Papers by Keyword: Multiferroic

Abstract: Magnetoelectric materials which simultaneously exhibit ferroelectricity and magnetism have attracted great attention in recent years due to their potent coupling effect, and potential application in the electronics industry. The work done in this study aims to investigate the effect of ferromagnetic (Fe₃O₄) nanoparticles on the thermal, mechanical, magnetic, and ferro-electrical properties of PVDF, and its co-polymer poly (vinlydene fluoride-co-trifluoroethylene), P (VDF-TrFE). These compounds are synthesized into flexible nanocomposite thin films, via a novel solvent casting method to influence crystallization and nucleation growth. Fe₃O₄ nanoparticles (NP) were integrated with polymers at varying weight percentages (1wt%, 3wt%, 5wt%, 7wt%, and 10wt %). Magnetoelectric nanocomposites were annealed at 150oC. Films were fabricated and processed at dimensions: 8-20μm thickness, 35 mm length, and 35 mm width. Neat and loaded samples are characterized using x-ray diffraction (XRD) to observe crystallinity and to obtain β - phase content distribution. Ferroelectric hysteresis loops are given from Radiant Multiferroic Analyzer, which resulted in an increase in peak polarization of 9.601μC/cm² with the addition of 5wt% magnetite nanoparticles to P(VDF-TrFE) polymer blend. Magnetic tests are done using Vibrating Sample Magnetometer (VSM), which yields the magnetic polarization with respect to changes in field magnitude. The highest magnetic moment occurs with the addition of 10wt% Fe₃O₄ nanoparticles at 3.66 emu/g. Target applications of nanocomposites are for microelectromechanical system (MEMS) devices such as memory cards, spintronic, sensors, electromagnetic shielding, and compact energy storage.

Abstract: In the present work, we have synthesized x [Co_0.9Ni_0.1Fe₂O₄]-(1-x) [0.5Ba_0.7Ca_0.3TiO₃-0.5BaZr_0.2Ti_0.8O₃], x = 0.3, 0.4 & 0.5 multiferroic composite by hydroxide co-precipitation method. The structural and morphological analysis of the composite was carried out by using X-ray diffraction and Scanning Electron Microscopy. The XRD spectra confirm the perovskite phase and spinel phase. Dielectric properties of the composite were studied using Impedance analyzer. The variation of dielectric constant and loss of tangent (Quality factor) in the frequency range of 100 Hz to 1 MHz were investigated. Magnetocapacitance were measured for magnetic field up to 1 Tesla, which increases with increase in magnetic field. Dielectric constant possesses contribution due to magnetic field dependent interfacial polarization and variation due to induced stress which can be explained on the observed MD effect. Saturation magnetization of composites increases with increase in CNFO content.

Abstract: Among other multiferroic materials, bismuth ferrite (BiFeO₃) attracts much attention due to its room-temperature properties and its wide potential applications. However, the synthesis to obtain a single-phase material is hard to be achieved because of the volatility of bismuth oxide. In this study, the BiFeO₃ powders were synthesized by using a sol-gel method from the nitrates of bismuth and iron salt with the various stoichiometric ratios between Bi and Fe of 1:1.02, 1:1, 1.02:1, and 1.03:1. The single-phase and a good stoichiometric ratio of Bi: Fe = 1:1 was obtained from the starting composition ratio of 1.03:1 with a quenching process from 550°C sintering temperature. The single-phase of BiFeO₃ shows a hysteresis curve of a weak antiferromagnetic with a coercive field of about 1.38 kOe at room temperature. The measurement of microwave oscillator was measured by using a dielectric resonator from 0 to 25 GHz does not show any resonant peak.

Abstract: A single layer of BiFeO₃ (BFO)/epoxy resin composite with thickness of 3 mm was fabricated by polymerized 70 wt% of sintered BFO as fillers and 30 wt% of epoxy resin polymer as matrix. The electromagnetic and the microwave absorption properties of BFO/epoxy resin composite were reported. The reflection loss (RL) of the same composite sample was measured by two different techniques of measurement, S_11a parameter (without metal backed reflector) and S_11b parameter (with metal backed reflector) in the range of 8-18 GHz using a network analyzer. Minimum RL (RL_min) from S_11b parameter for BFO/epoxy resin composite with metal backed is lower than the RL_min from S_11a composite without metal backed reflector. In details, the results showed BFO/epoxy resin composite with metal backed can achieve a strong absorption with RL_min of -40.5 dB over a 1.31 GHz bandwidth.

Abstract: We report on the magnetoelectric properties of Er₂CoMnO₆. This compound adopts the structure of a double perovskite with a strong monoclinic distortion. Our specimen exhibits a nearly perfect Co-Mn order. It undergoes a ferromagnetic transition at T_C~70 K due to the Co²⁺-O-Mn⁴⁺ ferromagnetic superexchange interaction. Below 30 K, the Er³⁺ moments start to order antiferromagnetically to the Co/Mn sublattice. Pyroelectric measurements reveal electrical polarization at low temperature but its strong dependence on the heating rate indicates the lack of a spontaneous ferroelectricity. Instead, electric polarization is derived from thermally stimulated depolarization currents.

Abstract: Pure BiFeO₃ (BFO), Ca-doped and Eu/Ca-codoped BFO nanoparticles were prepared by using a sol–gel method. The effects of Eu/Ca-codoped on the structural, magnetic and ferroelectric properties of the samples were studied. The X-ray diffraction (XRD) analysis reveals a structure transition in the codoped samples. Co-doped samples were obtained with the best ferromagnetic properties, with the largest remaining magnetization Mr = 0.20 emμ/g. The structure transition may be the main cause for the origin of improved magnetic properties, which destroys the space modulated spin structure of BFO and releases the locked magnetic. In addition, the doping of Eu into BFO can reduce the leakage current and enhance the ferroelectric properties.

Abstract: Neutron diffraction has been carried out to study temperature evolution of crystal and magnetic structure parameters of the multiferroic (0.9)BiFeO₃ + (0.1)BaTiO₃ over region (300 – 1000) K. Crystal structure is rhombohedral over whole temperature region and it is described by the R3c space group. The lattice parameters increase with temperature. The Ba ions are placed in the Bi sublattice and the Ti ions partly occupy the Fe sublattice. Assuming that the sample has a modulated magnetic structure with the propagation vector k = [0.0045, 0.0045, 0], we obtained a temperature dependence of the Fe-ion magnetic moment. The value of the moment is equaled to be μ = (3.46 ± 0.05) μ_B at 300 K and becomes zero at 600 K.

Abstract: In the last decade, considerable attention has been focused on the search of new multiferroic materials and the ways of improvement of their magnetoelectric properties. In this short review, we survey the progress in study of multiferroics focusing the high temperature multiferroic bismuth ferrite and rare earth iron garnets. We discuss the recent results of investigation of domain walls in multiferroics, concentrating the most important magnetoelectric manifestations (electric polarization and magnetization), and the pinning effect appearing as clamping of ferroelectric and magnetic domain walls.

Abstract: In this work we have researched the features of dynamic magnetoelectric and magnetoelastic interactions in multiferroic crystal, influenced by various external fields, with the group of symmetry . Based on the integrated approach, which combines N. N. Bogolyubov’s quantum-statistic methods, Green’s temperature functions, diagram technique and symmetry, energy spectrum’s and static spin susceptibility’s dependences on the temperature and external fields were calculated. The effective parameters of magnetoelectric and magnetoelastic interactions dependences on the external fields’ intesities were analysed. It is shown that these parameters have a distinct maximum in the resonance value. As was shown, it is possible to enhance the interactions between spins, ferroelectric and fonons subsystems in multiferroics by applicating the external fields in different crystallographic directions.

Abstract: Multiferroic composites of (x)NiFe₂O₄ + (1-x)BaTiO₃ with x = 0.2, 0.3 and 0.4 and (x)CoFe₂O₄ + (1-x)BaTiO₃ with x = 0.2, and 0.4 have been synthesized by mixing NiFe₂O₄ (CoFe₂O₄) spinel and BaTiO₃ piezoelectric. Distribution of Ni (Co) ions on 8a and 16d positions of spinel lattice (space group F d-3m) is determined by neutron powder diffraction. Wave vector of magnetic structure of the spinel is k = 0. The dielectric permittivity of the composites was measured for the frequency range 10² – 10⁵ Hz. At low frequencies the dielectric permittivity decreased from ~940 for x = 0.2 to ~360 for 0.4.