Synthesis,structural and magnetic characterization of nanocrystalline CuFe2O4 as obtained by a combined method reactive milling,heat treatment and ball milling

Nanocrystalline copper ferrite has been synthesized using a combined method which involves reactive milling, heat treatment and mechanical milling. After 4 h of reactive milling a solid solution between the starting oxides (CuO and α-Fe₂O₃) and a spinel phase is obtained. Increasing the milling time leads to a decomposition of those phases. After a heat treatment of the 30 h milled sample a single spinel CuFe₂O₄ phase is obtained. By mechanical milling the crystallite size of the copper ferrite is reduced down to 9 nm after 1 h of milling. For the CuFe₂O₄ samples milled between 2 and 4 h a decomposition of this phase is remarked and α-Fe₂O₃ is formed during milling. The spontaneous magnetization of the spinel decreases with increasing the milling time as results of the partial redistribution of the cations in the spinel and of spin canted effect. The magnetization of the milled samples does not saturate due to the presence of very fine ferrite particles which are superparamagnetic.     

Structural characteristics and electrical properties of copper doped manganese ferrite

A series of Mn_1?xCu_xFe₂O₄ ferrite samples with 0.2 ≤ x ≤ 0.5 were prepared using the co-precipitation method. X-ray analysis confirmed the formation of single phase cubic spinel structure for all concentrations. Rietveld refinement revealed that the Mn_1?xCu_xFe₂O₄ with all concentrations of x belongs to normal spinel structure. The lattice parameters decrease leading to the increase in the X-ray density with increasing the copper concentration and this may be due to the difference in the ionic radii between Mn²⁺ and Cu²⁺. The decrease in the crystallite size with increasing the copper content is attributed to the higher formation temperature. The IR absorption spectra analyses were used for the detection and confirmation of the chemical bonds in spinel ferrites. The AC electrical conductivity, real part of the dielectric constant and the loss tangent tan δ were studied as a function of the applied frequency and temperature. It was found that the AC electrical conductivity increased with increasing temperature, this increase may be related to the increase in the drift mobility of the charge carriers, which are localized at ions or vacant sites. The AC conductivity increases with increasing copper concentration which may be ascribed to the decrease in hopping length. The dielectric constant ?′ and dielectric loss showed a decrease with increasing frequency and increase with increasing temperature for all compositions. The dielectric behavior is explained by using the mechanism of polarization process.     

Effects of heat treatment conditions on the structural and magnetic properties of MgCuZn nano ferrite

Mg_0.5Cu_0.05Zn_0.45Fe₂O₄ nanoparticles were prepared through sol–gel method using polyvinyl alcohol as a chelating agent. The as prepared sample was annealed at three different temperatures (500 °C, 700 °C and 900 °C). The phase formation, morphology and magnetic properties with respect to annealing temperature were studied using the characterisation techniques like X-ray diffraction (XRD) as well as Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM), respectively. The crystallite size and magnetisation showed increasing trend with annealing temperature. The coercivity increased up to a particular annealing temperature and decreased thereafter, indicating transition from single domain to multi domain state with increasing annealing temperature. Further, to know the suitability of the material, as a ferrite core, in multilayer chip inductors, the powder sample annealed at 500 °C was compacted in the form of torroids and sintered at three different temperatures (800 °C, 900 °C and 950 °C). The permeability showed increasing trend with the increase of sintering temperature since the permeability depends on microstructure. The frequency dispersion of permeability, for the sintered samples, demonstrated high frequency stability as well as high operating frequency. The cut-off frequency for the sintered samples 800 °C, 900 °C and 950 °C is 32 MHz, 30.8 MHz and 30.4 MHz, respectively.     

Structural and magnetic properties of strontium substituted NiZn ferrite nanopowders

Sr-substituted NiZn ferrite nanopowders, Ni_0.5-xZn_0.5Sr_xFe_2.0O₄ (0≤x≤0.20), were synthesized by the sol-gel auto-combustion method. The effects of Sr substitution on the structural and magnetic properties have been investigated. Differential thermal analysis-thermogravimetry (DTA-TG), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) measurements were used to characterize chemical, structural and magnetic properties. The DTA-TG results indicate that there are three steps of combustion process. XRD results indicate that the lattice parameter increases, and the average crystallite size decreases with increasing Sr substitution. The Sr₂FeO₄ and SrFe₁₂O₁₉ impurity phases formed with excess Sr substitution. The saturation magnetization monotonically decreases with the increase of Sr substitution. Meanwhile, the coercivity initially decreases with the increase of Sr substitution when x≤0.15, and increases when x>0.15.     

Structural,magnetic and electrical properties of Ga-substituted NiCuZn nanocrystalline ferrite

In this work, we studied the substitution effect of iron by gallium on the structural, magnetic and electrical properties of the ferrite system; Ni_0.5Cu_0.25Zn_0.25Fe_2−xGa_xO₄ (x = 0–1.0), synthesized by using the urea combustion method. XRD patterns of the samples calcined at 700 °C show only cubic spinel ferrite with an average crystallite sizes in the range of 40–54 nm. The lattice parameters were slightly changed with increasing Ga content which can be explained on the basis of the relative ionic radii of Ga³⁺ and Fe³⁺ ions. FT-IR measurements show two fundamental absorption bands, assigned to the vibration of tetrahedral and octahedral complexes, which were slightly changed with increasing Ga content. Mössbauer measurements enable us to predict the possible cation distribution of the system. It was found that Ga³⁺ ion prefer to substitute Fe³⁺ ions located in the octahedral site. Superparamagnetic state was observed in the Mössbauer spectra of the samples with Ga content >0.5. The decrease of the magnetic hyperfine field with gallium concentration was explained on the basis of supertransferred hyperfine interaction. A semiconducting behavior was inferred for all samples and the conductivity values were found to decrease with increasing the Ga content. The conduction mechanism in the spinel ferrite compounds was explained in terms of the hopping conduction process. The dielectric constant measured as a function of frequency and temperature was found to be dependent on the Ga concentration. The determined transition temperature was found to decrease with increasing Ga content.     

Structural and magnetic properties of zinc ferrite incorporated in amorphous matrix

Glass ceramics in the (Fe₂O₃)_x·(B₂O₃)_(60−x)·(ZnO)₄₀ (x = 17.5 and 20 mol%) system were prepared by the melt-quench method and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and magnetization measurements. The samples contain a unique magnetic crystalline phase, the zinc ferrite (ZnFe₂O₄), embedded in an amorphous matrix. The ZnFe₂O₄ crystals precipitate during cooling from melting temperature. From the XRD data, the average unit-cell parameter, crystallite size and the quantitative ratio of the crystallographic phases in the samples were evaluated. FTIR data revealed that the BO₃ and BO₄ are the main structural units of these glass ceramics network. FTIR spectra of these samples show features at characteristic vibration frequencies of ZnFe₂O₄. From the magnetization curves it was found that the nanoparticles exhibit ferromagnetic interactions combined with superparamagnetism with a blocking temperature, T_B, which is composition dependent. In all samples hysteresis is present below T_B. The coercive field is dependent on composition and magnetic field being around 0.05μ_B/f.u. for measurements performed in maximum 0.4 T. Finally, the magnetic behavior of iron in this system is discussed.     

Structural,electrical, and magnetic properties of Zn substituted magnesium ferrite

Zinc substituted magnesium (Mg–Zn) ferrites with the general formula Mg_1−xZn_xFe₂O₄ (x=0.00, 0.25, 0.50, 0.75, and 1.00) were prepared using the solution combustion route. The dried powder after calcination (700 °C for 2 h) was compacted and sintered at 1050 °C for 3 h. The structural, morphological, dielectric and magnetic properties of the sintered ferrites were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), impedance spectroscopy, and vibration sample magnetometry (VSM). The XRD analysis of sintered samples confirmed that the expected spinel cubic phase was formed for all samples. The crystallite sizes evaluated using Scherre's formula were found to be in the range of 47–80 nm. SEM analysis showed homogeneous grains with a polyhedral structure. The electrical conductivity increased with increasing frequency, which is normal dielectric behavior for such materials. The dielectric constant, dielectric loss tangent, and AC conductivity were found to be lowest for x=0.50. The VSM results showed that the zinc concentration had a significant influence on the saturation magnetization and coercivity.     

PZT-nickel ferrite and PZT-cobalt ferrite comparative study: Structural,dielectric, ferroelectric and magnetic properties of composite ceramics

Comparative study of different PZT-based composite materials ((x)PbZr_0.52Ti_0.48O₃ + (1-x)CoFe₂O₄ and (x)PbZr_0.52Ti_0.48O₃ +(1-x)Ni_0.7Zn_0.3Fe₂O₄ (x = 0.8 and 0.9)) is presented in the frame of structural, dielectric, ferroelectric and magnetic properties. PZT and NZF/CF powders were synthesized by auto combustion technique. The composites were synthesized by mixing the appropriate amount of individual phases using conventional sintering. XRD data indicated the formation of well crystallized structure of PZT and NZF/CF, without the presence of undesirable phases. SEM micrographs revealed a uniform grain distribution of both, ferroelectric and ferromagnetic phases. Non-saturated hysteresis loops are evident in all samples due to the existence of non-ferroelectric ferrite phase. All the samples exhibit typical ferromagnetic hysteresis loop, indicating the presence of the order magnetic structure. Dielectric investigations revealed that ferrites are the main source of charge carriers, which must be of electronic origin. The activation energy of effective electrical resistivity is heavily influenced by the ferroelectric phase.     

Structural and magnetic properties of Co/Al2O3 cermet synthesized by mechanical ball milling

Cobalt nanoparticles in the alumina matrix were synthesized using high energy mechanical ball milling of Co₃O₄ and Al powders mixture. The effect of ball mill time of 1 up to 12 h on the phase formation and crystalline lattice of the samples was investigated by the fitting of the X-ray diffraction patterns with Fullprof software and Rietveld method. The results show that 6 h milling of the primary powders yields a nanocomposite of Co/Al₂O₃ cermet. The formation of Co/Al₂O₃ nanocomposite was confirmed by a morphological study using scanning electron microscopy and transmission electron microscopy. The prepared nanocomposite by 12 h ball mill time has ferromagnetic properties with a high saturation magnetization value of 118 emu/g. Also, using Henkel plot analysis, it was shown that there are strong dipole-dipole magnetic interactions between the prepared cobalt nanoparticles in the Al₂O₃ matrix.     

The influence of reactive milling on the structure and magnetic properties of nanocrystalline MnFe2O4

Nanocrystalline manganese ferrites (MnFe₂O₄) have been synthesized by direct milling of metallic manganese (Mn) and iron (Fe) powders in distilled water (H₂O). In order to overcome the limitation of wet milling, dry milling procedure has also been utilized to reduce crystallite size. The effects of milling time on the formation and crystallite size of wet milled MnFe₂O₄ nanoparticles have been investigated. It has been observed that single phase 18.4 nm nanocrystalline MnFe₂O₄ is obtained after 24 h milling at 400 rpm. Further milling caused deformation of the structure as well as increased crystallite size. With the aim of reducing the crystallite size of 18.4 nm, MnFe₂O₄ sample dry milling has been implemented for 2 and 4 h at 300 rpm. As a result, the crystallite size has been reduced to 12.4 and 8.7 nm, respectively. Effects of the crystalline sizes on magnetic properties were also investigated. Magnetization results clearly demonstrated that crystallite size has much more effect on the magnetic properties than average particle size.     

Magnetic properties of MnZn ferrite nanoparticles obtained by SHS and sol-gel autocombustion techniques

MnZn ferrite nanoparticles have been synthesized by self-propagating high temperature synthesis (SHS) and sol-gel autocombustion techniques. The crystallite size, microstructure and magnetic properties were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM) methods. The results showed that single phase manganese ferrite could be achieved directly without any post calcination. However, the crystallite size of the sol-gel autocombusted sample (44 nm) was finer than that of the SHS (57 nm). The SHS synthesized MnZn ferrite with the larger crystallite size exhibited the larger magnetization of 50.6 emu/g than that of 20.9 emu/g for the sol gel autocombusted nanoparticles, despite of its more structure inversity.     

Effect of the thermal treatment on the magnetic and structural properties of cobalt ferrite particles

We herein report a study on the sol-gel synthesis of CoFe₂O₄ and the effect of thermal treatment on the product outcome. Xerogels treated at 750, 800 and 850 °C had their structural and magnetic properties thoroughly studied, in order to correlate their synthesis conditions to the positions in which the cations are inserted in the spinel structure. X-ray diffractograms exhibit reflections representative of the spinel structure and demonstrate that the thermal treatment does not affect the lattice parameters of the material. Mossbauer spectroscopy studies indicate a very low inversion degree in the synthesized spinels, which is very unusual for CoFe₂O₄. A maximum in coercivity of 1405.2 Oersted was achieved for the sample treated at 800 °C.     

Electrical and magnetic properties of magnesium-substituted lithium ferrite

Magnesium-substituted lithium ferrite of different composition (Li_0.5Fe_2.5−xMg_xO_4−δ) were prepared for x = 0.0–1.0 by conventional ceramic technique. The crystal structure characterization and morphology were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM). Initial permeability and quality factor were measured in the frequency range of 1 kHz to 100 MHz. The permeability decreased gradually from μ (f = 10 MHz) = 34.0 for Li_0.5Fe_2.5O₄ to μ (f = 10 MHz) = 11.5 for Li_0.5Fe_1.5Mg_1.0O₄. Electrical conductivity measurements were carried in the range of 250–700 °C in air. The maximum electrical conductivity, σ_700 °C = 0.1274 S/cm has been found to be for Li_0.5Fe_2.5O₄ specimen. With increasing Mg-substituted content, the decreased in the electrical conductivity.     

Structural,magnetic, and antimicrobial properties of zinc doped magnesium ferrite for drug delivery applications

In this study, drug loading and release ability of the ferrite nanoparticle coated with PEG (polyethylene glycol) have been investigated for biomedical applications. The zinc-magnesium ferrite (Zn_xMg_(1-x)Fe₂O₄) was synthesized using sol-gel route. The doping concentration of Zn was gradually increased from zero to maximum (x = 1). XRD (X-ray diffraction) analysis of the samples shows the single phase with a cubic spinel structure. The Debye-Scherer formula has been used to calculate the average crystallite size (30.51 nm). The dumbbell and spherical shaped morphology (40–50 nm average particle size) have been investigated from the secondary electron images of FESEM (Field Emission Scanning Electron Microscopy). The antimicrobial assay has been carried out against E. coli bacteria by gentamicin (drug) loaded ferrite nanoparticles. The significant zone of inhibition might suggest that the drug-loaded ferrite nanoparticles can be used in drug delivery applications. PL (Photoluminescence) of the spinel ferrite shows that all the samples are in the visible range, and peaks at around 430 nm. The result reveals the synthesis of high purity ferrite nanoparticles with significant potential for drug delivery applications.     

X-ray phase analysis of copper oxides films obtained by DC reactive magnetron sputtering

The phase composition of the copper oxides films obtained by DC reactive magnetron sputtering at oxygen partial pressures of 0.06, 0.10, and 0.16 mTorr is studied by X-ray phase analysis (XRPA) before and after their heat treatment within the range 300–550°C. It is found that the original phase compositions of the films of each lot are different; after the heat treatment at 550°C, all the films contained only CuO of a monoclinic structure.     

Nanoparticles of ZnO obtained by mechanical milling

Structural and optical characterization of mechanically milled ZnO powders are presented in this paper. It is shown that the application of mechanical milling is a very effective and simple technique to produce nanocrystalline powders, with the possibility of obtaining large quantities of materials. The milled powders are analyzed by X-ray diffraction, positron annihilation spectroscopy, scanning electron microscopy (SEM) and photoluminescence spectroscopy (PL). As milling proceeds, a clear reduction of grain size and homogenization are observed.     

Electromagnetic and microwave-absorbing properties of magnetic nickel ferrite nanocrystals

The electromagnetic and microwave absorbing properties of nickel ferrite nanocrystals were investigated for the first time. There were two frequencies corresponding to the maximum reflection loss in a wide thickness range from 3.0 to 5.0 mm, which may be bought by the nanosize effect and the good crystallization of the nanocrystals.     

Structural and mechanical properties of nanograined magnesium ferrite produced by oxalate coprecipitation method

Magnesium ferrite (MgFe₂O₄) was prepared by simple low-cost oxalate coprecipitation method and characterized by XRD and SEM. The X-ray analysis confirmed the formation of a single-phase cubic spinel structure. The product revealed a non-uniform morphology and some certain extent of agglomeration. Crystallite size, texture coefficient, dislocation density, hopping length, and mechanical properties of the product are also reported.     

Increased sensibility of mixed ferrite humidity sensors by subsequent heat treatment

The study presents the effects of different calcination temperatures on the size and morphology of mixed Co‐Ni ferrites, and the respective changes in the magnetic and electrical properties, with emphasis on their applicability as humidity sensors. The data suggests that the heat treatment does not significantly change the magnetic properties, but significant variations on the morphology of the nanoparticles, correlated with large changes in the electrical properties of the nanoparticles in terms of electrical permittivity and resistivity with electrical field frequency and humidity, with a clear influence of the calcination temperature over the sensibility of the materials to humidity.     

Bimagnetic hard/soft and soft/hard ferrite nanocomposites: Structural,magnetic and hyperthermia properties

Recent studies show that the chemical composition and shape of magnetic nanoparticles (NPs) play an important role in their properties. In particular, the bimagnetic NPs display useful and in many cases, more interesting properties than single-phase NPs. In this work, we prepared Fe₃O₄ and CoFe₂O₄ cube-like NPs and bimagnetic hard/soft (CoFe₂O₄/Fe₃O₄) and soft/hard (Fe₃O₄/CoFe₂O₄) nanocomposites (core/coating) using a facile and eco-friendly co-precipitation method that allows the synthesis of the cube-like NPs at temperatures near room temperature. The phase purity and the crystallinity of the NPs with a spinel structure were confirmed by the X-ray diffraction and infrared spectra techniques. Transmission electron microscopy (TEM) images revealed that the NPs have a cubic-like shape with an average dimension of 20 nm. Energy dispersive X-ray analysis, Mössbauer spectroscopy and SQUID magnetic measurements indicated the co-existence of Fe₃O₄ and CoFe₂O₄ phases in nanocomposites. In addition, the hysteresis loops exhibited a single-phase behavior in the nanocomposites that indicates there is a good exchange-coupling interaction between the hard and soft magnetic phases. The CoFe₂O₄/Fe₃O₄ nanocomposites presented a larger saturation magnetization than the CoFe₂O₄ NPs that is effective for their use in magnetic hyperthermia. Finally, we studied the hyperthermia properties of samples in an alternating magnetic field with a frequency of 276 kHz and field amplitude of 13.9 kA/m. Our results showed that magnetic hyperthermia efficiency simultaneously depends on the composition of samples along with magnetic anisotropy and saturation magnetization.