JP5047706B2 - Method for producing metal nanoparticles - Google Patents

Description

  The present invention relates to a method for producing metal nanoparticles and metal nanoparticles produced by the production method.

  Metal nanoparticles are attracting attention for their industrial applications because of their unique physical and chemical properties. Various methods have been proposed so far for producing metal nanoparticles. Broadly speaking, there are wet methods and dry methods. A typical wet method is a method in which a metal salt or complex is reduced in a solution by a coexisting reducing agent, and a typical dry method is a metal ingot. The gas evaporation method (Non-patent Document 1). Among metal nanoparticles, alloy nanoparticles, especially alloys of noble metals such as platinum, palladium, gold, silver, rhodium, ruthenium and iridium with base metals such as iron, cobalt, nickel, copper and chromium Despite the fact that alloys that are practically important in terms of catalysis, electromagnetism or optical properties are known, their production requires multi-step operations and no simple method is known. It was. For example, solid solution alloys such as platinum-cobalt, platinum-nickel, platinum-iron, and platinum-cobalt-chromium have high electrochemical oxygen reduction mass activity and are useful as active species for fuel cell cathode catalysts. For the preparation, for example, platinum nanoparticles on a carbon support are allowed to react with a base metal salt such as cobalt and neutralized and supported with a base metal hydroxide, or treated with a reducing agent such as hydrazine and supported as a metal. Then, this is subjected to hydrogen reduction / alloying treatment at a high temperature of 800 to 900 ° C. or alloying treatment under argon flow to obtain an alloy catalyst. Due to this high temperature heat treatment, the alloy crystallite diameter is usually 5 nm or more, and it is difficult to obtain a fine alloy catalyst of 3 nm or less (for example, Patent Document 1).

  On the other hand, ordered alloy nanoparticles such as platinum-iron and platinum-cobalt are attracting attention as high-density magnetic recording materials because of their high magnetic anisotropy. After preparing irregular alloy nanoparticles by a polyol reduction method in a solvent, and then supporting this on a substrate, heat treatment is again performed at a high temperature of 500 ° C. or higher to obtain the desired regular alloy nanoparticles. (Patent Document 2, Non-Patent Document 2). Because of this regularity treatment, fine regular alloy nanoparticles having a particle diameter of less than 3 nm obtained by the wet nanoparticle production method could not be obtained.

On the other hand, several prior arts are known regarding methods of using laser light for the production of nanoparticles. A method of obtaining a high-temperature crystalline layer γ-phase alloy as fine particles, powder, or thin film by irradiating laser light to a gas of carbonyl compound of two kinds of transition metals such as Fe and Co or Fe and Cr (patent document) 3) This method is suitable for metal species having a compound that can be gasified, but is difficult to apply to alloys of heavy elements that are difficult to gasify, such as platinum and palladium.
A manufacturing method in which a coating liquid containing precursor non-ordered alloy nanoparticles is applied on a support and then the coating film is irradiated with a laser to form a CuAu type or Cu ₃ Au type hard magnetic order is reported (Patent Document 4). ) In addition, amorphous nanoparticles protected with organic ligands are manufactured and purified in advance by a wet method such as a hot soap method, and then the nanoparticles stabilized with organic ligands are irradiated with laser light. A method for producing crystallized magnetic nanoparticles has been reported (Patent Document 5).

  These conventional production methods require at least two stages and three to five stages of processing when adding purification and drying processes such as extraction in the middle to obtain the desired crystalline alloy nanoparticles, and the process is long and complicated. It is a process with a lot of loss of resources and energy due to heating or cleaning with a large amount of solvent. In addition, due to the heat treatment in the latter half, the aggregation and particle size growth of the fine particles obtained in the pre-folding step cannot be avoided.

  In addition, a method of forming fine particles of metal or metal oxide by a conventional laser ablation method is widely known (for example, Patent Document 6, Patent Document 7, and Non-Patent Document 3). This is a method of irradiating a solid metal raw material in the liquid phase with laser light to obtain fine particles with a particle size smaller than that of the raw material, but it is not a bottom-up method in which nanoparticles are formed from molecules, but a solid mass is finely divided. This is a so-called top-down method. This method has a problem that the atomization is limited and the control of the particle size distribution is not easy.

  By the way, in the case of a Pt—Fe alloy which is one of the alloys having the highest magnetic anisotropy among the currently known magnetic materials, the finest particle diameter reported so far is 3 to 4 nm. In addition, when the particle size of ferromagnetic particles is refined, the superparamagnetic critical diameter at which exchange interaction between electron spins loses ferromagnetism due to thermal disturbance is about 3 nm at 300K for Pt-Fe alloys. (Non-Patent Document 4).

  That is, for future ultra-high-density magnetic recording element applications, ferromagnetic nanoparticles as fine as possible, for example, 3 nm or less, are required, but a production method effective for producing such fine ordered alloy nanoparticles. It has been considered that it is difficult to achieve ferromagnetism in the normal temperature range because it is blocked by superparamagnetic walls, if any.

JP2000-323145A U.S. Pat.No. 6,265,462 Japanese Patent No. 3268793, Japanese Patent Laid-Open No. 5-65512 JP2003-260409 JP2005-48213 JP2005-272864 JP2003-306319 Masaaki Oda, Ultrafine Particles, Hayashi, Ueda, Tazaki, 115, 1988, Mita Publishing S. Sun et al., Science, Vol.287, 1989, 17 March 2000 S. Koda et al, J. Phys. Chem. B, 103, p1226-1232 (1999) M. Watanabe et al., Mater. Trans. JIM, Vol. 37, 489, 1996

  In order to overcome the above-mentioned problems of the prior art, the present invention aims at target metal nanoparticles, solid solution alloy nanoparticles of noble metal and base metal, and regular alloy nanoparticles that have conventionally required additional ordering treatment steps. It is another object of the present invention to provide a simple and high-yield production method in which a salt or / and complex solution of a constituent element is directly produced in a single step.

  As a means for solving the above-mentioned problems, the present invention provides a solution of a metal element salt and / or complex that is irradiated with laser light to decompose and / or reduce the salt and / or complex in the solution. There is provided a method for producing metal nanoparticles comprising directly producing metal nanoparticles having an average particle size in the range of 0.3 to 100 nm.

  A method for producing metal nanoparticles having an average particle diameter of preferably 0.3 to 10 nm, more preferably an average particle diameter of 0.3 to 3 nm is provided.

  The present invention also provides the above-mentioned method for producing metal nanoparticles in which a coordinating organic protective agent that coordinates with the generated metal nanoparticles to prevent aggregation is preexisted in the solution when the solution is irradiated with laser light. To do.

  Furthermore, the present invention provides the above-described metal in which a decomposition / reduction accelerator (hereinafter abbreviated as “accelerator”) that absorbs laser light and promotes decomposition and / or reduction of a metal salt and / or complex in a solution coexists. A method for producing nanoparticles is provided. And the manufacturing method of this metal nanoparticle whose said promoter is an oxygen-containing organic compound and also the manufacturing method of this metal nanoparticle whose promoter is alcohol are provided.

  The metal element salt and / or complex is a salt and / or complex of one metal element selected from the group consisting of platinum, palladium, gold, silver, rhodium, ruthenium, and iridium. A manufacturing method is provided.

In the present invention, the salt and / or complex of the metal element is a salt and / or complex of at least one element of the group (group A) consisting of platinum, palladium, gold, silver, rhodium, ruthenium, and iridium, The alloy nanoparticles comprising a salt and / or a complex of at least one element of the group consisting of iron, cobalt, nickel, copper, and chromium (group B), wherein the obtained metal nanoparticles are alloys of these elements. A manufacturing method is provided.
Moreover, the said manufacturing method whose said alloy is a solid solution alloy, Furthermore, the said manufacturing method of the metal nanoparticle whose this alloy is a regular alloy is provided.
Moreover, this invention provides the metal nanoparticle which is manufactured with said manufacturing method and has a particle size in the range of 0.3-100 nm. As the alloy nanoparticles, alloy nanoparticles, solid solution alloy nanoparticles, and regular alloy nanoparticles are also provided.

  Hereinafter, the present invention will be described in more detail. In the present invention, “room temperature” means 15 to 25 ° C. In the present invention, the nanoparticle refers to a fine particle having a particle size of 0.3 to 100 nm.

In the method for producing metal nanoparticles of the present invention, a salt and / or complex of a metal element is used as a raw material. Although it does not depend on the type of metal, it is preferably at least one of the group consisting of platinum, palladium, gold, silver, rhodium, ruthenium and iridium (hereinafter abbreviated as group A, these are often referred to as noble metal elements). is there. In the method for producing metal nanoparticles of the present invention, a solution of a salt and / or complex of a metal element is irradiated with laser light to cause decomposition and / or reduction of the salt and / or complex in the solution. That is, as a metal salt and / or complex, it does not spontaneously decompose and / or reduce under laser light irradiation, or does not spontaneously decompose and / or reduce, but promotes decomposition / reduction described later. A substance that decomposes and / or reduces under laser light irradiation by adding an agent is selected. Examples of the salt include hydrochloride, hydrobromide, hydroiodide, chlorate, bromate, iodate, nitrate, sulfate, acetate, propionate, butyrate, A salt of an organic carboxylic acid R—COOH such as oleate, benzoate or naphthylate (wherein R represents a C1-C20 alkyl group, aralkyl group, alkenyl group or aryl group) can be used. . Moreover, as a ligand of a complex, CO, NO, R—COO ⁻ , RCN, RNC, R ¹ R ² R ³ N, R ¹ COC (R ² ) = C (O ⁻ ) R ³ , R—C ₆ H ₄ O ⁻ , R—C ₆ H ₄ S ⁻ , R ¹ R ² R ³ P, R ¹ R ² R ³ PO (where R is as defined above, R ¹ , R ² , R ³ are independent) Or an alkyl group, an aralkyl group, or an aryl group, or R ¹ and R ² , R ² and R ^3, or R ³ and R ¹ may be linked to form a divalent group) Can take a ligand. Specific examples of such a ligand include CH ₃ COO ⁻ , C ₂ H ₅ COO ⁻ , CH ₃ CN, C ₆ H ₅ CN, NH ₃ , CH ₃ COCH═C (O ⁻ ) CH ₃ , CF ₃ COCF═C (O ⁻ ) CF _{3 and the} like can be mentioned, and CH ₃ COC (H) ═C (O ⁻ ) CH ₃ is preferable.

  Specific examples of metal salts and complexes include platinum chloride, chloroplatinic acid, sodium chloroplatinate, potassium chloroplatinate, tetraammineplatinum dichloride, dinitrodiaminoplatinum, dichlorodiammineplatinum, platinum acetylacetonate, when the metal is platinum. P-fluoroacetylacetonate platinum or the like can be preferably used.

In the production of the alloy of the present invention, a co-solution of constituent element salts or complexes is first prepared. When the alloy to be produced is an alloy of at least one element of group A and at least one element of group (group B) consisting of chromium, iron, cobalt, nickel, and copper, a salt of the element of group A And / or the salt and / or complex of the element and / or complex of the group B element, but the above-mentioned salts and / or complexes of the element A can be preferably used. Salts include hydrochloride, hydrobromide, hydroiodide, chlorate, bromate, iodate, nitrate, sulfate, acetate, propionate, butyrate, oleic acid A salt of an organic carboxylic acid R—COOH (wherein R is as described above) such as a salt, a benzoate, and a naphthylate can be used. Moreover, as a ligand of a complex, CO, NO, R—COO ⁻ , RCN, RNC, R ¹ R ² R ³ N, R ¹ COC (R ² ) = C (O ⁻ ) R ³ , R—C ₆ H ₄ O ⁻ , R—C ₆ H ₄ S ⁻ , R ¹ R ² R ³ P, R ¹ R ² R ³ PO (where R, R ¹ , R ² , and R ³ are as defined above, R ¹ and R ² , R ² and R ^3, or R ³ and R ¹ may be linked to form a divalent group). Specific examples of such a ligand include CH ₃ COO ⁻ , C ₂ H ₅ COO ⁻ , CH ₃ CN, C ₆ H ₅ CN, NH ₃ , CH ₃ COCH═C (O ⁻ ) CH ₃ , CF ₃ COCF═C (O ⁻ ) CF _{3 and the} like can be mentioned, and CH ₃ COC (H) ═C (O ⁻ ) CH ₃ is preferable.

  Examples of the metal salt of the group B element include, when the group B metal is iron, examples of the salt include ferrous chloride, ferric chloride, iron (II) bromide, iron (III) bromide, and fluorine. Ferric (III), ferric nitrate, ferrous sulfate, ferrous acetate, iron (III) citrate, iron (III) acrylate, ferrous ammonium sulfate, ferric ammonium sulfate, iron oxalate ( III) Ammonium, iron (II) gluconate, iron (III) gluconate), iron (II) naphthenate, etc. can be used, and iron (III) acetylacetonate, iron (III) ethoxide, pentacarbonyl iron as the complex , Nanocarbonyl diiron, dodecacarbonyl triiron, ferrocene, cyclopentadienyl iron (I) dicarbonyl dimer and the like can be suitably used.

  When a laser beam is irradiated to a solution containing only at least one salt or complex of the element of group B without using the element of group A, a dark color colloid is obtained and metal nanoparticles are generated at the initial stage of irradiation. However, when this colloid is left in the air, discoloration to a colored colloid peculiar to the group B metal oxide is observed. When the group A element coexists in the raw material solution, such discoloration does not occur, and the zero-valent state of the group B metal is stabilized by alloying with the group A element.

  The solvent is not particularly limited as long as it can dissolve a metal salt or complex. Depending on the type of salt or complex used, highly soluble solvents such as water, methanol, ethanol, n-propanol, isopropanol and other protic solvents, diethyl ether, tetrahydrofuran, acetone, acetonitrile, methylene dichloride, chloroform, etc. An aprotic polar solvent or a nonpolar solvent such as benzene, toluene or xylene can be selected and used. In particular, alcohol solvents such as methanol, ethanol, n-propanol and isopropanol are preferable because they themselves function as decomposition / reduction accelerators.

  The concentration of the salt or complex in the solvent is not particularly limited as long as the salt or complex is dissolved in the solvent. Usually 1.0 mol / L to 0.0001 mol / L, preferably 0.50 mol / L to 0.0005 mol / L, more preferably 0.10 mol / L to 0.002 mol / L.

  The wavelength of the laser applied to the solution is not particularly limited as long as the solution has a wavelength that absorbs. Usually, it is 200 to 12000 nm, preferably 300 to 1100 nm. That is, an infrared laser, a visible laser, an ultraviolet laser, a short wavelength ultraviolet laser, or the like can be used. An Nd-YAG pulse laser (wavelength 1064 nm, second harmonic 532 nm, third harmonic 355 nm), excimer pulse laser (248.5 nm), etc. can be used particularly suitably. Laser energy, pulse width, number of pulses, irradiation time, etc. are optimized according to the degree of decomposition / reduction in the solution of the raw material salt or complex, and the shape, composition, particle size distribution, etc. of the generated nanoparticles are determined. Can be controlled. Usually, the laser energy is preferably 1 mJ to 10 J, the output is 0.1 W to 20 W, the pulse speed is 0.1 Hz to 20 Hz, and the irradiation time is preferably 1 second to 1 hour.

  When the solution is an aqueous solution system, the solution can be put into a quartz beaker and irradiated with a laser directly vertically from its open upper surface. However, in the case of an organic solvent, a sealed container is used to place the laser incident surface side on the quartz window. As described above, it is preferable to perform laser irradiation after previously replacing the atmosphere with an inert gas. It is possible to detect the progress and end point of the reaction by monitoring the laser power absorbed by the solution by placing a laser power meter in contact with the quartz window on the opposite side of the laser light incident surface of the container. I can do it.

In irradiating the solution with laser light, it is preferable that a coordinating organic protective agent that coordinates with the generated metal nanoparticles to prevent aggregation is coexisted in the solution in advance. The coordinating organic protective agent is not particularly limited as long as it is an organic compound capable of covering or coordinating the surface of metal nanoparticles to prevent aggregation and fusion of metal nanoparticles. As the coordinating organic protective agent, for example, an organic ligand usually used for forming a metal complex, that is, an R ⁴ —X structure (R ⁴ can be an alkyl group, an alkenyl group, an aralkyl group, an aryl group, or the like, Can be NH ₂ group, CN group, COOH group, OH group, SH group or the like), R ¹ —Y—R ² structure (R ¹ and R ² each independently have the above meaning, Y is O , S, C═O, C═NH, NHCO, etc.) or ZR ¹ R ² R ³ structure (R ¹ , R ² and R ³ are as described above, Z is N or P, etc. Organic compound monomers and polymers containing these coordinating functional groups X, Y or Z can be used, and in particular, C6-C18 long-chain alkylamines, carboxylic acids, ethers or nitriles, tertiary Such as amine polymer, polyether, polyester, polyamide, etc. Rimmer is preferably used. The type of these coordinating organic compounds and the amount added to the solution should be selected and used in consideration of the shape, particle size, particle size distribution and application of the target metal nanoparticles. There is a need to. That is, if it is excessively stabilized, it may be difficult to decompose or desorb this ligand when it is used depending on the application, and may have a poisoning effect.

  In the metal nanoparticle production method of the present invention, when the metal salt and / or complex does not spontaneously decompose and / or reduce under laser light irradiation, the solution of the metal element salt or complex as a starting material A decomposition / reduction accelerator that absorbs laser light and accelerates the decomposition of the metal element salt and / or complex is coexisted therein. A “decomposition / reduction accelerator” is an organic compound having absorption in the wavelength region of laser light used for irradiation, and reduction and / or decomposition can be performed under laser light irradiation in a solution containing only a salt and / or complex as a raw material. When it does not occur, it can be added to cause reduction and / or decomposition of the metal salt and / or complex. The decomposition / reduction accelerator usually does not decompose at all or slows down the salt and / or complex even if it is present alone without irradiation with laser light at room temperature. Since the decomposition / reduction accelerator is preferably soluble in the raw salt and / or complex solution, a solvent and a decomposition / reduction accelerator are selected. As such a decomposition / reduction accelerator, an oxygen-containing organic compound is preferable, and alcohols such as ethanol, 1-propanol, 2-propanol, and 2-dimethoxyethanol can be particularly preferably used.

  In the production method of the present invention, the metal nanoparticles are obtained as a colloid dispersed in a solution in which a salt or complex of a raw material is dissolved. In some cases, nanoparticles stabilized with a coordinating organic protective agent can be isolated as a nanoparticle gel by adding a poor solvent after concentration under reduced pressure.

  On the other hand, it can be directly supported on a substrate in the state of a colloidal liquid or a concentrated liquid dispersion without isolation. Usable substrates such as a silicon substrate, a glass substrate, a polyimide substrate, and carbon paper can be used as the substrate, and the colloid can be coated on these substrates according to a conventional method such as a dropping method, a dip method, or a spin coating method. Furthermore, it is also possible to pattern on the substrate by an ink jet method, a dip pen lithography method or a contact print method. When the metal nanoparticles are used as a catalyst, they may be used as colloids or used by adsorbing and supporting them on a conventional carrier such as alumina, silica, titania, zeolite, activated carbon, carbon black, carbon nanotube, carbon horn, etc. You can also

  The shape, particle size distribution, average particle size and the like of the metal nanoparticles of the present invention are observed and measured with a transmission electron microscope (TEM). In the field of view of magnification of 1 million to 10 million times, select at least 100 particles randomly, measure the shape and particle diameter (representative diameter) of the transmission image, and statistically process it to obtain the number average particle diameter Find μ, standard deviation σ, and coefficient of variation (σ / μ). The particle size distribution can also be obtained by dynamic light scattering method (DPS), in which the colloidal solution is irradiated with light to obtain the particle size distribution from the optical Doppler effect of the scattered light. Particle size distributions are obtained and μ, σ, and (σ / μ) in each distribution are calculated, but are not necessarily effective in measuring the particle size distribution of sub-nanometer grade particles such as the nanoparticles of the present invention.

Using energy dispersive X-ray analysis (EDX) in combination with TEM, each individual particle observed in a high-power field of TEM is irradiated with an electron beam. Elemental analysis is possible, and this is measured for multiple particles to determine the average composition.
Also, in the case of alloy nanoparticles of Group A metal elements and Group B metal elements, if the average particle diameter exceeds 3 nm, whether the crystal structure is a solid solution or a regular alloy is determined from the diffraction pattern by X-ray diffraction. The degree of alloying can be evaluated based on the deviation of the diffraction angle 2θ from the intrinsic diffraction angle 2θ of a single metal, and the crystallite diameter can be evaluated from the half width of the main peak. However, in the case of ultrafine nanoparticles having an average particle size of 3 nm or less, particularly 1 nm or less, the X-ray diffraction peak is usually broad, and it is difficult to evaluate the crystal structure / regularity and crystallite size of the alloy. In the present invention, fine CuAu-type ordered alloy nanoparticles having an average particle size of 3 nm or less can be produced, and the regularity is confirmed by measuring magnetic properties unique to the ferromagnetic ordered alloy. Even in a crystallized alloy in which lattice fringes are observed by TEM observation at a high magnification of 5 to 10 million times, in the case of a simple solid solution alloy, the MH curve does not show a hysteresis loop in the vibration sample measurement method. In the case of regular alloying, the MH curve shows a hysteresis loop, and the degree of regularity can be evaluated from the value of H when M is zero, that is, the magnitude of the holding force Hc. In the case of an FePt alloy, which is one of the alloys with the highest magnetic anisotropy among the currently known magnetic materials, the finest particle diameter reported so far is 3 to 4 nm, which is higher than the conventional one. It has been considered that magnetic anisotropy is no longer exhibited in the room temperature region due to the superparamagnetic effect when it becomes finer.

  According to the method of the present invention, an average particle size of 0.3 to 100 nm, preferably an average particle size of 0.3 to 30 nm is preferably directly irradiated into a solution of a raw material salt or complex for a certain period of time, Preferably, metal nanoparticles of 0.3 to 3 nm can be produced.

  An alloy can be directly produced by using a co-solution of a plurality of metal elements. By irradiating at least one of platinum and palladium from group A elements, at least one of iron and cobalt from group B elements, and irradiating a co-solution of salts or complexes thereof with a laser, Conventionally, after producing amorphous alloy nanoparticles by high-temperature wet process at 300 ° C or higher, fct-type (face-centered tetragonal) regular alloy nanoparticles that were not produced without additional ordered alloy treatment are produced in one step. I can do it.

  Moreover, according to the VSM (vibrating sample magnetometer) evaluation, the fine ordered alloy manufactured by the manufacturing method of the present invention is conventionally considered to be superparamagnetism and no longer exhibit ferromagnetism. It is highly possible that this is the smallest ferromagnetic magnet reported so far. The reason why such a “minimum ferromagnetic magnet” can be produced by the production method of the present invention is still unclear, or a uniaxial magnetic anisotropic energy constant of a regular alloy produced by the production method of the present invention has been conventionally considered. It is estimated that it is because it is larger than the value.

  Such fine ferromagnetic nanoparticles may be applied to a wide range of applications, but are expected to be applied particularly in the following three fields: (1) ultra-high density magnetic recording media, (2) medical diagnosis Magnetically labeled nanoparticles, (3) spin-dependent single-electron devices.

  In (1), the ferromagnetic particles of the medium material require regular nanoparticles having a particle size as small as possible and a sharp particle size distribution in order to improve the S / N ratio during reproduction. In the case of FePt, In the past, the minimum particle diameter for maintaining ferromagnetism was 3 nm, and the recording density was 50 Tb / in 2. However, if the particle diameter can be reduced to 1 nm or less by the manufacturing method of the present invention, it is several times to an order of magnitude. Recording density is expected to be improved. In order to enable perpendicular magnetic recording, it is necessary to align the easy axis of magnetization (c-axis) of FePt perpendicular to the medium surface, but if it is ordered in the state of being manufactured like the nanoparticle of the present invention. There is a possibility that the orientation can be controlled by applying a strong magnetic field in the vertical direction after coating on the medium substrate. Such conventional orientation control is impossible when high temperature treatment is required for ordering after production as in the prior art.

  In (2), magnetic iron oxide nanoparticles have been used conventionally. However, magnetic iron oxide is superparamagnetic at room temperature, and it has been necessary to apply a magnetic field from the outside in order to enable magnetic detection.

  If the regular alloy nanoparticles of the present invention are used in place of the iron oxide nanoparticles, magnetic detection is possible without an external magnetic field, and the detection system can be downsized and simplified. The saturation magnetization of iron oxide in the ferromagnetic state is 5 to 6 kG. For example, the saturation magnetization of the regular alloy FePt of the present invention is 14.5 kG, which is twice to three times as strong as iron oxide. When using FePt particles, it is possible to detect a magnetic signal several times to an order of magnitude larger than that in the case of applying an external magnetic field to iron oxide.

  (3) is an application in the field of spin electronics, which has been actively researched and developed in recent years. The magnetic dots of the present invention are applied to the portion of the ferromagnetic material that performs switching in parallel and antiparallel to the magnetization of the magnetic material. Regular alloy nanoparticles having a particle size of 1 nm can be used.

  Examples of the present invention are shown below, but the present invention is not limited to the following examples.

<Example 1 >
Put 50 mL of ethanol as a solvent in a quartz beaker, 47.1 mg of iron (III) acetylacetonate and 26.2 mg of platinum (II) acetylacetonate, and 11.1 mg of poly N-vinylpyrrolidone (PVP) as a coordinating organic protective agent. Was dissolved. Ethanol functions as a solvent and an accelerator for decomposition and reduction of iron and platinum complexes. After the atmosphere was replaced with nitrogen, an excimer pulse laser was irradiated from the side surface of the quartz beaker for 20 minutes at HV 25 kV, laser energy 410 mJ, and frequency 40 Hz. The first clear yellow solution turned into a dark reddish brown colloidal solution. When this colloid was analyzed by TEM-EDX, it was confirmed that fine nanoparticles having an average particle diameter of μ1.5 nm and a standard deviation of σ0.2 nm and having a narrow particle size distribution were formed. The particles were too fine and no clear diffraction ring was detected by electron diffraction. However, when the photograph (refer FIG. 1) of magnification 5,000,000 was seen, although it was fine, the lattice fringe was observed inside each particle | grains and it showed that crystallinity was high.

  From EDX, Pt and Fe peaks were detected except for Cu and C peaks, and oxygen O peaks were not detected. The intensity ratio of the Fe and Pt peaks was about 1: 1.

  A colloid obtained by concentrating the colloid solution under reduced pressure at room temperature was dropped on a non-reflective silicon plate and air-dried at room temperature, and X-ray diffraction measurement was performed. FIG. 2 shows an X-ray diffraction pattern (XRD pattern) and its peak separation curve. Broad curves with peaks around 2θ = 23 deg and 40 deg were obtained. Subtracting the solvent-derived baseline and separating the peaks, the peak at 2θ = 23 deg belongs to fct (face-centered tetragonal) FePt (001), and the peak near 2θ = 40 deg belongs to Fe-Pt (111) The crystallite diameters were calculated as 0.8 nm and 0.6 nm, respectively.

Magnetization-magnetic field (MH) correlation data of FePt ordered alloy nanoparticles of Example 1 were measured at room temperature by applying a maximum magnetic field of 20 kOe with a vibrating sample magnetometer (VSM). FIG. 3 shows the VSM magnetic characteristic MH diagram obtained. A clear hysteresis loop was shown, indicating magnetic anisotropy. The holding force was 1.04 KOe.

<Example 2 >
In Example 1 , instead of PVP as a coordinating organic protective agent, a dark reddish brown colloid was treated in the same manner as in Example 1 except that a mixture of 70.6 mg of oleic acid and 66.9 mg of oleylamine was dissolved. Obtained. Nanoparticles finer than Reference Example 1 with an average particle size of μ0.7 nm and a standard deviation σ of 0.08 nm were obtained by TEM. Pt and Fe were detected from EDX, and the intensity ratio was about 2: 3. VSM showed magnetic anisotropy and the coercive force was 0.98 kOe. The MH diagram of the FePt ordered alloy nanoparticles of Example 2 is shown in FIG.

<Example 3 >
In Example 1, except for using 2-dimethoxy ethanol 50mL instead of the solvent ethanol was obtained colloid of dark red-brown were treated in the same manner as in Example 1. According to TEM, the average particle size was μ2.0 nm and the standard deviation was σ0.5 nm. Pt and Fe were detected from EDX, and the intensity ratio was about 3: 2. VSM showed magnetic anisotropy and the coercive force was 0.73 kOe. An MH diagram of the FePt ordered alloy nanoparticles of Example 3 is shown in FIG.

<Comparative Example 1>
Following the manufacturing method of S. Sun et al. (Non-Patent Document 1), Fe-Pt nanoparticles were manufactured by the polyol method as follows.

  Pyrex beaker was charged with 30 mL of octyl ether, the atmosphere was replaced with argon gas, and 0.197 g of platinum acetylacetonate, 0.177 g of iron acetylacetonate and 0.52 g of 1,2-hexadecanediol were added and stirred. The mixture was heated to 0 ° C. and held for 10 minutes to obtain a uniform solution as a whole. 0.16 mL of oleic acid and 0.17 mL of oleylamine were added, the temperature was increased while stirring, and the reflux was maintained at 263 ° C. for 5 hours. After allowing to cool to room temperature, the obtained black colloid was sampled and dropped on a non-reflective silicon plate, air-dried and then subjected to XRD measurement. A (111) peak of 2θ = 40 deg attributed to the solid solution alloy of Fe—Pt was detected and the crystallite diameter was measured to be 4 nm, but in the vicinity of 2θ = 23 deg attributed to (001) of the regular alloy. No peaks were detected.

  This colloid sample was evaluated for VSM magnetic properties by the same method as described in Example 1, but no hysteresis loop was obtained and the coercive force was zero.

The TEM photograph of the FePt ordered alloy nanoparticles of the present invention obtained in Example 1 is shown. The XRD pattern and peak separation curve of the FePt ordered alloy nanoparticles of the present invention obtained in Example 1 are shown. The VSM magnetic property MH figure of the FePt ordered alloy nanoparticle of this invention obtained in Example 1 is shown. The VSM magnetic property MH figure of the FePt ordered alloy nanoparticle of this invention obtained in Example 2 is shown. The VSM magnetic property MH figure of the FePt ordered alloy nanoparticle of this invention obtained in Example 3 is shown.

Claims (11)

Pt having an average particle size of 2 nm or less is obtained by irradiating a solution containing each salt and / or complex of platinum and iron with laser light to decompose and / or reduce the salt and / or complex in the solution. -Ferromagnetism for ultra-high density magnetic recording media, magnetically labeled nanoparticles for medical diagnostics or spin-dependent single-electron devices having an average particle size in the range of 2 nm or less, including directly generating Fe ordered alloy nanoparticles A method for producing Pt—Fe ordered alloy nanoparticles. The manufacturing method according to claim 1, wherein the Pt—Fe ordered alloy nanoparticles have an average particle size in the range of 0.7 to 2 nm. The manufacturing method according to claim 1 or 2, wherein the Pt-Fe ordered alloy nanoparticles are for an ultra-high density magnetic recording medium. The manufacturing method according to claim 1 or 2, wherein the Pt-Fe ordered alloy nanoparticles are for magnetic label nanoparticles for medical diagnosis. The manufacturing method according to claim 1 or 2, wherein the Pt-Fe ordered alloy nanoparticles are for a spin-dependent single electron device. The manufacturing method according to claim 1, wherein the laser light is excimer pulse laser light or Nd: YAG laser light. The method according to any one of claims 1 to 6, wherein a coordinating organic protective agent that coordinates with the produced alloy nanoparticles and prevents aggregation is coexisted in the solution in advance when the solution is irradiated with laser light. The production method according to any one of claims 1 to 7 , wherein a decomposition / reduction accelerator that absorbs laser light and promotes decomposition and / or reduction of a metal salt and / or complex coexists in the solution. The production method according to claim 8 , wherein the decomposition / reduction accelerator is an oxygen-containing organic compound. The production method according to claim 9 , wherein the decomposition / reduction accelerator is alcohol. The manufacturing method according to claim 10 , wherein the alcohol is ethanol.

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