Preparation of nickel and Ni-Zn ferrite films by thermal decomposition of metal acetylacetonates

Nickel and Ni-Zn ferrite (Ni_1–x Zn _x Fe₂O₄) films were prepared on various substrates (quartz glass, MgO single crystal, etc.) by thermal decomposition of metal acetylacetonates (Ni (acac)₂ · 2H₂O, Zn (acac)₂ · 2H₂O and Fe (acac)₃). Typical decomposition and heat treatment conditions for obtaining a single phase of NiFe₂O₄ film were as follows: evaporation temperature of Ni-Fe complexes: 230°C, the mole concentration of Fe (acac)₃,R (%) = Fe (acac)₃/(Fe (acac)₃ + Ni (acac)₂ · 2H₂O) = 33, substrate temperature: 330 to 550° C, and heat treatment of the as-grown film: 800 to 1000° C, 1 h. Ni_1–x Zn _x Fe₂O₄ films were obtained by controlling the compositionR in Ni-Fe complexes and the evaporation temperature of Zn (acac)₂ · 2H₂O. The Ni-Zn ferrite film at the compositionx = 0.37 (Ni_0.63Zn_0.37Fe₂O₄) gave the maximum saturation magnetization _s = 60 emu g^–1 and the coercive forceHc 25 Oe. These films showed a magnetic anisotropy which makes the magnetization easy parallel to film surface.     

Size variation and magnetic dilution effects on the structure and magnetic properties of cobalt zinc ferrite

Nanocrystalline cobalt zinc ferrites Co_1?xZn_xFe₂O₄ (x?=?0.0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0), have been prepared by employing a precursor combustion method via decomposition of the metal carboxylato hydrazinate precursors. This synthesis technique yields nanoparticles with particle size between 12 and 15 nm as determined from transmission electron microscopy (TEM) studies. The nanoferrites were then sintered at 1000 °C for 15 h to obtain micrometer size ‘bulk’ ferrites in the range of 0.3–0.8 μm. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) Spectroscopy confirmed the formation of the mixed ferrites without any impurities. Addition of non-magnetic ion like Zn²⁺ into the crystal structure of cobalt ferrite leads to a prominent change in the size, structure and properties. The saturation magnetization values (M_S) increases upto x?=?0.4 and then decreases with further increase in Zn concentration. A maximum M_S value of 90.85 emu/g and 79.59 emu/g for x?=?0.4 was obtained for the sintered and nanoferrite sample, respectively. The lower M_S and higher coercivity (H_C) values for nanoferrites than the sintered ferrites exhibited a strong dependence on the particle size due to the cation distribution and surface effects. The Curie temperature (T_C) was found to decrease appreciably with the reduction in particle size and with increasing concentration of Zn. The room temperature Mössbauer spectra showed a transition from ferrimagnetic to a paramagnetic state with increasing zinc concentration along with superparamagnetic features which was in corroboration with VSM studies.

     

Reactivity of oxygen-deficient Mn(II)-bearing ferrites (Mn x Fe3-x O4-δ, O⩽x⩽1, δ>0) toward CO2 decomposition to carbon

The reduction of CO₂ to carbon was studied in oxygen-deficient Mn(II)-bearing ferrites (Mn _x Fe_3-x O_4-, Ox1, >0) at 300 °C. They were prepared by reducing Mn(II)-bearing ferrites with H₂ gas at 300°C. The oxygen-deficient Mn(II)-bearing ferrites showed a single phase with a spinel structure having an oxygen deficiency. The decomposition reaction of CO₂ to carbon was accompanied by oxidation of the oxygen-deficient Mn(II)-bearing ferrites. The decomposition rate slowed when the Mn(II) content in the Mn(II)-bearing ferrites increased. A Mössbauer study of the phase changes of the solid samples during the H₂ reduction and CO₂ decomposition indicated the following. Increases in the Mn(II) content lowered the electron conductivity of the Mn(II)-bearing ferrites. Increases in the oxygen deficiency, , contributed to an increase in electron conductivity and suggested that electron conduction due to the electron hopping determines the reductivity of CO₂ to carbon by the donation of an electron at adsorption sites.     

Magnetic properties of NiCuZn ferrite nanoparticles synthesized using egg-white

A new process to prepare single-phase nano-sized ferrites, Ni_0.8−xCu_0.2Zn_xFe₂O₄ with x = 0.1-0.7, was developed using egg-white precursors. TG measurement showed that, the precursors must be calcined at 550 °C. XRD patterns indicated the formation of single-phase cubic ferrites with particle size in the range 28.7-48.4 nm. TEM image gave particle size agrees well with that estimated using XRD. FT-IR spectroscopy showed the characteristic ferrite bands. Hysteresis loops measurements exhibited an increase in the saturation magnetization value (M_s) up to zinc content of 0.2 followed by unexpected decrease, which suggests the preference of Zn²⁺ ions to occupy octahedral sites. The decrease in the coercivity (H_c) with increasing zinc content is attributed to the lower magneto-crystalline anisotropy of Zn²⁺ ions compared to Ni²⁺ ions. Temperature dependence of the molar magnetic susceptibility (χ_M) suggested a ferrimagnetic behavior of the investigated samples and showed a decrease in the value of the Curie temperature (T_C) with increasing zinc.     

Synthesis and characterization of Ni1−xZnxFe2O4 spinel ferrites from tailored layered double hydroxide precursors

In this paper, a series of pure Ni_1 − xZn_xFe₂O₄ (0 ≤ x ≤ 1) spinel ferrites have been synthesized successfully using a novel route through calcination of tailored hydrotalcite-like layered double hydroxide molecular precursors of the type [(Ni + Zn)_{1 − x − y}Fe_y²⁺Fe_x³⁺(OH)₂]^x+(SO₄²⁻)_x/2·mH₂O at 900 °C for 2 h, in which the molar ratio of (Ni²⁺ + Zn²⁺)/(Fe²⁺ + Fe³⁺) was adjusted to the same value as that in single spinel ferrite itself. The physico-chemical characteristics of the LDHs and their resulting calcined products were investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and Mössbauer spectroscopy. The results indicate that calcination of the as-synthesized LDH precursor affords a pure single Ni_1 − xZn_xFe₂O₄ (0 ≤ x ≤ 1) spinel ferrite phase. Moreover, formation of pure ferrites starting from LDHs precursors requires a much lower temperature and shorter time, leading to a lower chance of side-reactions occurring, because all metal cations on the brucite-like layers of LDHs can be uniformly distributed at an atomic level.     

Magnetic and electrical properties of hot-pressed Ni-Zn-Li ferrites

The magnetic properties of Ni-Zn ferrites have been upgraded by preparing hot-pressed Ni_0.4Zn_0.6–2xLi_xFe_2+xO₄ ferrites wherein 2xZn²⁺ ions have been substituted byxLi¹⁺ andxFe³⁺ ions. This results in an increase of saturation magnetization, Curie temperature and dielectric constant, whereas resistivity and initial permeability are reduced. The values of saturation magnetization, Curie temperature and dielectric constant are improved due to hot pressing in which grain growth and densification are controlled simultaneously. The variations of saturation magnetization and Curie temperature can be explained by the preferential site occupancy of Li¹⁺ and Ni²⁺ ions at the tetrahedral site, sublattice magnetization with canted spin structure, and magnetic exchange interactions. The inferences drawn from the bulk magnetic properties of these ferrites conform with the conclusions drawn from variations of internal magnetic field, obtained from Mössbauer studies of these samples. The decrease in d.c. resistivity due to substitution of Li¹⁺ ions is attributed to increased hopping due to formation of Fe²⁺ and Ni³⁺ ions.     

Optimization of synthesis of nickel-zinc-ferrite from oxalates and oxalato hydrazinate precursors

Ferrites, Ni _x Zn_1–x Fe₂O₄ are being synthesised by five different methods, namely (a) autocatalytic decomposition and air sintering of mixed-metal oxalato hydrazinate prepared by a solution method, (b) decomposition of oxalato hydrazinate precursors prepared by the under hydrazine method and sintering in air, (c) decomposition of mixed metal oxalates prepared by coprecipitation method in air and sintering in air, and (d) decomposing the oxalates in a controlled atmosphere (N₂ + H₂O + air) and sintering in (i) air and (ii) an N₂ atmosphere. The decomposition of the precursors and formation of ferrite was studied by differential thermal analysis (DTA), total weight loss studies, infrared, chemical analysis, and X-ray diffraction (XRD). The saturation magnetization values of all the decomposed products and at various stages of sintering were measured. TheX-T curves were plotted to find out the Curie temperature of the sintered ferrites and the shape of these curves was compared. The saturation magnetization was plotted against the concentration of solid solution of nickel ferrite with zinc addition. If -Fe₂O₃ is taken as one of the constituents in synthesis of ferrite, the spinelization is easy, it is obsesrved in our studies that -Fe₂O₃ type phase is formedin situ in methods (a), (b) and (d). Among all five methods, method (b) is the easiest.     

Nanocrystalline spinel Ni0.6Zn0.4Fe2O4: A novel material for H2S sensing

Nanocrystalline powders of Ni_1?xZn_xFe₂O₄ (0 ≤ x ≤ 0.5) mixed ferrites, with cubic spinel structure and average crystallite size ranging from 28 to 42 nm, were synthesized by the ethylene glycol mediated citrate sol–gel method. The structure and crystal phase of the powders were characterized by X-ray diffraction (XRD) and microstructure by transmission electron microscopy (TEM). The response of prepared Ni_1?xZn_xFe₂O₄ mixed ferrites to different reducing gases (liquefied petroleum gas, hydrogen sulfide, ethanol gas and ammonia) was investigated. The sensor response largely depends on the composition, temperature and the test gas species. The Zn content has a significant influence on the gas-sensing properties of Ni_1?xZn_xFe₂O₄. Especially, Ni_0.6Zn_0.4Fe₂O₄ composition exhibited high response with better selectivity to 50 ppm H₂S gas at 225 °C. Incorporation of palladium (Pd) further improved the response, selectivity and response time of Ni_0.6Zn_0.4Fe₂O₄ to H₂S with the shift in the operating temperature towards lower value by 50 °C. The enhanced H₂S sensing properties can mainly be attributed to the selectivity to oxidation of H₂S and noble metal additive sensitization. Furthermore, the sensor exhibited a fast response and a good recovery.     

Effect of W ion doping on magnetic and dielectric properties of Ni-Zn ferrites by “one-step synthesis”

W-doped Ni-Zn ferrites with a nominal composition of Ni_0.5Zn_0.5W_xFe_2−xO₄ (where x = 0, 0.02, 0.04, 0.06, and 0.08) were prepared by one-step synthesis through the incorporation of WO₃ into the raw powders. The magnetic and dielectric properties of the as-prepared Ni-Zn ferrites were investigated. All samples have a typical spinel cubic structure. With increasing amount of W ions doped, the lattice constant decreases, while the grain size increases. The density and diameter shrinkage of the samples raise with small amount of W ions doped, but drop down with large amount of W ions doped. However, an uneven abnormal growth and closed pores were observed when too much of WO₃ was added. The saturation magnetization of the samples increases with small amount of W ions doped, but decreases with large amount of W ions doped, and the coercivity shows an opposite trend. The Curie temperature raises with increasing amount of W ions doped. Both the real and imaginary parts of permeability of the ferrites decrease with increasing amount of W ions doped, while the natural resonance changes very little. Both the dielectric constant and dielectric loss present a decrease with small amount of W ions doped, but increase with large amount of W ions doped.     

Dielectric and magnetic properties of ZnCo-substituted X hexaferrites prepared by citrate sol-gel process

Ba₂Zn_2−xCo_xFe₂₈O₄₆ hexaferrites with x=2.0, 1.6, 1.2, 0.8, 0.4 and 0.0 were prepared by citrate sol-gel process. They were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetry-differential scanning calorimetry (TG-DSC). The frequency-response complex dielectric constant and complex permeability of Ba₂Zn_2-xCo_xFe₂₈O₄₆ sintered at 1000-1200 °C had been investigated in the range from 100 MHz to 6 GHz. The pronounced natural resonance phenomena were observed in μ″ spectrum for the samples annealed at 1100 and 1200 °C. The natural resonance frequency of Ba₂Zn_2−xCo_xFe₂₈O₄₆ ferrites was intensively affected by the substitution of Zinc ion and annealing temperature.     

Electrical conduction in γ-irradiated and unirradiated Fe3O4, CdFe2O4 and Co x ZN1−x Fe2O4 (0 ⩽x ⩽ 1) ferrites

The electrical conductivity of -irradiated and unirradiated finely divided ferrites of composition Fe₃O₄, CdFe₂O₄ and Co _x Fn_1–x Fe₂O₄(0 x 1) was studied in a nitrogen atmosphere as a function of temperature. Fe₃O₄, ZnFe₂O₄ and CdFe₂O₄ showed n-type conduction, whereas CoFe₂O₄ showed p-type conduction. For Co _x Zn_1-x Fe₂O₄ it was found that the type of conduction varies with the composition of ferrites. The electrical conduction in Fe₃O₄, and Co _x Zn_1–x Fe₂O₄(0 x 1) was explained by a hopping mechanism, whereas the conduction in ZnFe₂O₄ and in CdFe₂O₄ is interpreted on the basis of the transfer of charge carriers through cation vacancies present on octahedral sites. The effect of -irradiation on the conductivity, activation energy, charge carriers and the conduction mechanism is discussed.     

Bulk magnetic properties of Co-Zn ferrites prepared by the co-precipitation method

The alternating current (a.c.) susceptibility versus temperature and magnetization measurements are reported for the disordered spinel ferrite system Zn _x Co_1-x Fe₂ O₄ prepared by a wet chemical method before and after high temperature annealing. The low field a.c. susceptibility measurements indicate that the low temperature synthesis of wet prepared Co-Zn ferrites aids the formation of spin-clusters and thereby increases the magnetic inhomogeneity. The X-ray analysis shows that the samples are single phase spinels and the variation of lattice constant with zinc concentration deviates from Vegard's law [1]. The high temperature annealing changes the wet prepared ferrites into the ordered magnetic structure of the ceramic ferrites.     

Structure and magnetic properties of Ni0.11ZnxCo0.03Fe2.86-xO4 ferrite films deposited on Ag-coated glass substrates by wet chemical method

Ni_0.11Zn_xCo_0.03Fe_2.86-xO₄ spinel ferrite films with x = 0.00, 0.23, 0.34, 0.43 and 0.51 were prepared on Ag-coated glass substrates from nitrate and dimethylamine borane solution at 80 °C. The Ni_0.11Zn_xCo_0.03Fe_2.86-xO₄ ferrite films are singe-phased spinel ferrite. With the Zn content x increasing from 0 to 0.51, the lattice constant of the ferrite films increases from 0.8383 to 0.8425 nm. The Ni_0.11Zn_0.51Co_0.03Fe_2.35O₄ film is about 500 nm thick and composed of uniform equiaxed granules of about 40–50 nm. The Raman spectrum analysis indicates that the Zn²⁺ ions occupy the A sites. Saturation magnetization increases with x increasing from 0 to 0.35, reaches a maximum value of 460 kA/m at x = 0.35, and then decreases with further increase of x. Coercivity decreases monotonically from 12.3 to 1.7 kA/m with x increasing from 0 to 0.51. The change in magnetic properties may be explained by the decrease of A–B interactions and the anisotropy constant due to the incorporation of non-magnetic Zn²⁺ ions.     

Cation distribution in nanocrystalline Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel ferrites

We have studied the cation distribution over the tetrahedral and octahedral sites in the spinel structure of nanocrystalline Ni _x Zn_{1 ? x} Fe₂O₄ ferrites prepared by spray pyrolysis. ⁵⁷Fe Mössbauer spectroscopy data for the ferrites demonstrate that, depending on the composition of the materials, the tetrahedral site may accommodate only Fe³⁺ (inverse spinel, x ≥ 0.4) or both Fe³⁺ and Zn²⁺ cations (mixed spinel, x = 0 and 0.2), which accounts for the fact that the composition dependence of the unit-cell parameter for the ferrites deviates from Vegard’s law.     

Effect of sintering on the magnetization behaviour of Mg x Zn(1 −x)Fe2O4 system

Magnesium zinc ferrites with the general formula Mg _x Zn_{(1 −x)}Fe₂O₄ were prepared by the standard ceramic technology route involving double sintering. X-ray analysis was carried out to confirm the single-phase formation as well as to calculate the lattice parameters. Two sets of samples were prepared by sintering the samples at 1100°C for 15 and 30 h respectively. The high-field loop tracer was used to measure the hysteresis parameters. It is observed that the sintering conditions effectively modify the magnetization characteristics of these ferrites.     

Magnetic ordering in Cu-Zn ferrite

The variation of magnetization with temperature of the Zn _x Cu_1–x Fe₂O₄ system has been obtained between 300 K and the Néel temperature at a constant magnetic field of 5.57×10⁵ A m^–1 for x=0 to 0.8. The observations indicate the existence of a Yafet-Kittel (Y-K) type of magnetic ordering in the mixed ferrites. A molecular field analysis of the Y-K spin-ordering using a three-sublattice model is shown to explain the experimental data satisfactorily. For the sake of verification, Néel temperatures of Cu-Zn ferrites were also determined from Mössbauer studies.     

Magnetization and initial permeability studies of Nd3+ substituted Zn-Mg ferrite system

Polycrystalline ferrites, Zn _x Mg_1−x Fe_2−y Nd _y O₄ (x=0·00, 0·20, 0·40, 0·60, 0·80 and 1·00;y=0·00, 0·05 and 0·10), were prepared by standard ceramic method. The compositions, on characterization by X-ray diffraction, showed formation of single phase cubic spinels. Magnetic study of the compositions showed increase in magnetic moment,nβ, with Zn²⁺ concentration up tox=0·4 and a decrease thereafter. This was attributed to the existence of canted spin. The compositions forx=0·8 and 1·0 showed paramagnetic behaviour at and above room temperature. The substitution of Nd³⁺ ion caused reduction in the magnetic moment and Curie temperatures. Substituted Nd³⁺ ion showed its occupancy on octahedral (B) site. The dependence of the initial permeability was studied in the temperature range 298 K-700 K. This μ_i-T curve reflects the positive temperature coefficient of initial permeability for the compositionsx≤0·4 andy=0·00. On substitution of Nd³⁺ ion (i.e.y=0·05 and 0·10), the μ_i-T curves flatten, showing almost temperature independence of initial permeability. This is explained by positive contribution to the anisotropy constant,K ₁, by substituted rare-earth, Nd³⁺ ion.     

Structure and magnetic properties of NixZn1?xFe2O4 thin films prepared through electrodeposition method

Nanocrystalline nickel–zinc ferrites Ni _x Zn_1−x Fe₂O₄ thin films have been studied and synthesized via electrodeposition–anodization process. Electrodeposited (NiZn)Fe₂ alloys were obtained from non-aqueous ethylene glycol sulphate bath. The formed alloys were electrochemically oxidized (anodized) in aqueous (1 M KOH) solution, at room temperature, to the corresponding hydroxides. The parameters controlling the current efficiency of the electrodeposition of (NiZn)Fe₂ alloys such as the bath composition and the current density were studied and optimized. The anodized (NiZn)Fe₂ alloy films were annealed in air at different temperatures ranging from 850 to 1000 °C for different times from 1 to 4 h. The change in the crystal structure, crystallite size, microstructure, and magnetic properties of the produced ferrites were investigated using X-ray diffraction patterns (XRD), scanning electron microscope (SEM) and vibrating sample magnetometer (VSM). The results revealed the formation of Ni–Zn ferrites thin films were formed. The crystallite sizes of the produced films were in the range between 32 and 81 nm. High saturation magnetization of 48.81 emu/g was achieved for Ni_0.5Zn_0.5Fe₂O₄ thin film produced after annealing the alloy at 850 °C for 4 h. The annealing process of the oxidized alloy anodization process was found to be first order reaction. The activation energy of the crystallization of Ni–Zn ferrite was found to be 62 KJ/mol.     

Low temperature synthesis of nanosized Mn<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 and their characterizations

Nanosized Mn_1−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.     

Crystallographically oriented W-type barium hexaferrite BaZn2Fe16−xScxO27 with high squareness ratio

A series of oriented W-type barium hexaferrites of composition BaZn₂Fe_16?xSc_xO₂₇ (where x?=?0, 0.1, 0.2, 0.3, 0.4) has been synthesized by conventional ceramic methods and characterized by XRD, SEM, EDS, FTIR, and VSM. In this work, the effect of trivalent Sc substitution for trivalent Fe on the structure and magnetic properties of Zn₂W has been studied. The XRD results showed that all the specimens consisted of single phase of W-type ferrites. EDS analysis confirmed that the content of Ba, Zn, Sc, and Fe were closed to the elemental composition of BaZn₂Fe_16?xSc_xO₂₇. The SEM revealed the hexagonal platelet-like structure of the BaZn₂Fe_16?xSc_xO₂₇ and the average grain sizes of all samples remain in the range of single domain dimension (0.5 µm?~?1 µm). The SEM also demonstrated that the samples maintained high crystallographic c-axis texture when Sc³⁺ content was less than 0.4. The SEM results were consistent with magnetic hysteresis loops. As the function of Sc substitution, the squareness ratio (M_r/M_s) ranged from 0.78 to 0.82, which was critical for self-biased application. Moreover, the magnetocrystalline anisotropy field (H_a) decreased. The saturation magnetization (M_s) increased from 53.61 to 54.04 emu/g as x increased from 0 to 0.1, and then it decreased to 46.50 when x > 0.1. The samples showed other excellent magnetic properties, such as appropriate anisotropy field (~?9 kOe),and high coercive fields (~?1300 Oe). Therefore, the prepared Zn₂W ferrites are suitable candidate for the microwave devices operated at low frequency.