Structural,magnetic, and dielectric properties of Ni–Zn ferrite and Bi_2O_3 nanocomposites prepared by the sol-gel method

Ni–Zn ferrite and Bi_2O_3 composites were developed by the sol-gel method. The structural, magnetic, and dielectric properties were studied for all the prepared samples. X-ray diffraction(XRD) was performed to study the crystal structure.The results of field emission scanning electron microscopy(FE-SEM) showed that the addition of Bi_2O_3 can increase the grain size of the Ni–Zn ferrite. Magnetic properties were analyzed by a hysteresis loop test and it was found that the saturation magnetization and coercivity decreased with the increase of Bi_2O_3 ratio. In addition, the dielectric properties of the Ni–Zn ferrite were also improved with the addition of Bi_2O_3.     

Thermal hysteresis and domain states in Ni-Zn ferrites synthesized by oxalate precursor method

Nickel zinc ferrites with generic formula, Ni_XZn_1−XFe2O4 (with X=0.28-0.40) were synthesized by an oxalate precursor route starting with acetates to study their magnetic properties. The saturation magnetization versus temperature curves resemble those of R type ferrites. The system shows the presence of Yafet-Kittel type of spin. It is observed that magnetic moment (n_B) values increase with the addition of Ni²⁺. The remanance ratio R tends to increase with the addition of Ni²⁺, which has been attributed to the increase of magnetocrystalline anisotropy constant (K1). The values of R compare well with the theoretical value (0.87). The coercive force (H_c) tends to increase with the addition of Ni²⁺, which has been related to the reverse domain formation. Studies on temperature variation of R and H_c reveal that these parameters are thermally insensitive, which confirms the presence of multi domain grains in the material. These observations have been supported by a.c. susceptibility studies.     

Doping effect of Y ions on the microstructural and electromagnetic properties of Mn-Zn ferrites

Mn-Zn ferrites doped with different contents of Y³⁺ ions were prepared by conventional two-step synthesis method. The microstructure and electromagnetic properties of the as-prepared Mn-Zn ferrites were investigated. It was found that all the samples consisted of ferrite phases of typical spinel cubic structure, and when Y³⁺ ion content was upto 1.5 mol%, yttriumirongarnet (Y₃Fe₅O₁₂) phase with garnet structure was detected. With increasing doping content of Y³⁺ ions, the lattice constant and grain size increased, and after an increase to its maximum value, the sample apparent and relative densities dropped down. Through the analysis of magnetic properties, it was revealed that the saturation magnetization, and both the real and imaginary parts of permeability of the as-prepared samples raised with increasing doping content of Y³⁺ ions but decreased with more Y³⁺ ions, while their coercivity showed an opposite change trend; and the Curie temperature increased monotonously. The measurement of dielectric properties indicated that the dielectric constant of the doped Mn-Zn ferrites presented a rise with increasing Y³⁺ ion content, and dropped down gradually when more Y³⁺ ions were doped, while the dielectric loss tangent would decrease with Y³⁺ content upto 1.5 mol%, but after that, it increased.     

稀土元素La掺杂BaFe12O19微结构和磁性能的研究术

用固相法制备了镧掺杂M型钡铁氧体（Ba1--xLaxFel2O19,x=0．0-0．6）,针对不同取代量与不同温度的烧结,研究取代量和温度对钡铁氧体微结构和磁性能的影响．在烧结温度为1100-1175℃,当X=0．0-0．6时,样品主要有单一的六角M型钡铁氧体相构成．SEM表明,La离子的加入不会影响钡铁氧体微观形貌．在磁性能方面,随着La离子的增加,钡铁氧体的饱和磁化强度先增加后减小,矫顽力逐渐增加．在同一取代量下,钡铁氧体的饱和磁化强度随烧结温度升高呈现上升趋势,矫顽力随着烧结温度的升高而降低．饱和磁化强度在x=0．2,烧结温度1175℃时达到最大值62．8emu／g,矫顽力在x=0．6,烧结温度1125℃时达到最大值3911．5Oe．     

Enhanced dielectric properties of lead barium zirconate thin films by manganese doping

(Pb_0.5Ba_0.5)ZrO₃ (PBZ) and 1 mol% Mn-doped (Pb_0.5Ba_0.5)ZrO₃ (Mn-PBZ) sol were successfully fabricated, and corresponding thin films were deposited on Pt(1 1 1)/TiO₂/SiO₂/Si(1 0 0) substrates by spin-coating method. Effects of Mn doping on the microstructure and electrical properties of PBZ thin films were investigated systemically. X-ray diffraction patterns showed that both films had a polycrystalline perovskite structure, and that the degree of (1 1 1) orientation were increased by Mn doping. Dielectric measurements illustrated that Mn-doped PBZ thin films not only had a larger dielectric constant, but also possessed a smaller dielectric loss. Accordingly, the tunability and the figure of merit of PBZ films were improved by Mn doping.     

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.     

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.     

Effect of doping V on the half-metallic and magnetic properties of Mn3Al intermetallic compound

The effect of doping V on the electronic structure and magnetic properties of Mn₃Al has been studied by density functional calculations. It is found that the V atoms for all the doped compounds prefer to enter into the B sites, and further they tend to enter into the (A, C) sites in Mn₃Al. The calculations show that the alloys (Mn_12−xV_x)Al₄ (x=0, 1, 2, 3, 4, 5, 6, 7) are ferrimagnetic whereas V₂MnAl (x=8) is nonmagnetic. The compounds of x=0, 1, 2, 3, 4 exhibit the half-metallic character, and the compound of x=5 shows a nearly half-metallicity since the Fermi level slightly touches the valence bands. For x=6 and 7, the spin polarization is 59% and 69%, respectively. The reason is mainly attributed to the behavior of Mn(A,C)/V(A,C) atoms.     

Synthesis, microstructure, dielectric and magnetic properties of Cu substituted Ni-Li ferrites

Cu substituted Ni-Li spinel ferrites were prepared by a conventional sol-gel auto-combustion method. The structure, surface morphology, dielectric and magnetic properties were investigated by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, impedance spectroscopy and vibrating sample magnetometer, respectively. X-ray diffraction studies reveal the single phase spinel structure of the ferrites and the crystallite size varies from 23 to 35 nm. Incorporation of Cu in the Ni-Li ferrites increases the grain size. The dielectric parameters such as ε´, ε′′, loss tan δ and ac conductivity (σ_ac) have been measured for the annealed samples in the temperature range from 35 to 200 °C and over the frequency range from 10¹ to 10⁷ Hz. The saturation magnetization and coercivity show a dependence on the composition and microstructure. The values of saturation magnetization vary from 25.6 to 33.6 emu/g with increase in x for samples annealed at 600 °C. The values of the coercivity increase from 170 to 203 Oe with increase in x.     

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.     

Magnesium doping in hierarchical ZnO nanostructures and studies on optical properties

Magnesium doping in hierarchical zinc oxide nanostructures has been carried out using an aqueous method. The XRD results confirmed the hexagonal wurtzite structure for the magnesium doped zinc oxide nanoparticles. On doping with Mg²⁺, there is a change in morphology of the hierarchical nanostructures to nanorods. The optical absorption and photoluminescence properties of the nanostructures depend on the magnesium doping level. A blue shift of the band gap absorption and the near band edge emission is observed on Mg doping.     

Elastic,impedance spectroscopic and dielectric properties of TiO2 doped nanocrystalline NiCuZn spinel ferrites

ABSTRACT

Nanocrystalline Ni_0.4Cu_0.3Zn_0.3Fe₂O₄ ferrites doped with TiO₂ (0–10?wt %) were prepared by the sol-gel method. Elastic properties of synthesized samples were studied with the help of ultrasonic pulse transmission method. The elastic constants initially increase with an increase in TiO₂ up to 1?wt % and then decline. LCR-Q meter was used to study the dielectric properties within 50?Hz to 5?MHz range of the frequency. The dielectric constant (?′) and dielectric loss tangents were decreased continuously with increased frequency for all the selected samples at room temperature revealing normal dielectric behavior of ferrites. Also, the AC conductivity was increased with an increase in the frequency for all the selected samples. Cole-Cole plots were obtained for all investigated samples and showed single semicircle which indicates that the electrical conduction process appears only due to grain boundaries.     

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.     

Co doping effects on structural, electronic and magnetic properties in Mn2VGa

The electronic structure and magnetic properties of Co-doped Heusler alloys (Mn_1−xCo_x)₂ VGa (x=0.0, 0.25, 0.5, 0.75, 1.0) have been studied by first-principles calculations. The results show that the lattice constants decrease with increasing Co content except x=1.0. The spin polarization for x=0.5 is only 34%, much lower than the other concentrations. The compounds of x=0.0, 0.25 show nearly half-metallicity because the Fermi level slightly touches the valence bands. And the compounds of x=0.75, 1.0 exhibit the half-metallic character with 100% spin polarization. It is found the local moments of Mn(Co) basically show a linear increasing trend while the moments of V show a linear decreasing trend with increasing doping concentration. However, the local moments for x=0.5 quite depart from the linear trend. The majority-spin component at the Fermi level increases while the minority-spin component at the Fermi level decreases with the substitution of Co atoms for Mn atoms when x≤0.75. For x≥0.75, the majority-spin component remains more or less the same and the gap in the minority DOS increases with Co doping. The majority spin states are shifted to valence bands and the majority spin states around E_F increase due to a leakage of charge from the unoccupied spin-up states to the occupied majority states with increasing Co content.     

Microwave anneal effect on magnetic properties of Ni0.6Zn0.4Fe2O4 nano-particles prepared by conventional hydrothermal method

Ni_0.6Zn_0.4Fe₂O₄ ferrite nano-particles with a crystallite size of about 20 nm were prepared by the conventional hydrothermal method, followed by annealing in a microwave oven for 7.5-15 min. The microstructure and magnetic properties of the samples were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and vibrating sample magnetometry. The microwave annealing process has slight effect on the morphology and size of Ni_0.6Zn_0.4Fe₂O₄ ferrite nano-particles. However it reduces the lattice parameter and enhances the densification of the particles, and then greatly increases the saturation magnetization (50-56 emu/g) and coercive force of the samples as compared to the non-annealing condition. The microwave annealing process is an effective way to rapidly synthesize high performance ferrite nano-particle.     

Effect of doping MnO2 on magnetic properties for M-type barium ferrite

The crystalline structure and magnetic properties of M-type barium ferrite doped with small amounts of MnO₂ (0, 0.25, 0.5, 0.75, 1.0, 1.5, and 2.0 wt%, respectively) have been investigated by means of XRD, SEM and VSM. The results show that the crystalline structures of barium ferrite are still M-type hexagonal structure and Mn ions are distributed homogeneously in both the grains and the grain boundaries. The saturation magnetization and magnetocrystalline anisotropy constants both reach the highest values when x=0.75 wt%. The displacement of Fe ions from 4f₁ to 2b site is mainly responsible for the appearance of the maximum values.     

Effect of MgO additive on the high-frequency properties of Z-type hexaferrites

MgO was introduced into low-temperature sintered Z-type hexaferrites in order to improve their high-frequency electromagnetic properties. In the doped samples the major Z-type phase coexists with a small amount of W-type magnetoplumbite phase. The addition of MgO causes a decrease of the average grain size and an increase of the magnetocrystalline anisotropy (K₁) and the saturation magnetization (M_s) with the increment of K₁ being larger than that of M_s. These factors result in a reduce of the initial permeability. Also, the samples with MgO additive exhibit higher Q-factor and dc resistivity. Furthermore, the introduction of MgO can decrease the dielectric constant and improve the dielectric loss tangent of the samples by reducing the electronic transition in octahedral site (B-site) between Fe²⁺ and Fe³⁺ ions.     

Microstructure and magnetic properties of Sn-substituted MnZn ferrites

Sn-substituted MnZn ferrites were prepared by conventional oxide ceramic process. The influences of Sn substitution on microstructure and magnetic properties of MnZn ferrites were investigated. The results indicated that with increase of Sn substitute concentration, the diffraction peaks shifted slightly towards the lower angles and the lattice parameter (a) increased. And at room temperature, the bulk density (d_m), initial permeability (μ_i), saturation magnetic induction (B_s) and electrical resistivity (ρ) of Sn-substituted MnZn ferrites all increased initially and then decreased with the further increase of Sn substitute concentration, while the power losses decreased first and then increased subsequently. Meanwhile, the temperature of secondary maximum peak of μ_i-T curve and the minimum losses moved to lower temperature while the Sn substitute concentration increased. When the content of Sn substitution was 0.3 mol%, at room temperature, the initial permeability, saturation magnetic induction, density and electrical resistivity reached their maxima, while the hysteresis loss (P_h), eddy current loss (P_e) and total losses (P_cv) achieved their minima. The P_h∼T and μ_i-T curves varied contrarily, and due to the contribution of extra eddy current loss (P_e,exc) that was proportional to P_h, the P_e-T curve did not agree with its classical expression. Finally, MnZn ferrite substituted with 0.3 mol% SnO₂ shows the highest initial permeability (3894) and lowest losses (303 kW/m³) at room temperature.     

Magnetic and dielectric properties of low vanadium doped nickel-zinc-copper ferrites

The new spinel-type of general formula Ni_0.6+xZn_0.2Cu_0.2V_xFe_2−2xO₄ with 0.0≤x≤0.25 was synthesized by the usual ceramic method. Structure of the prepared ferrites was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). Room temperature magnetic hysteresis loops were measured using magnetic field strength up to 6 kOe. Saturation magnetization (M_s) increased with vanadium content up to x=0.05 and then decreased. Variation of (M_s) as a function of x is explained in terms of cation redistribution between A and B sublattices. Coercive force (H_c), remanent induction (B_r) and squareness of the hysteresis loop (B_r/M_s) as functions of x are presented. Dielectric permittivity (ε′, ε″) and dielectric loss tangent (tan δ) were measured as functions of frequency and temperature. These parameters were found to be strongly dependent on V₂O₅ concentration. The variation of dielectric loss tangent with frequency at different temperatures shows abnormal behavior, where more than one relaxation peaks were observed at low and high temperatures. This behavior could be attributed to the collective contribution of two types of carriers (p and n) to polarization.     

Structural and magnetic properties of Li-Cu mixed spinel ferrites

Li_0.5−x/2Cu_xFe_2.5−x/2O₄ (where x=0.0-1.0) ferrites have been prepared by solid-state reaction. X-ray diffraction was used to study the structure of the above investigated ferrites at various sintering temperatures. Samples were sintered at 1000, 1100 and 1200 °C for 3 h in the atmosphere. For the sintering temperature of 1000 °C, Li_0.5−x/2Cu_xFe_2.5−x/2O₄ undergoes cubic to tetragonal transformation for higher Cu content. However, for the sintering temperature of 1100 and 1200 °C, X-ray diffraction patterns are mainly characterized by fcc structure, though presence of tetragonal distortion was found by other temperature dependence of initial permeability curves. The lattice parameter, X-ray density and bulk density were calculated for different compositions. Curie temperature was measured from the temperature dependence of initial permeability curves. Curie temperatures of Li-Cu mixed ferrites were found to decrease with the increase in Cu²⁺ content due to the reduction of A-B interaction. As mentioned earlier, temperature dependence of initial permeability curves was characterized by tetragonal deformation for the samples containing higher at% of Cu. The complex initial permeability has been studied for different samples. The B-H loops were measured at constant frequency, f=1200 Hz, at room temperature (298 K). Coercivity and hysteresis loss were estimated for different Cu contents.