Effect of Zn and Mg doping on structural,dielectric and magnetic properties of tetragonal CuFe2O4

The Cu_1?xA_xFe₂O₄ (A = Zn, Mg; x = 0.0, 0.5) ferrites were successfully synthesized by chemical co-precipitation method. X-ray diffraction and Raman spectroscopy reveals that all the ferrite samples are in single-phase with tetragonal structure for CFO and cubic spinel structure for CZFO and CMFO samples. SEM micrograph shows the variation of grain size with Zn and Mg doping in parent CFO sample. Frequency dependent dielectric response confirms the dielectric polarization and electrical conduction mechanism in the present series with a maximum value of dielectric constant and loss tangent for CZFO sample. The anomaly ～493 K in temperature dependent dielectric constant and dielectric loss is assigned to tetragonal to cubic phase transition in CFO sample. The magnetic measurement explored that the saturation value (M_s) is maximum for CZFO as compared to CFO and CMFO ferrites samples.     

Al3+掺杂的CuZn铁氧体的结构，电学和磁学特性

采用固相合成反应技术制备纳米Cu_0.5Zn_0.5Fe_2-xAl_xO₂(x=0.0,0.1,0.2,0.3,0.4和0.5)铁氧体材料,研究Al³⁺含量对结构,电学和磁学性质的影响. 采用X射线衍射研究单相立方尖晶石结构. 利用Scherrer公式估算晶粒尺寸. 测定了温度依赖的直流电阻率.结果表明随Al³⁺含量的增加,晶格常数减小,孔隙度增加,饱和磁化强度值降低,Al³⁺对铁氧体的介电常数、介电损耗角的正切值和介质损耗因子等介电性能有明显影响,这可能与空间电荷极化有关.     

Magnetic and dielectric properties of nanophase manganese-substituted lithium ferrite

Nanocrystalline manganese-substituted lithium ferrites viz. Li_0.5Fe_2.5−xMn_xO₄ (2.5≤x≥0) were prepared by sol-gel autocombustion method. X-ray diffraction analysis confirmed that as the concentration of manganese increases the cubic phase changes to the tetragonal phase. The variation of saturation magnetization was studied as a function of manganese content. All the compositions indicate that they are ferrimagnetic in nature. The dielectric constant, dielectric loss tangent and ac conductivity of all samples were measured at room temperature as a function of frequency. These parameters decrease with increase in frequency for all of the samples. The substitution of manganese plays an important role in changing the structural and magnetic properties of these ferrites. The compositional variation of dielectric constant and d.c. resistivity shows an inverse trend of variation with each other.     

Magnetic, dielectric and complex impedance spectroscopic studies of nanocrystalline Cr substituted Li-ferrite

Nanocrystalline Li_0.5Fe_2.5−xCr_xO₄ (2.5≤x≥0) ferrites were prepared by a sol-gel autocombustion route. X-ray diffraction was employed to confirm the cubic spinel phase formation of the ferrites. The lattice parameter decreases with increase in Cr content. The saturation magnetization, coercivity and remanance were studied as a function of Cr content. The dielectric constant and dielectric loss were measured as a function of frequency in the frequency range 20 Hz-1 MHz. Frequency dependence of dielectric constant shows dielectric dispersion due to the Maxwell-Wagner type of interfacial polarization. In order to understand the conduction mechanism, complex impedance measurements were carried out. The substitution of chromium plays an important role in changing the dielectric and magnetic properties of lithium ferrites.     

Li0.5Fe2.5−xMnxO4 ferrite sintered from microwave-induced combustion

Li_0.5Fe_2.5−xMn_xO₄ (0≦x≦1.0) powders with small and uniformly sized particles were successfully synthesized by microwave-induced combustion, using lithium nitrate, ferric nitrate, manganese nitrate and carbohydrazide as the starting materials. The process takes only a few minutes to obtain as-received Mn-substituted lithium ferrite powders. The resultant powders annealed at 650 ^°C for 2 h and were investigated by thermogravimeter/differential thermal analyzer (TG/DTA), X-ray diffractometer (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and thermomagnetic analysis (TMA). The results revealed that the Mn content were strongly influenced the magnetic properties and Curie temperature of Mn-substituted lithium ferrite powder. As for sintered Li_0.5Fe_2.5−xMn_xO₄ specimens, substituting an appropriate amount of Mn for Fe in the Li_0.5Fe_2.5−xMn_xO₄ specimens markedly improved the complex permeability and loss tangent.     

Effect of Cd on the structural, magnetic and electrical properties of nanostructured Mn-Zn ferrite

Nanoparticles of Mn_0.5Zn_0.5−xCd_xFe₂O₄ (x=0.0, 0.1, 0.2 and 0.3) have been synthesized by a chemical co-precipitation method. The lattice constant increases with increasing Cd content. X-ray calculations indicate that there is deviation in the cation distribution in the nanostructured spinel ferrite. The dielectric constant and dielectric loss decrease for the samples with Cd content up to x=0.2. However the dielectric constant rises for x=0.3. This is due to an increase in the hopping process at the octahedral (B sites). The dielectric constant increases with increase in temperature, indicating a thermally activated hopping process. The DC resistivity increases with Cd content up to x=0.2 and decreases for Cd content x=0.3. The maximum magnetization of all the samples decreases with increase in Cd content.     

Electrical and switching properties of NiAlxFe2−xO4 ferrites synthesized by chemical method

Nickel-aluminum ferrite system NiAl_xFe_2−xO₄ has been synthesized by wet chemical co-precipitation method. The samples were studied by means of X-ray diffraction, d.c. electrical resistivity, a.c. electrical resistivity, a.c. conductivity and switching properties. The XRD patterns confirm the cubic spinel structure for all the synthesized samples. The crystallite size calculated from XRD data which confirm the nano-size dimension of the prepared samples. Electrical properties such as a.c. and d.c. resistivities as function of temperature were studied for various Al substitution in nickel ferrite. The dielectric constant and dielectric loss tangent were also studied as a function of frequency. The dielectric constant follows the Maxwell-Wagner interfacial polarization. A.C. conductivity increases with increase in applied frequency. The d.c. resistivity decreases as temperature increases, which indicate that the sample have semi-conducting nature. Verwey hoping mechanism explains the observed variation in resistivity. The activation energy is derived from the temperature variation of resistivity. Electrical switching properties were studied as I-V measurements. The current controlled negative resistance type switching is observed in all the samples. The Al substitution in nickel ferrite decreases the required switching field.     

Study of dielectric and impedance properties of Mn ferrites

The paper reports on the effect of Al substitution on the structural and electrical properties of bulk ferrite series of basic composition MnFe_2−2xAl_2xO₄ (0.0≤x≤0.5) synthesized using solid state reaction method. XRD analysis confirms that all the samples exhibit single phase cubic spinel structure excluding presence of any secondary phase. The dielectric constant shows a normal behaviour with frequency, whereas the loss tangent exhibits an anomalous behaviour with frequency for all compositions. Variation of dielectric properties and ac conductivity with frequency reveals that the dispersion is due to Maxwell-Wagner type of interfacial polarization in general and hopping of charge between Fe⁺² and Fe⁺³ as well as between Mn⁺² and Mn⁺³ ions at octahedral sites. The complex impedance plane spectra shows the presence of two semicircles up to x=0.2, and only one semicircle for the higher values of x. The analysis of the data shows that the resistive and capacitive properties of the Mn ferrite are mainly due to processes associated with grain and grain boundaries.     

Electromagnetic properties of lithium zinc ferrites doped with aluminum

We present the results of the effect of Al substitution on the magnetic and electrical properties of Li_0.2Zn_0.6Fe_2.2−xAl_xO₄ ferrites (0.0≤x≤0.5) prepared by the standard ceramic technique. The characterization has been performed using XRD, SEM, magnetic and dielectric response in frequency. XRD analysis confirms that the system exhibits polycrystalline single phase cubic spinel structure only for low dopant content. Doping decreases the dielectric loss tangent and the ferrite conductivity in more than two orders of magnitude in the whole analyzed frequency range. Attenuation has a maximum intensity (86 dB) near 90 MHz for x=0.4. The wider bandwidth at 20 dB (94.6 MHz) is for x=0.3.     

Influence of Al doping on electrical properties of Ni–Cd nano ferrites

We have reported the structural and electrical properties of nano particles of Al doped Ni_0.2Cd_0.3Fe_2.5O₄ ferrite using X-ray diffraction, dielectric spectroscopy and impedance spectroscopy at room temperature. XRD analysis confirms that the system exhibits polycrystalline single phase cubic spinel structure. The average particle size estimated using Scherrer formula for Lorentzian peak (3 1 1), has been found 5(±) nm. The results obtained show that real (ε′), imaginary (ε″) part of the dielectric constant, loss tangent (tan δ), and ac conductivity (σ_ac) shows normal behaviour with frequency. The dielectric properties and ac conductivity in the samples have been explained on the basis of space charge polarization according to Maxwell–Wagner two-layer model and the Koop’s phenomenological theory. The impedance analysis shows that the value of grain boundary impedance increases with Al doping. The complex impedance spectra of nano particles of Al doped Ni–Cd ferrite have been analyzed and explained using the Cole–Cole expression.     

Effect of sintering temperature and the particle size on the structural and magnetic properties of nanocrystalline Li0.5Fe2.5O4

Sintering temperature and particle size dependent structural and magnetic properties of lithium ferrite (Li_0.5Fe_2.5O₄) were synthesized and sintered at four different temperatures ranging from 875 to 1475 K in the step of 200 K. The sample sintered at 875 K was also treated for four different sintering times ranging from 4 to 16 h. Samples sintered at 1475 K have the cubic spinel structure with a small amount of α-Fe₂O₃ (hematite) and γ-Fe₂O₃ (maghemite). The samples sintered at≤1275 K do not show hematite and maghemite phases and the crystals form the single phase spinel structure with the cation ordering on octahedral sites. Particle size of lithium ferrite is in the range of 13-45 nm, and is depend on the sintering temperature and sintering time. The saturation magnetization increased from 45 to 76 emu/g and coercivity decreases from 151 to 139 Oe with an increase in particle size. Magnetization temperature curve recorded in ZFC and FC modes in an external magnetic field of 100 Oe. Typical blocking effects are observed below about 244 K. The dielectric constant increases with an increase in sintering temperature and particle size.     

Influence of 50 MeV Lithium Ion Irradiation on Hyperfine Interactions of Cr0.5 Li0.5 Fe2O4

Spinel oxide Cr_0.5 Li_0.5 Fe₂O₄ has been irradiated at Nuclear Science Centre, New Delhi, by 50 MeV lithium ions of fluence 5*10¹³ ions/cm² and irradiation effect on hyperfine interactions has been investigated by Mossbauer spectroscopy. The Mossbauer spectrum of irradiated sample shows no paramagnetic doublet contribution and the hyperfine fields corresponding to the Fe³⁺ in the octahedral (B) and the tetrahedral (A) sites are very well separated. That is the observed superimposed A and B sites in unirradiated sample are split into separate lines after Li irradiation. Further an increase of the intensity of the lines (2)–(5) with respect to (1)–(6) signals an orientation of the hyperfine magnetic field towards a direction perpendicular to the ion path due to the irradiation induced strain by the latent tracks. The computer simulation of Mossbauer spectra indicated that the irradiated Fe³⁺-site occupancy of the A-site hyperfine field increased from 43% to 55% whereas the B-site hyperfine field decreased from 57% to 45% compared to unirradiated sample.     

Structural,dielectric and magnetic properties of cobalt based spinel ferrites

CoYb_xFe_2-xO₄ (x = 0.00, 0.025, 0.05, 0.075, 0.10) spinel ferrites were synthesized by co-precipitation technique. Structural, dielectric and magnetic properties were measured. X-ray diffraction analysis showed that all the prepared spinel ferrites possessed cubic spinel structure. Dielectric constant, AC conductivity and dielectric loss decreased with the addition of rare earth ions. The impedance analysis explained the role of grains and grain boundaries with in prepared samples. Cole-Cole plots helped to measure the values of grains and grain boundary's resistance. The magnetic properties proved the soft nature of these ferrites. Saturation magnetization and remanence decreased while coercivity was enhanced with the addition of ytterbium concentration. All these parameters suggested that these prepared samples might be suitable for high frequency applications.     

Effect of Nd substitution on structural and electrical properties of nanocrystalline zinc ferrite

Polycrystalline soft ferrite samples with general formula ZnNd_xFe_2−xO₄ (where x=0, 0.01, 0.02 and 0.03) were synthesized by oxalate co-precipitation method. The samples were characterized by XRD and SEM techniques. The single phase cubic spinel structure of all the samples was confirmed by XRD. The lattice constant and grain size of the samples are found to decrease with increase in Nd³⁺ content. Room temperature DC resistivity of the Nd³⁺ substituted zinc ferrites is 10² times higher than that of zinc ferrite. The dielectric constant (ε′) and dielectric loss (tan δ) of all the samples were measured in the frequency range 20 Hz-1 MHz. The dielectric behaviour is attributed to the Maxwell-Wagner type interfacial polarization. The dielectric loss of the samples is found to decrease with increase in Nd³⁺ content. High resistivity and low dielectric loss makes these ferrites particularly suitable for high frequency applications.     

Impact of sonochemical synthesis condition on the structural and physical properties of MnFe2O4 spinel ferrite nanoparticles

Herein, we report sonochemical synthesis of MnFe₂O₄ spinel ferrite nanoparticles using UZ SONOPULS HD 2070 Ultrasonic homogenizer (frequency: 20 kHz and power: 70 W). The sonication time and percentage amplitude of ultrasonic power input cause appreciable changes in the structural, cation distribution and physical properties of MnFe₂O₄ nanoparticles. The average crystallite size of synthesized MnFe₂O₄ nanoparticles was increased with increase of sonication time and percentage amplitude of ultrasonic power input. The occupational formula by X-ray photoelectron spectroscopy for prepared spinel ferrite nanoparticles was (Mn_0.29Fe_0.42)[Mn_0.71Fe_1.58]O₄ and (Mn_0.28Fe_0.54) [Mn_0.72Fe_1.46]O₄ at sonication time 20 min and 80 min, respectively. The value of the saturation magnetization was increased from 1.9 emu/g to 52.5 emu/g with increase of sonication time 20 min to 80 min at constant 50% amplitude of ultrasonic power input, whereas, it was increased from 30.2 emu/g to 59.4 emu/g with increase of the percentage amplitude of ultrasonic power input at constant sonication time 60 min. The highest value of dielectric constant (ε′) was 499 at 1 kHz for nanoparticles at sonication time 20 min, whereas, ac conductivity was 368 × 10⁻⁹ S/cm at 1 kHz for spinel ferrite nanoparticles at sonication time 20 min. The demonstrated controllable physical characteristics over sonication time and percentage amplitude of ultrasonic power input are a key step to design spinel ferrite material of desired properties for specific application. The investigation of microwave operating frequency suggest that these prepared spinel ferrite nanoparticles are potential candidate for fabrication of devices at high frequency applications.     

Preparation and microwave absorption properties of Ce-substituted lithium ferrite

Ce-substituted lithium ferrite, Li_0.5Ce_xFe_2.5−xO₄ (x=0, 0.015 and 0.15), was prepared from metal nitrates and citric acid by the citrate sol-gel method. The thermal decomposition process was investigated by TG-DSC. The phase composition and microstructure of Li_0.5Ce_xFe_2.5−xO₄ was characterized by X-ray powder diffraction analysis (XRD) and a transmission electron microscope (TEM). The complex permittivity and complex permeability and microwave absorption properties of Li_0.5Ce_xFe_2.5−xO₄-paraffin wax composite were measured by the transmission/reflection coaxial line method in the range of 2-18 GHz. It is shown that the substitution of cerium ion had a close effect on the properties of Li_0.5Ce_xFe_2.5−xO₄ ferrites. Also, the present investigation demonstrates that microwave absorbers for applications over 15 GHz, with satisfactory reflection loss, of more than −20 dB for specific frequencies, could be obtained by controlling the substituted Ce element.     

Anomalies of internal friction of ferrimagnetic spinel Li0.5Fe2.5O4 in various structural states

The results of high-temperature (20≤T≤800°C) relaxation and magnetic investigations of ferrite Li_0.5Fe_2.5O₄ in various structural states are given. Anomalies of internal friction caused by the occurrence of ferrimagnetic and structural (ordering type) second-order phase transitions and by vibrations of domain walls of ferrimagnetic and antiphase domains were revealed. It is shown that the 1: 3 ordering of Fe³⁺ and Li⁺ ions in the octahedral sublattice of the spinel leads to a decrease in the Curie temperature, a change in the character of the temperature dependence of the low-field magnetization, and a narrowing of the temperature range of the structural phase transition, as well to a substantial weakening of dissipation processes connected with vibrations of ferrimagnetic domain walls in the field of elastic stresses.     

Dielectric behavior of nano-structured and bulk Li Ni Zn ferrite samples

The ac conductivity and dielectric properties of spinel ferrite nanoparticles of Li_0.1(Ni_1−xZn_x)_0.8Fe_2.1O₄ (x=0.0–1.0) prepared by the chemical co-precipitation method were investigated as functions of frequency and temperature by using a complex impedance technique. Parts of the precipitated powders were pressed into a disk-shape and were sintered at 1473 K for 2 h to increase the particle size to the bulk scale (dimensions >100 nm). The ac conductivity of the samples increases with increasing temperature, ensuring the semiconducting behavior of both nano and bulk samples, in agreement with the Koops model to describe heterogeneous structures. The significant decrease in ac conductivity σ′_ac, dielectric constant, and dielectric loss of the as-prepared nanosamples compared to their bulk counterparts is correlated to the small size of the grain compared to the grain boundary size. This might be useful for many applications requiring the reduction of eddy current effects.     

Remarkable influence on the dielectric and magnetic properties of lithium ferrite by Ti and Zn substitution

The effect of Zn and Ti substitution on the magnetic and electrical properties of Li_0.5Zn_xTi_xMn_0.05Fe_2.45−2xO₄ ferrites (x=0.0 to 0.30 in steps of 0.05) +0.5wt% Bi₂O₃ prepared by a standard ceramic technique has been investigated. Electrical conductivity and dielectric measurements at different temperatures from 300 K to 700 K in the frequency range from 100 Hz to 2 MHz have been analysed. The variation of the real part of dielectric constant (ε^′) and loss tangent (tanδ) with frequency and temperature has been studied; it follows the Maxwell–Wagner model based on the interfacial polarization in consonance with the Koops phenomenological theory. It is found that the permittivity of zinc and titanium substituted lithium ferrite improves and shows a maximum value ( 1.5×10⁵) at 100 Hz for the x=0.25 sample. The dielectric transition temperature (T_d) depends on the concentration of Ti and Zn in Li_0.5Zn_xTi_xMn_0.05Fe_2.45−2xO₄. The saturation magnetization and Curie temperature both decrease with increase in the concentration of Ti and Zn in the ferrite.     

Synthesis modified structural and dielectric properties of semiconducting zinc ferrospinels

The influence of preparation techniques on structural and dielectric properties of ZnCr_xFe_1−xO₄ (x=0, 0.1 abbreviated as Z and ZC) ferrite nano-particles synthesized using chemical co-precipitation (CCP), sol-gel (SG) and solid state reaction (SS) techniques is discussed. XRD profiles are used to confirm the single phase spinel ferrite formation. TEM images indicate the change in size and shape of particles on changing either the composition or the synthesis methodology. The TEM micrograph of samples obtained through CCP shows uniform particle size formation compared to those obtained through SG and SS. Sample prepared through CCP possess porosity >70% making these materials suitable for sensing applications. The dielectric loss, dielectric constant and ac conductivity are analyzed as a function of frequency, temperature and composition using impedance spectroscopy. A universal dielectric behavior has been predicted through temperature and frequency variations of different parameters. Dielectric constant is found to possess highest value for sample synthesized through SG which marks the possibility of using the SG derived ferrospinels as microwave device components.