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Magnetoelectric (ME) polymer nanocomposites find a wide range of applications as ME sensors, energy storage devices, magneto‐mechano‐electric nanogenerators, tissue engineering scaffolds, and so forth. Functionalizing ferrite fillers is an effective strategy to improve the ferrite‐polymer interaction and, thereby, the functional properties. In the present work, we developed ternary nanocomposite fibers of polyvinylidene fluoride loaded with hydrated salt and alginate functionalized ferrite nanoparticles. Nanocomposites with functionalized ferrite fillers were found to have better dielectric and ME properties. The highest values of dielectric constant (14.7) and ME coupling coefficient (18.2 mV cm−1 Oe−1) were obtained for ternary nanocomposite fiber with functionalized nickel ferrite nanoparticles. The present study opens new avenues for developing flexible ME nanocomposites for realizing flexible ME nanocomposites with the required properties for developing next‐generation devices for diverse applications. [ABSTRACT FROM AUTHOR]

Magnetoelectric (ME) materials are capable of use in multifunctional devices due to their eccentric properties. Flexibility is a beneficial trait for enabling ME materials to be utilized in advanced device fabrication. We introduced varying weight percentages (4, 8, 16 wt%) of magnetostrictive SrFe12O19 (SFO) nanoparticles into a piezoelectric PVDF-HFP to fabricate flexible magnetoelectric nanocomposite fibers. Structural and morphological modifications of the composite fiber mats were investigated using X-ray diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), and Transmission Electron Microscopy (TEM) analysis. Dielectric and Ferroelectric studies were conducted and an exceptional enhancement in the dielectric constant and ferroelectric parameters was observed for 16% of SFO loaded sample. The magnetoelectric coupling coefficient (MECC) improved to 19.9 mV/cm. Oe for the higher filler-loaded composite sample. Additionally, mechanical studies were also done to ensure the flexibility of the composite fiber mats. [ABSTRACT FROM AUTHOR]

Free-standing self-polarised films of Ho3+ modified Polyvinylidene fluoride co-hexafluoropropylene (PVDF-HFP) have been prepared using a simple and cost-effective solvent casting method. A study was initiated to bring out the impact of rare earth hydrated salt on the electroactive nucleation of PVDF-HFP. Holmium hydrated salt acts as an excellent filler to induce electroactive γ and β phases of PVDF-HFP. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy were used to authenticate the enhancement in the electroactive phases of PVDF-HFP. Furthermore, differential scanning calorimetric (DSC) measurements reveal an increase in the melting temperature, which indicates an enhancement in the polar β phase. An excellent enhancement in the dielectric constant value has been observed for Ho3+ incorporated composite films. The value reached 24 ~ (at 1 kHz), which is ~3 times greater than the pure polymer for the highest salt-loaded film. The effect of rare earth hydrated salt on the optical properties of the PVDF-HFP composite films has also been examined by analysing the direct and indirect band gaps of hybrid films. In addition, the ferroelectric properties of the prepared composites were also analysed by P-E measurements, and the composite films show remarkable improvement in polarisation. These multi-functionalities, such as the enhanced electroactive nature, flexibility lightweight, high value of dielectric constant, and the possibility for bandgap tuning make the prepared PVDF-HFP/Ho3+ cast films useful in piezo, photonic device applications. [ABSTRACT FROM AUTHOR]

The composite approach is very effective in developing multiferroic systems with remarkable magnetoelectric coupling coefficients. In this work, P(VDF-HFP)-based films containing 2, 4, 8 and 16 wt% Y3Fe5O12–Na0.5K0.5NbO3 nanocrystalline particles were developed via a simple solvent cast process. In order to facilitate the β-phase crystallization of the P(VDF-HFP), hydrated ferric nitrate was utilized during the preparation of the films, which resulted in significant improvement in the β-phase content. Moreover, the use of Y3Fe5O12–Na0.5K0.5NbO3 also triggered the β-phase crystallization of the P(VDF-HFP). At the highest filler loading of 16 wt%, a magnetoelectric coefficient of 33.6 mV cm−1 Oe−1 was achieved. Piezoelectric energy harvesting studies were also carried out using the composite film containing 16 wt% Y3Fe5O12–Na0.5K0.5NbO3 nanocrystalline particles. A maximum open-circuit voltage of 3.79 V was measured when a compressive force of 5 N was applied to the energy harvesting device. [ABSTRACT FROM AUTHOR]

Magnetoelectric (ME) flexible nanocomposite fiber mats with a ternary composition based on the electroactive polymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) loaded with nanoclay (Cloisite 30B) and NiFe2O4 (NFO) nanoparticles have been fabricated. Different weight percentages of nickel ferrite nanoparticles were incorporated into the polymer–clay systems and their morphological, dielectric, magnetic and magnetoelectric properties have been studied. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were used to validate the enhancement of the ferroelectric β phase of PVDF-HFP. Moreover, differential scanning calorimetric (DSC) measurements showed an improvement in the melting point of the polymer nanocomposite which also implies the enhancement of the ferroelectric β phase. The synergistic effect of the incorporation of clay and nickel ferrite nanoparticles into the PVDF-HFP matrix along with the electrospinning technique resulted in an enhancement of the electroactive nature of the polymer. The polymer nanocomposite fiber shows a magnetic saturation value of 1.54 emu g−1 for the maximum loading (8 wt%) of NFO nanoparticles. The electrospun nanocomposite system with 8 wt% NFO nanoparticles exhibited the highest values of the magnetoelectric coupling coefficient (MECC) and dielectric constant (≈17 mV cm−1 Oe−1 and ≈29, respectively). High flexibility along with room temperature multiferroic properties makes PVDF-HFP/clay/NFO polymer nanocomposite fibers suitable candidates for device applications. [ABSTRACT FROM AUTHOR]

Magnesium ferrite (MgFe2O4) nanocrystalline samples were prepared by sol–gel method and by sintering at temperatures from 300°C to 1000°C. X-ray diffraction and electron microscopic studies showed an increase in crystallite sizes and a decrease in lattice constants at higher sintering temperatures. UV-Vis absorption measurements depicted blue shift for samples of smaller crystallite sizes (dc) with a resultant increase of the band gap energies (Eg. = 2.07 eV at dc = 49 nm to 3.10 eV at dc = 6 nm, for samples sintered at 1000°C and 300°C, respectively). Fourier transform infrared spectroscopy of the samples proved the formation of the spinel structure while energy dispersive X-ray analysis pointed out the non-stoichiometric composition, which implied the presence of vacancy type defects that could modify the structural and magnetic characteristics of the compounds. This necessitated the use of positron annihilation lifetime and coincidence Doppler broadening spectroscopic studies for defect characterisation and the results indicated distinct redistribution of cations within the unit cells, making the compound overwhelmingly turn towards a normal spinel configuration at smaller nanocrystalline sizes. Positrons were trapped in larger vacancies of increasing numbers in smaller crystallites. The vacancies turned out to be formed at the octahedral sites where the increased ionic radius of Fe3+ became large enough to reduce the occupancy significantly. Mossbauer spectra analysis indicated an increase of the ferromagnetic properties in samples sintered at higher temperatures. At 300°C and 400°C, the samples dominantly showed paramagnetic behaviour. [ABSTRACT FROM AUTHOR]

Multiferroics that permit manipulation of the magnetization vector exclusively by electric fields have spawned extensive interest for memory and logic device applications. In line with this understanding, we herein report the encapsulation of non-ferroelectric magnesium ferrite (MgFe2O4) nanoparticles in a ferroelectric shell of BaTiO3 to produce a system with engineered dielectric, magnetic, magneto-electric and ferroelectric properties. The interface effect on the strain transfer was observed to strongly influence the magneto-electric coupling and the electric and magnetic properties of the system. The model polyhedral image of MgFe2O4@BaTiO3 has helped to get an insight into the core–shell structure. The multiferroicity induced by the excellent coupling between the ferroelectric and magnetostrictive phases at the core–shell interface unlocks wide prospects for device downscaling and information storage applications. The influence of magnetostrictive stress on the magneto-electric coupling effects and domain dynamics was further studied using transmission electron microscopy (TEM) and atomic force microscopy images. Interestingly, the realization of a superparamagnetic multiferroic system has been a breakthrough and facilitates ultra high density magnetic data storage technologies. Evidence for spontaneous polarization and the ferroelectric trait exhibited by the multiferroic samples was revealed from the P–E hysteresis loop. The investigation of defect evolution in the system was carried out using positron annihilation lifetime spectroscopy (PALS) and coincidence Doppler broadening spectroscopy (CDBS) of annihilation radiation and the studies revealed thermal diffusion of positrons into the interfacial regions within the core–shell structure and the “formation and pick-off annihilation of orthopositronium atoms”. It is concluded that interface engineering is a strong means for manipulation of the magnetic, dielectric and magneto-electric properties in multiferroic heterostructures for high density electrical energy and magnetic data storage. [ABSTRACT FROM AUTHOR]

The replacement of cations at the B-sites in the spinel ferrite ZnFe2O4by Mn3+ions brings in several interesting changes, the most striking among them being a transformation from the spinel cubic structure to a body-centered tetragonal one. Concomitantly, there are variations in the nanocrystallite sizes and also in the lattice parameters. These are examined through high-precision X-ray diffraction measurements and transmission electron microscopic analysis. A more interesting aspect is the success of positron annihilation spectroscopy comprising of the measurements of positron lifetime and coincidence Doppler broadening measurements in understanding the effects of cation replacement and the resultant generation of vacancy-type defects. There are definite changes in the positron lifetimes and intensities which show positron trapping in trivacancy-type defect clusters and the nanocrystallite surfaces. The presence of ortho-positronium atoms within the extended intercrystallite region is also identified, although in small concentrations. The cubic to tetragonal transformation is indicated through definite decrease in the values of the positron lifetimes. We also performed a model analysis to predict the expected effect of substitution on the positron lifetime in the bulk of the sample and the experimentally obtained positron lifetimes significantly differed, indirectly hinting at the possibility of a structural transformation. Finally, Mössbauer spectroscopic studies have indicated a ferromagnetic nature for one of the samples, i.e. the one with Mn3+doping concentrationx = 0.4, which incidentally had the lowest crystallite size ~10 nm. [ABSTRACT FROM PUBLISHER]

Highlights: [•] (1−x)ErMnO3–xY3Fe5O12 (0⩽ x ⩽1) composites show room temperature ME coupling. [•] Magnetic properties of the samples measured as a function of YIG concentration show soft magnetic behavior. [•] Strong ME coupling is demonstrated in the composite 0.5RMnO3–0.5YIG. [•] Phonon transport through these composites is effectively suppressed with YIG concentration. [ABSTRACT FROM AUTHOR]