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In this paper, we report a synthesis of magnetic porous hollow silica nanotubes (MPHSNTs) using sol-gel method. The MPHSNTs were fabricated by coating Fe3O4 nanoparticles and silica on surfactant hexadecyltrimethylammonium bromide (CTAB) modified CaCO3 nanoneedles surface under alkaline condition. CaCO3 nanoneedles and surfactant CTAB are introduced as nanotemplates to form the hollow and porous structures, respectively. After removing CTAB by calcination and etching CaCO3 nanoneedles away in diluted acetic acid, magnetic porous hollow silica nanotubes with Fe3O4 nanoparticles embedded in the silica shell were achieved. The products were characterized by scanning electron microscopy, transmission electron microscopy, and N2 adsorption-desorption isotherms. Superconducting quantum interference device measurement shows that the nanotubes exhibit superparamagnetism property at room temperature and ferromagnetism below the blocking temperature. Toxicity test was also performed for the magnetic nanocarriers, showing good bio-compatibility. Magnetic porous hollow silica nanotubes with advantages of high surface area, good bio-compatibility, and superparamagnetism are one of the novel drug nanocarriers for nanomedicine applications. [ABSTRACT FROM AUTHOR]

Magnetic porous hollow silica nanosphere is a new class of structured nanomaterials for drug delivery. In this paper, we report a synthesis of magnetic porous hollow silica nanospheres (MPHSNs) using CaCO3/Fe3O4 composite nanoparticles and cationic surfactant double templates. Fe3O4 nanoparticles were first mixed into CaCO3 using rotating packed bed forming CaCO3/Fe3O4 composite nanoparticles. Tetraethoxysilane was then added as precursor to form silica layer on the surface of CaCO3/Fe3O4 composite nanoparticles, while hexadecyltrimethylammonium bromide was used as a second template to direct the formation of porous silica shells. After the calcination of the surfactants and etching away CaCO3, MPHSNs were formed with the magnetite nanoparticles remaining in the cores. Transmission electron microscopy was applied for the nanostructure determination. The pore size can be measured by micromeritics analyzer. Magnetic properties of MPHSNs were measured by a superconducting quantum interface device. Zero-field-cooled and field-cooled magnetization data in the temperature range of 5–300 K show that the MPHSNs are superparamagnetism above the blocking temperature and ferromagnetism below the blocking temperature after the calcination. The MPHSNs can be used as potential nanocarriers for targeted delivery and controlled releasing. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles are usually present in the form of magnetic carriers and used in nanomedicine and biosystem. In this paper, magnetic hollow silica (MHS) nanoparticles were fabricated by a one-step synthesis of Fe3O4 nanoparticles and then coating of silica on nanosized spherical calcium carbonate under alkaline conditions, in which nanosized calcium carbonate (CaCO3, 25–60 nm) was used as a scarified template, tetraethoxysilane as a precursor, and Fe3O4 nanoparticles (∼5 nm), formed in the initial reaction stage, as magnetic agents. The as-synthesized nanoparticles were immersed in a weak acetic acidic solution to remove CaCO3, forming MHS carriers. The nanostructures of the MHS carriers were characterized by scanning electron microscope, transmission electron microscope, and x-ray diffraction. Superconducting quantum interference device measurement exhibited that the MHS nanoparticles were superparamagnetic. Toxicity was tested for MHS carriers using rat brain microvascular endothelial cells. The cells treated with concentration lower than 50 μg/ml of the MHS nanoparticles showed no significant toxicity. After modification by silane coupling agent, the MHS carriers have strong absorption for ibuprofen in nanomedicine field. [ABSTRACT FROM AUTHOR]

Different kinds of nanospheres are used in magnetic nanosphere fabrication for bioapplications. In this paper, we report a successful synthesis of magnetic hollow silica nanospheres (MHSNS). The MHSNS were fabricated with a one step coating of Fe3O4 magnetic nanoparticles sNPsd (∼10 nm) and silica on nanosized (20-100 nm) spherical calcium carbonate sCaCO3d surface under alkaline conditions, in which the nanosized CaCO3 were used as nanotemplates and tetraethoxysilane and magnetic NPs were used as precursors. The as-synthesized nanoshperes were immersed in an acidic solution to remove nanosized CaCO3, forming MHSNS. The MHSNS were characterized by SEM, TEM, and SQUID. SEM and TEM results showed that a smooth surface of MHSNS and a thin layer of silica (∼10 nm) embedded with the magnetic NPs was successfully formed. No nanosized CaCO3 nanotemplates were observed. SQUID measurement demonstrated that magnetization of MHSNS was dependent on temperature, exhibiting superparamagnetism. The MHSNS have potential applications in biomedicine and bioseparation. [ABSTRACT FROM AUTHOR]

Nanometer-sized ferrite magnetic materials are the subject of intense research interest due to their potential applications in high-density magnetic information storage. One of the most explored ferrite materials is the cobalt ferrite sCoFe2O4d. We have synthesized cobalt ferrite nanowires using cobalt ferrite nanoparticles in a porous anodic alumina template (AAT). The process of embedding ferrimagnetic particles into the pores was assisted by the magnetic field of a permanent magnet placed in vacuum directly under the substrate. Particles synthesized in the template were subsequently annealed at 600 °C for 2 h in Ar gas forming arrays of cobalt ferrite nanowires inside the AAT. The morphology of the ferrite before and after annealing was observed using a field-emission scanning electron microscope. The crystallographic structure of the nanowires was analyzed using x-ray diffraction and transmission electron microscopy. The magnetization was measured by a superconducting quantum interference device. The coercivity of the annealed ferrite in the form of nanowires is significantly larger than that of the separate ferrite nanoparticles in the pores. This effect is due to the clustering of nanoparticles when the organic solvent is removed by high-temperature annealing as well as an improvement in the crystallininty of the ferrite by reduction of defects. The Faraday spectra of the nanowires were measured before and after annealing. A significant peak was observed at 725 nm. The nanowire/AAT composite material had a Verdet constant of 0.1 min/ (Oe cm) at the peak. It is important to mention that not only the properties but also the form of the material-a regular array of pillars-may be important for microelectronic or information storage applications. [ABSTRACT FROM AUTHOR]

We have studied magnetic properties of a diluted system of ultrafine cobalt ferrite nanoparticles (d∼3.3 nm). From the peak of the zero-field-cooled measurements, we obtained the blocking temperature T[SUBB] of about 90.5 K and it is virtually independent of the applied magnetic field up to 5 kOe. At the superparamagnetic region T>T[SUBB], the system follows the modified Curie-law variation of the magnetic susceptibility χ = χ[SUB0]+C/T. We observed that the saturation magnetization follows a spin-wavelike temperature dependence at temperature above 10 K. In spite of the cubic structure for cobalt ferrite, at 2 K, the reduced remanence M[SUBr]/M[SUBs] is equal to 0.46 which is close to the theoretical value of 0.5 expected for noninteracting uniaxial single-domain particles with the easy axis randomly oriented. From the ac susceptibility measurements at different frequencies, we obtained a linear dependence of the logarithm of the experimental time window τ[SUBex] as function of inverse blocking temperature (1/T[SUBB]). The fitting results in the anisotropy constant value K of 3.15 × 10[SUP7] erg/cm[SUP3] that is one order of magnitude higher than 1.8-3.0 × 10[SUP6] erg/cm[SUP3] in bulk CoFe[SUB2]O[SUB4] materials. [ABSTRACT FROM AUTHOR]

The amorphous ternary material, Ni[SUB3](SbTe[SUB3])[SUB2] was prepared using a rapid precipitation reaction between the Zintl phase K[SUB3]SbTe[SUB3] and NiBr[SUB]2 in solution. This material induced by the incorporation) of ternary chalcogenide into long range ordered mesoporous SBA-15 was transformed into ternary nanoparticles. Structural confinement of the amorphous ternary chalcogenide in the mesoporous silica tube causes the suppression of phonon coupling to photoexcited carriers in the confined ternary chalcogenide, resulting in narrower photoluminescence (PL) band than those of the bulk ternary chalcogenide. It also gives rise to ferromagnetic behavior of the nanoparticles made from the material, which is a spin glass with the freezing temperature of 4.0 K in a bulk form. The physical and chemical properties of obtained ternary bulk and nanoparticles have been investigated by x-ray diffraction, superconducting quantum interference device, transmission electron microscopy, Brunauer - Emmett -- Teller, and PL (steady-state photoluminescence spectroscopy). The role played by the modified SBA-15 porous silica in controlling ternary chalcogenide size and quantities has been discussed. [ABSTRACT FROM AUTHOR]

Fe[sub 3]O[sub 4] thin film prepared by pulsed laser deposition on Si (100) substrate has been investigated by transmission electron microscopy from plane and cross-sectional views. The thin film, which shows a spinel structure as characterized by selected-area diffraction, is about 180 nm thick with granular growth of particle size about 50 nm. High resolution electron microscopy observations indicate reduced thickness of the native SiO[sub 2] layer between the thin film and Si due to rastering of the substrate surface by an unfocused laser beam before the deposition. By using a 220 diffraction spot in two beam condition near the <001> axis of a single Fe[sub 3]O[sub 4] grain, antiphase boundaries (APBs) inside the grains could be clearly resolved. The existence of APBs in the thin film is consistent with the magnetic experiments including an open hysteresis loop and unsaturated magnetization in relatively high magnetic fields. This study suggests that APBs are not uni! que to Fe[sub 3]O[sub 4] films grown on MgO substrates. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A novel resonant method based on a tunnel-diode oscillator is used to study the dynamic transverse susceptibility in a Fe nanoparticle system. The magnetic system consists of an aggregate of nanometer-size core (Au)-shell (Fe) structure, synthesized by reverse micelle methods. Static and dynamic magnetization measurements carried out in order to characterize the system reveal a superparamagnetic behavior at high temperature. The field-dependent transverse susceptibility at radio-frequencies for different temperatures reveals distinct peak structure at characteristics fields (±H[sub K],H[sub C]) which changes with temperature. It is proposed that relaxation processes could explain the influence of the temperature on the field dependence of the transverse susceptibility. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this article, metallic iron, and iron/platinum alloys nanoparticles have been synthesized via chemical assembly and magnetically characterized. Fabrication of iron and iron/platinum particles was achieved by reducing 0.1 M aqueous metal salts confined in the polar portions of inverse micelles of cetyltrimethylammonium bromide with borohydride. The dc susceptibility of a sample of 8 nm iron nanoparticles exhibits a blocking temperature of 54 K and coercivity of 200 G at 10 K. The presence of the gold coatings prevented oxidation and allowed the samples to be manipulated without additional precautions to prevent oxidation. Two iron/platinum alloys have been synthesized and verified by x-ray powder diffraction and transmission electron microscopy. Magnetic characterization is performed using superconducting quantum interference device magnetometry. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study which determined the effect of Li[sub3]N addition by mechanical alloying on Nd[sub2]Fe[sub14]B—Formation of NdN[sub2]. Nitrogen additions; Procedure used in mechanical alloying; Factor attributed to the curving up.