Morphological and magnetic characteristics of cobalt ferrite nanoparticles synthesized by sol–gel auto combustion method using nitrates of respective metal ions have been studied. X-ray diffraction ...pattern was indexed by a Rietveld program to calculate accurate unit cell dimension. A Transmission Electron Microscope (TEM) confirmed the formation of single phase cobalt ferrite nanoparticles in the range 11–40 nm depending on the annealing temperature and time. The size of the particles increases with annealing temperature and time while the coercivity goes through a maximum, peaking at around 25 nm. A very large coercivity (10.2 kOe) is observed on cooling down to 77 K while typical blocking effects are observed below about 260 K. The high field moment is observed to be small for smaller particles and approaches the bulk value for large particles. Mossbauer spectra recorded at room temperature is a sextet indicating that there is a strong magnetic coupling and increase in sintering temperature from 570
∘C to 800
∘C do not affect Mossbauer parameters.
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.
Nanocrystalline ferrites with general formula NiFe2−xCrxO4 (x=0.0−1.0) were prepared by the wet chemical method. Infrared spectra were scanned in the range of 300–800cm−1. Three absorption bands were ...observed in the infrared spectra, the high frequency band ν1 is assigned to tetrahedral complex, low frequency band ν2 to octahedral complex and a small band ν3 is due to Fe3+O2− complex. The force constant, bond length, and the Debye temperature was determined by infrared spectra analysis. The force constant and bond length decrease with the increase in Cr3+ content x which suggests the weakening of the inter atomic bonding. The force constant, lattice constant, and pore fraction have been used to calculate elastic moduli such as stiffness constant, Young's modulus, bulk modulus, rigidity modulus, Poisson's ratio, wave velocity and the Debye temperature. The values of elastic moduli and the Debye temperature decrease with the increase in Cr3+ content x whereas Poisson's ratio almost remains constant. Results have been explained on the basis of inter atomic bonding.
► Cr3+ substituted NiFe2O4 ferrite. ► Evaluation of elastic properties from infrared spectroscopy. ► Interaction between the inter-atomic bonding.
CoFe
2
O
4
, cobalt ferrite (CFO) nano-particles with composition CoZn
x
Ti
x
Fe
2−2
x
O
4
(0 ≤
x
≤ 0.4) were synthesized by sol-gel autocombustion method. The effect of Zn
2+
-Ti
4+
substitution on ...the structural, magnetic and frequency dependent permeability properties of the CFO nano-particles were investigated by X-ray diffraction,
57
Fe Mössbauer spectroscopy, vibrating sample magnetometry, transmission electron microscopy and permeability analysis. The Rietveld refinement of XRD patterns confirm the single spinel phase and the crystallite size is found in the range of 22-32 nm. Cation distribution was estimated by refining the XRD pattern by Rietveld method, and shows Zn
2+
ions at the tetrahedral A-sites, and Co
2+
and Ti
4+
ions at octahedral B-sites. The saturation magnetization (
M
s
) increased from 58 to 75 emu g
−1
for up to
x
= 0.2 and then decreased, while the coercivity decreased continuously with Zn
2+
-Ti
4+
substitution. Two distinct composition ranges with Zn
2+
-Ti
4+
substitution are identified for which
M
s
variation with
x
is explained by the Néel and Yafet-Kittel models. The room temperature Mössbauer spectra are analyzed in detail for probing the magnetic properties of Fe based Zn
2+
-Ti
4+
substituted CFO. The effect of Zn
2+
-Ti
4+
substitution on various Mössbauer parameters,
viz.
hyperfine field distribution, isomer shift, quadrupole splitting, and line width, has also been studied. The variation of nuclear magnetic fields at the A and B sites is explained on the basis of A-B and B-B supertransferred hyperfine interactions. The CFO nanoparticle is considered to possess a fully inverse spinel structure with a Néel-type collinear spin alignment, whereas the Zn
2+
-Ti
4+
substitution in CFO is found to be structurally and magnetically disordered due to the nearly random distribution of cations and the canted spin arrangement. This study also demonstrates that one can tailor the magnetic properties of CFO particles by optimizing the Zn
2+
-Ti
4+
substitution. The increase in the permeability, saturation magnetization and lower loss factor makes the synthesized materials suitable for applications in microwave devices and deflection yokes.
Crystal structure and spin arrangements of CoZn
x
Ti
x
Fe
2−2
x
O
4
and its relation to magneton number with Zn
2+
-Ti
4+
substitution.
► Cation distribution carried out by Rietveld refinement. ► Zn2+ substitution decrease the interatomic distance and elastic properties. ► Curie and Debye temperature decreases with Zn2+ substitution.
...Ni–Zn ferrite samples with the chemical formula Ni1−xZnxFe2O4 (x=0.0 to x=1.0) were prepared by solid state reaction. Using the Rietveld refinement the discrepancy factor, interatomic distance, atomic coordinates, cation occupancy and degree of inversion have been determined. SEM images revealed that the Zn2+ promotes grain growth in NiFe2O4. The IR spectra show two absorption bands in the wave number range of 400–600cm−1. The IR data have been used to calculate elastic moduli such as stiffness constant (C11, C12), longitudinal wave velocity (Vl), shear wave velocity (VS), mean wave velocity (Vm), Young modulus (E), bulk modulus (K), rigidity modulus (G), Poisson ratio (σ) and Debye temperature (θE). The values of elastic moduli and Debye temperature decreases with increasing Zn2+ composition x. AC susceptibility measurement confirms the decrease in Curie temperature with increasing Zn2+ content. Dielectric loss (ε″) increases with increasing Zn2+ content.
A series of ferrite with a chemical composition Co0.7Zn0.3GdxFe2−xO4 (where x=0.0 to x=0.1) were prepared by sol-gel auto-combustion method. X-ray diffraction pattern were used to determine the ...crystal structure and phase formation of the prepared samples. Scanning electron microscopy is used to study the surface morphology of the prepared samples. Elastic properties were determined from the infrared spectroscopy. Debye temperature, wave velocities, elastic constants found to increase with the increase in Gd3+ substitution. Dielectric properties such as dielectric constant and dielectric loss were studied as a function of Gd3+ substitution and frequency. Dielectric constant decreased with the increase in frequency and Gd3+ substitution. Behavior of dielectric properties was explained on the basis of Maxwell-Wagner interfacial polarization which in accordance with Koops phenomenological theory. Real and imaginary part of impedance was studied as a function of resistance and Gd3+ substitution. The behavior of impedance is systematically discussed on the basis of resistance-capacitance circuit.
Elastic behaviour of Cr3+ substituted Co–Zn ferrites Algude, S.G.; Patange, S.M.; Shirsath, Sagar E. ...
Journal of magnetism and magnetic materials,
January 2014, 2014, 2014-01-00, Volume:
350
Journal Article
Peer reviewed
The elastic behaviour of Cr3+ substituted Co–Zn ferrites system; Co0.7Zn0.3CrxFe2−xO4 where x=0.0 to 0.5 in step of 0.1 were prepared by ceramic method. Ultrasonic Pulse transmission method at room ...temperature was employed to determine the elastic properties of the presently investigated samples. Values of longitudinal and shear wave velocities were increased with an increases in Cr composition x. Using these value of velocities; Young's modulus, rigidity modulus, bulk modulus, longitudinal modulus and Poisson's ratio were calculated. The values of moduli were increased with an increases in Cr composition x. Debye temperature of all sample were calculate using the Anderson equation and it shows increasing trend with an increases in Cr composition x. The behaviour elastic moduli of Co0.7Zn0.3CrxFe2−xO4 are interpreted in terms of bonding force between atoms.
•Cr3+ substituted Co–Zn ferrite were prepared by ceramic method.•Ultrasonic pulse transmission technique was used to determine the elastic moduli.•Elastic moduli were increased with Cr composition x.•Debye temperature was increased with Cr composition x.
Nanocrystalline Ce-substituted yttrium iron garnet (YIG) powders of different compositions, Y 3−x Ce x Fe 5 O 12 (0 ≤ x ≤ 2.0), were synthesized by a combination of sol–gel auto-combustion and ...solid-state synthesis techniques. The as-obtained powder samples were sintered at 1150 °C for 10 h. The garnet structure formation is confirmed by the X-ray diffraction pattern, which shows that the calculated lattice parameter increased for x = 1.0 and shows a decreasing trend for x ≥ 1.0 with the addition of cerium ions. The lattice parameter increased from 12.38 Å to 12.41 Å for x ≤ 1.0 whereas it decreased from 12.412 Å to 12.405 Å with the cerium composition for x > 1.0. The average particle size determined by high resolution transmission electron microscopy is in the range of 50 to 90 nm and found to increase with the substitution of cerium ions in YIG. The room temperature magnetic parameters such as saturation magnetization, coercivity and remanence magnetization are greatly affected by the substitution of cerium ions. The values of saturation magnetization decrease from 25.5 to 15 emu g −1 whereas coercivity increases from 1 to 28 Oe with the substitution of cerium ions. The pure YIG sample shows polycrystalline nature that changed towards a single-crystal structure leading to a preferred-(100) orientation with the Ce substitution. The change from a ring to a spotty pattern observed in SAED confirmed the crystalline phase transformation and is well supported by HRTEM and magnetic measurements. The behavior of magnetic and electrical properties is well supported by the poly- and single-crystalline nature of YIG and Ce-YIG, respectively. The crystal structure transformation in YIG brought about by Ce substitution could unveil enormous opportunities in the preparation of single-crystal materials from their polycrystalline counterparts.
Stoichiometric compositions of ferrites with the chemical formula Li0.5−0.5xCoxFe2.4−0.5xDy0.1O4 with x=0, 0.25, 0.5, 0.75, 1.0 were prepared by the standard double sintering ceramic method. X-ray ...diffraction analysis confirmed the cubic spinel structure of the prepared samples. The structural, morphological and magnetic properties were studied by X-ray diffraction, infra-red spectroscopy (IR), scanning electron microscopy (SEM), vibrating sample magnetometry (VSM) and ac susceptibility measurements. Lattice constant, grain size and density increase whereas porosity decreases with the increase in Co2+ substitution. IR measurements show the characteristic ferrite bands. Spectral absorption bands were observed in IR spectroscopic analysis at ν1=564−601cm−1, ν2=486−519cm−1 and ν3=551−578cm−1. The cation distribution estimated by the X-ray diffraction is supported by magnetization and susceptibility studies. The saturation magnetization decreases from 44.25 to 17.14emu/g whereas coercivity remarkably increases from 240.69 to 812.14emu/g with increasing Co2+ substitution. The mechanisms involved are discussed.
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