Vol 88, No 10 (2024)

We presented the results of an experimental study of the features of the magnetic susceptibility of a magnetic fluid with a non-magnetic filler. It is established that the dependence of magnetic susceptibility on the concentration of non-magnetic filler has features. The explanation of the detected effects is based on the assumption of the influence of surface forces on the relaxation processes of the magnetic moment of magnetic particles. It was also found that the dependences of the magnetic susceptibility of a magnetic fluid with a non-magnetic filler on the magnitude of the external magnetic field differ from similar dependences for a magnetic fluid without a filler.

Magnetic properties of magnetopolymer composite materials were studied. Monodisperse and bidisperse theoretical models considering interparticle dipole-dipole interactions were verified using experimental data. It was obtained that the bidisperse approximation well describe the experimental results for real polydisperse composites.

Silicone-based elastomer containing Nd-Fe-B-alloy particles garnished with a small portion of nickel grains has been studied for the capability to conduct alternating current. The observations suggest that the presence of nickel expands the variation range of the conductivity and magnetocapacitance in external magnetic fields. In addition, the composite demonstrates the memory of primary magnetizing manifesting itself as certain specific features of the hysteresis loops depending on the polarity of the external magnetic field.

The effect of changes in the transparency of magnetic emulsions with deformable droplets of submicron size under the influence of a magnetic field has been studied. The influence of microdroplet concentration, orientation, and magnetic field strength on the amplitude of transparency changes was discovered. A comparison has been made of experimental data on the field dependence of the magneto-optical effect and the dependence on the angle of magnetic field orientation with calculations in the anomalous diffraction approximation. The possibility of estimating interfacial tension in magnetic emulsions based on studying the processes of relaxation of optical effects is discussed.

We investigated the orientation texturing of magnetic moments of four magnetic nanoparticles fixed at the vertices of a regular tetrahedron and formed a separate polyhedral particle. Numerical calculations of the probability density of the magnetic moment orientation, the static magnetization and the initial magnetic susceptibility of a multi-core particle are obtained by the Monte-Carlo method.

We investigated the static magnetic response of the multi-core particles (MCP) with a different number of nanocores. The cases of the MCPs containing 7, 8, 32, 33, 123 and 136 granules are considered. Their position remains unchanged in the nodes of a regular cubic lattice, but the magnetic moments can freely rotate inside the cores. The magnetization of the MCPs is determined by computer simulation using the Monte Carlo method and theoretically.

A photonic crystal was created using a magnetic fluid–epoxy resin composite. The amplitude-frequency characteristics of the reflection coefficient of electromagnetic radiation in the microwave range from the resulting structure were experimentally studied. The possibility of using magnetic composites to create controlled photonic crystals has been demonstrated.

We presented the results of studies of structural transformations in magnetic fluids when exposed to a constant electric field. The features of the formation of structural lattices in thin layers of colloids in an electric field directed perpendicular to the plane of the layer, as well as under the additional influence of a magnetic field, have been studied. New results were obtained related to the dependence of the threshold (critical) value of the electric field strength corresponding to the formation of a labyrinthine structure on the strength of an additionally applied magnetic field, layer thickness and temperature. The dependences of the formation time of the structure under study on temperature and the strength of an additionally applied magnetic field have been studied. A thermally induced effect of the appearance of a labyrinthine structure in a magnetic colloid in the subcritical region of the operating electric field strength under additional exposure to laser radiation has been discovered.

We studied the dynamics of non-magnetic droplets in magnetic liquids in microchannels with a “flow focusing” configuration under the action of an inhomogeneous magnetic field of an annular magnet. Two types of multiphase systems were studied: non-magnetic emulsions “oil in water”, “water in oil”, as well as “water in oil in water” and magnetic direct emulsions in which the magnetic liquid was used as a continuous phase. The dependences of the sizes of the generated non-magnetic inclusions on the flow rate of the continuous magnetic phase and the displacement of the magnetic field source relative to the dispersed phase supply connector horizontally along the channel axis are obtained.

The frequency of vapor bubble formation and heat transfer during boiling of a magnetic fluid in a homogeneous alternating horizontal magnetic field are studied experimentally. Bubble formation occurs at a single vapor formation center. To measure the frequency of vapor bubble formation, an induction method based on the occurrence of induction current in the coil turns through which the vapor bubbles move is used. It is found that the specific heat flux and the frequency of vapor bubble formation depend significantly on the frequency of the magnetic field. The obtained results indicate the possibility of effective non-contact control of the boiling process of magnetic fluid, which may have practical application.

The process of rising of an air bubble enclosed in a magnetic fluid shell in an external homogeneous magnetic field directed horizontally is investigated experimentally. It is shown that the magnetic field acting on the magnetic fluid shell leads to a change in the shape of the bubble, which in turn is reflected in the quantitative characteristics of the rising process. Oscillations in the shape of the air bubble during the rising process were also found. The obtained results indicate the possibility of realizing the control of small gas volumes, which may have practical applications.

The flow of a thin layer of a magnetic fluid along a horizontal plane near an fixed magnetizable cylindrical body in an applied uniform vertical magnetic field were investigated theoretically and experimentally. The shapes of the surface of the magnetic fluid at different times were plotted. The influence of the applied field on the flow of the layer was studied.

We considered a model medium of micron-sized magnetite particles and metal balls with a diameter of 1 mm in a viscous medium — glycerin. The processes of organization of this system in an external magnetic field as it increases are considered. The impact of shear vibrations on the processes of structure formation in the systems under study is also considered. The data obtained can serve as a basis for modeling the dynamics of disperse systems and expanding the understanding of their behavior and organization in magnetic fields and under mechanical influences.