Статті в журналах з теми "Magneto-dielectric Properties - Nanocomposites"

The aim of this work was to comprehensively study the effect of the variable atomic composition and structural-phase state of Cox(MgF2)100-x nanocomposites on their nonlinear transport and magnetic/magneto-optical properties. Micrometer-thick nanocomposite layers on glass substrates were obtained by means of ion-beam sputtering of a composite target in the argon atmosphere in a wide range of compositions (x = 16–59 at.%). Using a low metal content in the nanocomposite, magnesium fluoride was kept in the nanocrystalline state. As the metal content increased, nanocrystalline cobalt was formed. The value of the resistive percolation threshold, xper = 37 at.%, determined from the concentration dependences of the electrical resistance of the nanocomposites coincided with the beginning of nucleation of the metallic nanocrystals in the MgF2 dielectric matrix. The absolute value of the maximum negative magnetoresistive effect in the nanocomposites was 5% in a magnetic field of 5.5 kG at a Co concentration of x = 27 at.%.

In the present study two sets of nanocomposites consisting of an epoxy resin and BaFe12O19 or SrFe12O19 nanoparticles were successfully developed and characterized morphologically and structurally via scanning electron microscopy and X-ray diffraction spectra. The dielectric response of the nanocomposites was investigated by means of broadband dielectric spectroscopy and their magnetic properties were derived from magnetization tests. Experimental data imply that the incorporation of the ceramic nanoparticles enhances significantly the dielectric properties of the examined systems and their ability to store electrical energy. Dielectric spectra of all systems revealed the presence of three distinct relaxation mechanisms, which are attributed both to the polymer matrix and the nanoinclusions: Interfacial polarization, glass to rubber transition of the polymer matrix and the re-orientation of small polar side groups of the polymer chain. The magnetic measurements confirmed the ferromagnetic nature of the nanocomposites. The induced magnetic properties increase with the inclusion of hexaferrite nanoparticles. The nanocomposites with SrFe12O19 nanoparticles exhibit higher values of coercive field, magnetization, magnetic saturation and remanence magnetization. A magnetic transition was detected in the ZFC/FC curves in the case of the BaFe12O19/epoxy nanocomposites.

Zinc oxide doped magnesium ferrite (Mg1-xZnxFe2O4) nanocomposite was synthesized using sol-gel method and demonstrated to have a cubic spinel structure, with a range of crystallite sizes (19-40 nm) and lattice constants (8.432-8.399 Å). The material was found to have two prominent vibrational modes for tetrahedral (446 cm–1) and octahedral (584 cm–1). The dielectric constant was higher at low frequencies and decreased at higher frequencies, while the saturation magnetization decreased (16 to 6 emu/g) gradually with an increase in Zn2+, likely due to the presence of non-magnetic Zn2+. The magneto-dielectric constant was found to increase with the magnetic field for MgFe2O4 and up to a magnetic field of 2000 Oe for the zinc magnesium nanocomposites, after which it decreased for higher magnetic fields. A positive and negative change in magneto-capacitance as a function of the magnetic field was also observed. The antibacterial activity suggests that the substitution of Zn2+ into magnesium ferrite can be an effective method for improving antibacterial activity, with the potential to damage the bacterial membrane and other components through positively charged ions and ROS generated by nanoparticles. Potential uses for this synthetic material include magneto-optical recording and magnetic biosensors.

In this study nanocomposites consisting of an epoxy resin and ceramic zinc ferrite nanoparticles have been successfully developed and investigated morphologically and structurally by means of scanning electron microscopy (SEM) images and X-ray diffraction (XRD) spectra. The thermal properties of the nanocomposites were studied via differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The thermomechanical characterization of the fabricated nanocomposites was studied via dynamic mechanical analysis (DMA) and the magneto-dielectric response was assessed by means of a broadband dielectric spectroscopy (BDS) and by employing a superconducting quantum interference device (SQUID) magnetometer. Data analysis demonstrates that the incorporation of nanoinclusions into the matrix improves both the thermomechanical and the dielectric properties of the systems, as indicated by the increase of the storage modulus, the real part of dielectric permittivity and conductivity values with filler content, while at the same time induces magnetic properties into the matrix. Zinc ferrite nanoparticles and their respective nanocomposites exhibit superparamagnetic behavior at room temperature. Three relaxations were recorded in the dielectric spectra of all systems; originating from the filler and the polymer matrix, namely interfacial polarization, glass to rubber transition of the polymer matrix and the reorientation of small polar side groups of the polymer chain.

The symmetrized Maxwell-Garnett (SMG) approximation is considered as the most optimal method of an effective medium for the description of nanocomposite structures. This approximation takes into account the microstructure of the sample, which makes it possible to calculate the metal-dielectric system. Thus, SMG describes with good accuracy the structure of the nanocomposite. Besides, this approximation is applicable for granular alloys consisting of metal components. As a result, this technique can be considered as a universal approximation to describe a wide class of nanostructured materials. At the same time, this article discusses various methods of effective environment. In these methods, the metal component of nanocomposites and the dielectric matrix are replaced by an effective medium with effective permittivity εeff. It is necessary that the particles (granules) in such structures be small in comparison with the wavelength of electromagnetic radiation incident on the sample. Based on this, the spectral dependences of the transverse Kerr effect (TKE) in magnetic nanocomposites were calculated with (CoFeZr)(Al2O3) structure as an example at different concentrations of the magnetic component. The simulation was carried out at small and large concentrations (below and above the percolation threshold). The spectral dependences were obtained taking into account the form factor of nanoparticles and the quasi-classical size effect. Besides, the authors note and discuss in this paper the contribution of various mechanisms that affect the type of spectra of the transverse Kerr effect. Using the symmetrized Maxwell-Garnett approximation, the effective values of the granule size of the nanocomposites under study were found, and the tensor of effective dielectric permittivity (TEDP) was calculated. The obtained TEDP values allowed to simulate the spectral dependences of the magneto-optical transverse Kerr effect. The authors discuss and draw conclusions about the features of the obtained spectral dependences in both the visible and infrared regions of the spectrum. In addition, the practical and fundamental importance of the obtained results is noted. The importance of effective medium methods for the study of optical, transport and magneto-optical properties of magnetic nanocomposites is shown.

The results of complex studies of structural-phase transformations and magneto-optical properties of nanocomposites (CoFeZr)x (MgF2)100−x depending on the metal alloy content in the dielectric matrix are presented. Nanocomposites were deposited by ion-beam sputtering onto glass and glass-ceramic substrate. By studying the spectral and field dependences of the transversal Kerr effect (TKE), it was found that the transition of nanocomposites from superparamagnetic to the ferromagnetic state occurs in the region of xfm~30 at%, that corresponds to the onset the formation of ferromagnetic nanocrystals CoFeZr with hexagonal syngony in amorphous dielectric matrix of MgF2. With an increase of concentrations of the metal alloy for x > xfm, the features associated with structural transitions in magnetic granules are revealed in the TKE spectra. Comparison of the spectral and concentration dependences of TKE for nanocomposites on the glass and glass-ceramics substrates showed that the strongest differences occur in the region of the phase structural transition of CoFeZr nanocrystals from a hexagonal to a body-centered cubic structure at x = 38 at.% on the glass substrates and at x = 46 at.% on glass-ceramics substrates, due to different diffusion rates and different size of metal nanocrystals on amorphous glass substrates and more rough polycrystalline glass-ceramics substrates.

The aim of this work is a comprehensive study of the effect of variable atomic composition and structural-phase state of (CoFeZr)x(MgF2)100−x nanocomposites (NCs) on their nonlinear electronic and magnetic/magneto-optical properties. Micrometer-thick nanocomposite layers on the glass substrates were obtained by ion-beam sputtering of a composite target in the argon atmosphere in a wide range of compositions x = 9–51 at·%. The value of the resistive percolation threshold, xper = 34 at·%, determined from the concentration dependencies of the electrical resistance of NCs, coincides with the beginning of nucleation of metallic nanocrystals CoFeZr in MgF2 dielectric matrix. The absolute value of maximum magnetoresistance of NCs is 2.4% in a magnetic field of 5.5 kG at x = 25 at·%, up to the percolation threshold. Two maxima appear in the concentration dependencies of magneto-optical transversal Kerr effect, one of which, at x = 34 at·%, corresponds to the formation of CoFeZr alloy nanocrystals of a hexagonal structure, and the second one at x = 45 at·% corresponds to the phase transition of nanocrystals from a hexagonal to a cubic body-centered structure. The magnetic percolation threshold in (CoFeZr)x(MgF2)100−x system at xfm = 34 at·%, with the appearance of a hysteresis loop and a coercive force of Hc ≈ 8 Oe, coincides with the resistive percolation threshold xper = 34 at·%. Concentration dependence of the coercive force showed that at low contents of metallic alloy x < 30 at·%, NCs are superparamagnetic (Hc = 0). With an increase of the alloy content, in the region of magnetic and resistive percolation thresholds, NCs exhibit a magnetically soft ferromagnetic character and do not change it far beyond the percolation threshold, with the maximum value of the coercive force Hc < 30 Oe.

Recently, designers of electronic equipment have paid special attention to the issue of electromagnetic compatibility (EMC) of devices with their own components and assemblies. This is due to the high sensitivity of semiconductor microcircuits to electromagnetic interference. This interference can be caused either by natural phenomena, such as lightning strikes, or by technical processes, such as transients in circuits during fast periodic or random switching. Either way, interference implies a sudden change in voltage or current in a circuit, which is undesirable, whether it propagates along a cable or is transmitted as an electromagnetic wave. The purpose of this article is to review the works devoted to the development, creation, and investigation of modern polymeric nanocomposite materials used for shielding electromagnetic radiation and their effective application for solving problems of electromagnetic compatibility. Additionally, the approach to design EMI shielding complex media with predetermined parameters based on investigation of various properties of possible components is shown. In the review, all polymer composites are classified according to the type of filler. The issues of the interaction of a polymer with conductive fillers, the influence of the concentration of fillers and their location inside the matrix, and the structure of the nanocomposite on the mechanisms of electromagnetic interaction are considered. Particular attention is paid to a new generation of nanocomposite materials with widely adjustable electrical and magnetic properties. A wide class of modern filled polymeric materials with dielectric and magneto-dielectric losses is considered. These materials make it possible to create effective absorbers of electromagnetic waves that provide a low level of reflection coefficient in the microwave range. The model mechanisms for shielding electromagnetic radiation are considered in the paper. A detailed review of the electro-physical properties of polymer nanocomposites is provided. Multilayer electrodynamic media containing combinations of layers of filled polymer composite materials with nanoparticles of different compositions and manufactured using a single technology will make it possible to create electrodynamic media and coatings with the required electro-physical characteristics of absorption, transmission, and reflection. Within the framework of the two-layer coating model, the difference in the effects of the interaction of electromagnetic radiation with conductive layers located on a dielectric and metal substrate is demonstrated. It is shown that in order to achieve optimal (maximum) values of reflection and absorption of electromagnetic radiation in the appropriate frequency range, it is necessary to fit the appropriate layer thicknesses, specific conductivity, and permittivity. Such approach allows designers to create new shielding materials that can effectively vary the shielding, absorbing, and matching characteristics of coatings over a wide frequency band. In general, it can be said that the development of innovative polymer composite materials for shielding electronic devices from electromagnetic interference and excessive electromagnetic background is still an important task. Its solution will ensure the safe and uninterrupted operation of modern digital electronics and can be used for other applications.

Magnetic properties in amorphous multilayer nanostructures [(CoFeB)60C40/SiO2]200 and [(CoFeB)34(SiO2)66/C]46 with different content of the CoFeB magnetic alloy in metal-composite layers and inverse location of non-metallic phases C and SiO2 in composite layers or in interlayers, were investigated by magneto-optical methods in the transversal Kerr effect (TKE) geometry.Using the spectral and field dependences of the transversal Kerr effect TKE, it has been established that in the samples of both magnetic multilayer nanostructures (MLNS) the magneto-optical response and magnetic order are determined by the phase composition of the composite layers.In samples of MLNS [(CoFeB)60C40/SiO2]200 with a post-percolation content of metal clusters in metal-composite layers, the maximum of absolute TKE values decrease by about 2.5 times compared with the initial amorphous Co40Fe40B20 alloy, while the field dependences of TKE in samples of this MLNS has features that are characteristic of soft ferromagnets.In samples of MLNS [(CoFeB)34(SiO2)66/C]46 with a pre-percolation content of metal clusters in the oxide SiO2–x matrix of metal-composite layers, the TKE spectral dependences fundamentally differed from the TKE of the initial amorphous Co40Fe40B20 alloy both in shape and sign. 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Hybrid nanocomposites with barium ferrite and barium titanate nanoparticles embedded within an epoxy resin matrix, were prepared and studied, varying the fillers content. The morphology of the fabricated specimens was examined by means of scanning electron microscopy and energy dispersive X-ray spectroscopy. Dielectric and magnetic properties of the nanocomposites were investigated via broadband dielectric spectroscopy and magnetization tests, respectively. Fine dispersions of nanofillers were detected via electron microscopy in all studied cases. Dielectric permittivity increases with diminishing frequency and increasing temperature and filler content. Recorded relaxation processes are attributed to interfacial polarization, between matrix and nanoparticles, glass to rubber transition of the polymer matrix (α-relaxation), and re-arrangement of polar-side groups of the main polymer chain (β-relaxation). Magnetization and magnetic saturation increase with the amount of barium ferrite nanoparticles.

A heterostructured nanocomposite MCM-41<SFA> was formed using the encapsulation method, where a silicon dioxide matrix—MCM-41 was the host matrix and synthetic fulvic acid was the organic guest. Using the method of nitrogen sorption/desorption, a high degree of monoporosity in the studied matrix was established, with a maximum for the distribution of its pores with radii of 1.42 nm. According to the results of an X-ray structural analysis, both the matrix and the encapsulate were characterized by an amorphous structure, and the absence of a manifestation of the guest component could be caused by its nanodispersity. The electrical, conductive, and polarization properties of the encapsulate were studied with impedance spectroscopy. The nature of the changes in the frequency behavior of the impedance, dielectric permittivity, and tangent of the dielectric loss angle under normal conditions, in a constant magnetic field, and under illumination, was established. The obtained results indicated the manifestation of photo- and magneto-resistive and capacitive effects. In the studied encapsulate, the combination of a high value of ε and a value of the tgδ of less than 1 in the low-frequency range was achieved, which is a prerequisite for the realization of a quantum electric energy storage device. A confirmation of the possibility of accumulating an electric charge was obtained by measuring the I-V characteristic, which took on a hysteresis behavior.

AbstractSolid polymer electrolytes are an intriguing technology in terms of magneto‐opto electronic applications due to having a high dielectric constant, a small band gap, and excellent magnetic characteristics. In order to improve structural, optical, dielectric, conductivity, and magnetic characteristics, this research seeks to prepare nickel ferrite (NiFe2O4) nanoparticles and polyvinylalcohol (PVA)/carboxymethyl cellulose (CMC) films containing NiFe2O4. Nanoparticles of NiFe2O4 are prepared using the co‐precipitation method. The CMC/PVA–NiFe2O4 nanocomposites films are prepared using casting solution. To improve their structural, optical, conductivity, dielectric, and magnetic characteristics, these films electrolytes were examined using XRD, TEM, FT‐IR, UV–vis, and VSM measurements. According to the XRD analysis, the CMC/PVA blend polymer matrix demonstrates a considerable increase in amorphous nature with the NiFe2O4 nanoparticles (NPs) content, producing a highly flexible polymer backbone, increasing ionic conductivity of the CMC/PVA–NiFe2O4 nanocomposite films. The complexation of dopant cations with the CMC/PVA polymer matrix's backbone is confirmed by the FT‐IR spectroscopy. According to the UV–visible technique, the dopant NiFe2O4 concentration considerably affects the optical energy band gap, and Urbach energy of the pure CMC/PVA. At higher loading, these effects are more pronounced. At room temperature, ac conductivity, the dielectric behavior, and electrical modulus formalism were studied. The blend's highest AC conductivity is 4.77 × 103 S/cm. After increasing the loading of NiFe2O4 to 1.5 wt%, it increased to 8.07 × 104 S/cm. There has also been research on dielectric permittivity and electric modulus to further understand conductivity relaxation and charge storage qualities. The polymer nanocomposite, generally, displayed better optical, dielectric constant, conductivity, and magnetic characteristics compared to pure CMC/PVA being useable in terms of high energy storage nanoelectronics' manufacturing.Highlights NiFe2O4 nanoparticles were prepared by using the co‐precipitation method. Nanocomposite films of CMC/PVA–NiFe2O4 were successfully prepared by casting method. XRD patterns confirmed the increase in the degree amorphousity for nanocomposites films compare pure blend. From optical energy gap results for samples prepared was enhanced after addition NiFe2O4. The dielectric and magnetic properties showed that all nanocomposites films exhibited enhanced as compared to pure CMC/PVA film.

AbstractFacile assembly, co-precipitation, and drop casting procedures have been used to construct SnO2/SrSnO3/Fe3O4/PVDF flexible nanocomposites. SnO2/SrSnO3/Fe3O4 nanocomposites (TSF NCs') have been successfully incorporated into polyvinylidene fluoride polymers (PF), according to the microstructural exploration of the systems, which was revealed by XRD, EDX, and ATR-FTIR analysis. The FESEM and cross-section areas demonstrated that the addition of TSF NCs' to PF porous material enhanced its surface characteristics and decreased its surface roughness. The optical gap was lowered from 3.90 to 3.07 eV, and it was discovered that both the refractive index and optical conductivity had improved when TSF NCs' were incorporated into PF. According to the observations, the supplement ratios have a profound influence on the dielectric properties of the nanocomposites. Moreover, the electrical parameters of TSF/PF nanocomposite are significantly modified. The TSF/PF magnetic nanocomposite has good magnetic reactivity and can be easily extracted from the aqueous solution using an external magnetic field, as demonstrated by VSM. This research has been conducted to obtain TSF/PF nanocomposites to be used in promising magno-optoelectronic applications.