WO2015194650A1 - 酸化鉄ナノ磁性粉およびその製造方法 - Google Patents
酸化鉄ナノ磁性粉およびその製造方法 Download PDFInfo
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- WO2015194650A1 WO2015194650A1 PCT/JP2015/067669 JP2015067669W WO2015194650A1 WO 2015194650 A1 WO2015194650 A1 WO 2015194650A1 JP 2015067669 W JP2015067669 W JP 2015067669W WO 2015194650 A1 WO2015194650 A1 WO 2015194650A1
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- 238000000034 method Methods 0.000 title abstract description 9
- JEIPFZHSYJVQDO-UHFFFAOYSA-N ferric oxide Chemical compound O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 title abstract 4
- 239000013078 crystal Substances 0.000 claims abstract description 35
- 230000010287 polarization Effects 0.000 claims abstract description 18
- 239000006247 magnetic powder Substances 0.000 claims abstract description 17
- 239000000203 mixture Substances 0.000 claims abstract description 15
- 230000002269 spontaneous effect Effects 0.000 claims abstract description 9
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N iron oxide Inorganic materials [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 claims description 140
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 47
- 239000000843 powder Substances 0.000 claims description 36
- 239000006185 dispersion Substances 0.000 claims description 15
- 239000002105 nanoparticle Substances 0.000 claims description 13
- 239000006228 supernatant Substances 0.000 claims description 9
- 239000007788 liquid Substances 0.000 claims description 7
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 6
- IEECXTSVVFWGSE-UHFFFAOYSA-M iron(3+);oxygen(2-);hydroxide Chemical compound [OH-].[O-2].[Fe+3] IEECXTSVVFWGSE-UHFFFAOYSA-M 0.000 claims description 6
- 230000001590 oxidative effect Effects 0.000 claims description 5
- 229910052814 silicon oxide Inorganic materials 0.000 claims description 4
- 239000002131 composite material Substances 0.000 claims description 3
- 239000011258 core-shell material Substances 0.000 claims description 3
- 239000002184 metal Substances 0.000 abstract description 11
- 229910052751 metal Inorganic materials 0.000 abstract description 11
- 230000000704 physical effect Effects 0.000 abstract description 6
- 239000011858 nanopowder Substances 0.000 abstract 1
- 238000010586 diagram Methods 0.000 description 17
- 239000002244 precipitate Substances 0.000 description 15
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 12
- 238000002441 X-ray diffraction Methods 0.000 description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 8
- 238000003991 Rietveld refinement Methods 0.000 description 7
- 238000005119 centrifugation Methods 0.000 description 7
- 229910052742 iron Inorganic materials 0.000 description 7
- 238000004519 manufacturing process Methods 0.000 description 7
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 6
- 239000007864 aqueous solution Substances 0.000 description 6
- 230000007704 transition Effects 0.000 description 6
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 5
- 238000004364 calculation method Methods 0.000 description 5
- 229910052760 oxygen Inorganic materials 0.000 description 5
- 239000001301 oxygen Substances 0.000 description 5
- 239000002245 particle Substances 0.000 description 5
- 239000000463 material Substances 0.000 description 3
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonium chloride Substances [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 description 2
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 2
- BOTDANWDWHJENH-UHFFFAOYSA-N Tetraethyl orthosilicate Chemical compound CCO[Si](OCC)(OCC)OCC BOTDANWDWHJENH-UHFFFAOYSA-N 0.000 description 2
- 229910021529 ammonia Inorganic materials 0.000 description 2
- 235000011114 ammonium hydroxide Nutrition 0.000 description 2
- BFNBIHQBYMNNAN-UHFFFAOYSA-N ammonium sulfate Chemical compound N.N.OS(O)(=O)=O BFNBIHQBYMNNAN-UHFFFAOYSA-N 0.000 description 2
- 229910052921 ammonium sulfate Inorganic materials 0.000 description 2
- 235000011130 ammonium sulphate Nutrition 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 230000005284 excitation Effects 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 239000000696 magnetic material Substances 0.000 description 2
- 230000005415 magnetization Effects 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 239000004570 mortar (masonry) Substances 0.000 description 2
- 150000003377 silicon compounds Chemical class 0.000 description 2
- 238000001308 synthesis method Methods 0.000 description 2
- 239000012670 alkaline solution Substances 0.000 description 1
- 125000004429 atom Chemical group 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 230000005274 electronic transitions Effects 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 230000005307 ferromagnetism Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000012212 insulator Substances 0.000 description 1
- 229910000462 iron(III) oxide hydroxide Inorganic materials 0.000 description 1
- 229910021519 iron(III) oxide-hydroxide Inorganic materials 0.000 description 1
- 239000000693 micelle Substances 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 125000004430 oxygen atom Chemical group O* 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 238000003980 solgel method Methods 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
- C01G49/00—Compounds of iron
- C01G49/02—Oxides; Hydroxides
- C01G49/06—Ferric oxide [Fe2O3]
-
- 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
-
- 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
- G11B5/714—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 dimension of the magnetic particles
-
- 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
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/10—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials non-metallic substances, e.g. ferrites, e.g. [(Ba,Sr)O(Fe2O3)6] ferrites with hexagonal structure
- H01F1/11—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials non-metallic substances, e.g. ferrites, e.g. [(Ba,Sr)O(Fe2O3)6] ferrites with hexagonal structure in the form of particles
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
- C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
- C01P2002/77—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by unit-cell parameters, atom positions or structure diagrams
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/90—Other crystal-structural characteristics not specified above
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/42—Magnetic properties
Definitions
- the present invention is a novel iron oxide nanomagnetic powder (may be described as “ ⁇ -type iron oxide”, “ ⁇ -type iron oxide nanomagnetic powder”, or “ ⁇ -Fe 2 O 3 ” in the present invention) and its. It relates to a manufacturing method.
- the present inventors obtained an ⁇ -Fe 2 O 3 phase by a chemical nanoparticle synthesis method using a reverse micelle method and a sol-gel method. It was found that the obtained ⁇ -Fe 2 O 3 phase exhibited a huge coercive force of 20 kOe (1.59 ⁇ 10 6 A / m) at room temperature. And, the ⁇ -Fe 2 O 3 phase was found to have a huge magnetic anisotropy.
- the inventors disclosed a magnetic powder having a metal substitution type ⁇ -M x Fe (2-x) O 3 phase as Patent Document 1, and disclosed Patent Document 2 as Fe 3+ of ⁇ -Fe 2 O 3 crystal.
- a magnetic material comprising a crystal of ⁇ -Ga x Fe 2-x O 3 in which a part of ion sites is substituted with Ga 3+ ions is disclosed.
- the present inventors have studied the production method of epsilon-type iron oxide nano magnetic powder ( ⁇ -Fe 2 O 3) , has been disclosed by various presentation and application (e.g., see Patent Documents 1 and 2 ). And while the present inventors are proceeding with research into making the ⁇ -type iron oxide nanomagnetic powder into a shape with a large aspect ratio, the present inventors have a novel property with characteristics such as magnetic polarization, spontaneous electric polarization, physical properties close to half metal, etc. ⁇ -type iron oxide nanomagnetic powder, which is iron oxide nanomagnetic powder, was discovered.
- the present invention has been made under the circumstances, and the problem to be solved is ⁇ type, which is a novel iron oxide nanomagnetic powder having properties similar to magnetic polarization, spontaneous electric polarization, and half metal. It is to provide an iron oxide nanomagnetic powder and a production method thereof.
- ⁇ -FeO (OH) iron oxide hydroxide (III)
- ⁇ -FeO (OH) iron oxide hydroxide (III)
- the present inventors observed the XRD of the produced ⁇ -type iron oxide nanomagnetic powder, analyzed the crystal structure and physical properties by performing Rietveld analysis and first-principles calculation, and completed the present invention.
- the first invention for solving the above-described problem is Magnetic powder having a composition of Fe 2 O 3 and a crystal structure belonging to a monoclinic system.
- the second invention is It is a magnetic powder belonging to a simple lattice (P) having a composition of Fe 2 O 3 and a crystal structure of monoclinic system.
- the third invention is A magnetic powder having a composition of Fe 2 O 3 and having a pentacoordinate Fe coordination site in the crystal structure.
- the fourth invention is:
- the composition is Fe 2 O 3 , has magnetic polarization at room temperature and has spontaneous electric polarization, and the angle formed by the magnetic polarization with respect to the spontaneous electric polarization takes a value between 0 ° and 90 °. Magnetic powder.
- the fifth invention is: It is a magnetic powder having a composition of Fe 2 O 3 and capable of exciting only one circularly polarized light from left and right circularly polarized light in the visible to near infrared region.
- the sixth invention is: The nanomagnetic powder has a composition of Fe 2 O 3 , a difference in energy between the left and right circular polarizabilities of 0.5 eV or more, and a low energy value of 1.5 eV or less of the left and right circularly polarizable energies.
- the seventh invention The magnetic powder according to any one of the first to sixth inventions used for producing a composite magnet or a core-shell magnet.
- the eighth invention Using ⁇ -FeO (OH) (iron oxide hydroxide (III)) nanoparticle dispersion, the ⁇ -FeO (OH) nanoparticles are covered with silicon oxide, then heat-treated in an oxidizing atmosphere, and centrifuged. Then, the supernatant liquid is dried to obtain a ⁇ -type iron oxide nanomagnetic powder.
- ⁇ -FeO (OH) iron oxide hydroxide (III)
- ⁇ -type iron oxide which is a novel iron oxide nanomagnetic powder according to the present invention, is considered to have an electronic structure close to that of a half metal and is considered to exhibit the performance as a half metal.
- FIG. 3 is a schematic diagram showing a coordination structure of an ⁇ -Fe 2 O 3 phase.
- FIG. 3 is a schematic diagram showing a coordination structure of an ⁇ -Fe 2 O 3 phase.
- FIG. 3 is a schematic diagram showing a coordination structure of a ⁇ -Fe 2 O 3 phase.
- FIG. 3 is a schematic diagram showing a coordination structure of a ⁇ -Fe 2 O 3 phase.
- FIG. 2 is a conceptual diagram showing Rietveld analysis of an XRD pattern of a ⁇ -type iron oxide nanomagnetic powder according to an example described later. That is, the black dot is the actually measured XRD intensity.
- the XRD intensity is calculated as shown by the black solid line, and there is almost no difference from the actual measurement value. It was confirmed that the Fe 2 O 3 having a (gray solid line is the residual of the calculated and measured values of the XRD intensity.).
- the black bar is the Bragg peak position of the ⁇ -type iron oxide nanomagnetic powder.
- FIG. 3 shows an a-axis projection of the crystal structure of ⁇ -type iron oxide obtained by the Rietveld analysis described above.
- This crystal structure has broken inversion symmetry. From the result of the first principle calculation for the ⁇ -type iron oxide according to the present invention based on the above analysis result, the spontaneous electric polarization in the crystal a-axis and c-axis directions.
- ⁇ -type iron oxide exhibits ferromagnetism at room temperature from the result of magnetization measurement using SQUID (Superconducting Quantum Interferometer) of MPMS7 manufactured by Quantum Design Co., Ltd.
- the angle formed with respect to the electric polarization takes a value between 0 ° and 90 °.
- the unit cell of the crystal structure of the ⁇ -type iron oxide is composed of 16 iron atoms and 24 oxygen atoms, which are 8 types of non-equivalent iron sites (Fe1 to Fe8) and 12 types of iron sites. It is divided into oxygen sites (O1 to O12).
- atoms other than the asymmetric unit are shown with a thin shadow.
- FIG. 4 is an a-axis projection of the crystal structure of ⁇ -type iron oxide according to the present invention, showing gray shadows at Fe1 to Fe3 and Fe5 to Fe6 sites, and dark gray shadows at Fe4 sites (further surrounded by broken lines). ), Fe7 and Fe8 sites are shown with a gray shadow.
- 5 and 6 show the same shadow as in FIG. 4 in the b-axis projection and c-axis projection of the crystal structure of ⁇ -type iron oxide according to the present invention. 4 to 6, it is considered that the Fe1 to Fe3 and Fe5 to Fe6 sites have a six-coordinate structure, the Fe4 site has a five-coordinate structure, and the Fe7 and Fe8 sites have a four-coordinate structure.
- FIG. 11 shows a crystal structure diagram of ⁇ -type iron oxide having orthorhombic crystal (space group Pna2 1 ) as a crystal structure, and ⁇ -type having rhombohedral crystal (space group R-3C) as a crystal structure.
- FIG. 12 shows a crystal structure diagram of iron oxide
- FIG. 13 shows a crystal structure diagram of ⁇ -type iron oxide having cubic crystal (space group Fd-3m) as the crystal structure.
- FIG. 7 and 9 are graphs in which the horizontal axis represents the electron density state and the vertical axis represents energy.
- the broken line at the position of energy 0 eV indicates the Fermi level, the lower part is a valence band mainly composed of oxygen 2p orbital (O2p), and the upper part is mainly composed of iron 3d orbital (Fe3d). It is a band.
- the right side of the electron density diagram shows ⁇ spin and the left side shows ⁇ spin.
- the oxygen 2p orbital spin is represented by a gray solid line
- the iron 3d orbital spin is represented by a black thick solid line
- the total value of the oxygen 2p orbital spin and the iron 3d orbital spin is represented by a black thin solid line. It showed in.
- spins mainly composed of oxygen 2p orbitals (O2p) in the valence band and spins mainly composed of iron 3d orbitals (Fe3d) in the conduction band Existed.
- the band dispersion diagram in the vicinity of the Fermi level shown in FIGS. 8 and 10 is a graph with the Brillouin zone on the horizontal axis and the energy on the vertical axis, and the broken line at the position of energy 0 eV indicates the Fermi level.
- ⁇ spin is indicated by a thin solid line
- ⁇ spin is indicated by a thin dotted line.
- the solid line represents the transition with the lowest energy among the direct transitions from the ⁇ spin of the valence band to the ⁇ spin of the conduction band (the electronic transition excited by the right circularly polarized light, that is, only the right circular polarized light is absorbed).
- the transition with the lowest energy among the direct transitions from ⁇ -spin in the valence band to ⁇ -spin in the conduction band Is indicated by a broken-line arrow.
- the band gap from ⁇ spin to ⁇ spin is as small as 1.0 eV (1240 nm), whereas the band gap from ⁇ spin to ⁇ spin is as large as 2.1 eV (590 nm). It is considered that the electronic structure is close to that of a half metal. Therefore, it is considered that the ⁇ -type iron oxide according to the present invention exhibits the performance as a half metal. As a result, it is considered that the ⁇ -type iron oxide according to the present invention can enable only one circularly polarized light excitation among the left and right circularly polarized light excitations from the visible region to the near infrared region.
- the energy difference between the left and right circularly polarized light was 0.5 eV or more, and the low energy value of the left and right circularly polarized energy was 1.5 eV or less.
- optical isolator performance will be manifested for light having a wavelength in the vicinity of 1.24 ⁇ m with a high transition probability.
- a composite magnet or a core-shell magnet is manufactured by combining a ⁇ -type iron oxide having a half-metal characteristic with a pyroelectric magnetic body and a magnetic body having different physical properties such as a highly magnetized soft magnetic material.
- the ⁇ -type iron oxide shown in FIG. 10 has an electronic structure of a normal charge transfer insulator.
- the band gap from the ⁇ spin to the ⁇ spin was 2.7 eV (460 nm), and the band gap from the ⁇ spin to the ⁇ spin was 2.5 eV (500 nm).
- FIG. 1 is a process flow diagram of the method for producing iron oxide nanomagnetic powder according to the present invention.
- ⁇ -FeO (OH) nanoparticles having an average particle diameter of 15 nm or less iron oxide hydroxide (III)) and pure water are mixed, and the iron (Fe) equivalent concentration is 0.01 mol / L to 1 mol / L. A dispersion of L or less was prepared.
- the deposited precipitate was collected and washed with pure water, and then dried at about 60 ° C. Further, the dried precipitate was pulverized to obtain a pulverized powder.
- the pulverized powder was heat-treated at 900 ° C. or higher and lower than 1200 ° C., preferably 950 ° C. or higher and 1150 ° C. or lower for 0.5 to 10 hours, preferably 2 to 5 hours in an oxidizing atmosphere to obtain heat-treated powder. .
- air can be used as the oxidizing atmosphere, and air is preferable from the viewpoint of workability and cost.
- the obtained heat treated powder is pulverized and then added to a sodium hydroxide (NaOH) aqueous solution having a liquid temperature of 60 ° C.
- NaOH sodium hydroxide
- the centrifugation operation was repeated twice or more, preferably three times or more. At this time, it is preferable that the rotation speed of centrifugation operation shall be 5,000 rpm or more and 15,000 rpm or less.
- the (sigma) -type iron oxide nanomagnetic powder which concerns on this invention was able to be obtained by drying the supernatant liquid obtained by the centrifugation operation of the last round.
- iron oxide nanomagnetic powder having an average particle size of 15 nm or less was obtained from the precipitate obtained by the final centrifugation operation.
- ⁇ -type iron oxide nanomagnetic powder could be easily synthesized.
- the ⁇ -type iron oxide nanomagnetic powder according to the present invention is expected to be industrially applied in various applications from the viewpoint of the simplicity of the synthesis method and the safety and stability of the material.
- Example 1 [Procedure 1] Into a 1 L Erlenmeyer flask is placed 420 mL of pure water and 8.0 g of ⁇ -FeO (OH) nanoparticle (iron oxide hydroxide (III)) sol having an average particle diameter of 6 nm and stirred until a uniform dispersion is obtained. did. To this, 19.2 mL of a 25% aqueous ammonia solution was added dropwise and stirred at 50 ° C. for 30 minutes. Further, 24 mL of tetraethoxysilane (TEOS) as a silicon compound was dropped into this dispersion, and the mixture was stirred at 50 ° C.
- TEOS tetraethoxysilane
- the obtained heat-treated powder is pulverized in an agate mortar and then stirred with a 5 mol / L sodium hydroxide (NaOH) aqueous solution at a liquid temperature of 65 ° C. for 24 hours. This was removed to obtain a dispersed aqueous solution of Fe 2 O 3 nanoparticles.
- Centrifugation operation first time related to the operation for 10 minutes at 5,000 rpm (rpm: rotation per minute) was performed on the generated aqueous solution of Fe 2 O 3 nanoparticles to separate the precipitate from the supernatant. .
- FIG. 2 shows data obtained by X-ray diffraction measurement (XRD) and Rietveld analysis of the obtained ⁇ -type iron oxide nanomagnetic powder sample.
- FIG. 3 shows an a-axis projection of the crystal structure of ⁇ -type iron oxide obtained from the Rietveld analysis result.
- FIG. 7 shows an electron density diagram obtained from the result of the first principle calculation, and
- FIG. 8 shows a band dispersion diagram.
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Abstract
Description
本発明者らは特許文献1として、金属置換型ε-MxFe(2-x)O3相を有する磁性粉を開示し、特許文献2として、ε-Fe2O3結晶のFe3+イオンサイトの一部がGa3+イオンで置換されたε-GaxFe2-xO3の結晶からなる磁性材料を開示している。
そして、本発明者らは、当該ε型酸化鉄ナノ磁性粉をアスペクト比の大きい形状とする研究を進める内、磁気分極や自発電気分極、ハーフメタルに近い物性、等という特性を備えた新規な酸化鉄ナノ磁性粉であるσ型酸化鉄ナノ磁性粉を知見した。
本発明は、当該状況の下で成されたものであり、その解決しようとする課題は、磁気分極や自発電気分極、ハーフメタルに近い物性を備えた新規な酸化鉄ナノ磁性粉であるσ型酸化鉄ナノ磁性粉と、その製造方法とを提供することである。
ここで本発明者らは、生成したσ型酸化鉄ナノ磁性粉のXRDを観測し、リートベルト解析および第一原理計算を行って結晶構造および物性を解析し、本発明を成した。
組成がFe2O3で、結晶構造が単斜晶系に属する磁性粉である。
第2の発明は、
組成がFe2O3で、結晶構造が単斜晶系の単純格子(P)に属する磁性粉である。
第3の発明は、
組成がFe2O3で、結晶構造中に5配位のFe配位サイトを有する磁性粉である。
第4の発明は、
組成がFe2O3で、室温で磁気分極を有し且つ自発電気分極を有し、当該磁気分極が当該自発電気分極に対して成す角度が、0°と90°との間の値をとる磁性粉である。
第5の発明は、
組成がFe2O3で、可視域から近赤外域において、左右の円偏光励起の内、片方の円偏光励起のみが可能である磁性粉である。
第6の発明は、
組成がFe2O3で、左右の円偏光性のエネルギー差が0.5eV以上、当該左右の円偏光性のエネルギーの内、低いエネルギーの値が1.5eV以下であるナノ磁性粉である。
第7の発明は、
コンポジット磁石またはコア-シェル磁石の製造に用いる、第1から第6のいずれかの発明に記載の磁性粉である。
第8の発明は、
β-FeO(OH)(酸化水酸化鉄(III))ナノ微粒子分散液を用い、当該β-FeO(OH)ナノ微粒子をシリコン酸化物で覆った後、酸化性雰囲気下で熱処理し、遠心分離し、上澄み液を乾固してσ型酸化鉄ナノ磁性粉を得る、磁性粉の製造方法である。
本発明に係る新規な構造を有する、σ型酸化鉄ナノ磁性粉について説明する。
図2は、後述する実施例に係るσ型酸化鉄ナノ磁性粉のXRDパターンのリートベルト解析を示す概念図である。即ち、黒色ドットは実測のXRD強度である。そして、後述するσ型酸化鉄の結晶構造を用いた計算を行うと、XRD強度は黒色実線に示すように計算され、実測値との差がほぼなくなり、後述するような単斜晶の結晶構造を有するFe2O3であることが確認された(灰色実線はXRD強度の実測値と計算値の残差である。)。なお、黒色バーはσ型酸化鉄ナノ磁性粉のブラッグピーク位置である。
図3に示すσ型酸化鉄は、単純格子(P)に属する単斜晶系の結晶構造を有し、リートベルト解析により求められた構造の空間群はP1a1、格子定数はa=5.0995Å、b=8.7980Å、c=9.4910Å、β角度=90.60°である。この結晶構造は反転対称が破れており、上述の解析結果を基にして行った、本発明に係るσ型酸化鉄に対する第一原理計算の結果より、結晶a軸、c軸方向に自発電気分極を有することが示されている。また、σ型酸化鉄は室温で強磁性を示すことがカンタムデザイン社製MPMS7のSQUID(超伝導量子干渉計)を用いた磁化測定の結果から確かめられていることから磁気分極を有し、自発電気分極に対して成す角度が0°と90°との間の値をとる。
当該σ型酸化鉄の結晶構造の単位格子は、16個の鉄原子および24個の酸素原子から構成されており、これらは非等価な8種類の鉄サイト(Fe1~Fe8)と、12種類の酸素サイト(O1~O12)とに分けられている。
ここで、図3に示す結晶構造において、非対称単位以外の原子は薄いシャドウを付して示した。
図5、6は、本発明に係るσ型酸化鉄の結晶構造のb軸投影図およびc軸投影図において、図4と同様のシャドウを付して示したものである。
そして、図4~6において、Fe1~Fe3およびFe5~Fe6サイトは6配位構造、Fe4サイトは5配位構造、Fe7、Fe8サイトは4配位構造を有していると考えられる。
エネルギー0eVの位置の破線はフェルミ準位を示し、当該フェルミ準位より下部は、主に酸素2p軌道(O2p)から成る価電子バンドであり、上部は主に鉄3d軌道(Fe3d)から成る伝導バンドである。そして、電子状態密度図の右側はαスピン、左側はβスピンを示している。
すると、σ型酸化鉄およびε型酸化鉄とも、上述したように価電子バンドにおいては主に酸素2p軌道(O2p)から成るスピンが、伝導バンドにおいては主に鉄3d軌道(Fe3d)から成るスピンが存在した。
ところが、図7に示すσ型酸化鉄では、伝導バンドのαスピン領域において、主なσ型酸化鉄のスピンの低エネルギー側に鉄3d軌道(Fe3d)から成るスピンが存在した。そして当該スピンは、上述した5配位構造を有するFe4サイトに隣接する4配位構造のFe8サイトに由来するものであった。これは、5配位構造のFe4サイトが、4配位構造のFe8サイトの電子状態に影響していると考えられる。
一方、図9に示すε型酸化鉄においては、当該スピンは観測されなかった。
当該バンド分散図に、αスピンを細実線で、βスピンを細点線で記載した。
そして、価電子バンドのαスピンから伝導バンドのへαスピンへの直接遷移(右円偏光により励起される電子遷移、すなわち右円偏光のみ吸収される。)の中で最もエネルギーが小さい遷移を実線矢印で示し、価電子バンドのβスピンから伝導バンドのへβスピンへの直接遷移(左円偏光により励起される電子遷移、すなわち左円偏光のみ吸収される。)の中で最もエネルギーが小さい遷移を破線矢印で示したものである。
この結果、本発明に係るσ型酸化鉄は、可視域から近赤外域において、左右の円偏光励起の内、片方の円偏光励起のみを可能とすることが出来ると考えられる。具体的には、左右の円偏光性のエネルギー差が0.5eV以上、当該左右の円偏光性のエネルギーの内、低いエネルギーの値が1.5eV以下であった。
そして、例えば、遷移確率の大きい1.24μm近傍の波長の光に対しては、光アイソレーター性能が発現することが期待されるものである。
さらに、焦電性磁性体でありかつハーフメタルの特性を有するσ型酸化鉄と、例えば高磁化軟磁性材料のような異なる物性を示す磁性体とを組み合わせてコンポジット磁石またはコア-シェル磁石を製造することにより、高磁化・高保磁力でハーフメタルの特性を有するなど新規物性を示す材料を見出すことができると考えられる。
これに対し、図10に示すε型酸化鉄では、通常の電荷移動型絶縁体の電子構造をとっていた。そして、αスピンからαスピンへのバンドギャップは2.7eV(460nm)、βスピンからβスピンへのバンドギャップは2.5eV(500nm)と、両者にほとんど差異はみられなかった。
ここで、本発明に係る酸化鉄ナノ磁性粉の製造方法の一例について、本発明に係る酸化鉄ナノ磁性粉の製造方法の工程フロー図である図1を参照しながら説明する。
平均粒径15nm以下のβ-FeO(OH)ナノ微粒子(酸化水酸化鉄(III))と純水とを混合して、鉄(Fe)換算濃度が0.01モル/L以上、1モル/L以下の分散液を調製した。
当該分散液へ、前記酸化水酸化鉄(III)1モルあたり3~30モルのアンモニアを、アンモニア水溶液の滴下により添加して、0~100℃、好ましくは20~60℃で撹拌した。
さらに、当該アンモニアを添加した分散液へ、前記β-FeO(OH)ナノ微粒子1モルあたり0.5~15モルのケイ素化合物を滴下し、15時間以上、30時間以下で撹拌した後、室温まで放冷した。
当該放冷した分散液へ、前記β-FeO(OH)ナノ微粒子1モルあたり1~30モルの硫酸アンモニウムを加えて沈殿を析出させた。
当該析出した沈殿物を採集し純水で洗浄した後、60℃程度で乾燥させた。さらに当該乾燥した沈殿物を粉砕して粉砕粉を得た。
当該粉砕粉を酸化性雰囲気下、900℃以上、1200℃未満、好ましくは950℃以上、1150℃以下で、0.5~10時間、好ましくは2~5時間の熱処理を施し熱処理粉を得た。尚、当該酸化性雰囲気としては大気の使用が可能であり、作業性、コストの観点から大気の使用が好ましい。
得られた熱処理粉を、解粒処理したのち、強アルカリ液として液温60℃以上70℃以下の水酸化ナトリウム(NaOH)水溶液に添加し、15時間以上30時間以下、好ましくは20時間以上26時間以下攪拌することにより、当該熱処理粉からシリコン酸化物を除去し、酸化鉄ナノ磁性粒子の分散水溶液を生成させた。
次いで、生成した酸化鉄ナノ磁性粒子の分散水溶液へ遠心分離操作(1回目)を行い、沈殿物と上澄み液に分離させた。そして、当該沈殿物(1回目)を採取し、ここへ純水添加して分散後、再度の遠心分離操作(2回目)を行って沈殿物(2回目)を採取した。さらに所望により、当該沈殿物(2回目)へ純水添加して分散後、再々度の遠心分離操作(3回目)を行った。つまり、当該遠心分離操作を2回以上、好ましくは3回以上繰り返した。このとき、遠心分離操作の回転数は5,000rpm以上15,000rpm以下とすることが好ましい。
そして、最終回の遠心分離操作で得られた上澄み液を乾固させることにより、本発明に係るσ型酸化鉄ナノ磁性粉を得ることが出来た。
一方、最終回の遠心分離操作で得られた沈殿物中からは、ε型酸化鉄ナノ磁性粉であり平均粒径15nm以下である酸化鉄ナノ磁性粉を得ることが出来た。
本発明によって、σ型酸化鉄ナノ磁性粉を容易に合成することが出来た。
そして、本発明に係るσ型酸化鉄ナノ磁性粉は、合成法の簡便性や材料の安全性・安定性という観点からも、様々な用途での工業的応用が期待される。
[実施例1]
〔手順1〕1L三角フラスコに、純水420mLと平均粒径6nmのβ-FeO(OH)ナノ微粒子(酸化水酸化鉄(III))のゾル8.0gを入れ、均一分散液となるまで撹拌した。
ここに、25%アンモニア水溶液19.2mLを滴下し、50℃で30分間攪拌した。さらにこの分散液に、ケイ素化合物としてテトラエトキシシラン(TEOS)24mLを滴下し、50℃で20時間攪拌した後、室温まで放冷した。当該分散液が室温まで放冷したら、硫酸アンモニウム20gを加えて沈殿を析出させた。
〔手順2〕当該析出した沈殿物を遠心分離処理により採集した。採集した沈殿物を純水で洗浄し、シャーレに移して60℃乾燥機中で乾燥させた後、メノウ製乳鉢で粉砕し粉砕粉とした。
〔手順3〕当該粉砕粉を炉内に装填し、大気雰囲気下、1061℃、4時間の熱処理を施し熱処理粉とした。得られた熱処理粉を、メノウ製乳鉢で解粒処理したのち、5モル/Lの水酸化ナトリウム(NaOH)水溶液で、液温65℃、24時間攪拌することにより、熱処理粉からシリコン酸化物を除去し、Fe2O3ナノ粒子の分散水溶液を得た。
〔手順4〕
生成したFe2O3ナノ粒子の分散水溶液へ、5,000rpm(rpm:回転毎分)で10分間の操作に係る遠心分離操作(1回目)を行い、沈殿物と上澄み液とに分離させた。次に、当該沈殿物(1回目)へ純水添加して分散後、10,000rpmで5分間の操作に係る遠心分離操作(2回目)を行い、沈殿物と上澄み液とに分離させた。さらに、当該沈殿物(2回目)に純水添加して分散後、14,000rpmで60分間の操作に係る遠心分離操作(3回目)を行ない、沈殿物と上澄み液とに分離させた。当該上澄み液(3回目)を乾固させることにより、当該上澄み液(3回目)に含まれていた本発明に係るσ型酸化鉄ナノ磁性粉を得た。
さらに、リートベルト解析の結果から得られたσ型酸化鉄の結晶構造のa軸投影図を図3に示す。
また、第一原理計算の結果から得られた電子状態密度図を図7に、バンド分散図を図8に示した。
Claims (8)
- 組成がFe2O3で、結晶構造が単斜晶系に属する磁性粉。
- 組成がFe2O3で、結晶構造が単斜晶系の単純格子(P)に属する磁性粉。
- 組成がFe2O3で、結晶構造中に5配位のFe配位サイトを有する磁性粉。
- 組成がFe2O3で、室温で磁気分極を有し且つ自発電気分極を有し、当該磁気分極が当該自発電気分極に対して成す角度が、0°と90°との間の値をとる磁性粉。
- 組成がFe2O3で、可視域から近赤外域において、左右の円偏光励起の内、片方の円偏光励起のみが可能である磁性粉。
- 組成がFe2O3で、左右の円偏光性のエネルギー差が0.5eV以上、当該左右の円偏光性のエネルギーの内、低いエネルギーの値が1.5eV以下であるナノ磁性粉。
- コンポジット磁石またはコア-シェル磁石の製造に用いる、請求項1から6のいずれかに記載の磁性粉。
- β-FeO(OH)(酸化水酸化鉄(III))ナノ微粒子分散液を用い、当該β-FeO(OH)ナノ微粒子をシリコン酸化物で覆った後、酸化性雰囲気下で熱処理し、遠心分離し、上澄み液を乾固してσ型酸化鉄ナノ磁性粉を得る、磁性粉の製造方法。
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