Structure and magnetic properties of multi-morphological CoFe2O4/CoFe nanocomposites by one-step hydrothermal synthesis

Multi-morphological CoFe₂O₄/CoFe nanocomposites have been synthesized using a facile hydrothermal process. The effects of hydrazine hydrate amount during hydrothermal reaction on the structure and magnetic property of the specimens were studied. With increasing hydrazine hydrate amount, the CoFe₂O₄ transformed to CoFe and the morphology of the specimen changed from granular particles to faceted particles. The saturation magnetization monotonically increased and the coercivity monotonically decreased with increasing hydrazine hydrate amount. The magnetic interactions, determining the magnetic properties of the composites, result from the dominant dipole coupling and relative weak exchange coupling between CoFe₂O₄ and CoFe nanoparticles. The CoFe₂O₄/CoFe nanocomposite prepared with 2?mL hydrazine hydrate exhibited the optimal magnetic properties, with the saturation magnetization of 81?emu/g and coercivity of 636?Oe.     

Effect of the rare-earth substitution on the structural,magnetic and adsorption properties in cobalt ferrite nanoparticles

Rare-earth (RE) substituted cobalt ferrite CoFe_1.9RE_0.1O₄ (RE=Pr³⁺, Sm³⁺, Tb³⁺, Ho³⁺) nanoparticles are synthesized by a facile hydrothermal method without any template and surfactant. The effects of RE³⁺ substitution on structural, magnetic and adsorption properties of cobalt ferrite nanoparticles are investigated. Structure, morphology, particle size, chemical composition and magnetic properties of the ferrite nanoparticles are studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), high solution transmission electron microscopy (HRTEM), energy-dispersive spectrometer (EDS), Fourier transform spectroscopy (FTIR), Raman spectra and vibrating sample magnetometry (VSM). The results indicate that the as-synthesized samples have the pure spinel phase, uniform crystallite size and narrow particle size distribution. Meanwhile, the RE³⁺ substitution leads to the decrease in the particle size, magnetization and coercivity of the CoFe₂O₄ ferrite. Notably, it demonstrates that the RE³⁺ doping can apparently enhance the adsorption capacity for Congo red (CR) onto ferrite nanoparticles. Adsorption equilibrium studies show that adsorption of CR follows the Langmuir model. The monolayer adsorption capacities of CoFe_1.9Sm_0.1O₄ and CoFe_1.9Ho_0.1O₄ are 178.6 and 158.0 mg/g, respectively. The adsorption kinetics can be described by the pseudo-second-order model.     

Effect of lemon juice on microstructure,phase changes,and magnetic performance of CoFe2O4 nanoparticles and their use on release of anti-cancer drugs

Cobalt ferrite magnetic nanoparticles were synthesized and developed by a modified Pechini method using iron nitrate, cobalt nitrate, ethylene glycol (EG), and sucrose with different volumes of lemon juice (10, 20, 30, 40, 50, 60, and 70 ml) as the source of chelating agent as well as nonmagnetic elements such as Ca and Mg ions. The XRD patterns confirmed that all samples synthesized by different contents of extracted lemon juice had a cubic crystal structure with single-phase spinel. Scanning electron microscopy revealed that cobalt ferrite nanoparticles had a semi-spherical morphology. Also, the vibrating sample magnetometer indicated that the saturation magnetization of CoFe₂O₄ nanoparticles prepared with different values of extracted lemon juice increased from 18.6 emu/g for 10 ml extracted lemon juice to 75.7 emu/g for 50 ml extracted lemon juice, after which the saturation magnetization diminished. Afterwards, the CoFe₂O₄ nanoparticles were coated with polyethylene glycol (PEG) and doxorubicin (DOX) drugs, whereby drug delivery was detected at different pH levels. The CoFe₂O₄-PEG-DOX nanocomposite could release doxorubicin by more than 42% at pH = 5.4 in 75 h.     

Impact of rare earth europium (RE-Eu3+) ions substitution on microstructural,optical and magnetic properties of CoFe2−xEuxO4 nanosystems

In this study, pure cobalt ferrite (CoFe₂O₄) nanoparticles and europium doped CoFe₂O₄ (CoFe_2−xEu_xO₄; x = 0.1, 0.2, 0.3) nanoparticles were synthesized by the precipitation and hydrothermal approach. The impact of replacing trivalent iron (Fe³⁺) ions by trivalent rare earth europium (RE-Eu³⁺) ions on the microstructure, optical and magnetic properties of the produced CoFe₂O₄ nanoparticles was studied. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra exposed the consistency of a single cubic phase with the evidence of Eu₂O₃ phases for x ≥ 0.2. FTIR transmittance spectra showed that, the all investigated samples have three characteristic metal-oxygen bond vibrations corresponding to octahedral B-site (υ₁ and υ₂) and tetrahedral A-site (υ₃) around 415 cm⁻¹, 470 cm⁻¹ and 600 cm⁻¹ respectively. XRD and energy dispersive X-ray spectroscopy studies affirmed the integration of RE-Eu³⁺ ions within CoFe₂O₄ host lattice and decrease of average crystals size from 13.7 nm to 4.7 nm. Transmission electron microscopy (TEM) analysis showed the crucial role played by RE-Eu³⁺ added to CoFe₂O₄ in reducing the particle size below 5 nm in agreement with XRD analysis. High resolution-TEM (HR-TEM) analysis showed that the as-synthesized spinel ferrite, i.e., CoFe_2−xEu_xO₄, nanoparticles are single-crystalline with no visible defects. In addition, the HR-TEM results showed that pure and doped CoFe₂O₄ have well-resolved lattice fringes and their interplanar spacings matches that obtained by XRD analysis. Magnetic properties investigated by the vibrating sample magnetometer technique illustrated transformation of magnetic state from ferromagnetic to superparamagnetic at 300 K resulting in introducing RE-Eu³⁺ in CoFe₂O₄ lattice. At low temperature (~5 K) the magnetic order was ferromagnetic for both pure and doped CoFe₂O₄ samples. Substitution of Fe³⁺ ions in CoFe₂O₄ nanoparticles with RE-Eu³⁺ ions optimizes the sample nanocrystals size, cation distribution and magnetic properties for many applications.     

Synthesis, Characterization and Effects of Citric Acid and PVA on Magnetic Properties of CoFe2O4

Cobalt ferrite (CoFe₂O₄) particles were synthesized by sol–gel method using metal nitrates, citric acid (CA) and polyvinyl alcohol (PVA). X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM), thermogravimetry/differential scanning calorimetry analysis and vibrating sample magnetometer were used to study the structural, thermal and magnetic properties of the CoFe₂O₄ powder. XRD results indicate that the resultant particles have crystalline, pure single phase spinel structure. From HR-SEM images, a systematic decrease in particle size is observed with an increase in PVA concentration, along with addition of CA. CA at various concentrations of PVA significantly enhance the magnetic properties of the materials.     

Single-phase and binary phase nanogranular ferrites for magnetic hyperthermia application

The study demonstrates the performance of heating efficiency in single-phase and binary phase spinel ferrite nanosystems. Ferrimagnetic cobalt ferrite (CoFe₂O₄) (CFO) and superparamagnetic copper ferrite/copper oxide (CuFe₂O₄/CuO) (CuF) nanosystems of different particle sizes were synthesized through a microwave-assisted coprecipitation method. The heating behavior was observed in range of both field amplitudes (8-24 kA/m at 516 kHz) and frequencies (325-973 kHz at 12 kA/m). The heating efficiency was analyzed and compared by means of particle size, magnetization, effective anisotropy constant, and Néel relaxation mechanism. Indeed, the heating rate was maximized in larger ferrite particles with low effective anisotropy constant. Moreover, though the magnetization and effective anisotropy constant of single-phase CoFe₂O₄ nanoparticles were higher, the binary phase CuFe₂O₄/CuO nanosystems of similar crystallite size (28 nm) exhibited superior heating efficiency (4.21°C/s). For a field amplitude and frequency of 24 kA/m and 516 kHz, the heating rate of CuF and CFO ferrites with different crystallite sizes decreased in the order of 4.21 > 2.14 > 0.58 > 0.52°C/s for 29 nm > 25 nm > 12 nm > 15 nm, respectively. The results emphasize that binary phase ferrite nanoparticles are better thermoseeds than the single-phase ferrites for the magnetic hyperthermia application.     

Structure and magnetic properties of CoFe2O4/SiO2 nanocomposites obtained by sol-gel and post annealing pathways

The influence of the CoFe₂O₄ nanoparticles concentration in silica matrix on the structural and magnetic properties of xCoFe₂O₄/(100−x)SiO₂ nanocomposites with x=10, 30, 50, 70 and 90 was studied. Magnetic CoFe₂O₄ nanoparticles dispersed in silica matrix was obtained by sol-gel method, followed by annealing at 1100 °C. The X-ray diffraction pattern and FT-IR spectra revealed the single spinel ferrite structure for all samples. The FT-IR spectra also suggested the formation of the amorphous silica matrix. The results showed that the increase of cobalt ferrite concentration (x) in the silica matrix leads to high crystallinity, specific surface area and particle size. The magnetic CoFe₂O₄ nanoparticles have spherical shapes and size in the 6–35 nm range. The Mössbauer measurements were fitted with two Zeeman sextets, indicating that all the samples were completely magnetically ordered. The vibrating sample magnetometer studies showed that the saturation magnetization (Ms) and coercivity (Hc) of the CoFe₂O₄ nanocrystals embedded in silica matrix possessed a linear relationship with the mean crystallite size. Also, the saturation magnetization of the studied nanocomposites increases with the increase of cobalt ferrite concentration (x) in the silica matrix.     

Size-controlled high magnetization CoFe2O4 nanospheres and nanocubes using rapid one-pot sonochemical technique

Highly crystalline single phase spherical and monodisperse cobalt ferrite (CoFe₂O₄) nanoparticles (NPs) with uniform shape and size distribution have been synthesized by one pot-rapid sonochemical method. The effect of different solvents, such as aqueous, alcoholic, and a mix of water/ethanol in 1:1 volume ratio on the shape, size, and crystalline structure of CoFe₂O₄ NPs were studied using X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy. The size of CoFe₂O₄ nanoparticle was controlled in the range from 20 to 110 nm based on the solvent medium used in the synthesis process. Furthermore, the evolution from spherical to cubic morphology of cobalt ferrite NPs is achieved by simply changing the solvent medium from aqueous to alcoholic medium. The magnetic properties of all the synthesized CoFe₂O₄ NPs were studied by vibrating sample magnetometer (VSM) at room temperature. The magnetization value was found to be particle size dependent, and high magnetization (Ms) of 92.5 emu/g was obtained for the CoFe₂O₄ NPs sample synthesized in a mixed solution of water and ethanol. A possible reaction mechanism for the formation of cobalt ferrite NPs by the sonochemical technique was discussed. The facile method adopted in our study appears to be a promising route for synthesis of highly crystalline nanoparticles within short times and without the need for using any calcination process.     

Structural,magnetic, and antimicrobial properties of zinc doped magnesium ferrite for drug delivery applications

In this study, drug loading and release ability of the ferrite nanoparticle coated with PEG (polyethylene glycol) have been investigated for biomedical applications. The zinc-magnesium ferrite (Zn_xMg_(1-x)Fe₂O₄) was synthesized using sol-gel route. The doping concentration of Zn was gradually increased from zero to maximum (x = 1). XRD (X-ray diffraction) analysis of the samples shows the single phase with a cubic spinel structure. The Debye-Scherer formula has been used to calculate the average crystallite size (30.51 nm). The dumbbell and spherical shaped morphology (40–50 nm average particle size) have been investigated from the secondary electron images of FESEM (Field Emission Scanning Electron Microscopy). The antimicrobial assay has been carried out against E. coli bacteria by gentamicin (drug) loaded ferrite nanoparticles. The significant zone of inhibition might suggest that the drug-loaded ferrite nanoparticles can be used in drug delivery applications. PL (Photoluminescence) of the spinel ferrite shows that all the samples are in the visible range, and peaks at around 430 nm. The result reveals the synthesis of high purity ferrite nanoparticles with significant potential for drug delivery applications.     

Impact of Zn doping on the dielectric and magnetic properties of CoFe2O4 nanoparticles

Owing to its unique magnetic, dielectric, electrical and catalytic properties, ferrite nanostructure materials gain vital importance in high frequency, memory, imaging, sensor, energy and biomedical applications. Doping is one of the strategies to manipulate the spinel ferrite structure, which could alter the physico-chemical properties. In the present work, Co_1-xZn_xFe₂O₄ ($x$ = 0, 0.1, 0.2, 0.3, and 0.4 wt%) nanoparticles were prepared by sol-gel auto-combustion method and its structural, morphological, vibrational, optical, electrical and magnetic properties were studied. The structural analysis affirms the single-phase cubic spinel structure of CoFe₂O₄. The crystallite size, lattice constant, unit cell, X-ray density, dislocation density and hopping length were significantly varied with Zn doping. The Fe–O stretching vibration was estimated by FTIR and Raman spectra. TEM micrographs show the agglomerated particles and it size varies between 10 and 56 nm. The Hall effect measurement shows the switching of charge carriers from n to p type. The dielectric constant (ε′) varies from 0.2 × 10³ to 1.2 × 10³ for different Zn doping. The VSM analysis shows relatively high saturation magnetization of 57 and 69 emu/g for ZC 0.1 and ZC 0.2 samples, respectively than that of undoped sample. All the prepared samples exhibit soft magnetic behaviour. Hence, it can be realized that the lower concentration of Zn ion doping significantly alters the magnetic properties of CoFe₂O₄ through variation in the cationic distribution and exchange interaction between the Co and Fe sites of the inverse spinel structure of CoFe₂O_4.     

Facile micro-patterning of ferromagnetic CoFe2O4 films using a combined approach of sol–gel method and UV irradiation

CoFe₂O₄ photosensitive sol was prepared using iron nitrate and cobalt nitrate as precursors, acetyl acetone as a chelating agent, and ethanol as a solvent. CoFe₂O₄ photosensitive sol was used to fabricate smooth and micro-patterned CoFe₂O₄ films. The effects of UV irradiation on the crystallinity, surface morphology and ferromagnetic properties of CoFe₂O₄ films were investigated. For the film prepared using conventional sol-gel process, the crystallization of spinel CoFe₂O₄ phase was completely finished at ~ 600?℃, and no intermediate phase was formed. However, when the sol-gel process was combined with UV irradiation, Fe₂O₃ and CoO intermediate phases were firstly generated, and then reacted to form CoFe₂O₄ phase. Facile micro-patterning of CoFe₂O₄ films can be realized using a combined approach of sol-gel method and UV irradiation without using any photoresist. The structure and functional properties of the CoFe₂O₄ film have not been affected during the patterning process, and its magnetic properties have also not been changed.     

Phenol methylation over nanoparticulate CoFe2O4 inverse spinel catalysts: The effect of morphology on catalytic performance

A series of CoFe₂O₄ nanoparticles have been prepared via co-precipitation and controlled thermal sintering, with tunable diameters spanning 7–50 nm. XRD confirms that the inverse spinel structure is adopted by all samples, while XPS shows their surface compositions depend on calcination temperature and associated particle size. Small (<20 nm) particles expose Fe³⁺ enriched surfaces, whereas larger (50 nm) particles formed at higher temperatures possess Co:Fe surface compositions close to the expected 1:2 bulk ratio. A model is proposed in which smaller crystallites expose predominately (1 1 1) facets, preferentially terminated in tetrahedral Fe³⁺ surface sites, while sintering favours (1 1 0) and (1 0 0) facets and Co:Fe surface compositions closer to the bulk inverse spinel phase. All materials were active towards the gas-phase methylation of phenol to o-cresol at temperatures as low as 300 °C. Under these conditions, materials calcined at 450 and 750 °C exhibit o-cresol selectivities of 90% and 80%, respectively. Increasing either particle size or reaction temperature promotes methanol decomposition and the evolution of gaseous reductants (principally CO and H₂), which may play a role in CoFe₂O₄ reduction and the concomitant respective dehydroxylation of phenol to benzene. The degree of methanol decomposition, and consequent H₂ or CO evolution, appears to correlate with surface Co²⁺ content: larger CoFe₂O₄ nanoparticles have more Co rich surfaces and are more active towards methanol decomposition than their smaller counterparts. Reduction of the inverse spinel surface thus switches catalysis from the regio- and chemo-selective methylation of phenol to o-cresol, towards methanol decomposition and phenol dehydroxylation to benzene. At 300 °C sub-20 nm CoFe₂O₄ nanoparticles are less active for methanol decomposition and become less susceptible to reduction than their 50 nm counterparts, favouring a high selectivity towards methylation.     

Efficient visible light magnetic modified iron oxide photocatalysts

Magnetite iron oxide (Fe₃O₄) nanoparticles were synthesized via simple co-precipitation method using ferrous and ferric ions salts. Fe₃O₄ nanoparticles were modified by silica and titania. Pure and modified nanoparticles were employed for dye degradation under visible light. X-ray diffraction analysis indicated inverse spinel structure of Fe₃O₄ nanoparticles. The particle size of magnetite nanoparticles is decreased due to coating of silica and titania. Scanning and transmission electron microscopy indicated the spherical morphology for all samples. The synthesized Fe₃O₄ nanoparticles were ferromagnetic in nature with highest saturation magnetization value of 1.1034 emu as compared to silica and titania coated samples. Fourier transform infra-red spectra confirmed the incorporation of magnetite nanoparticles with silica and titania. Titania modified magnetite sample showed the highest photocatalytic activity as compared to silica modified magnetite nanoparticles and bare iron oxide under visible light irradiations.     

Synthesis and magnetic properties of monodisperse CoFe2O4 nanoparticles coated by SiO2

The monodisperse CoFe₂O₄ nanoparticles were synthesized by a modified chemical coprecipitation method. Coating SiO₂ on the surface of the CoFe₂O₄ nanoparticles was carried out to keep single domain particles non-interacting with cubic magnetocrystalline anisotropy. The Curie temperatures (T_c) of the monodisperse CoFe₂O₄ nanoparticles can be accurately measured because the SiO₂ shells prevented the aggregation and growth of nanoparticles at high temperature. The magnetic properties of the CoFe₂O₄@SiO₂ nanoparticles with core-shell structure in a wide temperature range (300～950?K) were investigated. It is remarkable that the coercive field (H_c) of CoFe₂O₄ nanoparticles increased from about 760?Oe to 1806?Oe after being coated with SiO₂, which increased by 137.6% compared to the uncoated samples at 300?K. The saturation magnetization (M_s) of the CoFe₂O₄@SiO₂ nanoparticles is 34.59?emu/g, which is about 52% of the naked CoFe₂O₄ nanoparticles value (66.51?emu/g) at 300?K. The hysteresis loops of the CoFe₂O₄@SiO₂ nanoparticles showed an orderly magnetic behavior at high temperature, such as the M_s, remanence magnetization (M_r) and H_c decreased as temperature increasing, being equal to zero near T_c. This is a good indication that the CoFe₂O₄@SiO₂ nanoparticles are suitable for a wide variety of technological applications at high temperature.     

Influence of Gd content on the structural,Raman spectroscopic and magnetic properties of CoFe2O4 nanoparticles synthesized by sol-gel route

The structural and magnetic properties of sol-gel synthesized Gd doped (x = 0.00 to 0.15) CoFe₂O₄ nanoparticles (NPs) have been studied. The x-ray diffraction (XRD) and FTIR spectroscopy along with Raman spectra confirmed the formation of face centered cubic inverse spinel structure. TEM images showed the NPs are well-dispersed with average particle size 30 nm. Room temperature magnetic measurement showed the value of coercivity fluctuates from 353 Oe to 1060 Oe for different % of Gd content. The maximum coercivity, saturation magnetization, magnetic moment, magnetic anisotropy, remnant magnetization found for 0.03% Gd content are 1060.19 Oe, 77.53 emu/gm, 3.29 μ, 4.11 × 10⁴ erg/cm³, 32.38 emu/gm, respectively. The large value of coercivity indicated that the interparticle interactions and crystalline anisotropy are high. Thus CoFe_2-xGd_xO₄ magnetic NPs might be a potential candidate for data processing, automotive and telecommunications.     

Magnetically recoverable CoFe1.9Gd0.1O4 ferrite/polyaniline nanocomposite synthesized via green approach for radar band absorption

The gadolinium substituted cobalt ferrite (CoFe_1.9Gd_0.1O₄) nanoparticles and CoFe_1.9Gd_0.1O₄/Polyaniline (PANI) microwave absorber were synthesized by sol-gel auto combustion technique using lemon juice and in-situ polymerization method respectively. X-ray patterns confirmed the formation of single phase cubic structure. The crystallite size of the synthesized CoFe_1.9Gd_0.1O₄ nanoparticles are within the range of 15–68 nm. The saturation magnetization of CoFe_1.9Gd_0.1O₄ ferrite/Polyaniline (PANI) composite was reduced due to nonmagnetic PANI. The reflection loss for microwave absorbing properties of CoFe_1.9Gd_0.1O₄ ferrite nanoparticles and CoFe_1.9Gd_0.1O₄/PANI nanocomposite were investigated and minimum value of reflection loss was found to be −16.85 dB at 13.52 GHz for nanoparticles of thickness 2.5 mm and −25.59 dB at 11.92 GHz for CoFe_1.9Gd_0.1O₄/PANI nanocomposite of thickness 2.0 mm) respectively. The prepared samples have low density, high surface resistivity and enhanced attenuation constant. The nanocomposite exhibits excellent absorption performance over a broad band range in the radar band.     

Bimagnetic hard/soft and soft/hard ferrite nanocomposites: Structural,magnetic and hyperthermia properties

Recent studies show that the chemical composition and shape of magnetic nanoparticles (NPs) play an important role in their properties. In particular, the bimagnetic NPs display useful and in many cases, more interesting properties than single-phase NPs. In this work, we prepared Fe₃O₄ and CoFe₂O₄ cube-like NPs and bimagnetic hard/soft (CoFe₂O₄/Fe₃O₄) and soft/hard (Fe₃O₄/CoFe₂O₄) nanocomposites (core/coating) using a facile and eco-friendly co-precipitation method that allows the synthesis of the cube-like NPs at temperatures near room temperature. The phase purity and the crystallinity of the NPs with a spinel structure were confirmed by the X-ray diffraction and infrared spectra techniques. Transmission electron microscopy (TEM) images revealed that the NPs have a cubic-like shape with an average dimension of 20 nm. Energy dispersive X-ray analysis, Mössbauer spectroscopy and SQUID magnetic measurements indicated the co-existence of Fe₃O₄ and CoFe₂O₄ phases in nanocomposites. In addition, the hysteresis loops exhibited a single-phase behavior in the nanocomposites that indicates there is a good exchange-coupling interaction between the hard and soft magnetic phases. The CoFe₂O₄/Fe₃O₄ nanocomposites presented a larger saturation magnetization than the CoFe₂O₄ NPs that is effective for their use in magnetic hyperthermia. Finally, we studied the hyperthermia properties of samples in an alternating magnetic field with a frequency of 276 kHz and field amplitude of 13.9 kA/m. Our results showed that magnetic hyperthermia efficiency simultaneously depends on the composition of samples along with magnetic anisotropy and saturation magnetization.     

Spinel CoFe2O4 /carbon nanotube composites as efficient bifunctional electrocatalysts for oxygen reduction and oxygen evolution reaction

In the development of fuel cells, it is the key to large-scale commercialization of fuel cells to rationally design and synthesize efficient and non-noble metals-based bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In this paper, spinel CoFe₂O₄/carbon nanotube composites (CoFe₂O₄/CNTs/FA) were synthesized by solvothermal and calcination method. XRD, TEM, XPS and BET characterizations indicate that the addition of complexing agent fumaric acid can improve the crystal growth kinetics and morphology of CoFe₂O₄/CNTs nanohybirds. The as-synthesized CoFe₂O₄/CNTs/FA pyrolyzed at 500 °C have an outstanding bifunctional catalytic activity for ORR and OER with the potential of 1.62V (vs. RHE) at a current density of 10 mA/cm² and half-wave potential E_1/2 = 0.808V (vs. RHE) in alkaline electrolyte, respectively. It is obviously better than unloaded CoFe₂O₄ nanoparticles and commercial CNTs. CoFe₂O₄/CNTs/FA also exhibit better methanol tolerance ability and durability than commercial Pt/C and RuO₂ catalyst. This investigation broadens an idea of simple compounding of spinel with carbon-based materials to improve electrochemical properties.     

The effect of agarose content on the morphology,phase evolution,and magnetic properties of CoFe2O4 nanoparticles prepared by sol‐gel autocombustion method

Hard‐magnetic CoFe₂O₄ nanoparticles were produced with the sol‐gel autocombustion route using agarose and citric acid as a neutral organic gel and combustion agent. For this purpose, the obtained gel is annealed at 800°C for 3 hours and then the spinel structure of the samples was confirmed by X‐ray diffraction (XRD). In addition, the existence of metal‐oxygen complexes in the gel and nanoparticles was investigated by Fourier transformation infrared (FTIR) spectra. Furthermore, FESEM images showed that semispherical and rod‐like particles were obtained by variation in agarose contents. For the rod‐like sample with 2.5 g agarose, the saturation magnetization and coercivity were measured equal to 71.7 emu/g and 10076.84 Oe, respectively.     

Enhancement of magnetic and dielectric properties of KNbO3–CoFe2O4 multiferroic composites via thermal treatment

In this work, multiferroic composites were produced from CoFe₂O₄ and KNbO₃ mixtures via control of the heat treatment temperature. For this, CoFe₂O₄ nanoparticles were produced by sol-gel method, while KNbO₃ was synthesized by microwave-assisted hydrothermal synthesis. The powders were homogenized and subjected to heat treatment at 300, 400 and 500 °C for 5 h. The structural, electrical and magnetic properties were characterized. The results of X-ray diffraction indicated that there was no formation of secondary phases with heat treatment. Raman vibrational modes confirmed the presence of KNbO₃ and CoFe₂O₄ in the prepared composites. SEM analysis showed that the composite microstructure consists of smaller ferrite particles arranged on the surface of largest cubic KNbO₃ particles. The improvement of coercivity (H_C = 382.1Oe) and dielectric constant (?’~7860) was observed for the composite thermally treated at 300 °C. The obtained results show the potential application of KN:CFO composites for multifunctional devices.