The bismuth (Bi
)-doped cobalt ferrite nanostructures with dual phase, i.e. cubic spinel with space group Fd3m and perovskite with space group R3c, have been successfully engineered via self-ignited ...sol-gel combustion route. To obtain information about the phase analysis and structural parameters, like lattice constant, Rietveld refinement process is applied. The replacement of divalent Co
by trivalent Bi
cations have been confirmed from energy dispersive analysis of the ferrite samples. The micro-structural evolution of cobalt ferrite powders at room temperature under various Bi
doping levels have been identified from the digital photoimages recorded using scanning electron microscopy. The hyperfine interactions, like isomer shift, quadrupole splitting and magnetic hyperfine fields, and cation distribution are confirmed from the Mossbauer spectra. Saturation magnetization is increased with Bi
-addition up to x = 0.15 and then is decreased when x = 0.2. The coercivity is increased from 1457 to 2277 G with increasing Bi
-doping level. The saturation magnetization, coercivity and remanent ratio for x = 0.15 sample is found to be the highest, indicating the potential of Bi
-doping in enhancing the magnetic properties of cobalt ferrite.
The influence of Bi
3+
-doping on the magnetic and Mössbauer properties of cobalt ferrite (CoFe
2
O
4
), wherein the Fe
3+
ions are replaced by the Bi
3+
ions to form CoBi
x
Fe
2−
x
O
4
ferrites, ...where
x
= 0.0, 0.05, 0.1, 0.15 or 0.2, has been investigated. The structural and morphological properties of undoped and doped ferrites, synthesized chemically through a self-igniting sol-gel method, are initially screened using X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy measurements. The changes in magnetic moment of ions, their coupling with neighboring ions and cation exchange interactions are confirmed from the Mössbauer spectroscopy analysis. The effect of Bi
3+
-doping on the magnetic properties of CoFe
2
O
4
ferrite is examined from the vibrating sample magnetometry spectra. Saturation magnetization and coercivity values are increased initially and then decreased, as result of Bi
3+
-doping. The obtained results with improved saturation magnetization (from 26.36 to 44.96 emu g
−1
), coercivity (from 1457 to 1863 Oe) and remanence magnetization (from 14.48 to 24.63 emu g
−1
) on 0.1-0.15 mol Bi
3+
-doping of CoBi
x
Fe
2−
x
O
4
demonstrate the usefulness for magnetic recording and memory devices.
Bi
3+
-doping improves the saturation magnetization, coercivity and the remanence magnetization, which can be applied for magnetic recording and memory devices, of CoFe
2
O
4
ferrite.
•Synthesis of single spinel phase Co-Zn-La nano ferrites.•Magnetization controlled by La composition, crystal size and YK angle of spin canting.•Electron hopping is responsible for the dielectric ...polarization.•The ε′ increases and tanδ decreases with the increasing La composition.
Co-Zn spinel ferrites with lanthanum (La3+) ion substitutions having formula Co0.7Zn0.3LaxFe2-xO4 (x = 0.0, 0.025, 0.05, 0.075, 0.1) were prepared using sol gel auto ignition route. The structural characterization of the ferrites was performed by the x-ray diffraction (XRD) method. The parameters calculated from the XRD analysis include lattice parameter, density, porosity, crystal size and lattice strain. The nanocrystallinity of the ferrite samples was observed with the crystallites of 20–30 nm size. The scanning electron microscopy (SEM) was employed to analyse the morphology of the ferrite crystals. The size and shape of the ferrite nanocrystals were confirmed from transmission electron microscopy (TEM) images. The crystal planes revealed from XRD calculations were confirmed by the selected area electron diffraction (SAED) analysis of the ferrites. Vibrating sample magnetometer (VSM) measurements of the ferrite samples were performed to study the magnetic properties of the ferrites. The effects of the La3+ substitution were observed on the coercivity and saturation magnetization of the ferrites. The variation of dielectric properties of the ferrites within 50 Hz to 5 MHz frequency band were studied at room temperature. The dielectric relaxation in the ferrites was governed by the electron hopping between divalent (Fe2+ and Co2+) and trivalent (Fe3+ and Co3+) cations. Remarkable impact of La3+ composition and the crystal size was observed on dielectric constant as well as loss tangent.
The structural modifications in Co–Zn ferrites due to the substitution of Gd3+ ions and their credible use as low loss dielectrics and H2S gas sensors are reported in the present study. The ...structural modifications lead to the enhancement in physical properties of the ferrites making it suitable for the applications. The nanocrystals of Co0·7Zn0·3Fe2-xGdxO4 (0 ≤ x ≤ 0.1, Δx = 0.025) were obtained using self-ignited citrate sol-gel route of synthesis. The X-ray diffractograms of the ferrites were refined by Rietveld method using the full-proof pdf software. The refinement asserts the creation of mono phase spinel ferrite crystals. The morphology of ferrite crystals analyzed from scanning electron microscopy (SEM) profiles depict that the ferrites exhibit the porous nature. The transmission electron microscopy (TEM) images confirms the nanocrystalline nature of the ferrites with an average dimension of 25 nm and high resolution TEM (HRTEM) confirms the spinel phase created within the ferrites. The frequency variation of dielectric parameters was analyzed to study the relaxation phenomenon in ferrites. The values of dielectric constant, dielectric loss and loss tangent were reported to decline with frequency and the Gd3+composition (x). The a.c. electrical conductivity increases with frequency and decreases with composition ‘x’. The room temperature gas sensing response of the ferrite for the hazardous H2S gas was much higher than that for LPG, SO2, NO2 and H2 gases. The ferrite sample with x = 0.025 exhibits a better sensor performance for H2S gas with small recovery and response time. The nanocrystalline nature, porosity and morphology of the ferrites bear control over response and other parameters.
•Confirmation of synthesis of single phase Gd substituted Co–Zn ferrites by Rietveld refinement method.•Dielectric behaviour controlled by the Gd substitution in the ferrite.•Rare earth Gd substituted ferrites for high frequency applications.•Gd substituted Co–Zn nano ferrites as H2S gas sensors.•H2S gas sensors with good response/recovery time and reproducibility/stability.
Self-assembled α-Fe2O3-GO nanocomposites (NCs) obtained via rapid, easy and economic microwave–assisted method through the carbonization of sugar in presence of ferric nitrate in different ...concentrations are envisaged for physical, magnetic and ammonia (NH3) sensing measurements. The α-Fe2O3-GO NCs are composed of uniformly distributed spherical particles of ∼20 nm in size. The effect of varying magnetic field on the surface and structure of the α-Fe2O3-GO NCs has also been investigated. Composites endow a better magnetization over the phase-pure. The highest gas response obtained for 100 ppm NH3 concentration at room-temperature (25 °C) for pristine GO is limited to 8%. Attributed to p-n hetero-junction effect and electron spill-over effect, on the α-Fe2O3 doping, the gas response is greatly improved to 80% at room-temperature. Mechanism for the enhanced sensitivity has carefully been addressed. Gas sensing activities of α-Fe2O3-GO NCs against various target gases are examined using computer assisted Keithley 6514 electro-source meter. Along with physical properties, magnetic and NH3 gas sensor performances of the α-Fe2O3-GO NCs are measured and reported in-depth.
•Metal oxide-graphene oxide nanocomposites.•Microwave-Oven assisted Cost-effective and ecofriendly synthesis.•Ammonia sensors with high detection ability.•Comparison of different metal oxides gas sensors.•Gas sensing mechanism on the basis of p-n heterojunctions.
TiO2 (0–10 wt %)-doped nanocrystalline Ni0.4Cu0.3Zn0.3Fe2O4 (Ni–Cu–Zn) ferrites were synthesized using the sol–gel route of synthesis. The cubic spinel structure of the ferrites having the Fd3m space ...group was revealed from the analysis of Rietveld refined X-ray diffraction (XRD) data. The secondary phase of TiO2 with a space group of I41/amd was observed within the ferrites with doping, x > 3 wt %. The values of lattice parameter were enhanced with the addition of TiO2 up to 5 wt % and reduced further for the highest experimental doping of 10 wt %. Field emission scanning electron microscopy (FESEM) images exhibit the spherical shape of the synthesized particles with some agglomeration, while the compositional purity of prepared ferrite samples was confirmed by energy-dispersive X-ray spectroscopy (EDX) and elemental mapping. The cubic spinel structure of the prepared ferrite sample was confirmed by the Raman and Fourier transform infrared (FTIR) spectra. UV–visible diffuse reflectance spectroscopy was utilized to study the optical properties of the ferrites. The value of band gap energy for the pristine sample was less than those of the doped samples, and there was a decrement in band gap energy values with an increase in TiO2 doping, which specifies the semiconducting nature of prepared ferrite samples. A magnetic study performed by means of a vibrating sample magnetometer (VSM) demonstrates that the values of saturation magnetization of the ferrites decrease with the addition of TiO2 content, and all investigated ferrites show the characteristics of soft magnetic materials at room temperature. The Mössbauer study confirms the decrease in the magnetic behavior of the doped ferrites due to the nonmagnetic secondary phase of TiO2.
The physical properties of La
3+
-doped Cu–Cd ferrites (CCF ferrites) were investigated with an aim to analyze the effect of large-sized La
3+
cations on the structure, morphology, magnetization, ...permeability, and dielectric parameters. Temperature-dependent permeability and permittivity of CCF ferrites are in good agreement with locomotion of grains and grain boundaries. The CCF ferrites are synthesized by a sol–gel method. The Rietveld refinement promoted for the structural confirmation reveals the cubic spinel structure of CCF ferrites. The morphology of all ferrites investigated by surface scanning analysis images indicates the presence of cubical and triangular crystallites. The analysis of magnetic parameters of CCF ferrites measured through a high-field magnetization evidences magnetic transition from paramagnetic to ferrimagnetic phase. The magnetic permeability increases and magnetic loss decreases on enhancing La
3+
content from 0.0 to 0.20. When temperature is stepped up from 25 to 150 °C, the permeability is improved. The increase in permittivity and decrease in ac conductivity is assigned to increase of grain size and reduction of grain boundaries as explained by Maxwell–Wagner model. The magnetic and electrical performance of CCF ferrites demonstrate their potential use in microwave devices. The CCF ferrites possessing soft magnetic behavior along with low magnetic and dielectric losses are promising nanomaterials for high-frequency applications too.
The structural, magnetic and dielectric properties of Mg–Zn mixed ferrimagnetic oxides are studied and reported with an aim to know the role of non-magnetic Zn2+ in modification of the properties. ...Ferrites with the general formula Mg1−xZnxFe2O4 (MZF) where ‘x’ varies from 0.0 to 0.5 were synthesized by microwave assisted sol-gel combustion method. Effects on the magnetic and electrical properties caused by changes in surface morphology, grain size, grain boundary, and micro-strain on account of Zn2+-substitution have been explored in-depth. These effects reveal considerable variations in coercive force, saturation magnetization and residual magnetization values obtained from hysteresis curves of MgFe2O4 on Zn2+ substitution. The effects of temperature and frequency on dielectric properties are investigated and reported.
•We report the effect of Zn-substitution on the structural, magnetic and dielectric properties of magnesium ferrite (MgFe2O4) nanostructures.•For structural and surface morphology analyses are performed as a function of non-magnetic Zn-doping.•Effect of temperature, varied from 243 K to 353 K, on the dielectric properties of Mg1−xZnxFe2O4 nanostructures has been attempted.
Lanthanum-doped copper-cadmium ferrite (La-CCF) nanocrystallite pallet sensors are synthesized using a sol-gel auto-combustion method and envisaged in ammonia gas sensing applications. The structure ...and morphology measurements of the La-CCF sensors are investigated by X-ray diffraction (XRD) pattern and scanning electron microscopy images. The single tetragonal spinel phase is confirmed from X-ray diffraction analysis. A secondary phase of LaO3 is observed when La doping level is ≥ 0.1 observed. The surface appearance of the La-CCF sensor changes from irregular polished course to irregular elevation type crystallites on La addition. The room-temperature gas sensing measurements suggest a better selectivity and sensitivity of La-CCF sensors for ammonia gas among several tested target gases. The sensing performance increases with La3+-doping level from x = 0.0 to 0.1 due to lattice defect introduced by a large sized La ion substitution.
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•We report the effect of La3+ doping on the structural, Morphological and sensing properties of copper cadmium ferrite (Cu0·5Cd0·5Fe2O4) nanostructures.•The structural and surface morphology analyses are performed as a function of La3+-doping.•Effect of La3+ doping on the sensing performance of Cu0·5Cd0·5Fe2O4 nanostructures has been attempted.•Effect of changes in room temperature and morphology of Cu0·5Cd0·5Fe2O4 for NH3 gas sensing of as function of lanthanum doping are identified and reported.
The cobalt-substituted copper zinc ferrite (Cu
0.3
Zn
0.7−
x
Co
x
FeAlO
4
, CZC ferrite) was chemically synthesized by the sol−gel methodology. The phase identification, crystal structure change ...confirmation, morphology analysis, and magnetic evolution of samples have been studied. The X-ray diffraction and vibrating sample magnetometer (VSM) were used for structural and magnetic studies of the prepared CZC ferrite samples. The cation distribution carried out from X-ray analysis confirms the occupancy of Fe
3+
, Zn
2+
and Cu
2+
on tetrahedral sites and Fe
3+
, Cu
2+
, Al
3+
and Co
2+
on octahedral sites in the crystal lattice. The spherical-shaped nanoparticles of 22−32 nm were observed from TEM images, and the nanocrystallinity of particles was confirmed from HRTEM. Hysteresis curves of the CZC demonstrate modifications in coercivity, magnetization and magnetic remanence with Co
2+
ions doping in CZC systems. All the samples show soft magnetic behavior. For
x
= 0.3, lower values of
H
c
and
M
r
indicate super-paramagnetic nature. The dielectric behavior of CZC system was analyzed with frequency variation of real and imaginary portion of dielectric constant. The effects of multi-elementals like Cu, Zn, Co, and Al on ferrite are studied in this paper. The transition of ferrite from ferrimagnetic to superparamagnetic is observed in this study.
Highlights
The cobalt-substituted copper zinc ferrite was prepared by the sol−gel auto-combustion method.
The cobalt-substituted copper zinc shows transition from ferrimagnetic to superparamagnetic.
The coercivity and remanence approaches very low values, showing superparamagnetic nature of the sample.
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