Preparation and magnetic properties of electrospun CuO/NiO bimetallic nanofibers via sol–gel electrospinning

We report the fabrication and magnetic properties of the CuO/NiO bimetallic composite nanofibers prepared by sol–gel electrospinning and followed by calcination. The added precursors (copper nitrate trihydrate (CuNT) and nickel chloride hexahydrate (NiCH)) significantly influenced the fiber formation and its morphologies during electrospinning. The magnetic properties were investigated by Vibrating Sample Magnetometer and Electron Spin Resonance (ESR) curves. After calcination for the production of the metallic nanofibers, the fiber morphologies were dramatically changed depending on the added amounts of precursors ranging from 2.5 to 7.5 wt%. From the magnetic hysteresis loop (M-H curve) and ESR analysis of the calcined electrospun CuO/NiO bimetallic nanofibers, it was found that the magnetization of the calcined electrospun CuO/NiO bimetallic nanofibers with various weight ratio of CuNT:NiCH = 9:1, 1:1, and 1:9 at an applied magnetic field of 10 kOe was 0.480, 0.402, and 0.337 emu/g, respectively, indicating that the calcined electrospun CuO/NiO bimetallic nanofibers have magnetic properties.     

Electrospun Fe3O4/PVP//Tb(BA)3phen/PVP magnetic–photoluminescent bifunctional bistrand aligned composite nanofibers bundles

Fe₃O₄/PVP//Tb(BA)₃phen/PVP magnetic–photoluminescent bifunctional bistrand aligned composite nanofibers bundles based on Fe₃O₄ nanoparticles (NPs) and terbium complex Tb(BA)₃phen (BA = benzoic acid) were fabricated by employing a parallel axial electrospinning setup and were characterized by X-ray diffraction, field-emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), transmission electron microscopy, fluorescence spectroscopy, and vibrating sample magnetometer. It is found that Fe₃O₄ NPs were only dispersed into one strand of the bistrand aligned composite nanofibers bundles, but no nanoparticles in the other strand. And the average diameter of the individual strand fiber was 200 ± 25 nm. The bistrand aligned composite nanofibers bundles exhibit strong green emissions under the excitation of 275 nm ultraviolet light, and the ⁵ D ₄ → ⁷ F ₅ hypersensitive transition at 545 nm was the predominant emission peak of Tb³⁺ ions. The newly obtained bifunctional nanofibers bundles exhibit excellent magnetism and high fluorescence intensity and are expected to apply in biology cell separation, magnetic resonance imaging, drug deliver, and fluorescence immunoassays/imaging.     

Synthesis and magnetic properties of polycrystalline films of Co x Fe y Cr3 − x − y O4 and Cr2O3/CoFe2O4 multiferroics

Magnetic properties of first obtained polycrystalline films of FeCr₂O₄, CoCr₂O₄, and CoFe_0.5Cr_1.5O₄ multiferroics and films of a Cr₂O₃/CoFe₂O₄ composite multiferroic have been studied. In particular, magnetization curves and temperature dependences of the magnetic moment of the samples were measured in the temperature range 4.2–300 K in fields of up to 10 kOe. It was shown that the Curie point of a multiferroic depends on its cation composition. It was found that an exchange bias of the hysteresis loop exists in films of the Cr₂O₃/CoFe₂O₄ composite multiferroic at temperatures below the Néel point of Cr₂O₃ (330 K).     

Preparation and characterization of CuCrO2–CeO2 nanofibers by electrospinning method

Journal of Materials Science: Materials in Electronics - In this study, CuCrO2–CeO2 nanofibers were prepared by the electrospinning method and the influences of different concentrations on...     

Preparation and characterization of the microstructure,dielectric and magnetoelectric properties of multiferroic Sr3CuNb2O9–CoFe2O4 ceramics

Different research methods were used to study the microstructural and magnetoelectric properties of multiferroic Sr₃CuNb₂O₉–CoFe₂O₄ (SCNO–CFO). X-ray verification provides fundamental information about the local symmetry of the two-phase SCNO–CFO ceramic. P4mm unit cell with minimal tetragonality and a cubic Fd-3m structure have been found for SCNO and CFO, respectively. Some additional traces of cupric oxide were also detected. SEM observations confirmed that the microstructure is built of various crystallites forming a two-component electroceramics and CuO-rich grain boundary segregation. Impedance spectroscopy studies reveal the thermally activated dielectric relaxations. The temperature-dependent behavior of the diffuse dielectric anomalies was successfully described by the modified Debye equation. Finally, magnetoelectric measurements clearly confirm intrinsic coupling between the piezoelectric and magnetic phases of SCNO–CFO.     

Photoluminescence and scintillation properties of Eu2O3–BaO–Nb2O5–TeO2 glass and glass ceramics

Journal of Materials Science: Materials in Electronics - 1Eu2O3–3BaO–20Nb2O5–76TeO2 glass and the corresponding glass-ceramics were synthesized with the aim to investigate the...     

Synthesis and luminescence properties of highly uniform SiO2@LaPO4:Eu3+ core–shell phosphors

SiO₂@LaPO₄:Eu³⁺ core–shell phosphors have been successfully synthesized by a one-step and economical wet-chemical route at low temperature. The as-obtained products were characterized by means of photoluminescence spectroscopy (PL), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS). The SEM, EDS and XPS analysis indicate that SiO₂@LaPO₄:Eu³⁺ core–shell phosphors can only be synthesized in a pH range of 8–11 and the possible mechanism has been proposed. The XRD results demonstrate that the structure of LaPO₄:Eu³⁺ layers is transferred into monoclinic phase from hexagonal phase after annealing at 800 °C for 2 h. The SiO₂@LaPO₄:Eu³⁺ phosphors show strong orange–red luminescence under ultraviolet excitation. The relative emission intensity of Eu³⁺ increases with increasing the annealing temperature and the number of coating cycles, and the optimum concentration for Eu³⁺ was determined to be 5 mol% of La³⁺ in SiO₂@LaPO₄ phosphors.     

Multiferroic properties of multilayered BaTiO3–CoFe2O4 composites via tape casting method

Multiferroic magnetoelectric (ME) BaTiO₃–CoFe₂O₄ (BTO–CFO) ceramic composites with different thicknesses were fabricated via tape casting technique. The interfacial morphology of the composite demonstrates the presence of plate-like grains with a thickness of ~400 nm. This could be associated with the residual stresses originated from lattice mismatch and different thermal expansion coefficients between BTO and CFO layers. The dielectric constant, piezoelectric constant, and ferroelectric properties of the multilayered composite are degraded in the presence of CFO layers in comparison with those of BTO bulk. Furthermore, the dielectric constant and polarization of the composite decrease with increasing frequency. The leakage current density and magnetic remanence ratio of the composite reach up to the order of 10^?6 A/cm² and 40 %, respectively. The direct and converse ME coefficients were measured to be 8.1 μV/cm Oe and 1.1 × 10^?3 G/V, respectively. Based on the converse ME effect, an electrically controlled ME inductor was designed using the composite as its core. The inductance and tunability of the inductor increase with increase of applied dc electric field.     

Sol–gel auto-combustion synthesis of PVP/CoFe2O4 nanocomposite and its magnetic characterization

Poly(vinyl pyrrolidone)/CoFe₂O₄ nanocomposite has been fabricated by a sol–gel auto-combustion method. Poly(vinyl pyrrolidone) was used as a reducing agent as well as a surface capping agent to prevent particle aggregation and stabilize the particles. The average crystallite size estimated from X-ray line profile fitting was found to be 20 ± 7 nm. The high field irreversibility and unsaturated magnetization behaviours indicate the presence of the core–shell structure in the sample. The exchange bias effect observed at 10 K suggests the existence of the magnetically aligned core surrounded by spin-disordered surface layer. The reduced remanent magnetization value of 0.6 at 10 K (higher than the theoretical value of 0.5) shows the PVP/CoFe₂O₄ nanocomposite to have cubic magnetocrystalline anisotropy according to the Stoner–Wohlfarth model.     

Optical absorption and photoluminescence properties of Eu3+-doped ZnF2–PbO–TeO2 glasses

Several physical, optical absorption and photoluminescence properties of Eu3+-doped ZnF2–PbO–TeO2 glasses have been studied. From the measured intensities of various absorption bands of these glasses the Judd–Ofelt parameters 2, 4 and 6 have been computed. The Judd–Ofelt theory has been applied to characterize the photoluminescence spectra of these glasses. From this theory, various radiative properties, such as transition probability, A, branching ratio, r, and emission cross-section, EP, for various emission levels of these glasses, have been determined and reported. © 1998 Chapman & Hall.     

The role of microstructural evolution during spark plasma sintering on the soft magnetic and electronic properties of a CoFe–Al2O3 soft magnetic composite

Journal of Materials Science - For transformers and inductors to meet the world’s growing demand for electrical power, more efficient soft magnetic materials with high saturation magnetic...     

Luminescence properties and tunable emission of Ca3MgSi2O8:Eu3+, Bi3+ phosphor with Bi3+ → Eu3+ energy transfer

Journal of Materials Science: Materials in Electronics - In this work, Ca3MgSi2O8:Bi3+, Ca3MgSi2O8:xEu3+ (x?=?0, 2, 4, 6, 8, and 10 mol%), and Ca3MgSi2O8:6%Eu3+, yBi3+...     

Effect of B2O3 on the densification and magnetic properties of Li–Zn ferrite

Densification, grain growth and magnetic properties of Li–Zn ferrite (Li_.30Zn_.4Fe_2.30O₄) doped with B₂O₃ as a sintering aid were investigated. B₂O₃ is a low melting point (460 °C) oxide and forms a liquid phase during sintering which affects the densification and grain growth of ferrites. Results showed that density and grain growth rate were sensitive to the B₂O₃ content and sintering temperature. At low amounts of B₂O₃ (<1 wt.%), an increase in the B₂O₃ content increased density and grain growth rate. The highest density and the maximum magnetization were obtained for the sample containing 1.0 wt.% B₂O₃ which was sintered at a lower temperature (1000 °C) for 1.5 h, in comparison with undoped samples. Higher B₂O₃ contents than 1.0 wt.% caused a decrease in density of samples due to secondary phases formation and evaporation of B₂O₃. The sample with the highest grain size showed the highest permeability and the lowest magnetic loss.     

Optical properties of Nd3+ and Er3+ ions in TeO2–WO3–PbO–La2O3 glasses

Multicomponent telluride-tungstate glasses containing Nd³⁺ and Er³⁺ ions were studied experimentally at 77 and 293 K using spectroscopic methods. The Judd–Ofelt intensity parameters were derived from the absorption spectra and used to calculate the radiative lifetimes and branching ratios. The quantum efficiency η = 0.95 of the ⁴F_3/2 level of Nd³⁺ ion is higher than the typical value of other tellurite-based glasses. For low concentration of Er³⁺ ions, the luminescence decay of the ⁴S_3/2 and ⁴I_11/2 levels is governed by radiative transitions and multiphonon relaxation involving the Te-O highest energy vibrations.