Synthesis,phase formation study and magnetic properties of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanopowder prepared by mechanical milling

In this work we report the phase formation and magnetic properties of CoFe₂O₄ nanopowder prepared by mechanical alloying technique using metallic cobalt and hematite powder (1:1 molar ratio) as the initial raw material in ambient air atmosphere. The formation of single phase cobalt ferrite of (Co _0.18 ²⁺ Fe _0.82 ³⁺ )[Co _0.82 ²⁺ Fe _1.18 ³⁺ ]O₄ stoichiometry was confirmed for the samples milled above 15 h without any heat-treatment by XRD and Mössbauer techniques. The average crystallite size of the sample milled for 30 h was ～13 nm. The highest room temperature value of the magnetization measured at 1.5 T was 51 e.m.u/g for the sample milled for 25 h which was much lower than the corresponding value of the bulk cobalt ferrite (80.8 e.m.u/g at 300 K) due to the size effect.     

The effect of capping agents on the structural and magnetic properties of cobalt ferrite nanoparticles

Microwave-assisted co-precipitation method was adopted to analyze the effect of polyethylene glycol (PEG) and urea concentrations on the properties of cobalt ferrite nanoparticles (NPs). The average crystallite size of single phase cubic spinel cobalt ferrite NPs was controlled within 10–14 nm with the effect of PEG, urea and the combination of them. The transmission electron micrographs revealed that the morphology of cobalt ferrites was not significantly influenced by the different concentration of capping agents but almost uniform morphology with nearly narrow size distribution was obtained. The interaction of PEG and urea molecules on the surface of nanoparticles was mediated through –OH hydroxyl group affected the crystal growth rate. The possible interaction mechanism was proposed with the help of IR vibrational spectra. All the samples exhibited ferromagnetism at room temperature and it was found that the capping agents showed an effect on the magnetic properties. The maximum saturation magnetization of 58 emu/g was achieved when the urea of 60 mg was used and the maximum coercivity of 311 Oe was attained when the mixture of PEG (40 mg) and urea (20 mg) were used. Ultrafine and hydrophilic cobalt ferrite NPs that showed appreciable magnetic properties obtained in the present experimental procedure would be of great interest in various biomedical applications.     

Synthesis and characterization of magnetic and microwave absorbing properties in polycrystalline cobalt zinc ferrite (Co<Subscript>0.5</Subscript>Zn<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>) composite

In this research work, magnetic and microwave absorption loss and other response characteristics in cobalt zinc ferrite composite has been studied. Cobalt zinc ferrite with the composition of Co_0.5Zn_0.5Fe₂O₄ was prepared via high energy ball milling followed by sintering. Phase characteristics of the as-prepared sample by using XRD analysis shows evidently that a high crystalline ferrite has been formed with the assists of thermal energy by sintering at 1250 °C which subsequently changes the magnetic properties of the ferrite. A high magnetic permeability and losses was obtained from ferrite with zinc content. Zn substitution into cobalt ferrite has altered the cation distribution between A and B sites in spinel ferrite which contributed to higher magnetic properties. Specifically, Co_0.5Zn_0.5Fe₂O₄ provides electromagnetic wave absorption characteristics. It was found that cobalt zinc ferrite sample is highly potential for microwave absorber which showed the highest reflection loss (RL) value of ??24.5 dB at 8.6 GHz. This material can potentially minimize EMI interferences in the measured frequency range, and was therefore used as fillers in the prepared composite that is applied for microwave absorbing material.     

Study of preparation and magnetic properties of silica-coated cobalt ferrite nanocomposites

The structure and the magnetic properties of silica-coated cobalt ferrite nanoparticles (80 wt% CoFe₂O₄), prepared by sol–gel method and submitted to thermal treatments in the range 800–1,000 °C, were investigated through XRD, FT-IR, TEM and VSM. The effects of thermal treatment temperatures on the structure and magnetic properties of nanoparticles were examined. A silica shell thickness of about 5 nm was synthesized on top of cobalt ferrite nanoparticles. The non-crystalline silica confines the growth of cobalt ferrite nanoparticles, i.e., the particle sizes are almost independent of the thermal treatment. Saturation magnetization (Ms) was decreased slightly and coercivity (Hc) was increased, when the non-crystalline silica was coated on the surface of cobalt ferrite nanoparticles.     

Structural,magnetic properties,and induction heating behavior studies of cobalt ferrite nanopowders synthesized using modified co-precipitation method

Nanocrystalline cobalt ferrite CoFe₂O₄ powders have been successfully synthesized via modified co-precipitation at low temperature. Obviously, well crystalline CoFe₂O₄ phase was obtained from the precipitated precursors at pH 10 using 5?M NaOH as a base thermally treated at 80°C for 1?h in aqueous medium in the absence and the presence of 1000?ppm cetyl trimethyl ammonium bromide (CTAB) as well as sodium dodecyl sulfate (SDS) as cationic and anionic surfactants, respectively. Meanwhile, the spinel ferrite was observed with the similar conditions using ethylene glycol as an organic solvent. The microstructures of the formed powders exhibited nanospheres like structure with narrow size distribution from 6 to 10?nm. The magnetic properties of the formed cobalt ferrite powders strongly depend on the synthesis conditions. For instance, the highest saturation magnetization (M_s?=?36.2?emu/g) was achieved in the aqueous medium, whereas the lowest saturation magnetization (M_s?=?16.2?emu/g) was accomplished in the ethylene glycol medium. Indeed, heating properties of the CoFe₂O₄ samples in an alternating magnetic field (AMF) at 160?kHz were estimated. Of note, it is clear that the specific heat rate SAR values were in the range from 104.5 to 302.0?W/g at different synthesis conditions, making co-ferrite appropriate for hyperthermia treatment of cancer.     

Enhancing absorption properties of Mg–Ti substituted barium hexaferrite nanocomposite through the addition of MWCNT

M-type barium ferrite with Mg–Ti substitution and MWCNT addition was synthesized using high-energy ball milling. The prepared sample was further analyzed using X-ray diffraction, field emission scanning electron microscope (FESEM), vibrating sample magnetometer and vector network analyzer. The results showed that the particle size had a wide range of distribution, and a hexagonal structure was formed in the sample. The sample was observed to have lower saturation magnetization and coercivity after Mg–Ti was substituted with MWCNT and added into the barium hexaferrite. Reflection loss was studied as a function of frequency and thickness of the sample. For Mg–Ti substituted barium hexaferrite composite with a thickness of 2.0 mm, the reflection loss peaked at ?28.83 dB at a frequency of 15.57 GHz with a bandwidth of 6.43 GHz at a loss of less than ?10 dB. The microwave absorption primarily resulted from magnetic losses caused by magnetization relaxation, domain wall resonance, and natural resonance. FESEM micrograph demonstrated that carbon nanotubes were attached to the external surface of the ferrite nanoparticles. The investigation of the microwave absorption indicated that with an addition of carbon nanotubes, the real and imaginary parts of permittivity and reflection loss had enhanced to ?34.16 dB at a frequency of 14.19 GHz with a bandwidth of 5.72 GHz.     

Solvothermal preparation of cobalt nanorods

Cobalt nanorods have been prepared through solvothermal process with hydrazine hydrate and dimethylglyoxime (DMG) as reducing and morphology directing agents. The phase structure, morphology and magnetic properties of the as-prepared product were extensively characterized by X-ray diffraction, transmission electron microscopy and superconducting quantum interference device magnetometer. X-ray diffraction pattern revealed that the as-synthesized product was cobalt with face-centered cubic structure. Transmission electron microscopy observation showed that the as-prepared product composed of rod-like shape with size around 10 nm. The presence of DMG molecules on the surface of Co nanostructures was confirmed by the FTIR spectra. Magnetic measurements revealed that the nanorod exhibit ferromagnetic behavior at 300 K. The coercive force value of cobalt nanorods is 340 Oe at 300 K. Compared with bulk cobalt, the nanorods exhibit significant increase in coercive force as a reflection of shape anisotropy. The saturation magnetization value of Co nano rod is 150 emu/g at room temperature.     

Structural,magnetic and magnetoelectric properties of the magnetoelectric composite material

(x) CoFe₂O₄ + (1 ? x) Ba_0.9Sr_0.1TiO₃ magnetoelectric (ME) composites with x = 0.1, 0.2, 0.3, 0.4 and 0.5 were prepared by a conventional standard double sintering ceramic method. The magnetic and ME properties of composites consisting of cobalt ferrite (CoFe₂O₄) and barium strontium titanate (Ba_0.9Sr_0.1TiO₃) were investigated. The X-ray diffraction analysis was carried out to confirm the phases formed during sintering and also to calculate the lattice parameters. The hysteresis measurements were done to determine saturation magnetization (Ms), remanence magnetization (Mr) and coercivity (Hc) of the samples. The ME voltage coefficient (dE/dH)_H was studied as a function of intensity of the magnetic field. The measured ME response demonstrated strong dependence on the volume fraction of CoFe₂O₄ and the applied magnetic field. A large ME voltage coefficient of about 1,380 µV/cm/Oe was observed for 10 % CoFe₂O₄ + 90 % Ba_0.9Sr_0.1TiO₃ composite.     

Effect of Heat Treatment to Magnetic Susceptibility on SS 304 as Material for OIML Weight Standard

The changes in the value of magnetic susceptibility of SS 304 due to heat treatment effect were examined in this research to observed its possibility to be used as material for OIML weight standards. Five samples of 100 g from SS 304 were prepared and their magnetic susceptibiity were measured based on the Bureau International des Poids et Mesures method following different heat treatment to each sample. Heating temperature points were selected at 800 and 1,100 °C, each of them followed by slow and rapid cooling method. Change in the value of magnetic suceptibility was confirmed with X-ray diffraction (XRD) method to examine the change in the amount of ferrite on each sample. The initial value of magnetic susceptibility measured on the sample without heat treatment was (0.0064 ± 0.0007), and the lowest value obtained from the different samples was (0.0040 ± 0.0004) measured on the sample with heat treatment at 800 °C. The lowest magnetic susceptibility value obtained in this research met the requirement of the international recommendation and the measured change of the value of magnetic susceptibility was consistent with the amount of ferrite that contained in the sample obtained based on XRD pattern.     

Tailoring magnetic and dielectric properties of Co<Subscript>0.9</Subscript>Cu<Subscript>0.1</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> with substitution of small fractions of Gd<Superscript>3+</Superscript> ions

This paper describes the structural, magnetic, and dielectric properties of Gd³⁺ substituted cobalt–copper ferrite. The influence of Gd³⁺ substitution on the structural, magnetic and electrical properties of cobalt–copper ferrite was investigated through various characterization techniques. Thermal analysis was carried out on the prepared gel to know the combustion and calcination temperature. The detailed structural analysis suggests that the substitution of a Fe³⁺ ion with a Gd³⁺ ion at B site results in lattice distortion, modification in crystallite size and grain size of the material. X-ray photoelectron spectroscopy confirmed the oxidation states of the elements present. Magnetic measurement performed at 300 and 50 K depicts the decrease in saturation magnetization (Ms) and increase in coercivity (Hc) with Gd³⁺ substitution in the cobalt–copper spinel ferrite. The dielectric measurements acquired over a wide range of frequencies and temperature showed an increase in dielectric constant with increasing Gd³⁺ concentration.     

Preparation and magnetic properties of hollow ferrite microspheres by a gas-phase diffusion method in an ionic liquid/H2O mixed solution

In this work, hollow ferrite microspheres were prepared using a gas-phase diffusion method with cobalt nitrate and ferric nitrate as metal salt sources, an ionic liquid 1-butyl-3-methylimidazolium-tetrafluoroborate and water-mixed solvent as medium and ammonium carbonate as precipitant. Their structures and magnetization were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, thermogravimetry, infrared spectroscopy, and vibrating sample magnetometer. The effects of reaction time, reaction temperature, precipitant loading, and mole ratio of Co to Fe n(Co/Fe) on the structures and magnetization of the microspheres were studied. The results showed that ferrite hollow microspheres with uniform morphology and high-magnetic performance were obtained at 60–80 °C for 12–16 h, while the (NH₄)₂CO₃ loading was 0.15 g/ml, n(Co/Fe) was 0.5:1, and calcination temperature was 550 °C. The obtained products consisted of CoFe₂O₄ phase accompanied by ferric oxide phase, with an average particle size about 1 μm and magnetization intensity about 10 emu/g.     

Dielectric and magnetic properties of DyMnO3 ceramics

This paper reports the dielectric and magnetic properties of DyMnO₃ (DMO) ceramics sintered at 1,100 and 1,350 °C temperature for 10 h. Sample sintered at 1,100 °C showed presence of secondary phases of Dy₂O₃ whereas the monophasic orthorhombic structure of DyMnO₃ sample is synthesized only at sintering temperature of 1,350 °C. The dielectric properties of the sintered sample of DMO were investigated as a function of temperature (T ≥ 300 K) and frequency (10 kHz–1 MHz). Both the sintered samples showed frequency independent dielectric anomaly at 313 K. These samples exhibited ferroelectric behavior at room temperature which was evidenced from the polarization hysteresis loop measurement. No magnetic transition has been observed at room temperature. However, magnetic field dependent magnetization and temperature dependent magnetization showed the paramagnetic behavior of the DyMnO₃ samples.     

Polymer-coated CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoassemblies as biocompatible magnetic nanocarriers for anticancer drug delivery

In this work, we report the preparation of cobalt ferrite nanoparticles (CFNPs) coated with hydrophilic polymers guar gum, gum arabic and poly (methacrylic acid) as magnetic nanocarriers and study their conjugation with doxorubicin for the drug release under applied magnetic field. The effect of polymer coating on structural properties is studied using Fourier transform infrared spectroscopy and powder X-ray diffractometry (XRD). The XRD analysis revealed that the polymer coating on the as-synthesized CFNPs has no influence on their crystallite size and it remains between 18 nm and 19 nm. The characteristic morphology, topography and the evidences of polymer coating over the CFNPs are investigated using scanning electron microscopy, atomic force microscopy and thermogravimetric analysis, respectively. Vibrating sample magnetometry revealed the ferromagnetic nature of uncoated CFNPs with a significant saturation magnetization ～77.2 emu g^?1. The dynamic light scattering measurements are also performed to determine the size of uncoated and coated CFNPs. UV–Visible spectroscopy demonstrated a profound loading (70–75%) of doxorubicin onto the magnetic nanocarriers and the efficient release of drug in the presence of external applied magnetic field. In vitro cytotoxic studies confirmed the cytocompatibility mode of coated CFNPs against Chinese Hamster Ovary and Huh-7 cell line, while 0.2 mg mL^?1 dose of drug-loaded magnetic nanocarriers inhibited the cell viability of Huh-7 up to 60%. These results strongly encourage the utilization of biocompatible magnetic nanocarriers in targeted drug delivery territory.     

Anomalous magnetic properties of mechanically milled cobalt oxide nanoparticles

Defect induced magnetic properties of CoO nanoparticles produced via mechanical ball milling have been assessed by detailed magnetic measurements. A progressive decrease in the particle size and a concomitant increase in the induced strain have been observed with the milling times. The mechanically milled nanoparticles of CoO exhibit anomalous magnetic properties such as FM hysteresis when compared with the unmilled CoO sample. The presence of weak ferromagnetism, with a highest value of magnetization of 0.532 emu/g at 10 K in the 100 h milled sample, is attributed to the uncompensated surface spins resulting from induced surface defects via mechanical milling. The ZFC coercive force, measured at 10 K, increases with milling time reaching a maximum value of 1066 Oe for the 100 h milled sample. The temperature dependent field-cooled (FC) and zero-field-cooled (ZFC) magnetic measurements indicate a presence of an exchange bias field arising from uncompensated moments generated by mechanical strain and the antiferromagnetic (AFM) core. The exchange bias field measured at 10 K reaches a value 210 Oe for the 50 h milled sample and decreases upon prolonged milling. The exchange bias field vanishes at a temperature approximately 200 K, a temperature much lower than the Neel temperature of CoO (TN approximately 291 K). The observed anomalous magnetic behavior of CoO could be interpreted in terms of the exchanged bias FM-AFM model.     

Structural and Magnetic Properties of Cobalt and Manganese Doped Ni-Ferrite Nanoparticles

This study reports that NiCoMn ferrite [Ni_(1?x)Co _x Mn _y Fe_(2?y)O₄ with (x=y=0.01,0.02)] powders are prepared by using the sol-gel combustion method. The effect of various calcination temperatures on their structural and magnetic properties is also investigated. Structural properties of the powders are carried out by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). According to XRD analysis, all samples of two compositions have cubic spinel structure, with an enlargement in crystalline size is observed with increasing of calcination temperature. The crystallite size of the nanopowders is estimated from (311) peaks using Scherrer’s formula. Spherical particles of nanocrystalline ferrite powders are shown in TEM photographs. The room temperature magnetic properties of particles are studied by using a vibrating sample magnetometer (VSM). The magnetization measurements also indicated that the saturation magnetization (M _s) increases as the calcinations temperature increases for both A and B samples in the range of 31.69 to 47.77 and 21.81 to 48.89 emu/gr, respectively. The value of coercivity fields (H _c) decrease with increasing the calcinations temperature. Furthermore, the properties of two samples synthesis at the optimum calcinations temperature (800 ^°C) compared together.     

In situ synthesis of manganese zinc ferrite nanoparticle/polymer hybrid nanocomposite from metal organics

A manganese zinc ferrite nanoparticle/polymer hybrid nanocomposite was synthesized in situ from metal acetylacetonates at 80 °C. A mixture of manganese(II) acetylacetonate (MA), zinc(II) acetylacetonate (ZA), and iron(III) 3-allylacetylacetonate (IAA) was hydrolyzed and polymerized, yielding a spinel oxide nanoparticle/organic hybrid. The crystallite size of the spinel particles was dependent upon the hydrolysis conditions of MA–ZA–IAA. Crystalline manganese zinc ferrite nanoparticles less than 5 nm in size were uniformly dispersed in the organic matrix. The magnetization of the hybrid increased as the amount of water for hydrolysis increased. The magnetization versus field curve for the manganese zinc ferrite nanoparticle/organic hybrid showed neither remanence nor coercivity above 11 K. The magnetization versus H/T curves from 50 to 200 K were superimposed on the same curve described by the Langevin equation. The remanent magnetization and coercive field of the hybrid were 2.1 emu/g and 20 Oe, respectively, at 4.2 K. The absorption edge of the hybrid film was blue-shifted as compared to that of bulk ferrite.     

Low Temperature and High Magnetic Field Dependence and Magnetic Properties of Nanocrystalline Cobalt Ferrite

The DC magnetic hysteresis loop measurements were carried out for temperatures varying from 5 to 300 K over a field range of ±10 T on nanocrystalline (～35 nm) cobalt ferrite samples (crystallized to \(Fd\bar {3} m\) space group with cubic symmetry) to validate the law of approach at low temperature for the nanocrystalline cobalt ferrite. A magnetocrystalline anisotropy constant and saturation magnetization have been obtained by analyzing the magnetization curve in saturation using the “law of approach (LA) to saturation.” The magnetocrystalline anisotropy constant is found to be almost constant in the temperature range of 5 to 150 K due to the freezing of spin at low temperature. Also, spin freezing leads to a decrease of coercivity with the increase in the temperature.     

Influence of coated SiC particulates on the mechanical and magnetic behaviour of Fe–Co alloy composites

Near-equiatomic Fe–Co alloy composites containing 0, 5 and 10 vol% of uncoated and coated SiC particles were prepared by applying a uniaxial pressure of 80 MPa at 900 °C for 5 min in a spark plasma sintering furnace. The SiC particles used in this study were coarse, with an average particle size of 20 μm and their surfaces were coated with four different types of coatings, namely Ni–P, Cu, Co and duplex Cu and Ni–P by an electroless plating method. Quasi D.C. magnetic, bending and hardness tests were performed on the composites. The influence of particulate coatings on the magnetic and mechanical behaviour of the composites was investigated by correlating their properties with their microstructures as observed using scanning electron microscopy and optical microscopy and crystallographic information as obtained using X-ray diffraction. The cobalt coated particles were found to exhibit the best wettability with the matrix without the formation of deleterious intermetallic compounds at the interface. Because of the better interfacial bonding in the composites with Co coated particles, there was an enhancement in flexural strength and permeability compared to the uncoated and other coated particulate composites studied. In addition, inclusion of cobalt coated SiC particulates produced an increase in hardness and a decrease in coercivity compared to the monolithic material.     

The Effects of Doping on Crystal Structure, Magnetic and Microwave Properties of SrFe12−2x La x (Mn0.5Zr0.5) x O19 Nanoparticles

M-type hexagonal ferrite powders, SrFe_12?2x La _x (Mn_0.5Zr_0.5) _x O₁₉ (x=0.0, 0.2, 0.4, 0.6, 0.8), have been synthesized by the coprecipitation method. The X-ray diffraction, field emission scanning electron microscope, vibrating sample magnetometer and vector network analyzer all were used to characterize the structure of the samples, their magnetic and microwave properties. The value of the saturation magnetization increased up to x=0.2 and then slowly decreased with increasing doping. A decreasing trend was observed in the value of coercivity with increasing substitution degree, and its value reached a minimum of 2420 Oe for x=0.6 and then increased with further increasing x. The relative complex permittivity and permeability of the composite powders were investigated in the X-band frequency range (8.2–12.4 GHz).     

Influence of Co<Superscript>++</Superscript> ion concentration on magnetic and microwave properties of Ba<Subscript>(4−X)</Subscript>Co<Subscript>(2+X)</Subscript>Fe<Subscript>36</Subscript>O<Subscript>60</Subscript> (Ba-M-Y) hexaferrite

The present paper reports the influence of cobalt content on the structural, electrical, magnetic and microwave properties of barium hexaferrite synthesized via chemical co-precipitation method. The samples were characterized for their structural, electrical, magnetic and microwave characterizations using XRD, SEM, TEM, VSM etc. The transmission electron microscopy results showed that stacking of nanoparticles of size?~?50 nm. In addition, the highest saturation magnetization of 29.82 emu/g was observed for composition x?=?0.2. The microwave permittivity and permeability decreases with frequency and it varies with the cobalt concentration. Cobalt concentration strongly affects the microwave and magnetic properties of hexaferrite.