Polydimethylsiloxane based magnetoactive elastomers demonstrate above the melting transition range (e.g. at room temperature) an induced uniaxial magnetic anisotropy, which grows with increasing ...magnetic field. By freezing a material down to 150 K, displaced iron microparticles are immobilized, so that the magnetic anisotropy can be measured. Magnetic anisotropy “constant” is a consequence of particle displacements and a characteristic of the energy of internal deformations in the polymer matrix. The maximum anisotropy constant of the filling is at least one order of magnitude larger than the shear modulus of the pure elastomer (matrix). In a magnetic field, the gain in the rigidity of the composite material is attributed to the magnetomechanical coupling, which is in turn a source of anisotropy. The concept of effective magnetic field felt by the magnetization allows one to explain the magnetization curve at room temperature from low-temperature measurements. The results can be useful for developing vibration absorbers and isolators.
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•Magnetic anisotropy induced by a magnetic field is experimentally observed.•To investigate magnetic anisotropy, a sample was frozen in a magnetic field.•Magnetic anisotropy “constant” depends on the magnitude of the magnetic field.•Magnetic anisotropy is a characteristic of internal deformations of the polymer matrix.•Effect of the effective magnetic anisotropy field on the magnetization is found.
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•The effect of blocking of particles displacement in MAE was observed from ZFC-FC.•M-H loops change the shape at solidification temperature of MAE.
The magnetization of a ...magnetoactive elastomer (MAE) with microparticles of soft magnetic carbonyl iron embedded in a highly elastic matrix has been studied. It is shown that at high temperatures its magnetization curve has the form of a specific hysteresis loop. This hysteresis is attributed to the influence of displacement of magnetized particles in the elastically soft elastomer matrix under the effect of magnetic forces, leading to the change of magnetic interaction between the particles. In this case, there is a maximum in the field dependence of the magnetic susceptibility, the occurrence of which has been associated with the competition between re-arrangement of particles, when they are displaced in a magnetic field, and saturation of particles’ magnetization. When the MAE is cooled below approximately 225 K, both the magnetic hysteresis and the maximum in the field dependence of the magnetic susceptibility disappear. When the MAE material is cooled below the solidification temperature of the elastomer matrix, the displacements of the magnetic particles during magnetization are blocked by the rigid matrix. The magnetization reversal of the MAE is reversible. This means that the shape of subsequent magnetization loops remains constant and the sample returns into the initial non-magnetized state after the magnetic field is turned off.
•structure and microwave properties of epoxy resin composites with graphite nanoplatelets decorated by FeNi nanoparticles.•The graphite phase i the investigated nanopowder is predominant, and ...Fe20Ni80 component contains fcc FeNi3.•decoration of the GNPs surface by Fe20Ni80 nanoparticles leads to an essential improvement of EMR absorption properties of composites in high frequency range.
This paper is concerned with investigation of the structure and microwave properties of epoxy resin composites with graphite nanoplatelets (GNPs) decorated by FeNi nanoparticles prepared by the salt impregnation. It was confirmed by SEM and XRD that the method gives nanopowder where the metal componentFe20Ni80 is in the form of nanoparticles (20–40 nm in diameter) which are distributed over the surface and edges of the GNPs. The graphite phase in the investigated nanopowder is predominant, and Fe20Ni80 component mainly contains fcc FeNi3. Measurements of magnetic properties confirmed that Fe20Ni80 are small, randomly oriented assembly of spherical (or close to spherical) particles on the GNPs surface. The saturation magnetization of GNP-Fe20Ni80 particles is 25 emu/g and it weakly depends on temperature. Electrical resistivity measurements have shown that decoration of GNPs leads to essential increase of conductivities well as improvements EMR absorption properties in high frequency range (26–60 GHz) in (GNP-Fe20Ni80)/with in compression GNP/epoxy under the same volume content of 1.45 vol.%(GNP-Fe20Ni80)/L285 composites demonstrated superior broadband absorption properties with microwave absorption efficiency higher than 97% in the whole investigated frequency region.The effective absorption bandwidths are as high as 12.2 GHz were observed at the frequency range 41.9 and 53.2 GHz and 13.3 GHz at the frequency range 51.1 GHz–64.4 for this composite. It is assumed that decoration of GNPs surface by nanoscale Fe20Ni80 particles leads to a formation of the multiple dielectric and magnetic loss mechanisms, such as interfacial polarization, dipole polarization, space-charge polarization, eddy current loss, Debye dipolar relaxation, natural resonance and exchange resonance, which improve the microwave absorption properties of the investigated composites.
The aim of the article was to conduct a comparative legal analysis of the features and problems of criminal prosecution of legal entities for environmental crimes. The research objectives were ...fulfilled through modern methods of cognition. The leading practical method was the method of observation. The study allowed to form a conceptual understanding of theoretical ideas about environmental crimes of legal entities in Ukraine. Currently, Ukraine is trying to focus in its legislative innovations on the implementation of progressive approaches to the introduction of a comprehensive institution of criminal law measures regarding the liability of these entities. Relevant legal mechanisms and comments identified in the practice of the European Union and substantiated by scholars, can be implemented in the legislation of Ukraine. Amendments to the rules governing the procedure for effective prevention of environmental crimes by legal entities are proposed. It seems reasonable to introduce an active monitoring analysis of anthropogenic activities of companies, and the creation of special units to identify relevant violations. The mechanisms for implementing the set of preventive and monitoring measures outlined in the article, set the background for further scientific research.
Abstract
Principal factors leading to the efficient alternating current (AC) field‐induced heating of magnetic fluids are determined based on the results of magnetic and calorimetric measurements on ...NaFeO
2
nanoparticles and their fluids. Features of the magnetic behavior are singled out, and characteristic magnetic parameters, such as the Curie and blocking temperatures, are determined for the NaFeO
2
nanoparticles. The dependence of the fluid caloric properties on the AC magnetic field amplitude and nanoparticle concentration is analyzed. It is shown that the heating efficiency of the weakly coercive NaFeO
2
nanoparticles displays an amplitude threshold character, and the heating rate is critically dependent on the AC magnetic field amplitude.
The X-ray diffraction, Raman and infrared spectroscopies and magnetic measurements were used to explore the correlated changes of the structure, lattice dynamics and magnetic properties of the LuFeO3 ...nanoparticles, which appear in dependence on their sintering temperature. We revealed a gradual substitution of the hexagonal phase by the orthorhombic phase in the nanoparticles, which sintering temperature increases from 700 C to 1100 C. The origin and stability of the hexagonal phase in the LuFeO3 nanoparticles is of the special interest, because the nanoparticle in the phase can be a room-temperature multiferroic with a weak ferromagnetic and pronounced structural and ferroelectric long-range ordering, while the antiferromagnetic and nonpolar orthorhombic phase is more stable in the bulk LuFeO3. To define the ranges of the hexagonal phase stability, we determine the bulk and interface energy densities of different phases from the comparison of the Gibbs model with experimental results. Using the Gibbs model parameters, we predict the influence of size effects and temperature on the structural and polar properties of the LuFeO3 nanoparticles. Analysis of the obtained results shows that the combination of the X-ray diffraction, Raman and infrared spectroscopy, magnetic measurements and theoretical modelling of structural and polar properties allows to establish the interplay between the phase composition, lattice dynamics and multiferroic properties of the LuFeO3 nanoparticles prepared in different conditions.
It is shown that in external magnetic fields, a uniaxial magnetic anisotropy comes into being in a magnetoactive elastomer (MAE). The magnitude of the induced uniaxial anisotropy grows with the ...increasing external magnetic field. The filler particles are immobilized in the matrix if the MAE sample is cooled below 220 K, where the anisotropy can be read out. The cooling of the sample is considered as an alternative methodological approach to the experimental investigation of the magnetized state of MAEs. The appearance of magnetic anisotropy in MAE is associated with restructuring of the filler during magnetization, which leads to an additional effective field felt by the magnetization. It is found that the magnitude of the effective magnetic anisotropy constant of the MAE is approximately two times larger than its effective shear modulus in the absence of magnetic field. It is proposed that the experimentally observed large (about 40) ratio of the magnetic anisotropy constant of the filler to the shear modulus of the matrix deserves attention for the explanation of magnetic and magnetoelastic properties of MAEs. It may lead to additional rigidity of the elastic subsystem increasing the shear modulus of the composite material through the magnetomechanical coupling.
Magnetic properties of a magnetoactive elastomer (MAE) filled with {\mu}m-sized soft-magnetic iron particles have been experimentally studied in the temperature range between 150 K and 310 K. By ...changing the temperature, the elastic modulus of the elastomer matrix was modified and it was possible to obtain magnetization curves for an invariable arrangement of particles in the sample as well as in the case when the particles were able to change their position within the MAE under the influence of magnetic forces. At low (less than 220 K) temperatures, when the matrix becomes rigid, the magnetization of the MAE does not show a hysteresis behavior and it is characterized by a negative value of the Rayleigh constant. At room temperature, when the polymer matrix is compliant, a magnetic hysteresis exists and exhibits local maxima of the field dependence of the differential magnetic susceptibility. The appearance of these maxima is explained by the elastic resistance of the matrix to the displacement of particles under the action of magnetic forces.
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