Magnetic Properties Of Nanocomposites Research Articles

Influence of design and annealing parameters on measurements of AC properties of NiFe-SiO2 multilayer structures

In this article, due to the exceptionally interesting electrical and magnetic properties of nanocomposites, which include ferromagnetic materials in a dielectric matrix, multilayer NiFe-SiO2 nanocomposites were obtained. The entire sequence of technological processes using magnetron sputtering equipment in the presence of argon was presented, the aim of which was to create structures with different numbers and thicknesses of layers, as well as in two measurement configurations. Measurements of AC electrical properties were carried out in a variable temperature range, i.e. from room temperature to 373 K, using the 4-point method. The obtained measurement results were compared in terms of design parameters, such as thickness and number of layers, as well as technological parameters, such as heating duration. Structural analysis was performed using scanning electron microscopy (SEM) to investigate the effect of oxidation on the multilayer structures and to confirm the granular structure of the nanocomposite. Additionally, the chemical composition of the obtained multilayers was examined using Energy-dispersive X-ray spectroscopy (EDX). Resistive parameters were tested in the range of magnetic field induction from 0 T to 0.3 T. Based on the conductivity relationships, it was proven that a hopping mechanism of current conduction occurs in the tested samples. Using the frequency dependencies of the phase shift angle, it is possible to adjust the equivalent RC electronic circuit, thereby determining the potential application of the tested materials.

Fabrication of Multiwalled Carbon Nanotubes (MWCNT) and Reduced Graphene Oxide (rGO)‐based thermoplastic polyurethane and polypyrrole nanocomposites for electromagnetic wave absorption application with a low reflection

AbstractElectromagnetic radiation (EMR) pollution is a serious concern in today's environment, causing problems not just for electronic gadgets but also for living society. The goal of this research is to fabricate thermoplastic polyurethane (TPU) and polypyrrole (PPy)‐based 95:5 blend nanocomposites using a simple solvent casting method at such a low concentration of rGO and MWCNT (0.3, 0.4, 0.5 php) (parts per hundred polymers), for electromagnetic wave (EMW) absorption applications. The chemical interaction between the different phases and morphology of the nanocomposites is characterized by Raman spectroscopy, X‐ray diffraction (XRD), and field emission scanning electron microscopy (FESEM) techniques. The material properties, such as dielectric and magnetic properties, are analyzed in X‐band frequency (8.2–12.4 GHz). The total shielding effectiveness of (SETot) 0.5 rGO system is found to be 27 dB, whereas, for corresponding MWCNT nanocomposites, it is 26 dB. Interestingly, in 0.5 rGO nanocomposites, absorption shielding effectiveness (SEAbs) is approximately 25 dB, and reflection shielding effectiveness (SERef) is less than 2 dB, which indicates the absorption of 70% of the electromagnetic wave, and the rest gets reflected. Apart from that, the rGO‐based nanocomposites possess a greater extent of thermal stability than the corresponding MWCNT‐based nanocomposites.Highlights Fabrication of TPU‐PPy‐rGO and TPU‐PPy‐MWCNT nanocomposites by solvent casting. Low reflection of TPU‐PPy‐rGO nanocomposites with a 70% absorption rate. FESEM confirms the multilayer interface structures. Tunable Dielectric and magnetic properties of nanocomposites in X‐band. Excellent absorption dominant properties of the fabricated nanocomposites.

Observation of interfacial magnetic interaction in Eu-doped BiFeO3 and YMnO3 nanocomposites

The results of structural and magnetic properties of (1-x)Bi0.96Eu0.04FeO3-(x)YMnO3 (x = 0.0,0.25,0.50,0.75,1) nanocomposites, synthesized using physical mixing method are presented in this work. The Eu doped bismuth ferrite and yttrium manganite nanoparticles are synthesized separately and then physically mixed using hydrothermal method. The physical mixing of the parent materials helps to retain the properties of both the materials in the nanocomposites. XRD patterns show the presence of both phases (R3c and P63cm) in the nanocomposites, without any structural distortion or presence of other intermediate phases. Morphological analysis of the samples is done using FESEM and HRTEM techniques. The FESEM results show that the particles in the parent as well as nanocomposites are irregularly distributed with agglomeration of particles in Eu doped BiFeO3 and the nanocomposite (BY-50). The interplanar distances corresponding to crystal planes of both phases are calculated for BY-50 nanocomposite from the HRTEM results. Chemical state analysis of BY-50, using XPS confirms the formation of nanocomposite. Multiple valence states for Fe (Fe2+ and Fe3+) and Mn (Mn2+, Mn3+ and Mn4+) are formed as a result of charge compensation phenomenon. The dominant Fe3+ and Mn3+ plays an important role in the magnetic properties of nanocomposites. Magnetic studies on the parent as well as the nanocomposites are done using room-temperature VSM. The M−H loops show wasp-waisted nature with the presence of weak ferromagnetism along with anti-ferromagnetic or paramagnetic ordering. The constricted nature of loops has been confirmed using ΔH (loop-width) versus M (magnetization) loops. The addition of YMnO3 in the nanocomposites slightly increases the maximum magnetization from 0.149 emu/g for Eu doped BiFeO3 nanoparticles to 0.364 emu/g for BY-75 nanocomposites. The maximum magnetization in the nanocomposites increases because of the constructive alignment of the spins at the interface. The presence of interfacial magnetic interaction in the samples has been corroborated through room-temperature X-band ESR analysis.

Metal oxide decorated polyaniline based multifunctional nanocomposites: An experimental and theoretical approach

When combined with metal oxide nanoparticles, conducting polymers may result in unique or synergistic effects in their properties. Fe/Mn/CuO/PANI (FMC/PANI) based nanocomposites (NCs) were explored for five different novel applications. FTIR, UV–visible, XRD, Raman, and FESEM methods were used to identify the NCs. The anti-corrosive, photocatalytic, magnetic, antibacterial, and electrical properties were investigated by experimental and theoretical (DFT) methods. The computational technique was used for frequency, geometry optimization, and energy study. Different thermodynamic, kinetic, and molecular orbital parameters were investigated by the DFT study for the NCs. The anti-corrosive, photocatalytic, antibacterial, electrical, and magnetic properties of NCs were investigated at different concentrations. The FMC/PANI NCs show a maximum of 85 ± 0.2% CIE for MS in 1.0 M HCl solution. The magnetic study proves the paramagnetic nature of NCs. The photocatalytic activity of FMC/PANI NCs was investigated against MO dye under UV light. The antibacterial property of FMC nanoparticles (NPs) was investigated against gram-positive and gram-negative bacterial strains, that is, B. subtilis and E. coli, respectively. The ZOI was compared with six standard antibiotics and found to be comparable with common antibiotics. The FMC/PANI-based NCs were proven to be perfect photocatalytic, magnetic, antibacterial, electrical conductors, and anti-corrosive agents.

Magnetic- and light-responsive shape memory polymer nanocomposites from bio-based benzoxazine resin and iron oxide nanoparticles

Shape memory polymers (SMPs) are a class of smart materials that can be programmed to recover from temporary shape to permanent shape by applying external stimuli (temperature, magnetic field, light, electric field, and moisture, etc.). This unique property of SMPs makes them an appealing candidate in application for soft robotics, such as smart actuators, artificial muscles, and biomedical devices. In this contribution, we have developed multi-stimuli-responsive SMPs from bio-based benzoxazine resin and iron oxide nanoparticles (Fe3O4 NPs) that could be actuated by magnetic field and light. The nanocomposites were characterized by infrared spectroscopy, in which molecular interaction between benzoxazine/epoxy copolymers and Fe3O4 NPs was observed. Effects of nanoparticle content (0–5 wt%) on magnetic, mechanical, thermal, and thermo-mechanical properties of nanocomposites were investigated. Shape memory performance of nanocomposites was significantly improved with incorporation of Fe3O4 NPs. Shape fixity increased from 85% of neat copolymers to 93% of copolymers filled with 3 wt% Fe3O4 NPs, while shape recovery increased from 94% to 98%. Moreover, shape fixity could be done without external force contact by 808 nm-light actuation and magnetic attraction, due to photothermal and magnetic properties of nanocomposites. Shape recovery was tested under actuation by magnetic field. The highest shape recovery ratio was 99% within 26 s for copolymers filled with 5 wt% Fe3O4 NPs. Lastly, preliminary application of nanocomposites was demonstrated as they could push a 1 g-object within 10 s of actuation by magnetic field. In overall, these nanocomposites with multi-stimuli-responsive shape memory property had a good potential to be applied for soft robotics.

Tuning magnetic and luminescent properties of iron oxide@C nanoparticles from hydrothermal synthesis: Influence of precursor reagents

Magneto-luminescent nanocomposites were obtained by coating coprecipitated iron oxide nanoparticles with a functionalized carbon layer by hydrothermal treatment, using different organic precursors (D-glucose and p-phenylenediamine). The nanomaterials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), RAMAN, infrared (FTIR), UV-vis and photoluminescence (PL) spectroscopic analysis, vibrating sample magnetometry (VSM) and zetametry. Remarkable contrasting changes in the structural and magnetic properties of nanocomposites were identified after the carbon coating, which was directly related to the precursor used. Crystalline phase transformations were observed with a decrease in the saturation magnetization (-80%) using p-phenylenediamine and an increase (+22%) using glucose, relative to uncoated magnetic core. The distinct photoluminescent properties with multicolored emissions on long-wavelength are ascribed to the carbon shell and to the chemical moieties, such as amino, carbonyl, carboxylate, and hydroxyl groups on the surface. This makes it possible for different surface states to be responsible for emission, and these chemical groups are also responsible for a higher colloidal stability of nanocomposites in alkaline medium. The tunability of the properties of nanocomposites from the conditions of synthesis opens a wide range of applications for these nanomaterials, such as ion detection, magnetohyperthermia, and theranostics.

Impact of the indium content on structural, magnetic, and electrodynamic properties of nanocomposites based on In-substituted Sr hexaferrite and Ni–Zn spinel ferrite with excellent absorption characteristics

SrInxFe12-xO4/Ni0.5Zn0.5Fe2O4 (0.00 ≤ x ≤ 0.04) nanocomposites (SIFO/NZFO NCs) were synthesized using a one-pot sol-gel auto-combustion technique. The EDX method was used to verify the chemical composition. An X-ray diffractometer (XRD) was used for the structural analysis. Scanning electron microscopy (SEM) was used to study the morphological characteristics. The impact of indium doping on the magnetic properties of the nanocomposites was investigated using magnetization measurements at T = 300. A kink was observed in the M − H curves for lower indium content (x ≤ 0.02), which was suppressed with further increasing indium content until it vanished at a higher content. A single peak at a higher indium content replaced two peaks at a lower indium content (x 0.02), according to the switching field distribution (i.e., dM/dH vs. H). When the indium concentration increased, the saturation, remanence magnetization, and coercive field increased until x = 0.01, and then decreased, according to the analysis of the M − H loops. The obtained results reveal that an exchange interaction at the surface of the SIFO and NZFO nanoparticles (NPs) exists. The degree of intergranular dipolar interactions diminishes with increasing indium content within the hard-soft ferrite SIFO/NZFO NCs and becomes insignificant at higher indium contents. Moreover, the core of the SIFO and NZFO NPs also contains magnetic super-exchange interactions between Fe and O ions. At high frequencies (2–20 GHz), a correlation was found between the hard phase composition (indium content) and electrodynamic characteristics. Analyses were performed on the evolution of essential parameters (real and imaginary permittivity and permeability) in relation to the frequency. In this frequency range, the effect of electromagnetic radiation absorption was observed. A significant level of electromagnetic absorption (>-12 dB) in the frequency range was observed for investigated nanocomposites (NCs). The NCs with lower indium content (0.00 ≤ x ≤ 0.01) have higher reflection looses coefficients (−18 … -36 dB). This opens broad perspectives for the practical application of magnetic media for intensive electromagnetic absorption.

Impact of GO on Non-stoichiometric Mg0.85 K0.3Fe2O4 Ferrite Nanoparticles

Graphene oxide (GO) nanostructures are systems with many fascinating novel properties that can be used to study new science and have significant promise for applications. In this study, graphene oxide was prepared using the modified Hummer’s method. In addition, potassium ferrite is a good candidate for biomedical application, as iron and potassium are biocompatible and non-toxic materials. Mg0.85K0.3Fe2O4/GO nanocomposites were prepared by the citrate auto-combustion method. The effect of adding GO to Mg0.85K0.3Fe2O4 on structure, morphology, electrical, and magnetic properties was discussed. Samples under investigation were characterized using XRD, infrared spectroscopy (IR), high-resolution transmission electron microscopy (HRTEM), and atomic force microscopy (AFM). The crystallite size of prepared samples was decreased from 28.098 to18.148 nm by increasing GO content. Scanning electron microscope (SEM) confirms the successful adhesion of Mg0.85K0.3Fe2O4 nanoparticles on graphene oxide sheets, which are dispersed in a metal oxide matrix. EDAX analysis confirms the existence of C, O, K, Mg, and Fe elements present in the samples. Magnetic properties were studied by VSM and Faraday's method. GO has a significant effect on the magnetic properties of nanocomposites. For instance, the saturation magnetization and Curie temperature have diverse values, which will be appropriate for numerous applications.

Single-electrode mode TENG using ferromagnetic NiO-Ti based nanocomposite for effective energy harvesting

This work presents the mechanochemical synthesis of ferromagnetic NiO-Ti-based nanocomposites and exploits them as a positive triboelectric layer to enhance the performance of a triboelectric nanogenerator (TENG). Magnetization and charge polarization play crucial roles in augmenting the triboelectric performance. Various physicochemical properties, such as structure, morphology, surface topology, and magnetic properties of nanocomposites, are presented. The fabricated single-electrode (SE) operating mode TENG device generates a voltage of 62 V and a current of 250nA. SE-TENG can power up low-power electronics such as a wristwatch and LEDs and harvest biomechanical energy from breathing (inhale and exhale) during standing, sitting, and bending positions.

Synthesis and characterization of Fe3O4–ZnS:Mn nanocomposites for biomedical applications

Fe3O4–ZnS:Mn nanocomposites were prepared by two combined chemical precipitation routes and further characterized to prove the formation of composite structure. The formation mechanism was discussed according to sequential steps of the composite formation. The crystalline structure, morphology and magnetic properties of nanocomposites were identified by XRD, TEM-HRTEM and VSM analyses respectively. The presence of ZnS:Mn shell on Fe3O4 surface was confirmed by XPS, EDX and EPR. The potential cytotoxicity of Fe3O4–ZnS:Mnx% nanocomposites has been investigated using human skin melanoma (A375) and normal human keratinocytes (HaCaT) cell lines. The cellular uptake on human skin melanoma (A375) was evidenced by CLFM and revealed that Fe3O4–ZnS:Mnx% nanocomposites penetrated the cells through endocytosis, in a concentration dependent manner. Hyperthermia measurements evidenced that Fe3O4–ZnS:Mnx% nanocomposites are adequate for magnetic hyperthermia applications. Except the latest case the Fe3O4–ZnS:Mnx% platforms are safe to use for biomedical applications as they show toxicity starting only from high concentration.

Synthesis and characterization of new bent-core liquid crystal with a ferroelectric-like switching / modified magnetite nanocomposite

A new bent-core liquid crystal (LC) compound 4-Cyano-1,3-phenylenebis[4-(4-(S)-2-Dodecyloxypropionyloxyphenoxycarbonyl)benzoate] (CyPDB) consisting of O-dodecyl lactate substituted terephthalate based rod-like units which were located at 1,3-positions of 4-cyanoresorcinol central unit has been synthesized and LC/1.0% modified Fe3O4 nanocomposite has been prepared. The effects of being the doped with 1.0% modified Fe3O4 (magnetite) nanoparticles on mesomorphic properties of the new bent-core liquid crystal, which exhibits an enantiotropic SmA phase with a ferroelectric-like switching, were investigated by differential scanning calorimetry, optical polarizing microscopy and electro-optic studies. The surface of Fe3O4 (magnetite) nanoparticles was modified with a silane surfactant, octadecyltrimethoxysilane (OTMS), used as a compatibilizer for the attractive interaction of liquid crystal molecule with Fe3O4 nanoparticles. The size, morphology and distribution of modified Fe3O4 (magnetite) nanoparticles in LC host were investigated by using Transmission Electron Microscope (TEM) and Scanning Electron Microscopy (SEM). The magnetic properties of nanocomposite were studied using a vibrating-Sample Magnetometer (VSM).

Design and Fabrication of Green Magnetic/Graphene Oxide/Chitosan/Allium sativum/Quercus/Nanocomposite: Characterization and Application

A novel nanocomposite based on green magnetic–graphene oxide—chitosan—Allium sativum—Quercus in presence of Alhagi maurorum as very effective green chemical agent was successfully synthesized and fabricated. The physicochemical properties of the fabricated nanocomposite including Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), zeta potential analyzer, Brunauer-Emmett-Teller surface area measurement (BET), scanning electron microscope (SEM), and UV-visible spectroscopy (UV) were investigated. The magnetic property of nanocomposite was also evaluated by vibrating sample magnetometer (VSM). Compared with graphene oxide and chitosan, the fabricated nanocomposite demonstrated excellent properties, which may be attributed to the fact that the structural properties of nanocomposite due to the natural components used chemically has been fundamentally promoted. According to the results, the developed nanocomposite provided the excellent feature, confirming that a more effective component for use at various industrial especially medical utilizations could be essentially considered.

Preparation and controlled inhibition behavior of Fe3O4/CS/inhibitors nanocomposite for carbon steel in 3.5% NaCl solution

The superparamagnetic Fe3O4/CS/inhibitor nanocomposite was synthesized by using ionic gel method with Fe3O4 as superparamagnetic core, chitosan as nanocarrier and molybdate (MoO42−) and benzoate (C6H5COO−) working as loaded inhibitors. The morphology, structure and magnetic property of nanocomposite were characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and vibrating sample magnetometer. The release behavior of nanocomposite with and without external magnetic field (“no MF” mode and “MF ON” mode) was conducted by UV–vis spectroscopy, and the corrosion inhibition performance of nanocomposite for carbon in 3.5% NaCl solution was investigated by polarization curve and electrochemical impedance spectrum methods. The results show that the obtained Fe3O4/CS/inhibitors was in a well-defined core-shell structure with MoO42− and C6H5COO- loaded flake-like chitosan shell stacking closely to Fe3O4 surface. Under no MF mode, the release behavior of nanocomposite was mainly ion exchange and Fickian diffusion mechanism. Under MF ON mode, the swelling of polymer chains and diffusion between magnetic nanoparticles were involved apart from the ion exchange and Fickian diffusion mechanism. With the addition of nanocomposite inhibitors in NaCl solution, the charge transfer resistance and inhibition efficiency of steel increased firstly and then decreased with the prolonging of immersion time. The highest inhibition efficiency of nanocomposite inhibitors in NaCl solution under on MF and MF ON mode was located in 30 min and 90 min respectively. The inhibition of nanocomposite for carbon steel in NaCl solution is resulting from the reduction of aggressive Cl- concentration in the solution due to the ion exchange between Cl- ions in solution and MoO42− and C6H5COO- ions in the nanocomposite, and the formation of ferric/ferrous molybdate, ferric/ferrous benzoate and basic ferric benzoate inhibition films on steel. This novel as-prepared composite owns superior loading capacity of inhibitors and its preparation process is especially simple relative to other nanocomposites in previous reported works.

Comparative Study of Structure, FMR and Magnetic Properties of Nanocomposite and Mixture Ferrite.

This investigation presents design of 20% M-type BaFe12O19 hexaferrite as a core coated by 80% MgFe2O4 spinel ferrite as a shell (〖Mg〗_80-H_20) in addition to, a mixture of 80% MgFe2O4 spinel ferrite and 20% M-type BaFe12O19 hexa-ferrite powders. The spinel and nanocompsite ferrite materials were synthesized by the wet mechano-chemical co-precipitation route and all prepared samples; spinel, nanocomposite and mixture are annealed at 1200 oC for 6 hours. The results of X-ray diffraction patterns, High Resolution Transmission electron microscope (HRTEM) images and Fourier-transform infrared spectroscopy (FT-IR) revealed the formation of two different composite materials. Comparing the FMR behavior of the nanocomposite and the mixed materials, the resonance field H_r of nanocomposite is lower than that of the mixture. This may be attributed to the effect of spring exchange coupling in the nanocomposite sample. The hysteresis loop of the 〖Mg〗_80-H_20 nanocomposite structure is similar to that of cubic spinel ferrite and exhibits the same Ms (18 emu/g) despite of its different values of Mr and Hc. Enhancing the remnant magnetization for the 〖Mg〗_80-H_20 nanocomposite and mixed materials is mainly attributed to the overcoming of magnetic exchange interaction and high magneto-crystalline anisotropy of hard phase in competition with dipolar interaction of soft phase. Comparing the FMR behavior of the nanocomposite and the mixed materials, the resonance field H_r of nanocomposite is lower than that of the mixture. This may be attributed to the effect of spring exchange coupling in the nanocomposite sample.

In English

The processes of adsorption of gemcitabine (GC) on the surface of nanosized singledomain magnetite (Fe 3 O 4 ) have been investigated. Under the experiment conditions, the value of adsorption capacity A was ~ 37.2 mg/g, the extraction extent U (%) – 33.13 %, the separation factor E = 82.58 mL/g. It has been determined that adsorption corresponds to the Freundlich model. The magnetic properties of nanocomposites (NС) Fe 3 O 4 @GC have been investigated. The average value of the thickness of the adsorbed layer of GC in the composition of Fe 3 O 4 @GC NC is 2.4±0.1 nm, as evaluated by the method of magnetic granulometry. Magnetic liquids (ML) have been synthesized based on magnetite and physiological solution (PS) stabilized with sodium oleate (Ol.Na) and polyethylene glycol (PEG), which contain GC and antibody (AB) HER2 (Fe 3 O 4 @GC/Ol.Na/PEG+PS). The properties of ML were investigated as well as cytotoxic/cytostatic activity with respect to HepG2 hepatocellular carcinoma of human liver. Parameters of ML based on magnetite were found: Fe 3 O 4 concentration – 14 mg/mL, Fe 3 O 4 particle size – 4–22 nm, average size of Fe 3 O 4 particles – 10.8 nm; the average size of Fe 3 O 4 particles stabilized with sodium oleate 16.8 nm, saturation magnetization M ∞ = 14.1±2.5 % Gs, hypsometric height – 25±10 % cm, viscosity η = 1.14±3 % mPa·s, density ρ ML = 1.14 ± 1.0 % g/cm 3 , the concentration of GC was 1.25 mg/mL, that of HER2 AB was 3.75 μg/mL. We have obtained the calculated and graphic data concerning the dependence of the surface area and the specific magnetization of saturation of Fe 3 O 4 @GC/Ol.Na/PEG on the thickness of GC layer, which can be useful for predicting of the nanoscale architecture of magnetically sensitive NC and ML in the manufacture of relative drugs. The synergistic nature of the influence of GC/Fe 3 O 4 /HER2 complex on HepG2 cells was revealed. It has been determined that IC50 for ML is 0.155 mg/mL, in the range of concentration of 0.025–0.1 mg/mL ML it is biocompatible with HepG2 cells. It has been shown that HER2 AB used alone in the investigated concentrations does not affect HepG2 cell viability/proliferation. In vitro, GC inhibits the proliferation of liver carcinoma cells, the IC50 value was 0.02 mg/mL. The use of ML in complex with GC can increase the cytotoxic activity of the composite by 8–10 %. The ML+GC+HER2 AB complexes caused the synergistic effect and an increase in the cytotoxic activity, compared with GC used alone, up to 18–20 %, while GC contents reduced to 0.008 mg/mL. The results of the studies indicate that the use of ML based on magnetite, gemcitabine, and antibody increases the effectiveness of the antitumor medicines with a significant reduction in their dose and, respectively, the toxico-allergic reactions of the body, and nanosized magnetite can be promising for the manufacture of magnetically sensitive adsorption materials for medical purposes, e.g. for detoxification of an organism after GC therapy.

Dielectric and Magnetic Properties of Nanocomposites Based on Opal Matrixes, Phosphates and Vanadates of Metals

Opal matrix is a regular 3D-packing of spherical particles of amorphous SiO2, forming an ordered system of voids. Opal matrixes with spherical particles of SiO2 diameter d ≈ 260 nm (Δd ≈ 2 %) were synthesized. The frequency dependences of the conductivity, real and imaginary components of the dielectric and magnetic conductivity of nanocomposites containing crystallites 16–65 nm in size of magnetic materials ‒ double phosphates (LiNiPO4, LiCoPO4) and vanadates (GdVO4 and DyVO4) were measured. The dielectric losses of nanocomposites remain low (at a level of ~ 0.06) in the frequency range 107–1010 Hz for nanocomposites with DyVO4 and LiCoPO4. The dielectric loss increases both in the direction of low frequencies (< 106 Hz) and in the direction of THz frequencies.

Preparation and properties of polyimide-based nanocomposites containing functionalized Fe3O4 nanoparticles

Polyimide (PI)/Fe3O4 nanocomposites were successfully prepared via the thermal curing of different amounts of Fe3O4 nanoparticles (2, 4, 6 and 8 wt%) functionalized by 3-aminopropyltriethoxy silane as a coupling agent, containing the poly(amic acid) derived from 5-diamino- N-(4-(4,5-diphenyl-1H-imidazol)phenyl)benzamide and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride. The effect of Fe3O4 nanoparticles on the structural, thermal and magnetic properties of nanocomposites was investigated. The Fourier transform infrared spectroscopy and scanning electron microscopy (SEM) results reveal that the surface of Fe3O4 nanoparticles is sufficiently compatible with PI through linkage of the coupling agent between Fe3O4 and the polymer. Also, the SEM image shows that Fe3O4 nanoparticles are dispersed uniformly in the polymer matrix, with a particle size of around 78 nm. The nanocomposites of 2 and 8 wt% exhibit the saturation magnetization values of 0.055 and 0.170 emu g− 1, respectively. The thermogravimetric analysis data show that the thermal stability of the nanocomposites is improved as compared to the pure PI.

Symmetrized Maxwell–Garnett Approximation as an Effective Method for Studying Nanocomposites

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.

Surface modification and polymerization on iron oxide nanoparticles obtained from mineral magnetite

Surface modified iron oxide nanoparticles with polymers have been used in the last years in different biomedical applications. In this work, iron oxide nanoparticles from mineral magnetite have been modified with an initiator of polymerization by two methods, direct and ligand exchange. The infrared analysis shows two types of bonds, unidentate and bidentate. Thermogravimetric analysis indicates that the ligand-exchange is four times better in the incorporation of organic molecules and transmission electron microscopy shows there fewer agglomerates by this method. The activity of the nanoparticles in fronts to a surface polymerization with n-butyl methacrylate monomer was developed. The polymeric nanocomposite was characterized by X-ray diffraction, infrared spectroscopy, Raman spectroscopy, and thermal analysis. A shifted of the signal of polymer to lower degree indicates an interaction between inorganic material and polymer. The magnetic properties of nanocomposite were studied by vibrating sample magnetization where is possible appreciate a Langevin curve with a superparamagnetic behavior and a magnetization remanence (Ms/Mr) under 0.01.

Строение, диэлектрические и магнитные свойства нанокомпозитов на основе опаловых матриц, фосфатов и ванадатов металлов.

Строение, диэлектрические и магнитные свойства нанокомпозитов на основе опаловых матриц, фосфатов и ванадатов металлов.