Nanocrystalline CoFe2O4 Research Articles

Impact of Green Synthesis on Crystallographic Structure, Optical and Magnetic Properties of Nanocrystalline CoFe2O4

Impact of Green Synthesis on Crystallographic Structure, Optical and Magnetic Properties of Nanocrystalline CoFe2O4

Structural, Magnetic, and Magnetostriction Properties of Flexible, Nanocrystalline CoFe2O4 Films Made by Chemical Processing.

We report on the simple, single-step, and cost-effective fabrication, characterization, and performance evaluation of cobalt ferrite (CoFe2O4; CFO) nanocrystalline (NC) thin films on a flexible mica substrate. The chemical solution-based drop-casting method employed to fabricate crystalline CFO films and their characterization was performed by studying the phase formation, surface morphology, and magnetic parameters, while sensor applicability was evaluated using combined magnetic and magnetostrictive properties. X-ray diffraction (XRD) indicates the single-phase and nanocrystalline nature of CFO films, where the crystallite size is ∼60 nm. The optimum conditions employed resulted in CFO NC films with surface particles exhibiting a spherical shape morphology with a homogeneous size distribution, as revealed by scanning electron microscopy analyses. Raman spectroscopic characterization of the chemical bonding indicates all of the active bands that are characteristic of the ferrite phase confirm the spinel structure, which is in agreement with XRD studies. The saturation magnetization (M S) and coercivity (H C), which are extracted from the field-dependent magnetization data, of CFO NC films were found to be 15.8 emu/g and 1.6 kOe, respectively, while the first-order magnetocrystalline anisotropy constant K 1 was ∼1.07 × 106 erg/cm3. The magnetostriction strain curve indicates that the CFO NC films exhibit a strain value of ∼86 ppm at an applied magnetic field of 8 kOe, indicating their suitability for flexible sensor devices.

Rapid microwave-assisted combustion route for production of MFe2O4 (M = Zn, Ni, Co) nanoferrites for gas sensors view point

Nanocrystalline ZnFe2O4, NiFe2O4 and CoFe2O4 were prepared using rapid microwave assisted combustion technique. Single phase Nanocrystalline structure of ferrites confirmed by X-ray diffraction and Rietveld refinement. Fine powder of Nanocrystalline Zn, Ni and Co ferrites resulted from rapid synthesis route were used for gas sensor fabrication in the form of thick film by screen printing method. Scanning electron microscopy was used to study surface of the sensing element and to study the surface morphology of the sensor. The gas sensing responses of the indigenously built sensor were analyzed by measuring the resistance of sensing element in presence and in absence of LPG. Amongst the studied sensors, NiFe2O4 thick film sensor showed superior response.

Hysteresis Energy Loss of Nanocrystalline CoFe2O4 Synthesized by Modified Citrate-Gel Method

Hysteresis Energy Loss of Nanocrystalline CoFe2O4 Synthesized by Modified Citrate-Gel Method

Effects of co-substitution of Al3+ and Cr3+ on structural and magnetic properties of nano-crystalline CoFe2O4 synthesized by the sucrose technique

Al–Cr substituted CoFe2O4 nano spinels (CoAlxCrxFe2−2xO4 where x = 0.1 to 0.6) were successfully prepared for the first time via sucrose sol–gel auto-combustion technique. The structural parameters as well as magnetic and electrical properties of the prepared ferrites have been investigated. X-ray diffraction (XRD) confirmed single-phase formation and showed a decrease in the calculated values of lattice parameters by substitution attributed to the difference in the ionic radii. Based on the obtained structural parameters, an appropriate cation distribution was proposed and discussed. In this distribution, most of Al3+ and Cr3+ ions preferred octahedral sites occupation however, small amount of Al3+ seek the tetrahedral sites. Accordingly, the magnetic characterization via vibrating sample magnetometer (VSM) measurements revealed a decrease in the saturation magnetization (Ms) by successive substitution from 57.9 to 4.7 emu/g, indicating the incorporation of non-magnetic Al3+ and anti-ferromagnetic Cr3+ ions in the octahedral sites instead of Fe3+ ions. The much lower magnetization values obtained than that prepared by other methods could be attributed to the present lower sizes. The coercivity measurements indicated soft ferrimagnetic properties favoring their uses as high frequency transformers. Ac-conductivity as well as dielectric properties, as a function of frequency and temperature, indicated semiconducting behavior with decreasing trend by Al–Cr substitution due to decreasing in the Fe3+-Fe2+ hopping probability in octahedral sites. The obtained results suggest the using of the present materials in electronic inductors, electromagnets and transformers and microwave devices.

CoFe2O4/porous carbon nanosheet composites for broadband microwave absorption

It is highly desirable yet challenging to develop high-performance microwave absorption materials with lightweight, thin thickness, and strong absorption capability over broad frequency ranges by simple and cost-effective methods. Herein, we design an ultralight (~54 mg cm−3) magnetic-carbon hybrid material to achieve superior microwave absorption performances. By instantaneous freezing-induced self-assembly of Fe3+, Co2+-glucose complexes on a cheap and water-removable template (i.e., NaCl), the as-made composite features 3D hierarchical porous structure and nanosheet-like carbon pore walls embedded with nanocrystalline CoFe2O4. The chemical composition can be controlled by simply altering the ratio of Co2+ (Fe3+) and glucose. Benefitting from the structural and compositional advantages, the optimized composite absorber exhibits a minimum reflection loss value of − 52.29 dB at a thin thickness of 2.0 mm and an effective absorption bandwidth reaching 5.36 GHz (12.64–18 GHz) at a low filler loading of 20 wt%. The microwave absorption mechanism survey reveals that the weak surface reflection and strong dissipation capacity induced by nanosheet-like pore walls combined with the multiple internal reflections caused by 3D hierarchical porous structure contribute to robust impedance matching and strong microwave attenuation ability. This work may offer new insights for designing highly effective magnetic-carbon microwave absorbers with low density and wide absorbing frequency.

Structural, morphological and dielectric studies of zirconium substituted CoFe2O4 nanoparticles

In this work, the influence of zirconium substitution in cubic spinel nanocrystalline CoFe2O4 on the structural, morphological and dielectric properties are reported. Zirconium substituted cobalt ferrite Co1-xZrxFe2O4 (x = 0.7) nanoparticles were synthesized by sol-gel route. The structural and morphological investigations using powder X-ray diffraction and high resolution scanning electron microscope (HRSEM) analysis are reported. Scherrer plot, Williamson–Hall analysis and Size-strain plot method were used to calculate the crystallite size and lattice strain of the samples. High purity chemical composition of the sample was confirmed by energy dispersive X-ray analysis. The atoms vibration modes of as synthesized nanoparticles were recorded using Fourier transform infrared (FTIR) spectrometer in the range of 4000–400 cm-1. The temperature-dependent dielectric properties of zirconium substituted cobalt ferrite nanoparticles were also carried out. Relative dielectric permittivity, loss tangent and AC conductivity were measured in the frequency range 50 Hz to 5 MHz at temperatures between 323 and 473 K. The dielectric constant and dielectric loss values of the sample decreased with increasing in the frequency of the applied signal.

Ferro to superparamagnetic transition: Outcome of Ni doping in polyethylene glycol capped CoFe2O4 nanoparticles

Nanocrystalline CoFe2O4 and Ni doped CoFe2O4 were synthesized via chemical precipitation method and their crystal structure, energy gap and magnetic properties were investigated at room temperature. The results revealed that the Ni doping dropped the crystallite size from 23.4 to 6.9 nm. FTIR spectra confirmed the formation of ferrites through the vibrational bonds at 462 and 591 cm−1. UV–Visible diffuse reflectance spectra confirmed that the synthesized ferrite samples are wide bandgap material whose bandgap varies between 3.73 and 4.01 eV. Photoluminescence study confirmed the visible emission of the samples. Transmission electron microscopy analysis confirmed the formation of single domain size of ∼15–72 nm and the morphological tailoring from nanocubes to nanoparticles. Compositional analysis established the consistent mixing of Co, Ni, Fe, and O atoms. The hysteresis analysis confirmed that Ni dopant favours for the magnetic transition from ferro to superparamagnetism. It also infers that Ni dopant reduces the saturation magnetization of cobalt ferrite from 57.83 to 27.13 emu/g and decreased the coercivity from 0.1253 to 0.0139 T as x varies from 0 to 1. Electron paramagnetic resonance spectra confirm the increase in super exchange interaction with the increase in Ni concentration. The dielectric study inferred that the dielectric constant decreases with the increase in frequency.

Solution combustion synthesis, characterization, magnetic, and dielectric properties of CoFe2O4 and Co0.5M0.5Fe2O4 (M = Mn, Ni, and Zn).

Nanocrystalline CoFe2O4 and Co0.5M0.5Fe2O4 (M = Mn, Ni, and Zn) ferrites were prepared by the solution combustion method using oxalyl dihydrazide as a fuel. These materials were characterized by several physicochemical techniques. X-ray diffraction (XRD) patterns indicate the cubic spinel structure of these ferrites. Field emission scanning electron microscopy (FESEM) images demonstrate the microporous nature of the materials because of the large amount of gas production during their synthesis. High resolution transmission electron microscopy (HRTEM) images show lattice fringes corresponding to the {220} and {311} planes of the spinel structure. Fourier transform infrared (FTIR) spectra exhibit absorption bands around the 500-600 cm-1 wavenumber region which are related to metal-oxygen bonds with tetrahedral coordination. Symmetric and asymmetric stretching and symmetric bending modes associated with tetrahedral and octahedral cations present in the spinel structures have been assessed by Raman spectroscopy. X-ray photoelectron spectroscopy (XPS) studies demonstrate the presence of Co2+, Mn2+, Ni2+, Zn2+, and Fe3+ in tetrahedral and octahedral coordinations in these ferrites. Co0.5Zn0.5Fe2O4 is observed to show the highest saturation magnetization among all these materials. The dielectric measurements reveal that the dielectric constant and loss values decrease with an increase in frequency and the ac conductivity increases at higher frequencies due to mobilization of the charge carriers.

The structural and magnetic properties of the nano-CoFe2O4 ferrite prepared by sol-gel auto-combustion technique

Single-phased nano-crystalline CoFe2O4 ferrite has been prepared using the sol-gel auto-combustion technique. The refinement analyses of X-ray diffraction patterns confirm crystallization of the sample in the (Fd3̅m) space group. The corresponding lattice constant was estimated to be aexp = 8.37 Å. Theoretical values of other structural parameters such as the ionic radii, bond lengths and the electronegativity at the tetrahedral and octahedral sites have been calculated and compared with values of other spinel systems. The cation distributions indicate that the present system is a partially inversed spinel with inversion factor 0.68. The FT-IR transmittance spectrum has been measured in the range (400–4000) cm−1. It shows the transmittance bands at (575, 1638, 2900 and 3465) cm−1. The 575 cm−1 band has been attributed to the oxygen-metal vibration at the tetrahedral sites. The Energy dispersive X-ray spectroscopy (EDXS) shows the consistency of the weight percentages of the Co and Fe ions with stoichiometric contents within 3% accuracy. Transmission electron microscopy (TEM) has been used in the estimation of the average particle size. The average particle sizes were estimated to be around 95 nm. Values of isomer shifts were found to be in the range (0.29–0.46) mm/s, which indicate that Fe3+ oxidation state is dominant and probably low percentage of ferrous Fe2+ ions. The saturation magnetization at room temperature was determined to be 69 emu/g and the reduced remanent magnetization value (Mr/Ms) was found to be 0.35. The Yafet-Kittel angle, the blocking (TB) temperature and Curie (TC) temperatures were estimated to be 33°, 724 K and 810 K respectively. The high values of TB and TC were attributed to the strength of the A-B super-exchange interactions experienced in the CoFe2O4 sample.

Nd:YAG laser irradiation effect on the physical properties of cobalt ferrite nanoparticles

Nanocrystalline CoFe2O4 ferrite samples have been synthesized by co precipitation method. The prepared samples were irradiated by second harmonic diode pumped Nd:YAG laser with average power 150 m W of wavelength 532 nm for 5 min at a distance of 30 cm. The prepared samples were characterized to study the different properties of samples. X-ray diffraction analysis reveals a single-phase cubic spinel structure before/after irradiation. The broadening of the peaks indicates a reduction in crystallite size with ultra-fine nature for irradiated samples. EDAX analysis shows that the predictable composition present in the samples agrees well with the nominal compositions. Nd:YAG laser irradiation shows remarkable changes on structural as well as magnetic properties. The decreasing of the coercivity for the irradiated samples suggests that laser-irradiation and roughness can be used to tune the magnetic hardness of the ferrite materials.

Thermal stability, electrochemical and structural characterization of hydrothermally synthesised cobalt ferrite (CoFe2O4).

Monophasic nano-crystalline CoFe2O4 (CFO) nanoparticles of high purity have been synthesised through a low temperature hydrothermal route, which does not involve hazardous chemicals, or conditions. The easy, green procedure involves a hydrothermal treatment at 135 °C of an aqueous suspension of the oxalate salts of the precursors. No further purification or annealing procedure was necessary to obtain the crystalline nano-structured oxide. The nanoparticles were characterized structurally and chemically by powder X-ray diffraction (PXRD), Inductively Coupled Plasma Spectrometry (ICP-MS) and Scanning Electron Microscopy (SEM), thus confirming the successful synthesis of the CoFe2O4 particles with the expected crystal phase and stoichiometry and an almost complete inverse spinel structure. From the nanoparticles pellets were pressed to investigate the electronic conduction properties using electrochemical impedance spectroscopy (EIS). At low temperatures, the conductivity measurements reveal a semiconducting behavior originating from hopping between Co sites and a total conductivity dominated by the grain boundary contribution. At higher temperatures (T > 400 °C) a metallic–insulator transition occurs, which is attributed to additional hopping of electrons between the Fe sites.

Large enhancement in the magnetostriction parameters of the composite of CoFe2O4 and CoFe1.9Ga0.1O4

A new strategy to enhance the magnetostriction parameters of cobalt ferrite (CoFe2O4) is illustrated. A composite comprising of nanocrystalline CoFe2O4 and bulk CoFe1.9Ga0.1O4 powders were mixed together then compacted and sintered at 1450 °C for 10 min. For a composite of 70 wt% CoFe2O4 and 30 wt% of CoFe1.9Ga0.1O4, maximum magnetostriction coefficient (λmax) of −350 ppm has been obtained at lower magnetic field which is nearly 20% and 65% higher than that obtained for CoFe2O4 and CoFe1.9Ga0.1O4, respectively. Moreover, the composite exhibited higher strain sensitivity [dλ/dH]max of −2.6 × 10−9 A−1 m against the individual components of the composite.

Structural, morphological and dielectric studies of zirconium substituted CoFe2O4 nanoparticles

In this work, the influence of zirconium substitution in cubic spinel nanocrystalline CoFe2O4 on the structural, morphological and dielectric properties are reported. Zirconium substituted cobalt ferrite Co1-xZrxFe2O4 (x = 0.7) nanoparticles were synthesized by sol-gel route. The structural and morphological investigations using powder X-ray diffraction and high resolution scanning electron microscope (HRSEM) analysis are reported. Scherrer plot, Williamson–Hall analysis and Size-strain plot method were used to calculate the crystallite size and lattice strain of the samples. High purity chemical composition of the sample was confirmed by energy dispersive X-ray analysis. The atoms vibration modes of as synthesized nanoparticles were recorded using Fourier transform infrared (FTIR) spectrometer in the range of 4000–400cm-1. The temperature-dependent dielectric properties of zirconium substituted cobalt ferrite nanoparticles were also carried out. Relative dielectric permittivity, loss tangent and AC conductivity were measured in the frequency range 50Hz to 5MHz at temperatures between 323K and 473K. The dielectric constant and dielectric loss values of the sample decreased with increasing in the frequency of the applied signal.

Synthesis, characterization and electrical properties of mesoporous nanocrystalline CoFe2O4 as a negative electrode material for lithium battery applications

Mesoporous nanocrystalline cobalt ferrite (CoFe2O4) as a negative electrode material for lithium battery was prepared by using simple urea assisted modified citrate combustion process. Formation of pure crystalline phase and nanocrystallite size were respectively identified and calculated from the analysis of the observed X-ray diffractometer pattern of the CoFe2O4 sample. The formation of uniform mesoporous nanocrystalline architecture was confirmed from the observed FE-SEM images of the CoFe2O4 sample. Specific surface area obtained from BET analysis of the sample is found to be 38.369 m2 g−1. The delivered discharge capacity of the lithium ion battery, fabricated using prepared mesoporous nanocrystalline CoFe2O4, is found to be 484 mAh g−1 after 30 cycles at 0.1 C rate. The observed high discharge capacity may be due to the unique mesoporous nanocrystalline structure of the CoFe2O4 sample. Hence, the electrochemical results reveal that the mesoporous nanocrystalline CoFe2O4 could be a promising high capacity, negative electrode material for lithium ion batteries.

Synthesis of Nanocrystalline Cobalt Ferrite by the Sonochemical Method in Highly Basic Aqueous Solution

This study reported the preparation of nanocrystalline CoFe2O4 in single step by the sonochemical method in highly basic aqueous solution without requiring of high temperature calcination process. To prepare nanocrystalline CoFe2O4, the mixed solution of the required molar ratio of cobalt nitrate hexahydrate (Co (NO3).6H2O) and ferric nitrate nonahydrate (Fe (NO3).9H2O) was precipitated in high concentration of sodium hydroxide medium solution (NaOH) under high intensity ultrasonic irradiation (20 kHz, 150 W/cm2). The effect of NaOH concentration (5, 10, 15 and 20 M) on phase formation, microstructure and magnetic property of CoFe2O4 was investigated. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA) results showed that the as-prepared powders were single phase CoFe2O4 with cubic spinel structure. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) study showed that nanocrystalline CoFe2O4 had monosized distorted spherical morphology and an agglomeration of the nanocrystalline CoFe2O4 into nanoparticles was observed when increasing the NaOH concentration. The nanocrystalline CoFe2O4 exhibited superparamagnetic property and the saturation magnetization (Ms) obtained from vibrating sample magnetometry (VSM) was found to correlate with the crystallite size and varied from 39-45 emu/g.

Structural, AC conductivity, impedance and dielectric study of nanocrystalline MFe2O4 (M = Mg, Co or Cu) spinel ferrites

Nanocrystalline MFe2O4 (M = Mg, Co or Cu) spinel ferrites were prepared using novel combustion method and its structural, AC conductivity, impedance and dielectric properties were investigated. The powder X-ray diffraction analysis shows that the size and lattice constant of nanocrystalline MgFe2O4, CoFe2O4 and CuFe2O4 are 10.4, 28.6 and 9.6 nm (8.330, 8.369, and 8.342 A), respectively. Further the Raman spectra confirm the spinel phase formation and five active Raman modes such as 1A1g, 1Eg, 3T2g are assigned for each ferrite. The Fourier transform infrared spectra confirms the formation of tetrahedral and octahedral sites. The electrical properties such as AC conductivity, impedance, dielectric constant and tan δ are reported. The value of AC conductivity at 30 °C (at 1 Hz) is 1.12 × 10−8, 1.91 × 10−10 and 9.19 × 10−8 S/cm, respectively for MgFe2O4, CoFe2O4 and CuFe2O4 ferrites. The activation energy of AC conductivity process, calculated using Arrhenius relation is ranged from 0.45 to 0.56 eV. The impedance analysis shows that the contribution of grain boundary is more than that of grain for the electrical behavior of the prepared samples. The dielectric study shows that the CoFe2O4 has the lowest value of dielectric constant and tanδ among the three investigated samples.

Effect of Gd3+ substitution on structural, magnetic, dielectric and optical properties of nanocrystalline CoFe2O4

Nanoparticles of CoGdxFe2−xO4 with x=0.0, 0.03, 0.05, 0.07, 0.10 and 0.15 were synthesized by co-precipitation method. Gd3+ substitution effect on different properties of nanocrystalline CoFe2O4 has been studied. X-ray diffraction and Raman spectroscopy confirmed the formation of single phase cubic mixed spinel structure. Cation distribution has been proposed from Rietveld refined data. Mössbauer spectra at room temperature showed two ferrimagnetic Zeeman sextets with one superparamagnetic doublet. Mössbauer parameters suggested that Gd3+ ions occupy the octahedral site in CoFe2O4. Room temperature magnetic measurements exhibited that the saturation magnetization decreased from 91emu/gm to 54emu/gm for x=0.0 to 0.15 samples. The coercivity decreased from 1120Oe to 340Oe for x=0.0 to 0.07 samples and increased from 400Oe to 590Oe for x=0.10 and 0.15 samples, respectively. Raman analysis showed that the degree of inversion with Gd3+ substitution supporting the variation of coercivity. Electron spin resonance spectra revealed the dominancy of superexchange interactions in these samples. Optical band gap measurement suggested that all samples are indirect band gap materials and band gap has been decreased with Gd3+ substitution. Both dielectric constant and dielectric loss is found to decrease because of the decrease in hopping rate with the Gd3+ substitution for Fe3+ at the octahedral sites. Low dielectric loss suggested the applicability of Gd3+ doped CoFe2O4 nanoparticles for high frequency microwave device applications.

Investigation of optical, electrical and magnetic properties of cobalt ferrite nanoparticles by naive co-precipitation technique

Inverse spinel cobalt ferrite (CoFe2O4) nanoparticles have fascinated massive attention owing to their incredible and remarkable combinations of properties, principally magnetic and optical properties. These properties are catered in CoFe2O4 which make it a fitting candidate in the field of electronics. Nanocrystalline CoFe2O4 powder was expediently synthesized by a primitive co-precipitation technique. Synthesized samples attributed to its significant crystalline nature which is characterized by powder X-ray diffraction and found that the sharp crystallographic profile contours the prominent peak ensuing (311) plane with crystallite size 29nm. The micrograph image of CoFe2O4 showed average particle size about 19 nm. The pH had no obvious influence on the morphology, but it affects the crystallite size. The potency and type of interionic bands were overt in FT-IR spectrum and the as-synthesized powder displayed a superior magnetic property. The band gap of CoFe2O4 is estimated to be 1.92eV. The PL studies reveal that excitation wavelength is at 417nm, which attributes to the recombination of electrons and holes. The A.C. conductivity measurements were carried out along with temperature and frequency dependent dielectric constant and dielectric loss of synthesized nanoparticles.

Impact of ignition temperature on particle size and magnetic properties of CoFe2O4 nanoparticles prepared by self-propagated MILD combustion technique

We prepared nanocrystalline CoFe2O4 by changing its ignition temperatures, using moderate and intense low-oxygen dilution (MILD) combustion technique. The effect of ignition temperature on the particle size and its magnetic behavior was investigated by HR-TEM and VSM respectively. We observed a vast change in the structural behavior and the magnetic properties of the prepared samples. X-ray diffraction studies revealed that the resultant samples had single phase with different grain sizes from 23±5nm to 16±5nm, which was understood by observing the growth of the grains through heat released from the combustion reaction. FE-SEM analysis showed high porosity with heterogeneous distribution of the pore size based on the adiabatic temperature and EPMA analysis, which confirmed the elemental compositions of the prepared samples. The saturation magnetization values measured at room temperature, employing vibrating sample magnetometer (VSM) decreased gradually from 50 to 34emu/g when the ignition temperature was increased from 243°C to 400°C. Some of Fe ions on the B sites moved periodically to the A sites because of quenching treatment. The presence of Fe2+ ions in the existing ferrite structure ruled the magnetic behavior of the sample, as confirmed by the Mössbauer analysis.