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.     

Magnetic and dielectric studies of nanocrystalline zinc substituted Cu-Mn ferrites

Ferrites with the general formula Cu_1−xZn_xFeMnO₄ (where 0≤x≤1) were prepared through a citrate gel auto-combustion route. Structural characterizations carried out by X-ray diffraction reveal that the lattice constant increases with increase in zinc content. Transmission electron microscopic measurements confirm the nanoscale nature of the particles. Room temperature saturation magnetization was measured as a function of zinc concentration. The saturation magnetization increases up to x=0.25 and then decreases as zinc concentration increases. Dielectric permittivity, dielectric loss tangent, ac conductivity and complex dielectric impedance were studied in the frequency range 20 Hz-1 MHz. The results indicated a usual dielectric dispersion due to the Maxwell-Wagner type of interfacial polarization. Dielectric loss showed similar behavior as dielectric permittivity. The ac conductivity increased linearly with frequency. Complex impedance spectroscopic studies confirmed that conduction in the samples is via grain boundaries. In general, substitution of zinc plays an important role in changing the structural, electrical and magnetic properties of these ferrites.     

Effect of magnesium substitution on dielectric and magnetic properties of Ni-Zn ferrite

The dielectric and magnetic properties of Mg incorporated Ni-Zn spinel ferrites have been investigated. Ni_0.5−xZn_0.5Mg_xFe₂O₄ ferrites have been prepared by sol-gel auto-combustion technique. The as prepared ferrites were annealed at 673, 873 and 1073 K. The X-ray diffraction studies reveal the spinel structure of annealed ferrites. The TEM results are in agreement with XRD results. FTIR study has also been carried out to get insight into the structure of these ferrites. The dielectric measurements show that the dielectric constant (ε′), dielectric loss (tan δ) and conductivity (σ_ac) increase on incorporation of Mg in the Ni-Zn ferrite. ε′, tan δ and σ_ac also show dependence on temperature, frequency of external applied electric field and microstructure of the samples. The magnetic moment measurements reveal that the saturation magnetization (M_s) increases and coercivity (H_c) decreases with the increase in concentration of Mg²⁺ ions. M_s and H_c also show dependence on the annealing temperature.     

Study of dielectric and ac impedance properties of Ti doped Mn ferrites

We have reported dielectric and ac impedance properties of Ti doped Mn_1+xFe_2−2xO₄ (0x0.5) ferrites prepared by solid-state reaction method, using dielectric and impedance spectroscopy in the frequency range of 42 Hz–5 MHz, between the temperatures (300K–473K). The dielectric constant and dielectric loss (tan δ) decreases with increasing frequency but these parameters increase with increasing temperature. The dielectric loss tangent curves exhibit dielectric relaxation peaks at high frequencies (3.6 kHz–5 MHz), which are attributed to the coincidence of the frequency of charge hopping between the localized charge states and the external field. The dielectric properties have been explained on the basis of space charge polarization according to Maxwell–Wagner’s two-layer model and the hopping of charge between Fe²⁺ and Fe³⁺ as well as between Mn³⁺ and Mn²⁺ ions at B-sites. The complex impedance analysis has been used to separate grain and grain boundary in studied samples. Two semicircles corresponding to grain and grain boundary have been observed at low temperature, while only one semicircle has been seen at high temperatures. The resistance of grain and grain boundary both increase with Ti⁴⁺ doping.     

Dielectric,electrical transport and magnetic properties of Er3+substituted nanocrystalline cobalt ferrite

Erbium substituted cobalt ferrite (CoFe_2−xEr_xO₄; x=0.0–0.2, referred to CFEO) materials were synthesized by sol-gel auto-combustion method. The effect of erbium (Er³⁺) substitution on the crystal structure, dielectric, electrical transport and magnetic properties of cobalt ferrite is evaluated. CoFe_2−xEr_xO₄ ceramics exhibit the spinel cubic structure without any impurity phase for x≤0.10 whereas formation of the ErFeO₃ orthoferrite secondary phase was observed for x≥0.15. All the CFEO samples demonstrate the typical hysteresis (M–H) behavior with a decrease in magnetization as a function of Er content due to weak superexchange interaction. The frequency (f) dependent dielectric constant (ε′) revealed the usual dielectric dispersion. The ε′–f dispersion (f=20 Hz to 1 MHz) fits to the modified Debye's function with more than one ion contributing to the relaxation. The relaxation time and spread factor derived are ∼10⁻⁴ s and ∼0.61(±0.04), respectively. Electrical and dielectric studies indicate that ε′ increases and the dc electrical resistivity decreases as a function of Er content (x≤0.15). Complex impedance analyses confirm only the grain interior contribution to the conduction process. Temperature dependent electrical transport and room temperature ac conductivity (σ_ac) analyses indicate the semiconducting nature and small polaron hopping.     

Role of Cu concentration on the structure and transport properties of Cr-Zn ferrites

The influence of Cu concentration on the transport and microstructure characteristics of Cu_yZn_1−yCr_0.8Fe_1.2O₄ with 0.2≤y≤1 ferrite was studied. X-ray, energy dispersive X- ray (EDAX) and infrared spectra (IR) were carried out to assure the formation of the sample in the proper form. The dielectric constant (ε′) and ac conductivity were measured at different frequencies ranging from 600 kHz to 5 MHz from room temperature up to 800 K. The obtained data reveals that, a single phase cubic spinel structure for all the concentrations. From the results of IR spectra, mainly two bands were observed. The dielectric constant and the dielectric loss tangent decrease with increasing frequency and Cu concentration. The dielectric constant shows a dispersion peak (ε′_max) which shifts to higher frequency with increasing the temperature. The results are explained as due to the fact that the dielectric polarization process is similar to that of conduction. The appearance of the dispersion peak is related to the contribution of two types of charge carriers.     

Structural and magnetic properties of cadmium substituted Ni-Al ferrites

Nickel Cadmium Aluminum Ferrites with the general formula Ni_1−xCd_xAl_0.6Fe_1.4O₄ where x=0, 0.25, 0.50 and 0.75 were prepared through standard double sintering reaction method. The crystallography, surface morphology and magnetic properties were studied by X-ray diffractometer (XRD), Scanning Electron Microscope (SEM) and Vibrating Sample Magnetometer (VSM), respectively. The expected single phase spinel structure was confirmed by XRD analysis. Lattice parameter and X-ray density were increased monotonically by increasing Cd concentration due to the larger ionic radii of the cadmium ion. Surface topography of the samples consists of fine cubical shape microstructures. The average grain size increased with increase in cadmium concentration. The saturation magnetization was found to be increased with increase in cadmium content up to x=0.50 and then decreased with further increasing cadmium concentration for x=0.75.     

Investigation of magnetic properties of Al substituted nickel ferrite nanopowders, synthesized by the sol-gel method

NiFe_2−xAl_xO₄ nanopowders, where x is from 0 to 1.5 with a step of 0.5, have been synthesized by the sol-gel method and the effect of non-magnetic aluminum content on their structural and magnetic properties were investigated. The X-ray diffraction (XRD) patterns revealed that the synthesized nanopowders are single phase with a spinel structure. Mean crystallite sizes of the samples were calculated by Scherrer's formula and were in the range 20-31 nm. The morphology of the nanopowders was investigated by TEM and the mean particle sizes of the samples were in the range 55-80 nm. Magnetic hysteresis loops were recorded at room temperature in a maximum applied field of 3000 Oe. The results show that by increasing the aluminum content, the magnetizations of the nanopowders are decreased. This reduction is caused by non-magnetic Al³⁺ ions, which by their substitutions the super exchange interactions between different sites will be reduced. It is also seen that the magnetizations of the nanopowders are lower than those related to their bulk counterparts. This reduction was found to be as a consequence of surface spin disorder. M-T curves of the samples were obtained using a Faraday balance and by which the Curie temperatures of the powders were determined. The results that are obtained show that the Curie temperatures of the nanopowders are higher than those of their bulk counterparts.     

The magnetic and dielectric properties of multiferroic Sr- substituted Zn2-Y hexagonal ferrites

The magnetic and dielectric properties of Sr-substituted Zn2-Y hexagonal ferrites （Ba2-x SrxZn2Fe12O22, 1.0 〈 x ≤ 1.5） are studied in this paper. Sr substitution will lead to the variation of cation occupation, which influences both the magnetic and electric properties. As Sr content x rises from 1.0 to 1.5, magnetic hysteresis loop gets wider gradually and the permeability drops rapidly due to the transformation from ferrimagnetic to antiferromagnetic phase. Moreover, permittivity rises with increasing Sr content. Under a certain external magnetic field, the phase transition of helical spin structure of Ba0.5Srl.5Zn2Fe12O22 at about 295 K seems to open a possibility for the room-temperature ferroelectricity induced by magnetic field. But its low resistivity prevents the observation of ferroelectric and magnetoelectric properties at room-temperature.     

Effects of Zr-substitution on microstructure and properties of YCaVIG ferrites

Y_2.6−xCa_0.4+xZr_xV_0.2Fe_4.8−xO₁₂ (Zr_x:YCaVIG) ferrite materials have been prepared by an oxide process. The phase formation and microstructure were analyzed by X-ray diffraction and scanning electron microscopy, respectively. The effects of Zr⁴⁺ substitution on phase compositions, sintering properties, microstructures and electromagnetic properties were investigated. The results indicate that all the sintered specimens with different Zr⁴⁺ contents show a single garnet structure. The addition of ZrO₂ can gradually increase the lattice constant, and lower the sintering temperature and the theoretical density. With the increase of Zr⁴⁺ content, the dielectric loss (tan δ_ε) and coercivity (H_c) decrease and then slightly increase, which is due to the variation of the microstructure. But the saturation magnetization (4πM_s) shows the opposite variation compared to the former two properties. However, the dielectric constant (ε_r) remains stable and remanence (B_r) monotonically declines. Finally, the specimen of Y_2.3Ca_0.7Zr_0.3V_0.2Fe_4.5O₁₂ sintered at 1350° possesses the optimum electromagnetic properties: ε_r=14.8, tan δ_ε=1.35×10⁻³, 4πM_s=1638 Gs, B_r=596 Gs, H_c=0.75 Oe and ΔH (ferromagnetic resonance linewidth)=66 Oe.     

Structural analysis, magnetic and electrical properties of samarium substituted lithium-nickel mixed ferrites

A series of Sm-doped Li-Ni ferrites with formula of (Li_0.5Fe_0.5)_0.4Ni_0.6Sm_yFe_2−yO₄, where 0.0≤y≤0.1 were prepared by double sintering ceramic technique. The structure was characterized by X-ray diffraction, which has confirmed the formation of single-phase spinel structure. The samarium concentration dependence of lattice parameters obeys Vegard's law. The octahedral site radii increased with Sm content while the tetrahedral site radii decreased. Deviation from the ideal crystal structure (Δ) is found to decrease with Sm substitution, and the hopping length on the octahedral site is found to increase with Sm content. Hall measurement confirmed p-type conductivity behavior for Sm-doped ferrite and the main charge transport mechanism is hopping of halls between Ni²⁺ and Ni³⁺. Sintering at 1300 °C resulted in low resistivity ferrite, which was found to increase with Sm content. Resistivity is governed by both charge carrier mobility and carrier concentration. It decreases with frequency, and this behavior with frequency is discussed according to Koop's theorem. The dielectric constant is found to decrease more rapidly at low frequencies than at higher frequencies while the dielectric constant increases with Sm content. The decrease in ε″ with frequency agrees with Deby's type relaxation process. Maximum in ε″ is observed when the hopping frequency is equal to the external electric field frequency. The variation in tan δ with frequency shows a similar nature to that of ε″ with frequency. The magnetization under applied magnetic field for the samples exhibits a clear hysteretic behavior. The scanning electron microscope (SEM) studies showed that the domain walls may tend to be trapped (pinned) by non-magnetic inclusions, precipitates and voids. The saturation magnetization (M_S) increases with the sintering temperature, while the coercivity (H_Ci) is found to decrease.     

The effect of urea-to-nitrates ratio on the morphology and magnetic properties of Mn0.8Mg0.2Fe2O4

Mn_0.8Mg_0.2Fe₂O₄ ferrite was synthesized using flash auto-combustion technique using urea as fuel. The effect of the urea-to-nitrates ratio was examined and found to affect the samples characteristics. The as-burnt powder was crystallized in single-phase spinel structure of cubic symmetry. The lattice parameter was decreased with increase in the urea-to-nitrates ratio (n) while the crystal size increased from 21 to 42 nm with n changing from 6.67 to 10. The coercivity increases while the saturation and remanence magnetization decreases with increase in n. This was attributed to the disturbance of the spin order as a result of the surface 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.     

Preparation and magnetic properties of barium ferrites substituted with manganese, cobalt, and tin

Barium ferrites substituted by Mn-Sn, Co-Sn, and Mn-Co-Sn with general formulae BaFe_12−2xMn_xSn_xO₁₉ (x=0.2-1.0), BaFe_12−2xCo_xSn_xO₁₉ (x=0.2-0.8), and BaFe_12−2xCo_x/2Mn_x/2Sn_xO₁₉ (x=0.1-0.6), respectively, have been prepared by a previously reported co-precipitation method. The efficiency of the method was refined by lowering the reaction temperature and shortening the required reaction time, due to which crystallinity improved and the value of saturated magnetization increased as well. Low coercivity temperature coefficients, which are adjustable by doping, were achieved by Mn-Sn and Mn-Co-Sn doping. Synthesis efficiency and the effect of doping are discussed taking into account accumulated data concerning the synthesis and crystal structure of ferrites.     

Structural and magnetic properties of Mg substituted NiCuZn Nano Ferrites

The present paper examines the effect of magnesium substitution on structural and magnetic properties of NiCuZn nano ferrites synthesised by sol-gel method. The prepared samples were characterised by using X-ray Diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Field Emission Scanning Electron Microscopy (FE-SEM) and Vibration sample magnetometer (VSM) techniques. The phase identification, unit cell parameter and crystallite size was determined using XRD analysis. The lattice constant reduced with increasing Mg content. Room temperature saturation magnetisation and coercivity showed reverse trend with increasing Mg content. Curie temperature (T_c) obtained from the thermo magnetic curves increases with Mg concentration. The initial permeability (μ_i) decreased with increasing Mg content. This is due to reduced magnetisation, grain size and increased magneto-crystalline anisotropy constant. Simultaneously, there is an upward shift of domain wall relaxation frequency with increasing Mg content. Also the permeability is observed to be constant up to 30 MHz frequency range showing compositional stability and quality of the material. The prepared samples were suitable for applications in Multilayer Chip Inductors due to their invariable permeability up to 30 MHz frequency and high thermal stability along with low sintering temperature.     

Effects of SnO2 addition on the microstructure and magnetic properties of NiZn ferrites

The microstructure and magnetic properties of SnO₂-doped NiZn ferrites prepared by a solid-state reaction method have been investigated. Due to its low melting point (∼1127 °C), moderate SnO₂ enhanced mass transfer and sintering by forming liquid phase, which accelerated the grain growth. However, excessive SnO₂ producing much of liquid phase retarded mass transfer and sintering, leading to a decrease in grain size. The diffraction intensity of the samples doped with SnO₂ addition was stronger than that of the sample without addition. The lattice constant initially decreased up to a content of 0.10 wt% and showed an increase at higher content up to 0.50 wt%. The initial permeability (μ_i) initially increased up to a content of 0.15 wt% and showed a decrease at higher content up to 0.50 wt%; however, losses (P_L) measured at 50 kHz and 150 mT changed contrarily. Both saturation induction (B_S) and Curie temperature (T_C) decreased gradually with increasing SnO₂. Finally, the sample doped with 0.10–0.15 wt% SnO₂ showed the higher permeability and lower losses.     

Structural and magnetic properties of holmium substituted cobalt ferrites synthesized by chemical co-precipitation method

CoHo_xFe_2−xO₄ ferrites (x=0.00–0.1) were prepared by the co-precipitation technique and the effect of holmium substitution on the magnetic properties was investigated. X-ray diffraction reveals that the substituted samples show a second phase of HoFeO₃ along with the spinel phase. The magnetic properties such as the saturation magnetization (M_s), coercivity (H_c) and remanence (M_r) are obtained from the hysteresis loops. It is observed that the M_s decreases while H_c increases with Ho³⁺ substitution. The decrease of saturation magnetization is attributed to the weakening of exchange interactions. The coercivity increases with increase of the Ho³⁺ concentration, which is attributed to the presence of an ultra-thin layer at the grain boundaries that impedes the domain wall motion. Low field AC susceptibility was also measured over the temperature range 300–600 K at the frequency of 200 Hz. It decreases with the increase of temperature following the Curie–Weiss law up to the Curie temperature. Above the Curie temperature it shows paramagnetic behavior. The increase in coercivity suggests that the material can be used for applications in perpendicular recording media.     

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.     

Relation of structure and magnetic properties in nickel substituted MgFe2O4

This study presents the structure-related magnetic properties of nickel substituted MgFe_2−xNi_xO₄ with x=0.01-0.20, synthesized using thermal decomposition of metal organic starting materials. The samples were annealed at temperatures ranging from 900 to 1100 °C in air. Magnetic and electric properties were characterized using vibrating sample magnetometer and an impedance analyzer, respectively. The fraction of inverse spinel structure was found to decrease with increase in nickel concentration. The samples exhibited soft magnetic behavior. The magnetization was found to depend on the substitution of Ni atoms on the octahedral sites and on the average number of valence electrons. The dielectric properties were found to have higher values at low frequency and decreased with increase in frequency. An enhancement of the dielectric constant was observed upon increase in the annealing temperature.     

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.