Magnetooptical Property of Sodium Borosilicate Gel-Glass Containing Bi-YIG Fine Particles

Composite materials which consist of ferro- or ferrimagnetic fine particles in a glass matrix are expected to have a large residual magnetization and coercive force because of their fine magnetic domain structure, and has potential for superior magneto-optical properties compared with single or polycrystalline materials. In this study, the sodium borosilicate (NBS) glass containing Bi-substituted yttrium iron garnet (Bi _x Y_3–x Fe₅O₁₂: BiYIG) fine particles, which show a superior magneto-optical effect, was prepared by the sol-gel method. BiYIG fine particles were stable in NBS gel-glass matrix during densification because the sintering temperature (580°C) of NBS gel was low enough to avoid pyrolysis of BiYIG and the reaction between BiYIG fine particles and the matrix. The Faraday rotation angle spectrum of the composite after deducting the contribution of the NBS glass matrix was intermediate between the reported ones of YIG and Bi_0.25YIG polycrystalline thin films. The change of the Faraday rotation angles of the composite with imposing magnetic field showed a hysteresis loop. It was in good agreement with that of the magnetization curve of the composite.     

Magneto-Optical Characteristics of Co, Ti-Substituted Barium Hexaferrite Films Deposited by the Dip-Coating Method

Pure and Co, Ti-substituted hexagonal barium ferrite (BaFe₁₂O₁₉, BaM) films were prepared by the dip-coating method from alkoxides. After repeated dipping, drying and calcining at 500°C for about 15 minutes in an oxygen atmosphere, polycrystalline films with a thickness of 1–1.8 μm on SiO₂ substrates were obtained. Spectral dependencies of the Faraday rotation and the optical transmission of BaCo _x Ti _x Fe_12−2x O₁₉(0≤x≤0.8) films were measured in the range from 500 to 2500 nm at room temperature. The absorption coefficient did not display much structure, but specific Faraday rotation spectra of Co, Ti-ferrite films showed local maxima at 720, 1475 and 1750 nm. At those wavelengths, the magneto-optical figure of merit attains its maximum values. For comparison of the crystallization and magnetic properties, Ba(CoTi) _x Fe_12−2x O₁₉ (x=0.9) powder has also been prepared by the sol-gel method.     

Disappearance of long range spin-order in ultrafine magnetite particles

Ferromagnetic properties of ultrafine magnetite (Fe₃O₄) particles were examined by the ESR and the static magnetic susceptibility measurements. Ferromagnetic resonance became to be observed at the particle size larger than 3.4 nm. This finding suggests that the bulk-like ferromagnetic state cannot be formed in the particle less than 3.4 nm diameter for magnetite. Magnetic moments in such a small diameter region were also determined by the analyses of magnetization curves and were found to be smaller than those expected from the particle size. These findings from ESR and magnetization are discussed to clarify the nature of spin-ordering in a finite size sample.     

Development of novel magnetic nano-carriers for high-performance affinity purification

We developed novel magnetic nano-carriers around 180 nm in diameter for affinity purification. Prepared magnetic nano-carriers possessed uniform core/shell/shell nano-structure composed of 40 nm magnetite particles/poly(styrene-co-glycidyl methacrylate (GMA))/polyGMA, which was constructed by admicellar polymerization. By utilizing relatively large 40 nm magnetite particles with large magnetization, the magnetic nano-carriers could show good response to permanent magnet. Thanks to uniform polymer shell with high physical/chemical stability, the magnetic nano-carriers could disperse in a wide range of organic solvent without disruption of core/shell structure and could immobilize various kinds of drugs. We examined affinity purification using our prepared magnetic nano-carriers with anti-cancer agent methotrexate (MTX) as ligand. Our magnetic nano-carriers showed higher performance compared to commercially available magnetic beads in terms of purification efficiency of target including extent of non-specific binding protein.     

Size effect of added LaB6 particles on optical properties of LaB6/Polymer composites

Modified LaB₆ particles with sizes ranging from 50 nm to 400 nm were added into polymethyl methacrylate (PMMA) matrix in order to investigate the effect of added LaB₆ particles on optical properties of LaB₆/PMMA composites. Method of in-situ polymerization was applied to prepare PMMA from raw material—methyl methacrylate (MMA), a process during which LaB₆ particles were dispersed in MMA. Ultraviolet-visible-near infrared (UV-vis-NIR) absorption spectrum was used to study optical properties of the as-prepared materials. The difference in particle size could apparently affect the composites' absorption of visible light around wavelength of 600 nm. Added LaB₆ particles with size of about 70 nm resulted in the best optical properties among these groups of composites.     

Fe3O4-LiMo3Se3 nanoparticle clusters as superparamagnetic nanocompasses

A scaleable chemical approach to functional nanoscale analogues of the magnetic compasses in magnetotactic bacteria is described. LiMo(3)Se(3)-Fe(3)O(4) nanowire-nanoparticle composites were synthesized by a reaction of 3-iodopropionic acid treated LiMo(3)Se(3) nanowire bundles with oleic acid-stabilized Fe(3)O(4) nanoparticles of 2.8, 5.3, and 12.5 nm size in tetrahydrofuran. Transmission electron micrographs show that the composite consists of Fe(3)O(4) nanoparticles attached to the surfaces of the 4-6 nm thick nanowire bundles. UV/vis spectra reveal absorptions from the nanowire (506 nm) and magnetite components (280-450 nm), and IR spectra show characteristic bands for the propionic acid linkers and for the residual oleic acid ligands on the magnetite particles. In the presence of excess oleic acid, the nanocomposites undergo rapid disassembly, suggesting that Fe(3)O(4) nanoparticles are bonded to nanowires via carboxylate groups from the linkers. Ultrasonication of a dispersion of the composite in THF produces individual LiMo(3)Se(3)-Fe(3)O(4) clusters, which are 340 +/- 107 nm long and 20 +/- 5 nm thick, depending on the sonication time and Fe(3)O(4) nanoparticle size. Field cooled and zero-field cooled magnetization measurements reveal that the blocking temperature (T(B) = 100 K) of the clusters with 5.3 nm Fe(3)O(4) is increased as compared to the free nanoparticles (T(B) = 30 K). Directional dipolar interactions in the clusters lead to magnetic anisotropy, which makes it possible to align the clusters in a magnetic field (900 Oe).     

Faraday rotation enhancement of gold coated Fe2O3 nanoparticles: comparison of experiment and theory

Understanding plasmonic enhancement of nanoscale magnetic materials is important to evaluate their potential for application. In this study, the Faraday rotation (FR) enhancement of gold coated Fe(2)O(3) nanoparticles (NP) is investigated experimentally and theoretically. The experiment shows that the Faraday rotation of a Fe(2)O(3) NP solution changes from approximately 3 rad/Tm to 10 rad/Tm as 5 nm gold shell is coated on a 9.7 nm Fe(2)O(3) core at 632 nm. The results also show how the volume fraction normalized Faraday rotation varies with the gold shell thickness. From the comparison of experiment and calculated Faraday rotation based on the Maxwell-Garnett theory, it is concluded that the enhancement and shell dependence of Faraday rotation of Fe(2)O(3) NPs is a result of the shifting plasmon resonance of the composite NP. In addition, the clustering of the NPs induces a different phase lag on the Faraday signal, which suggests that the collective response of the magnetic NP aggregates needs to be considered even in solution. From the Faraday phase lag, the estimated time of the full alignment of the magnetic spins of bare (cluster size 160 nm) and gold coated NPs (cluster size 90 nm) are found to be 0.65 and 0.17 μs. The calculation includes a simple theoretical approach based on the Bruggeman theory to account for the aggregation and its effect on the Faraday rotation. The Bruggeman model provides a qualitatively better agreement with the experimentally observed Faraday rotation and points out the importance of making a connection between component properties and the average "effective" optical behavior of the Faraday medium containing magnetic nanoparticles.     

Synthesis of spherical submicron-sized magnetite/silica nanocomposite particles

This paper describes a method for fabricating spherical submicron-sized silica particles that contained magnetite nanoparticles (magnetite/silica composite particles). The magnetite nanoparticles with a size of ca. 10 nm were prepared according to the Massart method, and were surface-modified with carboxyethylsilanetriol. The fabrication of magnetite/silica composite particles was performed in water/ethanol solution of tetraethoxyorthosilicate with ammonia catalyst in the presence of the surface-modified magnetite nanoparticles. The magnetite/silica composite particles with a size of ca. 100 nm were successfully prepared at 0.05 M TEOS, 15 M water, and 0.8 M ammonia with injection of the magnetite nanoparticle colloid at 2 min after the initiation of hydrolysis reaction of TEOS. Magnetite concentration in the composite particles could be raised to 17.3 wt.% by adjustment of the injected amount of the magnetite colloid, which brought about the saturation magnetization of 7.5 emu/g for the magnetite/silica composite particles.     

Preparation of fluoroalkyl end-capped oligomers/magnetite nanocomposites possessing a good dispersibility and stability

Fluoroalkyl end-capped vinylphosphonic acid cooligomers-encapsulated magnetite nanocomposites were prepared by the magnetization of aqueous ferric and ferrous ions in the presence of the corresponding fluorinated cooligomers and magnetic nanoparticles under alkaline conditions. These fluorinated cooligomers magnetic composites are nanometer size-controlled very fine particles and have a good dispersibility and stability in water and traditional organic solvents. These fluorinated nanocomposites were also applied to the surface modification of poly(methyl methacrylate) to exhibit a good oleophobicity imparted by fluorine on their surface. Fluoroalkyl end-capped 2-methacryloyloxyethanesulfonic acid oligomer-encapsulated magnetite nanocomposites and fluoroalkyl end-capped 2-acrylamide-2-methylpropanesulfonic acid oligomer-encapsulated magnetite nanocomposites were prepared in good isolated yields by the magnetization of iron chlorides in the presence of the corresponding oligomers and magnetic nanoparticles under similar conditions. Colloidal stability of these fluorinated nanocomposites thus obtained in water was demonstrated to become extremely higher than that of fluorinated vinylphosphonic acid cooligomers/magnetic nanocomposites.     

Molecular Design Guidelines for Large Magnetic Circular Dichroism Intensities in Lanthanide Complexes

Magneto optical devices based on the Faraday effects of lanthanide ion have attracted much attention. Recently, large Faraday effects were found in nano‐sized multinuclear lanthanide complexes. In this study, the Faraday rotation intensities were estimated for lanthanide nitrates [Ln^III(NO₃)₃?n H₂O: Ln=Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm) and Eu^III complexes with β‐diketone ligands, using magnetic circular dichroism. Eu ions exhibit the largest Faraday rotation intensity for ⁷F₀→⁵D₁ transitions, and high‐symmetry fields around the Eu ions induce larger Faraday effects. The molecular design for the enhancement of Faraday effects in lanthanide complexes is discussed.     

Nanocomposite particles with core-shell morphology II. An investigation into the affecting parameters on preparation of Fe3O4-poly (butyl acrylate-styrene) particles via miniemulsion polymerization

The encapsulation of inorganic particles with polymers is desirable for many applications in order to improve the stability of the encapsulated products and disperse ability in different media. Colloidal particles with magnetic properties have become increasingly important both technologically and for fundamental studies. This is due to their tunable anisotropic. In the absence of an applied magnetic field, the particles have isotropic sphere dispersion, whereas in an external magnetic field the particles form anisotropic structures. Here, latexes containing nanocomposite particles of styrene-butyl acrylate/Fe₃O₄ with core-shell structure were prepared through miniemulsion polymerization technique. Magnetic composite nanospheres with high magnetic content were synthesized through miniemulsion polymerization using a new process based on a three-steps preparation route including two miniemulsion processes: (1) preparing a dispersion of oleic acid coated magnetite particles in water; (2) mixing of modified magnetite particles with styrene/butyl acrylate in the presence of sodium dodecyl sulfate (SDS), sorbitane mono oleate (Span 80), hexadecane (HD) and (3) miniemulsification of the modified Fe₃O₄ into the monomer droplets to reach to complete encapsulation. Subsequent polymerization generated magnetic nanocomposite spheres. Hence, the copolymerization reaction was performed on the surface of such particles in order to obtain core-shell morphology for these nanoparticles, which were characterized by several techniques such as TEM, SEM, DLS, TGA, VSM and FT-IR. The magnetic copolymer particles with diameter of 120-170 nm were obtained. The effect of several parameters such as magnetite, surfactants and hydrophobe amounts on the stability, particle size and magnetization were investigated and also optimized.     

Spectral features of atomic magneto-optical rotation spectroscopy (the atomic Faraday effect) and Zeeman splittings of various elements

Spectral features of atomic magneto-optical rotation spectroscopy (AMORS) or the atomic Faraday effect of various elements are described. As a stable atomizer, an air-hydrogen flame is located between the pole pieces of the electromagnet. The dependence of the transmitted intensity on the magnetic field strength was recorded on an X-Y recorder by scanning the magnetic field. For most of the analytical lines of elements, the maximum energy was transmitted through the optical system in the Faraday configuration at magnetic field strengths of up to a few kilogauss. The theoretically calculated Zeeman splitting patterns are successfully related to the experimental results.     

Two step hydrothermal synthesis of flowerbud-like magnetite/graphene oxide hybrid with high-performance microwave absorption

A novel flowerbud-like magnetite/graphene oxide (GO) hybrid was synthesized from facile two-step hydrothermal process by using FeCl₃ as iron source, ethylene glycol as the reducing agent, and graphene oxide as template. The magnetite nanoparticles with the diameters of 70–80 nm were attached onto the surface of graphene oxide through the two-step self-assembly process which enhanced the magnetic properties of the hybrids. The final flowerbud-like magnetite/graphene oxide hybrid emerged with the saturated magnetization of ~84.5 emu g^–1. More importantly, owing to the combined contribution of enhanced dielectric and magnetic properties, the maximum microwave absorption of as-prepared magnetite/GO hybrid reached 30 dB with a thickness of 4 mm. Besides, the absorption bandwidth with a reflection loss above 23 dB ranged from 6.0 to 11.5 GHz.     

Magnetite nanorod thermotropic liquid crystal colloids: Synthesis, optics and theory

We have developed a facile method for preparing magnetic nanoparticles which couple strongly with a liquid crystal (LC) matrix, with the aim of preparing ferronematic liquid crystal colloids for use in magneto-optical devices. Magnetite nanoparticles were prepared by oxidising colloidal Fe(OH)(2) with air in aqueous media, and were then subject to alkaline hydrothermal treatment with 10moldm(-3) NaOH at 100°C, transforming them into a polydisperse set of domain magnetite nanorods with maximal length ～500nm and typical diameter ～20nm. The nanorods were coated with 4-n-octyloxybiphenyl-4-carboxylic acid (OBPh) and suspended in nematic liquid crystal E7. As compared to the conventional oleic acid coating, this coating stabilizes LC-magnetic nanorod suspensions. The suspension acts as a ferronematic system, using the colloidal particles as intermediaries to amplify magnetic field-LC director interactions. The effective Frederiks magnetic threshold field of the magnetite nanorod-liquid crystal composite is reduced by 20% as compared to the undoped liquid crystal. In contrast with some previous work in this field, the magneto-optical effects are reproducible on time scales of months. Prospects for magnetically switched liquid crystal devices using these materials are good, but a method is required to synthesize single magnetic domain nanorods.     

Superparamagnetic Composites Based on Ionic Resin Beads/CaCO3/Magnetite

The preparation of superparamagnetic composites obtained by CaCO₃ mineralization from supersaturate aqueous solutions is presented. The preparation was conducted in the presence of oleic acid stabilized magnetite nanoparticles as a water‐based magnetic fluid and insoluble templates as gel‐like cross‐linked polymeric beads. The presence of the magnetic particles in the composites provides a facile way for external manipulation using a permanent magnet, thus allowing the separation and extraction of magnetically modified materials. Two ion exchangers based on divinylbenzene/ethyl acrylate/acrylonitrile cross‐linked copolymer—a cation ion exchanger (CIE) and an amphoteric ion exchanger (AIE)—were used, as well as different addition orders of magnetite and CaCO₃ crystals growth precursors. The morphology of the composites was investigated by SEM, the polymorphs content by X‐ray diffraction, and the thermal stability by thermogravimetric analysis. Polymer, CaCO₃, and magnetite in the composite particles were shown to be present by energy dispersive X‐ray (EDX), XPS, and TEM. The sorption capacity for Cu^II ions was tested, as compared to samples prepared without magnetite.     

Superparamagnetic magnetite–divinylbenzene–maleic anhydride copolymer nanocomposites obtained by dispersion polymerization

Magnetite alternating copolymers divinylbenzene–maleic anhydride (DVB–MA) composites were prepared by dispersion polymerization. Because magnetite is used as a complex with oleic acid (Fe₃O₄OLA), the final hybrids show good dispersion of inorganic nanofillers in the polymer matrix. The obtained composites were analyzed by infrared absorption spectrometry, diffuse reflectance in visible light, thermogravimetry, X-ray fluorescence, X-ray diffraction, dynamic light scattering, scanning electron microscopy and vibrating sample magnetometry. The obtained results indicate the successful preparation of magnetite nanoparticles with an average size of about 23 nm dispersed in micrometer size copolymer spherical particles, which relative content can be controlled via the processing parameters. A relationship between the relative content of magnetite nanoparticles and the size of the polymer particles, with direct influence on the diffuse reflectance in the visible domain, was observed. A superparamagnetic behavior was evidenced at room temperature with a blocking temperature lower than as expected from the bulk anisotropy constant and the average size of the magnetite nanoparticles. Both the unexpected low blocking temperature and the observed low specific magnetizations were explained by a defected and poor crystalline structure of the magnetite nanoparticles, giving rise to spin disorder and diminished crystalline anisotropy constant.     

Preparation of CdS–TiO2/Fe3O4 photocatalyst and its photocatalytic properties

The CdS modified TiO₂/Fe₃O₄ photocatalysts were prepared by sol–gel and immersion methods. The morphological, structural and optical properties of as-prepared samples were characterized by X-ray diffraction (XRD), UV–Vis absorption spectra, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The TEM observation showed that the surface of magnetite particles (Fe₃O₄) were coated by CdS–TiO₂ layer as loose clusters, and average diameter of composites particles was about 250 nm. UV–Vis absorption spectra indicated that CdS–TiO₂/Fe₃O₄ composites had pronounced red-shift compared with that of TiO₂/Fe₃O₄. The CdS–TiO₂/Fe₃O₄ composites exhibit higher photocatalytic activity than pure TiO₂ and TiO₂/Fe₃O₄ for the degradation of Reactive Brilliant Red X-3B dye (X-3B) aqueous solution under simulated sunlight, and the optimum content of CdS is 1.0 % (mol ratio of CdS to TiO₂). In addition, a gradual loss of photocatalytic activity can be observed in reusability test of CdS–TiO₂/Fe₃O₄ composites, and degradation of X-3B reached still to 78.9 % after five runs.     

The preparation of hot-pressed chalcogenide spinels

The preparation of chalcogenide spinel powders is reviewed. Microcrystalline powders are formed by the thermal reaction of mixtures of anhydrous cadmium and chromium chlorides or coprecipitated cadmium and chromium hydroxides with H₂S, Ar + CS₂, or H₂ + Se. These spinel powders are hot pressed to form highly dense, polycrystalline disks. The effects of pressing variables on optical absorption coefficients are given. The spinel powders and hot-pressed disks are characterized and optical spectra, refractive index, and Faraday rotation data are given.     

Colloidal stability of magnetite/poly(lactic acid) core/shell nanoparticles

In this work, we describe an experimental investigation on the colloidal stability of suspensions of three kinds of particles, including magnetite, poly(lactic acid) (PLA), and composite core/shell colloids formed by a magnetite core surrounded by a PLA shell. The experiments were performed with dilute suspensions, so that recording the optical absorbance with time gives a suitable indication of the aggregation and sedimentation of the suspensions. The method allowed us to distinguish very accurately between the different surface and magnetic forces responsible for the structures acquired by particle aggregates. Thus, the pure PLA suspensions are very sensitive to ionic strength and almost unaffected by pH changes. On the contrary, the stability of magnetite systems is mainly controlled by pH. The effect of vertical magnetic fields on the stability of magnetite and magnetite/PLA suspensions is also investigated. The PLA shell reduces the magnetic responsiveness of magnetite, but it is demonstrated that the mixed particles can also form structures induced by the field, despite their lower magnetization, and they can be considered in magnetically targeted biomedical applications.     

Role of Magnetite Nanoparticles Size and Concentration on Hyperthermia under Various Field Frequencies and Strengths

Magnetite (Fe₃O₄) nanoparticles were synthesized using the chemical coprecipitation method. Several nanoparticle samples were synthesized by varying the concentration of iron salt precursors in the solution for the synthesis. Two batches of nanoparticles with average sizes of 10.2 nm and 12.2 nm with nearly similar particle-size distributions were investigated. The average particle sizes were determined from the XRD patterns and TEM images. For each batch, several samples with different particle concentrations were prepared. Morphological analysis of the samples was performed using TEM. The phase and structure of the particles of each batch were studied using XRD, selected area electron diffraction (SAED), Raman and XPS spectroscopy. Magnetic hysteresis loops were obtained using a Lakeshore vibrating sample magnetometer (VSM) at room temperature. In the two batches, the particles were found to be of the same pure crystalline phase of magnetite. The effects of particle size, size distribution, and concentration on the magnetic properties and magneto thermic efficiency were investigated. Heating profiles, under an alternating magnetic field, were obtained for the two batches of nanoparticles with frequencies 765.85, 634.45, 491.10, 390.25, 349.20, 306.65, and 166.00 kHz and field amplitudes of 100, 200, 250, 300 and 350 G. The specific absorption rate (SAR) values for the particles of size 12.2 nm are higher than those for the particles of size 10.2 nm at all concentrations and field parameters. SAR decreases with the increase of particle concentration. SAR obtained for all the particle concentrations of the two batches increases almost linearly with the field frequency (at fixed field strength) and nonlinearly with the field amplitude (at fixed field frequency). SAR value obtained for magnetite nanoparticles with the highest magnetization is 145.84 W/g at 765.85 kHz and 350 G, whereas the SAR value of the particles with the least magnetization is 81.67 W/g at the same field and frequency.