JP2015185602A - FePd / Fe nanocomposite magnet and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an FePd/Fe nano composite magnet of which the magnetic property is further improved; and a method for manufacturing such an FePd/Fe nano composite magnet.SOLUTION: An FePd/Fe nano composite magnet has L1crystal structure having an FePd core and an Fe shell. The FePd core has an octahedron structure having, on its surface, (111) plane of L1lattice. A method for manufacturing an FePd/Fe nano composite magnet comprises the steps of: producing Pd nanoparticles having an octahedron structure from cube Pd nanoparticles; producing Pd/FeOcomposite nanoparticles each including a core composed of the Pd nanoparticle having the octahedron structure and a shell of FeO; and subsequently, performing a hydrogen reduction treatment in which the Pd/FeOcomposite nanoparticles are heated in a hydrogen atmosphere.

Description

  The present invention relates to a FePd / Fe nanocomposite magnet having FePd nanoparticles as a core and Fe as a shell, and a method for producing the same.

  A nanocomposite magnet has a hard / soft two-phase composite structure in which a hard magnetic phase of a nanoparticle is a core and a soft magnetic phase of the nanoparticle is a shell. ) Has attracted attention for its characteristics that exchange coupling works between the hard / soft magnetic phases of the core / shell and the remanence and saturation magnetization can be greatly increased.

  As such a non-composite magnet, an FePd / Fe nanocomposite magnet having FePd nanoparticles as a core and Fe as a shell has been proposed (see Patent Document 1).

JP 2010-263121 A

  In the conventional FePd / Fe nanocomposite magnet, the magnetic properties may not be sufficient, and further improvement of the magnetic properties is required. An object of this invention is to provide the FePd / Fe nanocomposite magnet which further improved the magnetic characteristic, and its manufacturing method.

In order to achieve the above object, according to the present invention, an FePd / Fe nanocomposite magnet having an L1 ₀ crystal structure with FePd as a core and Fe as a shell, the FePd core having L1 _{0 on the} surface. There is provided an FePd / Fe nanocomposite magnet characterized by an octahedral structure having a (111) plane of a lattice.

In order to achieve the above object, according to the present invention, Pd nanoparticles having an octahedral structure are produced from cubic Pd nanoparticles, and the Pd nanoparticles having the octahedral structure are used as a core, and Fe ₂ O ₃ The Pd / Fe ₂ O ₃ composite nanoparticles having the shell as a shell are prepared, and then the Pd / Fe ₂ O ₃ composite nanoparticles are subjected to a hydrogen reduction treatment in which the Pd / Fe ₂ O ₃ composite nanoparticles are heated in a hydrogen atmosphere. A method for producing a / Fe nanocomposite magnet is provided.

By using a Pd nanoparticle having an octahedral structure as a starting material, an FePd / Fe nanocomposite magnet having FePd having an L1 ₀ crystal structure as a core part and α-Fe as a shell part is produced. Compared with a conventional FePd / Fe nanocomposite magnet having a structure, the magnetic properties can be improved.

It is a schematic diagram of the FePd / Fe nanocomposite magnet of the present invention. It is a TEM image of the FePd / Fe nanocomposite magnet of this invention produced in the Example. It is an XRD measurement chart of the FePd / Fe nanocomposite magnet of this invention produced in the Example.

As shown in FIG. 1, the FePd / Fe nanocomposite magnet of the present invention has FePd as a core and Fe as a shell, and the FePd core has an L1 ₀ crystal structure and has a L1 ₀ lattice (111) on the surface. It is an octahedral structure having a) plane.

  The FePd core preferably has an octahedral structure with all surfaces having {111}, and the particle size of the FePd / Fe nanocomposite magnet is such that the length of the ridge line of the octahedron is 5 nm to 100 nm. Is preferred. In the FePd / Fe nanocomposite magnet of the present invention, the composition (atomic ratio) of Fe: Pd is preferably 55:45 to 75:25, and more preferably 65:35. Further, when expressed as FePd: Fe, it is preferably 82:18 to 33:67, more preferably 54:46.

In FePd / Fe nanocomposite magnet of the present invention, by using a FePd of the core portion octahedral L1 ₀ crystal structure, octahedral faces {111}, and that specifically binds to Fe {110} of the shell become. As a result, it is considered that the exchange coupling action works in the core portion and the shell portion, and the coercive force is improved.

The FePd / Fe nanocomposite magnet of the present invention is made of Pd nanoparticles having an octahedral structure from cubic Pd nanoparticles, Pd nanoparticles having the octahedral structure as a core, and Pd having Fe ₂ O ₃ as a shell. / Fe ₂ O ₃ composite nanoparticles are produced, and then the Pd / Fe ₂ O ₃ composite nanoparticles are subjected to a hydrogen reduction treatment by heating in a hydrogen atmosphere.

  The cubic Pd nanoparticles have a particle size of 1 to 100 nm, desirably 1 to 10 nm. This can be formed in a conventional manner. Typically, a salt of Pd is reduced in a solvent to precipitate Pd nanoparticles. In that case, the following can be used. However, it is not necessary to limit to these.

  As a salt of Pd, which is a precursor of Pd, a metal complex having an organic ligand (acetylacetonate salt, acetate), palladium chloride, palladium chloride, sodium chloride, tetraammine palladium, dichloroethylenediamine palladium, dichloro Examples thereof include diammine palladium, dinitrodiammine palladium, dichlorotetraammine palladium, ammine palladium hydroxide, palladium sulfate, and palladium nitrate.

Salts of the Pd, polyvinylpyrrolidone and KBr added as a ligand, ascorbic acid, tannic acid as the reducing agent, monohydric alcohols (methanol, ethanol), although reduced by adding a polyol such as, this time, Br ^- is Cubic Pd particles that are selectively coordinated to the Pd {100} plane and have a side of 5 to 100 nm can be obtained.

  Next, Pd is grown on the surface of the cubic Pd particles by using the cubic Pd particles as a raw material, and adding the above-mentioned Pd salt, polyvinylpyrrolidone and formic acid as the ligand, and formaldehyde as the reducing agent. When formic acid specifically coordinates to Pd (111), Pd particles having an octahedral fcc crystal structure covered with a Pd {111} face can be obtained. The ridge line length of the Pd particles is preferably 5 to 100 nm.

Pd / Fe ₂ O ₃ nanocomposite particles having Pd nanoparticles having an octahedral structure as a core and Fe ₂ O ₃ as a shell are synthesized. This typically involves changing the ligand from polyvinylpyrrolidone (water soluble ligand) to oleylamine (lipid soluble ligand) and reducing or thermally decomposing the Fe salt or organometallic compound in a solvent. Then, it is deposited as Fe ₂ O _{3 on} the surface of the Pd particles. In that case, the following can be used. However, it is not necessary to limit to these.

  The Fe salt is preferably a metal complex having an organic ligand, such as an acetylacetonate salt (for example, iron (II) acetylacetonate, iron (III) acetylacetonate), acetate, chloride. , Sulfides, hydroxides, and the like, and examples of the organometallic compound include ferrocene and iron pentacarbonyl. The amount of Fe added is preferably about 1 to 4 moles of Pd.

  Surfactants include oleylamine, oleic acid, TOP (trioctylphosphine), TOPO (trioctylphosphine oxide), octadecylphosphonic acid, trioctylphosphoric acid, myristic acid, dodecylamine, tetraethylene glycol, dodecylbenzenesulfonic acid, etc. Can be used. The amount of the surfactant added is preferably equal to or greater than the mole of Fe salt.

When TOP, trioctyl phosphoric acid, oleylamine, oleic acid or tetraethylene glycol is used as the surfactant, these also function as a solvent, but a solvent may be added as necessary. As this solvent, since it is heated in the growth reaction of Fe ₂ O ₃ shell, a solvent having a high boiling point and stable is preferable. For example, 1-octanol, octyl ether, 1-octadecene, squalene, triphenylmethane, etc. are used. be able to.

  As the reducing agent, it is preferable to use a monohydric alcohol, a polyol (polyhydric alcohol), an amine-based substance, or diphenylsilane. Although it does not specifically limit as monohydric alcohol, For example, 1-octanol, 1-decanol, 1-dodecanol etc. can be used, and what has a boiling point higher than the reaction temperature which performs a reduction | restoration is preferable. The polyol is not particularly limited, and for example, 1,2-octanediol, 1,2-dodecanediol, 1,2-tetradecanediol, 1,2-hexadecanediol, and the like can be used. Those having a high boiling point are preferred. In addition, hydrazine, amine borane complex, sodium borohydride, tetrabutylammonium borohydride, diborane and the like can be used for reduction. The amount of the reducing agent added is preferably equal to or greater than the mole of Fe salt.

Finally, a hydrogen reduction treatment is performed in which the Pd / Fe ₂ O ₃ composite nanoparticles thus obtained are heated in a hydrogen atmosphere. In this hydrogen reduction treatment, the Pd / Fe ₂ O ₃ composite nanoparticles obtained above are heat-treated in a hydrogen atmosphere, whereby the core is mainly composed of FePd ordered phases (L1 ₀ -FePd) and is extremely fine ( FePd / Fe nanocomposite particles covered with an Fe phase shell (about 5 nm or less) are obtained.

That is, the heat treatment in this hydrogen reduction treatment step performs the following actions (1) and (2).
(1) Fe ₂ O ₃ is reduced with hydrogen on the surface of the Pd core of the Pd / Fe ₂ O ₃ composite nanoparticles as Fe, and diffused into the Pd core to form a FePd alloy (irregular phase); This is transformed into the ordered phase L1 ₀ -FePd. This increases the degree of order and increases the coercive force.

(2) Fe ₂ O ₃ is reduced with hydrogen on the surface of the Pd core of the Pd / Fe ₂ O ₃ composite nanoparticles, and Fe is self-diffused to cover the surface of the FePd core as ultrafine particles (about 5 nm or less). Make it. As a result, the exchange coupling length from the hard magnetic core phase reaches the soft magnetic shell phase, and the residual magnetization increases.

  By this hydrogen reduction heat treatment, coercive force and remanent magnetization can be simultaneously increased. The treatment temperature is preferably 470 to 570 ° C., more preferably 500 to 550 ° C., and the treatment time is preferably 3 hours or more, more preferably 10 hours or more.

  The slower the rate of temperature rise, the better, preferably 10 ° C./min or less, more preferably 3 ° C./min.

  As a pretreatment for the hydrogen reduction heat treatment, it is desirable to remove organic substances on the surface of the nanoparticles. The pretreatment method may be a method generally used for removing organic substances, and ozone treatment is desirable, but is not particularly limited. The smaller the remaining amount of surface organic matter is, the better.

Example 1
A 300 mL three-necked flask equipped with a condenser and a thermometer is charged with 25 mmol of polyvinylpyrrolidone (monomer conversion) and 3.75 mmol of L-ascorbic acid, dissolved in 250 mL of ultrapure water, and then the atmosphere is stirred with vigorous stirring. To 80 ° C. A solution prepared by dissolving 5 mmol of sodium palladium (II) chloride as a Pd precursor, 1.1 mmol of KBr and 65.4 mmol of KCl in 50 mL of ultrapure water was quickly poured into the solution and kept at 80 ° C. for 3 hours with stirring. Then, it cooled to room temperature and collect | recovered precipitation by centrifugation.

  The obtained Pd nanoparticles (cubic Pd particles) 0.3 mmol (in terms of Pd atoms) was placed in a 1 L three-necked flask equipped with a condenser and a thermometer, and further 51.6 mmol of polyvinylpyrrolidone (in terms of monomer) and 73.3 mmol of formaldehyde. Was added and dissolved in 500 mL of ultrapure water, and the solution was heated to 40 ° C. in the atmosphere with vigorous stirring. Here, a solution prepared by dissolving 8.1 mmol of sodium palladium (II) chloride as a Pd precursor in 100 mL of ultrapure water was quickly poured, and kept at 40 ° C. for 24 hours while stirring. Thereafter, acetone is added, and the precipitate is collected by centrifugation. Further, the precipitate is re-dispersed in an acetone / ethanol mixed solvent mixed at a volume ratio of 1: 3, and centrifuged to collect the precipitate, thereby collecting fine particles by size separation. Removal was performed.

  The polyvinylpyrrolidone-protected octahedral Pd nanoparticle (ridge length 18 nm) thus obtained was dissolved in 20 mL of chloroform together with 20 mmol of oleylamine and subjected to ultrasonic irradiation for 20 minutes, and then heated to 50 ° C. in an air atmosphere. Heat and stir for 30 minutes. Thereafter, ethanol was added and the mixture was centrifuged to collect the precipitate.

The oleylamine-protected octahedral Pd (111) nanoparticles (ridge length 18 nm) 1 mmol (Pd atom equivalent) thus obtained were put into a 300 mL three-necked flask equipped with a condenser and a thermometer, and 1-octadecene 125 mL was added to the nanoparticles. Was dissolved. Then, 10.4 mmol of oleic acid and 11.2 mmol of oleylamine were added thereto, and then degassed under reduced pressure at 80 ° C. for 1 hour while stirring the solution to remove dissolved oxygen in the solution. After putting the inside of the reaction vessel under a nitrogen atmosphere, 18.3 mmol of pentacarbonyl iron (Fe (CO) ₅ ) was quickly injected into the reaction solution maintained at 80 ° C. with vigorous stirring. Thereafter, the temperature was raised to 180 ° C. at 3 ° C./min and held for 1 hour to grow a γ-Fe ₂ O ₃ phase on the Pd surface. The reaction solution is cooled to room temperature, and in order to remove excess organic matter and fine iron oxide particles, a purification process is performed by adding an n-hexane / ethanol mixed solvent mixed at a volume ratio of 1: 2 and centrifuging, and Pd / A black precipitate of γ-Fe ₂ O ₃ nanoparticles was obtained.

The obtained Pd / Fe ₂ O ₃ composite nanoparticles were heated to 550 ° C. at a heating rate of 10 ° C./min in a 4% H ₂ —Ar atmosphere and subjected to hydrogen reduction heat treatment for 10 hours.

Comparative Example 1
Palladium acetylacetonate (Pd (acac) ₂ ) 0.17 mmol was placed in a 100 mL three-necked flask and the reaction vessel was filled with a nitrogen atmosphere, and then 1.0 mL of trioctylphosphine was added to dissolve Pd (acac) ₂ . Next, 10 mL of oleylamine was added to perform nitrogen substitution again, and then the temperature was raised to 250 ° C. at 5 ° C./min and held for 30 minutes. Thereafter, the mixture was cooled to room temperature, ethanol was added to the reaction solution, and the mixture was centrifuged and purified by precipitation.

The obtained Pd nanoparticles having a particle diameter of 5 nm were put into a 100 mL three-necked flask, the solvent was distilled off with an evaporator, and 20 mL of 1-octanol was added to dissolve the Pd nanoparticles. After adding 0.43 mmol of iron (III) acetylacetonate (Fe (acac) ₃ ) and 6.8 mmol each of oleic acid and oleylamine, nitrogen bubbling was performed while stirring the solution to remove dissolved oxygen in the solution. went. The reaction vessel was under a nitrogen atmosphere, were grown γ-Fe ₂ O ₃ phase over Pd surface by holding the temperature was raised for 1 hour to 180 ° C.. The reaction solution is cooled to room temperature, and in order to remove excess organic matter and fine iron oxide particles, a purification process is performed by adding an n-hexane / ethanol mixed solvent mixed at a volume ratio of 1: 2 and centrifuging, and Pd / A black precipitate of γ-Fe ₂ O ₃ nanoparticles was obtained.

Pd nanoparticles were further added to the obtained Pd / Fe ₂ O ₃ composite nanoparticles so that the amount of Pd added was Fe: Pd = 6: 4 or FePd: Fe = 8: 2. Pd nanoparticles and Pd / γ-Fe ₂ O ₃ nanoparticles were mixed by dissolving the 5 nm Pd nanoparticles in the prepared Pd / γ-Fe ₂ O ₃ nanoparticle hexane solution and applying ultrasonic treatment.

The obtained Pd-added Pd / Fe ₂ O ₃ composite nanoparticles were subjected to ozone treatment to remove surface organic substances, and then heated to 500 ° C. at a rate of 3 ° C./min in a 4% H ₂ —Ar atmosphere. A hydrogen reduction heat treatment for 10 hours was performed.

A TEM image of the FePd / Fe nanocomposite magnet produced in Example 1 is shown in FIG. From this image, the core-shell type nanocomposite magnet particle consisting of the core portion L1 ₀ -FePd and the shell portion α-Fe was confirmed with the octahedral ridge length of 20 nm.

Moreover, when the magnets produced in Example 1 and Comparative Example 1 were subjected to SQUID measurement at room temperature after 10T pulse magnetization, and the coercive force was measured, the coercivity of the particles produced in Example 1 was 4. On the other hand, the coercive force of the core-shell nanocomposite magnet particle composed of the spherical core portion L1 ₀ -FePd having a particle diameter of 5 nm and the shell portion α-Fe produced in Comparative Example 1 was 2.3 kOe. Furthermore, the XRD measurement result of the magnet produced in Example 1 is shown in FIG.

Claims (2)

An FePd / Fe nanocomposite magnet having an L1 ₀ crystal structure having FePd as a core and Fe as a shell, wherein the FePd core has an octahedral structure having a (111) face of an L1 ₀ lattice on the surface. FePd / Fe nanocomposite magnet characterized. Pd nanoparticles having an octahedral structure are prepared from cubic Pd nanoparticles, and Pd / Fe ₂ O ₃ composite nanoparticles having the Pd nanoparticles having the octahedral structure as a core and Fe ₂ O ₃ as a shell are prepared. Then, the method for producing an FePd / Fe nanocomposite magnet according to claim 1, further comprising subjecting the Pd / Fe ₂ O ₃ composite nanoparticles to a hydrogen reduction treatment by heating in a hydrogen atmosphere.