Ferromagnetic Composites Research Articles

3D printed ferromagnetic composites for microwave applications

The use of 3D technology in the field of microwave electronics requires the development of new materials adapted to these applications. In this study, magnetic composites composed of polyethylene (PE) matrix filled with Nickel–Iron alloy (Ni81Fe19) are prepared using two elaboration devices: first, a propeller mixer for small quantity of samples, and then, a twin screw extruder able to produce higher samples amounts. Microstructural and rheological characterizations are suggested in order to study the feasibility of shaping PE/NiFe composites with 3D printer using Fused Deposition Modeling technique. A shear-thinning behavior with the dispersion of NiFe micrometric particles allows the use of 3D printer to shape final composites. A microwave characterization is also performed. Electromagnetic properties are predicted by the adjustment of a model based on mixing laws taking into account demagnetization effect and interactions between NiFe particles. The production of composite filaments and first printing tests are also presented.

Tunable Electromagnetic and Microwave Absorption Properties of Ba3Co2Fe24O41/P(VDF-TrFE) Composites

The electromagnetic and microwave absorption properties of polymer-based Ba3Co2Fe24O41/P(VDF-TrFE) composites were investigated. The effective complex permeability and permittivity of the two-phase composites can be manipulated by either varying the Ba3Co2Fe24O41 content or applying the dc magnetic field ( H dc). The composite containing 90 wt% Co2Z obtains a maximum reflection loss (RL) due to a proper impedance match and relatively high magnetic loss. In addition, it is found that the position of RL peak was tuned from 5.5 to 7 GHz with H dc up to 50 mT, whereas the intensity obtains a remarkable enhancement of 67% at 15 mT. These results reveal great potential for the applications of ferroelectric–ferromagnetic composites with tunable microwave absorption.

Ultrafast transient dynamics in composite multiferroics

We investigate theoretically the dynamic multiferroic (MF) response of coupled ferroelectric (FE)/ferromagnetic (FM) composites upon excitation by a photo-induced acoustic strain pulse. Two magnetoelectric (ME) mechanisms are considered: interface strain- and charge-mediated ME couplings. The former results in demagnetization, depolarization and repolarization within tens of picoseconds via respectively magnetostriction and piezoelectricity. Charge ME interaction affects the FE/FM feedback response leading to magnetization recovery. Experimental realization based on time-resolved x-ray diffraction is suggested. The findings indicate the potential of composite MF for photo-steered, high-speed, multi-state electronic devices.

Cu-Containing Carbon Nanocomposites Based on Cellulose

Structural transitions of Fe-containing fibrous and microcrystalline flax and hemp cellulose during heat treatment in an inert medium were studied using IR spectroscopy, x-ray diffraction, electron microscopy, thermogravimetric analysis, and N2 adsorption. Mesoporous ferromagnetic graphitecontaining carbon composites with specific surface area 280-550 m2/g were produced. The nature and shape of the cellulose matrix and the iron-salt anion were found to affect the composition, shape, and size of metal particles and the catalytic graphitization process.

Ferromagnetic composites with polymer matrix consisted of nanocrystalline Fe-based filler

ObjectiveThe paper intends to present structural and magnetic behavior of ferromagnetic composites consisted of nanocrystalline powders obtained by annealing and milling of Fe78Si9B13 and Fe73,5Cu1Nb3Si13,5B9 metallic glasses. MethodsThe as-cast ribbons were subsequently milled using a high-energy ball mill. The prepared powders were separated into fractions with a particle mean diameter range of 200–500µm, 75–200µm and 25–75µm and then annealed to obtain the nanocrystalline powder materials. The powder particles were mixed and consolidated with a polymer to obtain composites in the form of the toroidal cores. The following experimental techniques were used: scanning and transmission electron microscopy, X-ray diffraction and vibration sample magnetometry. ResultsThe analysis of magnetic properties of the powders and the composites prepared from the powders revealed that the preparation process caused significant decrease in magnetic properties in a relation to ribbons in as-cast state. ConclusionThe structure and magnetic properties of the examined materials could be improved by means of a right choice of milling time as well as a thermal treatment and by a decrease of the demagnetization effect. Practice implicationsThe amorphous and nanocrystalline powders obtained by a milling of metallic glasses are an alternative to solid alloys and make it possible to obtain the ferromagnetic nanocomposites with controlled magnetic properties.

Magnetic and mechanical properties of Ni–Mn–Ga/Fe–Ga ferromagnetic shape memory composite**Projects supported by the National Natural Science Foundation of China (Grant Nos. 51271065 and 51301054), the Program for New Century Excellent Talents in Heilongjiang Provincial Education Department, China (Grant No. 1253-NCET-009), the Youth Academic Backbone in Heilongjiang Provincial Education Department, China (Grant No. 1251G022), the Projects of Heilongjiang, China, and China

A ferromagnetic shape memory composite of Ni–Mn–Ga and Fe–Ga was fabricated by using spark plasma sintering method. The magnetic and mechanical properties of the composite were investigated. Compared to the Ni–Mn–Ga alloy, the threshold field for magnetic-field-induced strain in the composite is clearly reduced owing to the assistance of internal stress generated from Fe–Ga. Meanwhile, the ductility has been significantly improved in the composite. A fracture strain of 26% and a compressive strength of 1600 MPa were achieved.

NiFe2O4, Fe3O4–FexNiy or FexNiy loaded porous activated carbon balls as lightweight microwave absorbents

The ferromagnetic PACB composites annealed at different temperatures in an Ar atmosphere exhibit varied crystalline phase, morphology and high-performance microwave absorbability.

The magnetoelectric coupling effect in multiferroic composites based on PZT–ferrite

In the multiferroic materials, the dielectric and magnetic properties are closely correlated through the coupling interaction between the ferroelectric and magnetic order. We attempted to determine the values of magnetoelectric coupling coefficient , from the temperature dependences of the dielectric permittivity for the ferroelectric–ferromagnetic composite PZT–ferrite type, namely PSZTC–NiZn and PBZTN–NiZn. The main component of the ferroelectric–ferromagnetic composite was PZT type powder (with ferroelectric properties), which was synthesized using sintering of a mixture of simple oxides in solid phase. The second element of the ferroelectric–ferromagnetic composite was the ferrite powder (with ferromagnetic properties). Ferrite powder was synthesized using calcination. Next, the mixed components were synthesized using sintering of the mixture of simple oxides in a solid phase (compaction by a free sintering method). The temperature dependences of the dielectric permittivity ( ε ) for the different frequencies and for both multiferroic composites were investigated. Based on dielectric measurements and theoretical considerations, the values of the magnetoelectric coupling coefficient were specified. • The magnetoelectric effect at two different ferroelectric–ferromagnetic composites based on a PZT and nickel–zinc ferrite. • Multiferroics composite incorporate both ferroelectric and magnetic phases. • The mechanism of the magnetoelectric coupling between ferroelectric and magnetic properties, in multiferroic composites, is caused by the strain. • The determination of the magnetoelectric coupling coefficient based on a theoretical model and the measurements of dielectric permittivity.

NiZn ferrite/Fe hybrid epoxy-based composites: extending magnetic properties to high frequency

Hybrid ferromagnetic composites composed of Ni0.4Zn0.6Fe2O4 ferrite powder and Fe particles in an epoxy matrix with various composition ratios were prepared by a simple mould casting route. Planetary ball milling was then introduced to pre-grind Fe and NiZn ferrite filler mixtures before casting, which resulted in fragmentation of the NiZn ferrites and modification of the Fe morphology from spherical particles to sub-micron flakes. Composites containing the ball-milled fillers exhibited a remarkable improvement in electromagnetic properties over the as-supplied materials, especially in the suppression of dielectric and magnetic loss. By combining the characteristics of high resonant frequency of the Fe and low energy losses of the ferrite, an optimum mixture of ball-milled 15 vol% NiZn ferrite and 38 vol% Fe in a hybrid epoxy-based composite gave an approximately one order of magnitude higher extended operating bandwidth over a ferrite-only containing composite, suppressing dielectric and magnetic loss tangents to approximately 10−2 up to 150 MHz without significant deterioration of permeability. This approach of manipulating multi-phase ferromagnetic material fractions and their structure provide for flexibility in the development of bespoke electromagnetic materials for applications in electrically small antenna and metamaterials.

Low Temperature Magnetic Properties of Ferromagnetic Layered Composites

A ferromagnetic layered composite ABAB....ABA is studied by means of Green function approach. Our attention is focused on the elementary excitations and low temperature magnetisation behavior. In the presented paper we take also into account the e ects of damping due spin-spin interaction. As a result not only the positions and relative intensities of resonance peaks are obtained, but also the resonance line-width is found. On the basis of Green function method the temperature dependence of magnetization of a ferromagnetic layered composite is calculated and the spin wave parameter B in the Bloch's law T 3/2 is found and presented in dependence of parameters characterizing the system under consideration.

Ferroelectric–Ferromagnetic Ceramic Composites Based on PZT with Added Ferrite

The study presents a ferroelectric–ferromagnetic composite based on a doped PZT‐type and ferrite powders. Ferroelectric powder (in amount of 90 wt‐%) was based on multicomponent PZT‐type materials, while nickel–zinc ferrite Ni1–xZnxFe2O4 (in amount of 10 wt‐%) served as the magnetic component of the composite. The syntheses of the ferroelectric–ferromagnetic composite's components were performed using solid‐phase sintering, while final densification of the synthesized powder was achieved using free sintering. X‐ray analysis of the composite confirmed the presence of strong maxima originating from particular PZT‐type material phases, as well as weak peaks from the Ni0.64Zn0.36Fe2O4 ferrite, without foreign phases. The microstructure of the fracture of the ferroelectric–ferromagnetic composites shows that the ferrite grains on the surface of the ferroelectric component are distributed heterogeneously. Magnetic studies have characterized composite as a soft ferromagnetic material. The study indicated the influence of the magnetic subsystem on the electrical properties. In the two‐phase PBZTMC–NZF ceramic composite, the magnetic component causes the decrease in electric permittivity and increased value of the dielectric losses.

Nonlinear magneto-electric effects in ferromagnetic-piezoelectric composites

Theory and results of a systematic study on the nature of nonlinear magnetoelectric (ME) interactions in layered ferromagnetic and ferroelectric composites are discussed. The model that considers the nonlinearity associated with magnetostriction of the ferromagnet is to result in (i) a dc component and (ii) frequency doubling when the composite is subjected to an ac magnetic field. In the presence of two ac magnetic fields of different frequencies, nonlinear effects give rise to generation of ME voltages at the sum and difference of the fields frequencies. The efficiencies of nonlinear ME interactions are shown to be a function of the second derivative of the magnetostriction with respect to the bias magnetic field. The predictions of the model are compared with data for bilayers of lead zirconate titanate (PZT) and ferromagnetic layers with wide variations in saturation magnetostrictions and saturation magnetic fields, i.e., an amorphous ferromagnetic (AF) alloy, Ni, or permendur. Under linear excitation conditions an enhancement in the ME voltage is measured when the ac magnetic field is applied at the acoustic mode frequencies. Under nonlinear excitation conditions the mechanical deformation and the ME response occur at twice the excitation frequency and the AF-PZT composite shows a much higher nonlinear ME effects. In addition, the AF-PZT shows an efficient frequency mixing than the samples with Ni or permendur when subjected to two ac magnetic fields. The frequency mixing is shown to be of importance for magnetic field sensor applications.

Internal Friction in the Ferroelectric – Ferromagnetic Composites

Abstract In the work, temperature Q-1(T) and amplitude Q-1(") dependences of internal friction for ferroelectric - ferromagnetic composites on the base of the PZT and ferrite were determined. The temperature dependences of internal friction Q-1 reveal the peak in the range of high temperatures. We have investigated the peak associated with the viscous-elastic mobility of ferroelectric domain walls. The internal friction due to the viscous-elastic mobility of ferroelectric domain walls was calculated and compared with the experimental data in the reference to the Wang’s theory. Based on internal friction measurements and theoretical considerations, the peak was described. Additionally the amplitude (isothermal) Q-1(") dependences for the composites were made. This allowed for the interpretation of the maximum observed on the temperature dependences of the internal friction Q-1(T).

Evidence of an embedded vortex translation mode in flake-shaped ferromagnetic particle composites

A low-frequency resonance (sub-GHz) is observed in microwave permeability spectra of anisotropic flake-shaped ferromagnetic particle composites. The resonance frequency of this peak increases linearly with the saturation magnetization of flakes, their aspect ratio, and the amplitude of a perpendicular static magnetic field. In addition, this resonance becomes extinct for a perpendicular RF exciting magnetic field. These experimental features are reproduced by an analytical model of vortex dynamics which militates in favor of an assignment of this low-frequency signal as an embedded vortex translation mode within a multidomain magnetic structure.

Effect of changeable demagnetizing state of ferrite on the permeability of BaTiO3/Ni0.5Zn0.5Fe2O4 composites

A BTO/NZFO ferroelectric/ferromagnetic ceramic composite was prepared by the traditional ceramic method and its permeability was analysed in detail. Results showed that as the BTO fraction increased, the permeability of the composite dropped much more rapidly than that predicted by Kirkpatrick's effective medium model, which was consistent with that usually observed in other ferromagnetic composites. A model was developed to interpret the permeability of ferrite particles with the usual multi-180°-domain structure in the composite by considering both the contributions of spin rotation and domain-wall motion. It was confirmed theoretically that the internal demagnetizing field on the ferrite particles, which was changeable with their shape and dispersion situation, and thus with their fraction, controlled the response of spin rotation and thus the permeability of ferrite particles dispersed in the composite. The rapid decrease in the effective permeability of the composite was ascribed to not only the universal compound effect, formation of defects by ion doping from the coexisting phases and the change in grain size with the ferrite fraction, but also the shielding of the spin rotation response of the ferrite, which depended on its demagnetizing state in the composite.

Preparation and Microwave Absorbing Properties of Carbon/Cobalt Ferromagnetic Composites

Carbon/cobalt ferromagnetic light composites with high performance of microwave absorbing properties were prepared by hydrothermal method using starch and hollow cobalt ferrites. It was concluded that after carbonization the spinel structure ferrites changed to Co3Fe7 alloys and the temperature of graphitization was significantly decreased for the catalytic of CoFe2O4/Co3Fe7. The increase of carbon content, and exist of CoFe2O4/Co3Fe7 heightened the microwave absorbing properties. Electromagnetic parameters were tested with 40% of the titled materials and 60% of paraffin wax composites by using HP8722ES vector network analyzer. The reflection was also simulated through transmission line theory. The microwave absorbers exhibited a maximum reflection loss -43 dB and the electromagnetic wave absorption less than -10 dB was found to exceed 3.0 GHz between 11.6 GHz and 15 GHz for an absorber thickness of 2 mm.

Design of an inchworm actuator based on a ferromagnetic shape memory alloy composite

A new inchworm actuator has been designed and fabricated based on a ferromagnetic shape memory alloy (FSMA) composite and the hybrid mechanism. The FSMA composite consists of a ferromagnetic material (soft magnet) and a superelastic grade shape memory alloy. The hybrid mechanism is found to provide relatively large force and stroke with fast response on the FSMA composite because it can be driven by a compact electromagnetic driver with high applied magnetic field gradient, providing a large stress capability and reasonably large strain. The inchworm actuator exhibits moderate output force and very large displacement, achieved by accumulating many small strokes based on the inchworm mechanism. The prototype inchworm actuator successfully produces 30 N force and 65 mm s−1 stroke velocity.

Low temperature fired and electromagnetic properties of a novel ferroelectric/ferromagnetic composite material

A series of Bi4Ti3O12/Ni0.25Cu0.2Zn0.55Fe2O4 ferroelectric–ferromagnetic composites were prepared by the usual ceramic technology and sintered at 900°C to adapt to the low temperature cofired ceramic (LTCC) technology. Among all samples, the relative density changes in the range of 94.9–96.4% and reaches the highest value in the composite with 30wt% Bi4Ti3O12 (BIT). When BIT content increases from 0 to 90wt%, the magnetic and dielectric properties show different change trends: the permeability (real part) at 1MHz reaches the maximum 170 in the composite with 10wt% BIT at first, and then gradually decreases from 170 to 1.4, while the saturation magnetization decrease from 2.85×105A/m to 1.6×104A/m; the dielectric loss tangent obtains a maximum value about 0.47 in the composite with 10wt% BIT at first, and then decreases sharply, while the permittivity (real part) at 1MHz increases from 8.8 to 100.3. The Maxwell Garnett mixing rule was used to predict the magnetic and dielectric properties of the composites with different assumptions. The calculated results basing on BIT matrix were more approximate to the measured in comparison to that basing on ferrite matrix.

Piezoelectric single crystal langatate and ferromagnetic composites: Studies on low-frequency and resonance magnetoelectric effects

Mechanical strain mediated magnetoelectric (ME) effects are studied in bilayers and trilayers of piezoelectric single-crystal lanthanum gallium tantalate (LGT) and magnetostrictive permendur (P). The ME voltage coefficient ranges from 2.3 V/cm Oe at 20 Hz to 720 V/cm Oe at bending resonance and is higher by an order of magnitude than in composites with ferroelectric lead zirconate titanate or lead magnesium niobate-lead titanate. The low-frequency magnetic noise for P-LGT-P is a factor of 2-10 smaller than for ferroelectrics based composites. Langatate is free of ferroelectric hysteresis, pyroelectric effects, and phase transitions up to 1450 °C and is of interest for ultrasensitive, high temperature magnetic sensors.

Low-frequency and resonance magnetoelectric effects in piezoelectric and functionally stepped ferromagnetic layered composites

The strain mediated magnetoelectric (ME) coupling is studied in bilayers of lead zirconate titanate (PZT) and a ferromagnetic layer that is functionally stepped. Nickel with negative piezomagnetic coefficient $q$ and Metglas with positive $q$ are bonded to achieve the desired step in $q$ for the ferromagnetic phase. Samples of PZT-Ni-Metglas and PZT-Metglas-Ni are used for measurements of ME voltage coefficient (MEVC) at low frequencies and at frequencies corresponding to bending resonance. It is shown that at low frequencies the bending moment due to stepped-$q$ counteracts the asymmetry-related flexural strain in the sample and enhances the strength of ME coupling. The MEVC is found to be as high as in symmetric trilayers in which flexural deformation is absent, and it ranges from 0.4 to 3.4 V/cm Oe depending on the grading scheme and the thickness of Metglas. A resonance enhancement of the MEVC to 40--220 V/cm Oe is measured at bending modes for samples clamped at one end. Samples of PZT-Ni-Metglas show a higher MEVC than for PZT-Metglas-Ni both at low frequencies and at bending resonance. The $q$-stepped composites are of importance for ultra-sensitive magnetic field sensors.