CoFe2O4 Content Research Articles

Structural studies, dielectric and electrical properties of (1-x) Pb(Zr0.52Ti0.48)O3– xCoFe2O4 multiferroics materials

This work aimed to develop a better combination of PbZr0.52Ti0.48O3 (PZT) and CoFe2O4 (CFO) ceramics with enhanced structural, dielectric, and electric properties. For this aim, (1-x)PZT-xCFO nanocomposites at (0.00, 0.10, 0.20, 0.30, 0.40, 0.50, and 1.00) were synthesized using the combination before calcination of sol–gel (for PZT ceramic) and solid-state (for CFO material) methods. The powder X-ray diffraction analysis reveals that the CFO crystallizes in a spinel cubic structure with the Fd3m space group structure, while the PZT compound crystallizes in two tetragonal and rhombohedral structures with P4mm and R3m space groups respectively, which is confirmed by Raman spectra which also demonstrate that CFO content in (1-x)PZT-xCFO composites affects the vibration types. The scanning electron micrographs (SEM) show that the grains are homogeneous and irregular, with several pores on the surface of ceramics. The dielectric properties of the ceramics were investigated as a function of temperature (from 25 to 500 °C) and frequency (from 100 Hz to 2 MHz) using complex impedance spectroscopy. It shows that with the increase of CFO ratio, the dielectric permittivity values increase in the composites until the composition corresponding to x = 0.3 From 485 to 1620 at 5KHz) and then decreases until 65 for x = 1.00. The dielectric constant a function of frequency at different temperatures of (1-x)CFO-xPZT composites indicated that the dielectric constant increases with the increase of CFO content. The impedance spectrum is characterized by simple semicircular arcs and shows a non-Debye relaxation. The electric conductivity reveals that as CFO increases, conductivity remains constant, and the frequency dependence of conductivity shifts away from high frequencies. Also, the value of the exponent n decreases from 1.44 to 0.26 with an increasing CFO concentration. The activation energy is between 0.32 and 0.16 which confirms that electron hopping is responsible for electrical conduction.

Conjugate electrospinning-constructed special-shaped Janus nanobelt with improved upconversion luminescence and regulable magnetism Bi-functionality

Developing multifunctional nanomaterials through the design and construction of advanced nanostructures that are highly compatible with various substances is a crucial approach. In this work, special-shaped Janus nanobelt with both up-conversion luminescence (UCL) and magnetism is firstly designed and fabricated via a conjugate electrospinning coupled with a di-crucible fluorination. [YF3: Yb3+, Ho3+@SiO2] belt-in-belt nanobelt//CoFe2O4 nanobelt conjugate electrospinning-constructed special-shaped Janus nanobelt (shorted as C-SJNB) was designed and successfully prepared for a case study. C-SJNB is composed of two mutually independent micro-zones, which are YF3: Yb3+, Ho3+@SiO2 belt-in-belt nanobelt (BNB) called as luminescent micro-zone, and CoFe2O4 magnetic nanobelt acted as magnetic micro-zone. In the C-SJNB structure, the design ensures that the luminescent substance does not directly contact with the magnetic substance, thereby reducing the adverse effects of the dark-brown magnetic CoFe2O4 on the luminescent performance. C-SJNBs with structural advantages exhibit 7 times the UCL intensity compared to counterpart luminescent-magnetic YF3: Yb3+, Ho3+/SiO2/CoFe2O4 hybrid nanobelts (HNBs) prepared by uniaxial electrospinning. Further, compared with [YF3: Yb3+, Ho3+@SiO2]//CoFe2O4 parallel electrospinning-constructed special-shaped Janus nanobelt (shorted as P-SJNB), C-SJNB possesses a higher quality of micro-morphology, and avoids the degradation of luminescence performance caused by the mixing of magnetic and luminescent substances at the interface. The UCL intensity and magnetism of C-SJNBs can be adjusted by changing the content of CoFe2O4. When the CoFe2O4 content increases from 0.5 mmol to 4 mmol, the saturation magnetization of C-SJNBs increases from 4.42 to 13.94 emu·g−1. The newly established technology eliminates the needs for complex electrospinning and post-processing procedures. The formation mechanism of C-SJNBs has been established, providing technical support for synthesizing other Janus nanobelts with a belt-in-belt structure on one side. These advanced Janus nanobelts are ideal for developing poly-functional nanomaterials and have important applications in dual-mode imaging, display devices, batteries, drug loading and delivery.

Wire-in-tube nanofiber as one side to construct specific-shaped Janus nanofiber with improved upconversion luminescence and tunable magnetism

It is an important strategy to rationally design and construct specific-shaped microscopic nanostructures for developing poly-functional nanomaterials for different advanced applications. In this work, a novel technique combining a parallel electrospinning with a subsequent bi-crucible fluorination is advanced and utilized to facilely synthesize a brand-new peculiar one-dimensional (1D) wire-in-tube nanofiber//nanofiber shaped Janus nanofiber (WJNF) to refrain from usual complicated preparation procedures. Partition of four independent domains in the peculiar-structured Janus nanofiber is microscopically realized. The Janus nanofiber with four microscopic partitions can be applied to assemble various functions to avoid adverse mutual impacts among functions to realize multi-functionalization of the materials. As a case study, [YF3:Yb3+, Er3+@SiO2]//CoFe2O4 WJNFs with synchronous excellent upconversion luminescence and tunable magnetism are designed and constructed by the above technique. One side of the WJNF is composed of YF3:Yb3+, Er3+@SiO2 wire-in-tube nanofiber with YF3:Yb3+, Er3+ nanofiber as core layer and SiO2 as shell layer, and the other side is composed of CoFe2O4 magnetic nanofiber. YF3:Yb3+, Er3+ green upconversion luminescent nanofiber is completely separated from CoFe2O4 to fully avoid the weakening of luminescent intensity caused by the direct contact between luminescent and magnetic substances, and thus the luminescent intensity of [YF3:Yb3+, Er3+@SiO2]//CoFe2O4 WJNFs is apparently enhanced. Up-conversion luminescent intensity and magnetism of the WJNFs are modulated by tuning the contents of CoFe2O4. With the increase of CoFe2O4 content, the saturation magnetization of the WJNFs increases from 3.91 to 12.90 emu·g−1, revealing the tunable magnetism of the product. The formation mechanism of WJNFs is advanced, and a corresponding facile construction technique is established to shun complicated process, which provides theoretical guidance and technical support for the design and preparation of other poly-functional nanomaterials.

Response of DC biased magnetoelectric coupling in 0–3 type particulate lanthanum modified PZT-CFO composites

Magnetoelectric effect (ME) has been investigated in particulate ferroelectric (FE)-ferrimagnetic (FM) composites in the present work. The composition of ceramic composites has been tailored in terms of (1 - x) Pb0.4La0.6Zr0.6Ti0.4O3 (PLZT) – (x)CoFe2O4 (CFO) [x = 0, 0.2, 0.4, 0.6 and 1] in order to observe the magnetoelectric coupling. The FE-FM (PLZT-CFO) composites prepared using solid state route were investigated in terms of structural, morphological, dielectric, ferroelectric and magnetic properties. Well crystallized PLZT-CFO composites were observed with binary rhombohedral (R3m) and cubic (Fd3m) phase of PLZT and CFO, respectively, along with well-defined grains for both parent phases. The appearance of relaxor behaviour in prepared composites was revealed from temperature dependent dielectric study. The saturation (Ps) and remnant (Pr) polarizations were observed to be vary from 45µC/cm2 to 10µC/cm2 and 36µC/cm2 to 7 µC/cm2, with the increment in the CFO content from 0 % to 80 %, respectively. The emergence of long-range ferromagnetic ordering is revealed from M-H curves. It is evident from magnetization and polarization studies that each composite exhibits exceptional sensitivity to both the electric and magnetic fields. The magnetoelectric coefficient, is found to be initially rise with x and achieved maximal value of 450 µV/cm.Oe for 40 % CFO content. The obtained results indicate that almost equal number of weight proportion is required for achieving maximum strain transfer between FE-FM phases which is beneficial for future FE-FERAM devices. It is also perceptible that these novel composites may provide knowledge pathway for development of ME multifunctional device miniaturization.

Structural, electronic and optical properties of BaTiO3-CoFe2O4 nanocomposites for optoelectronic devices

Structural, electronic and optical properties of BaTiO3 (BTO), CoFe2O4 (CFO) and their nanocomposites are presented. The XRD spectra of composites exhibited the superposed peak patterns of individual compounds with a consistent shift from BTO to CFO phase with the increase in CFO proportion. The XPS analysis revealed a lower concentration of Oxygen vacancies in the composite samples as compared to that in pure CFO. This finding is also confirmed by the consistent transformation of Co from +2 state in CFO to +3 state in the composite samples. The UV–Vis spectroscopy revealed that optical absorption of BTO is limited to the UV regime, however, CFO exhibited the absorption in visible and infrared (IR) region. However, after the formation of BTO-CFO composite, the optical absorption was broadened from UV to IR regions. The magnitude of absorption was further enhanced by increasing the CFO content in the composites.

Magnetoelectric coupling property of 0-3 type CoFe2O4-BaTiO3 nanocomposites

The 0-3 type CoFe2O4-BaTiO3 nanocomposites have been prepared by co-precipitation sintering process in this work. The structure, dielectric, magnetic properties and magnetoelectric (ME) coupling effect of nanocomposites are studied. It finds that the 0-3 connectivity in nanocomposites results in BaTiO3 hindering the merger and growth of CoFe2O4 leading to smaller particle size (in the range 52–55 nm), creating large interface area between CoFe2O4 and BaTiO3 in composites. Creating the space charge polarization dominant thereby the dielectric constant decreased sharply with increasing frequency. Magnetization data show typical ferromagnetic behavior. Nanocomposites have strong ME coupling effect, among which C40s (CoFe2O4 content is 40 wt%) sample has a maximum ME coupling coefficient of 587.3 mV/cm∙Oe at 1.8 kHz.

Greener synthesis of lightweight, self‐standing PMMA/CoFe2O4 polymeric film for magnetic, electronic, and terahertz shielding applications

AbstractThis work aims to develop a multifunctional PMMA/CoFe2O4 polymeric film of low loss dielectric constant, high magnetic properties, and perceptible terahertz shielding effectiveness. Pure cobalt ferrite magnetic nanoparticles (CoFe2O4 MNPs) were prepared by a facile‐modified solution deposition method. Then, the nanoparticles were loaded to poly (methyl methacrylate) of different ratios (x = 0, 5, 10, 15, and 20 wt%) to synthesize films by evaporative casting technique. X‐ray diffraction (XRD) evidenced the formation of CoFe2O4 MNPs in the cubic spinal structure. The FTIR confirmed the interaction of CoFe2O4 MNPs with PMMA chains. Compared to the pure PMMA, the PMMA/CoFe2O4 nanocomposites were more thermally stable, as evidenced by thermogravimetric analysis, (TGA) and differential scanning calorimetry (DSC). The micrograph images by FESEM unraveled that CoFe2O4 MNPs have formed in different geometrical shapes (nanocubes, nanotubes, and nano oval). The values of the band gap energy were computed by the absorption spectra fitting (ASF) method. It varied from 4.94 to 4.68 eV, as the CoFe2O4 MNPs contents were changed from 0 to 20 wt%. Compared to host PMMA, the dielectric permittivity was enhanced, while the dielectric loss was slightly decreased. Therefore, the prepared film can be employed as a passive component in electronic circuits, namely capacitors and supercapacitors. The shielding effectiveness (SE) was found to be improved with frequency and CoFe2O4 content, reflecting the applicability of PMMA/CoFe2O4 MNPs films in terahertz shielding. The magnetic parameters were investigated by a vibrating sample magnetometer (VSM) and were found to increase with CoFe2O4 content, which could be used as a flexible film in magnetic applications.

Correlation between the composition, structural parameters and magnetic properties of spinel-based functional nanocomposites

The “soft/soft” (CoFe 2O4)x/Ni0.4Cu0.2Zn0.4Fe2O4)y nanocomposites (NCs), as a function of the phase ratio, have been synthesized via the green sol–gel method using 6 dates. The correlation between chemical composition, structural parameters and magnetic properties was investigated. The average crystallite size (Dmax) of the products was found to be within the range of 24.6-41.1 nm. It was observed that an increase in the CoFe 2O4 content leads to an increase in the most probable size of the coarse fraction and a decrease in the most probable grain size of the fine fraction. As the (Ni0.4Cu0.2Zn0.4)Fe2O4 content increases, the average size of the fine and coarse fractions decreases. The magnetic properties were investigated in a wide magnetic field range (80 kOe) at 300 and 10 K. The maximum magnetization saturation or Ms (∼124.3 emu/g at 10 K and ∼81.2 emu/g at 300 K) was observed for the sample with the ratio 1/2 that was ∼30% higher than Ms for the pure (Ni0.4Cu0.2Zn0.4)Fe2O4 ferrite at 10 K (∼86.9 emu/g) and ∼35% higher than at 300 K (∼52.8 emu/g). This fact clearly demonstrates the presence of a synergetic effect in the NCs. The dominance of low-temperature Ms values was explained by the lack of thermal energy of the disordered spin. The presence of a synergetic effect in the (CoFe 2O4)x/Ni0.4Cu0.2Zn0.4Fe2O4)y NCs can be observed due to a strong coupling between the two magnetic phases, according to careful analysis of the correlation between the chemical composition, structural parameters and magnetic properties.

Hydrothermal synthesis of rGO/Al/CoFe2O4 with low infrared emissivity and strong microwave absorption

Due to the harmful influence of electromagnetic waves, electromagnetic absorption materials are being actively pursued. Herein, a one-step hydrothermal method is used to synthesize rGO/Al/CoFe2O4 composites with different amounts of CoFe2O4, and their electromagnetic properties and infrared emissivity are studied in detail. The results reveal that the rGO/Al/CoFe2O4 composite with a CoFe2O4 content of 0.06 g possesses a minimum reflection loss (RLmin) of −68.03 dB at 15.5 GHz at a thickness of 1.38 mm, while the effective absorption broadband (EAB) and infrared emissivity are found to be 3.3 GHz and 0.63, respectively. Hence, the as-designed rGO/Al/CoFe2O4 composites can be used for both wave absorption and low-infrared emissivity fields, and the proposed strategy is an effective solution for designing bifunctional wave absorption materials.

Tailoring ZnO/CoFe2O4 nanocomposites: structure, optical, dielectric and magnetic study

The structural, morphology, optical, magnetic and dielectric properties of the (ZnO)1–x(CoFe2O4)x, (x = 1, 3 and 5 wt%) nanocomposites synthetized by sonomechanical method were investigated using XRD, FE-SEM, HR-TEM, UV-visible, VSM and BDS. XRD analysis shows that, ZnO and CoFe2O4 acquired hexagonal and cubic phases, respectively. The optical band gap was reduced from 3.22 eV for pure ZnO to 3.15 eV after adding 5wt % of CoFe2O4. Addition of 1wt% CoFe2O4 to ZnO matrix showed a noticeable ferromagnetic behavior that was predominant in the prepared nanocomposites and confirmed by the convex Arrott–Belov–Kouvel curves. The dielectric constant, ε′, at higher frequencies of the investigated nanocomposites is relatively high (8–10) accompanied by low values of dielectric loss, ε″ ranging between 0.001 and 0.003 and hence very low values of the dissipation factor D (= ε″/ε′) making them applicable in the field of microwave shielding. On the other hand, the dc-conductivity, σ dc at 25 C shows a remarkable increase by Addition of 1wt% CoFe2O4 to ZnO matrix and decreases gradually with further increase of the ferrite. This indicates the effect of mobility and/or the number density of charge carriers on the conductivity. The investigation at higher temperature, 150 C, shows a gradual decrease in the conductivity with increasing CoFe2O4 content.

Highly stable MWCNT-CoFe2O4 photocatalyst. EGA-FTIR coupling as efficient tool to illustrate the formation mechanism

MWCNT-CoFe2O4 nanocomposites were prepared in sequential synthesis steps by decorating CoFe2O4 nanoparticles on the surface of functionalized MWCNT. Initially, the CoFe2O4 nanoparticles were obtained by chemical precipitation and subsequently, the obtained CoFe2O4 nanoparticles were anchored on functionalized MWCNT through polymer wrapping. The thermal analysis approaches namely, evolved gas analysis (EGA) coupled with FT-IR spectra were involved in highlighting the sequential steps mechanism for obtaining MWCNT-CoFe2O4 nanocomposites. The composite formation was proved by X-ray Diffraction (XRD), Scanning Transmission Electron Microscopy (STEM), FT-IR spectroscopy, X-ray Photoelectron Spectroscopy (XPS). The influence of CoFe2O4 content on the magnetic and textural properties (surface area and porosity measurements) of the obtained nanocomposites was evidenced. Depicting the importance of thermal stability of nanomaterials in different industrial applications, the thermal behavior of MWCNT and CoFe2O4 was pointed out. Furthermore, the photocatalytic activity against organic pollutants such as Rhodamine B (RhB) and oxytetracicline (OTC) were evidenced. Additionally, it was evidenced that the MWCNTs acquired ferromagnetic behavior through spin polarized electron transfer from the CoFe2O4. The electron spin resonance spectroscopy (ESR) coupled with spin trapping technique was used to evidence the generation of reactive oxygen species (ROS). The obtained results suggest the efficient anchoring of CoFe2O4 on MWCNT through polymer linkage resulting in a thermal stable magnetic recoverable photocatalyst. The photocatalytic mechanism was discussed in terms spin polarized transitions and ROS generation. During the irradiation superoxide anion (O2-), hydroxyl (•OH) radical and nitroxide were detected.

MOF-derived CoFe2O4/FeO/Fe nanocomposites as anode materials for high-performance lithium-ion batteries

Due to the high theoretical capacity and low cost, iron-based oxides are considered to be valuable anode materials for lithium-ion batteries (LIBs) with applications. Its nanoscale design can effectively overcome the disadvantages of volume expansion and slow ion/electron transport rate. In this study, CoFe2O4/FeO/Fe three-phase composite nanospheres with ~10 nm diameter were prepared by high-temperature roasting using Co-Fe MOF as the precursor. By adjusting the synthesis temperature, the ratio of each phase was changed and their electrochemical properties were investigated. Due to the synergistic effect of the multivalent states of iron, composites with optimal ratios (Fe-Co-700) can obtain capacities exceeding the theoretical limits (1129.8 mAh g−1 at 0.1 A g−1). Even at 2 A g−1 high current test, nanocomposites still show excellent properties (capacity of 1120.2 mAh g−1 after 500 cycles). In addition, the results show that the content of CoFe2O4 contributes significantly to the capacity, while the content of Fe has a positive effect on the electrical conductivity. According to the test of galvanostatic intermittent titration technique (GITT), the Li+ diffusion coefficient of Fe-Co-700 composite is larger than that of materials calcined at other temperatures. These excellent properties demonstrate the positive significance of phase ratio tuning of microstructures for the design of future energy storage materials.

One-pot hydrothermally prepared rGO/SiC/CoFe2O4 composites with strong microwave absorption at different thicknesses

Currently, to solve the problem of electromagnetic radiation, it is imperative to develop a thin, lightweight absorber, with a wide bandwidth and an excellent absorption ability. In this study, SiC and CoFe2O4 were combined on reduced graphene oxide (rGO) with immobilized rGO and SiC nanoparticles and varying amounts of CoFe2O4 nanoparticles. A facile one-pot hydrothermal technique was employed to prepare four rGO/SiC/CoFe2O4 composite samples with varied CoFe2O4 concentrations. The electromagnetic properties of rGO/SiC/CoFe2O4 composites were affected by CoFe2O4 content, and CoFe2O4 content was varied to change the electromagnetic properties of composites. The rGO/SiC/CoFe2O4 composite samples were prepared at a graphene oxide (GO) mass of 0.5 g, SiC mass of 0.25 g, and CoFe2O4 mass of 1.5 g, and this composite sample exhibited the best microwave absorption consumption. At 60 wt% of rGO/SiC/CoFe2O4 composite sample, the RLmin at 7.4 GHz with a thickness of 2.43 mm was −62.39 dB, and efficient absorption of broadband (EAB) was 1.4 GHz (6.8–8.2 GHz). The EAB was 3.2 GHz (11.8–15 GHz), and the RLmin was −59.77 dB at 13.2 GHz with a thickness of 1.39 mm. The RLmin at 17.2 GHz was −65.49 dB, and the EAB was 2.3 GHz (15.7–18 GHz), despite a thickness of only 1.06 mm. The rGO/SiC/CoFe2O4 composite comprised carbon materials, magnetic metals, and semiconductors. High-performance microwave absorption was achieved by the introduction of more than one loss mechanism and coordination and supplementation of multicomponent functions. The proposed carbon/semiconductor/magnetic composite material provides a feasible solution for the preparation of excellent microwave absorbing materials in the future.

Investigation of exchange coupling and microwave properties of hard/soft (SrNi0.02Zr0.01Fe11.96O19)/(CoFe2O4)x nanocomposites

This article deals with the synthesis and the investigation of the structural features, magnetic and microwave properties of hard/soft (H/S) SrNi0.02Zr0.01Fe11.96O19 (SrNiZr)/CoFe2O4 (CFO)x (x = 1.0, 1.5, 2.0, 2.5, 3.0) nanocomposites (NCs). Products were manufactured via one-pot sol-gel auto-combustion approach. The formation of hard/soft phases was verified via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HR-TEM) techniques. XRD analyses proved the presence of both hexagonal and cubic crystal structure in each H/S NCs. Vibrating sample magnetometer was employed to examine the magnetic features of the prepared NCs at room (RT; T = 300 K) and low temperatures (LT; T = 10 K). The magnetization (M) vs. applied field (H) curves displayed complete and good exchange coupling among the hard and soft phases for the different samples at 300 K. In contrast, an incomplete and weak exchange-coupled interaction was observed for all NCs at 10 K, excepting the SrNiZr/(CFO)1.0 NCs. The different magnetic parameters (Hc,Ms,Mr, and nB) were extracted for the H/S SrNiZr/(CFO)x (x = 1.0, 1.5, 2.0, 2.5, 3.0) NCs at both temperatures. All products exhibited a single magnetic domain since the value of squareness ratio is Mr/Ms> 0.5. The correlation of the electromagnetic properties (frequency dependences of the permittivity/permeability and reflection losses) as function of the magnetic phase ratio in H/S SrNiZr/(CFO)x (x = 1.0, 1.5, 2.0, 2.5, 3.0) functional NCs were analyzed from S11–S21 parameters (2–18 GHz). It was observed strong correlation between the CFO content (x) and electrodynamic parameters (permittivity, permeability, and reflection losses). It is established that these materials can be applied for electromagnetic compatibility and radar-technologies.

Efficient peroxymonosulfate activation by CoFe2O4-CeO2 composite: Performance and catalytic mechanism

CoFe2O4-CeO2 composites with different CoFe2O4 content were synthesized and used as catalysts for peroxymonosulfate (PMS) activation in water purification. Under the conditions of 200 mg/L 15%CoFe2O4-CeO2 and 0.15 mM PMS, complete atrazine degradation was achieved in the 15%CoFe2O4-CeO2/PMS system. The pseudo-first-order rate constant (kobs) in 15%CoFe2O4-CeO2/PMS system (0.224 min−1) was 2.4 and 4.8 times of that in CoFe2O4/PMS system (0.092 min−1) and (CoFe2O4 + CeO2)/PMS system (0.047 min−1). The main reactive species were verified through various quenching experiments and electron paramagnetic resonance tests, and the concentration of two main radicals was calculated. In addition, the interaction between CoFe2O4 and CeO2 involving Co(III)/Co(II), Fe(III)/Fe(II), and Ce(IV)/Ce(III) redox recycle for accelerating the degradation of organic compounds was explored. In addition, different from Cl−, HCO3− and NO3−, H2PO4− could promote atrazine degradation in 15%CoFe2O4-CeO2/PMS system by improving sulfate radical concentration in the reaction system. The main degradation intermediates of atrazine in the 15%CoFe2O4-CeO2/PMS and CoFe2O4/PMS systems were compared, as well as the degradation pathways. The toxicity analysis based on luminescent bacteria Vibrio fischeri indicated the superiority of 15%CoFe2O4-CeO2/PMS than CoFe2O4/PMS systems for ATZ degradation.

Enhanced magneto-electric properties and magnetodielectric effect in lead-free (1-x)0.94Na0.5Bi0.5TiO3-0.06BaTiO3–x CoFe2O4 particulate composites

The lead-free magnetoelectric particulate composites (1-x)0.94Na0.5Bi0.5TiO3-0.06BaTiO3–x CoFe2O4 (where, x = 0, 0.15, 0.25, 0.35, 0.45) were synthesized by the solid-state sintering technique. The coexistence of piezoelectric 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (NBBT) and ferromagnetic CoFe2O4 (CFO) phases were confirmed by structural studies. The average crystallite size and the strain produced in the composites between the interface of different phases were estimated using Williamson-Hall method. The microstructural analysis indicates that the closely dense-packed CFO grains are distributed in the NBBT matrix. The ferroelectric nature of the composites was confirmed by the polarization versus electric field hysteresis loop and found to decrease with CFO content, which is attributed to the conducting nature of CFO. The observed values of saturation (Ms), remanent (Mr) magnetization, and magnetic moment (µB) in the composites are 28.46 emu/gm, 5.01 emu/gm and 1.13 µB, respectively for the higher CFO content. The dielectric relaxation phenomena in the composites have been observed, and the enhanced dielectric constant (ε′) is explained based on the electron hopping mechanism. All composites exhibit a relaxor nature which is described by the Vogel–Fulcher relation. The magnetoelectric coupling is estimated in the composites indirectly by measuring the relative change in the dielectric constant in the presence of the external magnetic field. The estimated values of magneto-capacitance at 1 kHz frequency for 25 and 35 mol% are ~ − 5.5 and ~ − 6%, respectively, which indicate that these materials can be useful for magneto-dielectric based devices applications.

Study of Soft/Hard Bimagnetic CoFe²/CoFe²O⁴ Nanocomposite.

We report an experimental study of the bimagnetic nanocomposites CoFe₂/CoFe₂O₄. The precursor material, CoFe₂O₄ was prepared using the conventional stoichiometric combustion method. The nano-structured material CoFe₂/CoFe₂O₄ was obtained by total oxygen reduction of CoFe₂O₄ using a thermal treatment at 350 °C in H₂ atmospheres following the partial oxidation in O₂ atmospheres at 380 °C during 120; 30; 15, 10, and 5 min. The X-ray diffraction, Mössbauer spectroscopy and transmission electronic microscopy images confirmed the formation of the material CoFe₂/CoFe₂O₄. The magnetic hysteresis for the nanocomposite with different saturation magnetization (from 87 to 108 emu/g) also confirms the formation of the CoFe₂/CoFe₂O₄ with different content of CoFe₂O₄. Furthermore, the magnetic hysteresis curves for all samples presented a single magnetic behavior, suggesting the magnetic coupling between the phases of the nanocomposite. The effects of high energy milling on the magnetic properties of the precursor material and nanocomposites samples were evaluated.

Exchange spring behaviour in BaFe12O19/CoFe2O4 magnetic nanocomposites

Abstract In this work, nanopowders of BaFe12O19 and CoFe2O4 and nanocomposites of (1−x) BaFe12O19/xCoFe2O4, for x = 0.00, 0.25, 0.50, 0.75 and 1.00, were prepared via co-precipitation and high-speed ball milling techniques, respectively. For structural analysis, the X-ray diffraction revealed the formation of hexagonal BaFe12O19 and spinel CoFe2O4 ferrites, and the average crystallite sizes were about 35 nm and 15 nm, respectively. The transmission electron microscope indicated that the two phases are well distributed and the grain sizes of the composite powders are verified employing the size distribution histograms where two peaks were obtained separately for both ferrites. From EDX spectra, it was shown that all samples exhibit an excellent compositional homogeneity verifying the presence of both phases in the obtained nanocomposite powders. Magnetic measurements were performed via a vibrating sample magnetometer at 300 K and 77 K. The results showed a good single-phase magnetic behavior, proving the good exchange coupling between hard and soft phases. For low CoFe2O4 content, the dipolar interactions were dominated by the exchange-coupling interactions. Additionally, the optimum values of saturation and remanent magnetizations as well as the squareness ratio were obtained for the x = 0.5. This was attributed to the dominance of exchange-coupling interaction. Magnetic properties for nanocomposites were improved as the temperature falls from room temperature down to 77 K. This increase is skilled to the reduction in the thermal fluxes of magnetic moments at the surface.

Fabrication, mechanical, and electromagnetic studies of cobalt ferrite based‐epoxy nanocomposites

AbstractControlling the interface, contact of organic‐inorganic materials is necessary for the preparation of high‐performance hybrid nanocomposites. Herein, the cobalt ferrite (CoFe2O4) nanofiller was synthesized via coprecipitation route by the reaction of Fe2 (SO4)3, CoSO4, and triethylene glycol. The obtained CoFe2O4 nanoparticles were thermally treated at 600°C for 5 hours. As prepared, the CoFe2O4 nanoparticles were surface functionalized with 3‐(triethoxysilyl) propylamine (APTES). The modified CoFe2O4 nanoparticles were used as reinforcement during the fabrication of epoxy‐based CoFe2O4 nanocomposite. The synthesized nanofillers and nanocomposites were structurally examined by Fourier transform infrared, X‐ray diffraction analysis, scanning electron microscopy, and thermogravimetric analysis. The effect of nanofiller on surface resistivity, electrical conductivity, and mechanical performance was also investigated. The surface resistivity of EP‐CoFe2O4 nanocomposite decreases with increasing loading concentration of CoFe2O4, while thermal degradation temperatures are improved by 90 K (12.7%) compared to neat EP‐polymer. The mechanical properties, that is, stress‐strain and Young's modulus show an increase of about 60% and 35%, respectively, at 5 wt% CoFe2O4 content. The incredible improvement in the electrical conductivity, mechanical, and thermal stability of EP‐CoFe2O4 up to 5%wt. CoFe2O4 contents are attained due to smaller size and well dispersion of nanofillers in the polymeric matrix. These simultaneous enhancements in properties intend that the EP‐CoFe2O4 nanocomposites can be useful as protective coatings and corrosion‐resistant for a variety of applications

Identification of dielectric and magnetic properties of core shell ZnTiO3/CoFe2O4 nanocomposites

Electromagnetic core shell nanocomposites (1 − x) ZnTiO3/(x) CoFe2O4 were prepared successfully through sol–gel procedures, where (x ~ 0, 5, 10 and 15 wt%). The end product powders were identified through XRD, SEM, and TEM. The XRD results prove the presence of ZnTiO3 and CoFe2O4, while the SEM graph confirms the core–shell nanostructure. The dielectric properties such as dielectric constant (e′), loss tangent tan(δ), dielectric modulus M′ and M″, and ac conductivity (σ) are measured in the frequency range 0.1–107 Hz. The dielectric properties show a dependence behavior on the variation of CoFe2O4 content in the core–shell composite. CoFe2O4@ZnTiO3 nanocomposites manifest striking enhancement on dielectric properties compared to ZnTiO3. The dielectric permittivity (ɛ′) increases from 204 to 415 at low frequency with increasing the CFO content from zero to 15 wt%. The Loss tangent tan (δ) of the electromagnetic nanocomposite has a very tiny value of 3.8 × 10−3 in the high-frequency range proving a very high-quality factor (Q = ν × 1/tan (δ) ~ 2 × 109 at 107 Hz. Mʺ shows a peak that differentiates between the long-range hopping and the localized motion of the charge carriers. The conductivity of the electromagnetic composite is released from hopping charge carriers over the whole frequency range compared to CoFe2O4. The improvement of the micro capacitor due to the interfacial polarization enhances the dielectric characterization of CoFe2O4@ZnTiO3. The electromagnetic samples show a presence of magnetic order, in which the saturation magnetization of the electromagnetic samples increases from 0.113 to 9.35 emu/g with increasing CoFe2O4 concentration from 5 to 15 wt%.