Magnetic elastomers (MEs) based on a silicone matrix and magnetically hard NdFeB particles have been synthesized and their magnetic and viscoelastic properties have been studied depending on the size and concentration of magnetic particles and the magnetizing field. It has been shown that magnetic particles can rotate in soft polymer matrix under applied magnetic field, this fact leading to some features in both magnetic and viscoelastic properties. In the maximum magnetic field used magnetization of MEs with smaller particles is larger while the coercivity is smaller due to higher mobility of the particles within the polymer matrix. Viscoelastic behavior is characterized by long relaxation times due to restructuring of the magnetic filler under the influence of an applied mechanical force and magnetic interactions. The storage and loss moduli of magnetically hard elastomers grow significantly with magnetizing field. The magnetic response of the magnetized samples depends on the mutual orientation of the external magnetic field and the internal sample magnetization. Due to the particle rotation within the polymer matrix, the loss factor increases abruptly when the magnetic field is turned on in the opposite direction to the sample magnetization, further decreasing with time. Moduli versus field dependences have minimum at non-zero field and are characterized by a high asymmetry with respect to the field direction.

Polymer-based magnetoelectric composite materials have attracted a lot of attention due to their high potential in various types of applications as magnetic field sensors, energy harvesting, and biomedical devices. Current researches are focused on the increase in the efficiency of magnetoelectric transformation. In this work, a new strategy of arrangement of clusters of magnetic nanoparticles by an external magnetic field in PVDF and PFVD-TrFE matrixes is proposed to increase the voltage coefficient (α_ME) of the magnetoelectric effect. Another strategy is the use of 3-component composites through the inclusion of piezoelectric BaTiO₃ particles. Developed strategies allow us to increase the α_ME value from ~5 mV/cm·Oe for the composite of randomly distributed CoFe₂O₄ nanoparticles in PVDF matrix to ~18.5 mV/cm·Oe for a composite of magnetic particles in PVDF-TrFE matrix with 5%wt of piezoelectric particles. The applicability of such materials as bioactive surface is demonstrated on neural crest stem cell cultures.

Magnetic oxides are promising materials for alternative health diagnoses and treatments. The aim of this work is to understand the dependence of the heating power with the nanoparticle (NP) mean size, for the manganite composition La_0.75Sr_0.25MnO₃ (LSMO)—the one with maximum critical temperature for the whole La/Sr ratio of the series. We have prepared four different samples, each one annealed at different temperatures, in order to produce different mean NP sizes, ranging from 26 nm up to 106 nm. Magnetization measurements revealed a FC-ZFC irreversibility and from the coercive field as function of temperature we determined the blocking temperature. A phase diagram was delivered as a function of the NP mean size and, based on this, the heating mechanism understood. Small NPs (26 nm) is heated up within the paramagnetic range of temperature ($T>T_c$), and therefore provide low heating efficiency; while bigger NPs are heated up, from room temperature, within the magnetically blocked range of temperature ($T<T_B$), and also provide a small heating efficiency. The main finding of this article is related with the heating process for NPs within the magnetically unblocked range of temperature ($T_c>T>T_B$), for intermediate mean diameter size of 37 nm, with maximum efficiency of heat transfer.

The novel layered structures comprising piezoelectric polymer and magnetoactive elastomer (MAE) were developed and investigated. The influence of iron particles content in the elastomeric layer, its thickness and Young’s modulus of silicone on the multiferroic properties of the structures were analyzed. The investigation included the experimental and numerical characterization of the magnetoelectric effect. The giant values of bending deformations of MAEs in the external gradient magnetic field led to giant values of induced voltage (up to nearly 650 mV) in the composite. The displacement of ferromagnetic particles inside the elastomeric matrix under gradient magnetic field became the main basis for numerical modelling. The molecular dynamic method, ‘virtual springs’ method and Verlet algorithm were used to obtain the results of the numerical experiment. The energy transformation and magnetic field response in the novel composite allow it to be used in sensors and energy-harvesting devices.

We present the results of numerical simulation of magnetodielectric effect (MDE) in magnetorheological elastomers (MRE)—the change of effective permittivity of elastomer placed under the external magnetic field. The computer model of effect is based on an assumption about the displacement of magnetic particles inside the elastic matrix under the external magnetic field and the formation of chain-like structures. Such displacement of metallic particles between the planes of capacitor leads to the change of capacity, which can be considered as a change of effective permittivity of elastomer caused by magnetic field (magnetodielectric effect). In the literature, mainly the 2D approach is used to model similar effects. In this paper, we present a new approach of magnetorheological elastomers simulation—a 3D-model of the magnetodielectric effect with ability to simulate systems of ${10}^5$ particles. Within the framework of the model, three types of particle size distributions were simulated, which gives an advantage over previously reported approaches. Lognormal size distribution was shown to give better qualitative match of the modeling and experimental results than monosized type. The developed model resulted in a good qualitative agreement with all experimental data obtained earlier for Fe-based elastomers. The proposed model is useful to study these novel functional materials, analyze the features of magnetodielectric effect and predict the optimal composition of magnetorheological elastomers for further profound experimental study.