Cation distributions estimated using the magnetic moments of the spinel ferrites Co_(1-x)Cr_xFe_2O_4 at 10K

（A）[B]2O4 ferrite samples with the composition COl_xCrxFe204 （0.0 ≤ x ≤1.0） are prepared using a hydrothermal method, and subjected to calcining in a tube furnace with an argon-flow at 1673 K for 2 h. X-ray diffraction patterns indicate that each of all the samples has a single phase cubic spinel structure with a space group of Fd3m. Magnetic measurements show that the saturation magnetization decreases with as the Cr content x increases. The cation distribution of the samples is estimated by fitting the dependence of the magnetic moments on x at l 0 K, using the quantum mechanical model previously proposed by our group. The calculated sum of the content values of the Cr3＋ and Cr2＋ cations occupying the （A） sites increases as the value of x increases. In the fitting process, the magnetic moment directions of the Cr3＋ and Cr2＋ cations are assumed to be antiparallel to those of the Fe and Co cations, respectively, which is in accordance with Hund＇s rules.

Analysis of cerium substitution in Co-Sr based spinel ferrites for high frequency application

Spinel ferrites exhibit exceptional magnetic properties,making them a distinctive class of magnetic materials.The sol-gel technique was utilized for the synthesis of spinel ferrites with the chemical formula Co_(0.6)Sr_(0.4)Ce_(x)Fe_(2-x)O_(4). Following that,a comprehensive X-ray diffraction analysis unveiled the crystalline cubic structure of the synthesized materials.Through the utilization of the M-H loop approach,the ferromagnetic attributes of ferrites were assessed,and the assimilation of rare earth elements led to substantial enhancements in saturation magnetization,remanence,and coercivity.Spinel ferrites with a high concentration of rare earth elements have improved direct current resistivity and activation energy.The logarithm of a material's resistance increased from 5.29 to 8.12 Ω·cm as cerium is added.With a change in the amount of cerium,the activation energy goes up from 0.19 to 0.29.By changing the frequency from 5.5 to 9.5 GHz,the dielectric characteristics were determined.As the frequency goes up,the dielectric constant goes down.Spinel ferrites that have been made better in every way can be used in high-frequency applications.

Electrical and dielectric properties of Ni_(0.5)Co_(0.5)Ga_(x)Fe_(1.8-x)O_(4)(x≤1.0)spinel ferrite microspheres

Microspheres of Ni_(0.5)Co_(0.5)Ga_(x)Fe_(2-x)O_(4)(x≤1.0)microsphere spinel ferrites(NiCoGaFe-MSFs)and carbon spheres were prepared via a hydrothermal technique.The micro structure of microspheres was investigated through scanning and transmission electron microscopy(SEM and TEM),respectively,and X-ray diffraction(XRD).The electrical and dielectric properties of NiCoGaFe-MSF at temperatures ranging from20 to 120℃(between 293,1×10^(3)and 393.1×10^(3))for f≤3.0 MHz were systematically studied as a result of 3D graphical drawing of the data obtained from an impedance analyzer.Relevant parameters such as ac/dc conductivity,dielectric loss,dielectric constant,activation energy,dissipation factor and Cole-Cole impedance spectra were extensively evaluated for various Ga ion mole ratios in the substitution where x≤1.0.We notice that the ac conductivity mostly obeys exponential power law rules,which vary significantly with the substitution ratios of Ga ions.Impedance analyses confirm that differences in conduction mechanisms in NiCoGaFe-MSFs are mainly due to grain-to-grain boundaries related to Ga ion substitution ratios.The change in dielectric constant of NiCoGaFe-MSFs is strongly dependent on the substitution rates and results in a normal dielectric distribution with frequency.The tangential loss for all micro spheres is observed to vary with measured temperatures and their frequency dependencies can be attributed to the conduction mechanism similar to Koop’s phenomenological model.It is clearly seen that the formation of semicircles is dominated by all the NiCoGaFe-MSFs and the diameter of the semicircles mostly decreases with increasing temperature,as evidence of a temperaturedependent relaxation mechanism.

Effect of rare earth Nd^(3+)doping contents on physical,structural,and magnetic properties of Co-Ni spinel ferrite nanoparticles

Rare earth(RE)low doping has a significant influence on the structural,morphological,and magnetic properties of spinel ferrite nanoparticles.Therefore,rare earth neodymium(Nd)oxide was fully doped into spinel ferrite with a composition of Co_(0.80)Ni_(0.20)Nd_xFe_(2-x)O_4(x=0.0,0.05,0.10,and 0.15)using the sol-gel auto combustion method.Structural analysis of the synthesized samples with low doping of Nd using X-ray diffraction(XRD)and Rietveld refinements reveals a pure single-phase cubic structure,while the second phase appears with increasing content of Nd^(3+)at x=0.10 and 0.15.Scanning electron microscopy(SEM)and high-resolution transmission electron microscopy(HR-TEM)show well-shaped spherical grains within the nanometer range of the pure Co_(0.80)Ni_(0.20)Fe_(2)O_(4) sample,while larger grains with the presence of agglomeration are observed with doping of Nd^(3+)into the spinel ferrite nanoparticles.The magnetic parameters,i.e.,saturation magnetization M_s,remanence and magnetic moments exhibit decreasing trend with Nd^(3+)doping and M_s values are in 65.69 to 53.34 emu/g range.The coercivity of the Nd-doped Co-Ni spinel ferrite sample was calculated to be 1037.76 to~827.24 Oe.This work demonstrates remarkable improvements in the structural and magnetic characteristics of Nddoped Co-Ni spinel ferrite nanoparticles for multiple versatile applications.

Defect-rich spinel ferrites with improved charge collection properties for efficient solar water splitting

Spinel zinc ferrite(ZnFe_(2)O_(4),ZFO)is a potential photoanode material for photoelectrochemical(PEC)water splitting because of its ideal bandgap(1.9–2.1 eV)and superior chemical stability in aqueous solutions.However,the low charge collection efficiency significantly hinders the improvement in PEC activity.Herein,we report an ultrafast and effective flame activation route to enhance the charge collection properties of ZFO.First,high-temperature flame(>1300℃)facilitated surface and grain boundary diffusions,increasing the grain size and connectivity of the ZFO nanoparticles.Second,the reducing atmosphere of the flame enabled the formation of surface defects(oxygen vacancy and Fe^(2+)),thereby increasing the charge carrier density and surface adsorption sites.Significantly,these two factors promoted charge transport and transfer kinetics,resulting in a 10-fold increase in the photocurrent density over the unactivated ZFO.Furthermore,we deposited a thin Al_(2)O_(3)overlayer to passivate the ZFO surface and then the NiFeOx oxygen evolution catalyst(OEC)to expedite hole injection into the electrolyte.This surface passivation and OEC deposition led to a remarkable photocurrent density of~1 mA/cm^(2)at 1.23 V versus the reversible hydrogen electrode,which is the highest value among all reported ZFO photoanodes.Notably,the NiFeOx/Al_(2)O_(3)/F-ZFO photoanode achieved excellent photocurrent stability over 55 h(96%retention)and superior faradaic efficiency(FE>94%).Our flame activation method is also effective in improving the photocurrent densities of other spinel ferrites:CuFe_(2)O_(4)(93 times),MgFe_(2)O_(4)(16 times),and NiFe_(2)O_(4)(12 times).

Remarkable catalysis of spinel ferrite XFe2O4(X=Ni,Co,Mn,Cu,Zn)nanoparticles on the dehydrogenation properties of LiAlH_(4):An experimental and theoretical study

Safe,compact,lightweight and cost-effective hydrogen storage is one of the main challenges that need to be addressed to effectively deploy the hydrogen economy.LiAlH_(4),as a solid-state hydrogen storage material,presents several advantages such as high hydrogen storage capacity,low price and abundant sources.Unfortunately,neither thermodynamic nor kinetic properties of dehydrogenation for LiAlH_(4)can fulfill the requirements of practical application.Thus,a series of spinel ferrite nanoparticles such as XFe_(2)O_(4)(X=Ni,Co,Mn,Cu,Zn,Fe)were prepared by using the modified thermal decomposition method,and then doped into LiAlH_(4)by using ball milling.Our results show that LiAlH_(4)doped with 7 wt%NiFe_(2)O_(4)starts to release hydrogen at 69.1°C,and the total amount of hydrogen released is 7.29 wt%before 300°C.The activation energies of the two-step hydrogen release reactions of LiAlH_(4)doped with 7 wt%NiFe_(2)O_(4)are 42.32 kJ mol^(-1)and 71.42 k J mol,which are 59.0%and 63.6%lower than those of as-received LiAlH_(4),respectively.Combining the density functional theory(DFT)calculations,we reveal that both the presence of Ni FeOand in-situ formed AlNiin ball-milling decrease the desorption energy barrier of Al-H bonding in LiAlH_(4)and accelerate the breakdown of Al-H bonding through the interfacial charge transfer and the dehybridization of the Al-H cluster.Thus,the experimental and theoretical results open a new avenue toward designing high effective catalysts applied to LiAlH_(4)as a candidate for hydrogen storage.

Modulation of the magnetic properties of gold-spinel ferrite heterostructured nanocrystals

The rational design of complex nanostructures is of paramount importance to gain control over their chemical and physical properties.Recently,magnetic-plasmonic heterostructured nanocrystals have been recognized as key players in nanomedicine as multifunctional therapeutic-diagnostic tools and in catalysis.Here we show how the properties of gold-iron oxide heterostructured nanocrystals can be tuned by chemical doping of the magnetic subunit.The divalent cations in the iron oxide were substituted with cobalt and manganese to obtain a general formula Au-MFe2O4(M=Fe,Co,Mn).Magnetic properties of the heterostructures could be tuned,while maintaining well-defined plasmon resonance signatures,confirming the dual magnetic-plasmonic functional capability of these nanostructures.

Preparation and Sinterability of Mn-Zn Ferrite Powders by Sol-Gel Method

Mn-Zn spinel ferrites were synthesized by sol-gel method. Effects of calcined temperature on structure and particle size of MnZnFe2O4 were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD patterns indicate that the ultra fine Mn-Zn ferrite exhibits a spinel crystal structure. SEM images show that the powder fired at 900℃for 2 h has an average diameter of 60 ~ 90 nm. The particle size becomes larger with the increasing of calcined temperature and the distribution of particle becomes even more homogeneous. Sintering behaviors of synthesized ferrite powders depend on the powder characteristics and high temperatures have induced the good crystallization of particles.

Preparation and characterization of rice husk/ferrite composites

A novel ferrite composite using rice husk as substrate has been prepared via high temperature treatment under nitrogen atmosphere.The rice husk substrate consists of porous activated carbon and silica,where spinel ferrite particles with average diameter of 59 nm are distributed.The surface area of the composite is greater than 170 m^2 g^(-1) and the bulk density is less than 0.6 g cm^(-3).Inert atmosphere is indispensable for the synthesis of pure ferrite composites,while different preparation temperatures ...

Effects of Mg substitution on the structural and magnetic properties of Co0.5Ni（0.5-x）MgxFe2O4 nanoparticle ferrites

In this study, nanocrystalline Co-Ni-Mg ferrite powders with composition Coo.5Nio.5-xMgxFe2O4 are successfully synthesized by the co-precipitation method. A systematic investigation on the structural, morphological and magnetic properties of un-doped and Mg-doped Co-Ni ferrite nanoparticles is carried out. The prepared samples are characterized using x-ray diffraction （XRD） analysis, Fourier transform infrared spectroscopy （FTIR）, field emission scanning electron microscopy （FESEM）, and vibrating sample magnetometry （VSM）. The XRD analyses of the synthesized samples confirm the formation of single-phase cubic spinel structures with crystallite sizes in a range of - 32 nm to - 36 nm. The lat- tice constant increases with increasing Mg content. FESEM images show that the synthesized samples are homogeneous with a uniformly distributed grain. The results of IR spectroscopy analysis indicate the formation of functional groups of spinel ferrite in the co-precipitation process. By increasing Mg2- substitution, room temperature magnetic measurement shows that maximum magnetization and coercivity increase from - 57.35 emu/g to - 61.49 emu/g and - 603.26 Oe to 684.11 Oe （l Oe = 79.5775 A.m-l）, respectively. The higher values of magnetization Ms and Mr suggest that the opti- mum composition is Co0.5Ni0.4Mg0.1Fe204 that can be applied to high-density recording media and microwave devices.

Impedance spectroscopy study on Mn_(1+x)Fe_(2-2x)Ti_xO_4(0≤x≤0.5) ferrites

The complex impedance spectroscopy and surface morphology of Mn1+xFe2-2xTixO4(0≤x≤0.5) system,prepared using a conventional solid state reaction technique,were investigated.The impedance spectroscopy measurements were carried out at room temperature in the frequency range of 42-5 MHz.The electrical processes in the samples were modeled in the form of an equivalent circuit made up of a combination of two parallel RC circuits attributed to grain and grain boundaries.The DC conductivity obtained by extrapolation of AC data using impedance spectroscopy and four-probe method increases at 10% doping of Ti ions.The energy-dispersive X-ray(EDX) pattern confirmed the homogeneous mixing of the Mn,Fe,Ti and O atoms in pure and doped ferrite samples.

Preparation and Structural Properties of ZnAlxFe2-xO4 Spinel Oxide

The ZnAlxFe2-xO4 (x = 0.0, 0.2 and 0.4) spinel ferrites were prepared by the conventional solid state reaction in air at 1350°C. The X-ray diffraction of all the three samples showed sharp Bragg peaks indicating the formation of a single phase spinel structure. The lattice parameters of the samples were determined from the X-ray diffraction data using the Nelson-Riley extrapolation method. The lattice parameters, cation distribution and oxygen position parameters have also been determined by refining the data by the Rietveld method. Rietveld refinement of the XRD data reveals all the samples to possess cubic symmetry corresponding to the space group Fd3m. Lattice parameters were found to decrease with increasing Al concentration, i.e. 8.4322, 8.4002, and 8.3984 Åfor x = 0.0, 0.2 and 0.4, respectively.

EFFECT OF MnO_(2) ADDITIVE ON PERFORMANCES OF NiFe_(2)O_(4) SPINEL BASED INERT ANODE

The NiFe2O4 inert anode is synthesized by high-temperature solid-state reaction method using NiO and Fe2O3 as main raw materials and adding MnO2 powder as additive. Archimedes method using water immersion technique is used to measure the sintering performances of sampies. The static thermal corrosion rates of samples are measured by weight loss. SEM is employed for the observation of material microstructure, and phase structure of the sample surface after corrosion is determined by XRD. The experimental results indicate that a suitable MnO2 additive content is 2%, while the sintering performance is the best, and the static thermal corrosion rate is the lowest. Because of MnO2 dopant enriching at crystal boundary, the corrosion reaction of molten salt to crystal grain creates Mn2AlO4 phase, which is denser than NiFe2O4 phase, and prevents the cryolite molten salt to penetrate into the inert anode, thus reducing the corrosion.

Rare earth-doped mixed Ni-Cu-Zn ferrites as an effective photocatalytic agent for active degradation of Rhodamine B dye

In this study, a series of Gd^(3+)-doped mixed Ni-Cu-Zn ferrites with composition of Zn_(0.5)Ni_(0.3)Cu_(0.2)Fe_(2-x)Gd_(x)O_(4)(x = 0, 0.025, 0.05, 0.075, 0.1) was prepared using self-ignition sol-gel method. The prepared nanoparticles with an average size ranging from 22 to 26 nm show a single-phase cubic structure belonging to the spinel matrix. A rise in the Gd^(3+)concentration leads to an increase in crystallite size and lattice parameter. In Fourier transform infrared spectra, two main absorption bands belonging to the spinel structure are observed. The high-frequency bands(v_(1)) represent the tetrahedral complex, while the lowfrequency bands(v_(2)) signify the octahedral complex. The optical bandgap of the nanoferrites is found within the range of 2.91 to 2.41 eV, depending on their size. The magnetic characteristics of the material,such as saturation magnetization and coercivity are significantly altered with the concentration of Gd^(3+)in the solution. Using Rhodamine B(RhB) as a model organic pollutant, an in-depth investigation of the photocatalytic activity of the compounds was carried out. The present outcomes show that adding an adequate amount of Gd^(3+)significantly enhances the number of hydroxyl radicals produced by the ferrite,in turn, increasing the photocatalytic activity of the material. Mechanism elucidated by scavenger studies reveals that ·OH and holes are the primary reactive radicals responsible for the degradation process.Prepared photocatalysts show an insignificant performance loss in five consecutive cycles. Thus, it is concluded that these photocatalysts are highly suitable for the remediation of dye-contaminated wastewater.

Correlation between structural phase transition and physical properties of Co^(2+)/Gd^(3+)co-substituted copper ferrite

The doping of the spinel ferrites with selective cations usually improves the properties of the parent ferrite.The effect of Co^(2+)/Gd^(3+)co-substitution on the microstructure,optical,and magnetic properties of Cu1-xCoxFe2-xGdxO4 prepared by the citrate-nitrate auto-combustion synthesis was investigated.Characterization of the samples was performed with powder X-ray diffraction(XRD),Raman and Fouriertransform infrared(FTIR)spectroscopy,field-emission scanning electron microscopy,X-ray energydispersive spectroscopy,UV-Vis spectroscopy,and a vibrating sample magnetometer.The results of XRD,Raman,and FTIR analysis show a gradual structural phase transition from a tetragonal(I41/amd)structure to a cubic(Fd3m)structure.The bandgap energy of the studied samples is in a range of 1.57-1.75 eV with a minimum in sample x=0.06 and then increases.Magnetic investigations show that the presence of Co^(2+)/Gd^(3+)cations in an octahedral site of the copper ferrite structure could increase saturation magnetization and coercive field from 567.9 Oe and 23.62 emu/g to 929.4 Oe and 28.27 emu/g,respectively.

Effect of thulium substitution on conductivity and dielectric belongings of nanospinel cobalt ferrite

The CoTmx Fe2-x O4(x≤0.1) NPs were synthesized sonochemically.X-ray powder diffraction patterns and TEM images of the samples prove their chemical purity and cubic structure-morphology,respectively.Some substitution ratio of thulium ions to cobalt ferrites have an important effect on the characteristic evaluation of both electrical and dielectric characteristic measured at frequencies up to 3.0 MHz between room temperature and 120℃.Since the thulium substitution has a very strong effect on the characteristic evaluation of both electrical and dielectric properties of cobalt-ferrite samples,four substitutio nal ranges-none,small,medium and high were determined for the interpretation of contribution of thulium ratio to ac/dc conductivity,dielectric constant,dielectric loss and tangent loss.Conductivity increases with the incremental frequencies,in general depending on a variety of tendencies of both temperature and substitutional Tm ratios while the activation energy varies with a high dependency to the regional level of Tm substitution in Co-ferrites NPs.The Arrhenius graph appears to provide us with a single activation energy much higher than 400 meV for x=0.02,which can be attributed to electron hopping mechanisms,apart from other substituted spinel ferrites.

Influence of Ti^(4+) doping on hyperfine field parameters of Mg_(0.95)Mn_(0.05)Fe_(2-2x)Ti_(2x)O_4(0≤x≤0.7)

The mixed spinel ferrite system Mg0.95Mn0.05Fe2-2xTizxO4 （0 ≤x ≤ 0.7） was synthesized by the conventional solid-state reaction technique. The effect of Ti^4＋ doping was studied by using the Moessbauer spectroscopy measurements at room temperature. From the analysis of the Moessbauer spectra, it is observed that s-electron density, electric field gradient （EFG）, quadrupole coupling constant （QCC） and the net hyperfine magnetic fields acting on the Moessbauer nuclei-FeA^3＋ and FeB^3＋ change with the increase of Ti^4＋ doping in Mg0.95Mn0.05Fe2O4. The hyperfine magnetic field decreases with the increase of Ti^4＋ doping.

A new aluminum iron oxide Schottky photodiode designed via sol-gel coating method

A novel aluminum iron oxide （Al/AlFe2O4/p-Si） Schottky photodiode was successfully fabricated via the sol-gel coating process. The microstructure of the spinel ferrite （AlFe2O4） was examined by atomic force microscopy. The current-voltage characteristics of the fabricated photodiode were studied under dark and different illumination conditions at room temperature. By using the thermionic emission theory, the forward bias I-V characteristics of the photodiode are analyzed to determine the main electrical parameters such as the ideality factor （n） and barrier height （ФB0） of the photodiode. The values of n and ФB0 for all conditions are found to be about 7.00 and 0.76 eV, respectively. In addition, the values of series resistance （Rs） are determined using Cheung＇s method and Ohm＇s law. The values of Rs and shunt resistance （Rsh） are decreased with the increase of illumination intensity. These new spinel ferrites will open a new avenue to other spinel structure materials for optoelectronic devices in the near future.

Improvement of Heat Generation Ability in AC Magnetic Field and Magnetic Properties for Spinel Type MgFe_2O_4 Ferrite by Cu Substitution and Beads Milling

Mg_(1-X)Cu_XFe_2O_4 type spinel ferrite was prepared by solid reaction method in order to discuss the heat generation ability in AC magnetic field.The cubic type ferrite structure was obtained for X=0-0.6 samples calcined at 1200℃,and the mixture phase of cubic and tetragonal structures were obtained for X=0.7,0.8 samples from XRD result. The highest lattice parameter and highest hysteresis loss value were also shown at X=0.6 sample,the crystal distortion was increased with increase the Cu^(2+)substitution in cubic type ferrite structure.The sized nano Mg_(0.4)Cu_(0.6)Fe_2O_4 powder was prepared by physical milling method using beads milling.The highest heat generation in the AC magnetic field was obtained for the 6 h milled samples using 0.1mm beads.The Cu^(2+)substitution for MgFe_2O_4 ferrite and the beads milling were very effective for the improvement of their heat generation ability in AC magnetic field.

Synthesis of BaFe_(12)O_(19)/MFe_(2)O_(4)(M=Co,Mn)by sol-gel method

Composites of M-type hexaferrite BaFe_(12)O_(19) and spinel ferrites MFe_(2)O_(4)(M=Co,Mn)were directly synthesized by sol-gel method.The structure of composites was analyzed by X-ray diffraction(XRD)and scanning electron microscopy(SEM).The formation of BaFe_(12)O_(19)/CoFe_(2)O_(4) composite was proved by XRD patterns with coexistence of diffraction peaks of the two kinds of ferrites,BaFe_(12)O_(19) and CoFe_(2)O_(4).Compared with BaFe_(12)O_(19),the diffraction peaks of CoFe_(2)O_(4) are fairly weak,revealing the dominant structure of hexaferrite in the composite.SEM micrographs provide further evidence and the particle size of composites is about several hundred nanometer,meaning that the co-synthesizing sol-gel method can be in favor of the formation of finer particles.However,the diffraction peaks of MnFe_(2)O_(4) can be hardly found in BaFe_(12)O_(19)/MnFe_(2)O_(4) composite,revealing the synthesis conditions are not favorable for the formation of MnFe_(2)O_(4).Substitution reaction of Ba or Fe by Mn may be proposed.