O4 Ferrites Research Articles

Infrared absorption spectroscopic study of Nd3+ substituted Zn-Mg ferrites

Compositions of polycrystalline Zn x Mg1−x Fe2−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) ferrites were prepared by standard ceramic method and characterized by X-ray diffraction, scanning electron microscopy and infrared absorption spectroscopy. Far infrared absorption spectra show two significant absorption bands, first at about 600 cm−1 and second at about 425 cm−−1, which were respectively attributed to tetrahedral (A) and octahedral (B) sites of the spinel. The positions of bands are found to be composition dependent. The force constants,K T andK O, were calculated and plotted against zinc concentration. Compositional dependence of force constants is explained on the basis of cation-oxygen bond distances of respective sites and cation distribution.

Susceptibility Characterization of Phase Transition in Ti0.2Fe2.8O4 Ferrite

Titanomagnetite Ti 0.2 Fe 2.8 O 4 has been prepared by floating zone technique and its single crystal spinel structure confirmed by the inductively coupled plasma spectrometry method. Its magnetic behavior and its temperature dependence have been determined by VSM magnetometry. Particular attention has been paid to the measurements around the order temperature. This type of magnetic study has been performed in other ferrites such as nickel ferrite, but there is no previous result for this single crystal ferrite-like material. An analysis of the results using modified Arrot plots and the Kouvel-Fisher method has allowed us to evaluate the Curie temperature and the critical exponents for the spontaneous magnetization, β, and the zero field susceptibility, y. Critical exponents obtained suggest that the short-range interactions dominate in the critical region.

Sintering Behaviour and Properties of LiZn Ferrite Doped with PbO

Lead oxide (PbO) has been investigated as sintering aid for Li0.3Zn0.4Fe2.3O4 ferrite, prepared by conventional method, between 800 and 1100 °C. Sintering experiments were carried out with various small amounts of PbO, between 0 and 4 wt%. Due to its low melting point, liquid bridges between grain boundaries appear and material transport assisted by liquid phase favors sinterability at lower temperatures. Dense sintered specimens (95% of theoretical density) were obtained using 1.2 wt% PbO at relatively low temperature of 1050 °C, that is impossible without PbO. The densification behavior and physical properties of PbO-doped LiZn ferrite are closely related to microstructural changes caused by PbO. It was evidenced significant growth of grain sizes without compromising desirable material properties, except for electrical resistivity.

The Dependence of the Magnetoelastic Properties of Zn?Mn Ferrites on Their Magnetocrystalline Properties

This paper presents results of an investigation on the magnetoelastic properties of ferrites. Two ferrite samples with different magnetocrystalline anisotropy were investigated: Mn0.51Zn0.44Fe2.05O4 high permeability ferrite and Mn0.70Zn0.24Fe2.06O4 ferrite for power application. The influence of stresses on hysteresis loops and permeability of the investigated ferrites is presented. It is shown that in Mn-Zn ferrites with λs ≈ 0 the Villari point occurs for σ ≈ 0 and that these ferrites exhibit for |σ| ≫ 0 considerable magnetoelastic sensitivity, in spite of their small |λs| value. It is shown that the influence of stresses on the magnetic parameters of the materials should be taken into consideration in the case of construction of ferrite components.

Preparation and characterization of CoxMnmCrnNikFe3-(x+m+n+k)O4 ferrites and optimization of their structural and magnetic properties by Taguchi experimental design

Powders of spinel type ferrite, CoxMnmCrnNikFe3-(x+m+n+k)O4, have been prepared by a coprecipitation method. The spinel type ferrite was obtained by pre-sintering at 200–1000 °C for 30–120 min in air. In order to optimize the conditions to prepare ferrites of the highest crystallinity, factors such as metal content, temperature and time of reaction, temperature and time of pre-sintering and concentration of NaOH were considered and optimized with Taguchi experimental design and regression analysis. Crystallinity was investigated by XRD analysis. Variation of crystallinity, the average size of crystallites, lattice constant, density and the initial permeability were studied against Mn, Cr and Ni contents. Characterization studies were made on the basis of IR, TG, UV-vis, EDX-SEM, XRF, AAS, XRD, and BET. It was found that the average size of crystallites is decreased when the crystallinity and initial permeability are increased. Some of the results obtained for the final samples were as follows: The X-ray density was 5.34 g cm-3, the lattice constant, a=0.83662 nm, the average size of crystallites was 87.9 nm, the BET surface area was 1.4 m2g-1 and the initial permeability was 36.14.

Magnetic Properties of Ti-Doped Ultrafine CoFe 2 O 4 Powder Grown by the Sol Gel Method

Ultrafine Ti-doped CoFe2O4 powders, Ti0.2Co1.2Fe1.6O4, are fabricated by the sol gel method and their magnetic and crystallographic properties depending on annealing temperature are investigated by X-ray diffractometer, Mossbauer spectroscopy, and a vibrating sample magnetometer. With X-ray diffraction and Mossbauer spectroscopy measurements, the formation of nanocrystallized particles is confirmed when Ti0.2Co1.2Fe1.6O4 ferrite is annealed at 473 K. The samples annealed between 673 and 773 K, show that the ferrimagnetic phase and paramagnetic phase coexist. That is, the sample annealed at 673 K has the 18% ferrimagnetic phase, and the sample annealed at 773 K has the 88% ferrimagnetic phase. But the samples annealed at and above 873 K have only a single-phase spinel structure and behave ferrimagnetically. The Neel temperature of our sample is 643 K, which is lower than that of pure cobalt ferrite powder. The magnetic behaviour of Ti0.2Co1.2Fe1.6O4 powder shows that an increase in the annealing temperature yields a decrease in the coercivity and, in contrast, an increase in the saturation magnetization. The maximum coercivity and the saturation magnetization of Ti0.2Co1.2Fe1.6O4 ferrite powder are 1.56 kOe and 62.6 emu/g, respectively.

Effect of the spin-orbit interaction of Ni2+ ions with a triplet orbital ground state on the magnetostriction of NiFe0.5Cr1.5O4 ferrite

The magnetization σ and the longitudinal (λ∥) and transverse (λ⊥) magnetostrictions of the NiFe0.5Cr1.5O4 ferrite containing the tetrahedral ions Ni2+ with the triplet orbital ground state have been investigated for the first time at a temperature of 4.2 K in fields up to 55 kOe. It is revealed that the NiFe0.5Cr1.5O4 ferrite exhibits an anomalously large magnetic anisotropy (Hc=12.5 kOe) and magnetostrictions (λ∥≈−870×10−6 and λ⊥≈800×10−6). In strong fields, the magnetostrictions λ∥ and λ⊥ are found to be anisotropic in character; i.e., the susceptibility Δλ∥p and Δλ⊥p. The conclusion is drawn that the studied compound is characterized by two paraprocesses: one paraprocess in the B sublattice has an exchange nature, and the second process in the A sublattice is due to the spin-orbit interaction of NiA2+ ions.

Microstructure and magnetic properties of Li-Co ferrites

Abstract The microstructure and magnetic properties of Li0.5−x/2 Cox Fe2.5−x/2 O4 (where x=0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7) ferrites have been reported. The ferrite samples were prepared by standard double sintering ceramic technique and structural analysis was carried out using X-ray diffraction. The lattice parameter (a) increases with increase in x. The average grain size obtained from SEM micrographs shows an initial decrease up to x=0.4 and then it increases. The saturation magnetization (Ms) and initial permeability (μi) decrease with cobalt content up to x=0.4 and then a small increase is observed in case of μi. This has been attributed to high positive value of anisotropy constant (k1) for Co2+. The Curie temperature of the samples decreases with increase in the content of cobalt (x) due to reduction in the A–B interaction. The initial permeability of the samples remains almost independent of frequency in the frequency range studied viz. 1 kHz to 1 MHz. The measurement of AC susceptibility with temperature reveals the single domain (SD) state of the samples.

Combined effect of partial calcination and sintering condition on low loss Mn-Zn ferrite

In order to achieve highly densified lower loss Mn-Zn ferrite materials, various powder processing routes have been under investigation. In this report, a lower sintering temperature with lower oxygen partial pressure and proper attrition milling duration are suggested. From the previous study, a partial calcination procedure was studied and an optimum partial calcination level was found. Accordingly, Mn0.71Zn0.22Fe2.07O4 ferrite was prepared by \({\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{$2$}}\) calcination with small amounts of CaCO3, SiO2, Nb2O5 and SnO2. The partially calcined ferrites were made by calcining the mixture of the whole amount of ZnO and \({\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{$2$}}\) amount of Fe2O3 and Mn3O4 and sintering the mixture of the calcined powders and the remaining \({\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{$2$}}\) of Fe2O3 and Mn3O4. Initially, from the 40 min secondary milling and the \({\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{$2$}}\) partial calcination, lower temperature (1300°C) sintered samples showed a power loss of ∼340 mW cm−3 at 90°C. Secondly, several milling durations showed secondary milling had a more profound effect on magnetic properties than primary milling. The 20 min primary and 90 min secondary milling showed lower core loss around 320 mW cm−3 at 1300°C and 1250°C, suggesting the sintering temperature could be reduced to 1250°C. Thus, the proper sintering condition of lower oxygen partial pressure at 1250°C was studied. As a result, lower loss with higher density was realized.

Effects of Addition of Na2O, Sb2O3, CaO, and ZrO2 on the Properties of Lithium Zinc Ferrite

Some effects of CaO, Na2O, Sb2O3, and ZrO2 additions on Li0.3Zn0.4Fe2.3O4 ferrite were studied to improve its density and other material properties. The densification behavior of the ferrite depended on the amount and type of additive. A relative density of ∼98.5% was achieved with the addition of CaO. The grain size decreased with the addition of Na2O, CaO, and Sb2O3. The permeability and electrical resistivity increased with additives. CaO remarkably increased resistvity, whereas, ZrO2 increased permeability. Na2O and Sb2O3 increased the Curie temperature, whereas CaO and ZrO2 decreased it. These effects were attributed to mainly additive segregation on the grain boundaries, which suppressed grain‐size development during the sintering of lithium zinc ferrite.

Effect of Al3+-substitution on the electrical and magnetic properties of Ni1·05Sn0·05Fe1·9O4 ferrites

The effect of Al3+-substitution on d.c. resistivity, dielectric constant, initial permeability, saturation magnetization and Curie temperature has been studied for Ni1·05Sn0·05Al x Fe1·9−x O4 ferrites, whereinx varies from 0 to 0·5 in steps of 0·1. The d.c. resistivity increases slowly forx⩽0·3 followed by a rapid increase forx>0·3. The variation is explained on the basis of Verwey hopping as well as polaron hopping mechanisms, and the dilution effect of Al3+ ions. The behaviour of dielectric constant is attributed to interfacial polarization and follows the Koops model. The saturation magnetization and the Curie temperature decrease continuously with increasing Al3+ content and are explained using the concepts of sublattice magnetization and exchange interactions. The decrease in initial permeability is attributed primarily to decrease in saturation magnetization. The dispersions in initial permeability and magnetic loss tangent are also discussed.

Thermoelectric power in Gd3+-substituted Cu-Cd ferrites

Polycrystalline Cd x Cu1−x Fe2−y Gd y O4 ferrites fory=0·0 and 0·1 were prepared by ceramic technique. X-ray diffractograms of powder samples show cubic symmetry withx⩾0·2 fory=0·0 and 0·1, while compositions withx=0·0 fory = 0·0 and 0·1 are tetragonal. The thermopower measurements for Gd3+-undoped ferrites in the temperature range 300 K to 788 K shown-type conductivity forx⩾0·2. The substitution of Gd3+ changedn-type conductivity of the compositions top-type. The mobilities calculated show decreasing trend on Gd3+ substitution. The values of activation energy ΔE and drift mobilityE d suggest polaron formation in substituted samples. The conduction mechanism is explained on the basis of localized model and formation of Gd3++Fe2+ stable pairs at B site and Cu1++Fe3+ at A site.

Effect of substitution of In3+ ions on the electrical and magnetic properties and m�ssbauer study of Mg0.9Mn0.1In x Fe2?x O4 ferrites

The effect of substitution of diamagnetic In3+ ions on the electrical and magnetic properties of Mg-Mn ferrites was studied in the ferrite series Mg0.9Mn0.1 In x Fe2−x O4 wherex varied from 0–0.8 in steps of 0.1. The incorporation of In3+ ions in place of Fe3+ ions resulted in an increase of lattice parameter owing to the larger size of the substituted ions, and an increase of d.c. resistivity owing to reduction of Verwey's hopping mechanism. It also resulted in improvement of saturation magnetization and produced a marked increase in the value of initial permeability, thus upgrading the bulk magnetic properties of these ferrites. These bulk magnetic properties improve due to substitution of diamagnetic In3+ ions,x, up to 0.5 only, whereas they deteriorate for a higher content of In3+ ions. The variations of saturation magnetization have been explained on the basis of modified cation distribution and their magnetic interactions. A large increase in the value of initial permeability has been attributed to its dependence onM s and magnetocrystalline anisotropy constant. A comparison of bulk magnetic properties with the inferences drawn from Mossbauer studies of these samples shows a similar trend. It is concluded that the substitution of In3+ ions,x, up to 0.5 in Mg-Mn ferrites results in the production of a hyperfine field at A as well as B sites, followed by ferromagnetic relaxation and paramagnetic transition for higher concentrations of In3+ ions. These variations have been explained on the basis of the effect produced by In3+ ions on the magnetic interactions, supertransferred hyperfine fields and domain-wall oscillations.

Dependence of magnetic properties of Mn-Zn ferrites on the degree of calcination

Mn0.764 Zn0.187 Fe2.049 O4 and Mn0.687 Zn0.272 Fe2.041 O4 ferrites containing 0.05 wt% CaO, 0.05 wt% SnO2 and 0.05 wt% V2O5 were prepared by conventional methods using manganite (γ-MnOOH) as a source of MnO. The partial-calcined ferrites were made by calcining the mix consisting of total amount of ZnO and one third or half amount of Fe2O3 and MnO required for the formation of the Mn-Zn ferrites and sintering the mix consisting of the previously calcined mix and the remaining two thirds or half the amount of Fe2O3 and MnO. Calcination was conducted at 900 °C for 2 h and sintering at 1335 °C for 1 h. The secondary maximum in permeability (SMP) of uncalcined ferrites was shifted to higher temperature and does not clearly appear in the initial permeability against temperature plot. The values of initial permeability of the uncalcined ferrites increase rapidly with increasing temperature up to 100 °C, then either increased gently or levelled off. In the working temperature range, 80 to 100 °C, the values of all the ferrites, regardless of the degree of calcination were well above 2000. Above 80 °C, the uncalcined and one-third calcined ferrites had the lowest and the second lowest loss factor values (<3 × 10−6), respectively. A dense and homogeneous structure of smaller grains with small pores was prevalent in the uncalcined and one-third calcined ferrites.

Charge Carrier Transfer in Ferrite Spinels Affected by Magnetic Ordering

AbstractThe temperature dependences of the conductivity of single crystals of nickel‐zink Ni0.39Zn0.61Fe2.00O4 (Tc = 380 K) and manganese‐zink Mn0.66 Zn0.27 Fe2.07 O4 (Tc = 464 K) ferrites are studied in the temperature range 78 to 550 K. Measurements of thermoelectromotive force show that all the samples investigated have n‐type conductivity. In the region of the phase transition to the magnetically‐ordered state the logarithm of conductivity depends anomalously on the inverse temperature with increasing conductivity.

Effect of double-soak sintering on magnetic properties of MgxMnyAlzFe3?(x+y+z)O4 ferrites

A study was made to determine the effects of a double-soak sintering process on the saturation magnetization, Curie temperature and hysteresis properties of an Al-substituted MgMn-microwave ferrite. This process decreases saturation magnetization and magnetic induction, while increasing the loop squareness and the Curie temperature. The double-soak sintering process improves the properties of the ferrite for application in a low-microwave-frequency band (i.e. S-band) latching phase shifter. This improvement could not be achieved by increasing the Al3+ content, as this tends to reduce the Curie temperature, and thus decreases the thermal stability. The double-soak sintering process, however, enables a composition to be used which initially has a slightly higher saturation magnetization than the desired value.

Oxidizing Reaction in Ni&lt;sub&gt;0.7&lt;/sub&gt;Fe&lt;sub&gt;2.3&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; Ferrite

Oxidizing reaction of Ni0.7Fe2.3O4 ferrite in a gaseous flow was studied by measuring cation valence, saturation magnetizaton and crystal lattice constant of the samples heattreated at various temperatures between 530° and 1250°C in air, in pure nitrogen, and in nitrogen containing 5 or 0.5vol% oxygen. It was found that oxidation makes the amount of Fe2+, saturation magnetization and crystal lattice constant decrease, and that there are two kinds of reactions for oxidation of the ferrite. One of them is an oxidation in which α-Fe2O3 is separated as the second phase by the amount nearly corresponding to the excess oxygen given at the heat-treatment of the sample. The other is an oxidation in which the second phase is unseparated. By the latter oxidizing reaction the spinel structure of the ferrite becomes to contain cation vacancies on its B-sites (octahedral sites). To calculate the crystal lattice constant of the spinel containing cation vacancies, application of “the mean size of cation vacancies” was suggested.The two reactions proceed as follows:Ni0.72+Fe0.32+Fe23+O4+δ/2O2→3δFe2O3+1/aNi0.7a2+Fe(0.3-2δ)a2+Fe(2-4δ)a3+O4(Oxidation in which the second phase is separated)→1/bNi0.7b2+Fe(0.3-2δ)b2+Fe(2+2δ)b3+CV(3/4)δbO4(Oxidation in which the second phase is unseparated)where, a=1/(1-2δ), b=4/(4+δ), and CV is the cation vacancy.

The influence of oxidation degree on the redistribution rate of cations in Mg0.9Fe2.1O4 ferrite

The influence of oxidation degree on the redistribution rate of cations in Mg0.9Fe2.1O4 ferrite

Independent cluster model of ferromagnetic resonance linewidth broadening in Mn x Fe3−x O4 ferrites

The previously developed simple theory of ferromagnetic resonance linewidth broadening due to the thermal processing of the material, that was observed e.g. in Mn-ferrites, is reconsidered using the recently published independent-cluster model of two-phase systems. The composition, temperature, and angular dependences of the linewidth are explained, in good qualitative agreement with experiment. An estimate of cluster size necessary for the explanation of the observed effect is given. The theory seems to confirm the assumed connection between clustering and linewidth broadening for slowly cooled samples.

ИССЛЕДОВАНИЕ НОРМАЛЬНЫХ ФЕРРИТОВ-ШПИНЕЛЕЙ С ПОМОЩЬЮ ЭФФЕКТА МQDССБАУЭРА

The investigations of Mossbauer spectra of Zn[Fe2]O4 and Cd[Fe2]O4 ferrites were performed in the temperature range from 4.2 to 300°K. In the antiferromagnetic phase (below 10 and 10.5°K for Zn and Cd ferrites respectively) a double structure of effective magnetic fields was observed. This fact points to the presence of the magnetic superstructure as was recently suggested by K. P. Sinha and A. P. B. Sinha [J. Phys. Soc. Japan17 (1962), Suppl. B-1, 218]. The constants of hyperfine interaction of Fe3+ ions in octahedral sublattice were also determined. The following values of the quadrupole splittings at 300°K were obtained: 0.35 mm/sec and 0.81 mm/sec for Zn-ferrite and Cd-ferrite respectively. The extrapolation of the effective magnetic fields to 0°K gives an approximate value of 490 kOe for both ferrites.