal complex, synthesis is performed at a high temperature of 360 ° C. or higher, so that L1 ₀ having a high degree of ordering as described above. Phase FePt nanoparticles can be easily synthesized directly. Therefore, a high coercive force can be obtained.

In the first invention, the first solvent is 1,3,5-triphenylbenzene (C ₂₄ H ₁₈ , melting point: 172 to 174 ° C., boiling point: 460 represented by the following general formula (Formula 1). C), triphenylene (C ₁₈ H ₁₂ , melting point: 195 to 198 ° C., boiling point: 438 ° C.) represented by the general formula (Chemical Formula 2), and the like can be used.

Further, Examples of the second solvent, there can be used those containing a _{C n H 2n + 2 (n} = 22~30) with at least one or more of the linear hydrocarbon or branched hydrocarbon represented. That is, a mixture of one or more of the above linear hydrocarbons may be used, or a mixture of one or more of the above branched hydrocarbons may be used. Moreover, you may use what mixed the said linear hydrocarbon and the said branched hydrocarbon.

Examples of the linear hydrocarbon include tricosane (C ₂₃ H ₄₈ , melting point: 46 to 47 ° C., boiling point: 199 to 200/3 mmHg (385) represented by the following general formulas (Chemical Formula 3) to (Chemical Formula 6). ° C / 1 atm conversion)), tetracosane (C ₂₄ H ₅₀ , melting point: 49-52 ° C., boiling point: 391 ° C.), pentacosane (C ₂₅ H ₅₂ , melting point: 53-56 ° C., boiling point: 169-170 / 0. 05 mmHg (445 ° C./1 atm equivalent)), hexacosane (C ₂₆ H ₅₄ , melting point 55 ° C., boiling point: unknown), and the like can be used.

Examples of the branched hydrocarbon include squalane (C ₃₀ H ₆₂ , melting point: −38 ° C., boiling point: 176 ° C./0.05 mmHg (450 ° C./1 atmospheric pressure conversion) represented by the following general formula (Formula 7). ) Etc. can be used.
Further, the branched hydrocarbon preferably has at least one branch in which the number of C in the main chain is equal to or greater than that of the linear hydrocarbon shown above.

Further, in the second solvent _{(C n H 2n + 2)} , in the case of n <22, the above the boiling point of the solvent mixture is reduced, it may not be possible to obtain a highly regular degree-coercivity L1 ₀ phase . In the case of n> 30, the boiling point does not change so much, but the melting point becomes too high and cannot be used as a solvent. Further, since the production and synthesis are difficult, it is very expensive and cannot be used industrially. In addition, the second solvent is decomposed (C—C bond is broken) at a high temperature, and a low molecular organic substance may be generated.

The mixed solvent is preferably formed by mixing triphenylbenzene as the first solvent and tetracosane (C ₂₄ H ₅₀ ) as the second solvent (Claim 2).
In this case, it is possible to reliably direct synthesis of high regularity degree-coercivity L1 ₀ phase.

Moreover, it is preferable that the mixing ratio of the said 1st solvent and the said 2nd solvent exists in the range of 1: 2-2: 1 by mass ratio in the said mixed solvent (Claim 3).
When the mixing ratio is outside the above range, a low melting point and high-boiling, reduces the properties of the mixed solvent of high solubility of the metal complex, obtaining a high degree of ordering, the coercive force L1 ₀ phase There is a risk that it will not be possible.

The reducing agent is preferably tetraethylene glycol, 1,2-hexadecanediol, hydrazine or sodium borohydride (Claim 4).
In this case, in the above reaction step, iron acetylacetonate and platinum acetylacetonate as metal complexes can be more reliably reduced.

In the second invention, as the solvent, 4-benzoylbiphenyl represented by the following general formula (Chemical Formula 8) (C ₁₉ H ₁₄ O, melting point: 99 to 101 ° C., boiling point: 419 to 420 ° C.) 2-naphthyl phenyl ketone represented by the general formula (Chemical Formula 9) (C ₁₇ H ₁₂ O, melting point: 82 ° C., boiling point: 225 ° C./8 mmHg (converted to 390 ° C./1 atmospheric pressure)) and the like can be used.

The solvent is preferably 4-benzoylbiphenyl (claim 6).
In this case, it is possible to reliably direct synthesis of high regularity degree-coercivity L1 ₀ phase.

The reducing agent is preferably tetraethylene glycol, 1,2-hexadecanediol, hydrazine, or sodium borohydride (Claim 7).
In this case, in the above reaction step, iron acetylacetonate and platinum acetylacetonate as metal complexes can be more reliably reduced.

When the solvent is 4-benzoylbiphenyl, the reducing agent is particularly preferably tetraethylene glycol (molecular weight: 194.23).
And in the said solution preparation process, 0.025-0.75 mmol / g in total of iron (Fe) acetylacetonate and platinum (Pt) acetylacetonate with respect to 4-benzoyl biphenyl as said solvent, the said reducing agent It is preferable that 0.1 to 5 mmol / g of tetraethylene glycol is added to prepare the solution.
That is, for example, when 4-benzoylbiphenyl is 20 g, a total of 0.5 to 15 mmol of iron acetylacetonate and platinum acetylacetonate and 2 to 100 mmol of tetraethylene glycol may be added to prepare the above solution. .
In this case, it is possible to ordering high degree, more reliably direct synthesis of L1 ₀ phase having excellent magnetic characteristics such as coercive force.

Further, when the total addition amount of iron acetylacetonate and platinum acetylacetonate is less than 0.025 mmol / g with respect to 4-benzoylbiphenyl as the solvent, the amount of FePt nanoparticles obtained is reduced, Productivity may be reduced. Also, it may not be possible to obtain L1 ₀ phase of high saturation magnetization. On the other hand, if it exceeds 0.75 mmol / g, there is a risk that can not be obtained L1 ₀ phase high coercive force. Moreover, there is a possibility that the FePt nanoparticles having a uniform particle diameter cannot be obtained due to aggregation of the nanoparticles.

The total amount of iron acetylacetonate and platinum acetylacetonate added to 4-benzoylbiphenyl as the solvent is 0.15 mmol / g or more, that is, 0.15 to 0.75 mmol / g. preferable.
In this case, generation of impurities such as soot can be suppressed in the reaction step. Therefore, it is possible to synthesize a more L1 ₀ phase having excellent magnetic properties.

Moreover, when the addition amount of tetraethylene glycol is less than 0.1 mmol / g with respect to 4-benzoylbiphenyl as the solvent, the reduction reaction may not be sufficiently performed. Therefore, the amount of FePt nanoparticles obtained is reduced, and the productivity may be reduced. On the other hand, if it exceeds 5 mmol / g, there is a risk that can not be obtained L1 ₀ phase high coercive force.

The molar ratio of the total addition amount A of iron (Fe) acetylacetonate and platinum (Pt) acetylacetonate to be added to 4-benzoylbiphenyl as the solvent and the addition amount B of tetraethylene glycol as the reducing agent. (B / A) is preferably 1 to 100 (claim 9).
In this case, compared with the case where the value of the molar ratio (B / A) is out of the above range, generation of impurities such as soot in the reaction step can be sufficiently suppressed, and the magnetic characteristics are excellent. it is possible to obtain an L1 ₀ phase.

Moreover, in the said 1st and 2nd invention, the heating temperature of the said solution in the said reaction process shall be the temperature below the boiling point of the said mixed solvent. Moreover, when considering the glass apparatus, the heating device, and other raw materials used at the time of synthesis, the temperature is preferably less than 450 ° C. In the case of 450 ° C. or higher, it is necessary to synthesize using a special heat-resistant device, which is expensive and industrially difficult.
The heating time of the solution is preferably 0.1 hour or longer. In this case, it is possible to obtain a higher degree of ordering, the coercive force L1 ₀ phase.

The molar ratio of iron to the total amount of iron and platinum contained in the solution is preferably 50 to 65 mol% (claim 10).
Although FePt has a solid solution region, it is generally known that magnetic properties such as coercive force are improved with a slightly rich composition of Fe (about Fe ₅₀ Pt _{50 to} about Fe ₅₅ Pt ₄₅ ).
Therefore, when the molar ratio is less than 50 mol%, FePt ₃ having low magnetic properties may be generated. On the other hand, when it exceeds 65 mol%, other fine particles such as Fe ₃ Pt, Fe, and iron oxide having low magnetic properties may be formed.

The average particle size of the L1 ₀ phase FePt nanoparticles are preferably 6～100Nm (claim 11).
The FePt nanoparticles are suitably used for magnetic recording medium materials, permanent magnet materials, biomolecule labeling agents, drug carriers and the like. For use in these, the average particle size is preferably 6 to 100 nm, more preferably 6 to 20 nm.

Further, the coercive force of the L1 ₀ phase FePt nanoparticles, it is preferably at least 4 kOe (claim 12).
When the coercive force is less than 4 kOe, there is a possibility that excellent magnetic properties cannot be obtained.

Further, degree of ordering of the L1 ₀ phase FePt nanoparticles is preferably 0.5 or more (claim 13).
When the degree of ordering is less than 0.5, a high coercive force may not be obtained. That is, the L1 ₀ phase has a large magnetic anisotropy, but if the degree of ordering of the L1 ₀ phase is low, the coercive force also becomes low.

(Example 1)
A method for synthesizing FePt nanoparticles according to the embodiment of the first invention and the FePt nanoparticles obtained thereby will be described.
In this example, 1,3,5-triphenylbenzene (C ₂₄ H ₁₈ ) having the structure shown in the above general formula (Formula 1) is used as the first solvent, and the above solvent is used as the second solvent. Tetracosane (C ₂₄ H ₅₀ ) having a structure represented by the general formula (Chemical Formula 4) was used.
And FePt nanoparticle (sample A1-A5) was synthesize | combined under various conditions shown in Table 1, and the characteristic was evaluated. Samples A2 to A4 are products of the present invention using a mixed solvent, and samples A1 and A5 are comparative products using the first solvent or the second solvent alone.

<Solution preparation process>
First, in a quartz flask equipped with a quartz cooling tube, triphenylbenzene (first solvent) and tetracosane (second solvent) are mixed at a predetermined mixing ratio (mass ratio / 100: 0 to 0: 100). 20 g of the mixed solvent, iron (Fe) acetylacetonate and platinum (Pt) acetylacetonate were added together in an amount of 1 mmol (amount of raw materials (molar ratio) / Fe: Pt = 52: 48), and the flask was filled with nitrogen. Air and moisture were removed from the flask by replacement. During synthesis, nitrogen gas was always blown into the flask.

Next, the inside of the flask was heated with a mantle heater, and iron acetylacetonate and platinum acetylacetonate were dissolved in the mixed solvent to obtain a uniform solution. In addition, the temperature which prepares a solution changes with the kind of mixing solvent, a mixing ratio, etc.
Thereafter, the inside of the flask was cooled to room temperature, and 5 mmol of tetraethylene glycol (= TEG) (reducing agent) was added.

<Reaction process>
Next, the flask was heated to a predetermined temperature (reflux temperature: 400 to 420 ° C.) with a mantle heater, and then refluxed for 1 hour. After cooling, a solid sample was obtained in the flask.
Thereafter, the organic component in the solid sample was dissolved in chloroform, and the solution was filtered to separate the solid content (inorganic component), thereby obtaining FePt nanoparticles (samples A1 to A5).

Next, physical properties of the obtained FePt nanoparticles (samples A1 to A5) were evaluated.
Each measurement item and its measurement method are as follows.

(composition)
The composition (molar ratio) of FePt nanoparticles was measured by applying FePt nanoparticles to a glass substrate and using SEM-EDX (manufactured by Hitachi, S-3600N, acceleration voltage: 20 kV). And the ratio of Fe and Pt was calculated | required from the characteristic X-ray intensity ratio of FeK and PtL.

(Particle size)
The crystal grain size (average grain size) of FePt nanoparticles was determined from the half width of the (111) peak of X-ray diffraction using Scherrer's formula.

(Regularity)
The degree of ordering S is based on the following equation (Equation 1), using the peak areas of (111) and (110) of X-ray diffraction, taking the value of the JCPDS card (043-1359) as the degree of ordering 1. Asked.

  In addition, an orientation sample in a magnetic field is used for measurement of magnetic characteristics. A sample oriented in a magnetic field was filled with FePt nanoparticles and wax in a sample holder, and the holder was set on an electromagnet and heated while applying a magnetic field to melt the wax. Thereafter, the sample was cooled while applying a magnetic field to obtain a sample oriented in a magnetic field.

(Magnetic properties)
Magnetic properties were measured using a vibrating sample magnetometer (VSM) (manufactured by Toei Kogyo Co., Ltd .: VSM-38) at a maximum magnetic field of 18 kOe and room temperature. Then, a hysteresis curve was obtained, and a saturation magnetization σs, a residual magnetization σr, and a coercive force iHc were obtained therefrom.

Next, Table 1 shows the results of each measurement.
Moreover, in FIGS. 1-4, the XRD measurement result of sample A1, A3-A5 is shown. In the figure, the diffraction peaks are underlined Miller index is the diffraction peak of the superlattice structure with the L1 ₀ phase.
5 to 8 show hysteresis curves of samples A1 and A3 to A5. In the figure, the coercive force iHc is shown.

As is known from FIGS. 1-4, the present invention product (Sample A3, A4) are compared to the comparative product (sample A1, A5), it is understood that the diffraction peak of the superlattice structure with the L1 ₀ phase is strong . In other words, it indicates that the high ordering degree L1 ₀ phase was obtained.
5 to 8, it can be seen that the products of the present invention (samples A3 and A4) have a higher coercive force iHc than the comparative products (samples A1 and A5).

Further, as is known from Table 1, the products of the present invention (samples A2 to A4) show a higher degree of ordering S than the comparative products (samples A1 and A5). In addition, in the magnetic characteristics, the products of the present invention (samples A2 to A4) had a saturation magnetization σs of 20 to 30 emu / g, which was a little low value. This is because some of the solvent was carbonized / graphite during the reaction. This is considered to be the effect of soot and the like mixed as impurities. In any case, the products of the present invention (A2 to A4) exhibit high coercive force iHc.
In particular, Sample A3 exhibited a high degree of ordering S of 0.6 and a coercive force iHc of 6.2 kOe.

FIG. 9 shows the relationship between the mass ratio of tetracosane (second solvent) in the mixed solvent and the magnetic characteristics (saturation magnetization σs, coercivity iHc) based on the data shown in Table 1.
As can be seen from the figure, when tetracosane is 30 to 70 mass%, a high coercive force iHc is shown. Moreover, the saturation magnetization σs decreases as the mass ratio of tetracosane decreases. The reason for saturation magnetization σs decreases, lowering degree of ordering of the resulting FePt nanoparticle, that is, due to reduction in the amount of L1 ₀ phase. By the amount of L1 ₀ phase is lowered, and percentage fcc structure of the non-magnetic occupied increases.

(Example 2)
The method for synthesizing FePt nanoparticles according to the embodiment of the second invention and the FePt nanoparticles obtained thereby will be described.
In this example, 4-benzoylbiphenyl (C ₁₉ H ₁₄ O) having the structure shown in the above general formula (Chemical Formula 8) was used as the solvent.
And FePt nanoparticle (sample B1-B7) was synthesize | combined under various conditions shown in Table 2, and the characteristic was evaluated.

<Solution preparation process>
First, in a quartz flask equipped with a quartz cooling tube, 20 g of 4-benzoylbiphenyl (solvent), iron (Fe) acetylacetonate and platinum (Pt) acetylacetonate were combined, and 1 mmol (stock charge (mol) Ratio) / Fe: Pt = 55: 45 to 65:35), and the atmosphere in the flask was replaced with nitrogen to remove air and moisture from the flask. During synthesis, nitrogen gas was always blown into the flask.

Next, the inside of the flask was heated with a mantle heater, and iron acetylacetonate and platinum acetylacetonate were dissolved in a solvent to obtain a uniform solution.
Thereafter, the inside of the flask was cooled to room temperature, and 5 mmol of tetraethylene glycol (= TEG) (reducing agent) was added.

<Reaction process>
Next, the flask was heated to a predetermined temperature (390, 410 ° C.) with a mantle heater, and then refluxed for a predetermined time (1 minute, 10 minutes, 1 hour, 3 hours). After cooling, a solid sample was obtained in the flask.
Thereafter, the organic component in the solid sample was dissolved in chloroform, and the solution was filtered to separate the solid content (inorganic component), thereby obtaining FePt nanoparticles (samples B1 to B7).

Next, physical properties of the obtained FePt nanoparticles (samples B1 to B7) were evaluated.
Each measurement item and its measurement method are the same as those in the first embodiment.

Next, Table 2 shows the results of each measurement.
10 to 12 show XRD measurement results of Samples B3 to B5. In the figure, the diffraction peaks are underlined Miller index is the diffraction peak of the superlattice structure with the L1 ₀ phase.
13 to 15 show hysteresis curves of samples B3 to B5. In the figure, the coercive force iHc is shown.

As is known from FIGS. 10 to 12, the sample B3~B5 it is seen that the diffraction peaks of the superlattice structure with the L1 ₀ phase is observed strongly. In other words, it indicates that the high regularity of L1 ₀ phase was obtained.
Further, as can be seen from FIGS. 13 to 15, samples B <b> 3 to B <b> 5 have a high coercive force iHc.

Moreover, as is known from Table 2, the samples B1 to B7 show a high degree of ordering S. In addition, in the magnetic characteristics, the samples B3 and B4 had a saturation magnetization σs of 20 to 30 emu / g, which was a little low. This is because some of the solvent was carbonized and graphitized during the reaction, soot as an impurity. It is thought that this is an effect of mixing. In any case, Samples B1 to B7 show high coercivity iHc.
In particular, Sample B3 showed a high degree of ordering S of 0.60 and a coercive force iHc of 9.3 kOe, and Sample B4 showed a high degree of ordering S of 0.68 and a coercive force iHc of 10 kOe.

FIG. 16 shows the relationship between the reflux time (heating time) and the magnetic characteristics (saturation magnetization σs, coercivity iHc) based on the data of samples B1 to B4 shown in Table 2.
As can be seen from the figure, a high coercive force iHc can be obtained by setting the reflux time to 1 hour or longer. In contrast to the coercive force iHc, the saturation magnetization σs decreases as the reflux time increases. As described above, the cause of the decrease in the saturation magnetization σs is considered to be the effect of part of the solvent being carbonized / graphitized and soot as an impurity mixed therein.

FIG. 17 shows the relationship between the amount of raw material charged (Fe molar ratio) and magnetic characteristics (saturation magnetization σs, coercivity iHc) based on the data of samples B5 to B7 shown in Table 2.
As can be seen from the figure, the higher the molar ratio of Fe, the higher the coercive force iHc. Further, the saturation magnetization σs becomes higher when the molar ratio of Fe is 60 mol% or more. FePt is generally known to exhibit a higher coercivity iHc when the composition of Fe is slightly richer than Fe: Pt = 1: 1, and the results are consistent with this.

(Example 3)
This example is an example in which the raw material concentrations of iron (Fe) acetylacetonate and platinum (Pt) acetylacetonate added to 4-benzoylbiphenyl as a solvent in Example 2 and the addition amount of the reducing agent were changed. is there.
Under various conditions shown in Table 3, FePt nanoparticles (samples C1 to C7) were synthesized and their characteristics were evaluated.

<Solution preparation process>
First, in a quartz flask equipped with a quartz cooling tube, 20 g of 4-benzoylbiphenyl (solvent), iron (Fe) acetylacetonate and platinum (Pt) acetylacetonate are combined to 5 mmol or 10 mmol (raw material charge amount) (Molar ratio) / Fe: Pt = 52: 48 to 55:45), and the atmosphere in the flask was replaced with nitrogen to remove air and moisture from the flask. During synthesis, nitrogen gas was always blown into the flask.

Next, the inside of the flask was heated with a mantle heater, and iron acetylacetonate and platinum acetylacetonate were dissolved in a solvent to obtain a uniform solution.
Thereafter, the inside of the flask was cooled to room temperature, and a predetermined amount (5 to 50 mmol) of tetraethylene glycol (= TEG) (reducing agent) was added.

<Reaction process>
Next, the flask was heated to a predetermined temperature (390 ° C.) with a mantle heater, and then refluxed for a predetermined time (1 hour). After cooling, a solid sample was obtained in the flask.
Thereafter, the organic component in the solid sample was dissolved in chloroform, and the solution was filtered to separate the solid content (inorganic component), thereby obtaining FePt nanoparticles (samples C1 to C7).

Next, physical properties of the obtained FePt nanoparticles (samples C1 to C7) were evaluated.
Each measurement item and its measurement method are the same as those in the first embodiment.

Next, Table 3 shows the results of each measurement.
As known from Table 3, samples C1 to C7 show a high degree of ordering S. Further, in the magnetic characteristics, the saturation magnetization σs≈50 emu / g, which is a high value. This is because the generation of impurities such as soot during the reaction was suppressed by increasing the raw material concentration of iron (Fe) acetylacetonate and platinum (Pt) acetylacetonate and adjusting the amount of reducing agent added. It is believed that there is. Samples C1 to C7 show high coercivity iHc.
In particular, the sample C4 has an ordering degree S of 0.80, a saturation magnetization σs of 49 emu / g, a coercive force iHc of 10.0 kOe, and the sample C5 has an ordering degree S of 0.77 and a saturation magnetization σs of 52 emu / g. g, coercive force iHc was as high as 10.3 kOe.

FIG. 3 is an explanatory diagram showing the XRD measurement result of sample A1 in Example 1. Explanatory drawing which shows the XRD measurement result of sample A3 in Example 1. FIG. Explanatory drawing which shows the XRD measurement result of sample A4 in Example 1. FIG. Explanatory drawing which shows the XRD measurement result of sample A5 in Example 1. FIG. FIG. 3 is an explanatory diagram showing a hysteresis curve of Sample A1 in Example 1. FIG. 3 is an explanatory diagram showing a hysteresis curve of Sample A3 in Example 1. FIG. 3 is an explanatory diagram showing a hysteresis curve of Sample A4 in Example 1. FIG. 3 is an explanatory diagram showing a hysteresis curve of Sample A5 in Example 1. FIG. 3 is an explanatory diagram showing the relationship between the mixing ratio of the second solvent and the magnetic characteristics in Example 1. Explanatory drawing which shows the XRD measurement result of sample B3 in Example 2. FIG. Explanatory drawing which shows the XRD measurement result of sample B4 in Example 2. FIG. Explanatory drawing which shows the XRD measurement result of sample B5 in Example 2. FIG. Explanatory drawing which shows the hysteresis curve of sample B3 in Example 2. FIG. Explanatory drawing which shows the hysteresis curve of sample B4 in Example 2. FIG. Explanatory drawing which shows the hysteresis curve of sample B5 in Example 2. FIG. FIG. 6 is an explanatory diagram showing a relationship between a reflux time and magnetic characteristics in Example 2. FIG. 6 is an explanatory diagram showing the relationship between the molar ratio of Fe and magnetic characteristics in Example 2.

Claims (13)

A first solvent composed of triphenylbenzene or triphenylene, and a second solvent composed of at least one of linear hydrocarbons or branched hydrocarbons represented by C _n H _{2n + 2} (n = 22-30); A solution preparation step of preparing a solution containing iron (Fe) acetylacetonate, platinum (Pt) acetylacetonate and a reducing agent in a mixed solvent obtained by mixing
By reduction by heating the solution to above 360 ° C., the synthesis method of FePt nanoparticles; and a reaction step of obtaining an L1 ₀ phase FePt nanoparticles. In claim 1, the mixed solvent, the method of synthesis of FePt nanoparticles, characterized by comprising mixing a tetracosane (C _{24 H 50)} as triphenyl benzene and the second solvent as the first solvent .   3. The FePt nanoparticle according to claim 1, wherein the mixed solvent has a mixing ratio of the first solvent and the second solvent within a range of 1: 2 to 2: 1 by mass ratio. Synthesis method.   The method for synthesizing FePt nanoparticles according to any one of claims 1 to 3, wherein the reducing agent is tetraethylene glycol, 1,2-hexadecanediol, hydrazine, or sodium borohydride. A solution preparation step of preparing a solution containing iron (Fe) acetylacetonate, platinum (Pt) acetylacetonate and a reducing agent in a solvent composed of 4-benzoylbiphenyl or / and 2-naphthylphenylketone;
By reduction by heating the solution to above 360 ° C., the synthesis method of FePt nanoparticles; and a reaction step of obtaining an L1 ₀ phase FePt nanoparticles.   6. The method for synthesizing FePt nanoparticles according to claim 5, wherein the solvent is 4-benzoylbiphenyl.   7. The method for synthesizing FePt nanoparticles according to claim 5, wherein the reducing agent is tetraethylene glycol, 1,2-hexadecanediol, hydrazine, or sodium borohydride. In Claim 6, the reducing agent is tetraethylene glycol,
In the solution preparation step, iron (Fe) acetylacetonate and platinum (Pt) acetylacetonate in a total amount of 0.025 to 0.75 mmol / g with respect to 4-benzoylbiphenyl as the solvent, A method for synthesizing FePt nanoparticles, comprising adding 0.1 to 5 mmol / g of tetraethylene glycol to prepare the solution.   The total addition amount A of iron (Fe) acetylacetonate and platinum (Pt) acetylacetonate added to 4-benzoylbiphenyl as the solvent in claim 8, and the addition amount B of tetraethylene glycol as the reducing agent, The FePt nanoparticle synthesis method, wherein the molar ratio (B / A) is 1 to 100.   The method for synthesizing FePt nanoparticles according to any one of claims 1 to 9, wherein the molar ratio of iron to the total amount of iron and platinum contained in the solution is 50 to 65 mol%. In any one of claims 1 to 10, the average particle size of the L1 ₀ phase FePt nanoparticles, the synthesis method of FePt nanoparticles, which is a 6～100Nm. The method for synthesizing FePt nanoparticles according to any one of claims 1 to 11, wherein the coercive force of the L1 ₀ phase FePt nanoparticles is 4 kOe or more. In any one of claims 1 to 12, degree of ordering of the L1 ₀ phase FePt nanoparticles, the synthesis method of FePt nanoparticles, characterized in that not less than 0.5.

Images