Fe2O4 Ferrites Research Articles

Optical properties of three-dimensional magnetic opal photonic crystals

We have studied the optical properties of opal photonic crystals infiltrated with the M0.35Zn0.65Fe2O4 (M = Ni, Co) ferrites. The crystals consisted of amorphous SiO2 nanospheres. The visible reflectivity spectra of the crystals were used to determine parameters of their photonic band gap and their refractive index.

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

Ni0.35Zn0.65Fe2O4 ferrite is prepared through combustion synthesis in the external electromagnetic field. The highest magnetic field strength for the experiment is 1.1T. 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 0.54T, the saturation magnetization is improved up to 56.05emu/g (42%) as compared to that of ferrite in zero magnetic field. Through SEM analysis of Ni0.35Zn0.65Fe2O4 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.

Low temperature synthesis of nanosized Mn1−x Zn x Fe2O4 ferrites and their characterizations

Nanosized Mn1−x Zn x Fe2O4 (x = 0, 0·1, 0·3, 0·5, 0·6, 0·7, 0·9) mixed ferrite samples of particle size < 12 nm were prepared using the co-precipitation technique by doping the Zn2+ ion impurities. Autoclave was employed to maintain constant temperature of 80°C and a constant pressure. The X-ray analysis and the IR spectrum analysis were carried out to confirm the spinel phase formation as well as to ascertain the cation distribution in the ferrite samples. This clearly points to the fact that the Zn2+ ion’s presence is not restricted to A-site alone for some of the Mn-Zn ferrite series. The real part of a.c. susceptibility measurements clearly indicated the superparamagnetic behaviour of the ferrite samples. There is a systematic decrease in the particle size, Curie temperature and magnetization with the increase in the Zn2+ ion doping, measured using magneto thermal gravimetric analysis (MTGA) and vibrating sample magnetometer (VSM), respectively. The lattice constant is found to be constantly decreasing till x = 0·6 and beyond this an unusual slight increase in the lattice constant is found.

Engineering structural and magnetic properties of Mg0.95Mn0.05Fe2O4 thin films using 200 MeV Au ions

Pulsed laser deposited thin films of Mg0.95Mn0.05Fe2O4 ferrite were irradiated by 200 MeV Au14+ with a maximum dose up to 1 × 1012 ions/cm2. The as-deposited and irradiated thin films are investigated using X-ray diffraction (XRD), Raman Spectroscopy, Field emission electron microscopy (FESEM) and dc magnetization measurements. XRD and Raman spectroscopy measurements reflect the cubic spinel structure of films before and after irradiation. FESEM measurements demonstrate that films are composed of nano rods and nanocrystalline grains. Magnetic hysteresis loop measurements reveal that all the films have ferrimagnetic ordering at room temperature with enhancement in the coercive field and remnant magnetization due to irradiation.

The structural characteristics of Zn-Mn ferrite synthesized by spray pyrolysis

The applicability of IR spectroscopy in studies of the structural characteristics of the ferrite spinel phase was shown for Zn0.5Mn0.5Fe2O4 samples prepared by the pyrolysis of aerosols of aqueous solutions of metal nitrates. The IR spectra of synthesized (ZnMn)Fe2O4 ferrites, Fe2O3, ZnO, MnO, and Mn2O3 pure oxides, and mixtures of these oxides in the region of characteristic M-O stretching vibration and M-O-H bending vibration frequencies were compared to determine the degree of concentration and structural uniformity of the ferrite spinel phase.

Microstructure and Complex Magnetic Permeability of Ni&lt;sub&gt;0.3&lt;/sub&gt;Zn&lt;sub&gt;0.7&lt;/sub&gt;Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; Ferrite

Ni-Zn ferrites are magnetic ceramics that are widely used in electric and electronic components. Among Ni1-xZnxFe2O4 ferrites, Ni0.3Zn0.7Fe2O4 is known to be the one of highest magnetic permeability in lower frequencies. This work is divided into two parts: the first part deals with the influence of sintering temperature and forming conditions on the microstructure of Ni0.3Zn0.7Fe2O4 ferrite. The second part deals with the influence of sintering temperature and environmental variations of temperature on the complex magnetic permeability of such ferrite. The ferrite studied in this work was fabricated by means of the conventional ceramic method. Complex magnetic permeability between 100 kHz – 100 MHz is discussed in relation to sintering temperature. The influence of environmental variations in temperature (-40 oC to +50 oC) on the complex magnetic permeability of the ferrite sintered at 1300 oC is discussed.

Magnetic and Mössbauer spectral studies of nano crystalline cobalt substituted magnesium ferrites (MgxCo1 − xFe2O4)

Nano size Mg x Co1 − x Fe2O4 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) ferrites have been prepared using sol gel method and characterized using i.r., TEM, XRD, magnetic and Mossbauer spectral studies. The particle size of as obtained samples was found to be ~6 nm, which increases up to ~80 nm after annealing at 1,000°C. The saturation magnetization decreases from 80.0–27.5 emu/g on increasing the Mg2 + ions after annealing at 1,000°C due to the diamagnetic behaviour of the Mg2 + ions. Room temperature (RT) Mossbauer spectra (MS) of as obtained samples exhibit a broad doublet, suggesting super paramagnetic nature of the sample. However, annealed samples exhibited a broad sextet, resolved into two sextets, corresponding to tetrahedrally and octahedrally coordinated Fe cations.

Avaliação da microestrutura e das propriedades magnéticas de ferritas Ni-Zn dopadas com cobre

A microestrutura e as propriedades magnéticas das ferritas Ni0,5-xCu xZn0,5Fe2O4 com x = 0,1/0,2/0,3/0,4 mol de cobre, preparadas a partir de pós obtidos por reação de combustão com tamanho de partícula na faixa de 23 a 29 nm, foram avaliadas. Os pós obtidos foram prensados uniaxialmente e sinterizadas a 1000 ºC/2 h. As amostras foram caracterizadas por medidas de densidade e porosidade aparente, difração de raios X, microscopia eletrônica de varredura e medidas magnéticas M-H. Os difratogramas de raios X mostram a presença da fase majoritária cristalina do espinélio inverso em todos os sistemas, e traços da fase secundária Fe2O3 nas amostras com x = 0,1 e 0,4. O aumento do teor de cobre causou um pequeno aumento no tamanho médio de grão (0,65 para 0,68 µm), uma redução da porosidade aparente (33,7% para 6,6%) e redução da magnetização de saturação de 69 para 54 emu/g.

Synthesis, Microstructure and Magnetic Properties of Nanocrystalline Ni-Zn Ferrite by a Modified Wet Chemical Method

Nanocrystalline Ni1-xZnxFe2O4 ferrites with 0 ≤ x ≤ 1 were prepared by sprayingcoprecipitation method. The microstructure was investigated by TG-DSC, XRD, SEM, TEM and BET. Magnetic properties were measured with vibrating sample magnetometer at room temperature. The results showed that uniform and fine nanocrystalline Ni1-xZnxFe2O4 ferrites are obtained. The grain size of sample calcined at 600°C for 1.5h is about 30nm. There are a few agglomerates with average sizes below 100nm. The specific saturation magnetization, Ms, of the sample increases with increasing Zn2+ concent x at room temperature, and the maximum Ms is 66.8 A·m2·kg-1 as the Zn2+ content x is around 0.5mol. As calcining temperature increased from 400°C to 1050°C, the Ms of Ni0.5Zn0.5Fe2O4 ferrite increases from 40.2 A·m2·kg-1 to 75.6 A·m2·kg-1. The coercivity maximum is about 5.97 kA·m-1 as its critical grain size is about 62.0nm. The relation between coercivity and grain size for nanocrystalline Ni0.5Zn0.5Fe2O4 ferrite may be explained based on random anisotropy theory.

Long-wavelength magnetic excitations in the Zn0.55Mn0.45Fe2O4 ferrite

The small-angle neutron scattering energy spectra of the Zn0.55Mn0.45Fe2O4 ferrite are analyzed at different temperatures (both below and above TC ≃ 390 K) and scattering angles. The thermal expansion coefficient α(T) is measured in the temperature range 80–600 K. It is revealed that inelastic neutron scattering is governed not only by spin waves of the Holstein-Primakoff type but also by the substantial contribution of additional long-wavelength magnetic excitations. The physical nature of these low-energy magnetic excitations is discussed.

Local amorphization of atomic structure in Mg0.54Zn0.46Fe2O4 ferrites

The structure of Mg0.54Zn0.46Fe2O4 ferrites has been studied using x-ray diffraction techniques. It is established that high-temperature annealing (T = 1280°C, τ = 0.5–8.0 h) leads to a change in the crystal structure of samples, which is accompanied by their local amorphization.

Effect of Nickel–Cobalt–Zinc Ferrite Filler on Magnetic and Thermal Properties of Thermoplastic Natural Rubber Composites

A sample of Ni0.25Co0.25Zn0.5Fe2O4 ferrite was prepared by a double-staged sintering method in air. Thermoplastic natural rubber (TPNR) was prepared by melt blending of natural rubber (NR), liquid natural rubber (LNR), and high density polyethylene (HDPE) in an internal mixer Brabender Plasticorder PL 2000. Magnetic polymer composites were prepared from the ferrite and TPNR matrix using the same melt blending method at 135°C with mixing rate of 50 r.p.m. for 12 min. The fillers were varied from 5 to 30 weight percent. A uniform dispersion of the filler in the matrix was confirmed by thermogravimetric analysis (TGA). The density of the composites was determined using densitometer MD 200S. Magnetic properties were studied using a vibrating sample magnetometer (VSM) at room temperature (25°C). The results show that magnetization (M), saturation magnetization (MS), remanent magnetization (MR), initial susceptibility (χi) and initial permeability (μi) increase with increasing filler content at all compositions. The composites can be classified as soft magnetic materials as their coercivities are in the range of 30–36 Oe. The differential scanning calorimetric (DSC) results indicate that the glass transition temperature (Tg) and the melting point (Tm) of all the composites are independent of the filler content. The thermal conductivity of the composites was found to be in the range of 0.26 to 0.52 W m−1 K−1.

Carbon Combustion Synthesis of Ferrites: Synthesis and Characterization

Submicrometer powders of Mn−Zn and Ni−Zn ferrites have been produced by carbon combustion synthesis of oxides (CCSO). The self-propagating temperature front had a maximum temperature of a up to 1300 °C and moved at a velocity 3.5 mm/s. Solid-state interactions between the precursors and crystal growth of the crystalline spinel ferrites started in the early period of the combustion and continued in the postcombustion zone. The crystalline Ni0.35Zn0.65Fe2O4 and Mn0.25Zn0.75Fe2O4 ferrites formed using reactant mixtures containing up to 40% carbon and did not require further calcination to get complete conversion. The product particle size increased with increasing carbon content in the reactants mixture and oxygen concentrations. At least twice the amount of required stoichiometric oxygen was needed to generate a stable combustion front and form pure spinel ferrite structure. The emission of carbon dioxide increased the porosity and friability of the products. The synthesized ferrites had soft magnetic properties which compared well with those obtained by other synthesis methods.

Regulation mechanism of EM parameters in natural ferrite and its application in microwave absorbing materials

Electromagnetic (EM) parameters (e′, e″, μ′, μ″) of several M2+Fe2O4 and Fe2O3 type natural ferrites with different geological occurrences are measured in this paper. The measurement results show that EM parameters of a magmatic-occurring natural ferrite is very different from other types occurring from sedimentary-metamorphic iron deposit, hydrothermal vein iron deposit, outer contact of magmatic iron deposit. It has potential to be used as magnetic absorbent in microwave absorbing materials. After mineral separation and concentration, this magmatic-occurring natural ferrite was processed into type A ferrite absorbent. Type A natural ferrite absorbent is a kind of magnetic material with low dielectric constants, high magnetic conductivity and high EM loss. Its EM parameters are e′ = 58.60, e″ = 10.0, μ′ = 1.2–1.5, μ″ = 1.0–1.2, respectively. In order to illuminate the regulation mechanism of EM parameters, we studied the chemical and mineral composition of type A ferrite absorbent. There is high concentration of natural impurities, which regulate the EM parameters of type A ferrite greatly. For comparison, the other types of natural ferrite, single-phase magnetite and two-phase iron minerals (ilmenite and magnetite), have few impurity. Thus regulation mechanism of EM parameters was absent in these ferrites. As a result, the regulation of EM parameters is advantageous to develop type A natural ferrite as excellent absorbent, lowers the reflectivity coefficients and enhances the absorbing efficiency of MAM made from it. Furthermore, the impurities in type A natural ferrite and its effects on EM parameters are very difficult to simulate in the synthesize ferrite. The carbonyl-iron powder is another kind of absorbent that is used extensively in MAM. To compare the absorbing properties of these two absorbent, type A natural ferrite and carbonyl-iron powder were mixed with rubber and processed into microwave absorbing sheets with the same procedures and technics. The measurement results show that the microwave absorbing bandwidth of type A ferrite absorbent sheet material is larger than that of carbonyl-iron powder. The reflectivity coefficient is also improved in the frequency of 8–12 GHz. For the reason of low price and abundant resource, the stable performance in EM properties, type A natural ferrite absorbent is a good substitute of carbonyl-iron powder in MAM.

Synthesis of Fine Mg1−xCaxFe2O4 Ferrite Powder Having High Heat Ability under AC Magnetic Field

Abstract Fine Mg1−xCaxFe2O4 ferrite powders for local thermal coagulation therapy were synthesized by a reverse coprecipitation method. The enhancement of temperature under an AC magnetic field was improved by the partial Ca2+ substitution. A high heat ability was obtained for the samples calcined at 300 and 800 °C.

Low-temperature synthesis of Mn0.2Ni0.2Zn0.6Fe2O4 ferrites by citrate precursor method and study of their properties

Mn0.2Ni0.2Zn0.6Fe2O4 ferrite nano-particles are processed at temperatures as low as 60 °C by the citrate precursor method. The lattice parameter is observed to increase from 8.415 to 8.438 Å with increase in calcination temperature from 60 °C to 500 °C. The increase in saturation magnetization from 19 to 43 emu/gm (A m2/kg) with increase in calcination temperature is attributed to a change in the cation distribution and random canting of particle surface spins in nanosize particles. For improved magnetic properties, samples are sintered at temperatures ranging from 1100–1400 °C. The substantial increase in initial relative permeability (from 150 to 700) with increase in sintering temperature is attributed to an increase in intra-granular domain walls. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis of Nanocrystalline Ni0.5Zn0.5Fe2O4by Aerosol Route and Its Characterization

Nano-size particles of Ni0.5Zn0.5Fe2O4 ferrite were prepared through aerosol route. The solutions of iron, nickel and zinc nitrates were mixed in stoichiometric proportion, passed through a pneumatic nebulizer, to get very fine mist (aerosols), and a furnace at ~600°C in air atmosphere. Through various events in succession, metal atoms form ferrite in air. The average particle size was found to be 16±6 nm which increased to 80±8 nm after annealing at 1000°C. The room-temperature magnetic moment of the sample as obtained and after annealing it at various temperatures indicate that the saturation magnetization increases from 1.80 to 72.8 emu/g, while remanent magnetization increases from 0.28 to 25.0 emu/g. Mossbauer spectrum of the sample at room temperature exhibited a doublet with δ (Fe) = 0.33 mm s−1 and Δ EQ = 0.78 mm s−1 suggesting superparamagnetic nature. However, after annealing at 1000°C this doublet got converted into two magnetic sextets with B = 52.4 T and 49.0 T suggesting increase in particle size on annealing. These observations are in conformity with Transmission Electron Microscope (TEM) and X-Ray Diffraction (XRD) results that the particle size increases after annealing the sample at higher temperatures.

Effects of some ionic substitutions on sintering, structure and humidity sensitivity of MgCu ferrite

The effect of Y3+, La3+, Ga3+, Ti4+ and Nb5+ ions on the physical properties of stoichiometric Mg0.5Cu0.5Fe2O4 ferrite is investigated. The substitutions partially replace the Fe3+ ions and the chemical formula of the investigated ferrites is Mg0.5Cu0.5Fe2−xMe3x/nO4, where Me = Y, La, Ga, Ti and Nb, x = 0 and 0.2, and n is the valence of Me. It is found that the magnetic and electrical properties of MgCu ferrite change with the substituent species. La ions play an important role in increasing the density, while Nb ions favour ferritization at low temperature. Ga substitution increases the electrical resistivity and saturation magnetization, but decreases the density. The humidity sensitivity of the samples with and without substitutions is also investigated. The electrical resistance of Ga-containing ferrite decreases by two orders of magnitude when the relative humidity increases from 33 to 100%. The results are discussed in terms of microstructural changes induced by the substitutions. Conclusions are drawn concerning the optimization of response time to humidity change for the development of ceramic humidity sensors which are more chemically and thermally stable than polymeric sensors. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of Cu substitution on the microstructure and magnetic properties of MnFe2O4 ferrite

The effect of compositional variation on grain size and porosity of Mn1 − xCu x Fe2O4 ferrite, where x = 0.0, 0.25, 0.50, 0.75, 1.00, prepared by standard ceramic method are reported. From microstructure analysis it follows that porosity increases with the Cu concentration where as coercivity increases up to x = 0.50. Above x = 0.5 the decrease in coercivity is explained on the basis of Neel's mathematical model treating the demagnetizing influence of non-magnetic material in cubic crystals. The coercivity, varies inversely with the grain size upto x = 0.5. The decrease in coercivity above x = 0.5 with grain size can be correlated with the inter-granular domain wall movement because of large porosity.

Preparation and characterization of nanosize Mn0.4Zn0.6 Fe2O4 ferrite by citrate precursor method

Abstract Syntheses of nanosize Mn 0.4 Zn 0.6 Fe 2 O 4 particles from metal nitrate solution through citrate precursor method are reported. Soft ferrites have been prepared by a wet chemical process, known as the citrate precursor method, which involves the formation of citrate complexes of the constituent cations. The electrical and magnetic measurements on Mn–Zn ferrite have shown electrical resistivity higher by more than two orders of magnitude compared to that observed for sample prepared by conventional ceramic method and low magnetic losses, making these ferrites specially suitable for high frequency applications. The saturation magnetization, initial permeability and Curie temperature are found to be more in precursor method as compared with ceramic method because of uniformity and homogeneity in grains and smaller grain size in precursor method. Curie temperature and saturation magnetisation has shown initial increase and then decreases with sintering temperature. These changes in properties are explained on the basis of various theories and models.