RU30141U1 - MAGNETIC FILM - Google Patents

Description

Description of the utility model Magnetic film

The utility model relates to the field of magnetic films made of a polymer nanocomposite containing polyvinyl alcohol (LAN) and a mixture of magnetite (ResOd) and magemite (γ-Fe2O3) as a nanophase as a polymer matrix. Such films can be used to create magnetic recording media with a high density of recording and storage of information, as well as magnetic sensors. Moreover, the generally accepted term nanocomposition is usually used for microheterogeneous highly dispersed systems in the solid state of aggregation containing two or more components, w the particle size of the dispersed phase not exceeding 100 nm, which is distributed in a continuous dispersion medium called a matrix.

It should be noted that the nanoparticles of magnetite and magemite (like any other ferromagnet) in the polymer matrix can be in two different magnetic states - blocked and superparamagnetic. In this case, the superparamagnetic state in the generally accepted sense of this term means the state of a system of magnetically ordered nanoparticles at a temperature above a certain temperature, called the blocking temperature Tv, when this system behaves like a paramagnet.

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A blocked state implies the state of a system of magnetically ordered nanoparticles below Th, when this system behaves like a ferromagnet, if the dispersed phase is ferromagnetic (I.P. Suzdalev, A.S. Plachinda, V.N. Buravtsev, Yu.V. Maksimov, S.I. Reiman, V.I. Khromov, D.A.Dmitriev, Chemical Physics, Vol. 17, No. 7, pp. 104, 1998; R.Rgepe, E.Trong, JP.Jolivet, J.Livage, R. Cherkaoui, M. Nogues, JL Dormann, D. Fiorani. IEEE Trans, on magnetics. V. 29. No. 6. P. 2658, 1993). The analysis of the magnetic state of nanophase particles of iron oxides is traditionally carried out by the gamma-resonance (Mössbauer) spectroscory by the presence or absence in the spectra of a magnetic ultra-superficial structure (sextet) or quadrupole doublet, which are characteristic of the state below and above TV, and by measuring magnetization by the presence or absence magnetic hysteresis and related residual magnetization. Nanocomposites in a blocked state are promising for creating magnetic recording media. Nanocomposites in a superparamagnetic state can be used to develop magnetic sensors based on the so-called giant (negative or positive) magnetoresistance effect (GMR effect) that has recently been discovered and is being studied intensively. Phenomenon

GMR, characteristic of nanosystems in the superparamagnetic state, consists in a strong change in the electrical resistance of the composition (more than 1%) when a magnetic field is applied to it (A.E. Berkowitz, Phys. Rev. Lett. V.68. P.3745, 1992; AE Varfolomeev, AB Volkov, D.Yu. Godovsky, G.A. Kapustin, M.A. Moskvina.Letters to JETP, vol. 67, issue 1. P. 37, 1998).

A known magnetic film made of a polymer nanocomposite containing chemically non-crosslinked PVA as a polymer matrix, as well as a mixture of magemite and magnetite with a particle size of 5.8 nm as a nanophase, with a dispersed component content of up to 1.8 vol.% In superparamagnetic at room temperature temperature condition (N. Pardoe, W. Chua-anusom, T.O. St. Pierre, J. Dobson. J. Magn. Magn. Mater. V. 225. P. 41. 2001). The effect of GMR in the resulting nanocompositions has not been investigated.

A known magnetic film made of a polymer nanocomposite containing chemically non-crosslinked PVA and maghemite with a particle size of 5.2-10.7 nm as a nanophase with a dispersed component content of up to 21 vol.% (R. Rgepe, E.Trong J.P. Jolivet, J. Livage, R. Cherkaoui, M. Nogues, JL Dormann, D. Fiorani. IEEE Trans, on magnetics V. 29. No. 6. P. 2658, 1993). Bee nanocompositions (except one) at room

temperature are in a superparamagnetic state. One nanocomposition with a low content of a dispersed component of 0.53 vol.% Obtained in a blocked state. The effect of GMR in the resulting nanocompositions has not been investigated.

Closest to the claimed one is a known magnetic film 100 μm thick made of a polymer nanocomposite containing chemically non-crosslinked PVA as a polymer matrix and a mixture of magnetite and magemite with a particle size of 10 nm as a nanophase, with a dispersed component up to 24 vol.% (A .E. Varfolomeev, A.V. Volkov, D.Yu. Godovsky, G.A. Kapustin, M.A. Moskvin. Letters to JETP. Vol. 67, issue 1. P. 37, 1998 - prototype). The specified film at room temperature is superparamagnetic. In the resulting film nanocomposite, the GMR effect was detected.

The disadvantages of this film are the poor mechanical properties of a chemically non-crosslinked composition in an aqueous medium and the difficulties associated with its preparation, the relatively low content of iron oxides in the composition and the inability to obtain a nanocomposite with a dispersed phase in a blocked state at room temperature.

The technical task of the utility model is to create a magnetic film made of a polymer nanocomposite containing PVA as a polymer matrix and a mixture of magnetite and magemite as a nanophase, in which the nanophase can be depending on the production method both in a blocked and superparamagnetic state, moreover, in a superparamagnetic state, the film has the property of a strong decrease in electrical resistance when a magnetic field is applied to it (GMR effect).

The specified technical result is achieved in that the magnetic film made of a polymer nanocomposite containing polyvinyl alcohol as a polymer matrix and a mixture of magnetite and magemite as a magnetic nanophase contains chemically cross-linked polyvinyl alcohol as a polymer matrix, the film thickness being from 1 to 300 μm, and the average particle size of the magnetic nanophase is from 10 to 20 nm at a concentration of up to 47 vol.%.

The inventive film is obtained by sequential processing of a polymer composition consisting of PVA, water (in an amount up to 97% with respect to the total mass of PVA and water) and a mixture of water-soluble salts of ferric and ferrous iron in molar

a ratio of from 0.5 to 2, respectively, initially, but at least one water-soluble dialdehyde as a crosslinking agent at a pH of from O to 3 in the presence of an acid as an acidifying agent, then an aqueous alkali solution with the introduction of alkali in an amount of at least providing the full course of the alkaline hydrolysis reaction of a mixture of iron salts with the formation of a mixture of magnetite and magemite, followed by drying of the resulting comnosium. Under these conditions, the chemical crosslinking of PVA proceeds sequentially with the formation of acetal bonds between the hydroxyl groups of the PVA matrix and the aldehyde groups of dialdehyde to produce a polymer gel, then alkaline hydrolysis of a mixture of water-soluble salts of ferric and ferrous iron in the bulk of the polymer matrix - gel with the formation of a nanophase of iron oxides - mixtures of magnetite and magemite. After the formation of a PVA polymer gel (a hydrated gel with a water content of up to 97% with respect to the total mass of PVA and water) containing a mixture of iron salts, if necessary, the composition is dried to form an air-dry dehydrated gel with a sufficiently long drying time. The concentration of the dispersed phase of iron oxides in nanocompositions obtained using hydrated PVA gel with

with a water content of 97%, reaches 47 vol.%, when using a dehydrated (dried) gel with a water content of 5% reaches 25 vol.%. The particle size determined by the X-ray scattering method is 18-20 nm in the first case and 10 nm in the second. The nanophase of iron oxides in the compositions obtained using a hydrated PVA gel with a water content of 97% is in a blocked state; when using a dehydrated (dried) gel with a water content of 5% - in a superparamagnetic state. Nanocompositions in a blocked state with an average particle size of 18–20 nm, possessing remanent magnetization (memory effect), are promising for creating magnetic recording media, nanocomposites in a superparamagnetic state with an average particle size of 10 nm, not possessing a memory effect (magnetic hysteresis and related no residual magnetization), can be used in the development of reversible sensitive magnetic sensors (magnetic field sensors) based on the GMR effect.

Nanocompositions in a superparamagnetic state with a nanophase content of iron oxides above 16 vol.% Are characterized by the presence of a giant negative

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The thickness of the film nanocompositions can be varied over a wide range from 1 to 300 μm (films / from 1 to 5 μm on a substrate - see Fig. 1, for which, for example, glass or quartz plates, as well as these substrates coated with electrically conductive layer of ITO - mixed indium and tin oxide; films from 5 to 300 μm in a free state, that is, not connected with the substrate, see Fig. 2).

The above data are illustrated by the following example.

1 g of PVA with a molecular weight is dissolved in 19 ml of distilled water to obtain a 5% aqueous solution of PVA. To the resulting solution in a beaker add 10 ml of an aqueous solution containing 2.38 g (8.8-10 moles) of FeCl3z6H2O and 0.88 g (4.4-10 moles) (molar ratio). By. (1 learned solution is thoroughly mixed for 20 minutes, then a mixture of 5 ml of water, 0.25 ml of 96% sulfuric acid and 2.8-10 g (2.8-10 mol) of glutaraldehyde are quickly added to the resulting mixture (GD), the pH of the solution is 1. The resulting mixture is thoroughly mixed for 10 minutes, then poured into a standard plastic Petri dish with a diameter of 9.7 cm. Then the gel is dried in a Petri dish at room temperature for 4 days.

The dried, smooth, transparent, yellow-colored iron salts film of an air-dried gel with a water content of 5% relative to the total mass of PVA and water is separated from the Petri dish and immersed in 50 ml of a 6 molar aqueous alkali solution (potassium hydroxide). In this case, the film immediately becomes black as a result of the formation of a nanophase of iron oxides. After 20 hours, the film is removed from the solution of w; the Christmas tree, washed with distilled water for 24 hours until neutral, and then dried between sheets of filter paper under load. The thickness of the resulting film nanocomposite is 105 μm, the content of iron oxides in the composition is 17 06.%, the average particle size of the nanophase of iron oxides, determined by X-ray scattering, is 10 nm. According to Mössbauer spectroscopy and magnetization measurements, the dispersed nanophase of iron oxides in the obtained nanocomposition at room temperature is in a superparamagnetic state. This indicates the presence of a central quadrupole doublet in the Mössbauer spectra of the sample, as well as the absence of hysteresis on the magnetization curve and the associated remanent magnetization.

The resulting nanocomposition is characterized by the presence of a giant negative magnetoresistance effect - 10-12% in a field of 10 kiloersted (kOe) with an absolute value of change

resistance equal to Ohm, the value of the magnetoresistive sensitivity of 2-3% / kOe in low fields up to 2 kOe.

Claims (1)

A magnetic film made of a magnetic nanocomposite containing polyvinyl alcohol as a polymer matrix, and as a magnetic nanophase a mixture of magnetite (Fe ₃ O ₄ ) and magemite (γ-Fe ₂ O ₃ ), characterized in that it is made of a polymer nanocomposition, containing chemically cross-linked polyvinyl alcohol as a polymer matrix, the film thickness being in the range from 1 to 300 microns, and the average particle size of the magnetic nanophase is from 10 to 20 nm at a concentration of up to 47 vol.%.