Effect of calcination temperature on structural,magnetic and optical properties of multiferroic YFeO3 nanopowders synthesized by a low temperature solid-state reaction

Nanosize multiferroic YFeO₃ powders have been synthesized via the low temperature solid-state reaction. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy all indicated that the phase-pure orthorhombic YFeO₃ powders were obtained at 800 °C with a size below 150 nm. X-ray photoelectron spectroscopy (XPS) showed the Fe³⁺ ions to be predominant. Magnetic hysteresis loops exhibited some ferromagnetic behaviour of the YFeO₃ nanopowders at ambient temperature. The maximum and remnant magnetizations of the powders were about 2.49 and 0.88 emu/g, respectively. Moreover, optical measurements demonstrated that the optical band gap of the nanopowders was around 2.4 eV, proving that they can strongly absorb visible light. So an easy and efficient way to synthesize YFeO₃ nanopowders with promising application in the magnetic and optical fields has been successfully developed.     

Effect of electric poling on structural,magnetic and ferroelectric properties of 0.8PbFe0.5Nb0.5O3-0.2BiFeO3 multiferroic solid solution

The effect of electric poling on structure, magnetic and ferroelectric properties of 0.8PbFe_0.5Nb_0.5O₃-0.2BiFeO₃ (0.8PFN-0.2BFO) multiferroic was studied through XRD, Raman, magnetic and ferroelectric measurements. Single step solid state reaction method was adopted to synthesize single phase 0.8PFN-0.2BFO multiferroic at lower calcination and sintering temperature. Room temperature (RT) XRD pattern before and after poling confirmed the monoclinic structure with Cm space group. Rietveld refined XRD for poled and unpoled sample shows the influence of electric poling on Fe-O1, Fe-O2, Nb-O and Bi-O modes. There is a small variation in the lattice parameters after electric poling. The structural properties were also studied in detail for the poled and unpoled 0.8PFN-0.2BFO using Raman spectroscopy. Raman measurements were carried out over a wide range of temperature (250–550 K) for both poled and unpoled samples. At RT unpoled 0.8PFN-0.2BFO multiferroic exhibit 8 active modes at 211, 263, 440, 484, 571, 706, 785 and 1120 cm^-1 in the frequency range 100–1200 cm^-1. The Raman peaks exhibits significant changes in intensity as well as shape of the spectra at the characteristic temperature T_C (470 K) and T_N (310 K). Poled Raman spectra show major changes in the Fe/Nb-O modes intensities around T_N and are due to dynamic nature of spin phonon coupling. Changes observed in the temperature dependent magnetic measurements i.e. ZFC/FC and M − H loop evidence the existence of converse magneto-electric coupling (CME) and this is due to the poling effects on Fe-O, Nb-O active modes. Due to rotation of the oxygen octahedral the electric field induced strain will originate in the system. P-E loops after poling show an increase in remnant polarisation and coercive field due to an improvement in domain ordering. The potential tunability of magnetisation with electric poling is an ideal tool for realisation of application in practical devices.     

Structural,magnetic and optical properties of Ce substituted BiFeO3 nanoparticles

Ce substituted Bi_1−xCe_xFeO₃ (x=0.03, 0.05, 0.07 and 0.10) nanoparticles were prepared by a tartaric acid based sol–gel route. X-ray diffraction patterns and Raman spectra revealed a structural phase transition from rhombohedral to orthorhombic phase for x=0.10 sample. Room temperature magnetic measurements showed weak ferromagnetic ordering and enhancement in magnetization with increasing Ce concentration. The improved magnetic properties due to the breaking of spin cycloid with Ce substitution have been observed from electron spin resonance (ESR) study. The measured g-values for all samples are greater than 2 and the ESR lines shift towards higher g-value with increasing Ce concentration, indicating ferromagnetic nature of these samples. UV–visible diffuse reflectance spectra showed a sharp absorption in the visible region with two d–d and three charge transfer (C-T) transitions. Prominent red shift in the band gap indicates a significant change in the band structure of the doped nanoparticles.     

Effect of Dy-substitution on structural,electrical and magnetic properties of multiferroic BiFeO3 ceramics

The polycrystalline samples of dysprosium (Dy)-modified bismuth ferrite (i.e., Bi_1−xDy_xFeO₃; x=0–0.2 with the interval of 0.05) (BDFO) were synthesized using a high-temperature solid-state reaction method. Preliminary X-ray structural analysis showed that the reported crystal structure of BiFeO₃ (rhombohedral) is invariant even with Dy-substitution at the Bi-site upto x=0.2. The scanning electron micrograph of the compounds showed (i) the uniform distribution of grains on the sample surface with high density and (ii) reduction of grain size on increasing Dy content in BiFeO₃ (BFO). Studies of impedance, electrical modulus and electric conductivity of the materials in wide frequency (10–1000 kHz) and temperature (30–500 °C) ranges using a complex impedance spectroscopy technique have provided new and interesting information on the contribution of grains, grain boundary and interface in these parameters. Detailed studies of impedance spectroscopy clearly exhibit the dielectric relaxation of non-Debye type. The ac conductivity of the Dy-substituted BFO obeyed Jonscher's universal power law. An increase in Dy-content in BDFO results in the increase of spontaneous magnetization of BFO due to the collapse of spin cycloid structure.     

Influence of Eu and Sr co-substitution on multiferroic properties of BiFeO3

Pure BiFeO₃ (BFO), and Eu-Sr co-substituted BFO samples were prepared by a sol–gel method. The effects of Eu and Sr codoped on the structural, morphological, magnetic and ferroelectric properties were systematically investigated. The X-ray diffraction and Fourier transform infrared spectroscopy reveal that substitution of Eu and Sr at the Bi site results in structural change and single phase formation. The maximum remnant magnetization of 0.287 emu/g and coercive field of 10.305 kOe are observed in the Bi_0.85Eu_0.05Sr_0.10FeO₃ sample. The suppression of spin cycloid caused from the structural distortion can play an important role in the improvement of magnetic properties. The Eu and Sr co-doped samples also exhibit good ferroelectric properties, which may be attributed to suppressing the formation of oxygen vacancies by Eu substitution.     

Effect of (Zn,Mn) co-doping on the structure and ferroelectric properties of BiFeO3 thin films

BiFe_1-2xZn_xMn_xO₃ (BFZMO, with x = 0–0.05) thin films were synthesized via sol–gel method. Effects of (Zn, Mn) co-doping on the structure, ferroelectric, dielectric, and optical properties of BiFeO₃ (BFO) films were investigated. BFZMO thin films exhibit rhombohedral structure. Scanning electron microscopy (SEM) images indicate that co-doping leads to a decrease in grain size and number of defects. Leakage current density (4.60 × 10^?6 A/cm²) of BFZMO film with x = 0.02 was found to be two orders of magnitude lower than that of pristine BFO film. Owing to decreased leakage current density, saturated P–E curves were obtained. Maximum double remnant polarization of 413.2 μC/cm² was observed for BFZMO thin film with x = 0.02, while that for the BFO film was found to be 199.68 μC/cm². The reason for improved ferroelectric properties is partial substitution of Fe ions with Zn and Mn ions, which resulted in a reduction in the effect of oxygen vacancy defects. In addition, co-doping was found to decrease optical bandgap of BFO film, opening several possible routes for novel applications of these (Zn, Mn) co-doped BFO thin films.     

Effect of solvent on structure and optical properties of PZT nanoparticles prepared by sol-gel method, in infrared region

Single-phase perovskite Pb(Zr_0.52,Ti_0.48) nanoparticles, PZT-NPs were prepared by the sol-gel method with two different solvents, 2-methoxyethanol, EGME, and poly ethylene glycol, PEG. X-ray diffraction (XRD) was used to study of the structure of the PZT-NPs. Fourier transform infrared spectroscopy (FTIR) was used to measure the infrared reflectivity spectrum in the range of 4000-280 cm⁻¹. Infrared active vibration modes of BO₆ octahedral (ν₁ and ν₂) were observed for PZT-NPs below 600 cm⁻¹. The third vibration mode of Pb against the TiO₃ group, ν₃, occurred below the experimentally accessible range. The Kramers-Kronig method (K-K) and classical dispersion theory were applied to analyze the data and calculation of the optical constants such as reflective index (N(ω))and permittivity (?(ω)). The results showed that the structure and optical properties of PZT-NPs were changed by different type of solvent.     

Structural,magnetic and electrical properties of Y1-xScxFeO3 (x= 0, 0.5 & 1) nanoparticles synthesized by the sol-gel method

Nanoparticles exhibiting crystalline and single-phase characteristics with Y_1-xSc_xFeO₃ (x = 0, 0.5 & 1) nanoparticles synthesized by sol-gel method. The sizes of nanocrystals determined by X-Ray Diffractometry (XRD) were obtained between 30 and 39 nm. The shape of nanoparticles and the surface morphology of the samples were carried out using Field Emission Scanning Electron Microscopy (FE-SEM) and energy dispersive spectroscopy (EDS). The magnetic properties of Y_1-xSc_xFeO₃ samples were investigated by Vibrating Sample Magnetometry (VSM) and Field-Cooled (FC) and Zero-Field-Cooled (ZFC) measurements. The results showed antiferromagnetic and paramagnetic behaviors for these prepared perovskites. The electrical properties of the samples were investigated by measuring the polarization-electric loops, dielectric constant changes and dielectric loss through frequency and temperature. These measurements showed the T_N values of the samples to be 628 and 578 K for YFeO₃ and ScFeO₃ nanoparticles, respectively. In addition, diffuse reflectance spectroscopy analysis was used to calculate the band gap energy of the samples based on the Kubelka-Munk function. The achieved values showed the band gap energy of 2.97 and 3.07 eV for YFeO₃ and ScFeO₃.     

Effect of dysprosium substitution on crystal structure and physical properties of multiferroic BiFeO3 ceramics

The polycrystalline samples of multiferroic Bi_1−xDy_xFeO₃ (x = 0, 0.1, and 0.2) were prepared by a modified solid state reaction method and characterized by X-ray diffraction, scanning electron microscopy, differential thermal analysis, dielectric and magnetic measurements. It was shown that the introduction of the Dy³⁺ ions stabilizes the perovskite structure and improves phase purity. The coexistence of the rhombohedral and orthorhombic phases was found to exist within the investigated concentration range 0.1 ≤ x ≤ 0.2. The changes and anomalies observed in dielectric response over a wide frequency range were correlated with the structural evolution and the development in microstructure. The SQUID measurements of the field-dependent magnetization at different temperatures demonstrated Dy doping to be a very effective method for inducing a weakly ferromagnetic state in the ferroelectric R3c phase of BiFeO₃ in the absence of an external magnetic field.     

Structural,dielectric, vibrational and magnetic properties of Sm doped BiFeO3 multiferroic ceramics prepared by a rapid liquid phase sintering method

Rare earth Sm substituted Bi_1−xSm_xFeO₃ with x=0, 0.025, 0.05, 0.075 and 0.10 polycrystalline ceramics were synthesized by a rapid liquid phase sintering method. The effect of varying composition of Sm substitution on the structural, dielectric, vibrational, optical and magnetic properties of doped BiFeO₃ (BFO) ceramics have been investigated. X-ray diffraction patterns of the synthesized rare earth substituted multiferroic ceramics showed the pure phase formation with distorted rhombohedral structure with space group R3c. Good agreement between the observed and calculated diffraction patterns of Sm doped BFO ceramics in Rietveld refinement analysis of the X-ray diffraction patterns and Raman spectroscopy also confirmed the distorted rhombohedral perovskite structure with R3c symmetry. Dielectric measurements showed improved dielectric properties and magnetoelectric coupling around Néel temperature in all the doped samples. FTIR analysis establishes O–Fe–O and Fe–O stretching vibrations in BiFeO₃ and Sm-doped BiFeO₃. Photoluminescence (PL) spectra showed visible range emissions in modified BiFeO₃ ceramics. The magnetic hysteresis measurements at room temperature and 5 K showed the increase in the magnetization with the increase in doping concentration of Sm which is due to the structural distortion and partial destruction of spin cycloid caused by Sm doping in BFO ceramics.     

Influence of Y doping on structural,vibrational, optical and magnetic properties of BiFeO3 ceramics prepared by Mechanical Activation

Y substituted BiFeO₃ (Bi_1−xY_xFeO_3; x=0.0–0.1) polycrystalline ceramics were synthesized by Mechanical Activation. The effect of varying composition of Y substitution on the structural, vibrational, optical and magnetic properties of doped BiFeO₃ (BFO) ceramics has been investigated. Rietveld refinement of X-ray diffraction patterns reveals that all samples crystallize in distorted rhombohedral structure with R3c symmetry and no structural transition has been observed. Raman spectroscopy also confirmed the distorted perovskite structure with R3c space group. Optical studies in the spectral range 1–4.5 eV were dominated by two d-d and three charge transfer (C-T) transitions. The optical band gap decreases from 2.11 to 2.01 eV with increasing Y substitution. Room temperature magnetic measurements showed weak ferromagnetic ordering and enhancement in magnetization with increasing Y concentration. Mechanical activation leads to significantly altered magnetic properties, particularly in higher Y-doping samples. The Mössbauer spectra demonstrate the suppression of spiral spin modulation of the magnetic moments resulting in enhanced ferromagnetism with increasing doping concentration. Significant increase in Néel temperature T_N in the substituted compounds was discussed on the basis of structural distortions.     

Structural,electrical, magnetic and magnetoelectric properties of Co-doped BaTiO3 multiferroic ceramics

In this work, BaTi_1-xCo_xO₃ (BTCO) ceramics with x?=?0, 2.5, 5, 7.5 and 10?mol% have been synthesized and their structural, electrical, magnetic and magnetoelectric have been investigated. Rietveld refinement of XRD data reveals that pure BTO has pure tetragonal phase. On the other hand, between 2.5?≤?x?≤?7.5, BTCO shows both tetragonal as well as hexagonal phases. At x?=?10?mol%, BTCO shows only hexagonal phase. The grain size of the BTCO samples is found to increase with Co doping concentration. The ferroelectric polarization and relative permittivity of BTCO samples reduce with an increase in the Co concentration. A standard magnetization equation is used for fitting the magnetic hysteresis (M-H) curve, thus deconvoluting the ferromagnetic (FM) and paramagnetic (PM) components. The saturation magnetization (M_s) gradually increases from x?=?2.5 to x?=?10?mol%, the value being 0.8 memu/g and 8.92 memu/g respectively. The origin of magnetization is due to the oxygen vacancies and their associated exchange interaction. The magnetodielectric coefficient (MD) shows a reducing trend from 1.80 to 0.18 for x?=?2.5 to x?=?10?mol% respectively. The magnetoelectric coefficient $({\alpha }_{\mathit{ME}})$ for x?=?2.5?mol% is 3.399?mV/cm. Oe, while for x?=?10?mol% it is 0.896?mV/cm. Oe.     

Effect of annealing temperature on structural and magnetic properties of Co2TiO4 ceramics prepared by sol-gel method

In this paper, polycrystalline Co₂TiO₄ ceramics have been synthesized using a sol-gel process followed by annealing at different temperatures. The lattice size and the average grain size of the samples increases with rise in annealing temperature. The temperature-dependent inverse paramagnetic susceptibilities recorded under zero-field-cooling condition have been fitted according to the Néel's expression for ferrimagnets. Subsequently, the molecular field constants and the corresponding exchange constants have been calculated. The fitting result shows that the magnetic interaction in the system becomes weaker as the annealing temperature rises. In addition, negative magnetization is observed during field-cooling process. The higher annealing temperature is beneficial to the growth of tetrahedral sublattice, leading to a decrease on compensation temperature. Furthermore, magnetization hysteresis loops for all the samples demonstrate the crucial role of grain size on the magnetic properties.     

Investigation of structural,optical, dielectric and magnetic studies of Mn substituted BiFeO3 multiferroics

A series of Mn doped BiFeO₃ with composition BiMn_xFe_1−xO₃ (x = 0.0, 0.025, 0.05, 0.075, 0.1) was synthesized via a citrate precursor method. Structural, morphological, optical, electrical and magnetic properties were investigated by using various measurement techniques. XRD patterns confirmed that the materials possess distorted rhombohedral structure with space group R3c. Average crystallite size was found to be in the range 18–36 nm. A decrease in the value of lattice parameters has been observed due to contraction of unit cell volume with Mn doping. Higher tensile strain for the prepared nanoparticles was observed in Hall-Williamson Plot. Field Emission Scanning Microscopy (FESEM) showed the spherical, uniform, dense nanoparticles in the range 80–200 nm. Reduction in grain size was observed which may be due to suppression of grain growth with Mn doping. FTIR studies reported two strong peaks at 552 cm⁻¹ and 449 cm^-1 which confirmed the pervoskite structure. Dielectric properties were studied by measuring the dielectric constant and loss in the frequency range 1 kHz to 1 MHz. Magnetic hysteresis loop showed the retentivity (M_r) increasing from 0.0514 emu/g of BFO to 0.0931 emu/g of 10% Mn doping. Coercivity was found to increase upto 0.0582 T for 5% Mn doping and then reduced to 0.0344 T for 7.5% Mn doping. Saturation magnetization was observed to increase from 0.6791 emu/g for BFO to 0.8025 emu/g for 7.5% and then reduced to 0.6725 emu/g for 10% Mn doping in BFO. Improvement in dielectric and magnetic properties makes this material as a promising candidate for multifunctional device applications.     

Structural,vibrational, optical,magnetic and dielectric properties of Bi1−xBaxFeO3 nanoparticles

Bi_1−xBa_xFeO₃ (x=0.05, 0.10 and 0.15) nanoparticles were synthesized by the sol–gel method. X-ray diffraction and Raman spectroscopy results showed the presence of distorted rhombohedral structure of Bi_1−xBa_xFeO₃ nanoparticles. Rietveld refinement and Williamson–Hall plot of the x-ray diffraction patterns showed the increase in lattice parameters, unit cell volume and the particle size. Infrared spectroscopy and Raman analysis revealed the shifting of phonon modes towards the higher wavenumber side with increasing Ba concentration. These samples exhibited the optical band gap in the visible region (2.47–2.02 eV) indicating their ability to absorb visible light. Magnetic measurement showed room temperature ferromagnetic behavior, which may be attributed to the antiferromagnetic core and the ferromagnetic surface of the nanoparticles, together with the structural distortion caused by Ba substitution. The magnetoelectric coupling was evidenced by the observation of the dielectric anomaly in the dielectric constant and the dielectric loss near antiferromagnetic Neel temperature in all the samples.     

Enhanced ferroelectric properties of (Zn,Ti) equivalent co-doped BiFeO3 films prepared via the sol-gel method

High-quality BiFe_1-2xZn_xTi_xO₃ (BFZTO with x = 0, 0.01, 0.02, 0.03, 0.04, and 0.05) films were successfully prepared on fluorine-doped tin oxide (FTO)/glass substrates via the sol-gel method. The influence of (Zn, Ti) equivalent co-doping on the structure, surface morphology, and ferroelectric properties of BFZTO films was investigated systematically. X-ray diffraction (XRD) and Raman spectra analysis indicate that co-doping results in structural transformations. Scanning electron microscope (SEM) images show that BFZTO films with x = 0.02 exhibit uniform fine grains and higher density, which is instrumental for the development of ferroelectric properties. X-ray photoelectron spectroscopy (XPS) analysis reveals that BiFe_0.96Zn_0.02Ti_0.02O₃ film can inhibit the conversion of Fe³⁺ into Fe²⁺, thereby greatly reducing oxygen vacancy concentration. Therefore, under the electric field strength of 150 kV/cm, BiFe_0.96Zn_0.02Ti_0.02O₃ film was found to have the lowest leakage current density, J = 1.13 × 10^?6 A/cm², which is five orders of magnitude lower than that of pure BiFeO₃ (BFO) film. Furthermore, this film exhibits the largest remnant polarization at room temperature, P_r = 131.9 μC/cm², which is more than twice as large as that of pure BFO (P_r = 52.6 μC/cm²). Additionally, by comparing P-E hysteresis loops of different regions on the surface of BiFe_0.96Zn_0.02Ti_0.02O₃ film, it was found that the film has high uniformity and stable overall performance. Dielectric and magnetic properties were also enhanced via (Zn, Ti) co-doping.     

Effects of Nd3+ and high-valence Nb5+ co-doping on the structural,dielectric and magnetic properties of BiFeO3 multiferroics

Bi_0.90Nd_0.10Fe_1?xNb_xO₃ (0 ≤ x ≤ 0.05) multiferroics have been studied to reveal the effect of Nb doping on the physical properties of the neodymium modified BiFeO₃. These samples have been synthesized via conventional solid state reaction method. The structural characterization was performed by XRD technique and Rietveld refinement. Rietveld refinement results confirmed that all samples crystallized in rhombohedral symmetry. In the vicinity of anti-ferromagnetic Neel-temperature (T_N), an anomaly was observed in dielectric constant (?′) and loss tangent (tan δ) which indicates the existence of magnetoelectric coupling. It is observed that with Nb doping dielectric constant was reduced and Neel temperature shifted towards higher temperature. The impedance (Nyquist plots) and modulus spectroscopy revealed that materials possess non-Debye type of relaxation. The doping of donor ion is able to suppress the existence of oxygen vacancies which results in increase in resistivity. The B-site doping by higher valence ion suppresses the existing modulated spin structure by structural distortion, results in released net magnetization. The room temperature remanent magnetization increased with Nb doping and all powder samples possess weak ferromagnetism. The possible reasons for the notable magnetic and dielectric performance of prepared samples were discussed.     

Effect of Fe doping on the magnetic properties of PbPdO2 nanograin film fabricated by sol-gel method

The single-phase Fe-doped PbPdO₂ film was prepared using a sol-gel spin-coating method. The film had a nanograin structure consisting of compacted particles with an average crystallization size of about 35.2 nm. Large amount of Pb vacancies were found in the film. The valences of the Pb, Pd and Fe ions of the film were confirmed to be near 2+, 2+ and 3+, respectively. The additional electron provided by Fe³⁺ and the high ionization energy of Fe³⁺ ensure the stability of the valence of doped Fe ions. The measurement of hysteresis loops and the theoretical fitting of the zero-field-cooled and field-cooled magnetization versus temperature curve indicated that the ferromagnetism and the paramagnetism coexist in the Fe-doped PbPdO₂. And the ferromagnetism persisted up to 380 K. A bound magnetic polaron model based on the Pb vacancies, the carriers and the doped Fe ions was utilized to account for the origin of the film's ferromagnetism. The isolated Fe ions or magnetic polarons were believed to be responsible for the paramagnetism in the film.     

Crystal structure transformation and improved dielectric and magnetic properties of La-substituted BiFeO3 multiferroics

Samples of Bi_1−xLa_xFeO₃ with x = 0.1, 0.3, 0.5, and 0.7 have been synthesized by two stage solid state reaction method. Structural characterization was performed using powder x-ray diffraction at room temperature. The crystal structure of perovskite phases are further characterized via Rietveld analysis which revealed a structural transition from R3c symmetry of the parent phase of BiFeO₃ to orthorhombic Pnma symmetry of LaFeO₃. However the intermediate samples with x = 0.3 and 0.5 are bi – phasic (i.e. a combination of rhombohedral R3c and orthorhombic Pbam phases co-exist). Rietveld Refinement presents a good agreement between measured and simulated patterns. The transition from a rhombohedral to orthorhombic unit cell is suggested to be driven by the dilution of the stereochemistry of the lone pair of Bi³⁺ at A- site. M-H hysteresis loops are recorded at room temperature up to a field of 15 kOe. The G-type antiferromagnetic spin structure and the magnetic moment are very sensitive to increasing La concentration at A-site. La substitution transformed antiferromagnetic BiFeO₃ into ferromagnetic which is closely related to the structural phase transition and modification of antiparallel spin structure. Dielectric constant (ε′) and dissipation factor (tan δ) measured in frequency range 1 kHz to 5 MHz showed dispersion behaviour at low frequencies.     

Effect of Ni2+ substitution on structural,magnetic, dielectric and optical properties of mixed spinel CoFe2O4 nanoparticles

Nanoparticles of Co_1−xNi_xFe₂O₄ with x=0.0, 0.10, 0.20, 0.30, 0.40 and 0.50 were synthesized by co-precipitation method. The structural analysis reveals the formation of single phase cubic spinel structure with a narrow size distribution between 13–17 nm. Transmission electron microscope images are in agreement with size of nanoparticles calculated from XRD. The field emission scanning electron microscope images confirmed the presence of nano-sized grains with porous morphology. The X-ray photoelectron spectroscopy analysis confirmed the presence of Fe²⁺ ions with Fe³⁺. Room temperature magnetic measurements showed the strong influence of Ni²⁺ doping on saturation magnetization and coercivity. The saturation magnetization decreases from 91 emu/gm to 44 emu/gm for x=0.0–0.50 samples. Lower magnetic moment of Ni²⁺ (2 µ_B) ions in comparison to that of Co²⁺ (3 µ_B) ions is responsible for this reduction. Similarly, overall coercivity decreased from 1010 Oe to 832 Oe for x=0.0–0.50 samples and depends on crystallite size. Cation distribution has been proposed from XRD analysis and magnetization data. Electron spin resonance spectra suggested the dominancy of superexchange interactions in Co_1−xNi_xFe₂O₄ samples. The optical analysis indicates that Co_1−xNi_xFe₂O₄ is an indirect band gap material and band gap increases with increasing Ni²⁺ concentration. Dispersion behavior with increasing frequency is observed for both dielectric constant and loss tangent. The conduction process predominantly takes place through grain boundary volume. Grain boundary resistance increases with Ni²⁺ ion concentration.