X-ray, IR and bulk magnetic properties of Cu1 + x Mn x Fe2–2x O4 ferrite system

The structural, IR and magnetic properties of the mixed spinel Cu_{1 + x} Mn _x Fe_2-2x O₄ (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) system have been investigated by means of X-ray diffraction, Infrared spectroscopy, magnetization and a.c. susceptibility measurements. X-ray results confirm single-phase spinel structure for all the concentrations. The structure of CuFe₂O₄ is tetragonal and changes to cubic for x = 0.1 to 0.4. For x = 0.5 and 0.6 the structure become tetragonal. The lattice parameter and X-ray density are deduced and their variation with Mn⁴⁺ concentration is studied. The cation distribution derived from the X-ray diffractometry data was found to agree very well with the cation distribution obtained from magnetization measurements. X-ray intensity calculations indicate that Mn⁴⁺ occupy only octahedral [B] sites and Cu²⁺ and Fe³⁺ ions occupy both octahedral [B] and tetrahedral (A) sites. The infrared spectra obtained at room temperature in the range 200–800 cm^–1 showed two absorption bands. The force constants have been obtained from IR data. The variation of the saturation magnetization per formula unit as a function of Mn⁴⁺ content x has been satisfactorily explained on the basis of Neel's collinear spin ordering model for all values of x. The Curie temperature T _C determined from a.c. susceptibility data decreases with increase of Mn⁴⁺ concentration x, suggesting decrease in ferrimagnetic behaviour.     

Magnetic and crystallographic properties of Fe1−x(Cu0.5In0.5)xCr2S4 spinels

Fe_1?x(Cu_0.5In_0.5)_xCr₂S₄ spinel powders with 0 ≤ x ≤ 1 were prepared. Their lattice constant (a_o) increases linearly with x from a_o = 0.9995 nm for x = 0 to 1.0065 nm for x = 1. Cu⁺, In³⁺, and Fe²⁺ ions occupy tetrahedral A sites of the spinel lattice and Cr³⁺ ions the octahedral B sites. Spinels with 0 ≤ x ≤ 0.82 are ferrimagnets with Curie temperatures decreasing from 171 K for x = 0 to 116 K for x = 0.82. Spinels with 0.82< x≤ 1 are antiferromagnets with Néel temperatures between 31 K and 36 K. The magnetic moment of Fe_0.18Cu_0.41In_0.41Cr₂S₄ spinels was determined by susceptibility measurements to be 5.85 $\text{μ}{}_{\mathrm{<mtext>B</mtext>}}\text{molecule}$, which is equal to the calculated spin-only magnetic moment.     

Study of the oxidation kinetics of finely-divided magnetites. II - Influence of chromium substitution

The oxidation kinetics of magnetites substituted by chromium (Fe²⁺Fe³⁺_2?xCr³⁺_x)O^2?₄ (0 < x < 2) into γ(Fe³⁺_1?yCr³⁺_y)₂O^2?₃, (x = 3y), which is a metastable phase, was found out to be ruled by the law of diffusion, under variable working conditions, of vacancies generated at the surface. The chemical diffusion coefficient is a function of the substitution ratio, crystallite size and the number of vacancies in the spinel lattice. Contrary to magnetites substituted by aluminum, the activation energy varies irregularly with the substitution ratio.     

Microscopic and macroscopic magnetic properties of MgAl<Subscript>x</Subscript>Cr<Subscript>x</Subscript>Fe<Subscript>2 − 2x</Subscript>O<Subscript>4</Subscript> spinel ferrite system

In order to study the effect of co-substitution of Al^{3 +} and Cr^{3 +} for Fe³⁺ in MgFe₂O₄ on its structural and magnetic properties, the spinel system MgAl _x Cr_xFe_{2 ? 2x}O₄ (x = 0.0–0.8) has been characterized by X-ray diffraction, high field magnetization, low field a.c. susceptibility and ⁵⁷Fe Mössbauer spectroscopy measurements. Contrary to the earlier reports, about 50% of Al^{3 +} is found to occupy the tetrahedral sites. The system exhibits canted spin structure and a central paramagnetic doublet was found superimposed on the magnetic sextet in the Mössbauer spectra (0.5 > x > 0.2). Thermal variation of a.c. susceptibility exhibits normal ferrimagnetic behaviour.     

Structural and Magnetic Studies on Chromium substituted Ni-Zn Nano Ferrite Synthesized by Citrate Gel Auto Combustion Method

Nano crystalline Ni_0.5Zn_0.5Cr_xFe_2?xO₄ particles with x varying from 0.00 to 0.25 in steps of 0.05 have been synthesized through citrate gel autocombustion method. When Ni_0.5Zn_0.5Fe₂O₄ nano particles were annealed at 1000 °C, the crystallite size increased while the lattice constant decreased slightly. For, the Cr³⁺ substituted samples annealed at 1000 °C, the variation in lattice constant, bondlengths, M_e-M_e distances and other structural parameters have been attributed to the dissimilarity in the ionic radius of the displaced (Fe³⁺) ion and the substituted (Cr³⁺) ion. Thermal studies indicated the autocombustion process which is an exothermic reaction between the nitrates salt solutions and the citric acid took place at about a temperature of 400 °C for Ni_0.5Zn_0.5Fe₂O₄. The M-H loops for all samples indicated a soft ferrite nature for all samples. The non-saturated hysteresis loop and high coercivity for the as prepared Ni_0.5Zn_0.5Fe₂O₄ nano particles has been attributed to the core-shell structure of the fine particles. When annealed at 1000 °C the saturation magnetization of Ni_0.5Zn_0.5Fe₂O₄ nano particles increased and attained the bulk value (70emu/gm). The specific saturation magnetization has been observed to decrease with increasing Cr³⁺ substitution and is ascribed to the reduction in the predominant A-B exchange interaction mechanism. By considering the site preferences cations a suitable distribution of the cations among the A & B-sites has been proposed for Ni_0.5Zn_0.5Cr_xFe_2?xO₄ nano particles annealed at 1000 °C and has been verified using the X-ray diffraction line intensity calculations. The FT-IR spectra of the annealed ferrite powders showed two significant absorption bands in the wave numbers around 400 cm^?1 & 580 cm^?1 and an additional shoulder at 360cm^?1. The position and width of the bands have been observed to vary with Cr³⁺ substitution. The results of IR spectra are in support of the proposed cation distribution.     

Effect of Cr doping on the phase structure,surface appearance and magnetic property of BiFeO<Subscript>3</Subscript> thin films prepared via sol–gel technology

Multiferroic BiFeO₃ (BFO) and BiFe_1?xCr_xO₃ (BF_1?xC_xO, x?=?0.05, 0.1, 0.15 and 0.2) thin films were successfully synthesized on silicon (111) substrates via sol–gel technology. The effect of Cr³⁺ ion doping on the phase structure, surface morphology, valence states for Fe element and magnetic property was investigated. The introduction for simulation images of ionic space arrangement was to better comprehend the substitution site and superexchange interaction between the Fe³⁺ (Cr³⁺) and O^2? ions. The phase structure of Cr-doping thin films transition from rhombohedral to orthorhombic was confirmed by the X-ray diffraction (XRD) and Raman measurements, and the obtained results also demonstrated that the Cr³⁺ ions successfully located in Fe²⁺ and Fe³⁺ ions sites of BFO lattice system. The Field Emission Scanning Electron Microscopy (FESEM) patterns clearly exhibited that the grains sizes were remarkably decreased by Cr³⁺ ions doping, and the surfaces textures got glossier and smoother judging from the Atomic Force Microscope (AFM) images. The dense surface structure can restrict the O^2? ions escaping from the lattices system, which is beneficial for the release of magnetic property due to superexchange interaction of improvement. It was found that the saturation magnetization (Ms) was significantly linearly increased accompanying the adding of Cr-doping due to destroying of spatial modulation helical structure and enhancing of superexchange interaction. Moreover, the Hall-effect results firstly revealed that the carrier concentration and mobility rate played significant roles in magnetoelectric effect behaviors.     

Structural and Magnetic Properties of Co(Cr1−y Al y )2O4 (y=0.0–0.2) Compounds

We present the structural and magnetic properties of Co(Cr_1?y Al _y )₂O₄ compounds prepared by the sol-gel technique for y=0.00,0.025,0.05,0.075,0.10,0.15 and 0.20. It has been observed that non-magnetic Al⁺³ substitution for Cr⁺³ enhances the magnetization at low temperatures compared to that of the parent compound. With increase in Al concentration spiral magnetic transition observed at around 24 K becomes less prominent, without affecting the ferrimagnetic transition temperature at around 97 K. The saturation magnetization values after subtracting the paramagnetic contribution vary from 0.036 μ_B/f.u to 0.376 μ_B/f.u. The enhanced ferromagnetic interaction and resultant magnetization could be explained in terms of decrease in Cr⁺³–O–Cr⁺³ bond angle with increase in doping concentration.     

Magnetic properties of the mixed spinel Co1+x Si x Fe2−2x O4

The structural and magnetic properties of the mixed spinel Co_1+x Si _x Fe_2?2x O₄ system for 0·1≤x≤0·6 have been studied by means of X-ray diffraction, magnetization, and Mössbauer spectroscopy measurements. X-ray intensity calculations indicate that Si⁴⁺ ions occupy only tetrahedral (A) sites replacing Fe³⁺ ions, and the added Co²⁺ ions substitute for (B) site Fe³⁺ ions. The Mössbauer spectra at 300 K have been fitted with two sextets in the ferrimagnetic state corresponding to Fe³⁺ at the A and B sites, forx≤0·3. The Mössbauer intensity data shows that Si possesses a preference for the A site of the spinel. The variation of the saturation magnetic moment per formula unit measured at 300 K with the Si content, is explained on the basis of Neel’s collinear spin ordering model forx≤0·3 which is supported by Mössbauer, and X-ray data. The Curie temperature decreases nearly linearly with increase of the Si content, forx=0·1–0·6.     

Microscopic and Macroscopic Magnetic Properties of the MgAl x Cr x Fe2 − 2x O4 Spinel Ferrite System

To determine the influence of the substitution of Al³⁺ and Cr³⁺ for Fe³⁺ in MgFe₂O₄ ferrites on the structural and magnetic properties, the MgAl _x Cr _x Fe_{2 – 2x} O₄ (x = 0.0–0.8) spinel systems were studied by using the X-ray diffraction analysis, magnetization in strong fields, magnetic susceptibility in weakly variable electric fields, and Mössbauer spectroscopy. Unlike previous investigations, it was discovered that a half of Al³⁺ occupies tetragonal positions. The system forms a noncollinear spin structure and a central paramagnetic doublet is superimposed over the magnetic sextet in the Mössbauer spectrum (0.5 > x > 0.2). The dependence of the magnetic susceptibility on temperature reveals the normal ferromagnetic properties of the material.     

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.     

A crystallization conditions study of the Ti‐doped barium hexaferrite powders synthesized with the glass crystallization technique for microwave applications

For microwave applications Titanium doped M‐type hexagonal ferrites have been synthesized by means of glass crystallization technique varying the crystallization parameters and the melt doping concentrations. The chosen melt dopings were x = 5.4 and 7.2 mole‐% TiO₂ with the following basic composition (mole‐%): 40 BaO + 33 B₂O₃ + (27‐x) Fe₂O₃ + x TiO₂. We have studied the dependencies between the magnetic properties, the valence of the iron ions in the glasses and the powders, the formation of new dielectric phases and the microwave absorption. After the Ti⁴⁺ ions substitutions, the magnetocrystalline anisotropy changed, this effect was observed in the static magnetic properties (_JH_C and M_S) measured using a vibration sample magnetometer. Furthermore the Ti⁴⁺ ions preferably occupy mainly the 2a as well as slightly the 2b sites in the lattice of the barium hexaferrite, which are studied using Mössbauer spectroscopy. Besides, the X‐ray diffraction studies proved that the formation of the ferrimagnetic (BaFe_12‐xTi_xO₁₂) and dielectric (BaTi₆O₁₃) phases are dependent on the crystallization parameters. The controlled influencing of lattice sites occupation and of the Fe²⁺ content in the ferrimagnetic phase as well as the controlled formation of the dielectric phase rate during the annealing are possibilities to optimize the microwave absorption of Ti‐doped barium hexaferrite powders synthesized by glass crystallization technique.     

Magnetic properties of Nd-Y<Subscript>3</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> nanoparticles

Nb³⁺-substituted garnet nanoparticles Y_3−xNd_xFe₅O₁₂ (x = 0.0, 0.5, 1.0, 1.5, and 2.0) were fabricated by a sol-gel method and their crystalline structures and magnetic properties were investigated by using X-ray diffraction (XRD), thermal analysis (DTA/TG), and vibrating sample magnetometer (VSM). The XRD patterns of Y_3−xNd_xFe₅O₁₂ have only peaks of the garnet structure and the sizes of particles range from 34 to 70 nm. From the results of VSM, it is shown that when the Nd concentration x ( 1.0, the saturation magnetization of Y_3−xNd_xFe₅O₁₂ increases as the Nd concentration (x) is increased, and gets its maximum at x = 1.0, but when x ( 1.0, the saturation magnetization decreases with increasing the Nd concentration (x), this may be due to the distortion of the microstructure of Y_3−xNd_xFe₅O₁₂, which leads to the decrease of the effective moment formed by Fe³⁺. Meanwhile, it is observed that with the enhancement of the surface spin effects, the saturation magnetization rises as the particle size is increased.     

A.c. susceptibility study of CaCl<Subscript>2</Subscript> doped copper-zinc ferrite system

Polycrystalline soft ferrites, Zninx Cu_1−x Fe₂O₄ (x = 0.30, 0.50, 0.70, 0.80 and 0- 90), doped with controlled amount of calcium chloride (CaCl₂) were prepared by standard ceramic route and studied for a.c. susceptibility. X- ray diffraction studies of the compositions reveal formation of single- phase cubic spinel. The values of lattice constant increase as doping percentage of CaCl₂ increased from 001% to 005% and afterwards decrease slightly. The presence of chlorine ions is confirmed by absorption peak in far IR spectra near 650 cm^{− 1} for all the samples. The variation of a.c. susceptibility with temperature shows the existence of single domain structure forx = 0.3 and exhibits transition from single domain to multidomain structure with increased Ca²⁺ contents from 0.01 to 0.1%. The composition,x = 0.5, shows multidomain structure independent of Ca²⁺ content. The samples forx = 0.70, 0.80 and 0.90 show paramagnetic behaviour at and above room temperature.     

Microstructure and magnetic transition in Cr-substituted Mg–Zn spinel ferrite powders prepared via hydrothermal method

Mg–Zn ferrite powder specimens with the nominal composition Mg_0.5Zn_0.5Cr _x Fe_2?x O₄ (x = 0.0–1.0 with steps of 0.2) were synthesized via hydrothermal method. It is found that all the specimens exhibit a typical spinel structure, and the lattice parameter increases slightly with x, which confirms the substitution of Cr³⁺ for Fe³⁺. The average crystallite size first increases but then decreases with x, which is not the same as the results in previous reports on spinels. The particles in specimens are the aggregate of small nanoscale crystallites, and roughly aggregate more extensively with the increasing Cr content. With the increase of x, the saturation magnetization decreases rapidly, and it becomes more and more difficult for the specimens to magnetize to saturation. The increase of coercivity from 0.6 (x = 0.0) to 32.3 kA m^?1 (x = 1.0) shows a transition from a typical soft magnetic behavior to a hard magnetic behavior with the increase of Cr content, which was not reported before.     

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.     

Sur le mecanisme de substitution des cations Sn4+ et Fe2+ dans la magnetite

The distribution of Fe²⁺ and Fe³⁺ in Fe_3?xSn_xO₄ solid solution has been established from saturation magnetization measurements. From these results it may be suggested that Fe²⁺ in A site destabilizes Fe³⁺ in A site at the expense of Fe²⁺ in B site.     

Ti-Ca-Al-doped YCrO3 pigments: XRD and UV-vis investigation

Compounds based on the YCrO₃ perovskite structure, doped with Al, Ti and Ca, were studied by XRD and DRS, aiming at assessing their potential as green ceramic pigments. Nine samples were synthesized by the ceramic route according to the Y_1−yCa_yCr_1−x−yAl_xTi_yO₃ stoichiometry, where 0 < x < 0.5 and 0 < y < 0.2. Doping affected the phase composition (minor amounts of Y₂O₃ and Y-Ti oxides were found) and induced a series of structural rearrangements in perovskite without symmetry changes, involving unit cell parameters, metal-oxygen distances and distortion of cation sites. Different trends were observed varying x and y. Optical properties were influenced by changes in perovskite crystal structure and stoichiometry. In particular, the oxidation of Cr³⁺ to Cr⁴⁺ had a deleterious effect on its green colour, turning to gray-brown. The occurrence of Cr⁴⁺ in the perovskite lattice was required to balance the replacement of Y³⁺ by Ca²⁺ ions not fully compensated by the designed coupled substitution of Ti⁴⁺ for Cr³⁺.     

Magnetic properties of magnesium-cobalt ferrites synthesized by co-precipitation method

The alternating current (a.c.) low field susceptibility vs temperature, magnetization and⁵⁷Fe Mössbauer effect measurements are reported for the spinel solid solution series Mg _x Co_1?x Fe₂O₄ synthesized by a wet-chemical method before and after high temperature annealing. The observed features for the wet samples, such as the coexistence of paramagnetic doublet and magnetic sextets in Mössbauer spectra and lower saturation magnetization values confirm small particle ferrite behaviour. Especially, Mössbauer spectra of wet samples reveal the presence of superparamagnetic particles which exist simultaneously with ferrimagnetic regions in the materials well supported by a.c. susceptibility data. The high temperature annealing changes the wet-prepared ferrites into the ordered magnetic structure of ceramic ferrites.     

Le systeme V1−xFexO2: Proprietes structurales et magnetiques

The system V_1?xFe_xO₂ (x ? 0.020) was investigated by X-ray diffraction, DTA, magnetic susceptibility measurements and Mössbauer spectroscopy. The phase diagram and the magnetic properties are similar to those of the V_1?xCr_xO₂ and V_1?xAl_xO₂ systems previously studied. In oxygen deficient materials appears a Magnéli type shear phase, the Fe³⁺ ions occupying the shear planes.     

Structural and Magnetic Properties of (Al/Mg) Co-doped Nano ZnO

The doped ZnO systems Zn_1?x?y Mg _x Al _y O (ZMAO) (x=0, 0.05, 0.1 and y=0, 0.05 and 0.1) were prepared as polycrystalline nanoparticle by a simple sol–gel process. Structural and microstructural analyses were carried out applying X-ray diffraction (XRD) and Rietveld method. Analysis showed that Mg²⁺ and Al³⁺ replace Zn²⁺ substitutionally yielding ZMAO single phase. Replacing Zn⁺² affects the lattice parameters in opposite ways, the parameter c decreases while a increases with an overall decrease in the ratio c/a, which deviates the ZMAO lattice gradually from the wurtzite hexagonal structure. The magnetization versus temperature was measured with zero-field cooled (ZFC) and field cooled (FC) at different applied fields. Also, measurement of magnetization versus applied field was carried out at different temperatures. The system exhibits ferromagnetic properties at room temperature. The saturation magnetization increases as Al doped amount increases.