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In this paper, ferrogels comprising nanocrystalline Fe₃O₄ and γ-FeOOH dispersed in polyvinyl alcohol gel matrix were synthesized via a novel route, without using any cross-linking agent. A moderately high-pressure environment instead was used for the synthesis. The ferrogels were found to be stable over a long period of time and were characterized by transmission electron microscopy (TEM), Mössbauer spectroscopy and DC magnetization studies. TEM studies showed that the particles are mostly spherical with an average size of 10 nm. Mössbauer spectra of the as prepared gels at different temperatures showed the presence of superparamagnetic particles in them. The gels were found to be magnetically ordered at 20 K giving characteristic six-finger Mössbauer patterns. Bulk magnetic properties of the gels were studied by DC magnetization measurements.

A nanoferrite superparamagnetic system synthesized through co-precipitation method and subsequently dispersed in a medium of de-ionized water was encapsulated with a matrix polymer under constant sonication using chemical oxidative polymerization technique. The polymer coated functional microstructure thus obtained shows enhanced magnetization as evidenced from the results reported elsewhere. The magnetic core crystal growth and anti-spin canting hypothesis were given to be the most general justification behind the unusual enhancement in magnetization and more specifically the rationale could understand recently in accordance with spin injection behavior in functional core-shell microstructures. In this paper, an attempt has been made to correlate the previous magnetization results with spin injection behavior, in conjunction with the thermo gravimetric and dielectric results.

In recent years, use of magnetic nanoparticles in biomedical applications has increased tremendously. In particular, magnetite $({\mathrm{\text{Fe}}}_3{\mathrm{\text{O}}}_4)$ nanoparticles being highly biocompatible are rated very high due to their potential applications in biomedicines, for instance in anticancer drug delivery. In this work, the ${\mathrm{\text{Fe}}}_3{\mathrm{\text{O}}}_4$ nanoparticles have been synthesized using a novel sol–gel based autocombustion technique. The crystal structure of the ${\mathrm{\text{Fe}}}_3{\mathrm{\text{O}}}_4$ phase was confirmed by the data obtained from X-ray diffraction. Scherrer’s formula was employed to estimate the crystallite size of the ${\mathrm{\text{Fe}}}_3{\mathrm{\text{O}}}_4$ nanoparticles. The structural morphology, investigated by using a scanning electron microscopy (SEM), revealed well-dispersed and uniform sized grains in the sample prepared using enhanced fuel concentration. A vibrating sample magnetometer (VSM) was employed to investigate the magnetic characteristics of the samples which confirmed the superparamagnetic nature of the ${\mathrm{\text{Fe}}}_3{\mathrm{\text{O}}}_4$ samples, essentially required for cancer treatment. These nanoparticles could further be modified and functionalized by suitable polymers to achieve better biocompatibility before being injected into the diseased cells.

The magnetic properties of MnP:GaP nanoparticles are calculated using a statistical mechanical approach and effect of various factors on magnetization of nanoparticles is studied. The calculation is based on solution of localized partition function and evolution of magnetic moment affected by thermal fluctuation and external field is included by solving master equation. Instead of constant magnetic saturation approximation, a temperature dependent magnetic moment saturation is included to improve calculation efficiency for larger nanoparticles. In the present work, the field-cooled and zero-field-cooled (FC/ZFC) magnetization of randomly oriented anisotropy and log-normal volume distributed nanoparticles are calculated.

Magnetite (Fe₃O₄) nanoparticles (MPs) capped with polyethylene glycol (PEG) were prepared by a hydrothermal method, and their antibacterial activity was examined against Staphylococcus aureus, Escherichia coli and Psudomonas aeruginosa. The functionalized NPs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), Fourier transform infrared (FTIR) spectroscopy, and Thermogravimetry (TG). The average size of the Fe₃O₄ was in the range 9–20nm, while the functionalized PEG–Fe₃O₄ had an average size of 5–15nm. The PEG–Fe₃O₄ exhibited superparamagnetism and high saturation magnetization at room temperature. The antibacterial activity of the Fe₃O₄ and PEG–Fe₃O₄ were evaluated against E. coli, S. aureus, and P. aeruginosa using the agar well diffusion method. The changes in the morphology of the studied bacterial species were observed via SEM, while the mode of action of the studied agents was determined via the detection of reactive oxygen species (ROS) using Acridine orange-ethidium bromide (AO/EtBr) staining method. The results showed that PEG-functionalized magnetic (Fe₃O₄) NPs as a novel DNA-mediated antibacterial agent. The PEG–Fe₃O₄ NPs were observed to destroy the bacterial cells by permeating the bacterial nucleic acid and cytoplasmic membrane, resulting in the loss of cell-wall integrity, nucleic acid damage, and increased cell-wall permeability. The PEG–Fe₃O₄ NPs could serve as a potential antibacterial agent in future biomedical and pharmaceutical applications.

A template polymerization approach is reported to prepare uniform functional sandwiched magnetic composite nanomicrospheres with polymer core, magnetic Fe₃O₄ mezzanine and multicomponent polymer shell. The fine superparamagnetic properties, thermostability and stability in a wide pH range of aqueous solution made the composite mirospheres had the potential applications in biology and medicine.

Fe₃O₄ nanoparticles of size 10 and 12 nm were synthesized by chemical reduction method and characterized for their structural, optical, thermal and magnetic properties at room temperature. Photoacoustic analysis shows a reduction in thermal conductivity atleast by one order from the bulk but within the nanoregime, thermal conductivity increases with decreasing particle size. VSM measurements indicate superparamagnetism in Fe₃O₄ nanoparticles.

Magnesium ferrite (MgFe₂O${}_4)$ being a soft magnetic material with fast frequency response, high a.c. heat power generation and high biocompatibility, is widely used in biomedical fields such as targeted drug delivery, magnetic hyperthermia, etc. This paper reports the synthesis of magnetic MgFe₂O₄ nanoparticles by hydrothermal method using chloride salts of metal ions. The effect of calcination on the structural and magnetic properties is studied by XRD, FTIR, VSM and Mossbauer spectrum analysis. Fine particles in the size range 3–24nm are obtained. On calcination, crystallite size increases and lattice parameter decreases. From the magnetic characterization, it is seen that the magnetic properties mainly depend on crystallite size and cation distribution. The mixed spinel states of the prepared materials are confirmed from the FTIR and Mossbauer spectrum analysis. The doublet spectrum obtained in the Mossbauer studies indicates the superparamagnetic relaxation at room temperature.

We are interested in defining new energy functionals and solving them by using the variational approach method and Darboux equations. That is, we aim to define a new class of elastic curves on the regular surface $\mathrm{\Lambda }$. We further improve an alternative method to find critical points of the bending energy functionals acting on a class of magnetic curves on $\mathrm{\Lambda }$. As a result, we classify these critical curves as elastic magnetic curves of the Darboux vector family.

In this paper, Fe₃O₄@SiO₂@CeO₂@Au core/shell microspheres were synthesized through hydrolysis and solvothermal processes. The results indicated that the magnetic Fe₃O₄ cores were well wrapped by the coating layer of SiO₂/CeO₂ with a thickness of 50 nm, and Au nanoparticles with 35 nm in diameter were attached on the shell. The microspheres showed a monodispersity and superparamagnetism. The composites showed excellent ability to absorb a wide range of wavelengths including visible and NIR region (from 250 nm to 800 nm), making it a potential full solar spectrum response photocatalyst for sunlight applications.

This paper presents a survey of the methods of statistical physics which are applied to the problem of thermal agitation in magnetic materials. The main focus of the work is the stochastic dynamics described by the Landau-Lifshitz-Gilbert equation for which most analytic results are known, and which has been most commonly used in numerical simulations. We also present the much more recent Landau–Lifshitz–Bloch equation and the numerical calculations describing magnetization dynamics close to the Curie point. The paper is concluded by a description of the newly introduced jump-noise and of the Barkhausen jumps.

The thermally activated dynamics of an uniaxial superparamagnetic particle are studied here from the point of view of approach towards a steady state minor hysteresis loop representing a limiting cycle. The particle is initially at an arbitrary state, and is driven by a sufficiently small external applied ac magnetic field till the limiting minor hysteresis loop is reached with a desired precision. The number of periods required to reach the limiting cycle is found to satisfy an Arrhenius-type law, with an exponential dependence on the inverse ambient temperature. We tentatively associate this result with energy dissipation, its origin, however, remains quite unclear.

Assemblies of magnetic nanoparticles show a great potential for application in biomedicine, particularly, magnetic hyperthermia. However, to achieve desired therapeutic effect in magnetic hyperthermia, the assembly of nanoparticles should have a sufficiently high specific absorption rate (SAR) in alternating magnetic field of moderate amplitude and frequency. Using the Landau–Lifshitz stochastic equation, it is shown that dilute assemblies of iron oxide nanoparticles of optimal diameters are capable of providing SAR of the order of 400–600W/g in alternating magnetic field with the amplitude $H_0=100$Oe in the frequency range f = 300–500kHz. Unfortunately, in dense clusters of magnetic nanoparticles, which are often formed in a biological medium, there is a sharp decrease in SAR due to the influence of strong magneto-dipole interaction of closest nanoparticles. To overcome this difficulty, it is suggested covering the nanoparticles with nonmagnetic shells of sufficient thickness or using non-single-domain nanoparticles being in magnetization curling states.

We present results of magneto-optical investigations of (CoFeZr)${}_x$(Al₂O${}_3{)}_{100-x}$ film nanocomposites in transverse Kerr effect (TKE) geometry in the spectral range 0.5–4.0eV and magnetic field up to 3.0kOe. Nanocomposites were deposited onto a glass-ceramic substrate by ion-beam sputtering. The TKE response at room temperature strongly depends on the wavelength of light, applied magnetic field H and the volume metallic fraction. From the analysis of the field dependences of TKE at different wavelengths, it follows that in the as-deposited samples, the interaction between nanoparticles at $x<30$at.% is small and the nanocomposite is an ensemble of superparamagnetic particles; as x increases to 32at.%, a superspinglass-type state arises, then, in the vicinity of 34at.%, along with individual superparamagnetic particles, superferromagnetic regions appear. Long-range ferromagnetic order arises at concentrations x less than the percolation threshold for conductivity $x_{\mathrm{\text{per}}}=42.6$at.%. In the presence of two different magnetic states in the samples, TKE is not proportional to the magnetization. Both the field dependences at near-infrared region and the spectral dependences of TKE change significantly after annealing of the samples, while the changes in the field dependences of the magnetization are almost imperceptibly.

A template polymerization approach is reported to prepare uniform functional sandwiched magnetic composite nanomicrospheres with polymer core, magnetic Fe₃O₄ mezzanine and multicomponent polymer shell. The fine superparamagnetic properties, thermostability and stability in a wide pH range of aqueous solution made the composite mirospheres had the potential applications in biology and medicine.

Water-soluble, ultrasmall, and superparamagnetic Fe₃O₄ nanoparticles were in-situ prepared using one-step coprecipitation method by using poly (amidoamine) (PAMAM) dendrimer templates. Photographs show that Fe₃O₄ nanoparticles prepared at the Fe³⁺/Fe²⁺/PAMAM molar ratio no higher than 40/30/1 disperse stably in water, forming clear colloidal solutions. TEM images show Fe₃O₄ nanoparticles have uniform size and good dispersity. The average diameter of particles is less than 8 nm. The HRTEM image indicates these Fe₃O₄ nanoparticles are of high crystallinity, and their crystal structure belongs to cubic system. XRD patterns show these nanoparticles as prepared are Fe₃O₄ of reverse spinel phase. The hysteresis loops confirm the superparamagnetism of Fe₃O₄ nanoparticles, and the saturation magnetization reaches 48.6 emu/g. FTIR spectra show the strong interactions between Fe₃O₄ nanoparticle surfaces and PAMAM dendrimers. Fe₃O₄ nanoparticles colloidal solutions prepared at the Fe³⁺/Fe²⁺/PAMAM molar ratio no higher than 20/15/1 keep on clarify and transparent after 6 months.