Optical sensing characteristics of the photonic crystal fiber filled with magnetic fluid

A novel photonic crystal fiber sensing theory filled with magnetic fluid is proposed based on the change of the MF refractive index under varied magnetic field. The magnetically induced tuning of the magnetic fluid filled PCF propagation properties were investigated by the full-vector finite element method with a perfectly matched layer. Theoretical calculations show that both the effective refractive index and the effective mode area increase vs. the increased magnetic field, and the PCF filled MF with larger d/Λ is more sensitive to magnetic field. When the wavelength λ = 1550 nm, the duty ratio d/Λ = 0.9, d/Λ = 0.6, the effective refractive indexes increase respectively from 1.598279 to 1.617572, from 1.61948 to 1.632484, and the effective mode areas increase respectively from 3.561115 μm² to 7.052360 μm², from 6.167494 μm² to 37.221998 μm² as the magnetic field changes from 25 Oe to 175 Oe. This scheme provides theoretical foundation to use magnetic field to control light in photonic crystal fiber and also offers a potential method for magnetic field sensing based on the TIR-PCF.     

Synthesis of magnetite nanoparticles for AC magnetic heating

Magnetite particles with different average diameter (D_m) suitable for magnetic fluid hyperthermia (MFH) were synthesized by controlled coprecipitation technique. In this method, the reaction pH was stabilized using the pH buffer and the average particle diameter decreased with increasing reaction pH. The size-dependent magnetic behavior of the magnetite nanoparticles was studied and the optimum size range required for magnetic fluid hyperthermia (MFH) has been arrived at. Among the samples studied, the maximum specific absorption rate of 15.7 W/g was recorded for the magnetite sample with D_m of 13 nm, when exposed to an AC magnetic field strength of 3.2 kA/m and a frequency of 600 kHz. The AC magnetic properties suggested that the size distribution of the sample was bimodal with average particle size less than ∼13 nm.     

Particles size effects of single domain CoFe2O4 on suspensions stability

Single domain magnetic CoFe₂O₄ nanoparticles with spinel structure were prepared by the coprecipitation method. Particles with size of 16, 20, 40 and 60 nm were synthesized by sintering the precursor at 500, 600, 800 and 900 °C, respectively. The magnetic hysteresis measurement of CoFe₂O₄ particles showed that particles were single domain particles with similar saturation magnetization (∼300 emu/cm³) at room temperature. The zeta potential study of suspensions (CoFe₂O₄-acetylacetone system) with various particle sizes showed the suspension systems had similar zeta potential values (∼40 mV). The effects of magnetic particle size on the suspension stability characterized by electrophoretic deposition yields and sediment volumes were studied. The suspension stability decreased with an increase in particle size and a flocculation threshold of particle radius a was found at 30 nm. A suspension stability theory approaching to the phenomenon was established. The theory based on the DLVO theory was developed by introducing an extra magnetic interaction force. Dormann model was adopted, in which the magnetic interactions of two spherical nanoparticles were investigated in terms of dipole-dipole interactions. Compared to DLVO, suspension's physical parameters not only zeta potential ζ and the Debye length 1/κ, but also particles' radius a brought about stable to flocculation transition in the theory.     

Templated synthesis of monodisperse mesoporous maghemite/silica microspheres for magnetic separation of genomic DNA

A novel method is described for the preparation of superparamagnetic mesoporous maghemite (γ-Fe₂O₃)/silica (SiO₂) composite microspheres to allow rapid magnetic separation of DNA from biological samples. With magnetite (Fe₃O₄) and silica nanoparticles as starting materials, such microspheres were synthesized by the following two consecutive steps: (1) formation of monodispersed organic/inorganic hybrid microspheres through urea-formaldedyde (UF) polymerization and (2) removal of the organic template and phase transformation of Fe₃O₄ to γ-Fe₂O₃ by calcination at elevated temperatures. The as-synthesized particles obtained by heating at temperature 300 °C feature spherical shape and uniform particle size (d_particle=1.72 μm), high saturation magnetization (M_s=17.22 emu/g), superparamagnetism (M_r/M_s=0.023), high surface area (S_BET=240 m²/g), and mesoporosity (d_pore=6.62 nm). The composite microsphere consists of interlocked amorphous SiO₂ nanoparticles, in which cubic γ-Fe₂O₃ nanocrystals are homogeneously dispersed and thermally stable against γ- to α-phase transformation at temperatures up to 600 °C. With the exposed iron oxide nanoparticles coated with a thin layer of silica shell, the magnetic microspheres were used as a solid-phase adsorbent for rapid extraction of genomic DNA from plant samples. The results show that the DNA templates isolated from pea and green pepper displayed single bands with molecular weights greater than 8 kb and A₂₆₀/A₂₈₀ values of 1.60-1.72. The PCR amplification of a fragment encoding the endogenous chloroplast ndhB gene confirmed that the DNA templates obtained were inhibitor-free and amenable to sensitive amplification-based DNA technologies.     

The influence of a demagnetizing field on hysteresis losses in a dense assembly of superparamagnetic nanoparticles

The electrodynamic method is used to measure the hysteresis losses of a dense assembly of magnetite nanoparticles with an average diameter D=25 nm in the frequency range f=10–150 kHz and for magnetic field amplitudes H₀=100–300 Oe. It is found that the specific loss power is determined by a demagnetizing factor of a whole sample. It diminishes approximately 4.5 times when the sample aspect ratio decreases from L/d=11.4 to L/d≈1, where L and d are the sample length and diameter, respectively. For H₀≤300 Oe the maximal specific loss power 120 W/g is obtained for the sample with L/d=11.4 at f=120 kHz. For comparison, the assembly specific absorption rate has been determined also by means of direct measurement of the temperature difference between the inner and outer surfaces of a flat cuvette containing magnetic nanoparticles. For both methods of measurement close values for the specific absorption rate are obtained for samples with similar demagnetizing factors.     

Magnetic field heating study of Fe-doped Au nanoparticles

Fe-doped Au nanoparticles are ideal for biological applications over magnetic oxides due to their conjugation chemistry, optical properties, and surface chemistry. We present an AC magnetic field heating study of 8 nm Fe-doped Au nanoparticles which exhibit magnetic behavior. Magnetic heating experiments were performed on stable aqueous solutions of the nanoparticles at room temperature. The nanoparticles exhibit magnetic field heating, with a specific absorption rate (SAR) of 1.84 W/g at 40 MHz and H=100 A/m. The frequency dependence of the heating follows general trends predicted by power loss equations and is similar to traditional materials.     

Effects of crystalline grain size and packing ratio of self-forming core/shell nanoparticles on magnetic properties at up to GHz bands

Self-forming core/shell nanoparticles of magnetic metal/oxide with crystalline grain size of less than 40 nm were synthesized. The nanoparticles were highly concentrated in an insulating matrix to fabricate a nanocomposite, whose magnetic properties were investigated. The crystalline grain size of the nanoparticles strongly influenced the magnetic anisotropy field, magnetic coercivity, relative permeability, and loss factor (tan δ=μ″/μ′) at high frequency. The packing ratio of the magnetic metallic phase in the nanocomposite also influenced those properties. High permeability with low tan δ of less than 1.5% at up to 1 GHz was obtained in the case of the nanoparticles with crystalline grain size of around 15 nm with large packing ratio of the nanoparticles.     

Solid-state synthesis and magnetic properties of epitaxial FePd3(0 0 1) films

The solid-state synthesis of magnetically soft phase FePd₃ in epitaxial Pd(0 0 1)/Fe(0 0 1)/MgO(0 0 1) film systems was studied experimentally. The system had a Fe to Pd ratio of 1:3. An increase to 450 °C leads to the formation of three variants of ordered L1₀-FePd crystallites. At 500 °C, the solid-state reaction of unreacted Pd with L1₀-FePd crystallites initiates the growth of an ordered epitaxial L1₂-FePd₃(0 0 1) layer. When annealing at 650 °С, a gradual disordering is observed. The magnetic anisotropy (K₁=−2.0×10³ erg/cm³) and the saturation magnetization (M_S=650 emu/cm³) of the disordered FePd₃ phase were determined.     

Synthesis of aqueous ferrofluids of ZnxFe3−xO4 nanoparticles by citric acid assisted hydrothermal-reduction route for magnetic hyperthermia applications

Superparamagnetic and monodispersed aqueous ferrofluids of Zn substituted magnetite nanoparticles (Zn_xFe_3−xO₄, x=0, 0.25, 0.3, 0.37 and 0.4) were synthesized via hydrothermal-reduction route in the presence of citric acid, which is a facile, low energy and environmental friendly method. The synthesized nanoparticles were characterized by X ray diffraction (XRD) analysis, Fourier transform infrared (FTIR) spectroscopy, scanning and transmission electron microscopy (SEM and TEM) and the dynamic light scattering (DLS) method. The results showed that a certain amount of citric acid was required to obtain single phase Zn substituted magnetite nanoparticles. Citric acid acted as a modulator and reducing agent in the formation of spinel structure and controlled nanoparticle size and crystallinity. Mean particle sizes of the prepared nanoparticles were around 10 nm. The results that are obtained from XRD, magnetic and power loss measurements showed that the crystallinity, saturation magnetization (M_S) and loss power of the synthesized ferrofluids were all influenced by the substitution of Zn in the structure of magnetite. The Zn substituted magnetite nanoparticles obtained by this route showed a good stability in aqueous medium (pH 7) and hydrodynamic sizes below 100 nm and polydispersity indexes below 0.2. The calculated intrinsic loss power (ILP) for the sample x=0.3 (e.g. 2.36 nH m²/kg) was comparable to ILP of commercial ferrofluids with similar hydrodynamic sizes.     

Heat generation of aqueously dispersed CoFe2O4 nanoparticles as heating agents for magnetically activated drug delivery and hyperthermia

Self-heating from magnetic nanoparticles under AC magnetic field can be used either for hyperthermia or to trigger the release of an anti-cancer drug, using thermo-responsive polymers. The heat generated by applying an AC magnetic field depends on the properties of magnetic nanoparticles (composition, size, crystal structure) as well as the frequency and amplitude of the magnetic field. Before these systems can be efficiently applied for in vitro or in vivo studies, a thorough analysis of the magnetically induced heating is required. In this study, CoFe₂O₄ nanoparticles were synthesized, dispersed in water, and investigated as heating agents for magnetic thermo-drug delivery and hyperthermia. The temperature profiles and infrared (IR) camera images of heat generation of CoFe₂O₄ nanoparticles under various AC magnetic fields of 127–700 Oe at 195, 231, and 266 kHz were measured using an IR thermacam, excluding the external AC magnetic field interruption. The CoFe₂O₄ nanoparticles were successfully dispersed in water using an 11-mercaptoundecanoic acid ligand exchange method to exchange the solvent used for synthesis of hexane for water. During the heating experiments, each of CoFe₂O₄ nanoparticle solutions reached a steady state where the temperature rose between 0.1 and 42.9 °C above ambient conditions when a magnetic field of 127–634 Oe was applied at 231 or 266 kHz. The heat generation was found to be dependent on the intensity of AC magnetic field and applied frequency. Therefore, the desired heating for magnetically triggered drug delivery or hyperthermia could be achieved in water-dispersed CoFe₂O₄ nanoparticles by adjusting the AC magnetic field and frequency.     

Non-linear optical properties of silver nanoparticles prepared by hydrogen reduction method

Silver nanoparticles have been prepared using hydrogen gas as the reducing agent for silver nitrate and poly(vinyl pyrrolidone) as the capping agent; the reaction was carried out at 70 °C for 3 h. The size of the nanoparticles was found to be about 20 nm as analyzed using transmission electron micrographs. The X-ray diffraction pattern revealed the face-centered cubic (fcc) structure of silver nanoparticles. The linear absorption of Ag nanoparticles, α, is obtained about 3.71 cm⁻¹. The non-linear refractive indices of silver nanoparticles were defined by the z-scan technique using CW He-Ne laser (λ = 632.8 nm) at different incident intensities. The magnitude of non-linear refractive index (n₂) was measured to be in the order of 10⁻⁷ (cm²/W) with a negative sign. Therefore self-defocusing phenomena is taking placed for Ag nanoparticles.     

Electromagnetic properties of manganese-zinc ferrite with lithium substitution

Polycrystalline manganese-zinc ferrite with lithium substitution of composition Li_0.5xMn_0.4Zn_0.6−xFe_2+0.5xO₄ (0.0≤x≤0.4) was prepared by the usual ceramic method. X-ray diffraction analysis confirmed that the samples have a spinel structure and are of single phase for some values of Li content. Lithium doping considerably modifies saturation magnetization since its value increases from 57.5 emu/g for x=0.0 to 82.9 emu/g for x=0.4. Lithium inclusion increases the real permeability (over 1 MHz) while the natural resonance frequency shifts to lower values as the fraction of Li increases. These ferrites show good electromagnetic properties as absorbers in the microwave range of 1 MHz - 1 GHz.     

Textural and electronic characteristics of mechanochemically activated composites with nanosilica and activated carbon

Nanosilicas (A-50, A-300, A-500)/activated carbon (AC, S_BET = 1520 m²/g) composites were prepared using short-term (5 min) mechanochemical activation (MCA) of powder mixtures in a microbreaker. Smaller silica nanoparticles of A-500 (average diameter d_av = 5.5 nm) can more easily penetrate into broad mesopores and macropores of AC microparticles than larger nanoparticles of A-50 (d_av = 52.4 nm) or A-300 (d_av = 8.1 nm). After MCA of silica/AC, nanopores of non-broken AC nanoparticles remained accessible for adsorbed N₂ molecules. According to ultra-soft X-ray emission spectra (USXES), MCA of silica/AC caused formation of chemical bonds Si-O-C; however, Si-C and Si-Si bonds were practically not formed. A decrease in intensity of OK_α band in respect to CK_α band of silica/AC composites with diminishing sizes of silica nanoparticles is due to both changes in the surface structure of particles and penetration of a greater number of silica nanoparticles into broad pores of AC microparticles and restriction of penetration depth of exciting electron beam into the AC particles.     

Magnetic entropy change in GdCo13−xSix intermetallic compounds

The magnetic entropy change in GdCo_13−xSi_x (x=3.8, 4, 4.1, and 4.2) intermetallic compounds has been investigated by means of magnetic measurements in the vicinity of their Curie temperature. It was found that the magnetic ordering temperatures decrease from 60 K at x=3.8 to 28 K for x=4.2. The magnetic entropy change is calculated from isothermal magnetization versus magnetic field at various temperatures using the Maxwell relation. As a result, the maximum magnetic entropy changes of the investigated compounds, at their Curie temperatures, decrease from 11.5 J/kg K for x=4.2 to 6.86 J/kg K for x=3.8 in a field change of 0-3 T, whereas it decreases from 5.13 J/kg K for x=4.2 to 2.60 J/kg K for x=3.8 in a field change of 0-1 T. Moreover, the maximum value of the magnetic entropy change obtained at a higher field for GdCo_13−xSi_x with x=4 (23.75 J/kg K at 5 T) is comparable to that of various types of compounds with a cubic NaZn₁₃-type structure. Finally, the maximum of the magnetic entropy change is found to decrease with increasing Si content.     

Synthesis and characterization of manganese ferrite nanoparticles by thermal treatment method

Cubic structured manganese ferrite nanoparticles were synthesized by a thermal treatment method followed by calcination at various temperatures from 723 to 873 K. In this investigation, we used polyvinyl pyrrolidon (PVP) as a capping agent to control the agglomeration of the nanoparticles. The characterization studies were conducted by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The average particle sizes of manganese ferrite nanoparticles were determined by TEM, which increased with the calcination temperature from 12 to 22 nm and they had good agreement with XRD results. Fourier transform infrared spectroscopy confirmed the presence of metal oxide bands at all temperatures and the absence of organic bands at 873 K. Magnetic properties were demonstrated by a vibrating sample magnetometer, which showed a super-paramagnetic behavior for all samples and also saturation magnetization (M_s) increases from 3.06 to 15.78 emu/g by increasing the calcination temperature. The magnetic properties were also confirmed by the use of electron paramagnetic resonance spectroscopy, which revealed the existence of unpaired electrons and also measured peak-to-peak line width, resonant magnetic field and the g-factor.     

Synthesis and investigation of nonlinear optical properties of semiconductor ZnS nanoparticles

ZnS nanoparticles were prepared by a simple chemical method and using PVP (poly vinylpyrrolidone) as capping agent. The sample was characterized by UV-vis spectrophotometer, X-ray diffraction (XRD) and Z-scan technique. XRD pattern showed that the ZnS nanoparticles had zinc blende structure with an average size of about 2.18 nm. The value of band gap of these nanoparticles was measured to be 4.20 eV. The nonlinear optical properties of ZnS nanoparticles in aqueous solution were studied by Z-scan technique using CW He-Ne laser at 632.8 nm. The nonlinear absorption coefficient (β) was estimated to be as high as 3.2×10⁻³ cm/W and the nonlinear refractive index (n₂) was in order of 10⁻⁸ cm²/W. The sign of the nonlinear refractive index obtained negative that indicated this material exhibits self-defocusing optical nonlinearity.     

Study on the interaction of tropisetron hydrochloride and l-tryptophan by spectrofluorimetry and its analytical application

A new method to determine tropisetron hydrochloride with l-tryptophan in the medium with pH=9.0 was studied, which is based on the fluorescence quenching effect of tropisetron hydrochloride on l-tryptophan. The fluorescence quenching mechanism and various factors influencing fluorescence quenching were discussed. Under the optimum conditions, the linear range and detection limit were 0.03-12.0 and 0.01 μg/mL (correlation coefficient r=0.9970), respectively. The calibration curve equation was ΔF=6.17+12.56 C (μg/mL). RSD was 3.4% (c=4.0 μg/mL, n=5); the detection limit estimated (S/N=3) was 0.01 μg/mL. The proposed method had been successfully applied to determine tropisetron hydrochloride in real samples and the obtained results were in good agreement with the results of the official method.     

Synthesis and surface modified hard magnetic properties in Co0.5Pt0.5 nanocrystallites from a rheological liquid precursor

Small crystallites of a metastable phase Co_0.5Pt_0.5 are precipitated by heating a rheological liquid precursor of cobalt–hydrazine complex and platinum chloride H₂PtCl₆·xH₂O in polymer molecules of poly(vinylpyrrolidone) (PVP) in ethylene glycol. The hydrazine co-reduces nascent atoms from the Co²⁺ and Pt⁴⁺ that recombine and grow as Co_0.5Pt_0.5. The PVP molecules cap a growing Co_0.5Pt_0.5 as it achieves a critical size so that it stops growing further in given conditions. X-ray diffraction pattern of a recovered powder reveals a crystalline Co_0.5Pt_0.5 phase (average crystallite size D∼8 nm) of a well-known Fm3m-fcc crystal structure with the lattice parameter a=0.3916 nm (density ρ=14.09 g/cm³). A more ordered L1₀ phase (ρ=15.91 g/cm³) transforms (D≥25 nm) upon annealing the powder at temperature lesser than 700 °C (in vacuum). At room temperature, the virgin crystallites bear only a small saturation magnetization M_s=5.54 emu/g (D=8 nm) of a soft magnet and it hardly grows on bigger sizes (D≤31 nm) in a canted ferromagnetic structure. A rectangular hysteresis loop is markedly expanded on an optimally annealed L1₀ phase at 800 °C for 60 min, showing a surface modified coercivity H_c=7.781 kOe with remnant ratio M_r/M_s=0.5564, and M_s=39.75 emu/g. Crystallites self-assembled in an acicular shape tailor large H_c from ideal single domains and high magnetocrystalline anisotropy of a hard magnet L1₀ phase.     

Effect of growth parameters on the structure and magnetic properties of thin polycrystalline Fe films fabricated on Si〈1 0 0〉 substrates

This paper deals with the experimental investigation of the structure and magnetic properties of thin polycrystalline Fe films. Two sets of 50 ± 2 nm thick Fe films were fabricated on Si〈1 0 0〉 substrates with native oxides in place by varying (i) the sputter pressure p_Ar and (ii) the Fe sputter power P_Fe. X-ray diffraction (XRD) study revealed that all films grew with strong 〈1 1 0〉 texture normal to the film plane. No higher order peaks were observed in any of the films studied. For both film sets, the lattice constant (a) was less than the bulk Fe lattice constant (a₀ = 2.866 Å), which suggested the existence of compressive strain in all films. Two regions of homogeneous strain were observed over the range of p_Ar studied. Magneto-optical Kerr effect (MOKE) measurements showed that all films exhibited magnetically isotropic behaviour. The magnetic properties were observed to be influenced strongly by p_Ar. The film grown at p_Ar = 4 μbar was the most softest (H_s = 100 ± 8 kA m⁻¹, M_r/M_s = 0.87 ± 0.02) film among all the films studied. The magnetic properties were found to be independent of P_Fe. The effective saturation magnetostriction constant λ_eff determined (using the Villari method) was positive (4 ± 1 ppm) and observed to vary within the calculated error.     

Preparation of non-oriented silicon steel with high magnetic induction using columnar grains

Columnar grains can lead to detrimental surface ridging and an inhomogeneous microstructure, although their {1 0 0}〈0 v w〉 texture is considered desirable due to their good magnetic properties in non-oriented silicon steel. Based on the hereditary tendency of {1 0 0}〈0 v w〉 texture, the effects of lubrication and heating rate on texture and on final magnetic properties were investigated using a cast slab containing 100% columnar grains. Hot rolling with lubrication, normalization at low heating rate, two-stage cold rolling, and final annealing at 1000 °C helped achieve high performance. As a result, a new non-oriented silicon steel with high magnetic induction (B₅₀=1.82 T) and low core loss (P_1.5=2.35 W/kg) was prepared. The possibility of further performance optimization was also discussed.