Proposed Cation Distribution Research Articles

Role of Mn2+ ion in the optimization of the structural and dielectric properties of Co–Zn ferrite

Mn-substituted Co–Zn ferrite nanomaterials with the general form Co0.8−x Mnx Zn0.2 Fe2O4 (x = 0.0, 0.1, 0.2, and 0.3) were prepared using the coprecipitation method. Based on X-ray diffraction, it can be confirmed that all samples have a single-phase cubic structure with an average crystallite size ranging from 23.46 to 32.66 nm. In addition, the lattice parameter increased from 8.32 to 8.37 Å. In this study, the theoretical density was calculated, and the Fourier-transform infrared spectra of the prepared samples were investigated. Further, the cation distribution of the system was estimated. The proposed cation distribution was confirmed by calculating the theoretical lattice parameter and comparing it with the experimental lattice parameter. We conducted transmission electron microscopy to confirm the obtained particle size. At room temperature, the electrical measurements of the prepared samples were performed using the LCR circuit as a function of frequency up to 5 MHz. In this study, we obtained enhanced dielectric properties by substituting Mn ions in the Co–Zn ferrite. As the Mn concentration increases, the AC resistivity of the samples increases. Consequently, the dielectric loss decreases, and its minimum value can be observed at x = 0.2, making the Co–Mn–Zn ferrite suitable for applications in the microwave frequency range. The results show that all dielectric properties exhibit a normal behavior with frequency. We obtained an improvement in the dielectric properties of the prepared samples, making them suitable for use in high-frequency applications due to the substitution by Mn ions.

Structural, Magnetic, and Optical Studies of Ni–Mg Ferrites Synthesized by Polyol Method

Magnesium and nickel‐substituted ferrites belong to an important class of spinel ferrites with wide variety of applications. Herein, preparation and characterization of pure, single‐phase Ni–Mg ferrites using a cost‐effective method, which yield high‐quality nanosized particles with good chemical homogeneity, are reported. A series of NixMg(1−x)Fe2O4 nanocrystalline powders (x = 1,0.75,0.5,0.25,0) is prepared using polyol method and a detailed investigation on the effect of dopant substitution on microstructural magnetic as well as optical properties is conducted. The as‐prepared samples are subsequently characterized using X‐ray diffractometer (XRD), X‐ray photoelectron spectroscopy (XPS), Fourier‐transform infrared spectroscopy (FTIR), Field‐emission scanning electron microscope (FESEM), Brunauer, Emmett, and Teller (BET), Mossbauer spectroscopy, Vibrating sample magnetometer (VSM), and UV–visible diffuse reflectance spectroscopy. Rietveld refinement confirms the single‐phase cubic structure with Fd‐3m (227) space group of NixMg(1−x)Fe2O4 series. The cation distribution can be represented as [Mg(1−x−y)Fe(δ)]A[Mg(x)Ni(y)Fe(2−δ)]BO4. FTIR bands at the finger print region of ferrites and Mossbauer analysis confirms the proposed cation distribution from Rietveld refinement. The magnetic nature is confirmed from Mossbauer and VSM analysis. In VSM, the saturation magnetization of the samples exhibits an increasing trend with nickel substitution. The optical studies of the series NixMg(1−x)Fe2O4 are conducted by UV–visible diffuse reflectance spectroscopy.

Evidence of Superparamagnetism in nano phased copper doped nickel zinc ferrites synthesized by Hydrothermal Method

Nanophased Ni0.65Zn0.35CuxFe(2–2x/3)O4, ferrites with lower dopant concentrations i.e., for x ranging from 0 to 0.05 in steps of 0.01 have been synthesized using hydrothermal route. Structural characterization is carried out by powder X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and far –IR spectroscopy (FTIR). XRD confirms the formation of pure spinel structure of Ni-Cu-Zn ferrites. Proposed cation distribution is able to explain properties of Cu2+ doped Ni-Zn ferrites. Variation of lattice constant a is explained through occupancy of dopant ions both in tetrahedral (A)-sites and octahedral (B)-sites. Crystallite size, determined for high intensity (3 1 1) peak using Debye-Scherrer method, W-H plots and Size-Strain plots, is found to exhibit an overall decreasing trend (62.75–31.56 nm) with x. Observed FTIR absorption bands at 400–600 cm −1 confirm the formation of ferrite structure. Vibrating Sample magnetometer (VSM) studies reflect upon improved magnetic properties mainly due to adopted hydrothermal synthesis route, replacement of Fe3+ ions with very low dopant concentrations of Cu2+ ions of the order of 0.01%. Non-linear variation of Ms with x is attributed to Y-K angles and crystallite size. Highest value of M s of 73.25 emu/gm is obtained for x = 0.02. Relatively higher values of Ms coupled with lower values of H c in nanophased Ni-Cu-Zn ferrites make them usable for high frequency and power applications. Lower values of coercivity (Hc) observed in the range of 32–80 Oe reveal the soft magnetic nature of these ferrites. Existence of single domain particles witnessed from variation of Hc with D indicate the superparamagnetic nature and confirms that these materials can be used for biomedical applications.

Co-Cd nanoferrite for high frequency application with phenomenal rise in DC resistivity

The communication concentrates on the possibility of developing a composition suitable for high-frequency operation as a magnetic core through an extensive understanding of the cation distribution of cobalt ferrite containing cadmium. The samples having a composition, Co1-xCdxFe2O4, were processed by the sol–gel method using polyvinyl alcohol (PVA) as a chelating agent and characterized by standard techniques. Substantial growth in specific saturation magnetization from 82.2 emu/g to 99 emu/g and DC resistivity from 1.54 × 106 Ω-cm to 1.34 × 1011 Ω-cm, requisite characteristics for high-frequency application were provided with increasing concentration of cadmium. The average crystallite size ranging from 5.7 nm to 17 nm has been estimated by X-ray diffraction patterns using Williamson-Hall analysis. The proposed cation distribution based on saturation magnetization data established the amount of cadmium occupying the tetrahedral sites of spinel lattice, which was well supported by the variation of DC resistivity with cadmium. The unparalleled matching between the experimentally observed lattice constant and that provided by the proposed cation distribution as well as Rietveld refinement confirms the amounts of cadmium entering tetrahedral and octahedral sites of the spinel lattice. All the samples of cadmium substituted cobalt ferrite assure their suitability for high frequency application with the pertinent properties.

An Accurate Low Temperature Cation Distribution of Nano Ni-Zn Ferrite Having a Very High Saturation Magnetization

Structural and magnetic properties of nanocrystalline Ni0.65Zn0.35Fe2O4 synthesized by sol-gel method have been analyzed using various characterization techniques. The single-phase spinel structure and crystallite size have been obtained from X-ray diffraction (XRD). The experimentally observed high specific saturation magnetization, 176 emu/g at 10 K, has been discussed in terms of core-shell contributions based on spin canting of nano Ni0.65Zn0.35Fe2O4 with the help of infield Mossbauer study at 5 K. The proposed cation distribution relied upon infield Mossbauer spectra and the Rietveld analysis of the neutron diffraction and XRD data and provides an insight to improve the properties of this material suitable for high-frequency applications.

Enhanced magnetic properties at low temperature of Mn substituted Ni-Zn mixed ferrite doped with Gd ions for magnetoresistive applications

Mn substituted Ni-Zn mixed ferrites doped with Gd3+ ions belonging to the series Mn0.2Ni0.6Zn0.2GdxFe2-xO4 (x=0.00, 0.02, 0.04, 0.06) have been synthesized by sol-gel method. The effect of Gd3+ substitution on the structural, cationic distribution, magnetic and dielectric properties has been investigated in detail. X-Ray analysis reveals formation of single phase spinel cubic ferrite nanoparticles with no secondary phases. The average crystallite size estimated using Scherrer’s relation lie in the 11–13 nm range with the size decreasing with increase in Gd ion content. Lattice constants calculated from proposed cation distribution are in close agreement with reported values. Surface morphology studies using SEM and HRTEM show spherical shaped nanoparticles which are slightly agglomerated. EDX analysis confirms the expected stoichiometry. The valence state of materials was characterized by XPS. The dielectric variations with frequency and temperature were analyzed using a precision impedance analyzer. The relative permittivity and dielectric loss show an increasing trend with Gd concentration up to x=0.04 and then decrease with further increase in doping. Increasing the temperature increases the relative permittivity. Measurements of magnetic parameters using VSM were performed at room temperature and at 77K. M−H loops recorded have shown that the synthesized ferrite nanoparticles exhibit soft ferrimagnetism. The saturation magnetization and coercivity decrease with increase in Gd doping. The samples possess high magnetization and coercivity at low temperatures. A remarkable difference in the magnetic moments estimated from measured magnetic parameters and from the cation distribution over A and B sites on the basis of Neel’s two sublattice model of ferrimagnetism was noted in all the samples. Higher Y-K angles obtained imply their potential use in synthesis of magnetoresistive (MR) materials.

Observation of anomalous site occupancy in Ni-Co-Cu-Cr ferrite system synthesized by sol-gel method

Anomalous variation in cation distribution in chromium doped Ni-Co-Cu-Cr ferrites synthesized by sol-gel method has been observed the formation of spinel structure and explained with the help of DTA/TG and X-ray diffraction analysis. Error estimated between theoretical and calculated lattice parameter based on proposed cation distribution is found be in range of 0.0014% to 0.00005%, which confirms the cation distribution predicted for the present samples. In this present work, it appears that most of the cobalt and 50% of nickel ions are observed to occupy A-sites instead of B-sites of spinel lattice, which is a drastic deviation from the reports published till date. The g-value have been found to be lower for x = 0.02 concentration as observed from ESR analysis. Fourier transform infrared spectroscopic techniques (FTIR) show no variation in peak position of vibrational bands, indicates the uniform bond length in the spinel ferrite, even for different concentration of chromium. This is further confirmed by the bond length calculation using empirical formulas and experimental lattice parameters, showing least error for shared and unshared ion for tetrahedral or octahedral sites.

Structural, magnetic and dielectric properties of Gd3+ substituted NiFe2O4 nanoparticles

NiGdxFe2-xO4 nanoparticles with x = 0.0, 0.03, 0.05, 0.07, and 0.10 were synthesized by co-precipitation method and effect of Gd3+ substitution on various properties of nanocrystalline NiFe2O4 has been studied. Formation of single phase cubic mixed spinel structure is confirmed by X-ray diffraction and Raman spectroscopy and cations distribution has also been proposed from Rietveld refined data. Room temperature Mössbauer spectra showed two ferrimagnetic Zeeman sextets with one superparamagnetic doublet. Octahedral site occupancy of Gd3+ ions in these nanoparticles is suggested by Mössbauer parameters. Within the framework of X-ray photoelectron spectroscopy analysis, the ratio of cation concentration at tetrahedral and octahedral sites has been found to be consistent with proposed cation distribution. Magnetic measurements at room temperature exhibit the reduction in the saturation magnetization from 36 emu/gm to 4.9 emu/gm for x = 0.0 to 0.10 samples. The discrepancy in measured and calculated magnetic moment may be ascribed to the nonzero Yafet–Kittel angles of B site spins, which weaken A–B interaction. The coercivity decreases from 121 Oe to 48 Oe for x = 0.0 to 0.07 samples and again increases to 153 Oe for x = 0.10 sample. The degree of inversion calculated by Raman analysis varies with Gd3+ concentration which is supported by the variation of coercivity. The calculated spin numbers from electron spin resonance spectra decreases with Gd3+ doping which confirms the reduction in magnetization. Both dielectric constant and dielectric loss are found to decrease with the Gd3+ substitution because of the reduced hopping rate for Fe3+ at the octahedral sites in doped nanoparticles. Lower values of dielectric loss suggest that Gd3+ doped NiFe2O4 nanoparticles are suitable for high frequency microwave device applications.

Development of least sized magnetic nanoparticles with high saturation magnetization

Magnetic nanoparticles of high saturation magnetization with least particle size are essential candidates for certain biomedical applications like hyperthermia. The development of such nanoparticles requires stringent processing conditions in arriving at desired characteristics. Magnesium substituted cobalt ferrite nanoparticles of size around 4 nm were processed by sol-gel method with high saturation magnetization and characterized by techniques XRD, TEM, FESEM and FTIR in elucidating the structural parameters. Magnetic properties were discussed in terms of a proposed cation distribution and occupancy of magnesium was established from electrical resistivity measurements.

Structural and electrical properties of Cu-doped Ni–Zn nanocrystalline ferrites for MLCI applications

Polycrystalline Cu substituted Ni–Zn ferrites with chemical composition Ni[Formula: see text]Zn[Formula: see text]-Cu[Formula: see text]Fe2O4 (x = 0.00 to 0.25 in steps of 0.05) have been prepared by citrate gel autocombustion method. The samples for electrical properties have been sintered at 900[Formula: see text]C for 4 h. The X-ray diffraction patterns of all samples indicate the formation of single phase spinel cubic structure. The value of lattice parameter is decreases with increasing Cu concentration. The estimated cation distribution can be derived from X-ray diffraction intensity calculations and IR spectra. The tetrahedral and octahedral bond lengths, bond angles, cation–cation and cation–anion distances were calculated by using experimental lattice parameter and oxygen positional parameters. It is observed that Cu ions are distributed in octahedral site and subsequently Ni and Fe ions in tetrahedral site. The grain size of all samples has been calculated by Scanning Electron Microscopy (SEM) images. The variations in DC electrical resistivity and dielectric constant have been explained on the basis of proposed cation distribution.

Enhancement in A-B super-exchange interaction with Mn substitution in Mg-Zn ferrites as a heating source in hyperthermia applications

Abstract We report nanoparticles of Mn 2+ doped Mg 0.5 Zn 0.5−x Mn x Fe 2 O 4 ( x = 0, 0.125, 0.250, 0.375, 0.500) ferrites synthesized via co-precipitation route for hyperthermia applications. The prepared samples have been characterized by XRD, FT-IR, FE-SEM, VSM and Photoluminescence spectroscopy for various physical properties. The variation in structural parameters has been obtained with Mn 2+ substitution. The confirmation of intrinsic vibration of metal ions at octahedral sites and tetrahedral sites obtained with the help of FT-IR spectra has been reported. The inception of soft-ferri-magnetic behaviour with Mn 2+ substitution ( x > 0) has been obtained. The variation in magnetic behaviour with Mn 2+ substitution indicates enhancement in A-B super-exchange interaction. The confirmation of enhancement in A-B super-exchange interaction with the help of Yafet-Kittel angles and proposed cation distribution has also been reported. The room temperature photoluminescence spectra show a non-linear variation in band edge emission with Mn 2+ substitution. The nanoparticles have shown soft ferri-magnetic behaviour for Mn 2+ doped samples and results support the candidature of synthesized nanoparticles for hyperthermia applications.

Structural and Magnetic Properties of Cu2+ Substituted Co–Zn Ferrite Nanoparticles, Synthesized by Sol–Gel Combustion Method

In this work, the effect of Cu content on structural and magnetic properties of Cobalt–Zinc Ferrite nanoparticles synthesized by sol–gel combustion method have been investigated. All the samples exhibit cubic spinel structure and the lattice constant decreases linearly with increasing Cu-content. Average crystallite sizes calculated from Debye–Scherrer formula are in the range of 51–100 nm. The broadening of X-ray diffraction peaks decrease with increasing Cu content ‘x’ suggest that crystallite size increases with increasing ‘x’. Cation distribution estimated form X-ray line intensity calculations show that Cu ions simultaneously occupy tetrahedral (A) and octahedral (B) sites with different ratio and Zn and Co ions occupies A and B sites respectively. With increasing Cu content a fraction of Co ions migrate to A site when x >0.2. Grain sizes estimated from SEM are found to be increase with increasing Cu content. Particle size calculated using TEM for the undoped Co–Zn ferrites is about 55 nm. Saturation magnetization (Ms), Coercivity (Hc) and remanent magnetization (Mr) that varies significantly with Cu-Content. Saturation magnetization decreases from 90.7 emu/g (x = 0.0) to 51 emu/g (x = 0.4). The proposed cation distribution supports the variation in saturation magnetization and Coercivity with increasing Cu content.

Effect of γ-rays irradiation on the structural, magnetic, and electrical properties of Mg–Cu–Zn and Ni–Cu–Zn ferrites

Nanoparticles of Ni0.35Cu0.15Zn0.5Fe2O4 and Mg0.35Cu0.15Zn0.5Fe2O4, have been synthesized by citrate precursor method. Then some of the prepared samples have been irradiated by γ-rays of 60Co radioactive source at room temperature with doses of 1Mrad and 2Mrad, at a dose rate of 0.1Mrad/h to study the effect of γ-rays irradiation on some structural, magnetic and electrical properties of the samples. The X-ray diffraction analysis (XRD), transmission electron microscopy, Fourier transform infrared spectroscopy and vibrating sample magnetometer measurements have been used to investigate the samples. The XRD results show that the irradiation has caused a decrease in the crystallite size and the measured density and an increase in the porosity, specific surface area, and microstrain in the case of Ni–Cu–Zn ferrite whereas in the case of Mg–Cu–Zn ferrite the reverse trend has been noticed. The lattice constant of the investigated samples has been increased with the increase of irradiation due to the conversion of Fe3+ (0.67Å) to Fe2+ (0.76Å). The magnetization results show an increase in saturation and remnant magnetizations for the two prepared ferrites after γ-rays irradiation. The main reason of this behavior is most probably due to the redistribution of the cations between A and B sites. The cation distribution has been proposed such that the values of theoretical and experimental magnetic moment are identical and increase as the magnetization increases. Moreover, a theoretical estimation of the lattice constant has been calculated on the basis of the proposed cation distribution for each sample and compared with the corresponding experimental values obtained by XRD analysis; where they have been found in a good agreement with each other. This can be considered as another confirmation of the validity of the cation distribution. Moreover, the cation distribution is thought to play an important role in increasing the values of dc conductivity of all samples with increasing the irradiation dose. The frequency dependence of ac conductivity, dielectric constant and dielectric loss of all samples have been studied. The Cole–Cole plots of (Z″ vs. Z′) give different two overlapping incomplete semi-circles depending upon the electrical parameters. Also, The Cole–Cole plots of (M″ vs. M′) insure that the electric stiffness is the dominant property of the investigated samples.

Improvement in magnetic behaviour of cobalt doped magnesium zinc nano-ferrites via co-precipitation route

Nanoparticles of spinel ferrites have attracted huge interest in various technological applications due to their distinct magnetic behaviour. These magnetic nanoparticles acquire surface and finite size effects. We report an improvement of magnetic characteristics in Co2+ substituted MgZn nano-ferrites synthesized by co-precipitation route. Physical properties have been investigated for Mg0.5Zn0.5−xCoxFe2O4 (x = 0, 0.125, 0.250, 0.375, 0.500) nano ferrites using XRD, FTIR, FESEM, EDS, VSM, photoluminescence and UV spectroscopy. Single phase cubical spinel structure has been observed. A phase transition from superparamagnetic to ferrimagnetic behaviour for x > 0.125 has been observed. Saturation magnetization has been found to be enhanced. Frequency dependent dielectric behaviour shows normal dispersion. Absorption spectra show a shift in position of maximum absorption towards longer wavelength with increasing Co2+ content. Photoluminescence spectroscopy has also confirmed the red shift in band edge emission with increasing Co2+ content. Some theoretical parameters, using proposed cation distribution, like theoretical lattice parameter, oxygen positional parameter, bond length etc., have also been calculated and found to support our experimental results.

Structural and dielectric studies of Mg2+ substituted Ni–Zn ferrite

AbstractPolycrystalline ferrites having the chemical formula Ni0.65−xZn0.35MgxFe2O4 (0 ⩽ x ⩽ 0.2) were prepared by solid state reaction route in steps of x = 0.04. The effect of incorporation of diamagnetic divalent magnesium at expense of nickel on the structural properties of these ferrites has been studied. The proposed cation distribution was derived from theoretical X-ray diffraction intensity calculations. These intensity calculations were done by varying the concentration of magnesium ions over two sites in the lattice. For a certain amount of magnesium concentration, the calculated and observed X-ray diffraction intensities were found to be in good agreement. Site occupancy of divalent diamagnetic magnesium was established from this cation distribution. The octahedral environment facilitates magnesium to enter the B-site at about 95 % and the remaining 5 % occupy tetrahedral sites (A-sites). The movements of cations between tetrahedral and octahedral sites as a result of magnesium substitution were discussed in the view of structural parameters, such as tetrahedral and octahedral bond lengths, cation-cation and cation-anion distances, bond angles and hopping lengths, which were calculated using experimental lattice constants and oxygen parameters. All structural parameters showed slight deviations from ideal values. Among all magnesium substituted samples, the ones with x = 0.12 exhibited insignificant variation in view of structural properties. Dielectric measurements were conducted at a standard frequency of 1 kHz. Large values of the recorded dielectric constants displayed typical characteristics of bulk ferrites. Both dielectric constant and loss values showed mixed variations, attributed to the loss of zinc ions during the sintering process.

Structural, magnetic and dielectric studies of copper substituted nano-crystalline spinel magnesium zinc ferrite

Nano-crystalline Mg0.5Zn0.5−xCuxFe2O4 (x=0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) ferrite powders were synthesized using co-precipitation method. The influence of Cu2+ ions substitution on the structural and magnetic properties was investigated. X-ray diffraction measurements revealed the formation of nano-crystalline ferrite with single cubic spinel phase. The lattice constant was found to decrease with increasing Cu2+ ions content. Infrared spectral analysis confirmed formation of the spinel structure for the respective ferrite system. Magnetic data showed that the saturation magnetization (Ms) increases with Cu2+ concentration up to x=0.2 and then decreases with further increase of Cu2+ ions in this ferrite system. The proposed cation distribution deduced from X-ray diffraction, infrared spectra and magnetization data indicated mixed ferrite type. Dielectric constants ε′, dielectric loss ε′′, dielectric loss tangent tanδ and ac conductivity, σac, were investigated as a function of frequency and temperature. Influence of Cu2+ substation on the ac conductivity exhibited significant behavior at low frequencies and low temperatures, T⩽100°C. Both dielectric constants (ε′, ε″) found to increase with the increase of the temperature. At low temperatures, dielectric loss tanδ indicated a decrease with frequency with slight change at high temperatures.

Cation Distribution of Cobalt-manganese Ferrite for Torque Sensor Applications

A series of five samples have been prepared by conventional double sintering ceramic method with a composition CoMnxFe2-xO4 (x = 0.0, 0.1, 0.3, 0.4, 0.6). The effect of manganese substitution on the structural, magnetic and magnetostrictive properties has been studied using X ray diffraction, VSM and strain gauge methods. The saturation magnetization (except at x = 0.1 and 0.6) and lattice constant has been observed to increase continuously with Mn concentration (x) whereas the variations of magnetostrictive coefficient and strain derivative are in opposite trend. The observed variations are explained on the basis of cation site occupancies, its valence states and their magnetostrictive contribution. Cation distribution is proposed in accordance with the variations of observed saturation magnetization values. Lattice constants are estimated and compared with the experimentally observed results. Very good agreement among these parameters clearly suggests that the proposed distributions are correct. The observed variations of magnetostrictive properties further support the proposed cation distribution. The manganese substitution produced large strain derivative value at higher manganese (x = 0.4) concentrations and the observed maximum strain derivative in the system has been attributed to the migration of cobalt ions to tetrahedral site.

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

Nano crystalline Ni0.5Zn0.5CrxFe2−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 Ni0.5Zn0.5Fe2O4 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, Me-Me 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 Ni0.5Zn0.5Fe2O4. 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 Ni0.5Zn0.5Fe2O4 nano particles has been attributed to the core-shell structure of the fine particles. When annealed at 1000 °C the saturation magnetization of Ni0.5Zn0.5Fe2O4 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 Ni0.5Zn0.5CrxFe2−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.

New scheme for cation distribution and electrical characterization of nanocrystalline aluminum doped magnesium ferrite MgAlxFe2−xO4

MgAlxFe2−xO4 (x=0.0 up to 1 step 0.2) was prepared using co-precipitation method. The value of lattice constant is found to decrease with increasing Al3+ concentration. The particle size of the samples calculated using the Sherrer formula was obtained in the range of 15–28nm. The two main bands corresponding to tetrahedral and octahedral sites were observed to be around 600cm−1 and 450cm−1, respectively. These bands are shifted to high frequencies with more doping of Al3+ ions which may be attributed to the decrease in the mean radius of the tetrahedral and octahedral sites. The threshold frequency (νth) for the electronic transition decreases with increasing the Al3+content. The tetrahedral force constant (KT) increases continuously with Al3+ concentration.The bandwidth of the tetrahedral site is found to increase gradually with the Al3+ content. The validity of the proposed cation distribution is confirmed by considering the X-ray intensity ratios of diffraction lines sensitive to the tetrahedral and octahedral sites. DC conductivity measurements exhibited metallic and semiconductor-like behavior with temperature for all compositions. The decrease of Curie temperature with the increase of non-magnetic ions of aluminum indicates their preference to the octahedral sites as well and confirms the validity of the cation distribution.

Structural, magnetic, and dielectric properties of nanocrystalline Cr-substituted Co0.8Ni0.2Fe2O4 ferrite

The structural, magnetic, and electric properties of Co0.8Ni0.2CryFe2−yO4 (0.00≤y≤0.75; step 0.15) prepared via citrate precursor method are investigated. The structural properties of the produced nano-particles were examined through X-ray diffraction (XRD) and infrared spectroscopy (IR). The XRD pattern revealed a single phase cubic spinel structure for all the samples. The crystallite size decreases with increasing Cr content. Magnetic properties were recorded using vibrating sample magnetometer (VSM). The saturation magnetization increased first with y=0.15 then decreased continuously with further increase of Cr3+ content. Quite reasonable cation distribution was proposed for all the samples relying on the experimental results of lattice parameters, magnetization, and IR spectrum. Theoretically estimated lattice parameters and magnetic moments (using Neel's two sub-lattice model) obtained from the proposed cation distribution are in conformity with those experimentally obtained from XRD and VSM results, respectively. Chromium substitution was found to improve ac electric properties, which was revealed by analyzing frequency-dependent ac conductivity and loss factor.