X-ray and magnetic studies of Zn2+ substituted Ni-Pb ferrites

Seven samples of the polycrystalline, Ni_1.25-xZn_xPb_0.25Fe_1.5O₄ (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) ferrites, were prepared by usual double sintering ceramic method. X-ray diffraction patterns of the samples revealed single-phase cubic spinel structure. The magnetic properties were investigated by means of magnetization and a.c. susceptibility (χ) measurements. A.C. susceptibility was measured from room temperature to the Curie temperatureT _C) of the samples. Variation of a.c. susceptibility (χ) with temperature showed that the samples withx = 0.3 and 0.5 contain single-domain (SD) particles whereas the samples with x = 0.4 and 0.6 showed multi-domain (MD) nature. Values of Curie temperature ( T _C)as obtained from the study of variation of a.c. susceptibility with temperature were found to decrease with increase in the Zn ²⁺ concentration (x bd. Magnetic measurements showed increase in magnetization as Zn²⁺ content was increased from 00 to 0.5. Further increase in Zn²⁺ contentx bd reduces the magnetization.     

Al替代和烧结温度对NiZn铁氧体磁性能的影响

采用陶瓷工艺制备了Al替代的Ni0.5Zn0.5AlxFe2-xO4(x=0~0.10)铁氧体材料,用XRD、B-H分析仪和阻抗分析仪对其结构和磁性能进行了研究。实验发现,最佳烧结温度为1 250℃,过高和过低的烧结温度不利于降低磁芯损耗。当Al3+替代量x=0.06时,铁氧体能获得较好综合磁性能。     

Conduction in Mn substituted Ni-Zn ferrites

The d.c. electrical resistivity ‘ρ’ and thermoelectric power ‘α’ are studied as a function of temperature for Mn substituted ferrites with general formula Zn_0·3Ni_0·7+x Mn _x Fe_2−2x O₄. At lower Mn concentrations, the increase in d.c. resistivity is attributed to the hindering of Verwey mechanism Fe²⁺ ⇌ Fe³⁺ due to stable bonds of Mn³⁺ + Fe²⁺ pair. The decrease in resistivity at higher Mn concentrations (i.e. whenx > 0·15) is attributed to the formation of Mn³⁺ cluster and Ni²⁺ ⇌ Ni³⁺. The activation energy values show one to one correspondence with resistivity values. The compositional variation of thermoelectric power showsn-type behaviour for the samples withx < 0·2 whereasp-type behaviour for the samples withx ⩾ 0·2. Thep −n transition is attributed to the formation of Ni³⁺, Fe²⁺ + vacancies which act asp-type carriers. The temperature dependences ofα, ρ, and mobility clearly confirm the conduction mechanism to be due to polaron hopping.     

Electrical conductivity studies of copper-substituted and non-substituted Ni-Zn mixed ferrites

The electrical conductivity of Ni-Zn and copper-substituted Ni-Zn ferrites is investigated in the range 300 to 1000 K. It is seen that the plots of log against 10³/T exhibit a linear relationship. There are four distinct regions exhibited by the Ni-Zn ferrite. However, with the substitution of copper there appears to be gradual disappearance of the fourth region. Also for the samples of Ni-Zn ferrite with more than 80% Zn, there are only three regions in the variation of log with 10³/T. The breaks and discontinuities are attributed to several sources. The electrical conduction in these ferrites is explained on the basis of a hopping mechanism. The activation energy in the paramagnetic region is found to be more than that for the ferri magnetic region. This is attributed to the effect of the magnetic ordering in the conduction process.     

Effect of antimony doping on magnetic properties of Ni-Zn ferrites

The influence of Sb⁵⁺ doping on magnetic initial permeability () and magnetic loss factor () in Ni-Zn ferrites over a frequency range from 10 kHz to 1 GHz at room temperature is studied. The Curie temperature (T _c), saturation magnetization (M _s), lattice constant (a) and mean grain diameter (D _m) of the pure and doped ferrites have also been evaluated. Domain wall relaxation has been observed in all the samples. Using the existing theories the magneto-crystalline anisotropy constant (K) and certain domain wall constants like wall damping parameters (), domain wall energy (_w), the wall mobility () and the wall mass (m _w) have been evaluated and the results are compared and discussed with the similar data available on other ferrimagnetic oxides.     

Band gap determination of Ni-Zn ferrites

Nanocomposites of Ni-Zn with copolymer matrix of aniline and formaldehyde in presence of varying concentrations of zinc ions have been studied at room temperature and normal pressure. The energy band gap of these materials are determined by reflection spectra in the wavelength range 400–850 nm by spectrophotometer at room temperature. From the analysis of reflection spectra, nanocomposites of copolymer of aniline and formaldehyde with Ni_1-xZn_xFe₂O₄ (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 10) have been found to have direct band gaps ranging from 1.50–1.66 eV.     

Pentavalent vanadium ion addition to Ni-Zn ferrites

Systematic studies of the changes in microstructure and the grain-growth kinetics of iron-deficient and iron-excess Ni-Zn ferrites with varying contents of V₂O₅ have been undertaken. The basic composition of an iron-deficient Ni-Zn ferrite showed a duplex structure. Modified microstructures with pore-free and uniform grains were obtained on V₂O₅ doping. A regular increase in grain size was found with increasing V₂O₅ content both in iron-deficient and iron-excess compositions. The square of the average grain diameter varied linearly with sintering time up to 0.0 to 0.4 mol % V₂O₅. For higher V₂O₅ contents (0.6 to 1.0 mol %), the cube of the average grain diameter was directly proportional to the sintering time. Modifications in the microstructure and the grain growth have been explained in terms of the solubility of V₂O₅ in the lattice and liquid-phase formation at the grain boundaries.     

Structural, electrical and magnetic properties of cadmium substituted nickel-copper ferrites

Polycrystalline ferrites with the general formula Ni_0.95−xCd_xCu_0.05Fe₂O₄ in which x varies from 0.1 to 0.3 were synthesized by standard double sintering ceramic technique. The existence of single phase cubic spinel structure of ferrites was confirmed from XRD measurement. Surface morphology and compositional features were studied by SEM and EDX measurements. Absorption bands observed in FTIR spectra at 600 cm⁻¹ (υ₁) and 410 cm⁻¹ (υ₂) corresponds to vibrations of tetrahedral and octahedral complexes respectively. In the dc conductivity measurements the decrease of dc resistivity with increase of temperature indicates the semiconducting nature of ferrites. The dielectric measurement of the samples at room temperature studied in the frequency range 20 Hz to 1 MHz shows dispersion in the low frequency region and remains constant at high frequency region. However, the small polaron hoping type of conduction mechanism was inferred from the linear increase of ac conductivity. The magnetic properties of ferrites such as saturation magnetization, magnetic moment and Y-K angles was estimated as a function of cadmium content by VSM technique. The smaller value of Mr/Ms reveals the existence of multidomain (MD) particles in the ferrite samples.     

The influence of Cu2+ substitution on the magnetic properties of Fe-Zn and Ni-Zn ferrites

The influence of a Jahn-Teller ion on magnetization,g-values and linewidth in Zn _x Fe_3?x O₄ and Ni_1?x Zn _x Fe₂O₄ spinel ferrites has been investigated by introducing small quantities of Cu²⁺ ions. The magnetization of Cu substitution in both the systems but the curie temperature is affected only in FeZn ferrites. The lattice constant in NiZn is significantly reduced while in FeZn there is only a slight increase. The change ing _eff on copper substitution,_Δ g _eff, is very different in the two systems. In NiZn,_Δ g _eff has a uniform value, ～ 0·2, for all values ofx while in FeZn it has a peak atx=0·3 and vanishes atx=0 andx?0·5. The ferromagnetic linewidth_ΔH does not change significantly on copper substitution in both the systems. An explanation based on the perturbation produced due to the local lattice distortion by the Jahn-Teller mechanism explains the observed results satisfactorily.     

Pentavalent vanadium ion addition to Ni-Zn ferrites

The d.c. And a.c. Electrical conductivities of iron-excess and iron-deficient compositions of Ni-Zn ferrites, with varying V₂O₅, content sintered at different temperatures (1200 to 1300° C) for 2 h in air, has been studied. The electrical conductivity increased with a 0.2 mol % addition of V₂O₅. The minimum d.c. And a.c. Electrical conductivities were found at a V₂O₅ content of 0.4 mol % followed by a small increase for still higher concentrations of V₂O₅ (? 0.6 to 1.0 mol %). The minima at 0.4 mol % were unaffected by the sintering temperature in both the iron-excess and iron-deficient cases. The activation energies for a.c. Conduction at 1 MHz were always less than the corresponding values for d.c. conduction. The results obtained can be explained in terms of solubility of V₂O₅, which creates ferrous ions and localizes Fe²⁺ ions by forming triplets in the ferrite matrix.     

自蔓延高温合成Ni-Zn铁氧体的研究

采用SHS方法合成Ni0.35Zn0.65Fe2O4铁氧体 ,取代了传统铁氧体工艺耗能、耗时的预烧环节。以XRD、SEM、阻抗分析仪等对铁氧体的微观结构、磁性能进行表征,并与传统工艺对比,获得了性能优良的铁氧体。     

Susceptibility and magnetization studies of Gd3+ substituted Mg-Cd ferrites

Studies on lattice parameters, magnetization and ac susceptibility measurements for the ferrite system Cd _x Mg_1−x Gd _y Fe_2−y O₄ (withx = 0·2, 0·3, 0·4 andy = 0·1, 0·2, 0·3, 0·4) are presented. The ac susceptibility was measured from room temperature to 800K at a constant magnetic field of 7 oersted.X _ac vsT variations show that all the samples contain predominantly multidomain (MD) particles. Magnetization measurements of the system indicate that as the Cd²⁺ content increases magnetization increases while the addition of Gd³⁺ reduces the magnetization. The observations further indicate the existence of Y-K type of magnetic ordering in the system.     

镍锌铁氧体的制备及其吸波性能的研究

利用溶胶直接自蔓延反应制备了镍锌铁氧体纳米粉末，采用XRD分析了其结构。以聚乙烯醇为基体（PVA）制备了炭黑，镍锌铁氧体复合材料吸波平板；采用矢量网络分析仪测量了其在2～18GHz频带上的吸波性能。结果表明：具有双层结构的炭黑，镍锌铁氧体复合材料具有较好的吸波效果，试样厚度为3mm；当面层镍锌铁氧体的质量分数为40％，底层炭粉的质量分数为20％时，在8～18GHz的测试频段范围内，复合材料最大吸收峰值为-15．7GHz，优于-6dB的有效带宽为6．4GHz；当底层炭粉的质量分数为15％时，复合材料最大吸收峰值为-13．6GHz，优于-6dB的有效带宽为8．2GHz。     

Synthesis, characterization and magnetic properties of Zn substituted Li-Ni nano ferrites

Nanosized Li-Ni-Zn ferrites with general chemical formula Li0.5 Ni(0.75-x/2) Zn(x/2) Fe2O4 (0 < x < 1) were synthesized from a simple polymer matrix based precursor solution. The solution was composed of metal nitrates, polymer (PVA) and disaccharide (sucrose). Thermolysis/flame pyrolysis of the precursor mass in an external temperature resulted in the oxide phase formation. X-ray diffraction studies confirm the formation of single phase ferrites. The microstructural analysis was carried out by scanning electron microscopy (SEM). The average grain diameter was estimated by the Scherrer method and grain diameter is found to vary from 16 nm to 33 nm. The saturation magnetization was studied as a function of composition.