Nanometer-sized Magnetic Particles Research Articles

Synthetic Study and Merits of Fe3O4 Nanoparticles as Emerging Material

Iron (III) oxide magnetic nanoparticles have provided us a multitude of new tools to explore biological and other scientific systems on small length scales. The opening up of single cell or single molecule phenomena to experimental investigations present an important step forward and promises to yield new insights. This review depicts some important and most commonly used methodologies for the engineering of iron oxide magnetic nanoparticles including superparamagnetic iron oxide nanoparticles and ultra-small superparamagnetic iron oxide nanoparticles, important features of these synthesis methods and their applications in different fields of life proving it as an emerging material. Most important task in nanoscale synthesis of iron oxide is to control morphology and contain it within a narrow size distribution. These processes include sol–gel method, hydrothermal method, sonochemical method, co-precipitation and micro emulsion methods. These processes are essentially highly controlled to fabricate the desire material with appropriate properties. Synthesis of mono disperse nanometer-sized magnetic particles of metal alloys and metal oxides is an active research area because of their potential technological ramifications ranging from ultrahigh-density magnetic storage media, to biological imaging. Size, size distribution, shape, and dimensionality are important for the properties of these magnetic materials. Nanoparticles of various iron oxides (Fe3O4 and c-Fe2O3 in particular) have been widely used in a range of biological applications. Iron oxide magnetic nanoparticles can be designed to exhibit novel and significantly improved physical, chemical and biological properties, phenomena and strategies as a result of the limited size of their constituent particles. Iron oxide nanoparticles can be designed to exhibit novel and significantly improved physical, chemical and biological properties, phenomena and strategies as a result of the limited size of their constituent particles by using various methodologies.

Nanometer-size hard magnetic ferrite exhibiting high optical-transparency and nonlinear optical-magnetoelectric effect.

Development of nanometer-sized magnetic particles exhibiting a large coercive field (Hc) is in high demand for densification of magnetic recording. Herein, we report a single-nanosize (i.e., less than ten nanometers across) hard magnetic ferrite. This magnetic ferrite is composed of ε-Fe2O3, with a sufficiently high Hc value for magnetic recording systems and a remarkably high magnetic anisotropy constant of 7.7 × 106 erg cm−3. For example, 8.2-nm nanoparticles have an Hc value of 5.2 kOe at room temperature. A colloidal solution of these nanoparticles possesses a light orange color due to a wide band gap of 2.9 eV (430 nm), indicating a possibility of transparent magnetic pigments. Additionally, we have observed magnetization-induced second harmonic generation (MSHG). The nonlinear optical-magnetoelectric effect of the present polar magnetic nanocrystal was quite strong. These findings have been demonstrated in a simple iron oxide, which is highly significant from the viewpoints of economic cost and mass production.

Damping Property of Magnetic Functional Fluids Containing Both of Nanometer-size Needle-like Magnetic Particles and Micrometer-size Spherical Magnetic Particles

New magnetic functional fluids containing both of nanometer-size needle-like magnetic particles and micrometer-size spherical magnetic particles are produced and its damping properties are investigated experimentally by using a simple prototype damper. Damping force is variable by changing intensity of applied magnetic field. Damping property of the damper depends on mixture ratio of nanometer-size magnetic particles to micrometer-size magnetic particles. Higher ratio of volume fraction of needle-like magnetic particles against that of all particles increases the damping force; in contrast higher ratio of volume fraction of nanometer-size magnetic particles against the total volume fraction of particles in a magnetic compound fluid decreases the damping force. In the absence of magnetic field, the fluid behaves like a Bingham fluid, while the fluid can be treated as a pseudoplastic fluid in the presence of magnetic field.

Application and advancement of magnetic iron-oxide nanoparticles in tumor-targeted therapy

Recently, nanometer-sized magnetic particles have been intensively concerned and investigated due to their particularly large surface-to-volume ratio, quantum-size effect, magnetic character as well as their potential application in the area of bioscience and medicine. The most promising nanoparticles are magnetic iron oxide nanoparticles with appropriate surface modification, which have been widely used experimentally for numerous in vivo applications such as magnetic resonance imaging contrast enhancement, tissue repair, immunoassay, detoxification of biological fluids, drug delivery, hyperthermia and cell separation. To focus on one of the most important and fascinating subjects in nanobiotechnology, this review describes the current situation and development of magnetic iron oxide nanoparticles and their applications in drug delivery and hyperthermia in tumor-targeted therapy. The possible perspectives and some challenges to further development of these nanoparticles are also analyzed and discussed.

Resistance force of a shock absorber using magnetic functional fluids containing both micrometer-sized and nanometer-sized magnetic particles

In this paper, properties of resistance force of a shock absorber using magnetic functional fluids having both micrometer- and nanometer-sized magnetic particles are reported. The resistance force can be controlled by changing strength of the magnetic field applied to the magnetic functional fluid. The resistance force is influenced by the mixture ratio of the micrometer- to the nanometer-sized magnetic particles.

Microwave absorption and Mössbauer studies of Fe3O4 nanoparticles

Materials consisting of nanometer-sized magnetic particles are currently the subject of intensive research activities. Especially, much attention has been paid to their promising features for microwave magnetic properties. Well dispersed Fe3O4 nanoparticles of 30 nm have been synthesized by oxidization method with NaNO2, and the microwave magnetic properties of the composites have been studied. The real and imaginary part of relative permittivity remained low and nearly constant in the region of 0.1–18 GHz, respectively. As a result, the resin composites having a thickness of 2.0–3.2 mm, and containing 20 vol% Fe3O4 in the form of nanoparticles with an average diameter of 30 nm, exhibited excellent electromagnetic wave absorption properties in the frequency range of 4.5–12.0 GHz.

Direct Observation of Nanomechanical Properties of Chromatin in Living Cells

Precise manipulation of nanometer-sized magnetic particles using magnetic tweezers has yielded insights into the rheology of the cell cytoplasm. We present first results using this approach to study the nanomechanics of the cell nucleus. Using a custom-designed micro-magnetic-tweezers instrument, we can achieve sufficiently high magnetic forces enabling the application and measurement of controlled distortion of the internal nuclear structure on the nanometer scale. We precisely measure the elasticity and viscosity inside the nucleus of living HeLa cells. The high value of the Young's modulus (Y = 2.5 x 10(2) Pa) measured relative to the cytoplasm is explained by a large-scale model for in vivo chromatin structure using a polymer network model.

Experimental and theoretical profiles of the frequency-dependent complex susceptibility of systems containing nanometer-sized magnetic particles

Measurements of the frequency-dependent complex susceptibility \ensuremath{\chi}(\ensuremath{\omega})=\ensuremath{\chi}\ensuremath{'}(\ensuremath{\omega})-i\ensuremath{\chi}\ensuremath{''}(\ensuremath{\omega}) of ferrofluids and magnetic tape are presented and compared with susceptibility profiles generated by means of classical models. In the case of ferrofluids, fitting is realized by means of a combination of the equations of Raikher and Shliomis and of Debye. These equations are for monodispersed particles, and as ferrofluids consist of polydispersed particles, it is demonstrated that to achieve a good fit to the experimental data it is necessary to provide for both a distribution of particle radii r and anisotropy constant K. In terms of the parallel, ${\mathrm{\ensuremath{\chi}}}_{\mathrm{\ensuremath{\parallel}}}$(\ensuremath{\omega}), and transverse, ${\mathrm{\ensuremath{\chi}}}_{\mathrm{\ensuremath{\perp}}}$(\ensuremath{\omega}), components of the susceptibility, it is shown that the incorporation of a distribution of particle radii is required to fit the parallel component ${\mathrm{\ensuremath{\chi}}}_{\mathrm{\ensuremath{\parallel}}}$(\ensuremath{\omega}) of the susceptibility, while a distribution of anisotropy constants is required to fit the resonant ${\mathrm{\ensuremath{\chi}}}_{\mathrm{\ensuremath{\perp}}}$(\ensuremath{\omega}) component. Susceptibility data for magnetic tape are fitted to the equations of Landau and Lifshitz, suitably adapted to provide for a distribution of K alone. The usefulness of the fitting technique in ascertaining average values of the damping parameter \ensuremath{\alpha} and anisotropy constant K is demonstrated.

Magnetic Nanoparticles Produced in Spontaneous Cationic-Anionic Vesicles: Room Temperature Synthesis and Characterization

Unilamellar vesicles formed spontaneously by forming solutions of single-tailed cationic and anionic surfactants [cetyltrimethylammonium bromide (CTAB) and dodecylbenzenesulfonic acid (HDBS), respectively] have been used as reactors for the direct, room temperature synthesis of nanometer-sized magnetic particles within their internal cores. A micellar anionic surfactant solution was titrated slowly into a micellar cationic surfactant solution containing ferrous chloride, forming defect-free unilamellar vesicles that contained the reactant ferrous ions. CTAB/HDBS molar ratios of 13/7 and 6/4 and ferrous chloride concentrations of 0.1 and 0.05 M were used. Extravesicular ferrous ions were replaced with sodium ions by passing this suspension through a gel permeation chromatography column saturated with isotonic sodium chloride solution. Addition of sodium hydroxide to the extravesicular region caused hydroxyl ions to permeate into the vesicles and react with the available ferrous ions to form the product. Powder X-ray diffraction of the particulate sample showed the intense peaks of magnetite or γ-ferrite. Bragg peak broadening was characteristic of crystallites of roughly the same diameter as particles measured by transmission electron microscopy, indicating that each particle was monocrystalline. All of the intense peaks were distinctly asymmetric. Magnetization measurements showed that the particles were superparamagnetic. Using the Langevin function folded with the particle size distribution to model the magnetization of the sample in response to an applied magnetic field yielded "magnetic" diameter distributions that were consistently smaller than particle size distributions obtained from transmission electron microscopy. The magnetic size is consistent with the existence of a magnetically anomalous surface layer on each particle, as has been reported with other ferrites. The asymmetric diffraction peaks may be explained with a model that permits surface relaxation, and it is possible that the two phenomena are linked.

Collapse of Apo- and Magnetoferritins at the Air-Water Interface

Synthesis of nanometer-size magnetic particles within the confined environment of apoferritin might have several uses in biomedical applications and in magnetic information storage devices. Successful use of these protein-encapsulated mineral particles in industrial and biomedical applications depends on the structural stability of these particles at various interfaces. We studied adsorption of apoferritin and magnetoferritin at the air-water interface. Transmission electron microscopy analyses of the protein films at the air-water interface indicate that the spherical protein shell of both apoferritin and magnetoferritin collapses into a two-dimensional disk shape at the interface. In the collapsed state, the magnetite core is released from the protein shell. The results suggest that the oligomeric state of magnetoferritin is not stable at hydrophobic surfaces.

New nanocomposites based on “tailor dressed” magnetic particles in a polypyrrole matrix

Nanometer‐sized magnetic particles can be included into polypyrrole to produce composites by means of a novel method involving ferrofluids, in which a magnetic core such as γ‐Fe2O3 is surrounded by an anionic complexing shell (see Figure). This organic coating, leading to the formation of a macroanion, allows the ion to act as a classical doping ion during the polymerization. magnified image

Magnetocaloric effect of ferromagnetic particles

The entropy change accompanying the removal of an applied magnetic field (i.e. the magnetocaloric effect) is calculated for a system of magnetic spins independent of each other and also clustered together into independently acting magnetic particles. Mean-field-theory calculations are made for interacting, single magnetic spins and also for interacting, magnetic particles. In both cases, there are found temperature and field regimes where the entropy changes are larger when the spins are coupled together into nanometer-sized magnetic particles. Entropy change data is shown for a new Gd/sub 3/Ga/sub 5-x/Fe/sub x/O/sub 12/ (x >