Role of Mn doping on magnetic properties of multiferroic NiCr2O4 nanoparticles

The structural and magnetic properties of Mn doped Nickel Chromite (Ni_1-xMn_xCr₂O_4, x = 0, 0.2, 0.3, 0.4, 0.6, 0.8) nanoparticles (NPs) were studied in detail. The X-ray diffraction analysis affirms normal spinel structure for all the samples and average crystallite size was found in the range 31–58 nm. The spinel structure of these nanoparticles was also confirmed by Fourier transform infrared spectroscopy which revealed the formation of tetrahedral and octahedral vibrational bands in the range 607 -628 cm^?1 and 486 - 491 cm^?1, respectively. Transmission electron microscopy images depicts less agglomerated and non-spherical shaped NPs. The temperature dependent zero field cooled and field cooled magnetic measurements revealed a paramagnetic to ferrimagnetic transition T_c at 87 K for NiCr₂O₄ NPs, which is shifted to low temperatures by Mn doping. This effect was attributed to cationic distributions between adjacent sites produced by Mn doping. M ? H loops of Ni_1-xMn_xCr₂O₄ NPs revealed enhanced saturation magnetization with increase in Mn doping which is attributed to a large magnetic moment of Mn ions. Ni_1-xMn_xCr₂O₄ (x = 0.6 and 0.8) NPs show steps in their M ? H loops because of exchange interactions between two sites of these NPs.     

The influence of Zr and Ni co-substitution on structural,dielectric and magnetic traits of lithium spinel ferrites

The impact of Ni²⁺ and Zr⁴⁺ on the physical properties of LiFe₂O₄ ferrites is investigated and synthesized via the microemulsion technique. X-ray diffraction pattern of pure and substituted lithium ferrites exhibited spinel structure. The constant lattice increases with increasing dopants concentration up to x = 0.2 and decreases for higher x. The crystallite size value varies from 8.15 to 12.37 nm. The incorporation of heavier ions with lighter ions increased the X-ray density of lithium ferrites. The value of dielectric parameters such as dielectric constant and dielectric loss decreases with the substation of Ni²⁺ and Zr⁴⁺ ions. The Maxwell Wagner model ascribes the decrease in dielectric parameters. Substituted lithium ferrites observe a high Q value. The magnetic studies revealed that saturation magnetization and coercivity were significantly affected by Ni²⁺ and Zr⁴⁺ ions. The inclusion of Ni²⁺ and Zr⁴⁺ ions improves the dielectric and magnetic properties making it suitable for high-frequency applications.     

Structural dependence of microwave dielectric properties in ilmenite-type Mg(Ti1-xNbx)O3 solid solutions by Rietveld refinement and Raman spectra

Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics were prepared by the conventional solid-state reaction method. The phase composition, sintering characteristics, microstructure and dielectric properties of Ti⁴⁺ replacement by Nb⁵⁺ in the formed solid solution Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics were systematically studied. The structural variations and influence of Nb⁵⁺ doping in Mg(Ti_1-xNb_x)O₃ were also systematically investigated by X-ray diffraction and Raman spectroscopy, respectively. X-ray diffraction and its Rietveld refinement results confirmed that Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics crystallised into an ilmenite-type with R-3 (148) space group. The replacement of the low valence Ti⁴⁺ by the high valence Nb⁵⁺ can improve the dielectric properties of Mg(Ti_1-xNb_x)O₃ (x = 0–0.09). This paper also studied the different sintering temperatures for Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics. The obtained results proved that 1350 °C is the best sintering temperature. The permittivity and Q × f initially increased and then decreased mainly due to the effects of porosity caused by the sintering temperature and the doping amount of Nb₂O₅, respectively. Furthermore, the increased Q × f is correlated to the increase in Ti–O bond strength as confirmed by Raman spectroscopy, and the electrons generated by the oxygen vacancies will be compensated by Nb⁵⁺ to a certain extent to suppress Ti⁴⁺ to Ti³⁺, which was confirmed by XPS. The increase in τ_f from ?47 ppm/°C to ?40.1 ppm/°C is due to the increment in cell polarisability. Another reason for the increased τ_f is the reduction in the distortion degree of the [TiO₆] octahedral, which was also confirmed by Raman spectroscopy. Mg(Ti_0.95Nb_0.05)O₃ ceramics sintered at 1350 °C for 2 h possessed excellent microwave dielectric properties of ε_r = 18.12, Q × f = 163618 GHz and τ_f = ?40.1 ppm/°C.     

Production of Cr3+ substituted Li–Zn nanocrystalline ferrite by citrate method: Studies on structure,cation occupancy,elastic, optical and magnetic performance

The structural, elastic, optical and magnetic characteristics of Li_0.4Zn_0.2Cr_xFe_2.4-xO₄ (0.0 ≤ x ≤ 0.5; step 0.1) produced using a citrate precursor were studied. X-ray powder diffraction data indicate that all of the generated samples are single-phase spinel structures with no additional phases. The lattice parameter reduces from 8.355 Å to 8.333 Å when the chromium content rises. The crystallite sizes of the compositions were assessed by Scherrer's and Williamson-Hall (W–H) approaches. Infrared (IR) spectroscopy revealed two significant absorption bands generated by vibrations at the tetrahedral and octahedral sites. The elastic moduli (bulk modulus ‘B’, rigidity modulus ‘G’ and Young's modulus ‘E’) as well as the Debye temperature (θ_D) assessed by IR spectroscopy rise as the Cr³⁺ ions concentration increases. Chromium addition inhibits grain growth and enhances the mechanical strength of Li–Zn nanoferrites. Diffuse reflectance spectra (DRS) were utilized to evaluate the optical band gap (E_g) of Li–Zn–Cr nanoferrite, which was found to drop from 1.96 to 1.84 eV. The vibrating sample magnetometer (VSM) was used to perform the magnetic analysis, and various magnetic parameters were derived using the M ? H curves results. Acceptable values of saturation magnetization (78.6–44.05 emu/g) and coercivity (30.87–44.65 G) were found in this system, making these nanoferrites ideal for high-density recording medium and electromagnets applications. Based on the experimental results of lattice parameters, and magnetization, a quite reasonable cation distribution was postulated for all samples. Theoretically predicted lattice parameters and magnetic moments derived from the suggested cation distribution agree with those determined empirically from XRD and VSM results, respectively. The switching field distribution curves were schemed utilizing the first derivative of magnetization data from M ? H loops. The Curie temperature decreases significantly with Cr³⁺ substitution.     

Influence of Gd content on the structural,Raman spectroscopic and magnetic properties of CoFe2O4 nanoparticles synthesized by sol-gel route

The structural and magnetic properties of sol-gel synthesized Gd doped (x = 0.00 to 0.15) CoFe₂O₄ nanoparticles (NPs) have been studied. The x-ray diffraction (XRD) and FTIR spectroscopy along with Raman spectra confirmed the formation of face centered cubic inverse spinel structure. TEM images showed the NPs are well-dispersed with average particle size 30 nm. Room temperature magnetic measurement showed the value of coercivity fluctuates from 353 Oe to 1060 Oe for different % of Gd content. The maximum coercivity, saturation magnetization, magnetic moment, magnetic anisotropy, remnant magnetization found for 0.03% Gd content are 1060.19 Oe, 77.53 emu/gm, 3.29 μ, 4.11 × 10⁴ erg/cm³, 32.38 emu/gm, respectively. The large value of coercivity indicated that the interparticle interactions and crystalline anisotropy are high. Thus CoFe_2-xGd_xO₄ magnetic NPs might be a potential candidate for data processing, automotive and telecommunications.     

Low-temperature firing and microwave dielectric properties of MgNb2-xVx/2O6-1.25x ceramics

MgNb_2-xV_x/2O_6-1.25x (0.1≤x≤0.6) ceramics with orthorhombic columbite structures were prepared at low-temperature by a solid-phase process. The phase component, microscopic morphology, low-temperature sintering mechanism and microwave dielectric performance of MgNb_2-xV_x/2O_6-1.25x ceramics were comprehensively investigated. Low-temperature sintering densification of dielectric ceramics was achieved via the nonstoichiometric substitution of vanadium (V) at the Nb-site. In contrast to pure MgNb₂O₆ ceramics, the sintering temperature of MgNb_2-xV_x/2O_6-1.25x (x = 0.2) ceramics was reduced by nearly 300 °C owing to the liquid-phase assisted sintering mechanism. The liquid phase arises from the autogenous low-melting-point phase. Meanwhile, MgNb_2-xV_x/2O_6-1.25x (x = 0.2) samples with nonstoichiometric substitution could achieve a more than 900% improvement in the Q × f value, compared with stoichiometrically MgNb_2-xV_xO₆ (x = 0.1, 0.2) ceramics. Finally, MgNb_2-xV_x/2O_6-1.25x dielectric ceramics possess outstanding microwave dielectric properties: ε_r = 20.5, Q × f = 91000, and τ_f = -65 ppm/°C when sintered at 1030 °C for x = 0.2, which provides an alternative material for LTCC technology and an effective approach for low-temperature sintering of Nb-based microwave dielectric ceramics.     

Effect of substituting Al3+ for Ti4+on the microwave dielectric performance of Mg2Ti1-xAl4/3xO4 (0.01 ≤ x ≤ 0.09) ceramics

In this paper, Mg₂Ti_1-xAl_4/3xO₄ ceramics (0.01 ≤ x ≤ 0.09) were synthesized through conventional solid-state ceramic route. The cubic spinel structure, microstructure and microwave properties of Mg₂Ti_1-xAl_4/3xO₄ (x = 0.01, 0.03, 0.05, 0.07, 0.09) ceramics were investigated by X-ray diffraction, Raman spectra, infrared spectra. Rietveld refinements confirm that a spinel structure phase with space group Fd-3m is formed. The variation of the permittivity was concerned with the ionic polarizability, and the value of τ_f was influenced by the bond valence. Both Q × f values and relative density showed an identical trend. Intrinsic properties of Mg₂Ti_1-xAl_4/3xO₄ ceramics were analyzed by infrared spectra and Raman spectra. In addition, the Mg₂Ti_1-xAl_4/3xO₄ ceramic sintered at 1420 °C for 4 h possessed optimal dielectric properties (ε_r = 14.65, Q × f = 182347 GHz, τ_f = −57.7 ppm/°C) when x = 0.09.     

Effect of calcination temperature on optical,magnetic and dielectric properties of Sol-Gel synthesized Ni0.2Mg0.8-xZnxFe2O4 (x = 0.0–0.8)

The Ni_0.2Mg_0.8-xZn_xFe₂O₄ (x = 0.0, 0.2, 0.4, 0.6 & 0.8) nanomaterials were prepared via sol-gel technique. These samples were calcined at three different temperatures (T) such as 400, 450 and 500 °C/5 h. Furthermore, the X-ray diffraction (XRD) patterns of all the calcined samples revealed the single phase cubic spinel structure. The lattice constants (a = b = c) were noticed to be increasing with increase of ‘x’. The grain shape, size and distribution of x = 0.0–0.8 contents were analyzed using field emission electron microscope (FESEM). The x = 0.2 content provided higher optical band gap energy (E_g) value than the remaining contents. Furthermore, the magnetization versus magnetic field (M − H) curves indicated the superparamagnetic nature of x = 0.0–0.8 contents. The high saturation magnetization (M_s) was noticed for x = 0.4 and 0.6 contents. In addition, the distribution of cations like Ni⁺², Mg⁺², Zn⁺², Fe⁺³ and Fe⁺² was performed between the tetrahedral (A) and octahedral (B) sites. The frequency dependence of dielectric constant (ε′), dielectric loss (ε") and ac-electrical conductivity (σ_ac) was investigated as a function of composition. Moreover, the temperature variation of ε′ showed the decreasing trend of dielectric transition temperature (T_e) with increase of ‘x’. The high ε′ of 163.1 (at 1 MHz) was noticed at x = 0.2 content calcined at 500 °C. Using the power law fit applied to the log σ_ac-log ω plots, the dc-electrical conductivity (σ_dc) and exponent (n) parameters were calculated.     

Influence of rare-earth La3+ ion doping on microstructural,magnetic and dielectric properties of Mg0.5Ni0.5Fe2-xLaxO4 (0 ≤ x ≤ 0.1) ferrite nanoparticles

A series of La³⁺ ion doped magnesium nickel ferrites, Mg_0.5Ni_0.5Fe_2-xLa_xO₄ (0 ≤ x ≤ 0.1) having a cubic spinel structure were prepared by the co-precipitation method. Various characterization techniques, including X-ray diffractometer (XRD), high resolution transmission electron microscopy (HR-TEM), electron spin resonance (ESR) and vibrating sample magnetometer (VSM) were used to investigate structural and magnetic properties. The average crystallite size decreases and lattice parameter increases with La³⁺ ion doping and lie in the range of 12–7 nm and 8.347–8.361 Å respectively. Analysis of ESR spectra reveals that, g-value with La³⁺ ion addition decreases from 2.57 to 2.12. The saturation magnetization and the coercivity decrease with increasing rare-earth content. Magnetic-hysteresis (M − H) loop shifts from a ferromagnetic to a superparamagnetic nature with La³⁺ ion addition. The dielectric study was carried out in the frequency range of 1 KHz to 4000 KHz and temperature ranging 30 °C–350 °C using the impedance analyzer. The dielectric constant decreases with increasing frequency and the La³⁺ ion concentration. The dielectric loss of the sample increases with increasing temperature. The magnetic properties of the synthesized nanoparticles make them a potential material for stable ferrofluid application and the low tangent loss value makes these material a potential candidate for frequency-based applications.     

Y3+ composition and particle size influenced magnetic and dielectric properties of nanocrystalline Ni0.5Cu0.5YxFe2-xO4 ferrites

The rare earth Yttrium (Y³⁺) doped Ni–Cu nanoferrites (NCY ferrites) with chemical formulation, Ni_0.5Cu_0.5Y_xFe_2-xO₄ (x = 0–0.125) were prepared successfully by the sol gel route. The X-ray diffraction (XRD) of NCY ferrites revealed that a single phase of cubic spinel is created within the synthesized ferrites. The crystallite sizes obtained by XRD pattern are in the range of 51–84 nm, in good agreement with those obtained by transmission electron microscopy (TEM) and field emission scanning electron microscopy (FSEM). The calculated lattice parameter of NCY ferrite unit cells initially decreases up to x = 0.1 and increase afterwards for x = 0.125. From FESEM and TEM micrographs, surface morphology and microstructure of NCY nanoferrites were studied. The energy dispersive X-ray spectroscopy (EDS) patterns have confirmed the stoichiometric presence of Ni, Cu, Y, O and Fe, those were used to prepare the samples. The variations in the magnetic properties with Y³⁺ compositions were investigated by obtaining the hysteresis loops of NCY ferrites. The magnetic hopping lengths L_A and L_B were calculated from XRD. The saturation magnetization, Bohr magneton number, coercivity and retentivity of the ferrites were influenced by the structural parameters like crystallite size and lattice strain. The frequency variation of dielectric constant and loss tangent exhibit space charge polarization as a phenomenon governing the dielectric behavior of the ferrites.     

Effect of doping on dielectric and optical properties of barium hexaferrite: Photocatalytic performance under solar light irradiation

A series of Co-doped and Cr-doped Ba_1-xCo_xFe_12-yCr_yO₁₉ nanoparticles (NPs) were synthesized via the microemulsion route. The effects of Co and Cr substitution on the structural, dielectric, optical, and photocatalytic properties of the NPs were investigated. The Ba_1-xCo_xFe_12-yCr_yO₁₉ NPs were characterized using Fourier-transform infrared spectroscopy, X-ray diffraction analysis, scanning electron microscopy, Raman scattering, and dielectric measurements. The Ba_1-xCo_xFe_12-yCr_yO₁₉ NPs were obtained in a single phase with an average crystallite size of 18 nm. The dielectric constant of the NPs decreased, while the dielectric loss and tangent loss increased with increasing dopant (Co and Cr) contents. The photocatalytic activities (PCAs) of the Ba_1-xCo_xFe_12-yCr_yO₁₉ and BaFe₁₂O₁₉ NPs were appraised by carrying out the degradation of CV (crystal violet) dye under solar light irradiation. The doping improved the PCA of BaFe₁₂O_19, and up to 64.23% of the CV dye could be degraded within 60 min under visible light irradiation. The Ba_1-xCo_xFe_12-yCr_yO₁₉ NPs showed great potential for application as an economic photocatalyst as they required solar light irradiation for the degradation of CV.     

Nanostructured quaternary Ni1-xCuxFe2-yCeyO4 complex system: Cerium content and copper substitution dependence of cation distribution and magnetic-electric properties in spinel ferrites

Quaternary Ni_1-xCu_xFe_2-yCe_yO₄ complex nano-ferrites system with different cerium content ratio and copper substitution degree were synthesized via co-precipitation wet chemical technique. The newly obtained nanoparticles, with general formula Ni_1-xCu_xFe_2-yCe_yO₄ (where x = 0.0, 0.3, 0.6 and y = 0.00, 0.03, 0.05, 0.08 and 0.10) were heated up to 600 °C to stabilize the specific crystalline spinel structure. The limit of cerium content was quantitively determined to be around 0.08 and up to 0.10. Furthermore, the powders were pelletized in a 13 mm wide pellets and thermally treated at 950 °C. The thermal treatment affected even more the phases segregation process, as CeO₂ was identified in the sample with lowest degree of cerium insertion – 0.03. Also, a difference in color and size of pelletized samples was noticed after the 950 °C thermal treatment. The Rietveld refinement, crystal structure confirmation, morphology magnetic and electrical properties of samples have been deeply studied. The cation distribution carried out from Rietveld refinement confirms the occupancy of (Fe³⁺) on tetrahedral sites and [Ni²⁺], [Cu²⁺], [Fe³⁺] and [Ce²⁺] on octahedral sites in the crystal lattice. Preliminary information regarding the cation distribution in spinel structures were suggested by FTIR spectral results, precisely in the 650-520 cm^?1 region, as a consequence of peak shape and lack of shiftiness of M^Td – O bond. Spherical-shaped quaternary nano-ferrites of 17–28 nm were determined from FE-SEM analysis and the samples composition was confirmed by EDX analysis. Hysteresis loops shows modifications in coercivity, magnetization and magnetic remanence with Ni²⁺ and Cu²⁺ ions doping in Ni_1-xCu_xFe_2-yCe_yO₄ complex systems with typical ferrimagnetic behavior. Dielectric measurements were employed in order to determine the electrical permittivity, dielectric losses and conductivity values in a 10 Hz – 1 MHz frequency range.     

Influence of Cr and Fe doping on the structure,magnetic and optical properties of nano CuCo2O4

Nano CuCo_2-xM_xO₄ (x = 0, 0.1, 0.2, M = Cr or Fe) samples were synthesized by hydrothermal method. Synchrotron x-ray diffraction data obtained for the samples were subjected to phase analysis and manifested a single-phase cubic spinel structure for Cr-doped samples, while for Fe-doped samples two phases were identified. Cation distribution and cell parameter (a) were obtained from Rietveld X-ray diffraction analysis. FTIR analysis affirmed the formation of the cubic spinel and the cation distribution obtained. The nano nature of the samples and the particle morphology were examined by high-resolution transmission electron microscope (HRTEM) with selected area electron diffraction (SAED). UV-diffuse reflectance revealed that all samples have two optical energy gaps. For all Fe doped samples, the optical band gaps decreased, while for Cr-content x = 0.1 the bandgaps increased then reduced for x = 0.2. Doped samples exhibited a blue or red shift depending on the kind and amount of the dopant ions. The PL intensity and the emitted colors depended on the kind and amount of the dopant ions. Magnetic measurements disclosed the paramagnetic nature of CuCo₂O₄, while a weak ferromagnetic is revealed for CuCo_2-xCr_xO₄ and a ferromagnetic nature for CuCo_2-xFe_xO₄. Lowering the bandgap upon doping could make better mobility of lattice oxygen and enhancing the catalyst reducibility. Thus, the Cr and Fe-doped samples are expected to have better catalytic activity than the pristine one.     

Structural and dielectric properties,and nonlinear electrical response of the CaCu3-xZnxTi4O12 ceramics: Experimental and computational studies

CaCu_3-xZn_xTi₄O₁₂ ceramics (x = 0, 0.05, 0.10) were successfully prepared by a conventional solid-state reaction method. Their structural and dielectric properties, and nonlinear electrical response were systematically inspected. The X-ray diffraction results indicated that single-phase CaCu₃Ti₄O₁₂ (JCPDS no. 75–2188) was obtained in all sintered ceramics. Changes in the lattice parameter are well-matched with the computational result, indicating an occupation of Zn²⁺ doping ions at Cu²⁺ sites. The overall tendency shows that the average grain size decreases when x increases. Due to a decrease in overall grain size, the dielectric permittivity of CaCu_3-xZn_xTi₄O₁₂ decreases expressively. Despite a decrease in the dielectric permittivity, it remains at a high level in the doped ceramics (~3,406–11,441). Besides retention in high dielectric permittivity, the dielectric loss tangent of x = 0.05 and 0.10 (~0.074–0.076) is lower than that of x = 0 (~0.227). A reduction in the dielectric loss tangent in the CaCu_3-xZn_xTi₄O₁₂ ceramics is closely associated with the enhanced grain boundary response. Increases in grain boundary resistance, breakdown electric field, and conduction activation energy of grain boundary as a result of Zn²⁺ substitution are shown to play a crucial role in improved grain boundary response. Furthermore, the XPS analysis shows the existence of Cu⁺/Cu²⁺ and Ti³⁺/Ti⁴⁺, indicating charge compensation due to the loss of oxygen lattice. Based on all results of this work, enhanced dielectric properties of the Zn-doped CCTO can be explained using the internal barrier layer capacitor model.     

Multiple magnetic phase transitions in NixMn1-xCo2O4

We prepared pure-phase Ni_xMn_1-xCo₂O₄ (x = 0, 0.25, 0.5, 0.75 and 1) nanoparticles using a low-temperature solid-state reaction method. Magnetization measurement results showed that with Ni doping, the Curie temperature and coercivity of Ni_xMn_1-xCo₂O₄ increased. Multiple magnetic phases that transition from paramagnetic to ferrimagnetic to ferrimagnetic and antiferromagnetic were observed to coexist in the Ni_0.5Mn_0.5Co₂O₄ sample. At low temperatures, the ferromagnetic and antiferromagnetic phases coexist in Ni_xMn_1-xCo₂O₄ (x = 0 and 0.25), and as the concentration of Ni increases, Ni_xMn_1-xCo₂O₄ (x = 0.75 and 1) show a spin glass state. The structure of Ni_xMn_1-xCo₂O₄ (x < 0.5) is mainly affected by cation defects, and by cation substitution when x is greater than 0.5. The results of first-principles calculations show that covalent bonds exist in Ni_xMn_1-xCo₂O₄ and that the strength of the Ni-O bond is greater than that of the Mn-O bond.     

Two phase Mg0.7Cd0.3Fe2O4–BaTiO3 composite ceramics with excellent magneto-dielectric properties for antennas in GHz band

Two phase-based composites comprising barium titanate (BaTiO₃) and spinel magnesium ferrite (1-x)Mg_0.7Cd_0.3Fe₂O₄ +xBaTiO₃ (x = 0.00, 0.03, 0.06, 0.09, and 0.12) were investigated. The phase structure revealed the coexistence of the perovskite BaTiO₃ and spinel MgFe₂O₄ phases. The microstructural analysis indicated that the average crystallite size initially increased and then decreased, as the increase in x weakened magnetisation, decreased saturation magnetisation (from 47.5 to 35.9 emu/g) and coercivity (150–0 Oe) were obtained, resulting in reduced permeability at low frequency. The permittivity gradually increased owing to tuning by barium titanate, which has strong dielectric properties, promising a relatively large miniaturisation factor. Further, low magnetic loss (tan δ_μ ∼10⁻²) and dielectric loss (tan δ_ε ∼ 10⁻² to 10⁻³) guarantee high quality factor. The low losses and enhanced dielectric properties of the as-synthesised composites could be conducive to improving the behaviour of such magneto-dielectric composite systems in microwave applications.     

Impact of Zn doping on the dielectric and magnetic properties of CoFe2O4 nanoparticles

Owing to its unique magnetic, dielectric, electrical and catalytic properties, ferrite nanostructure materials gain vital importance in high frequency, memory, imaging, sensor, energy and biomedical applications. Doping is one of the strategies to manipulate the spinel ferrite structure, which could alter the physico-chemical properties. In the present work, Co_1-xZn_xFe₂O₄ ($x$ = 0, 0.1, 0.2, 0.3, and 0.4 wt%) nanoparticles were prepared by sol-gel auto-combustion method and its structural, morphological, vibrational, optical, electrical and magnetic properties were studied. The structural analysis affirms the single-phase cubic spinel structure of CoFe₂O₄. The crystallite size, lattice constant, unit cell, X-ray density, dislocation density and hopping length were significantly varied with Zn doping. The Fe–O stretching vibration was estimated by FTIR and Raman spectra. TEM micrographs show the agglomerated particles and it size varies between 10 and 56 nm. The Hall effect measurement shows the switching of charge carriers from n to p type. The dielectric constant (ε′) varies from 0.2 × 10³ to 1.2 × 10³ for different Zn doping. The VSM analysis shows relatively high saturation magnetization of 57 and 69 emu/g for ZC 0.1 and ZC 0.2 samples, respectively than that of undoped sample. All the prepared samples exhibit soft magnetic behaviour. Hence, it can be realized that the lower concentration of Zn ion doping significantly alters the magnetic properties of CoFe₂O₄ through variation in the cationic distribution and exchange interaction between the Co and Fe sites of the inverse spinel structure of CoFe₂O_4.     

Synthesis of Ni doped barium hexaferrite by microemulsion route to enhance the visible light-driven photocatalytic degradation of crystal violet dye

The pristine and Ni doped BaNi_xFe_12-xO₁₉ (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) NPs have been fabricated via facile microemulsion approach and the impact of dopants was explored based dielectric, optical, structural and the photocatalytic properties of BaNi_xFe_12-xO₁₉ nanoparticles. X-ray diffraction and Raman study confirmed the formation of regular hexagonal geometry with space group P6₃/mmc with crystallite size in 32–50 nm range. Functional groups were identified using FTIR analysis. The remanence (Pr), saturation polarization (Ps) and coercivity (Hc) was explored by P-E loop analysis and the value of Pr and Ps was enhanced with the concentration of dopant. According to PL spectra, highly doped materials had a higher charge separation (e^?- h⁺) and low recombination rate, which resulted in higher photocatalytic degradation activity of fabricated nanomaterials. The optical band gap was found to be 1.78 eV versus undoped (2.60 eV for pristine BaFe₁₂O₁₉). Due to polarizations, the dielectric loss, dielectric constant and tangent loss values were declined, while AC conductivity was enhanced. Photocatalytic performance of doped and undoped samples under visible right irradiation was studied for crystal violet dye. For 100 min exposure to visible light, the highly doped catalyst exhibits 97% degradation versus 60% in case of pristine this is attributed to efficient electron-hole pair separation. Furthermore, quenching effect of different scavengers indicated that hydroxyl radical had a main role, and e^? or h⁺ played a minimal role in CV dye degradation. The enhanced properties due to doping make BaNi_xFe_12-xO₁₉ a potential candidate for photocatalytic applications under visible light irradiation.     

Rapid solution combustion synthesis of novel superfine CaLaAl1-xCrxO4 red ceramic pigments

Superfine CaLaAl_1-xCr_xO₄ (x = 0.02, 0.05, 0.08, 0.10) red ceramic pigments have been prepared by solution combustion reaction and subsequent high-temperature calcination. All of the pigments were characterized by X-ray diffraction (XRD), Field scanning electron microscopy (FESEM), UV–Vis spectrophotometry, Laser particle size analyzer and CIE L*a*b* spectrophotometry. Moreover, the effects of the doping amount of Cr³⁺ ion, calcination temperature, salt assistance and synthetic routes on chromatic performance and particle size distributions of the pigments were also investigated. The results showed that CaLaAl_1-xCr_xO₄ pigment particles prepared via solution combustion reaction and subsequent calcination were well-dispersed and uniform in size. With the increase of doping amount of Cr³⁺ ion, the brightness value L* of CaLaAl_1-xCr_xO₄ pigments decreased obviously and the redness value a* increased gradually. When x = 0.08, it showed the best chromatic performance (L* = 39.37, a* = 21.33, b* = 13.99). In addition, the synthetic pigments possess excellent high temperature stability which is conducive to the application of ceramic pigments. Most importantly, the synthetic method of CaLaAl_1-xCr_xO₄ red ceramic pigments is not only cheap in raw materials, but also easy to industrialize.