JP2006235570A - Magneto-optical material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new magneto-optical material capable of controlling its magnetism under light as a complex of organic molecules and an inorganic substance. <P>SOLUTION: The magneto-optical material is a complex of spiropyran-based photochromic molecules and inorganic magnetic particles or a complex of azobenzene-based photochromic molecules and ferromagnetic alloy particles. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a new magneto-optical material that is useful for a switching element, a memory element, a display device, and the like and that can change magnetism by light irradiation.

  Magneto-optical materials that can control magnetism by controlling light irradiation, that is, irradiation and blocking, or changing conditions such as irradiation intensity and wavelength, have attracted attention. Such magneto-optical materials are used as switching elements and memory elements. It is expected to be applicable to display devices and the like.

  As such a magneto-optical material, a magneto-optical material capable of controlling magnetism with light by combining an organic substance, particularly a photochromic molecule and an inorganic substance, has been studied. A magneto-optical material in which fine particles and azobenzene-based photochromic molecules are combined has been developed and proposed (Non-Patent Document 1).

However, with regard to the magneto-optical material that is a composite of organic and inorganic materials, the fact is that most of the studies have not obtained specific results, despite great expectations for future industrial applications. Furthermore, it has been a big problem to enable reversible control of magnetization by light irradiation at room temperature.
Angew. Chem. Int. Ed., 2004, 43, 6135-6139

  The present invention is based on the background as described above, and provides a new magneto-optical material capable of controlling magnetism by light as a complex of organic molecules and inorganic substances based on the inventors' previous studies. It is said. Furthermore, another object of the present invention is to provide a magneto-optical material as a composite of an organic molecule and an inorganic substance that can control magnetism by light at room temperature.

  The present invention is characterized by the following in order to solve the problems as described above.

  1st: A magneto-optical material characterized in that spiropyran-based photochromic molecules and inorganic magnetic particles are combined.

  Second: The above-mentioned magneto-optical material, wherein the inorganic magnetic particles are oxide particles.

  Third: A magneto-optical material, wherein the oxide particles are iron oxide particles.

  Fourth: Spiropyran-based photochromic molecule is

(Wherein R is an alkyl group, a hydroxyalkyl group, an alkyl (polyoxyalkylene) group, or a hydroxyalkyl (polyoxyalkylene) group)
A spiropyran represented by the above, which may have a substituent.

  Fifth: R is a magneto-optical material having 1 to 12 carbon atoms.

  6th: A magneto-optical material characterized in that azobenzene-based photochromic molecules and ferromagnetic alloy particles are combined.

  Seventh: A magneto-optical material, wherein the ferromagnetic alloy particles are FePt fine particles.

  Eighth: The magneto-optical material, wherein the FePt fine particles are synthesized by a heat reduction reaction of an iron compound and a platinum compound with a polyol compound.

  Ninth: The azobenzene photochromic molecule has an amino group or a carboxyl group at the end of the carbon chain of the molecule.

  Tenth: Any one of the above magneto-optical materials, wherein a linear alcohol having 6 to 12 carbon atoms coexists.

  Eleventh: Any one of the above magneto-optical materials, which is formed as a film, a sheet, a thin film on a substrate, or a powder (solid).

  Twelfth: Any one of the above magneto-optical materials, wherein the photochromic molecule, the solvent dispersion, and the solvent dispersion of inorganic magnetic particles are mixed and cast-molded.

  Thirteenth: Any one of the above magneto-optical materials, wherein the magnetic strength is distinguishable visually by a change in color.

  According to the present invention as described above, there is provided a new magneto-optical material capable of controlling magnetism by light as a complex of organic molecules and inorganic substances, which can be used for switching elements, memory elements, display devices, and the like. Can be applied. Furthermore, magnetic control by light irradiation at room temperature is also possible.

  The present invention has the features as described above, and an embodiment thereof will be described below.

  The magneto-optical material of the present invention is characterized in that spiropyran-based photochromic molecules and inorganic magnetic particles are combined. The inorganic magnetic particles constituting the photomagnetic material may be various magnetic particles, and may be various inorganic particles exhibiting ferromagnetism in the nano size. It may be an oxide, nitride, metal, alloy or the like. For example, it may be derived from iron, cobalt, nickel, noble metal elements, rare earth elements, molybdenum, tungsten and the like. Among these, for example, iron oxide particles are exemplified as one suitable from the viewpoints of handleability, cost, photomagnetism, and the like. Also suitable are FePt alloy particles, NdFe alloy particles, CoSm alloy particles and the like.

  The inorganic magnetic particles such as iron oxide particles are preferably in the nanoscale, and for example, it is generally considered that the average particle size is generally 50 nm or less, further 10 nm or less.

  In the magneto-optical material using the spiropyran-based photochromic molecule of the above invention, as the spiropyran-based photochromic molecule as one component, for example, the following formula

As described above, spiropyran having photochromic properties by molecular isomerization, or various derivatives thereof may be used. These spiropyran-based photochromic molecules are considered to enable magnetic control by light by capping the above-described inorganic magnetic particles.

  As the spiropyran-based photochromic molecule, more preferably, the following formula as described above:

Is taken into account. Here, the symbol R represents an alkyl group of — (CH ₂ ) _n —CH _3, a hydroxyalkyl group of — (CH ₂ ) _n —CH ₂ OH, such as — (C ₂ H ₄ O) _m — (CH ₂ ) _n. An alkyl (polyoxyalkylene) group of —CH ₃ , for example, an alkyl (polyoxyalkylene) group of — (C ₂ H ₄ O) _m — (CH ₂ ) _n —CH ₂ OH.

  For coefficients, 0-11, and for n 1-5 are considered as suitable ranges, for example. It is also suitably considered that the total number of carbons as R is 1-12.

  Furthermore, the above spiropyran-based photochromic molecules may have various permissible substituents in the molecular skeleton, although they are not clearly shown in the molecular structural formula. Those that have various substituents in consideration of dispersibility in solvents and control of capping strength to inorganic magnetic particles, etc., if the photochromic properties due to isomerization are not lost or if this is further enhanced It is good.

  On the other hand, in the above invention using azobenzene-based photochromic molecules as photochromic molecules, ferromagnetic alloy particles are used as magnetic particles. Examples of the ferromagnetic alloy particles in this case include FePt, NdFe, CoSm, or fine particles of an alloy mainly composed of FePt.

  Among them, in the present invention, FePt ferromagnetic nanoparticles are exemplified as one suitable. The FePt nanoparticles are generally known as having superparamagnetism, but in the present invention, FePt fine particles converted to ferromagnetism are used. It can be used as converted from a superparamagnetic fcc structure to a ferromagnetic fct structure. Since FePt nanoparticles are attracting attention as a configuration of a magnetic recording medium, realization of a magneto-optical material as a ferromagnetic FePt nanoparticle composite according to the present invention is of great value.

  The conversion to ferromagnetic FePt is possible by annealing, but in this case, since the particle size increases, it is more preferable to use the one synthesized directly by the polyol reduction method. .

  In this polyol reduction method, for example, an iron compound or a platinum compound, for example, a complex thereof is heated to a structural rearrangement temperature (280 ° C.) or higher in the presence of a polyol compound such as EG (ethylene glycol) or PEG (polyethylene glycol). This is realized.

For example, the azobenzene-based photochromic compound combined with the nanoferromagnetic particles as described above may have, for example, R ^1- , R ¹ O-, NH ₂ -R ^2- , R on the benzene ring forming the azobenzene molecular skeleton. _{^{1 -NH-, NH 2 -R 2 -NH}} -R 3 -, NH 2 -R 2 -O-, -O- NH 2 -R 2 -NH 2 -R 3, HOOC-R 2 -O -, ( R ¹ in the formula may have an alkyl group, and R ² and R ³ may have an alkyl chain). Of course, it is not limited to these.

  More preferably, the number of carbon atoms of the alkyl group or alkylene chain is, for example, about 3 to 10, and a compound having an amino group or a carboxy group at one carbon chain end is considered.

  Further, it goes without saying that the benzene ring forming the azobenzene molecular skeleton may have various acceptable substituents other than those described above.

  The magneto-optical material of the present invention is a film obtained by mixing and stirring the solvent dispersion of inorganic magnetic particles as described above and the solvent dispersion of spiropyran-based photochromic molecules, and developing the film by casting or spin coating on a substrate. , A sheet, a thin film on a substrate, or a powder (solid). As the solvent in this case, it is preferable to use an organic solvent having a relatively low polarity such as toluene, benzene, hexane and the like. Of course, the magneto-optical material of the present invention is not limited to the above forming method.

  In the magneto-optical material of the present invention, it is also effective to allow a linear alcohol having 6 to 12 carbon atoms or a linear amine compound to coexist with inorganic magnetic particles and photochromic molecules.

  The above magneto-optical material can be visually discriminated by the change in color of the magnetic force. Such a magneto-optical material has not been realized so far and can only be realized by the present invention.

  Therefore, an example will be shown below and will be described in more detail. Of course, the invention is not limited by the following examples.

Reference Example 1 Synthesis of γ-Fe ₂ O _{3 Using} 1,2-propanediol as a solvent, FeCl ₃ -6H ₂ O, CH ₃ COONa, H ₂ O, and n-octylamine are mixed and heated at reflux for 5 hours. did. Thereafter, the mixture was centrifuged to obtain γ-Fe ₂ O ₃ particles having an average particle diameter of 5 nm. This was dispersed in toluene at room temperature for 15 hours.

FIG. 1 shows the results of zero-field cooling magnetization measurement of this iron oxide particle and the magnetic field dependence of magnetization. Note that T _B = 16.07K.
<Example 1>
Γ-Fe ₂ O ₃ toluene dispersion according to Reference Example 1 and spiropyran (SP1) of the following formula

1 ml of toluene solvent solution was mixed with 1 ml each and stirred in a dark room for 30 minutes. Subsequently, it was cast (developed) on a glass substrate to form a thin film (solid).

  FIG. 2 shows the TEM image and UV-vis spectrum.

When the magnetic field dependence of magnetization was measured for this thin film (solid), the result of FIG. 3 was obtained. It was confirmed that it exhibits a ferromagnetic characteristic with a coercive force of 300 G and a residual magnetization of 2.6 EMU / g. Therefore, when the change in magnetization due to light was measured for this product, the result of FIG. 4 was obtained. It was confirmed that the magnetization increased with UV irradiation and decreased with vis irradiation, and the switching width was 3.00%.
<Example 2>
As a spiropyran-based photochromic molecule,

Of hydroxyalkyl derivative: 0.28 g (8 × 10 ⁻⁴ mol) of SP— (CH ₂ ) ₂ —OH, 0.3 ml of γ-Fe ₂ O _{3 and 3} ml of toluene were stirred in a dark room for 3 days. The solid obtained after flying with toluene once was centrifuged in 2-propanol. The remaining solid was dissolved in 1.0 ml toluene and then cast on a glass substrate.

  FIG. 5 shows the UV-vis spectrum of the thin film (solid) in this case, and FIG. 6 shows the change in magnetization due to light irradiation.

  The switching width was 9.97%.

Further, when the color of the thin film (solid) was observed, it was observed that the color was purple when the magnetic force was strong, and the color was brown when the magnetic force was weak.
<Example 3>
In Example 2, 1-octanol was allowed to coexist and composite with γ-Fe ₂ O ₃ was carried out in the same manner as in Example 2. The molar ratio of SP- (CH ₂ ) ₂ —OH to 1-octanol was 1: 1.

  FIG. 7 shows a UV-vis spectrum of the obtained thin film (solid), and FIG. 8 shows changes in magnetization due to light irradiation.

  The switching width was 30.0%.

Further, when the color of this thin film (solid) was observed, it was observed that the color was purple when the magnetic force was strong, and the color was brown when the magnetic force was weak, and it was confirmed that the strength of the magnetic force could be identified visually.
<Reference Example 2>
Fe (acac) ₃ and Pt (acac) ₂ were heated for 3 hours in tetraethylene glycol (TEG) at a temperature of 300 ° C. for polyol reduction to synthesize FePt nanoparticles having an fct structure. FIG. 9 shows an XRD pattern of the FePt nanoparticles, and the appearance of superlattice peaks (001), (110), (201), and (112) is confirmed. FIG. 10 shows the magnetic field dependence of magnetization, and hysteresis is confirmed even at room temperature. The measured temperatures in the figure are A: 5K and B: 300K.
<Example 4>
The FePt nanoparticles synthesized in Reference Example 2 have the following formula:

And n-octylamine are mixed in equal amounts and stirred in a two-layer system of TEG and toluene to extract and separate the composite nanoparticles in which the azobenzene ligand and n-octylamine are coordinated on the FePt surface from the toluene layer did. Composite nanoparticles were obtained as powder by separating and purifying the separated toluene layer with ethanol and purification.

  FIG. 11 is a TEM image of this composite nanoparticle. For example, from FIG. 11, it is confirmed that the particles are present with a uniform interval, unlike the aggregated state immediately after the synthesis. From this, it is considered that the azobenzene ligand and n-octylamine are coordinated with the FePt nanoparticles, and a monomolecular film is formed on the particle surface.

In addition, as shown in FIG. 12, in this composite nanoparticle, even in a solid powder state, a decrease in absorption attributed to the π-π ^* transition of the azobenzene trans body seen in the vicinity of 340 nm by irradiation with ultraviolet light. The increase was observed by irradiation with visible light, and reversible photoisomerization of azobenzene on the surface of FePt nanoparticles was observed.

  Furthermore, along with the photoisomerization of azobenzene, an increase in the magnetization of the composite nanoparticles by irradiation with ultraviolet light and a decrease in the magnetization by irradiation with visible light were observed at a temperature of 300 K and 10 G as shown in FIG. . It was possible to reversibly control the magnetization by light irradiation at room temperature. This is presumably because the change in the charge state of the surface of the FePt nanoparticles was induced by the change in the dipole moment due to the photoisomerization of azobenzene, which affected the itinerant of free electrons in the FePt nanoparticles.

It is a diagram showing the magnetic field dependence of the result and the magnetization of the zero-field cooling magnetization measurements γ-Fe ₂ O _3. It is the TEM image and UV-vis spectrum figure of the magnetooptical material of SP1. It is the figure which showed the magnetic field dependence of magnetization of the magnetooptical material of SP1. It is the figure which showed the change of the magnetization by light irradiation of the magnetooptical material of SP1. SP1- (CH ₂₎ a UV-vis spectrum of light magnetic material ₂ -OH. SP1- (CH ₂₎ is a diagram showing a change in magnetization by light irradiation of the light magnetic material ₂ -OH. SP1- (CH _{2) 2} -OH: a UV-vis spectrum of 1-octanol light magnetic material. SP1- (CH _{2) 2} -OH: is a diagram showing a change in magnetization by light irradiation of the light magnetic material octanol light magnetic material. It is the figure which showed the XRD pattern of the FePt nanoparticle. It is the figure which showed the magnetic field dependence of the magnetization of a FePt nanoparticle. 2 is a TEM image of FePt composite nanoparticles. It is a UV-vis spectrum figure of a FePt composite nanoparticle. It is the figure which showed the change of the magnetization by the light irradiation of a FePt composite nanoparticle.

Claims (13)

  A magneto-optical material comprising a composite of spiropyran-based photochromic molecules and inorganic magnetic particles.   2. The magneto-optical material according to claim 1, wherein the inorganic magnetic particles are oxide particles.   The photomagnetic material according to claim 2, wherein the oxide particles are iron oxide particles. Spiropyran-based photochromic molecules have the following formula
(Wherein R is an alkyl group, a hydroxyalkyl group, an alkyl (polyoxyalkylene) group, or a hydroxyalkyl (polyoxyalkylene) group)
4. The magneto-optical material according to claim 1, which is a spiropyran represented by the formula (1), and may have a substituent.   The magneto-optical material according to claim 4, wherein R has 1 to 12 carbon atoms.   A magneto-optical material comprising a composite of azobenzene photochromic molecules and ferromagnetic alloy particles.   The magneto-optical material according to claim 6, wherein the ferromagnetic alloy particles are FePt fine particles.   The magneto-optical material according to claim 7, wherein the FePt fine particles are synthesized by a heat reduction reaction of an iron compound and a platinum compound with a polyol compound.   The photomagnetic material according to any one of claims 6 to 8, wherein the azobenzene-based photochromic molecule has an amino group or a carboxyl group at a carbon chain terminal portion of the molecule.   The photomagnetic material according to any one of claims 1 to 9, wherein a linear alcohol compound or a linear amine compound having 6 to 12 carbon atoms coexists.   11. The magneto-optical material according to claim 1, wherein the magneto-optical material is formed as a film, a sheet, a thin film on a substrate, or a powder (solid).   12. The photomagnetic material according to claim 11, wherein the photochromic material is cast-molded after the photochromic molecule, the solvent dispersion, and the solvent dispersion of the inorganic magnetic particles are mixed.   The magneto-optical material according to any one of claims 1 to 8, wherein the magnetic strength can be visually identified by a change in color.