Preparation and Faraday rotation of Bi-YIG/PMMA nanocomposite

Bismuth-substituted yttrium iron garnet (Bi-YIG) nanoparticles (NPs) were prepared by coprecipitation and subsequent heating treatment. Thermal gravity-differential thermal analysis was performed to investigate the thermal behavior of the Bi-YIG precursors and to decide the best annealing temperature. Phase formation of garnet NPs was investigated by X-ray powder diffraction. The size of Bi-YIG NPs was investigated by transmission electron microscopy, and the magnetic properties of Bi-YIG NPs were measured using a vibrating sample magnetometer. The results show that the temperature needed for the transformation of Bi-YIG from the amorphous phase to the garnet phase decreases with increasing Bi content, and Bi-YIG NPs with sizes of 28–78 nm are obtained after heating treatment at 650–1000 °C. The saturation magnetization of Bi-YIG NPs increases as the Bi content increases. Moreover, the Faraday rotation of polymethyl methacrylate (PMMA) slices doped with Bi-YIG NPs was investigated. The results indicate that the angle of Faraday rotation increases with increasing Bi content in PMMA composites, and the maximum value of the figure of merit is 1.46°, which is comparable to the value of a sputtered film. The Bi-YIG NPs-doped PMMA slices are new promising materials for magneto-optical devices.     

Magneto-optical imaging using a garnet indicator film prepared on glass substrates

We observed the magnetic domains of a magnetic card by using the bismuth-substituted yttrium iron garnet (Bi-YIG; Bi₁Y₂Fe₅O₁₂) thin films as the indicator films. The magnetic domains’ dependence on the preparation conditions of the garnet thin film crystals was visualized by using a magneto-optical microscope. Garnet thin films were fabricated on glass substrates using a metal-organic decomposition method (MOD). We found that bigger Faraday rotation was measured in the better crystallized indicator films. Polycrystalline Bi-YIG thin films were successfully obtained for the annealing temperature of 700 °C and an annealing time of 1 h. The thickness of the film was about 47 nm for a single coating during the MOD process. The Faraday-rotation angle of the films was estimated as −2.47°/μm and the angle was comparable to other synthesis methods, such as the sol-gel and the RF-magnetron sputtering. Using these indicator films, we could image the magnetic domains of magnetic materials.     

Effects of heating rate on the magneto-optical properties of bismuth-substituted yttrium iron garnet films prepared via modified metal-organic decomposition

This work investigated the effects of heating rate and annealing on the magneto-optical properties of bismuth-substituted yttrium iron garnet (Bi-YIG) thin films on glass and (111)-oriented single-crystalline gadolinium gallium garnet (GGG) substrates fabricated by metal-organic decomposition (MOD). We modified the MOD method by eliminating the pre-annealing process. We performed annealing at various temperatures to determine the optimal temperature for obtaining the Bi-YIG phase. We then annealed at the optimized temperature using various heating rates. The optimal conditions were annealing for 1 h at 750 °C at a heating rate of 30 °C/min on GGG to obtain highly crystallized fine grains. The Faraday rotation for this film was about −10.5°/μm. The optimized heating rate enhanced the magneto-optical properties due to improved crystallinity and saturated magnetization. The Bi-YIG thin films prepared by this prescribed MOD method exhibited excellent magneto-optical performance and are potential candidates for applications in optical devices.     

Conventional wet impregnation versus microwave-assisted synthesis of SnO<Subscript>2</Subscript>/CNT composites

Carbon nanotubes decorated with SnO₂ nanoparticles were prepared by conventional and microwave-assisted wet impregnation. The composites were thoroughly characterized by X-ray diffraction, Raman spectroscopy, BET-surface area measurement, Scanning and transmission electron microscopy. The XRD studies revealed the formation of tetragonal phase of SnO₂. The microwave method produced CNTs heavily decorated with SnO₂ nanoparticles with average size 5 nm in a total reaction time of 10 min because of the rapid volumetric heating. DC conductivity increased significantly for the nanocomposite samples when compared with the pure CNTs. In electrical conductivity properties, sample prepared by microwave method was found to be superior to the one prepared by conventional procedure due to homogeneous distribution of nanoparticles.     

Influence of synthesis method on structural and magnetic properties of cobalt ferrite nanoparticles

The Co–ferrite nanoparticles having a relatively uniform size distribution around 8 nm were synthesized by three different methods. A simple co-precipitation from aqueous solutions and a co-precipitation in an environment of microemulsions are low temperature methods (50 °C), whereas a thermal decomposition of organo-metallic complexes was performed at elevated temperature of 290 °C. The X-ray diffractometry (XRD) showed spinel structure, and the high-resolution transmission electron microscopy (HRTEM) a good crystallinity of all the nanoparticles. Energy-dispersive X-ray spectroscopy (EDS) showed the composition close to stoichiometric (~CoFe₂O₄) for both co-precipitated nanoparticles, whereas the nanoparticles prepared by the thermal decomposition were Co-deficient (~Co_0.6Fe_2.4O₄). The X-ray absorption near-edge structure (XANES) analysis showed Co valence of 2+ in all the samples, Fe valence 3+ in both co-precipitated samples, but average Fe valence of 2.7+ in the sample synthesized by thermal decomposition. The variations in cation distribution within the spinel lattice were observed by structural refinement of X-ray absorption fine structure (EXAFS). Like the bulk CoFe₂O₄, the nanoparticles synthesized at elevated temperature using thermal decomposition displayed inverse spinel structure with the Co ions occupying predominantly octahedral lattice sites, whereas co-precipitated samples showed considerable proportion of cobalt ions occupying tetrahedral sites (nearly 1/3 for the nanoparticles synthesized by co-precipitation from aqueous solutions and almost 1/4 for the nanoparticles synthesized in microemulsions). Magnetic measurements performed at room temperature and at 10 K were in good agreement with the nanoparticles’ composition and the cation distribution in their structure. The presented study clearly shows that the distribution of the cations within the spinel lattice of the ferrite nanoparticles, and consequently their magnetic properties are strongly affected by the synthesis method used.     

Fabrication, characterization and measurement of thermal conductivity of Fe3O4 nanofluids

Magnetite Fe₃O₄ nanoparticles were synthesized by a co-precipitation method at different pH values. The products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electronic microscopy. Their magnetic properties were evaluated on a vibrating sample magnetometer. The results show that the shape of the particles is cubic and they are superparamagnetic at room temperature. Magnetic nanofluids were prepared by dispersing the Fe₃O₄ nanoparticles in water as a base fluid in the presence of tetramethyl ammonium hydroxide as a dispersant. The thermal conductivity of the nanofluids was measured as a function of volume fraction and temperature. The results show that the thermal conductivity ratio of the nanofluids increases with increase in temperature and volume fraction. The highest enhancement of thermal conductivity was 11.5% in the nanofluid of 3 vol% of nanoparticles at 40 °C. The experimental results were also compared with the theoretical models.     

Magneto-optic Faraday effect in maghemite nanoparticles/silica matrix nanocomposites prepared by the Sol–Gel method

Bulk monolithic samples of γ-Fe₂O₃/SiO₂ composites with different iron oxide/silica ratios have been prepared by the sol–gel technique. Iron oxide nanoparticles are obtained in-situ during heat treatment of samples and silica matrix consolidation. Preparation method was previously optimized to minimize the percentage of antiferromagnetic α-Fe₂O₃ and parallelepipeds of roughly 2×5×12 mm³, with good mechanical stability, are obtained. RT magnetization curves show a non-hysteretic behavior. Thus, magnetization measurements have been well fitted to an expression that combines the Langevin equation with an additional linear term, indicating that some of the nanoparticles are still superparamagnetic as confirmed by X-ray diffraction and electron microscopy measurements. Zero field cooled /field cooled experiments show curves with slightly different shapes, depending on the size and shape distribution of nanoparticles for a given composition. Magneto-optical Faraday effect measurements show that the Faraday rotation is proportional to magnetization of the samples, as expected. As a demonstration of their sensing possibilities, the relative intensity of polarized light, measured at 5° from the extinction angle, was plotted versus applied magnetic field.     

Urchin-like CdS/ZrO2 nanocomposite prepared by microwave-assisted hydrothermal combined with ion-exchange and its multimode photocatalytic activity

A series of urchin-like CdS/ZrO₂ nanocomposites with different mole ratios of Cd/Zr were prepared by a two-step method combining the microwave-assisted hydrothermal and ion exchange methods. The products were characterized by X-ray diffraction, ultraviolet–visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and N₂ adsorption–desorption measurements. The results of the study revealed that the CdS/ZrO₂ nanocomposites had mixed phases of tetragonal ZrO₂ and hexagonal CdS. Moreover, the samples prepared by the microwave-assisted hydrothermal method possessed the urchin-like structure with a surface composed of protrude-like nanoparticles in large quantities. The absorption in the visible region changed slightly with increasing mole ratio of Cd/Zr. Moreover, compared to the nanocomposites prepared by the conventional heating, the nanocomposites prepared by the microwave-assisted hydrothermal synthesis showed significantly different Brunauer–Emmett–Teller values, and the urchin-like CdS/ZrO₂ structures were obtained. The photocatalytic degradation of methyl orange under ultraviolet (UV) light irradiation indicated that the photocatalytic activity of the CdS/ZrO₂ nanocomposite with CdS/ZrO₂ molar ratio of 30 % was higher than those of CdS, ZrO₂, and other different ratios of CdS/ZrO₂ nanocomposites. Moreover, under UV light, visible light, and microwave-assisted multimode photocatalytic degradation, the urchin-like CdS/ZrO₂ nanocomposites significantly affected the photodegradation of various dyes. To understand the possible reaction mechanism of the photocatalysis by the CdS/ZrO₂ nanocomposites, a series of controlled experiments were performed, and the stability and reusability of the CdS/ZrO₂ nanocomposites were further investigated by the photocatalytic reaction.     

Bi4Ge3O12晶体的磁光法拉第旋转

在可见光范围测量了Bi₄Ge₃O₁₂晶体磁光法拉第旋转的色散关系,也测量了从室温到液氮温度磁光旋转在633nm的变化。大的磁光旋转和很宽光波范围的高透过率表明晶体在磁光应用上也是很有价值的。扼要讨论了Bi离子在抗磁晶体中对磁光旋转的重要作用。 关键词：     

Microwave resonant and zero-field absorption study of pure and doped ferrite nanoparticles

Microwave absorption was studied for magnetic nanoparticles of Fe₃O₄ (A) prepared by co-precipitation and Ni_0.35Cu_0.15Zn_0.5Fe₂O₄ (B) nanoparticles prepared by the sol-gel combustion method at different temperature. In all cases only one ferromagnetic resonance line was observed which indicated that the materials were magnetically uniform. The linewidths were large mainly because of the wide variations in particle sizes, shapes and orientations. As expected, A type nanoparticles showed no absorption at zero-field. However, B type nanoparticles exhibited a sizable loss at a zero-field and the effect increases with the increase of reaction temperature. Mechanical crushing of the sample further enhanced the absorption.     

Faraday rotation in gadolinium orthochromite

Faraday rotation and linear birefringence of GdCrO₃ were measured in the spectral range 0.8 to 2.0 μm at liquid nitrogen temperature. Good agreement is obtained between the experimental data and the theoretical values of rotation, calculated by the use of the formula describing Faraday rotation in the presence of the linear birefringence. The intrinsic Faraday rotation as a function of the wavelength is determined and it is probably due to higher-energy optical transitions.     

Reciprocity of Faraday effect in ferrofluid: Comparison with magneto-optical glass

The transmission light intensity method is carried out on a classical platform to study the reciprocity of Faraday effect in water-based Fe₃O₄ ferrofluid and its diluents. Setting the polarization direction of the analyzer at an angle of 45° to that of the polarizer, the switchable DC magnetic field and the alternating magnetic field are imposed to ferrofluid. The ferrofluid film is replaced by magneto-optical glass for contrastive experiments. The results indicate that ferrofluid is different with magneto-optical glass. Even though the direction of magnetic field is reversed, the rotation direction of the polarized light does not change for ferrofluid. The theoretical model of magneto-optical rotation was used to describe the origin of the reciprocity of Faraday effect in ferrofluid and the non-reciprocity in magneto-optical glass. These findings suggest that the magnetic moments of nanoparticles in ferrofluid tend to the same orientation with the magnetic field because of the rotation of particles.     

The roles of hydrochloric acid and polyethylene glycol in magnetic fluids

Increasing interest has been drawn to the studies of magnetic fluids due to their multiple applications from industry to medicine. However, further exploration is still required for the techniques of preparing satisfying, convenient and stable magnetic fluids. We explored characteristics of magnetic liquids prepared by employing co-precipitation techniques of hydrochloric acid (HCl) and polyethylene glycol (PEG), and the functions of HCl and PEG in the magnetic liquid. According to the improved technique, after preparing Fe₃O₄ by a co-precipitation method, hydrochloric acid and PEG2000 react with magnetic particles at a certain temperature to generate the anticipated magnetic nanoparticles. The process could be under an air atmosphere rather than a N₂ atmosphere. Compared with traditional techniques, the magnetic nanoparticles prepared by this method have smaller size, better dispersion and stability, with the average hydrodynamic diameter adjustable between 8 and 50 nm. This study revealed that reduction of nanoparticles size is not mainly due to a [Cl⁻] coating over the magnetic nanoparticles, but that HCl reacts with Fe₃O₄ particles after being heated. Meanwhile, PEG can stabilize or coat Fe₃O₄ nanoparticles as a dispersing and stabilizing agent.     

A comparative study of magnetic transferability of superparamagnetic nanoparticles

The aspect of magnetic transferability was established using an automated magnetic particle transfer workstation. Maghemite (γ-Fe₂O₃) nanoparticles were synthesized via conventional co-precipitation procedure. Their transferability was determined in addition to several commercial nanoparticles that ranged in diameter, surface functionality, and composition. Transmission and scanning electron micrographs and infrared spectrum, respectively, provided size and surface information on the synthesized particles for comparison to commercially available magnetic nanoparticles.     

Magnetic studies of Bi x Y3-x Fe5O12 fabricated using conventional method

A series of Bi substituted yttrium iron garnet (Bi-YIG) nanoparticles with nominal formula of Bi _x Y_3???x Fe₅O₁₂ in which x varied in steps of 0.0, 0.25 and 0.5 are prepared by conventional method. Vibration sample magnetometer (VSM) at Room temperature (RT) shows saturation magnetization decreases from 27.4 to 25.2 (emu/g) as x value increases from 0.0 to 0.5. Room temperature ⁵⁷Fe Mössbauer spectra are recorded for these series. The hyperfine field value for octahedral and tetrahedral of samples increases from 484 and 390 kOe to 491 and 397 kOe respectability, as Bi replaces Y in (Bi _x Y_3???x Fe₅O₁₂) atom with increasing x value. The effect of Bi^3?+? substitution for Y^3?+? on lattice constants, morphology and magnetic properties of pure YIG has been investigated.     

The study of transition on NiFe2O4 nanoparticles prepared by co-precipitation/calcination

In this study, the NiFe₂O₄ nanoparticles have been prepared by co-precipitation and calcination process. Using a vibrating sample magnetometer (VSM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectrometer of X-ray (EDX), and X-ray photoelectron spectroscopy (XPS), the samples obtained by co-precipitation and then by further calcination have been analyzed. The experimental results show that the precursor synthesized by co-precipitation is the composite of both amorphous FeOOH and Ni(OH)₂, but has no amorphous NiFe₂O₄. The results of both EDX and XPS revealed that the FeOOH species is wrapped up by Ni(OH)₂ species. In the calcination process, the amorphous composite is dehydrated and transformed gradually into crystalline NiFe₂O₄ nanoparticles, with the metal ions diffusing. The reaction is different from the one used to prepare other ferrite (e.g., CoFe₂O₄, MnFe₂O₄, Fe₃O₄, etc.) nanoparticles directly by co-precipitation. With increasing calcination temperature, the NiFe₂O₄ grains grow and the magnetization is enhanced.     

Growth and magnetic behavior of bismuth substituted yttrium iron garnet nanoparticles

Crystal growth and the magnetic properties of bismuth substituted yttrium iron garnet (Bi-YIG) nanoparticles were studied with particular focus on the bismuth composition dependence of the magnetic properties of the particles and the effects of annealing on the garnet phase formation. The Bi-YIG nanoparticles of 47–67 nm in size can be chemically synthesized when they are annealed at 650–850 °C. Both the lattice constant and the magnetization of the garnet nanoparticles linearly increase when the bismuth composition in the Bi-YIG particles increases. We have found that chemically synthesized nanoparticles transform from the amorphous to the garnet phase when annealed at temperatures below 650 °C, while the onset of magnetic moment of iron in the garnet nanoparticles is observed slightly above 650 °C. According to Mössbauer effect measurements, the hyperfine fields of ⁵⁷Fe at the tetrahedral and octahedral sites in the garnet are 39 and 48 T, respectively.     

Synthesis of Fe3O4 magnetic fluid used for magnetic resonance imaging and hyperthermia

Fe₃O₄ magnetic nanoparticles were prepared by co-precipitation from FeSO₄·7H₂O and FeCl₃·6H₂O aqueous solutions using NaOH as precipitating reagent. The nanoparticles have an average size of 12 nm and exhibit superparamagnetism at room temperature. The nanoparticles were used to prepare a water-based magnetic fluid using oleic acid and Tween 80 as surfactants. The stability and magnetic properties of the magnetic fluid were characterized by Gouy magnetic balance. The experimental results imply that the hydrophilic block of Tween 80 can make the Fe₃O₄ nanoparticles suspending in water stable even after dilution and autoclaving. The magnetic fluid demonstrates excellent stability and fast magneto-temperature response, which can be used both in magnetic resonance imaging and magnetic fluid hyperthermia.     

Synthesis and characterization of MnWO4 nanoparticles encapsulated in mesoporous silica SBA-15 by fast microwave-assisted method

The MnWO₄ nanoparticles encapsulated in mesoporous silica (MnWO₄/SBA-15) was successfully synthesized by a fast microwave-assisted method. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen absorption–desorption isotherm, and Fourier transform infrared spectroscopy (FTIR). Our results showed that the MnWO₄/SBA-15 nanocomposites have the ordered hexagonal meso-structure of SBA-15, indicating MnWO₄ nanoparticles were successfully distributed into the channels of SBA-15. The size of MnWO₄ nanoparticles in SBA-15 is significantly smaller than the size of MnWO₄ nanoparticles prepared without SBA-15, indicating that the MnWO₄/SBA15 nanocomposites would be very promising for improving photocatalytic activity of MnWO₄ nanoparticles.     

CuFe2O4 magnetic heterogeneous nanocatalyst: Low power sonochemical-coprecipitation preparation and applications in synthesis of 4H-chromene-3-carbonitrile scaffolds

The paper presents the synthesis and catalytic activity of CuFe₂O₄ nanoparticles. The CuFe₂O₄ nanoparticles have been prepared by sonochemical route under low power ultrasonic irradiation (UI) and using silent stirring at room temperature only (ST) along with co-precipitation method, without using any additive/capping agent. The synthesized magnetic nanoparticles were successfully used and compared for the synthesis of 4H-chromene-3-carbonitrile derivatives. The CuFe₂O₄ nanoparticles obtained by sonochemical route exhibit higher catalytic activity because of small size (0.5–5 nm), high surface area (214.55 m²/g), high thermal stability up to 700 °C, recyclability and reusability due to its magnetic characteristics than CuFe₂O₄ nanoparticles obtained by room temperature silent stirring. The synthesized CuFe₂O₄ nanoparticles were characterized by FT-IR, SEM–EDX, HR-TEM, XRD, TGA/DTA/DTG, BET, VSM techniques. The present method is of great interest due to its salient features such as environmentally compatible, efficient, short reaction time, chemoselectivity, high yield, cheap, moisture insensitive, green and recyclable catalyst which make it sustainable protocol.