WO2004105985A1 - Synthesis of iron-based alloy nanoparticles - Google Patents

Synthesis of iron-based alloy nanoparticles Download PDF

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Publication number
WO2004105985A1
WO2004105985A1 PCT/US2003/017005 US0317005W WO2004105985A1 WO 2004105985 A1 WO2004105985 A1 WO 2004105985A1 US 0317005 W US0317005 W US 0317005W WO 2004105985 A1 WO2004105985 A1 WO 2004105985A1
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Prior art keywords
alloy nanoparticles
iron alloy
iron
acetylacetonate
solution
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PCT/US2003/017005
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French (fr)
Inventor
Chao Liu
Xiaomin Yang
Dieter K. Weller
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Seagate Technology Llc
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Priority to PCT/US2003/017005 priority Critical patent/WO2004105985A1/en
Priority to AU2003232436A priority patent/AU2003232436A1/en
Publication of WO2004105985A1 publication Critical patent/WO2004105985A1/en

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/02—Making ferrous alloys by powder metallurgy
    • C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
    • C22C33/0278—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5%
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/05—Metallic powder characterised by the size or surface area of the particles
    • B22F1/054—Nanosized particles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
    • B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
    • B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/04—Making non-ferrous alloys by powder metallurgy
    • C22C1/0466—Alloys based on noble metals
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/48—Coating with alloys
    • C23C18/50—Coating with alloys with alloys based on iron, cobalt or nickel
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
    • G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
    • G11B5/706—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material
    • G11B5/70605—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material metals or alloys
    • G11B5/70615—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material metals or alloys containing Fe metal or alloys
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/84—Processes or apparatus specially adapted for manufacturing record carriers
    • G11B5/8416—Processes or apparatus specially adapted for manufacturing record carriers coating a support with a magnetic layer by precipitation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy

Definitions

  • the present invention relates to iron-based nanoparticles, and more particularly relates to a method of synthesizing FePt and FePd nanoparticles from iron salts and Pt or Pd salts.
  • the FePt and FePd nanoparticles are useful in applications such as magnetic recording media, permanent magnet materials and magneto-transport systems.
  • Fe-based alloy nanoparticles with controlled size and size distribution has been explored.
  • Colloidal chemistry synthesis has been investigated as a method of making monodispersed nanoparticles.
  • Conventional solution phase chemical synthesis is based on thermal decomposition of iron pentacarbonyl and reduction of a metal salt simultaneously in a solution in the presence of surfactant molecules.
  • iron pentacarbonyl is highly toxic and highly flammable at room temperature.
  • the amount of iron pentacarbonyl is difficult to control, which is essential to the chemical composition of the Fe-based alloy.
  • the present invention provides an alternative method for synthesizing Fe-based alloy nanoparticles without using iron pentacarbonyl.
  • An aspect of the present invention is to provide a method of making iron alloy nanoparticles.
  • the method comprises providing a solution comprising at least one iron salt, at least one noble metal salt comprising a platinum salt and/or a palladium salt, and at least one reducing reagent; heating the solution; and recovering iron alloy nanoparticles comprising Fe and the noble metal.
  • Another aspect of the present invention is to provide a method of making a magnetic film such as a magnetic recording medium.
  • the method comprises providing a solution comprising at least one iron salt, at least one noble metal salt comprising a platinum salt and/or a palladium salt, and at least one reducing reagent; heating the solution; depositing iron alloy nanoparticles from the heated solution on a substrate; and annealing the iron alloy nanoparticles.
  • a further aspect of the present invention is to provide iron alloy nanoparticles comprising Fe from an iron salt, and a noble metal from a noble metal salt, wherein the noble metal comprises Pt and/or Pd.
  • Fig. 1 is a flow diagram illustrating a process for forming Fe-based alloy nanoparticles in accordance with an embodiment of the present invention.
  • Fig. 2 is a flow diagram illustrating a process for forming Fe-based alloy nanoparticles in accordance with another embodiment of the present invention.
  • Fig. 3 is a bright field TEM image of monodispersed FePt nanoparticles self-organized into a superlattice produced in accordance with an embodiment of the present invention.
  • Fig. 4 is a HRTEM image of as-prepared FePt nanoparticles produced in accordance with an embodiment of the present invention.
  • Fig. 5 is an X-ray diffraction pattern demonstrating the presence of the Ll 0 crystal phase in an annealed FePt nanoparticle film produced in accordance with an embodiment of the present invention.
  • Fig. 1 illustrates the production of Fe-based alloy nanoparticles in accordance with an embodiment of the present invention.
  • a solution including an iron salt, a noble metal salt, and a reducing reagent is provided.
  • the solution is heated in order to precipitate nanoparticles comprising an alloy of Fe and the noble metal.
  • surfactant molecules and or other ligands are used to provide repulsive forces to prevent agglomeration of the particles.
  • Suitable iron salts include Fe(II) acetylacetonate, Fe(III) acetylacetonate, anhydrous Fe(II) chloride, anhydrous Fe(III) chloride, Fe(III) ethoxide, anhydrous Fe(II) acetate, anhydrous Fe(II) bromide, anhydrous Fe(III) bromide, Fe(III) i-propoxide and/or Fe(II) stearate.
  • the iron salt may comprise Fe(II) acetylacetonate and/or Fe(III) acetylacetonate.
  • the iron salt concentration is typically from about 0.001 Mol/L to about 0.1 Mol/L in the solution.
  • the noble metal of the Fe-based alloy is preferably Pt and/or Pd, and may be provided from salts such as Pt(II) acetylacetonate, Pd(II) acetylacetonate, Pt(II) 1,1,1, 5,5, 5-hexafluoro2,4-pentanedionate, Pd(II) acetate, Pt(II) chloride and/or Pd(II) chloride.
  • the noble metal salt may comprise Pt(II) acetylacetonate and/or Pt(II) l,l,l,5,5,5-hexafluoro2,4-pentanedionate, with Pt(II) acetylacetonate being particularly suitable.
  • the noble metal salt concentration is typically from about 0.001 Mol/L to about 0.1 Mol/L in the solution.
  • the relative amounts of iron salts and noble metal salts may be selected based upon the desired final alloy composition.
  • the iron and noble metal salt amounts may be chosen based upon the desired atomic ratio of Fe:Pt in the alloy.
  • the chemical composition can be readily controlled by the relative amounts of Fe(II) acetylacetonate (or Fe(III) acetylacetonate) and Pt(II) acetylacetonate.
  • Suitable reducing reagents include 1,2-hexadecanediol, 1,2-dodecanediol and/orl ,2-octanediol.
  • the reducing reagent may comprise 1 ,2- hexadecanediol.
  • the reducing reagent concentration is typically from about 0.005 Mol/L to about 0.5 Mol/L in the solution.
  • the process of the present invention reduces the iron salt together with the other Pt or Pd component salts for the Fe-based alloy system.
  • Such salts in solid powder form are relatively easy to handle, and the amount of chemicals added can be more accurately controlled.
  • the reducing reagent such as 1 ,2-hexanedanediol with large hydrocarbon chains, may be chemically stable at room temperature, but may be a very strong reducing reagent under high temperature.
  • the solution may further include a surfactant such as oleic acid, oleylamine, trioctylphosphine oxide (TOPO), hexanoic acid, dodelcyl-benzene sodium sulfate and/or sodium dodecylsulfonate.
  • a surfactant such as oleic acid, oleylamine, trioctylphosphine oxide (TOPO), hexanoic acid, dodelcyl-benzene sodium sulfate and/or sodium dodecylsulfonate.
  • TOPO trioctylphosphine oxide
  • hexanoic acid dodelcyl-benzene sodium sulfate
  • sodium dodecylsulfonate sodium dodecylsulfonate.
  • oleic acid and/or oleylamine may be particularly useful.
  • the surfactant concentration is typically from about 0.0001 Mol/L to about
  • the solution may include a solvent with high boiling point and adequate solubility for the Fe and the noble metal salts.
  • the solvent can be octyl ether and/or phenyl ether.
  • the solution may optionally include other ingredients such as Co(II) acetylacetonate, Ag(I) acetate, Ni(II) acetylacetonate, Cu(II) acetylacetonate and/or Au(III) chloride in a total chemical amount of up to about 90 percent to replace Fe and/or noble metal salts in the solution.
  • other ingredients such as Co(II) acetylacetonate, Ag(I) acetate, Ni(II) acetylacetonate, Cu(II) acetylacetonate and/or Au(III) chloride in a total chemical amount of up to about 90 percent to replace Fe and/or noble metal salts in the solution.
  • the solution may be heated to a temperature of at least about 240°C.
  • the solution may be heated to a temperature from about 250°C to about 300°C.
  • the iron alloy nanoparticles typically comprise from about 5 to about 95 atomic percent Fe, and from about 5 to about 95 atomic percent noble metal.
  • the iron alloy nanoparticles may comprise from about 25 to about 75 atomic percent Fe, and from about 25 to about 75 atomic percent Pt and/or Pd.
  • the iron alloy nanoparticles typically have an average size of from about 2 to about 15 nm, for example, from about 3 to about 10 nm.
  • the iron alloy nanoparticles are substantially monodispersed. As used herein, the term "monodispersed" means that the standard deviation of diameter over average diameter is less than 10 percent.
  • the iron alloy nanoparticles may be deposited in the form of a superlattice on any suitable substrate such as a thermally oxidized Si substrate, Si 3 N , glass or the like.
  • the as-deposited nanoparticles may typically be chemically disordered.
  • as-deposited FePt may comprise a disordered face-center-cubic phase.
  • the iron alloy nanoparticles may be annealed. Suitable annealing temperatures may range from about 450 to about 800°C, typically from about 500 to about 650°C. Upon annealing, the nanoparticles have a crystalline microstructure. For example, annealed FePt nanoparticles may have an Ll 0 structure.
  • the annealed iron alloy nanoparticles may have a room temperature coercivity of at least 300 Oe, typically greater than about 500 Oe.
  • FePt alloys are particularly suitable for use in permanent magnets due to their large uniaxial magnetocrystalline anisotropy energy.
  • FIG. 2 Another synthesis process to obtain monodispersed Fe-based alloy nanoparticles is shown in Fig. 2.
  • the process includes: mixing the iron salt and Pt/Pd salt precursors into the solvent together with the reducing reagent and surfactant molecules; heating inside the reaction vessel and reflux; and performing a standard size selective precipitation process to obtain the monodispersed particles, e.g., if the size distribution is more than 10 percent.
  • monodispersed FePt nanoparticles may be synthesized using 0.0025 mol 1 ,2-hexadecanediol as the reducing agent, 20.0 ml octyl ether as the solvent, 0.001 mol oleic acid and oleylamine as the surfactant molecules, 0.0005 mol Fe(II) acetylacetonate (or Fe(III) acetylacetonate) and 0.0005 mol Pt(II) acetylacetonate as the salts for Fe and Pt, respectively.
  • the solution is heated to refluxing at 286°C and held at this temperature for 30 minutes. At such high temperature the metal cations are reduced.
  • a possible mechanism is that one molecule of 1 ,2-hexadecanediol loses one molecule of water and becomes a reducing agent, which could be an aldehyde or its isomerization form.
  • the reducing reagent is oxidized by the metal cations, or the metal cations, e.g., Fe(II) (or Fe(III)) and Pt(II), are reduced by the aldehydes.
  • the heat source is then removed and the product solution cooled to room temperature.
  • the solution is then purified using a flocculent such as ethanol, followed by dispersion in an apolar solvent such as hexane.
  • the monodispersed FePt alloy particles self-organize into the superlattices shown in Figs. 3 and 4.
  • An HRTEM image of a similar sample is shown in Fig. 4. The images show that the particles have uniform lattice fringes across the particles, which may be attributed to good crystallinity of the chemically disordered FCC crystalline phase. Identification of random lattice fringes for FCC FePt (111) and (200) planes indicates that the particles are randomly oriented.
  • FIG. 5 An X-ray diffraction pattern of FePt nanoparticles having an Ll 0 crystal structure is shown in Fig. 5.
  • the chemically ordered Ll 0 crystalline phase, as shown in Fig. 5, is obtained after annealing at 650°C for 30 minutes using standard rapid thermal annealing techniques. Hysteresis measurements show that the coercivity of the chemically ordered sample is 12.7kOe at room temperature and 23.1kOe at 5K.

Abstract

A method of forming iron-based alloy nanoparticles is disclosed. A solution containing iron salt, noble metal salt and a reducing reagent is heated, resulting in the precipitation of monodispersed nanoparticles such as FePt and FePd. The solution may also include a surfactant. After deposition, the iron-based alloy nanoparticles may be annealed in order to produce the desired crystal structure and magnetic properties. The annealed nanoparticles may comprise FePt having an L10 crystal structure and high magnetic coercivity. The magnetic iron-based nanoparticles are suitable for use in applications such as magnetic recording media, permanent magnet materials and magneto-transport systems.

Description

SYNTHESIS OF IRON-BASED ALLOY NANOPARTICLES
FIELD OF THE INVENTION
The present invention relates to iron-based nanoparticles, and more particularly relates to a method of synthesizing FePt and FePd nanoparticles from iron salts and Pt or Pd salts. The FePt and FePd nanoparticles are useful in applications such as magnetic recording media, permanent magnet materials and magneto-transport systems.
BACKGROUND INFORMATION
The synthesis of Fe-based alloy nanoparticles with controlled size and size distribution has been explored. Colloidal chemistry synthesis has been investigated as a method of making monodispersed nanoparticles. Conventional solution phase chemical synthesis is based on thermal decomposition of iron pentacarbonyl and reduction of a metal salt simultaneously in a solution in the presence of surfactant molecules. However, iron pentacarbonyl is highly toxic and highly flammable at room temperature. In addition to safety concerns, the amount of iron pentacarbonyl is difficult to control, which is essential to the chemical composition of the Fe-based alloy. The present invention provides an alternative method for synthesizing Fe-based alloy nanoparticles without using iron pentacarbonyl.
SUMMARY OF THE INVENTION
An aspect of the present invention is to provide a method of making iron alloy nanoparticles. The method comprises providing a solution comprising at least one iron salt, at least one noble metal salt comprising a platinum salt and/or a palladium salt, and at least one reducing reagent; heating the solution; and recovering iron alloy nanoparticles comprising Fe and the noble metal.
Another aspect of the present invention is to provide a method of making a magnetic film such as a magnetic recording medium. The method comprises providing a solution comprising at least one iron salt, at least one noble metal salt comprising a platinum salt and/or a palladium salt, and at least one reducing reagent; heating the solution; depositing iron alloy nanoparticles from the heated solution on a substrate; and annealing the iron alloy nanoparticles. A further aspect of the present invention is to provide iron alloy nanoparticles comprising Fe from an iron salt, and a noble metal from a noble metal salt, wherein the noble metal comprises Pt and/or Pd.
These and other aspects of the present invention will be more apparent from the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a flow diagram illustrating a process for forming Fe-based alloy nanoparticles in accordance with an embodiment of the present invention.
Fig. 2 is a flow diagram illustrating a process for forming Fe-based alloy nanoparticles in accordance with another embodiment of the present invention.
Fig. 3 is a bright field TEM image of monodispersed FePt nanoparticles self-organized into a superlattice produced in accordance with an embodiment of the present invention.
Fig. 4 is a HRTEM image of as-prepared FePt nanoparticles produced in accordance with an embodiment of the present invention.
Fig. 5 is an X-ray diffraction pattern demonstrating the presence of the Ll0 crystal phase in an annealed FePt nanoparticle film produced in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION
Fig. 1 illustrates the production of Fe-based alloy nanoparticles in accordance with an embodiment of the present invention. A solution including an iron salt, a noble metal salt, and a reducing reagent is provided. The solution is heated in order to precipitate nanoparticles comprising an alloy of Fe and the noble metal. In one embodiment, surfactant molecules and or other ligands are used to provide repulsive forces to prevent agglomeration of the particles.
Suitable iron salts include Fe(II) acetylacetonate, Fe(III) acetylacetonate, anhydrous Fe(II) chloride, anhydrous Fe(III) chloride, Fe(III) ethoxide, anhydrous Fe(II) acetate, anhydrous Fe(II) bromide, anhydrous Fe(III) bromide, Fe(III) i-propoxide and/or Fe(II) stearate. For example, the iron salt may comprise Fe(II) acetylacetonate and/or Fe(III) acetylacetonate. The iron salt concentration is typically from about 0.001 Mol/L to about 0.1 Mol/L in the solution. The noble metal of the Fe-based alloy is preferably Pt and/or Pd, and may be provided from salts such as Pt(II) acetylacetonate, Pd(II) acetylacetonate, Pt(II) 1,1,1, 5,5, 5-hexafluoro2,4-pentanedionate, Pd(II) acetate, Pt(II) chloride and/or Pd(II) chloride. For example, the noble metal salt may comprise Pt(II) acetylacetonate and/or Pt(II) l,l,l,5,5,5-hexafluoro2,4-pentanedionate, with Pt(II) acetylacetonate being particularly suitable. The noble metal salt concentration is typically from about 0.001 Mol/L to about 0.1 Mol/L in the solution.
The relative amounts of iron salts and noble metal salts may be selected based upon the desired final alloy composition. For example, the iron and noble metal salt amounts may be chosen based upon the desired atomic ratio of Fe:Pt in the alloy. In accordance with an embodiment of the present invention, the chemical composition can be readily controlled by the relative amounts of Fe(II) acetylacetonate (or Fe(III) acetylacetonate) and Pt(II) acetylacetonate.
Suitable reducing reagents include 1,2-hexadecanediol, 1,2-dodecanediol and/orl ,2-octanediol. For example, the reducing reagent may comprise 1 ,2- hexadecanediol. The reducing reagent concentration is typically from about 0.005 Mol/L to about 0.5 Mol/L in the solution.
The process of the present invention reduces the iron salt together with the other Pt or Pd component salts for the Fe-based alloy system. Such salts in solid powder form are relatively easy to handle, and the amount of chemicals added can be more accurately controlled. The reducing reagent, such as 1 ,2-hexanedanediol with large hydrocarbon chains, may be chemically stable at room temperature, but may be a very strong reducing reagent under high temperature.
The solution may further include a surfactant such as oleic acid, oleylamine, trioctylphosphine oxide (TOPO), hexanoic acid, dodelcyl-benzene sodium sulfate and/or sodium dodecylsulfonate. For example, oleic acid and/or oleylamine may be particularly useful. The surfactant concentration is typically from about 0.0001 Mol/L to about 0.2 Mol/L in the solution.
The solution may include a solvent with high boiling point and adequate solubility for the Fe and the noble metal salts. For example, the solvent can be octyl ether and/or phenyl ether.
In addition to the Fe and noble metal salts, reducing reagent, surfactant and solvent, the solution may optionally include other ingredients such as Co(II) acetylacetonate, Ag(I) acetate, Ni(II) acetylacetonate, Cu(II) acetylacetonate and/or Au(III) chloride in a total chemical amount of up to about 90 percent to replace Fe and/or noble metal salts in the solution.
The solution may be heated to a temperature of at least about 240°C. For example, the solution may be heated to a temperature from about 250°C to about 300°C.
Upon deposition, the iron alloy nanoparticles typically comprise from about 5 to about 95 atomic percent Fe, and from about 5 to about 95 atomic percent noble metal. For example, the iron alloy nanoparticles may comprise from about 25 to about 75 atomic percent Fe, and from about 25 to about 75 atomic percent Pt and/or Pd.
The iron alloy nanoparticles typically have an average size of from about 2 to about 15 nm, for example, from about 3 to about 10 nm. The iron alloy nanoparticles are substantially monodispersed. As used herein, the term "monodispersed" means that the standard deviation of diameter over average diameter is less than 10 percent. The iron alloy nanoparticles may be deposited in the form of a superlattice on any suitable substrate such as a thermally oxidized Si substrate, Si3N , glass or the like. The as-deposited nanoparticles may typically be chemically disordered. For example, as-deposited FePt may comprise a disordered face-center-cubic phase.
After deposition, the iron alloy nanoparticles may be annealed. Suitable annealing temperatures may range from about 450 to about 800°C, typically from about 500 to about 650°C. Upon annealing, the nanoparticles have a crystalline microstructure. For example, annealed FePt nanoparticles may have an Ll0 structure.
The annealed iron alloy nanoparticles may have a room temperature coercivity of at least 300 Oe, typically greater than about 500 Oe. FePt alloys are particularly suitable for use in permanent magnets due to their large uniaxial magnetocrystalline anisotropy energy.
Another synthesis process to obtain monodispersed Fe-based alloy nanoparticles is shown in Fig. 2. The process includes: mixing the iron salt and Pt/Pd salt precursors into the solvent together with the reducing reagent and surfactant molecules; heating inside the reaction vessel and reflux; and performing a standard size selective precipitation process to obtain the monodispersed particles, e.g., if the size distribution is more than 10 percent.
As a particular example, monodispersed FePt nanoparticles may be synthesized using 0.0025 mol 1 ,2-hexadecanediol as the reducing agent, 20.0 ml octyl ether as the solvent, 0.001 mol oleic acid and oleylamine as the surfactant molecules, 0.0005 mol Fe(II) acetylacetonate (or Fe(III) acetylacetonate) and 0.0005 mol Pt(II) acetylacetonate as the salts for Fe and Pt, respectively. The solution is heated to refluxing at 286°C and held at this temperature for 30 minutes. At such high temperature the metal cations are reduced. While not intending to be bound by any particular theory, a possible mechanism is that one molecule of 1 ,2-hexadecanediol loses one molecule of water and becomes a reducing agent, which could be an aldehyde or its isomerization form. The reducing reagent is oxidized by the metal cations, or the metal cations, e.g., Fe(II) (or Fe(III)) and Pt(II), are reduced by the aldehydes. The heat source is then removed and the product solution cooled to room temperature. The solution is then purified using a flocculent such as ethanol, followed by dispersion in an apolar solvent such as hexane.
The monodispersed FePt alloy particles self-organize into the superlattices shown in Figs. 3 and 4. A bright field TEM image of an as-prepared FePt nanoparticle sample, without going through the size selective precipitation process, is shown in Fig. 3. An HRTEM image of a similar sample is shown in Fig. 4. The images show that the particles have uniform lattice fringes across the particles, which may be attributed to good crystallinity of the chemically disordered FCC crystalline phase. Identification of random lattice fringes for FCC FePt (111) and (200) planes indicates that the particles are randomly oriented.
An X-ray diffraction pattern of FePt nanoparticles having an Ll0 crystal structure is shown in Fig. 5. The chemically ordered Ll0 crystalline phase, as shown in Fig. 5, is obtained after annealing at 650°C for 30 minutes using standard rapid thermal annealing techniques. Hysteresis measurements show that the coercivity of the chemically ordered sample is 12.7kOe at room temperature and 23.1kOe at 5K.
Whereas particular embodiments of this invention have been described above for puφoses of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.

Claims

WHAT IS CLAIMED IS:
1. A method of making iron alloy nanoparticles, the method comprising: providing a solution comprising at least one iron salt, at least one noble metal salt comprising a platinum salt and/or a palladium salt, and at least one reducing reagent; heating the solution; and recovering iron alloy nanoparticles comprising Fe and the noble metal.
2. The method of Claim 1 , wherein the iron salt comprises Fe(II) acetylacetonate, Fe(III) acetylacetonate, anhydrous Fe(II) chloride, anhydrous Fe(III) chloride, Fe(III) ethoxide, anhydrous Fe(II) acetate, anhydrous Fe(II) bromide, anhydrous Fe(III) bromide, Fe(III) i-propoxide and/or Fe(II) stearate.
3. The method of Claim 1, wherein the iron salt comprises Fe(II) acetylacetonate and/or Fe(III) acetylacetonate.
4. The method of Claim 1 , wherein the noble metal salt comprises Pt(II) acetylacetonate, Pd(II) acetylacetonate, Pt(II) l,l,l,5,5,5-hexafluoro2,4- pentanedionate, Pd(II) acetate, Pt(II) chloride and/or Pd(II) chloride.
5. The method of Claim 1 , wherein the noble metal salt comprises Pt(II) acetylacetonate.
6. The method of Claim 1 , wherein the noble metal salt comprises Pt(II) 1,1,1 ,5,5,5-hexafluoro2,4-pentanedionate.
7. The method of Claim 1 , wherein the reducing reagent comprises 1 ,2-hexadecanediol, 1 ,2-dodecanediol and/or 1 ,2-octanediol.
8. The method of Claim 1 , wherein the reducing reagent comprises 1 ,2-hexadecanediol.
9. The method of Claim 1, wherein the solution is heated to a temperature of at least 240°C.
10. The method of Claim 1, wherein the solution is heated to a temperature of from about 250 to about 300°C.
11. The method of Claim 1 , wherein the iron alloy nanoparticles comprise from about 5 to about 95 atomic percent Fe, and from about 5 to about 95 atomic percent Pt.
12. The method of Claim 1, wherein the iron alloy nanoparticles have an average size of from about 2 to about 15 nm.
13. The method of Claim 1 , wherein the iron alloy nanoparticles are monodispersed.
14. The method of Claim 1 , wherein the iron alloy nanoparticles are deposited on a substrate in the form of a superlattice.
15. The method of Claim 1, wherein the solution further comprises a surfactant.
16. The method of Claim 15, wherein the surfactant comprises oleic acid, oleylamine, trioctylphosphine oxide, hexanoic acid, dodelcyl-benzene sodium sulfate and/or sodium dodecylsulfonate.
17. The method of Claim 15, wherein the surfactant comprises oleic acid and/or oleylamine.
18. The method of Claim 1 , wherein the solution comprises a solvent including octyl ether.
19. The method of Claim 1 , wherein the solution comprises a solvent including phenyl ether.
20. The method of Claim 1 , further comprising annealing the iron alloy nanoparticles.
21. The method of Claim 20, wherein the iron alloy nanoparticles are annealed at a temperature of from about 450 to about 800°C.
22. The method of Claim 20, wherein the annealed iron alloy nanoparticles have an Ll0 crystal structure.
23. The method of Claim 20, wherein the annealed iron alloy nanoparticles have a room temperature coercivity of at least 300 Oe.
24. A method of making a magnetic film, the method comprising: providing a solution comprising at least one iron salt, at least one noble metal salt comprising a platinum salt and/or a palladium salt, and at least one reducing reagent; heating the solution; depositing iron alloy nanoparticles from the heated solution on a substrate; and annealing the iron alloy nanoparticles.
25. The method of Claim 24, wherein the iron salt comprises Fe(II) acetylacetonate, Fe(III) acetylacetonate, anhydrous Fe(II) chloride, anhydrous Fe(III) chloride, Fe(III) ethoxide, anhydrous Fe(II) acetate, anhydrous Fe(II) bromide, anhydrous Fe(III) bromide, Fe(III) i-propoxide and/or Fe(II) stearate, and the noble metal salt comprises Pt(II) acetylacetonate, Pd(II) acetylacetonate, Pt(II) 1,1,1,5,5,5- hexafluoro2,4-pentanedionate, Pd(II) acetate, Pt(II) chloride and or Pd(II) chloride.
26. The method of Claim 24, wherein the deposited iron alloy nanoparticles are in the form of a monodispersed superlattice.
27. Iron alloy nanoparticles comprising: Fe from an iron salt; and a noble metal from a noble metal salt, wherein the noble metal comprises Pt and/or Pd.
28. The iron alloy nanoparticles of Claim 27, wherein the nanoparticles are in the form of a monodispersed superlattice.
29. The iron alloy nanoparticles of Claim 27, wherein the deposited iron alloy nanoparticles comprise from about 5 to about 95 atomic percent Fe and from about 5 to about 95 atomic percent Pt.
30. The iron alloy nanoparticles of Claim 27, wherein the annealed iron alloy nanoparticles have a room temperature coercivity of at least 300 Oe.
PCT/US2003/017005 2003-05-29 2003-05-29 Synthesis of iron-based alloy nanoparticles WO2004105985A1 (en)

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