RU2445256C2 - Ordered arrays of nanowires of photochromic ferromagnets, method of their production, membrane to preserve magnetic information and application of ordered arrays of nanowires of photochromic ferromagnets as light-sensitive magnetic media - Google Patents

Abstract

FIELD: nanotechnologies.

SUBSTANCE: invention relates to ordered photochromic ferromagnet arrays of nanowires on the basis of (tris)oxalates of transition meals and cations of spirocyclic row and may be used as light-sensitive magnetic nanomedia with supercapacious magnetooptic memory. The assigned task is solved by compounds in the form of derivative (tris)oxalates of transition metals and cations of spirocyclic row with general formula PCMe₁Me₂(C₂O₄)₃, where M₁, M₂ - 3d metals, PC - photochromic cations having photomagnet properties. Ordered arrays of nanowires of photochromic ferromagnets are produced by incorporation of above compounds into pores of the membrane from anodixed aluminium oxide (AOA), density of which makes 10¹¹-10¹³ cm^-2, and pore size is 20-200 nm. Ordered arrays of nanowires of photochromic ferromagnets are used as light-sensitive magnetic media for production of materials with supercapacious magnetooptic memory of up to 10¹³ bit/cm².

EFFECT: development of ordered arrays of nanostructures, in which elementary cells are nanowires of photochromic material with magnetic ordering.

3 cl, 6 dwg

Description

The invention relates to ordered arrays of photochromic ferromagnet nanowires based on (tris) transition metal oxalates and spirocyclic cations and can be used as photosensitive magnetic nanomedia with ultra-high magneto-optical memory.

One of the key areas in the nanotechnology industry is the organization of nano-objects into a system of interacting elements controlled by external influences and compatible with the existing elemental base of electron-optical devices. The creation of powder nanostructures is widespread and brings certain results, showing that the physical properties of organic and metal-organic materials change significantly as a result of nanostructuring [1-3].

[one]. P.V. Kamat, JACS, 130 (42), 14020 (2008).

[2] .Organic Nanostructures, Edited by J.L. Atwood and J.W. Steed, Wiley-VCH Verlag Gmbh, p. 320, 2008.

[3] .Physics, Chemistry and Application of Nanostructures, edited by V.E. Borisenko, S.V. Gaponenko, V.S. Gurin, World Scientific, p. 488, 2001.

However, the real application of nanoobjects of polyfunctional compounds (compounds combining photochromic and magnetic sublattices in one crystal lattice) is possible if they are organized into ordered structures. Massive samples of photochromic crystals exhibit diverse photomagnetic effects associated with the influence of light on the coercive force [4-6],

[four]. S. M. Aldoshin, Journal of Photochemistry and Photobiology, 200, 19 (2008).

[5]. R. B. Morgunov, F. B. Mushenok, S. M. Aldoshin, N. A. Sanina, E. A. Yurieva, G. V. Shilov, V. V. Tkachev, New J. Chem., 33, 7, 1 (2009).

[6]. R.B.Morgunov, F.B.Mushenok, S.M. Aldoshin, E.A. Yuryeva, G.V. Shilov, Solid State Physics, Volume 51, Issue 8, pp. 1568-1575 (2009 change in thermally induced magnetism of photochromic spiropyran molecules [4], SMAldoshin, Journal of Photochemistry and Photobiology, 200, 19 (2008). redistribution of electrons between organic photochromic and inorganic magnetic subsystems [5], RBMorgunov, FBMushenok, SMAldoshin, NASanina, EA Yureva, GVShilov, VVTkachev, New J. Chem., 33, 7, 1 (2009).

[7]. R. B. Morgunov, F. B. Mushenok, S. M. Aldoshin, E. A. Yurieva, G. V. Shilov, Y. Tanimoto, J. Solid State Chem., (2009), doi: 10.1016 / j.jssc. 2009.03.011]. The use of each of these phenomena in a two-dimensional ensemble of photomagnetic nanoelements would make it possible to create a magneto-optical analogue of the MRAM memory element [8] RB Morgunov, AI Dmitriev. Solid State Physics, Volume 51, Issue 9, 2009, in which magnetic information could be read / written with the help of light into separate photochromic structures.

All this imposes the following minimum requirements for the organization of an ensemble of nanoparticles:

- The set and known architecture of arrays of nanoparticles and the ability to control their location and connection. The ability to digitally set the coordinates of individual nanocells.

- Clear and manageable conditions for the interaction of nanoparticles with each other. In particular, the dipole-dipole interaction of ferromagnetic nanoparticles.

- The synergism of magnetism and photochromism, which allows light to record and erase bits of magnetic information into individual nanocells.

- High speeds of “reading” or passing information through a nano-object, which should exceed the performance of elements of modern computers. Optical switching of the magnetic states of nanostructures is quite capable of providing high speed.

- Finally, the ability to achieve new physical qualities of photochromic ferromagnets while limiting their sizes is less than the characteristic parameters of physical processes in them (spin correlation lengths, light penetration depths, etc.).

The first results indicating the possibility of filling nanomatrices with photochromic spiropyran molecules were obtained earlier by the inventors [9] M.Zhu, L.Zhu, J.J. Han, W.Wuwei, J.K. Hurst, A.D.Q. Li, J Am Chem Soc. 2006 April 5; 128 (13), 4303.

[10]. I.Vlassiouk, Ch. Park, SAVail, D. Gust, and S. Smirnov, Nano Lett., 2006, 6 (5), 1013], which also found several specific effects caused by nanostructuring (optically switched luminescence, photocontrolled nanocontrol valves , regulating the passage of solvent molecules through nanopores, as well as photo-switching of electrical conductivity). All these results indicate that the nanostructuring of multifunctional photomagnetic compounds can also lead to the discovery of new physical effects in them.

The present invention is the creation of ordered arrays of nanostructures, in which the unit cells are nanowires of photochromic material with magnetic ordering.

The problem is solved by obtaining ordered arrays of nanowires of photochromic ferromagnets of the formula FHMe ₁ Me ₂ (C ₂ O ₄ ) ₃ ,

where M ₁ , M ₂ are 3d metals (Cr, Fe, Mn, etc.), and PF is photochromic cations. Preferably, the FCs are spirocyclic cations (spiropyranes, spiroxazines, chromenes, etc.):

The problem is also solved by the method of producing ordered arrays of nanowires of photochromic ferromagnets FHMe ₁ Me ₂ (C ₂ O ₄ ) ₃ (FH - 1- {1 ′, 3 ′, 3′-trimethyl-6-nitro-5′-spiro [2Н-1 -benzopyran-2,2′-indoline] -8yl) methyl} pyridinium) anodized alumina (AOA) incorporated into the pores with diameters of 20 nm and 200 nm. This method allows for the first time to obtain the claimed materials in the form of nanowires.

In addition, the problem is solved by the use of photomagnetics nanowires as photosensitive magnetic media for the production of materials with ultra-high magneto-optical memory.

The invention consists in the following.

In order to create an array of nanostructures satisfying the above requirements, compounds were selected as samples with the expected photomagnetic effect

- SpFeMn (C ₂ O ₄ ) ₃ with the spiropyranic cation Sp ⁺ - 1- {1 ′, 3 ′, 3′-trimethyl-6-nitro-5′-chlorospiro [2Н-1-benzopyran-2,2′-indoline ] -8-yl) methyl} pyridinium and the anion - (tris) oxalate of manganese (II) and iron (III).

- HrFeMn (C ₂ O ₄ ) ₃ with the chromene cation Hr ⁺ -7-methyl-3,3-diphenyl-3H-pyrano [3,2-f] quinolinium cation and the anion - (tris) manganese (II) oxalate and iron (III).

The reaction of obtaining micro- (Fig. 1) and SpFeMn (C ₂ O ₄ ) ₃ nanocrystals was carried out according to Scheme 1:

In a solution of open ("merocyanine" - Ms ⁺ ) form of spiropyran chloride Ms ⁺ Cl ^{- a} matrix was fixed (Scheme 3) and the solution was irradiated with constant stirring until its initial raspberry color completely changed to light green, characteristic of closed ("spiropyran" - Sp ⁺ ) forms, Sp ⁺ Cl ^- . Next, an aqueous solution of a mixture of salts of K ₃ [Cr (C ₂ O ₄ ) ₃ ] and MnCl _{2 was} poured. When methanol was removed from the reaction mixture, a bright green precipitate formed in the matrix and in the bulk of the solution. When the matrix was dried in air (at room temperature) and in daylight, the color of the precipitate changed dark red. Apparently, the reaction product formed in the pores of the matrix, in the absence of ultraviolet irradiation (UV), transfers (partially) to the compound with Ms ⁺ cation. The same effect was observed for microcrystals of the product crystallizing outside the matrix.

The reaction of obtaining micro- and nanocrystals of HrFeMn (C ₂ O ₄ ) ₃ was carried out according to scheme 2 (for chromene, the stage of irradiation of the Ms ⁺ form was not required):

A matrix was fixed in a solution of chromene chloride and an aqueous solution of a mixture of salts of K ₃ [Cr (C ₂ O ₄ ) ₃ ] and MnCl _{2 was} poured. When methanol was removed from the reaction mixture, a green precipitate formed in the matrix and in the bulk of the solution. When the matrix was dried in air (at room temperature) and in daylight, the color of the precipitate did not change. The same effect was observed for microcrystals of the product crystallizing outside the matrix.

As the matrix in which the nanocrystals of the above-described substance were grown, anodized aluminum oxide (AOA) membranes from Whatman, Grait Britain with through holes with a diameter of 20 nm and 200 nm arranged in a predictable manner (approximately in the hexagonal configuration) were used (Fig. 2). The membrane thickness was 60 μm. To obtain a membrane containing nanocrystals, chemical synthesis was carried out only on one side of the membrane. As a result of chemical reactions on the other side of the membrane, traces of a synthesized photomagnet, which were formed as a result of crystal growth through nanopores of AOA, were detected. After this procedure, macroscopic traces of the compound were carefully removed from the working surface of the membrane, and a non-working surface was used to check the pore fullness in the membrane, which remained outside the synthesis zone during the growth of nanocrystals.

Electron microscopic studies were performed on a Jeol microscope in scanning mode. Before measurements, the surface of the samples was sprayed with a thin carbon layer to create electrical conductivity. In addition to electron microscopy, surface scanning was carried out using an atomic force microscope (AWP Integra, NT-MDT).

The magnetic moments M of the powder samples were investigated using a SQUID magnetometer MPMS 5XL, Quantum Design. The dependence of the magnetic moment on temperature M (T) was measured in the temperature range T = 2-300 K with a constant magnetic field of intensity H = 1 kOe. The dependence of the magnetic moment on the magnetic field strength M (H) was measured in the field interval H = 0-50 kOe at a temperature of 2 K. The temperature during the measurement was maintained with an accuracy of 0.01 K, and the magnetic field with an accuracy of 0.1 Oe. Palladium was used as a reference sample, the magnetic susceptibility of which at T = 293.1 K was 560.1 · 10 ^-6 cm ³ / mol and corresponded to the measured value with an accuracy of 99.5%.

Figure 3 presents the results of scanning the surface of the AOA membranes using an atomic force microscope. You can see that before the reaction, the scan allows you to detect hollow holes with a diameter of 200 nm in the membrane (figure 4). After the reaction, part of the pores is filled, and filling takes place over the entire length of the pores. The only way that the observed growths could form is through the penetration of the material through the pores of the AOA. Similar results were obtained by us for AOA membranes with a pore diameter of 20 nm (not shown in Fig. 3).

Crystal structure and magnetic properties of bimetallic molecular magnets of the form A ⁺ M ^II M ^III (C ₂ O ₄ ) ₃ , where A ⁺ is a cation, M ^II and M ^III are transition metal ions. Such compounds consist of alternating layers of the anionic oxalate network of transition metals M ^II M ^III (C ₂ O ₄ ) ₃ and A ⁺ cations [14]. E. Coronado, J.-R. Galán-Mascarós, C.-J. Gómez-García, J. Ensling, P. Gutlich Chem. Eur. J.3, 6 (2000).

[fifteen]. H. Tamaki, Z.-J. Zhong, N. Matsuto, S. Kida, M. Koikawa, N. Achiwa, Y. Hashimoto, H. Okawa, J. Am. Chem. Soc. 114, 6974 (1992)]. Depending on the electronic structure of metal ions, M ^II , M ^III, at low temperatures (T <50 K), ferro [15] is observed. H. Tamaki, Z.-J. Zhong, N. Matsuto, S. Kida, M. Koikawa, N. Achiwa, Y. Hashimoto, H. Okawa, J. Am. Chem. Soc. 114, 6974 (1992)], ferromagnetic [16]. H. Tamaki, M. Mitsumi, K. Nakamura, N. Matsumoto, S. Kida, H. Okawa, S. Iijima Chem. Lett. 1975 1992, long-range ordering or state of a noncollinear antiferromagnet [17]. C. Mathoniere, J. Nutall, S.-G. Carling, P. Day, Inorg. Chem. 35 1201 (1996). In compounds where M ^II = Mn ²⁺ and M ^III = Fe ³⁺ , noncollinear antiferromagnetism is observed [14]. Coronado, J.-R. Galán-Mascarós, C.-J. Gómez-García, J. Ensling, P. Gutlich Chem. Eur. J. 3, 6 (2000)], which is characterized by the absence of saturation in the field dependence of the magnetic moment and a smooth decrease in the effective magnetic moment with decreasing temperature.

The magnetic properties of the initial microcrystalline material SpMnFe (C ₂ O ₄ ) ₃ used in our work were similar to those described in [14]. Coronado, J.-R. Galán-Mascarós, C.-J. Gómez-García, J. Ensling, P. Gutlich Chem. Eur. J. 3, 6 (2000) [17]. C. Mathoniere, J. Nutall, S.-G. Carling, P. Day, Inorg. Chem. 35 1201 (1996)]. On the dependence of the product of the magnetic moment of sample M by temperature T, a transition to the antiferromagnetic state was observed at 30–50 K (Fig. 5). Those. the MT value, proportional to the square of the effective magnetic moment, strongly deviated downward from the constant value that should have been observed for paramagnetic material. The presence of distant antiferromagnetic ordering is indicated by the dependence of the magnetic moment of sample M on the magnetic field H (Fig.6). On this dependence, in the region of H _c = 8 kOe, a fracture is observed characteristic of spin-flop transitions in noncollinear antiferromagnets. The shape of the M (H) dependence is very different from the Brillouin function expected in the case of the paramagnetic state of the material. A change in the M (H) dependence is a typical sign of a non-collinear (spin-canted) antiferromagnet in which the Dzyaloshinsky-Mori interaction leads to the existence of magnetization perpendicular to two-dimensional oxalate networks.

где N_A - число Авогадро, g=2 - g-фактор, µ_B - магнетон Бора, S_Fe=S_Mn=5/2 - спин-ионов Fe³⁺ и Mn²⁺, k - постоянная Больцмана. Теоретическое значение М оказалось близким к экспериментально определенному значению (фиг.5). О правильности такой оценки свидетельствует также взвешивание мембраны в заполненном состоянии и сравнение ее веса с пустой мембраной. Эта процедура позволяла определить количество вещества в нанопорах, которое оказалось соответствующим экспериментальному значению МТ.The dependences MT (T) and M (H) for nanowires (Figs. 5 and 6) are significantly different in comparison with microcrystalline samples. In the temperature dependence of the MT value, a smooth maximum appears at 70-100 K, and the MT decay, indicating a transition to the antiferromagnetic state, occurs at lower temperatures of ~ 20 K (Fig. 5). The dependence of the magnetic moment of the nanostructured sample degenerates into a straight line (Fig. 6), since the kink observed on the microcrystalline sample at H _c = 8 kOe disappears. Note that the temperature and field dependences of the micro- and nanostructured samples cannot be combined with each other by multiplication by a constant number. Therefore, the observed results cannot be explained by artifacts associated with incorrect determination of the mass of the samples or the additional contribution of the membrane. The dependences M (T) and M (H) were normalized by equating the magnetic moments of micro- and nanostructured samples at 300 K, i.e. in the region where the magnetic order is absent and all dimensional effects should disappear. At 300 K, an estimate of the molar magnetic moment was obtained by the formula

where N _A is the Avogadro number, g = 2 is the g factor, μ _B is the Bohr magneton, S _Fe = S _Mn = _5/2 are the spin ions Fe ³⁺ and Mn ²⁺ , k is the Boltzmann constant. The theoretical value of M turned out to be close to the experimentally determined value (figure 5). The validity of this assessment is also evidenced by weighing the membrane in the filled state and comparing its weight with an empty membrane. This procedure made it possible to determine the amount of substance in nanopores, which turned out to be consistent with the experimental MT value.

Since the transition from microcrystals (Fig. 1) to nanoscale objects (Fig. 3) leads to a change in the magnetic properties (Fig. 5, Fig. 6), it can be assumed that the sizes of the nanostructures turned out to be less than the characteristic lengths essential for establishing a long-range magnetic order in them. In turn, this can lead to the artificial specification of the main axis of the magnet along the length of the nanowires and to the suppression of the noncollinear magnetization component. Earlier in [18]. L.O. Atovmyan, G.V.Shilov, R.N. Lyubovskaya, E.I. Zhilyeva, N.S. Ovanesyan, S.I. Pirumova, I.G. Gusakovskaya, JETF Lett, 58, 766 (1993).

[19]. N.S. Ovanesyan, G.V.Shilov, N.A. Sanina, A.A. Pyalling, L.O. Atovnyan, L. Bottyán. Mol. Cryst. and Liq. Cryst, 335, 91 (1999).

[twenty]. L. Bottyán, N.S. Ovanesyan, A.A. Pyalling, N.A. Sanina, A.B. Kashuba, Hyperfine Interactions 126, 149 (2000).] It was shown that two phases with collinear and noncollinear spin orders coexist in two-dimensional networks of iron and manganese oxalates. It is possible that in our experiments, limiting the diameter of nanowires leads to a predominant growth of the collinear phase and suppression of the phase exhibiting spin-canting. This is evidenced by the absence of an inflection in the field dependence of the magnetic moment (Fig.6). In addition, a sharper temperature transition to the antiferromagnetic state near 30 K in a nanostructured material is indicative of the above point of view, compared with a diffuse transition in microcrystals due to the coexistence of two phases in them. Earlier, by the method of Mössbauer spectroscopy in the oxalate networks of iron and manganese, a regularity was observed similar to that observed in our work: with a decrease in the particle size, the contribution of the noncollinear phase decreased [18]. L. O. Atovmyan, G. V. Shilov, R. N. Lyubovskaya, E. I. Zhilyeva, N. S. Ovanesyan, S. I. Pirumova, I. G. Gusakovskaya, JETF Lett, 58, 766 (1993)].

Note that a decrease in pore diameter and, correspondingly, nanowires grown in them from 200 nm to 20 nm, did not lead to a change in the magnitude of the effect caused by nanostructuring in magnetic properties. Therefore, the critical size essential for establishing long-range magnetic order in nanowires is several hundred nanometers.

Ordered arrays of nanowires of the photochromic ferromagnet SpFeMn (C ₂ O ₄ ) ₃ , arranged in nanowires in the pores of anodized alumina, have been created. In the initial microcrystalline state, the presence of noncollinear antiferromagnetism is observed, which manifests itself in the field dependence of the magnetic moment in the form of a fracture at 8 kOe. In nanostructures, a decrease in the contribution of the noncollinear antiferromagnetic phase is observed, which leads to the disappearance of the fracture in the M (H) dependence. It is most likely that the phase growth with noncollinear ordering of spins is caused by limitations in the diameter of nanowires during synthesis.

Writing and reading information into digital matrices of photo-controlled elements can be carried out by step-by-step switching of the interference distribution of light wave energy. The wavelength of light required to switch the photomagnetic element is 300-400 nm, i.e. comparable with the distance between nanowires (100-200 nm). If desired, an exact match can be easily achieved.

Thus, the claimed invention solves the problem of creating ordered arrays of nanowires of photochromic ferromagnets. A new method for their preparation is proposed, as well as a membrane for storing magnetic information and the use of ordered arrays of photomagnetics nanowires as photosensitive magnetic media.

Claims (3)

1. Ordered arrays of photochromic ferromagnet nanowires from compounds in the form of derivatives (tris) of transition metal oxalates and cations of the spirocyclic series of the general formula FHMe ₁ Me ₂ (C ₂ O ₄ ) ₃ , where M ₁ , M ₂ are 3d metals, FH are photochromic cations representing spirocyclic cations: azomethine, metal chelates, benzoxaborins, spiropyrans, fulgimides, chromenes, fulgides, spiroperimincyclohexadienones, spirooxazines, acylaminomethylene, and having photomagnetic properties, consisting of oriented nanowires to in the pores of anodized alumina. 2. A method of obtaining ordered arrays of photochromic ferromagnet nanowires by incorporating compounds in the form of derivatives (tris) of transition metal oxalates and cations of the spirocyclic series of the general formula FHMe ₁ Me ₂ (C ₂ O ₄ ) ₃ , where M ₁ , M ₂ are 3d metals, FH is photochromic cations, which are cations of a spirocyclic series: azomethine, metal chelates, benzoxaborins, spiropyrans, fulgimides, chromenes, fulgides, spiroperimincyclohexadienones, spirooxazines, acylaminomethylene, into the pores of the anodized alumina membrane (AOA), whose density is 10 ¹¹ -10 ¹³ cm ^-2 , and the pore size is 20-200 nm. 3. The use of ordered arrays of photochromic ferromagnet nanowires from compounds in the form of derivatives (tris) of transition metal oxalates and spirocyclic cations according to claim 1 as photosensitive magnetic media for producing materials with ultra-high magneto-optical memory up to 10 ¹³ bit / cm ² .

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