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In this study, the sol-gel autocombustion route was used to synthesize Cd-Zn-Cr ferrites/graphene nanoplatelets nanocomposites having chemical formula Cd 0.35 Zn 0.65 Cr 0.03 Fe 1.97 O 4 /GNP x (x= 0–5 wt%). Thermogravimetric examination (TGA) was utilized to estimate the annealing temperature of about 1173 K. The manufacturing of a mono-phase cubic spinel structure was verified through XRD data. The composites' lattice constant (a) and crystalline size (D) ranged from 8.43 Å to 8.47 Å and 29.66 nm to 38.32 nm, respectively. SEM micrographs revealed the nano-size particles attached to a sheet-like structure. The UV/Vis methodology revealed an energy band gap (E g) between 4.20 and 4.95 eV. Two probe DC electrical measurements (IV) indicated the increased electric conductivities of prepared nanocomposites. Room-temperature dielectric analysis has shown an increase in dielectric constant (ε′), AC conductivity (σ ac), and capacitance of the pellet (C p) by increasing the GNP concentration due to the conducting network. The dielectric constant, capacitance, and ac conductivity of the nanocomposites were found to be 2.57, 1.18×10−09 F, and 1.25×10−10 (Ω.cm)−1 for GNP=5.00 wt% as compared to 1.95, 6.63×10−10 F, and 3.09×10−11 (Ω.cm)−1 for GNP=0.00 wt%, respectively. These composites are useful as high-performance electrodes in charge storage devices at high frequencies. The saturation magnetization (M s) of the synthesized ferrites/GNP nanocomposites ranged from 4.1 to 11.5 emu/g, and the coercivity (H c) varied from 109 to 452 Oe. The demonstrated nanocomposites provide a strategy for designing high-efficiency electrode materials for supercapacitors. • CZCF/GNP nanocomposites were investigated for structural, magnetic, dielectric, and electrochemical properties. • SEM micrographs revealed the attachment of nano-sized ferrite particles attached to a sheet-like structure. • DC electrical measurements (IV) indicated the increased electric conductivity as a function of GNP content. • Both M s and H c showed a significant change by increasing the GNP concentration in the CZCF crystal matrix. • Enhanced capacitance and ac conductivity of CZCF/GNP nanocomposites suggest them for designing high-efficiency electrode materials for supercapacitors. [ABSTRACT FROM AUTHOR]

Ho-substituted Li–Ni ferrites with composition L i 1.2 Ni 0.4 Ho x Fe 2- x O 4 ; 0≤ x ≤ 0.15 were synthesized by a self-ignited sol-gel process. An annealing temperature of 950 °C is estimated via thermal-gravimetric (TGA) analysis. X-ray diffraction (XRD) scans have confirmed the formation of the ferrite phase with a spinel structure in all samples. Substitution of Ho ions on the B-site significantly reduced the porosity from 38 -to 23% and the crystallite size from 23.4 -to 21.7 nm. Microstructural analysis revealed a denser structure with an increase in Ho content. Dielectric results showed that both the dielectric loss and dielectric constant depict a nonlinear variation with the addition of Ho. Complex impedance behavior with a single semicircle for all samples suggests the predominant effect of the grain boundary mechanism. The substitution of Ho ions in place of Fe ions significantly decreased the electrical conductivity. The anisotropic Ho3+ ions reinforce the L-S coupling which consequently enhanced the coercive force from 145 -to 389 Oe, and thus the anisotropy constant. [ABSTRACT FROM AUTHOR]

In the present study, the impact of holmium (Ho) substitution on structural, spectral, dielectric and magnetic behavior of Li 1.2 Zn 0.4 Ho x Fe 2−x O 4 (0.00 ≤ x ≤ 0.15) ferrites was investigated. The development of spinel phase and structural changes induced by Ho doping were confirmed by X-ray diffraction. The accommodation of Ho ions into spinel lattice was restricted for x ≥ 0.06 as indicated by ortho phase (HoFeO 3 ) traces. The decrease in lattice parameter ( a ) was attributed to the segregation of Ho ions on grain boundaries. FTIR spectra featured two intrinsic vibrational bands v 1 (617 cm −1 ) and v 2 (488 cm −1 ) for x = 0 due to tetrahedral and octahedral vibrations respectively. The compositional dependence of force constants and bond lengths has explained on the basis of cations distribution and oxygen-cation bond distances of respective sites. The addition of Ho ions decreased the saturation magnetization and optimized the coercivity from 59 to 335 Oe, proposing these ferrites for magnetic recording media. Dielectric results for the entire range of frequency (1 MHz to 3 GHz) revealed that ac conductivity increased from 3.5 × 10 5 to 1.8 × 10 6 (Ω-cm) −1 up to x = 0.09 and then it decreased slightly for x = 0.12. The effective contribution of grain-interior mechanism to dielectric behavior was confirmed by complex impedance study. The results of dielectric studies displayed that Ho doped lithium ferrites are suitable low loss potential materials for high frequency based applications. [ABSTRACT FROM AUTHOR]

The present study investigates the photocatalytic activity of NiCoPrFe 2 O 4 and Cd-NiCoPrFe 2 O 4 synthesized by the self-ignition sol-gel process. NiCoPrFe 2 O 4 @CNTs was prepared via ultrasonication approach. Methyl violet was used as a dye to examine the photodegradation activities of synthesized photocatalysts under visible light. The spinel crystalline structure is confirmed by XRD. The morphology of the as prepared samples was observed via scanning electron microscopy. NiCoPrFe 2 O 4 , Cd-NiCoPrFe 2 O 4 , and NiCoPrFe 2 O 4 @CNTs showed 55.46%, 78.29%, and 85.96% percentage degradation of methyl violet respectively. The photocatalytic performance of CNT based nanocomposite is found to be increased due to the enhanced charge separation property of CNT. • The sol-gel method was used for the preparation of NiCoPrFe2O4. • XRD and FTIR corroborate the structure and composition of elemental features. • SEM analysis confirms the morphology of the material. • NiCoPrFe2O4@CNT composite had shown excellent result is the photo-degradation of methyl violet. [ABSTRACT FROM AUTHOR]

Nano-sized Zr-Co doped nickel ferrites with nominal composition, NiZr x Co x Fe 2-2x O 4 ( x =0.0, 0.2, 0.4, 0.6, 0.8) were synthesized using the micro-emulsion route. The structural elucidation of the synthesized materials was carried out by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The XRD analysis confirmed face centered cubic (FCC) structure of all compositions of NiZr x Co x Fe 2-2x O 4 nanocrystallites. Crystallite size was calculated by Scherrer's formula found in the range 10–15 nm. The variation in lattice parameter as determined by XRD data agreed with size variation of host (Fe 3+ ) and guest (Zr 4+ and Co 2+ ) cations. FTIR spectra of doped NiFe 2 O 4 exhibited the typical octahedral bands at 528.4 cm −1 which is the characteristic feature of spinel structure of spinel ferrites. The characterized spinel NiZr x Co x Fe 2-2x O 4 nano-ferrites were evaluated for their potential applications by magnetic hysteresis loops and dielectric measurements. The value of saturation magnetization ( M s ) decreased from 47.9 to 13.09 emu/g up to x =0.8 with ups and downs fluctuations in between x=0.0 to x=0.8. The high values of Ms of some compositions predicted the potential applications in high density perpendicular recording media and microwave devices. The frequency dependent behavior of permittivity (ε') is recorded and discussed with the help of hopping mechanism of both holes and electrons. The dielectric and magnetic data of NiZr x Co x Fe 2-2x O 4 nano-ferrites suggested the potential applications of these ferrite nanoparticles in high frequency and magnetic data storage devices fabrication. [ABSTRACT FROM AUTHOR]

Ni 0.5 Sn 0.5 Co x Mn x Fe 2−2x O 4 ferrites with x = 0.0–0.8 have been prepared by the micro-emulsion method, using CTAB as a surfactant material. X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR) and vibrational sample magnetometer (VSM) were used to investigate the effects of Co and Mn substitutions on cationic distribution, crystallite size, lattice constant, spectral, magnetic and dielectric properties. Lattice constant and crystallite size were found to increase from 7.4 to 9.25 Å and from 11.8 to 19.7 nm respectively with increasing substitution of Co and Mn ions. Saturation magnetization (M S ) gradually increased from 20.5 to 47.6 emu/g with increase in the value of x. However, Coercivity increased from 152.7 to 462.4 Oe up to x = 0.4 and then it decreased thereafter. The dielectric constant, complex dielectric constant and tan loss (tanδ) were observed to decrease with increase in frequency, depicting the semiconductor behavior of the ferrites. Dc resistivity was observed to decrease considerably upon addition of Co and Mn content. The outcome for the tunable magnetic properties and achieved modification of the synthesized nanocrystallites may be chosen for tremendous applications; such as miniaturized memory devices that are based on the energy storage principles and capacitive components. [ABSTRACT FROM AUTHOR]

CoTb 0.03 Fe 1.97 O 4 ferrite and poypyrrole (PPy) polymer nano composites were prepared by mixing the nano crystalline ferrite with poypyrrole (PPy) by following the solid state reaction synthesis route. The XRD patterns of CoTb 0.03 Fe 1.97 O 4 spinel ferrite powders and polymer (PPy) exhibited single phase spinel structure. The amorphous nature of PPy was evidenced by the broad peaks of XRD patterns. The surface morphology unfolded heterogeneous distribution in composites and ferrite. The grains in ferrite were spherical in shape with clear boundaries. The morphology was appreciably altered by the inclusion of ferrite contents. The higher activation energy and resistivity aroused due to blocking of conduction mechanism owing to nanoparticles embedded in the PPy matrix. A downfall in the dielectric loss of the composites is observed as the frequency of the applied field is increased. The incorporation of ferrite contents optimized the magnetic parameters of the composites. The enhanced coercivity (Hc) of these nanocomposites might be beneficial for memory devices. [ABSTRACT FROM AUTHOR]

The substitution of Neodymium (Nd) in the cobalt - zinc (Co–Zn) ferrite was analyzed. The sol-gel technique was used to synthesize the se ceramic samples. The crystalline structural, molecular characterizations, and magnetic properties were analyzed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) experiments, and vibrating sample magnetometer (VSM) respectively. XRD patterns revealed the single-phase cubic spinel structure of the samples. Lattice p arameter varied from 8.41 to 8.38 Å with the inclusion of Nd concentration. The existence of two characteristic frequency bands in the range of 400–1400 cm−1 was confirmed by FTIR spectra. VSM measurements showed the magnetic behaviour at room temperature. The saturation magnetization was noted to decrease from 81 to 66 emu/g with increasing the Nd concentration. The sample having step size x = 0.025 revealed the highest coercivity and retentivity. Dielectric properties were studied and showed variation in dielectric constant, dielectric loss, ac conductivity, and energy dissipation (tangent loss) in the prepared material s. • Auto-citric combustion method was used to prepare Co0·6Zn0.4NdxFe2-xO4 ferrites. • The estimated value of constant lattice decreases upon increasing Nd ions. • Intrinsic vibrational bands revealed a shift with increasing the Nd content. • The porosity of the samples increased from 0.41 to 0.55. • Nd inclusion optimized saturation magnetization and coercivity. [ABSTRACT FROM AUTHOR]

A series of holmium (Ho) doped nanocrystalline Ni 0.7 Zn 0.3 Ho 2x Fe 2–2x O 4 ; 0.0≤x≤0.07 ferrite was synthesized using the conventional ceramic technique. The cubic spinel structure was confirmed by powder X-ray diffraction (XRD). The lattice parameter increases with increase in Ho content due to large ionic radius of Ho 3+ (0.901 Å) as compared to Fe 3+ (0.67 Å). Room temperature DC electrical resistivity and activation energy both increase with the increase of holmium contents. The saturation magnetization (M s ) decreased gradually from 78.92 to 54.17 emu/g due to holmium ions substitution in Ni-Zn ferrites. This decrease in M s is explained on the basis of redistribution of cations amongst the sites and weakening the A-B exchange interactions. An increase in electrical resistivity made this material suitable for its use in high frequency device applications. [ABSTRACT FROM AUTHOR]

• Sol-gel technique was employed to synthesize Ba 4 Cu 2-x Ni x Fe 36 O 60 ferrites. • Cole-Cole plots markedly distinguished grain boundary contribution. • Coercivity (H c) increased (1844.44–2946.83 Oe) by increasing Ni contents. • The squareness ratio (0.471–0.450) revealed single magnetic domain. • The results suggest their potential use in high-frequency applications. This paper reports the impacts of nickel substitution on dielectric, magnetic, and structural characteristics of Ba 4 Cu 2-x Ni x Fe 36 O 60 hexaferrites prepared via the sol–gel method. The sample was annealed for 5 h at 1200 °C. The crystalline structure, magnetic and dielectric features were examined by X-ray diffraction, vibrating sample magnetometer, and impedance analyzer individually. The specific absorption bands of hexagonal ferrites were identified by FTIR spectroscopy and in the 420–600 cm−1 range. M−H loops of samples were determined to examine the magnetic properties of synthesized materials. Magnetic measurement shows that samples exhibit ferrimagnetic behavior at room temperature. The magnetic properties are described in cation distribution and grain size effect. Dielectric properties of the samples were observed in the frequency range (1–3 GHz). Cole-Cole graphs of prepared materials revealed the influence of grain boundaries. A single semi-circle in the impedance Cole-Cole plots approves a special part of grain boundaries in the conduction process. Dielectric properties are affected by the electron hopping mechanism between Fe2+ and Fe3+ ions. These performances expose that these nanomaterials are appropriate for high-frequency applications. [ABSTRACT FROM AUTHOR]

Dy–Ni substituted Mn 1-x Ni x Fe 2-y Dy y O 4 (x = 0.0–0.1 and y = 0.0–0.2) soft magnetic oxides were synthesized using a size controlled micro-emulsion method. X-ray diffraction (XRD) analysis was employed to confirm the spinel structure of synthesized ferrites. Crystallite size was found to decrease (33-22 nm) while lattice constant was increased (8.58–8.63 Å) by increasing dopants content. FTIR bands observed in the range 500–600 cm−1 is the evidence to form the spinel structure of these ferrites. Dielectric constant (ε′) and dielectric loss (ε") were observed to decrease with the increase of frequency due to hopping mechanism. Hysteresis curves exhibited soft nature of synthesized nanoferrites. Remanence (M R) and saturation magnetization (M S) were increased with the incorporation of Dy and Ni ions. The decreased in dielectric losses and increased in magnetic parameters suggested that these ferrites are potential candidates for magnetic recording heads. [ABSTRACT FROM AUTHOR]