Nano-sized Ferrites Research Articles

The role of Ga substitution on magnetic and electromagnetic properties of nano-sized W-type hexagonal ferrites

A series of nano-sized single phase W-type SrGaxZn2Fe16−xO27 (x = 0.0, 0.1, 0.2, 0.3, 0.4) hexaferrites prepared by sol gel technique and sintered at 950 °C have been investigated. The thermal decomposition behavior of nitrate–citrate gel of as prepared powder was investigated by means of DTA/TGA analysis. The sintered powders were characterized by FTIR, XRD, SEM, VSM and vector network analyzer (VNA). X-ray diffraction patterns for pure and substituted W-type hexaferrites show the single phase structure with no impurity phase. The lattice parameters (a and c) decrease with the increase of Ga contents (x). The grain size estimated from SEM images is in the range of 139–76 nm which confirms the nanocrystalline nature of the investigated samples. The saturation magnetization (Ms) decreases whereas coercivity (Hc) increases with the increase of Ga contents (x). The values of Hc for all of the investigated samples lie in the range of few hundred oersteds which is one of the necessary conditions for EM materials. The microwave absorption property is enhanced in the frequency (with respect to −20 dB) from 0.5 to 13 GHz, and the bandwidth reaches 0.899 GHz. The attenuation peak value is −32 dB at the matching thickness of 3.4 mm.

Characterization of Stoichiometric Nanocrystalline Spinel Ferrites Dispersed on Porous Silica Aerogel

Stoichiometric magnetic nanosized ferrites MFe2O4 (M = Mn, Co, Ni) were prepared in form of nearly spherical nanocrystals supported on a highly porous silica aerogel matrix, by a sol-gel procedure. X-ray diffraction and transmission electron microscopy indicate that these materials are made out of non-agglomerated ferrite nanocrystals having size in the 5-10 nm range. Investigation by Mössbauer Spectroscopy was used to gain insights on the superparamagnetic relaxation and on the inversion degree. Magnetic ordering at room temperature varies from superparamagnetic in the NiFe2O4 sample, highly blocked (approximately 70%) in the MnFe2O4 sample and nearly fully blocked in the CoFe2O4 sample. A fitting procedure of the Mössbauer data has been used in order to resolve the spectrum into the tetrahedral and octahedral components; in this way, an inversion degree of 0.68 (very close to bulk values) was obtained for 6 nm silica-supported CoFe2O4 nanocrystals.

Magnetic properties of Co1−xNix/2Srx/2Fe2O4 (x = 0−1) ferrite nanoparticles synthesized by self-assembling media of reverse micelles

Co1−xNix/2Srx/2Fe2O ferrite nanoparticles were prepared using reverse micelle process. Mean particle size of pure ferrite nanoparticles is approximately 9 nm as determined by transmission electron microscopy (TEM). The heating thermograms of samples confirmed that there are no hydroxides in the ferrites fabricated via reverse micelles. Vibrating sample magnetometer (VSM) was employed to probe magnetic properties of nanosized. It was found that with increasing the amount of Ni and Sr in nanosized ferrites, the saturation magnetization decreases. Magnetic dynamics of the samples was studied by the measurement of AC magnetic susceptibility versus temperature at different frequencies. The phenomenological Néel – Brown and Vogel – Fulcher models were employed to distinguish between interacting or non-interacting system. Results show that there is strong interaction between fine particles.

Physico-chemical investigation on mixed alkali metal ferrites prepared by solution combustion method – A comparative study

Mixed alkali metal nanoferrites of the compositions M 0.5− X/2 Zn X Mn 0.05Fe 2.45− X/2 O 4 (M = Li, Na and K), where x varies from 0→0.5 in steps of 0.1, have been prepared by solution combustion method. Powder X-ray diffraction analysis for all the samples show the formation of single phase cubic spinel structure. The lattice parameter increases linearly with Zn content, which is attributed to ionic size differences of the cations involved. Both X-ray as well as experimental densities show upward trend with increasing ‘ x’ due to increase in the molecular weight of the ferrite composition. Mössbauer spectra display the superimposition of paramagnetic doublet over ferrimagnetic sextet with increasing diamagnetic ‘Zn’ content. The key magnetic properties of the ferrite obtained, such as saturation magnetization and Curie temperature have also been studied. The combustion method used for the synthesis is a rapid approach for direct conversion of the stoichiometric reactant solutions into fine nanoparticles of ferrite product at a temperature (600 °C) much lower than that of the conventional ceramic method. Scanning electron micrographs confirm the formation of nanosized ferrites.

Synthesis and characterization of nanosized ferrites from the thermolysis of strontium and barium tris(succinato)ferrate(III) precursors

Thermal analysis of alkaline earth metal tris(succinato)ferrate(III) precursors, M3[Fe(C4H4O4)3]2.xH2O (M = Sr, Ba) has been monitored isothermally and nonisothermally employing various physico-chemical techniques viz. simultaneous thermo gravimetry-derivative thermo gravimetry-differential scanning calorimetry (TG-DTG-DSC), XRD, Mössbauer spectroscopy, VSM, and TEM to characterize the intermediates/end products. Simultaneous TG-DTG-DSC depicts the sequence of the solid-state reactions in which dehydration is the first step followed by the decomposition of anhydrous precursors to yield iron(II) oxalate, Fe(II)C2O4, and respective metal oxalate intermediate species in the temperature range 150–210°C. A subsequent oxidative decomposition of iron(II) species leads to the formation of α-Fe2O3 and respective alkaline earth metal carbonate in the temperature range of 250–350°C. Finally, the alkaline earth metal carbonates decompose into their respective oxides in the temperature range of 590–680°C, followed by a solid-state reaction (>700°C) with α-Fe2O3 leading to the formation of ferrites of the stoichiometry, Sr2Fe2O5 and BaFe2O4. TEM studies reveal the formation of ferrite nanoparticles with average grain size of 25–30 nm.

Thermally synthesized nanosized copper ferrites as catalysts for environment protection

Nanosized copper ferrites were prepared by thermal method from the corresponding hydroxide carbonate precursors varying the temperature of synthesis. The phase composition of the obtained materials was characterized by XRD, Mössbauer spectroscopy, DSC and TPR analysis. Their catalytic properties were tested in total oxidation of toluene and methanol decomposition to CO and hydrogen. The relation between the synthesis parameters, phase composition of the samples and their transformation under the oxidation or reduction reaction medium was investigated in turns to understand the catalytic behavior of the obtained materials.

Low-temperature synthesis of nanocrystalline NiCuZn ferrite and the effect of Cr substitution on its electrical properties

In this study, nano-sized ferrites of compositions (Ni 0.6 Cu 0.20 Zn 0.20 Fe 2− x Cr x O 4 ), where x =0–1.0, were synthesized through nitrate–citrate auto-combustion method at relatively low temperature. XRD revealed the formation of nano-sized ferrite particles with cubic spinel structure. An exception was obtained for samples with Cr content ≤0.2, where weak diffraction peaks attributed to the presence of CuO and Fe 2 O 3 were appeared. The average crystallite sizes are much dependent on the chromium content and were found to decrease with its increase. The lattice parameter ( a ) slightly decreases with Cr substitution, which can be explained on the basis of the relative ionic radii of Cr 3+ and Fe 3+ ions. X-ray density was found also to decrease slightly with increase in chromium content, which indicates lower densification by the addition of Cr. FT-IR measurements show the characteristic ferrite bands. The Mössbauer spectra varied from Zeeman sextets to a relaxed doublet by increase in Cr content, which indicates a decrease in the hyperfine field at the octahedral site. Electrical property measurements revealed that Cr 3+ ions do not participate in conduction process but limit the degree of Fe 3+ –O 2− –Fe 3+ conduction resulting in a decrease in the conductivity and increase in conduction activation energy.

Synthesis and characterization of novel conductive and magnetic nano-composites

In the last years, a great deal of attention has been paid to use nano-sized ferrites as advanced additives in conducting polymers. The embedding of the ferrite materials into polymeric matrices is the simplest way to take advantage of some novel physical characteristics. In the present work, the preparation of a polyaniline/Co 1− x Mg x Fe 2O 4 nano-composite ( x = 0, 0.5, 1) with good magnetic and electrical properties was described. The structure, morphologies and properties of the samples were characterized by XRD, FT-IR, TEM, TGA, VSM and conductivity measurements. Nano-particles appear well dispersed in the polymer matrix and the results of TGA indicated that the ferrite nano-particles could improve the composite thermal stability. The electrical conductivity of the pure polyaniline decreased while the saturation magnetization ( M s ) and coercivity ( H c ) increased with ferrite. The ability of the composites to remove the toxic dyes from waste water was investigated.

Magnetically Responsive Phase-Change Microspheres with Large Magnetization Using Ferrite Nanoparticles

Magnetically responsive phase-change microspheres were prepared and studied in this article. In the synthetic process, oleic acid was used to modify the iron oxide nanoparticles. The ferrite nanoparticles, about 10 nm in diameter, were highly dispersed due to the oleic acid on the surface of the particles, and they were encapsulated in polymethyl methacrylate (PMMA) by microemulsion polymerization with paraffin, which could be presumed from the differential scanning calorimetry (DSC) curves. According to the morphology in the scanning electron microscopy (SEM) image, the average diameter of the microspheres was about 200 nm, a large amount of nano-sized ferrite can be observed in a transmission electron microscope (TEM) image showing the structure of the microspheres. Finally, in the magnetization curve from a vibrating sample magnetometer, the saturation magnetization of microspheres was 12.2 emu/g, which was effective in the compatibility of infrared simulation and microwave absorption.

Inverse magnetocaloric effect in sol–gel derived nanosized cobalt ferrite

The magnetocaloric properties of cobalt ferrite nanoparticles were investigated to evaluate the potential of these materials as magnetic refrigerants. Nanosized cobalt ferrites were synthesized by the method of sol–gel combustion. The nanoparticles were found to be spherical with an average crystallite size of 14 nm. The magnetic entropy change (ΔSm) calculated indirectly from magnetization isotherms in the temperature region 170–320 K was found to be negative, signifying an inverse magnetocaloric effect in the nanoparticles. The magnitudes of the ΔSm values were found to be larger when compared to the reported values in the literature for the corresponding ferrite materials in the nanoregime.

Magnetic properties of NiCuZn ferrite nanoparticles synthesized using egg-white

A new process to prepare single-phase nano-sized ferrites, Ni 0.8− x Cu 0.2Zn x Fe 2O 4 with x = 0.1–0.7, was developed using egg-white precursors. TG measurement showed that, the precursors must be calcined at 550 °C. XRD patterns indicated the formation of single-phase cubic ferrites with particle size in the range 28.7–48.4 nm. TEM image gave particle size agrees well with that estimated using XRD. FT-IR spectroscopy showed the characteristic ferrite bands. Hysteresis loops measurements exhibited an increase in the saturation magnetization value ( M s) up to zinc content of 0.2 followed by unexpected decrease, which suggests the preference of Zn 2+ ions to occupy octahedral sites. The decrease in the coercivity ( H c) with increasing zinc content is attributed to the lower magneto-crystalline anisotropy of Zn 2+ ions compared to Ni 2+ ions. Temperature dependence of the molar magnetic susceptibility ( χ M) suggested a ferrimagnetic behavior of the investigated samples and showed a decrease in the value of the Curie temperature ( T C) with increasing zinc.

Low temperature sintering study of nanosized Mn–Zn ferrites synthesized by sol–gel auto combustion process

The objective of present research was to sinter nanosized Mn-Zn ferrites (MZF) at low temperature (B1,000 C) by avoiding the formation of nonmagnetic phase (hematite). For this purpose, MZF powder was synthesized by sol-gel auto combustion process at 220 C and further calcined at 450 C. In calcined powder, single phase (spinel) was confirmed by X-ray diffraction analysis. Pellets were pressed, having 43% of the theoretical density and showing 47 emu gm -1 saturation magnetization (Ms). Various combinations of heating rate, dwelling time and gaseous environment were employed to meet optimum sintering conditions at low temperature (B1,000 C). It was observed that sintering under air or N2 alone had failed to prevent the formation of nonmagnetic (hematite) phase. However, hematite phase can be suppressed by retaining the green compacts at 1,000 C for 180 min in air then further kept for 120 min in nitrogen. Under these condi- tions, spinel phase (comprising of nano crystallites), 90% of theoretical density and 102 emu gm -1 of saturation

Structural and magnetic phase evolution study on needle-shaped nanoparticles of magnesium ferrite

Nanoparticles of magnesium ferrite (MgFe 2O 4) have been synthesized by chemical co-precipitation route. The microstructure, infrared spectral and magnetic properties have been studied by means of X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, infrared spectroscopy, high field magnetization, low field ac susceptibility and Mossbauer spectroscopic measurements. Transmission electron microscopy (TEM) observation showed that the nanocrystals present a needle-like shape with an aspect ratio of around 3.5 and long axis of 37 nm. The kinetics of needle-shaped nanocrystals formation has been discussed. The Mg 2+ seems to play key role in governing the rate of growth of growing planes of nanocrystals. The magnetic behaviour is explained by invoking the concept of super-paramagnetism assuming core–shell structure of the nanoparticles. Mossbauer spectral and susceptibility studies showed that the as-prepared nano-sized ferrite is super paramagnetic at room temperature and magnetic ordering evolves on baking and annealing the nanopowdered sample due to increase in the crystalline size. The high temperature annealing transforms the nanostructured ferrite to ordered magnetic structure of ceramic ferrite having long range ferrimagnetic ordering. Infrared (IR) spectral analysis reveals the weak high frequency shoulder due to disparity in the masses of cations present at tetrahedral sites, while splitting of low and high frequency absorption bands has been explained on the basis of Jahn–Teller effect in Fe 2+-ions which lead to a non-cubic component of the crystal field potential.

On the structural, magnetic and electrical properties of sol–gel derived nanosized cobalt ferrite

Nanoparticles of cobalt ferrite were synthesized by sol gel method. These particles were structurally characterized by using X-Ray Diffraction and Transmission Electron Microscopy, High Resolution Transmission Electron Microscopy, Energy Dispersive Spectrum and Inductively Coupled Plasma Analysis and the results confirmed the formation of spherically shaped nanoparticles of cobalt ferrite having a size lying in the range of 13–14 nm. The as prepared sample was sintered at 800 °C and the structural, magnetic and dielectric properties were measured. The dielectric properties were studied and analyzed as a function of temperature and frequency. The ac and dc conductivity studies were carried out to delve into the conduction mechanism. The existing models based on quantum mechanical tunneling were effectively employed to explain the frequency dependent conductivity.

A Structural and Magnetic Investigation of the Inversion Degree in Ferrite Nanocrystals MFe2O4(M = Mn, Co, Ni)

The structural and magnetic properties of nanocrystalline manganese, cobalt, and nickel spinel ferrites dispersed in a highly porous SiO2 aerogel matrix were studied. X-ray diffraction and high-resolution transmission electron microscopy indicate that single crystalline ferrite nanoparticles are well dispersed in the amorphous matrix. The cation distribution between the octahedral and tetrahedral sites of the spinel structure was investigated by X-ray absorption spectroscopy. The analysis of both the X-ray absorption near edge structure and the extended X-ray absorption fine structure indicates that the degree of inversion of the spinel structure increases in the series Mn, Co, and Ni spinel, in accordance with the values commonly found in the corresponding bulk spinels. In particular, fitting of the EXAFS data indicates that the degree of inversion in nanosized ferrites is 0.20 for MnFe2O4, 0.68 for CoFe2O4, and 1.00 for NiFe2O4. Magnetic characterization further supports these findings.

Mössbauer studies of nanosized ferrites prepared by the combustion of metal nitrates–oxalyl dihydrazide solutions

Alkaline earth metal ferrites have been prepared by combustion of redox mixtures containing metal nitrates and oxalyl dihydrazide (ODH) at 673 K. On rapid heating, ODH–metal nitrate mixture undergoes an abrupt exothermic redox chemical reaction that facilitates atomic scale mixing of cations. This leads to the formation of stoichiometrically pure and single-phase nanoparticle ferrites at comparatively reduced temperature (400°C) and in less time than possible by the conventional ceramic method. Because of their different cationic size, polarizability etc., alkaline earth metal cations yield different type of ferrites i.e. MFe2O4 (M = Mg, Ba), Ca2Fe2O5 and SrFe12O19.

Colony-forming activity of unipotent hemopoietic precursors under the effect of nanosized ferrites in a constant magnetic field in vitro

We studied in vitro effect of ferrimagnetic nanoparticles in a dose of 3 mg/liter (10 maximum permissible concentrations) on colony-forming capacity of bone marrow granulocytic and monocytic precursors in a constant magnetic field at magnetic field intensity of 200 Oe. We tested powders obtained by the methods of electrical explosion of conductors (magnetite and a mixture of hematite with magnetite) or mechanochemical synthesis (cobalt ferrite). According to electron microscopy, size of particles was within 6-65 nm. Specific effect of nanopowders on functional properties of hemopoietic and stromal cells were demonstrated; this effect was not related to dissolution of these powders, but had a complex nature. It depends on the size and magnetic characteristics of powder particles, the route and dose of administration, and the presence of external magnetic field. It was emphasized that in multicellular systems a reaction of committed hemopoietic precursors mediated via cells (factors) of microenvironment cannot be excluded, the state of this system varying in different individuals and under different conditions. Our data open new vistas for the creation and targeted use of nanosized materials and technologies for individual therapy in the context of personalized medicine.

Fabrication and electrochemical performance of nickel ferrite nanoparticles as anode material in lithium ion batteries

Nano-sized nickel ferrite (NiFe 2O 4) was prepared by hydrothermal method at low temperature. The crystalline phase, morphology and specific surface area (BET) of the resultant samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and nitrogen physical adsorption, respectively. The particle sizes of the resulting NiFe 2O 4 samples were in the range of 5–15 nm. The electrochemical performance of NiFe 2O 4 nanoparticles as the anodic material in lithium ion batteries was tested. It was found that the first discharge capacity of the anode made from NiFe 2O 4 nanoparticles could reach a very high value of 1314 mAh g −1, while the discharge capacity decreased to 790.8 mAh g −1 and 709.0 mAh g −1 at a current density of 0.2 mA cm −2 after 2 and 3 cycles, respectively. The BET surface area is up to 111.4 m 2 g −1. The reaction mechanism between lithium and nickel ferrite was also discussed based on the results of cycle voltammetry (CV) experiments.

Anomalous magnetic properties of mechanically alloyed spinel-ferrite nanopowders

The phase composition, structure parameters, and basic magnetic properties of several magnetically alloyed spinel-ferrite nanopowders produced from salt solutions are studied. Particle-size and surface effects on the saturation magnetization and magnetic anisotropy of the examined materials are investigated. The validity of the core-shell model for describing the magnetic properties of the nano-sized spinel ferrites under review is discussed.

Preparation and characterization of [formula omitted] nano spinels for electrocatalysis of oxygen evolution in alkaline solutions

Some new nano-sized ternary ferrites with molecular formula, CuFe 2 - x Cr x O 4 ( 0 ⩽ x ⩽ 1 ) have been prepared by a precipitation method and were investigated as electrocatalysts for the oxygen evolution reaction (OER) in alkaline solutions. The reaction followed first-order kinetics with respect to OH - concentration, regardless of the nature of the electrocatalyst. The Tafel slope for the OER was ∼ 2.3 RT / F with each oxide at low overpotentials. The replacement of Fe by Cr in the CuFe 2O 4 matrix was found to improve both geometrical as well as electronic properties of the material in favour of electrocatalysis of O 2 evolution considerably.