Structural and Magnetic Properties of NiFe2−2xSnxCuxO4

The substituted nickel ferrite (NiFe_2−2xSn_xCu_xO₄, x=0, 0.1, 0.2, 0.3) was prepared by the conventional ceramic method. The effect of substitution of Fe³⁺ ions by Sn⁴⁺ and Cu²⁺ cations on the structural and magnetic properties of the ferrite was studied by means of ⁵⁷Fe Mössbauer spectroscopy, alternating gradient force magnetometry (AGFM) and Faraday balance. Whereas undoped NiFe₂O₄ adopts a fully inverse spinel structure of the type (Fe)[NiFe]O₄, Sn⁴⁺ and Cu²⁺ cations tend to occupy octahedral positions in the structure of the substituted ferrite. Based on the results of Mössbauer spectroscopic measurements, the crystal-chemical formula of the substituted ferrite may be written as (Fe)[NiFe_1−2xSn_xCu_x]O₄, where parentheses and square brackets enclose cations in tetrahedral (A) and octahedral [B] coordination, respectively. The Néel temperature and the saturation magnetization values of the NiFe_2−2xSn_xCu_xO₄ samples were found to decrease with increasing degree of substitution (x). The variation of the saturation magnetization with x measured using the AGFM method and that calculated on the basis of the Mössbauer spectroscopic measurements are in qualitative agreement.     

First-principles study of the electronic and magnetic properties of a Nickel-Zinc ferrite: ZnxNi1−xFe2O4

Using first-principles density functional theory within the generalized gradient approximation method, the effect of Zn doping on electronic and magnetic properties of NiFe₂O₄ ferrite spinel has been studied. The crystal structure of the compounds is assigned to a pseudocubic structure and the lattice constant increases as the Zn concentration increases. Our spin-polarized calculations give a half-metallic state for NiFe₂O₄ and a normal metal state for Zn_xNi_1−xFe₂O₄ (0<x≤0.5). Based on the magnetic properties calculations, it is found that the saturation magnetic moment enhances linearly with increase in the Zn content in NiFe₂O₄. The Zn doping in NiFe₂O₄ also induces strong ferrimagnetism since it decreases the magnetic moment of A-sites.     

Structural, thermal and magnetic properties of Ni1−xMnxFe2O4 nanoferrites

In this paper, the structural, thermal and magnetic properties of Ni_1−xMn_xFe₂O₄ are presented. It is observed that high concentration of Mn²⁺ ions into NiFe₂O₄ tends to reduce the particle size. Calcination at 500 °C has resulted in the growth of Ni_1−xMn_xFe₂O₄ nanoparticles, but the calcination at 900 °C has led to the evaporation of the majorities of the polyvinyl alcohol. After calcination at 900 °C, crystallographically oriented NiMnFe₂O₄ nanoparticles are formed. These Ni_1−xMn_xFe₂O₄ nanoparticles show hysteresis behaviour upon magnetization. On the other hand, saturation magnetization (Ms) values decreases with increasing Mn content in ferrite due to the influence of Mn²⁺ ion in the sub lattice.     

Structural and magnetic investigations of sub-nano Mn-Mg ferrite prepared by wet method

Manganese-magnesium ferrite nanoparticles Mn_1−xMg_xFe₂O₄; 0≤x≤0.25 were prepared by the co-precipitation route. The samples were characterized by X-ray diffraction (XRD), which confirms the single phase spinel structure. Crystallite size, calculated from the (3 1 1) peak using the Scherrer formula, was found to increase with increasing Mg²⁺ concentrations and was found to be within the range 3-6 nm. TEM was also used to characterize the microstructure of nanosized Mn_1−xMg_xFe₂O₄. Nominal composition of the samples was determined by Atomic Absorption analysis (AA). Hysteresis loops of manganese-magnesium ferrite were obtained at room temperature and revealed lower saturation magnetization values associated with nanocrystalline Mn_1−xMg_xFe₂O₄ particles. This behavior was attributed to structural distortion of surface spins compared to that of the bulk one.     

Influence of copper cations on the magnetic properties of NiCuZn ferrite nanoparticles

Ni_0.6−xCu_xZn_0.4Fe₂O₄ (x=0-0.5) ferrite nanoparticles were prepared, employing a reverse micelle process. X-ray diffraction and transmission electron microscopy evaluations demonstrated that single phase spinel ferrites with narrow size distribution were obtained. Vibrating sample magnetometer was employed to probe the magnetic properties of the samples. It was found that with an increase in copper content, the saturation magnetization decreases. Magnetic dynamics of the samples was studied by measuring a.c. magnetic susceptibility versus temperature at different frequencies. The phenomenological Néel-Brown and Vogel-Fulcher models were employed to distinguish between the interacting or non-interacting systems. The system exhibits that there is strong interaction among fine particles.     

Synthesis and characterization of Ni-Zn ferrite nanoparticles

Nickel zinc ferrite nanoparticles Ni_xZn_1−xFe₂O₄ (x=0.1, 0.3, 0.5) have been synthesized by a chemical co-precipitation method. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, electron paramagnetic resonance, dc magnetization and ac susceptibility measurements. The X-ray diffraction patterns confirm the synthesis of single crystalline Ni_xZn_1−xFe₂O₄ nanoparticles. The lattice parameter decreases with increase in Ni content resulting in a reduction in lattice strain. Similarly crystallite size increases with the concentration of Ni. The magnetic measurements show the superparamagnetic nature of the samples for x=0.1 and 0.3 whereas for x=0.5 the material is ferromagnetic. The saturation magnetization is 23.95 emu/g and increases with increase in Ni content. The superparamagnetic nature of the samples is supported by the EPR and ac susceptibility measurement studies. The blocking temperature increases with Ni concentration. The increase in blocking temperature is explained by the redistribution of the cations on tetrahedral (A) and octahedral (B) sites.     

Study of magnetic and structural properties of ferrofluids based on cobalt-zinc ferrite nanoparticles

Ferrofluids are colloidal systems composed of a single domain of magnetic nanoparticles with a mean diameter around 30 nm, dispersed in a liquid carrier. Magnetic Co_(1−x)Zn_xFe₂O₄ (x=0.25, 0.50, 0.75) ferrite nanoparticles were prepared via co-precipitation method from aqueous salt solutions in an alkaline medium. The composition and structure of the samples were characterized through Energy Dispersive X-ray Spectroscopy and X-ray diffraction, respectively. Transmission Electron Microscopy (TEM) studies permitted determining nanoparticle size; grain size of nanoparticle conglomerates was established via Atomic Force Microscopy. The magnetic behavior of ferrofluids was characterized by Vibrating Sample Magnetometer (VSM); and finally, a magnetic force microscope was used to visualize the magnetic domains of Co_(1−x)Zn_xFe₂O₄ nanoparticles. X-ray diffraction patterns of Co_(1−x)Zn_xFe₂O₄ show the presence of the most intense peak corresponding to the (311) crystallographic orientation of the spinel phase of CoFe₂O₄. Fourier Transform Infrared Spectroscopy confirmed the presence of the bonds associated to the spinel structures; particularly for ferrites. The mean size of the crystallite of nanoparticles determined from the full-width at half maximum of the strongest reflection of the (311) peak by using the Scherrer approximation diminished from (9.5±0.3) nm to (5.4±0.2) nm when the Zn concentration increases from 0.21 to 0.75. The size of the Co-Zn ferrite nanoparticles obtained by TEM is in good agreement with the crystallite size calculated from X-ray diffraction patterns, using Scherer's formula. The magnetic properties investigated with the aid of a VSM at room temperature presented super-paramagnetic behavior, determined by the shape of the hysteresis loop. In this study, we established that the coercive field of Co_(1−x)Zn_xFe₂O₄ magnetic nanoparticles, the crystal and nanoparticle sizes determined by X-ray Diffraction and TEM, respectively, decrease with the increase of the Zn at%. Finally, our magnetic nanoparticles are not very hard magnetic materials given that the hysteresis loop is small and for this reason Co_(1−x)Zn_xFe₂O₄ nanoparticles are considered as soft magnetic material.     

Correlation between site preference and magnetic properties of substituted strontium ferrite thin films

SrFe_12−x(Sn_0.5Zn_0.5)_xO₁₉ thin films with x=0−5 were synthesized by a sol-gel method on thermally oxidized silicon wafer (Si/SiO₂). The site preference and magnetic properties of Zn-Sn substituted strontium ferrite thin films were studied using ⁵⁷Fe Mössbauer spectroscopy and magnetic measurements. Mössbauer spectra displayed that the Zn-Sn ions preferentially occupy the 2b and 4f₂ sites. The preference for these sites is responsible for the anomalous increase in the magnetization at high Zn-Sn substitutions. X-ray diffraction (XRD) patterns and field emission scanning electron microscope (FE-SEM) micrographs demonstrated that single phase c-axis hexagonal ferrite films with rather narrow grain size distribution were obtained. Vibrating sample magnetometer (VSM) was employed to probe magnetic properties of samples. The maximum saturation of magnetization and coercivity at perpendicular direction were 265 emu/g and 6.3 kOe, respectively. It was found that the complex susceptibility has linear variation with static magnetic field.     

Structural and magnetic properties of nanocrystalline stannic substituted cobalt ferrite

The structural and magnetic properties of the spinel ferrite system Co_1+xFe_2−2xSn_xO₄ (x=0.0–1.0) have been studied. Samples in the series were prepared by the ceramic technique. The structural and microstructural evolutions of the nanophase have been studied using X-ray powder diffraction and the Rietveld method. The refinement result showed that the type of the cationic distribution over the tetrahedral and octahedral sites in the nanocrystalline lattice is partially an inverse spinel. Far infrared absorption spectra show two significant absorption bands, around 600 cm⁻¹ and 425 cm⁻¹, which are respectively attributed to tetrahedral (A) and octahedral [B] vibrations of the spinel. Scanning Electron Microscopy (SEM) was used to study surface morphology. SEM images reveal particles in the nanosize range. The transmission electronic microscope (TEM) reveals that the grains are spherical in shape. TEM analysis confirmed the X-ray results. The magnetic properties of the prepared samples were characterized by using a vibrating sample magnetometer.     

Superconductivity and magnetism of La2Cu1−xZnxO4+δ chemically oxidized by NaClO

The structural, superconducting and magnetic properties of La₂Cu_1−xZn_xO_4+δ (0≤x≤0.1) chemically oxidized by NaClO at room temperature were studied. All the samples before and after oxidation are single phase with orthorhombic structure, as indicated by their powder X-ray diffraction analysis. The iodometric titration results indicate that Zn-substituted La₂Cu_1−xZn_xO₄ is more favorable for the insertion of the excess oxygen, as compared to the Zn-free La₂CuO₄. The T_c suppression rate resulting from Zn substitution in La₂Cu_1−xZn_xO_4+δ is −12.4 K/%. The effective magnetic moment induced by the non-magnetic Zn ion is the order of one Bohr magneton, which decreases with increasing the Zn concentrations in the range examined. The latter two results are qualitatively well consistent with those obtained in La_2−xSr_xCu_1−yZn_yO₄ with the Sr optimal doping. This reveals that the non-magnetic Zn ions play the same role in both of the La₂Cu_1−xZn_xO_4+δ with the excess oxygen content of about 0.1 and the La_2−xSr_xCu_1−yZn_yO₄ with the Sr optimal doping.     

X-ray and IR analysis of Cu-Si ferrite

Polycrystalline soft ferrite, Cu_1+xSi_xFe_2−2xO₄ (x=0.0, 0.05, 0.1, 0.15, 0.2 and 0.3) were prepared by standard ceramic technique. The X-ray analysis confirmed the single phase formation of the samples up to x=0.1 beside a second phase for x?0.15. The lattice parameter was found to decrease with composition(x), which is attributed to ionic size difference of cations involved. The bulk density measurements shows two different behavior for x< >0.15. The IR spectra of Cu-Si ferrite system have been analyzed in the frequency range 200-1200 cm⁻¹. It revealed two prominent bands ν₁ and ν₂ which are assigned to tetrahedral and octahedral metal complexes, respectively. The position of the highest frequency band is around 575 cm⁻¹ while the lower frequency band is around 400 cm⁻¹.     

Synthesis and magnetic properties of Mn–Zn ferrite nanoparticles

Mn–Zn ferrite nanoparticles (Mn_1−xZn_xFe₂O₄) are synthesized by a hydrothermal precipitation approach using metal sulfate solution and aqueous ammonia. The analysis methods of XRPD, TEM, TGA, and VSM are used to characterize the magnetic nanoparticles. Through the characterization of the precipitated nanoparticles, the effects of the reacting component proportions and preparation techniques on the Curie temperature, the magnetization, and the size distribution of Mn–Zn ferrite nanoparticles are discussed. Furthermore, the Mn–Zn ferrite nanoparticles are used to prepare ferrofluid. Variation of the magnetic properties of the ferrite nanoparticles with the composition content x of Zn and the magnetic moment of the nanoparticles are discussed.     

Nanostructural and magnetic studies of virtually monodispersed NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanocrystals synthesized by a liquid–solid-solution assisted hydrothermal route

This study presents a comprehensively and systematically structural, chemical and magnetic characterization of ~9.5 nm virtually monodispersed nickel ferrite (NiFe₂O₄) nanoparticles prepared using a modified liquid–solid-solution (LSS) assisted hydrothermal method. Lattice-resolution scanning transmission electron microscope (STEM) and converged beam electron diffraction pattern (CBED) techniques are adapted to characterize the detailed spatial morphology and crystal structure of individual NiFe₂O₄ particles at nano scale for the first time. It is found that each NiFe₂O₄ nanoparticle is single crystal with an fcc structure. The morphology investigation reveals that the prepared NiFe₂O₄ nanoparticles of which the surfaces are decorated by oleic acid are dispersed individually in hexane. The chemical composition of nickel ferrite nanoparticles is measured to be 1:2 atomic ratio of Ni:Fe, indicating a pure NiFe₂O₄ composition. Magnetic measurements reveal that the as-synthesized nanocrystals displayed superparamagnetic behavior at room temperature and were ferromagnetic at 10 K. The nanoscale characterization and magnetic investigation of monodispersed NiFe₂O₄ nanoparticles should be significant for its potential applications in the field of biomedicine and magnetic fluid using them as magnetic materials.     

Magnetic and microwave absorption properties of BaFe12−x (Mn0.5Cu0.5Zr)x/2O19 synthesized by sol–gel processing

BaFe_12−x (Mn_0.5Cu_0.5Zr)_x/2O₁₉ hexaferrites with x=1, 2 and 3 were prepared by sol–gel process. The ferrite powders possess hexagonal shape and are well separated from one another. The powders of these ferrites were mixed with polyvinylchloride (PVC) plasticizer to be converted into a microwave absorbing composite ferrite with a thickness of 1.8 mm. X-ray diffractometer (XRD), scanning electron microscope (SEM), ac susceptometer, vibrating sample magnetometer and vector network analyzer were used to analyze its structure, electromagnetic and microwave absorption properties. The results showed that magnetoplumbite structures for all samples were formed. The sample with higher magnetic susceptibility and coercivity exhibits a larger microwave absorbing ability. Also the present investigation demonstrates that a microwave absorber using BaFe_12−x(Mn_0.5Cu_0.5Zr)_x/2O₁₉ (x=2 and 3)/PVC with a matching thickness of 1.8 mm can be fabricated for applications over 15 GHz, with reflection loss more than −25 dB for specific frequencies, by controlling the molar ratio of the substituted ions.     

Structural and magnetic characteristics of Co1−xNix/2Srx/2Fe2O4 nanoparticles

Co_1−xNi_x/2Sr_x/2Fe₂O₄ (x=0–0.5 in steps of 0.1) ferrite nanoparticles have been synthesized at room temperature, without calcination, using a reverse micelle process. The site preference was determined by Mössbauer spectroscopy at 300 K. The hyperfine parameters were obtained, for the whole series of solid solutions. For the X≤0.20 samples, the spectra were fitted with two discrete sextets and for the X>0.20 samples, a magnetic hyperfine field distribution and a doublet were also imposed in the fit procedure. Hysteresis loops were measured using a superconducting quantum interference device magnetometer at 2 K and 300 K. The results indicate that the relative decrease in saturation magnetization of nanoparticles compared to the submicron particles could be attributed to a surface spin termination and disorder. Magnetic dynamics of the nanoparticles was studied by the measurement of ac magnetic susceptibility versus temperature at different frequencies and it is found that the results are well described by the Vogel–Fulcher model.     

A.C. and D.C. conductivity of NiZn ferrite nanoparticles in wet and dry conditions

Promising future applications of ferrite nanoparticles in medicine, drug delivery, sensors and ferrofluids are expected to be in wet or humid environments. Therefore nanostructured powders of ferrites having the chemical compositions.Ni_xZn _(1−x)Fe₂O₄ with (x=0.0, 0.25, 0.5, 0.75, and 1) were pressed immediately after preparation - by the co-precipitation method - without any drying to simulate a humid environment. The nanoparticles were characterized by X-ray diffraction analysis (XRD) to be sure of the formation of the ferrite in nanoscale. The infrared (IR) spectroscopy of the samples ensures the existence of water as well as the characteristic absorption bands of ferrites. The ac and dc conductivity of the samples had been investigated immediately after preparation (the as-prepared samples). Then, the samples were dried at 200 °C for about 12 h and reinvestigated. The behavior of conductivity differs significantly in the two cases showing a noticeable effect due to humidity. Also, the magnetic induction of the as-prepared samples was investigated by using the vibrating sample magnetometer (VSM). The samples show superparamagnetic behavior.     

Complex permittivity, complex permeability and microwave absorption properties of ferrite-paraffin polymer composites

We have investigated the electromagnetic (EM) characteristics of Co_xMn_1−xFe₂O₄ spinel ferrite (where x=0.0, 0.5 and 1.0) nanoparticles (NPs)/paraffin nanocomposite material at 8-20 GHz. Co_xMn_1−xFe₂O₄ NPs have been synthesized by cetyltrimethylammonium assisted hydrothermal route using NaOH. A variation in complex dielectric permittivity and magnetic permeability at room temperature with frequency in the range 8-20 GHz has been studied. Particles showed phase purity and crystallinity in powder X-ray diffraction (XRD) analysis. At the same time, Co_xMn_1−xFe₂O₄ NPs demonstrated a spinel cubic structure from XRD results. A reflection loss of −46.60 dB was found at 10.5 GHz for an absorber thickness of 2 mm. Co_xMn_1−xFe₂O₄ may be attractive candidates for EM wave absorption materials.     

Synthesis and characterization of Ni1−xCoxFe2O4 nanoparticles

Ni_1−xCo_xFe₂O₄ (x=0.6, 0.8 and 0.9) nanoparticles have been synthesized with various crystallite sizes depending on the thermal treatments and composition (cobalt content) using the sol-gel combustion method. The size of nanoparticles has been controlled by thermal treatment. On the other hand, the magnetic property of the ferrite has been controlled by changing the heat treatment. Morphology and particle sizes of Ni_1−xCo_xFe₂O₄ have been studied using atomic force microscopy (AFM) and transmission electron microscopy (TEM). The presence of functional group has been identified by Fourier Transform Infrared (FTIR) spectra. From TGA-DTA studies, the weight gains of Ni_1−xCo_xFe₂O₄ nanoparticles have been observed and it might be due to capping organic molecules with oxygen at temperatures above 200 °C. Magnetic properties of Ni_1−xCo_xFe₂O₄ particles have been analysed using VSM and it is found that saturation magnetization (M_s) has increased with particle size and has coercivity (H_c) increased initially and then decreased. The M_s and H_c values decreased with the increase of content of cobalt in Ni_1−xCo_xFe₂O₄.     

Fabrication and magnetic property analysis of monodisperse manganese-zinc ferrite nanospheres

Monodisperse Mn-Zn ferrite (Mn_1−xZn_xFe₂O₄) nanospheres have been prepared via a simple solvothermal method. The as-synthesized samples were characterized in detail by X-ray diffraction pattern (XRD), transmission electron microscope (TEM), high-solution transmission electron microscope (HRTEM), select area electron diffraction pattern (SAED), scanning electron microscope (SEM), and vibrating sample magnetometer (VSM). The results show that a large number of the high-purity Mn_1−xZn_xFe₂O₄ nanocrystallites were synthesized and these nanocrystallites oriented aggregated to nanospheres. The dependence of magnetic properties of Mn_1−xZn_xFe₂O₄ nanospheres on the composition content x of Zn was studied. The maximum saturation magnetization value of the as-prepared sample (Mn_0.6Zn_0.4Fe₂O₄) reached 52.4 emu g⁻¹.     

Structural and electrical properties of Cu doped NiFe2O4 nanoparticles prepared through modified citrate gel method

Nanoparticles of polycrystalline NiFe_2−xCu_xO₄ (0.0≤x≤0.05) ferrites were prepared through the modified citrate-gel method. The samples were obtained as dried gel after the successful chemical reaction of their respective metal nitrate solutions in the midst of citric acid as catalyst. X-ray diffraction (XRD) and selective area electron diffraction (SAED) confirmed the single phase nature of all the samples with an average particle size of 19.8 (±1). Fourier transformation infrared spectroscopy (FTIR) shows the presence of two broad vibrational bands between 400 and 1000 cm⁻¹ corresponding to the tetrahedral and the octahedral sites. The variation of dielectric properties (ε′, ε″, tan δ) and ac conductivity (σ_ac), with frequency reveals that the dispersion is due to the Maxwell–Wagner type of interfacial polarization in general and due to hopping of charges between Fe⁺² and Fe⁺³ as well as between Ni⁺² and Ni⁺³ ions at B-sites. The complex impedance spectroscopy has been used to study the effect of grain and grain boundary on the electrical properties of all the ferrite nanoparticles.