1,721,188 research outputs found
Understanding dynamics of interacting magnetic nanoparticles: From the weak interaction regime to the collective superspin glass state
No full textFocus on Metastable, Amorphous and Nanostructured Materials: Editorial note for the special issue - ISMANAM 2018
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Time and temperature dependent magnetic viscosity experiments on Sr/Co nanoferrite particles
No full textMagnetic viscosity experiments have been performed in order to investigate the magnetization reversal in Sr nanoferrite particles (nanoscale SrFe12O19) and interacting Sr/Co nanoferrite particles (SrFe12O19-CoFe2O4 nanocomposites). The magnetic viscosity S = d M ( t ) / d l n ( t ) , where M ( t ) is the magnetization as a function of time, has been collected. For Sr nanoferrite S shows a maximum close to the coercive field, reflecting the relation between S and the energy barrier distribution. We evidence that magnetic viscosity experiments on Sr nanoferrite and interacting Sr/Co nanoferrite particles provide reliable qualitative results for the different magnetic field sweep rate and saturating field H s a t considered. In addition, the activation volumes extracted from the magnetic viscosity experiments performed at different temperatures on Sr nanoferrite are quantitatively correlated to anisotropy changes
Optimization of a NdFeB permanent magnet configuration for in-vivo drug delivery experiments
No full textWe propose a new concept of magnetic focusing for targeting and accumulation of functionalized superparamagnetic nanoparticles in living organs through composite configurations of different permanent magnets. The proposed setups fulfill two fundamental requirements for in vivo experiments: 1) reduced size of the magnets to best focusing on small areas representing the targeted organs of mice and rats and 2) maximization of the magnetic driving force acting on the magnetic nanoparticles dispersed in blood. To this aim, several configurations of permanent magnets organized with different degrees of symmetry have been tested. The product B·gradB proportional to the magnetic force has been experimentally measured, over a wide area (20 × 20 mm2), at a distance corresponding to the hypothetical distance of the mouse organ from the magnets. A non-symmetric configuration of mixed shape permanent magnets resulted in particularly promising to achieve the best performances for further in vivo experiments
Determination of blocking temperature in magnetization and Mössbauer time scale: a functional form approach
No full textWe studied the temperature dependence of the magnetization in an ensemble of monodomain nanoparticles both with dc magnetometry and Mössbauer spectroscopy. The analytical form of the temperature dependence is given by the complementary cumulative distribution function. This allows to determine the magnetization blocking temperatures of the sample by a fitting procedure. It is possible to calculate the Mössbauer blocking temperature by a single spectrum and the dc magnetization blocking temperature by two points of the thermoremanent magnetization curve, thus with a large reduction of the experimental work. The method may be used for particles with not too strong interactions, such happens in the Fe28 sample and not for samples with strong interactions as N30; it may be used for interparticle interaction energies up to 2 yJ and not for energies larger than 60 yJ. This method of analysis of the data should be used in the future work concerning the thermoremanent magnetization and Mössbauer spectra of magnetic nanoparticles
Surface spin freezing effects on enhanced saturation magnetization and magnetic anisotropy in CoFe2O4 nanoparticles
No full textThe magnetic properties of ultra-small (3 nm) CoFe2O4 nanoparticles have been investigated by
DC magnetization measurements as a function of temperature and magnetic field. The main
features of the magnetic behaviour are blocking of non-interacting particle moments
(zero-field-cooled magnetization Tmax ≈ 40 K), a rapid increase of saturation magnetization (up
to values higher than for the bulk material) at low T and an increase in anisotropy below 30 K
due to the appearance of exchange bias. The low temperature behaviour is determined by a
random freezing of surface spins. Localized spin-canting and cation distribution between the
two sublattices of the spinel structure account quantitatively for the observed increase in
saturation magnetization
Biocatalyst immobilization on magnetic nano‐architectures for potential applications in condensation reactions
No full textIn this review article, a perspective on the immobilization of various hydrolytic enzymes onto magnetic nanoparticles for synthetic organic chemistry applications is presented. After a first part giving short overview on nanomagnetism and highlighting advantages and disadvantages of immobilizing enzymes on magnetic nanoparticles (MNPs), the most important hydrolytic enzymes and their applications were summarized. A section reviewing the immobilization techniques with a particular focus on supporting enzymes on MNPs introduces the reader to the final chapter describing synthetic organic chemistry applications of small molecules (flavour esters) and polymers (polyesters and polyamides). Finally, the conclusion and perspective section gives the author's personal view on further research discussing the new idea of a synergistic rational design of the magnetic and biocatalytic component to produce novel magnetic nano-architectures.In this critical review article, a perspective on the immobilization of various hydrolytic enzymes onto magnetic nanoparticles for synthetic organic chemistry applications is presented.imag
Effect of organic coating on the charge distribution of CoFe2O4 nanoparticles
No full textWe have studied the charge distribution of organic surfactant coated CoFe2O4 spherical nanoparticles together with the uncoated ones, using density functional theory (DFT)calculations. The coatings used are the diethylene glycol (DEG)and oleic acid (OA). Our results showed that the coating influences more the charge of the Co atoms and less the Fe atoms charge while the influence is very small in the O atoms and that the effect is more pronounced in the charge of the DEG coated particles. The average electrostatic potential and electric field have higher strength of interaction in the coated particles, especially the ones with the DEG coating
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