Magnetic properties of Nd-Y<Subscript>3</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> nanoparticles

Nb³⁺-substituted garnet nanoparticles Y_3−xNd_xFe₅O₁₂ (x = 0.0, 0.5, 1.0, 1.5, and 2.0) were fabricated by a sol-gel method and their crystalline structures and magnetic properties were investigated by using X-ray diffraction (XRD), thermal analysis (DTA/TG), and vibrating sample magnetometer (VSM). The XRD patterns of Y_3−xNd_xFe₅O₁₂ have only peaks of the garnet structure and the sizes of particles range from 34 to 70 nm. From the results of VSM, it is shown that when the Nd concentration x ( 1.0, the saturation magnetization of Y_3−xNd_xFe₅O₁₂ increases as the Nd concentration (x) is increased, and gets its maximum at x = 1.0, but when x ( 1.0, the saturation magnetization decreases with increasing the Nd concentration (x), this may be due to the distortion of the microstructure of Y_3−xNd_xFe₅O₁₂, which leads to the decrease of the effective moment formed by Fe³⁺. Meanwhile, it is observed that with the enhancement of the surface spin effects, the saturation magnetization rises as the particle size is increased.     

Fast microwave synthesis of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Ag magnetic nanoparticles using Fe<Superscript>2+</Superscript> as precursor

A simple and quick microwave method to prepare high performance magnetite nanoparticles (Fe₃O₄ NPs) directly from Fe has been developed. The as-prepared Fe₃O₄ NPs product was fully characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The results show that the as-prepared Fe₃O₄ NPs are quite monodisperse with an average core size of 80 × 5 nm. The microwave synthesis technique can be easily modified to prepare Fe₃O₄/Ag NPs and these NPs possess good magnetic properties. The formation mechanisms of the NPs are also discussed. Our proposed synthesis procedure is quick and simple, and shows potential for large-scale production and applications for catalysis and biomedical/biological uses.     

Synthesis and microwave absorption properties of sandwich-type CNTs/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/RGO composite with Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> as a bridge

A novel sandwich-type CNTs/Fe₃O₄/RGO composite with Fe₃O₄ as a bridge was successfully prepared through a simple solvent-thermal and ultrasonic method. The structure and morphology of the composite have been characterized by Fourier-transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. This new structure can effectively prevent the agglomeration of GO and the combination of CNTs/Fe₃O₄ and RGO shows a strong reflection loss (R_L) (?50 dB) at 8.7 GHz with absorber thickness of 2.5 mm. Moreover, compared with CNTs/Fe₃O₄/GO composite, it is found that the thermal treating process is beneficial to enhance the microwave absorption properties, which may be attributed to high conductivity of RGO. On this basis, the microwave absorbing mechanism is systematically discussed. All the data show that the CNTs/Fe₃O₄/RGO composite exhibits excellent microwave absorption properties with light density and is expected to have potential applications in microwave absorption.     

Microwave-hydrothermal synthesis of Y<Subscript>3</Subscript>Fe<Subscript>3.35</Subscript>Al<Subscript>1.65</Subscript>O<Subscript>12</Subscript> nanoparticles for magneto-hyperthermia application

Crystalline aluminum substituted yttrium iron garnet nanoparticles Y₃Fe_3.35Al_1.65O₁₂ (YIG) was synthesized by hydrothermal microwave synthesis at 140 °C with soaking times ranging from 15 to 60 min. X-ray diffraction confirmed the single-phase YIG nanoparticles excluding the presence of any other phases in the reaction products. The Raman spectra revealed that the largest soaking time provides greater energy crystallization causing changes of lattice vibration and a certain degree of disorder in the crystal lattice. Field emission gun-scanning electron microscopy and high resolution transmission electronic microscopic revealed a homogeneous size distribution of nanometric YIG powders with agglomerated particles. Magnetic measurements were achieved by using a vibrating-sample magnetometer unit. YIG nanoparticles have great potential in magneto-hyperthermia application once in vivo applications magnetic induction heating ferromagnetic compounds generate heat in AC magnetic fields.     

The magnetic properties of BiY<Subscript>2</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> nanoparticles doped with Cr ions

BiY₂Cr _x Fe_5?x O₁₂ (x = 0, 0.05, 0.1, 0.2, 0.3) nanocrystals were synthesized by using a sol-gel method. Samples were characterized by the powder X-ray diffraction (XRD), the thermal gravity analysis (TGA) and the differential thermal analysis (DTA), the vibrating sample magnetometer(VSM) and Mössbauer spectrums. The average sizes of the particles were determined by the Scherrer’s formula. The special Ms and Mössbauer spectra of BiY₂Cr _x Fe_5?x O₁₂ nanocrystals are researched at room temperature. It is seen that the special Mss of samples are initially increased with increasing Cr³⁺ content (x < 0.1), and decreased with increasing content of Cr³⁺ ions (x > 0.1).     

Study of structural,morphological and magnetic properties of Ba<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>Fe<Subscript>12</Subscript>O<Subscript>19</Subscript>

Single-phase barium Strontium hexaferrite (Ba_0.5Sr_0.5Fe₁₂O₁₉—BSF) was synthesized by sol–gel method using metal nitrates as source and d-Fructose as a fuel. The phase formation, surface morphology and magnetic properties of the samples were analyzed by X-ray Diffraction, High-resolution Scanning Electron Microscope (HR-SEM) and Vibrating Sample Magnetometer (VSM). X-ray analysis indicates that the sintered samples were remained in hexagonal structure. The densities of the sintered samples at 1,150 °C were found to be 93% of theoretical density. HR-SEM and VSM studies reveal that the sintered samples were resulted in hexagonal structure with good magnetic properties. The average diagonal of the grains varies from 0.95 to 1.7 μm. The thermal treatment effects the growth of the hexagonal grains of ferrites.     

Characterization and electrical properties of semiconducting Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-K<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript> glasses

Semiconducting glasses of the Fe₂O₃-Bi₂O₃-K₂B₄O₇ system were prepared by the press-quenching method and their dc conductivity in the temperature range 223–393 K was measured. The glass transition temperature values (T_g) of the present glasses were larger than those of tellurite glasses. This indicates a higher thermal stability of the glass in the present system. The density for these glasses was consistent with the ionic size, atomic weight and amount of different elements in the glasses. Mössbauer results revealed that the relative fraction of Fe increases with increasing Fe₂O₃ content. Electrical conductivity showed a similar composition dependency as the fraction of Fe. The glasses had conductivities ranging from 10 to 10 Scm at temperatures from 223 to 393 K. Electrical conduction of the glasses was confirmed to be due to non-adiabatic small polaron hopping and the conduction was primarily determined by hopping carrier mobility.     

Visible photocatalytic degradation of methylene blue on magnetic semiconducting La<Subscript>0.2</Subscript>Sr<Subscript>0.7</Subscript>Fe<Subscript>12</Subscript>O<Subscript>19</Subscript>

Methylene blue (MB) is a representative of a class of dyestuffs resistant to biodegradation. This paper presents a novel photocatalytic degradation of MB by La_0.2Sr_0.7Fe₁₂O₁₉ compound, which is a traditional permanent magnet and displays a large magnetic hysteresis (M–H) loop. The remnant magnetic moment and coercive field are determined to be 52 emu/g and 5876 Oe, respectively. UV–Visible optical spectroscopy reveals that La_0.2Sr_0.7Fe₁₂O₁₉ is simultaneously a semiconductor, whose direct and indirect band gap energies are determined to be 1.47 and 0.88 eV, respectively. The near infrared band gap makes it a good candidate to harvest sunlight for photocatalytic reaction or solar cell devices. This magnetic compound demonstrates excellent photocatalytic activity on degradation of MB under visible illumination. The colour of MB dispersion solution changes from deep blue to pale white and the absorbance decreases rapidly from 1.8 down to zero when the illumination duration extends to 6 h. Five absorption bands did not make any blue shifts along with the reaction time, suggesting a one-stepwise degradation process of MB, which makes La_0.2Sr_0.7Fe₁₂O₁₉ a unique magnetic catalyst and differs from TiO₂ and other conventional catalysts.     

Al-doped Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles and Their Magnetic Properties

Al-doped Fe₃O₄ nanoparticles were synthesized for the first time via the Composite-Hydroxide-Mediated (CHM) method from Fe₃O₄ and Al₂O₃ without using any capping agent. The synthesis technique was one-step and cost effective. The obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersion spectroscopy (EDS). Samples with a tunable size of 500–1500 nm, 200–800 nm, and 100–700 nm could be obtained by adjusting the reaction time and temperature. Magnetic property of the as-synthesized Al-doped Fe₃O₄ nanoparticles was investigated. Magnetic hysteresis loops measured in the field range of −10 kOe<H<10 kOe, indicated the ferromagnetic behavior with coercivity (H _c) of 470 and 110 Oe and remanence magnetization (M _r) of 13 and 6.4 emu/g at the temperature of 5 and 300 K, respectively. The saturation intensity (M _s) was 46.1 emu/g at 5 K, while it was about 43.6 emu/g at 300 K.     

Structural studies of a new electroceramic composite: Pb(Fe<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>)O<Subscript>3</Subscript> (PFN)-Cr<Subscript>0.75</Subscript>Fe<Subscript>1.25</Subscript>O<Subscript>3</Subscript>(CRFO)

A study of the structural characteristics of the composites [Pb(Fe_0.5Nb_0.5)O₃(PFN)] _x -[Cr_0.75Fe_1.25O₃(CRFO)]_100?x (x = 0 (CRFO100), 10, 50, 90, 100) was performed in this work. The compounds PFN100 and CRFO100 were prepared by conventional solid-state method and investigated by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and ⁵⁷Fe Mössbauer Spectroscopy techniques. The X-ray analysis shows that PFN100 is tetragonal and the CRFO100 phase has a trigonal symmetry. The refinement of all the composites was also performed and discussed in this paper. The Mössbauer spectrum for the composite samples shows a paramagnetic doublet and a sextet probably assigned to a magnetic phase associated to Fe⁺³. For the sample PFN100, only a magnetic field of 49.5 T (isomer shift (δ) = 0.21 mm/s) was detected. For the composite sample, the δ and Δ are typical of Fe ions at sites of octahedral coordination.     

The effect of sintering temperature on magnetic and dielectric properties of Ho<Subscript>3</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> ceramics

Ho₃Fe₅O₁₂ ceramics were fabricated by the solid-state reaction method. The results revealed an increase of the grain size, dielectric constant, and dielectric loss, while a decrease of the remnant magnetization and coercive field with increasing sintering temperature. A dielectric relaxation behavior was observed, which might be associated with the charge carrier hopping between Fe²⁺ and Fe³⁺. A cole–cole fitting to loss peaks revealed a dependence of the activation energy and the broaden factor on the relative density of the samples. Furthermore, at appropriate frequencies, the 1250 °C-sintered samples showed high dielectric constant, low dispassion, and good temperature stability around room temperature.     

Morphological control of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> particles via glycothermal process

Acicular magnetite (Fe₃O₄) powders were synthesized through new glycothermal dehydration by using crystalline α-FeOOH as precursor and glycols as solvent. When ethylene glycol was used as solvent, the phase was in-situ transformed from acicular α-FeOOH to α-Fe₂O₃ and finally to Fe₃O₄ at 270 °C for 6 h without morphological change. When water was added as a co-solvent in glycothermal reaction, Fe₃O₄ powders were synthesized through dissolution–recrystallization process at 230 °C for 3 h. The volume ratio of ethylene glycol to water (E/W) in the reaction has a strong effect on the morphology of the synthesized Fe₃O₄ particles. The particle shape of Fe₃O₄ particles changed from needle to sphere when the water content in E/W volume ratio increased from 0.5 to 1 mL in mixed glycothermal condition. When the water were added by more than 10 ml, the particle shape of Fe₃O₄ changed from sphere to octahedron truncated with the {100} faces and finally distinct octahedron with only {111} faces. Also, it is demonstrated that the size of Fe₃O₄ particles can be controlled from 1–2 μm to 100–200 nm by varying the reaction conditions such as the volume ratio of water to ethylene glycol and additive in glycothermal reaction.     

Synthesis and structure of the CsSmP<Subscript>4</Subscript>O<Subscript>12</Subscript> cyclotetraphosphate (cubic CsNdP<Subscript>4</Subscript>O<Subscript>12</Subscript> structure)

CsSmP₄O₁₂ crystals have been prepared at 300°C in molten polyphosphoric acids containing Cs, Mg, and Sm cations, and their crystal structure has been determined: sp. gr. I \(\bar 4\) 3d, a = 15.1225(8) Å, Z = 12, CsNdP₄O₁₂ structure.     

Dielectric properties of iron doped calcium copper titanate,CaCu<Subscript>3</Subscript>Ti<Subscript>3.9</Subscript>Fe<Subscript>0.1</Subscript>O<Subscript>12</Subscript> ceramic

Dielectric properties of iron doped CaCu₃Ti₄O₁₂ (CCTO), viz. CaCu₃Ti_3.9Fe_0.1O₁₂ (CCTFO) prepared by a novel semi-wet route have been investigated. X-ray diffraction of powder sintered at 900 °C show formation of single phase solid solution. Energy dispersive X-ray spectroscopy (EDX) confirmed the presence of CuO rich phase at grain boundaries of CCTFO. Nature of dielectric relaxation observed above room temperature is studied using complex plane impedance analysis and modulus spectroscopy. It has been found that out of the two relaxations reported earlier above room temperature, one occurring at lower temperature is due to grainboundaries interfacial polarization.     

Thermodynamic properties of SrAl<Subscript>12</Subscript>O<Subscript>19</Subscript> and SrAl<Subscript>4</Subscript>O<Subscript>7</Subscript>

Strontium aluminates are important compounds with interesting properties such as long-duration phosphorescence and elastico-deformation luminescence. They have potential application in flexible light emitting panels. Since there are serious discrepancies in available thermodynamic data for these compounds, a redetermination of their Gibbs energies of formation was undertaken using solid-state electrochemical cells incorporating single-crystal SrF₂ as the electrolyte in the temperature range from 1000 to 1300 K. However, the measurements were restricted to SrAl₁₂O₁₉ and SrAl₄O₇ because of the formation of strontium oxyfluoride phase between SrAl₂O₄ and SrF₂. For the reactions, SrO + 6 Al₂O₃ → SrAl₁₂O₁₉, ΔG ^o/J mol^?1 (± 280) = ?83386 ? 25.744 (T/K), and SrO + 2Al₂O₃ → SrAl₄O₇, ΔG ^o/J mol^?1 (± 240) = ?80187 ? 25.376 (T/K). The high entropy of SrAl₄O₇ and SrAl₁₂O₁₉ can be partly related to their complex structures. The results of this study are consistent with calorimetric data on enthalpy of formation of other Sr-rich aluminates and indicate only marginal stability for SrAl₄O₇ relative to its neighbours, SrAl₁₂O₁₉ and SrAl₂O₄. The thermodynamic data explain the difficulty in direct synthesis of phase pure SrAl₄O₇ and the formation of SrAl₂O₄ as the initial ternary phase when reacting SrO and Al₂O₃ or crystallizing from amorphous state, irrespective of composition.     

An efficientfficient,controllable and facile two-step synthesis strategy: Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@RGO composites with various Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles and their supercapacitance properties

An efficient,controllable,and facile two-step synthetic strategy to prepare graphene-based nanocomposites is proposed.A series of Fe3O4-decorated reduced graphene oxide (Fe3O4@RGO) nanocomposites incorporating Fe3O4 nanocrystals of various sizes were prepared by an ethanothermal method using graphene oxide (GO) and monodisperse Fe3O4 nanocrystals with diameters ranging from 4 to 10 nm.The morphologies and microstructures of the as-prepared composites were characterized by X-ray diffraction,Raman spectroscopy,nitrogen adsorption measurements,and transmission electron microscopy.The results show that GO can be reduced to graphene during the ethanothermal process,and that the Fe3O4 nanocrystals are well dispersed on the graphene sheets generated in the process.The analysis of the electrochemical properties of the Fe3O4@RGO materials shows that nanocomposites prepared with Fe3O4 nanocrystals of different sizes exhibit different electrochemical performances.Among all samples,Fe3O4@RGO prepared with Fe3O4 nanocrystals of 6 nm diameter possessed the highest specific capacitance of 481 F/g at 1 A/g,highlighting the excellent capability of this material.This work illustrates a promising route to develop graphene-based nanocomposite materials with a wide range of potential applications.     

Solvothermal synthesis and characterization of size-controlled monodisperse Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles

Monodisperse Fe₃O₄ nanoparticles with narrow size distribution could be successfully synthesized in large quantities by a facile solvothermal synthetic method in the presence of oleic acid and oleylamine. Well-defined assembly of uniform nanoparticles with average sizes of 8 nm can be obtained without a further size-selection process. The sizes of final products could be readily tuned from 5 to 12 nm by adjusting the experimental parameters such as reaction time, temperature, and surfactants. The phase structures, morphologies, and magnetic properties of the as-prepared products were investigated in detail by X-ray diffraction, transmission electron microscopy, selected area electron diffraction, high-resolution transmission electron microscopy, and magnetometry with a superconducting quantum interference device. The magnetic study reveals that the as-synthesized nanoparticles are ferromagnetic at 2 K while they are superparamagnetic at 300 K.     

Study of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nano-Magnetic Ferrofluid by Atomic Force Microscope

The magnetic ferrofluid is a special intelligent material and its many properties can be controlled by external magnetic field. This paper introduces the preparation, performance and applications of Fe₃O₄ nano-ferrofluid, principally observed by the microstructure characterization by Atomic Force Microscopy (AFM), and we measured the particle size and morphology of nano-ferrofluid. The magnetic property was analyzed from the microstructure characterization, and the analysis results show that the size of the Fe₃O₄ nano-particle is about 5 nm; the magnetic property is closely related to the chain microstructure and is influenced by the nano-particle distribution in the Fe₃O₄ magnetic ferrofluid.     

Synthesis and applications of fluorescent-magnetic-bifunctional dansylated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> nanoparticles

Bifunctional magnetic-luminescent dansylated Fe₃O₄@SiO₂ (Fe₃O₄@SiO₂-DNS) nanoparticles were fabricated by the nucleophilic substitution of dansyl chloride with primary amines of aminosilane-modified Fe₃O₄@SiO₂ core–shell nanostructures. The morphology and properties of the resultant Fe₃O₄@SiO₂-DNS nanoparticles were investigated by transmission electron microscopy, FT–IR spectra, UV–vis spectra, photoluminescence spectra, and vibrating sample magnetometry. The Fe₃O₄@SiO₂-DNS nanocomposites exhibit superparamagnetic behavior at room temperature, and can emit strong green light under the excitation of UV light. They show very low cytotoxicity against HeLa cells and negligible hemolysis activity. The T ₂ relaxivity of Fe₃O₄@SiO₂-DNS in water was determined to be 114.6 Fe mM⁻¹ s⁻¹. Magnetic resonance (MR) imaging analysis coupled with confocal microscopy shows that Fe₃O₄@SiO₂-DNS can be uptaken by the cancer cells effectively. All these positive attributes make Fe₃O₄@SiO₂-DNS a promising candidate for both MR and fluorescent imaging applications.