Preparation and magnetic properties of BaFe12O19/Ni0.8Zn0.2Fe2O4 nanocomposite ferrite

Nanocomposite of hard (BaFe₁₂O₁₉)/soft ferrite (Ni_0.8Zn_0.2Fe₂O₄) have been prepared by the sol–gel process. The nanocomposite ferrite are formed when the calcining temperature is above 800 °C. It is found that the magnetic properties strongly depend on the presintering treatment and calcining temperature. The “bee waist” type hysteresis loops for samples disappear when the presintering temperature is 400 °C and the calcination temperature reaches 1100 °C owing to the exchange-coupling interaction. The remanence of BaFe₁₂O₁₉/Ni_0.8Zn_0.2Fe₂O₄ nanocomposite ferrite with the mass ratio of 5:1 is higher than a single phase ferrite. The specific saturation magnetization, remanence magnetization and coercivity are 63 emu/g, 36 emu/g and 2750 G, respectively. The exchange-coupling interaction in the BaFe₁₂O₁₉/Ni_0.8Zn_0.2Fe₂O₄ nanocomposite ferrite is discussed.     

Effect of reaction condition on microstructure and properties of (NiCuZn)Fe2O4 nanoparticles synthesized via co-precipitation with ultrasonic irradiation

Nano-spinel ferrites synthesized via chemical co-precipitation method are small in size and have serious agglomeration phenomenon, which makes separation difficult in the subsequent process. Ni_0.4Cu_0.2Zn_0.4Fe₂O₄ ferrites nanoparticles were synthesized via co-precipitation assisted with ultrasonic irradiation produced by ultrasonic cleaner with 20 kHz frequency using chlorinated salts and KOH as initial materials. The effects of ultrasonic power (0, 40 W, 60 W, 80 W) and reaction temperature on the microstructure and magnetic properties of ferrite nanoparticles were investigated. The structure analyses via XRD revealed the successful formation of pure (NiCuZn)Fe₂O₄ ferrites nanospinel without any impurity. The crystallites sizes were less than 40 nm and the lattice constant was near 8.39 Å. The TEM showed ferrite particle polygonal. M−H analyses performed the saturation magnetization and coercivity of ferrite nanoparticles obtained at the reaction temperature of 25℃ were higher than at 50℃ with same power. The samples exhibited the highest values of Ms 55.67 emu/g at 25℃ and 47.77 emu/g at 50℃ for 60 W and the lowest values of Hc 71.23 Oe at 25℃ for 40 W and 52.85 Oe at 50℃ for 60 W. The squareness ratio (SQR) were found to be lower than 0.5, which revealed the single magnetic domain nature (NiCuZn)Fe₂O₄ nanoparticles. All the outcomes show the ultrasonic irradiation has positive effects on improving the microstructure and increasing magnetic properties.     

Structural,electrical transport,and magnetic properties of Ni1−xZnxFe2O4

Structural, electrical, and magnetic properties of Ni_1−xZn_xFe₂O₄ (x=0.2, 0.4) samples sintered at various temperatures have been investigated thoroughly. The bulk density of the Ni_0.8Zn_0.2Fe₂O₄ samples increases as the sintering temperature (T_s) increases from 1200 to 1300 °C and above 1300 °C the bulk density decreases slightly. The Ni_0.6Zn_0.4Fe₂O₄ samples show similar behavior of changes to that of Ni_0.8Zn_0.2Fe₂O₄ samples, except that the bulk density is found to be the highest at 1350 °C. The DC electrical resistivity, ρ(T)$\rho (T)$, decreases as the temperature increases indicating that the samples have semiconductor-like behavior. As the Zn content increases, the Curie temperature (T_c), resistivity, and the activation energy decrease while the magnetization, initial permeability, and the relative quality factor (Q) increases. A Hopkinson peak is obtained near T_c in the real part of the initial permeability vs. temperature curves. The ferrite with higher permeability has a relatively lower resonance frequency. The initial permeability and magnetization of the samples has been found to correlate with density, average grain sizes. Possible explanation for the observed structural, magnetic, and changes of resistivity behavior with various Zn content are discussed.     

Synthesis and characterization of Ni-Zn ferrite nanoparticles

Nickel zinc ferrite nanoparticles Ni_xZn_1−xFe₂O₄ (x=0.1, 0.3, 0.5) have been synthesized by a chemical co-precipitation method. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, electron paramagnetic resonance, dc magnetization and ac susceptibility measurements. The X-ray diffraction patterns confirm the synthesis of single crystalline Ni_xZn_1−xFe₂O₄ nanoparticles. The lattice parameter decreases with increase in Ni content resulting in a reduction in lattice strain. Similarly crystallite size increases with the concentration of Ni. The magnetic measurements show the superparamagnetic nature of the samples for x=0.1 and 0.3 whereas for x=0.5 the material is ferromagnetic. The saturation magnetization is 23.95 emu/g and increases with increase in Ni content. The superparamagnetic nature of the samples is supported by the EPR and ac susceptibility measurement studies. The blocking temperature increases with Ni concentration. The increase in blocking temperature is explained by the redistribution of the cations on tetrahedral (A) and octahedral (B) sites.     

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.     

Magnetic properties and magneto electric effect in ferroelectric rich Ni0.5Zn0.5Fe2O4+BPZT ME composites

Magneto electric composites with composition (x) Ni_0.5Zn_0.5Fe₂O₄+(1-x) Ba_0.8Pb_0.2Zr_0.8Ti_0.2O₃ (BPZT—barium lead zirconate titanate) in which x varies as 0.0, 0.15, 0.30, 0.45 and 1.0 mol% were prepared by standard double sintering ceramic method. The presence of constituent phases such as ferrite and ferroelectric was confirmed by X-ray diffraction. The structural analyses were carried out by using X-ray diffraction pattern. Scanning electron micrographs (SEM) were taken to understand the microstructure of the samples. The calculated values of the porosity of the samples lie between 4.5% and 16.2%. The hysteresis measurements were made to determine saturation magnetization (M_s), magnetic moment (μ_B) and coercivity (H_c). From the AC susceptibility measurements the contribution of both the single domain (SD) particles of the ferrite phase and mixed domain (SD+MD) particles of the composites in ME output were explained. The static magneto electric voltage coefficients (dE/dH)_H were measured as a function of intensity of magnetic field and the maximum ME coefficient were observed for the composites with 30% of ferrite+70% of ferroelectric phase.     

Effect of sintering temperature on structural and magnetic properties of NiCuZn and MgCuZn ferrites

The low temperature microwave sintered NiCuZn and MgCuZn ferrites with compositions Ni_0.35Cu_0.05Zn_0.60Fe₂O₄ and Mg_0.35Cu_0.05Zn_0.60Fe₂O₄ were synthesized by conventional mixed oxide method. NiCuZn and MgCuZn ferrite samples obtained showed better sintered densities at 950 and 900 °C, respectively. The scanning electron micrographs of both the ferrite samples appear to be very much similar. The magnitude of initial permeability of MgCuZn ferrite samples is found to be obviously higher than those of NiCuZn ferrite samples at all sintering temperatures. This is mainly due to the fact that MgCuZn ferrite has smaller magnetocrystalline anisotropy constant and magnetostrictive constant. NiCuZn ferrites have higher saturation magnetization than MgCuZn ferrites, which is due to the higher magnetic moment of NiCuZn ferrites. Our results indicate that the microwave sintering method seems to be a potential technique in the MLCI technology.     

The static and hyper-frequency magnetic properties of a ferromagnetic-ferroelectric composite

This paper reports the static and hyper-frequency magnetic properties, as well as their relationship with microstructure, of the ferromagnetic-ferroelectric co-fired composite ceramic, (1−x)Ba₂Zn_1.2Cu_0.8Fe₁₂O₂₂-xPb(Ni_1/3Nb_2/3)_0.8Ti_0.2O₃. The X-ray diffraction results did not detect any other phase in the co-fired ceramics, but found a crystal structural distortion of ferrite phase. Scanning electron microscopy photos showed that two phases’ grains matched well and stacked compactly and the hexagonal ferrite changed its grain morphology. The saturation magnetization increased with the reduction of magnetic phase in the range of 0<x<0.65 because of the stress-induced structural distortion. The permeability decreases monotonically with the reduction of magnetic phase in the whole composition range.     

Effects of sintering temperature on grain growth and the complex permeability of Co0.2Ni0.3Zn0.5Fe2O4 material prepared using mechanically alloyed nanoparticles

Nanoparticle-sized Co_0.2Ni_0.3Zn_0.5Fe₂O₄ was prepared using mechanical alloying and sintering. The starting raw materials were milled in air and subsequently sintered at various temperatures from 600 to 1300 °C. The effects of sintering temperature on physical, magnetic and electrical characteristics were studied. The complex permittivity and permeability were investigated in the frequency range 10 MHz to 1.0 GHz. The results show that single phase Co_0.2Ni_0.3Zn_0.5Fe₂O₄ could not be formed during milling alone and therefore requires sintering. The crystallization of the ferrite sample increases with increasing sintering temperature; which decrease the porosity and increase the density, crystallite size and the shrinkage of the material. The maximum magnetization value of 83.1 emu/g was obtained for a sample sintered at 1200 °C, while both the retentivity and the coercivity decrease with increasing the sintering temperature. The permeability values vary with both the sintering temperature and the frequency and the absolute value of the permeability decreased after the natural resonance frequency. The real part of the permittivity was constant within the measured frequency, while the loss tangent values decreased gradually with increasing frequency.     

Synthesis,magnetic properties and microstructure of Ni–Zn ferrite by sol–gel technique

In the study, the Ni–Zn ferrite powder of a Ni_0.3Zn_0.7Fe₂O₄ composition was synthesized by sol–gel route using metal acetates at low temperatures. Both the scanning electron microscope and X-ray diffraction analyses of various gel samples heated at different temperatures were used to identify the reaction stages where the amorphous-gel-to-crystalline phase transition occurred. The electrical, magnetic and microstructural properties of the toroidal cores were studied. It was found that the initial permeability increased with a large frequency band (0.1–31.39 MHz) and the magnetic loss was small. The electrical resistivity was higher as compared to the ones which were obtained by the conventional process. Therefore, well–defined polycrystalline microstructure nickel–zinc ferrite and a short processing time of gel preparation have become the major achievements of this study.     

Structure and magnetic properties of Co-substituted NiZn ferrite thin films synthesized by the sol-gel process

Co-substituted NiZn ferrite thin films, Ni_0.5Zn_0.5Co_xFe_2−xO₄ (0≤x≤0.2), were synthesized by the sol-gel process. The structure and magnetic properties of Ni_0.5Zn_0.5Co_xFe_2−xO₄ ferrite thin films have been investigated. The diffraction peak shifted towards the lower angle and the lattice parameter increased with Co substitution. There is little influence of Co substitution on the microstructure of NiZn ferrite thin films. The saturation magnetization gradually increases with the increase in Co substitution when x≤0.10, and decreases when x>0.10. Meanwhile, the coercivity initially decreases with the increase in Co substitution when x≤0.10, and increases when x>0.10.     

Infrared diffuse reflectance spectra of micropowders of Ni<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> ferrites

The results of experimental studies of the IR diffuse reflectance spectra in the range from 4000 to 50 cm^–1 of Ni_1–xZn_xFe₂O₄ ferrite micropowders with different concentrations of nickel and zinc are presented. The dependence of the intensity of the IR spectra of these ferrites on the changing concentrations of Fe²⁺ and Fe³⁺ cations in ferrites of different compositions is found. The features of change of the reflectance spectra are studied depending on the ferrite compositions, and an interpretation of the observed spectral structures is proposed.     

Effect of electromagnetic field strength on Ni0.35Zn0.65Fe2O4 as performed by combustion synthesis

Ni_0.35Zn_0.65Fe₂O₄ ferrite is prepared through combustion synthesis in the external electromagnetic field. The highest magnetic field strength for the experiment is 1.1 T. Reactions temperatures were monitored by infrared radiation thermometer, the synthesized ferrite prepared in different magnetic fields is analyzed by XRD, SEM, and VSM. The results indicate that the coercivity of ferrite gradually decrease with the increase of magnetization. When the magnetic field strength is 0.54 T, the saturation magnetization is improved up to 56.05 emu/g (42%) as compared to that of ferrite in zero magnetic field. Through SEM analysis of Ni_0.35Zn_0.65Fe₂O₄ ferrite, homogeneous grains of the crystal are observed. With the increase of external magnetic field, the ferrite grain improved. This paper also systematically explores the effect of the electromagnetic field on ferrite by combustion synthesis.     

Structural and magnetic properties of NiCuZn ferrite/SiO2 nanocomposites

Ni_0.53Cu_0.12Zn_0.35Fe₂O₄/SiO₂ nanocomposites with different weight percentages of NiCuZn ferrite dispersed in silica matrix were prepared by microwave-hydrothermal method using tetraethylorthosilicate as a precursor of silica, and metal nitrates as precursors of NiCuZn ferrite. The structure and morphology of the composites were studied using X-ray diffraction and scanning electron microscopy. The structural changes in these samples were characterized using Fourier Transform Infrared Spectrometer in the range of 400-1500 cm⁻¹. The bands in the range of 580-880 cm⁻¹ show a slight increase in intensity, which could be ascribed to the enhanced interactions between the NiCuZnFe₂O₄ clusters and silica matrix. The effects of silica content and sintering temperature on the magnetic properties of Ni_0.53Cu_0.12Zn_0.35Fe₂O₄/SiO₂ nanocomposites have been studied using electron spin resonance and vibrating sample magnetometer.     

Thermal properties of gamma-ray irradiated Co–Zn ferrite

Co-Zn ferrite samples of the system Co_1-xZn_xFe₂O₄ (x = 0, 0.2, 0.3, 0.5, 0.6 and 0.8) were prepared using the usual ceramic double sintering technique. Thermal conductivity and specific heat were measured at different temperatures for different compositions. The effect of Co-60 γ-irradiation dose (10⁶ rad) on the thermal conductivity and specific heat were studied.     

Observation of the exchange spring behavior in hard-soft-ferrite nanocomposite

Nanocomposite of hard (BaFe₁₂O₁₉) and soft ferrite (Ni_0.8Zn_0.2Fe₂O₄) are prepared by the mixing of the individual ferrite components at appropriate ratio and subsequent heat treatment. Initially the microstructure of the individual phases is controlled by suitable processing. We have observed the exchange spring behavior in the soft-hard ferrite composite for the first time by tailoring the particle size of the individual phases and by suitable thermal treatment of the composite. It is found that the exchange interaction dominates over the dipolar interaction for smaller particle sizes of the soft ferrite. The magnetization of the composite showed hysteresis loop that is characteristic of the exchange spring system. This gives experimental proof for some theoretical modeling as well as paves way for developing magnet with higher (BH)_max product based on ferrites.     

Characterization of Ni–Cu mixed spinel ferrite

Crystal structure, X-ray density, porosity, compressive strength of Ni_1−xCu_xFe₂O₄ have been investigated along with scanning electron microscopy (SEM) to study the effect of composition and microstructure on the magnetic and electrical properties. The formation of single-phase ferrite is confirmed by the X-ray diffraction. Tetragonal deformation is observed for the sample of composition x=1, i.e. for pure CuFe₂O₄ Crystal structure for samples of other compositions are face centered cubic (FCC). SEM micrographs exhibit increase in grain size with the increase of copper content. Compressive strength decreases with the increase of Cu. Initial magnetic permeability and saturation magnetization is maximum for the composition of x=0.2, i.e. for Ni_0.8Cu_0.2Fe₂O₄, which can be attributed to the maximum sintered density obtained for this composition. Resistivity decreases with the increase of Cu content.     

Effect of zinc concentration on the structural,electrical and magnetic properties of mixed Mn–Zn and Ni–Zn ferrites synthesized by the citrate precursor technique

Mixed manganese-zinc and nickel-zinc ferrites of composition Mn_0.2Ni_0.8−xZn_xFe₂O₄ where x=0.4$x=0.4$, 0.5 and 0.6 have been synthesized by the citrate precursor technique. Decomposition of the precursor at temperatures as low as 500 °C gives the ferrite powder. The ferrites have been investigated for their electrical and magnetic properties such as saturation magnetization, initial permeability, Curie temperature, AC-resistivity and dielectric constant as a function of sintering temperature and zinc content. Structural properties such as lattice parameter, grain size and density are also studied. The mixed compositions exhibited higher saturation magnetizations at sintering temperatures as low as 1200 °C. While the Curie temperature decreased with zinc content, the permeability was found to increase. The AC-resistivity ranged from 10⁵–10⁷ Ω cm and decreased with zinc content and sintering temperature. The dielectric constants were lower than those normally reported for the Mn–Zn ferrites. Samples sintered at 1400 °C densified to about 94% of the theoretical density and the grain size was of the order of about 1.5 μm for the samples sintered at 1200 °C and increased subsequently with sintering temperature.     

Influences of Fe-deficiency on electromagnetic properties of low-temperature-fired NiCuZn ferrites

Low-temperature-fired NiCuZn ferrites with the formula Ni_0.45Cu_0.2Zn_0.35Fe_2−xO_4−3/2x with x values ranging from 0.00 to 0.25 in steps of 0.05 and sintered at 900 °C have been investigated in the present work. It was found that the content of Fe-deficiency could obviously influence the microstructure, sintering behavior, saturation magnetization, permeability and permittivity spectra properties of the ferrites. The variations were much different from those of the high-temperature-fired NiZn ferrites. And the corresponding mechanisms involved were discussed in detail. All-around consideration, the NiCuZn ferrite with 0.10 Fe-deficiency in composition had the best performances on sintering behavior and electromagnetic properties.     

Study of NiCuZn ferrite powders and films prepared by sol gel method

This paper reports that a series of NiCuZn ferrite powders and films are prepared by using sol-gel method.The effects of raw material composition and the calcinate temperature on magnetic properties of them are investigated.The NiCuZn ferrite powders are prepared by the self-propagating high-temperature synthesis method and subsequently heated at 700 C～1000 C.The results show that NiCuZn ferrite powders with single spinel phase can be formed after heat-treating at 750 C.Powders obtained from Ni 0.4 Cu 0.2 Zn 0.4 Fe 1.9 O 4 gel have better magnetic properties than those from gels with other composition.After heat-treating at 900 C for 3 h,coercivity H c and saturation magnetization M s are 9.7 Oe (1 Oe=80 A/m) and 72.4 emu/g,respectively.Different from the powders,NiCuZn films produced on Si (100) from the Ni 0.4 Cu 0.2 Zn 0.4 Fe 2 O 4 gel formed at room temperature possess high properties.When heat-treating condition is around 600 C for 6 min,samples with low H c and high M s will be obtained.The minimal H c is 16.7 Oe and M s is about 300 emu/cm 3.In comparison with the films prepared through long-time heat treating,the films prepared through short heat-treating time exhibits better soft magnetic properties.