A. Ślawska-Waniewska

About the interfacial zone in nanocrystalline alloys

Abstract We discuss the concept of an interfacial zone resulting from the symmetry restriction at the periphery of crystalline grains in the nanocrystalline alloys. The different experimental features are essentially based on Mossbauer investigations performed in a wide temperature range. The results obtained are related to the atom probe field ion microscopy, EXAFS and FMR analysis. The experimental evidence for the existence of the interfacial zone (with a thickness of about 2–3 atomic layers) is presented. The structural, chemical and magnetic properties of the interfaces are discussed including their role in the overall magnetic interactions in nanocrystalline structure.

Coexistence of various magnetic phases in nanocrystalline Fe-based metallic glasses

Abstract It is shown that, besides the promising prospects of applications, nanocrystalline Fe-based metallic glasses (nominal composition Fe73.5Cu1Nb3Si13.5B9) are interesting objects for basic research because of the variety of magnetic phases which they can show at elevated temperatures. These unusual particulate media show ferromagnetic behavior for temperatures below the Curie point of the residual amorphous matrix, however, in the temperature range above this point they may display superferromagnetic or superparamagnetic properties depending on the size and volumetric fraction of the nanoparticles created within the material by the appropriate annealing. The results of a number of experiments are presented, which show that all the magnetic phases mentioned above can be created in the nanocrystalline material considered.

Adsorption of As(III) on chitosan-Fe-crosslinked complex (Ch-Fe)

It was reported the adsorption of As(III) on the surface of the chitosan-Fe-crosslinked complex. Theoretical correlation of the experimental equilibrium adsorption data for As(III)/Ch-Fe system is best explained by the non-linearized form Langmuir-Freundlich isotherm model. At optimum conditions, pH 9.0, the maximum adsorption capacity, calculated using the Langmuir-Freundlich isotherm model was 13.4 mg g⁻¹. The adsorption kinetics of As(III) onto Ch-Fe are described by the pseudo-first-order kinetic equation. The results of the Mössbauer spectroscopy showed that there is no redox process on the surface of the adsorbent.

Surface effects in CoFe2O4 magnetic fluids studied by Mössbauer spectrometry

Abstract Magnetic properties of CoFe2O4 particles were investigated by means of zero-field and in-field Mossbauer spectrometry. The studies include superparamagnetic (SP) relaxation as well as the surface phenomena of samples with different particle sizes both in the form of ferrofluids and powders. A core–shell model was applied to estimate the thickness of the surface “spin-canted” shell around particles.

Synthesis, characterization and in vitro drug release of magnetic N-benzyl-O-carboxymethylchitosan nanoparticles loaded with indomethacin

Magnetic N-benzyl-O-carboxymethylchitosan nanoparticles were synthesized through incorporation and in situ methods and characterized by Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, and magnetization measurements. Indomethacin was incorporated into the nanoparticles via the solvent evaporation method. The indomethacin-loaded magnetic nanoparticles were characterized by the same techniques, and also by transmission electron microscopy. The nanoparticles containing the polymer showed a drug loading efficiency of between 60.8% and 74.8%, and the magnetic properties were not significantly affected by incorporation of the drug. The in vitro drug release study was carried out in simulated body fluid, pH 7.4 at 37°C. The profiles showed an initial fast release, which became slower as time progressed. The percentage of drug released after 5 h was between 60% and 90%, and the best fitting mathematical model for drug release was the Korsmeyer-Peppas model, indicating a Fickian diffusion mechanism.

Saturation magnetostriction of FeZrB(Cu) nanocrystalline alloys

The results of the magnetostriction constants for Fe89Zr7B4 and Fe85Zr7B6Cu2 alloys with different crystalline fractions are reported and interpreted in terms of surface and bulk contributions from α-Fe grains.

Magnetostriction and its temperature dependence in FeCuNbSiB nanocrystalline alloy

Abstract The temperature dependencies of the linear saturation magnetostriction of Fe73.5CuNb3Si15.5B7 nanocrystalline alloy have been measured for the samples exhibiting a wide range of the crystalline phase volumetric fraction obtained by a proper annealing procedure. It has been proved that the effective magnetostriction of this material can be interpreted as a volumetrically weighted balance among two contributions, a negative one (for the bcc-Fe(Si) nanocrystallites) and a positive one (for the residual amorphous matrix). The measured temperature dependencies of the effective magnetostriction have been analyzed in order to calculate both contributions to this quantity. This analysis was performed assuming linear as well as quadratic approximation of the dependence of the effective magnetostriction on the nanocrystalline fraction showing that the former reflects better the properties of the material. The above analysis also showed that, in order to obtain zero-magnetostrictive material at room temperature, the fraction of nanocrystallites should be relatively large (∼ 70–80%).

SURFACE EFFECTS IN FE-BASED NANOCRYSTALLINE ALLOYS

FeZrBCu nanocrystalline materials obtained by controlled crystallization of the amorphous alloy are composed of bcc-Fe grains (10 nm in diameter) embedded in a residual amorphous matrix. In this article it has been shown that in such a mesoscopic system the interfaces exhibit identifiable properties that differ from those of the interior. In the Mossbauer spectra, besides of contributions from bcc phase and that of the residual amorphous matrix, an additional component was observed and attributed to the crystalline grain-amorphous matrix interfaces. The effect of the surface layer on the effective magnetostriction is also presented and discussed.

The effect of particle size and surface-to-volume ratio distribution on giant magnetoresistance (GMR) in melt-spun Cu–Co alloys

Abstract Giant magnetoresistance (GMR), magnetization and structure of granular Cu 90 Co 10 alloy were investigated. The annealed sample is inhomogeneous with respect to the Co-particle sizes and interparticles distances and, therefore, not all particles behave superparamagnetically. The observed deviation from the expected theoretically quadratic dependence of GMR on magnetization can be attributed to differentiated surface-to-volume ratio of superparamagnetic particles as well as to the presence of a small amount of ferromagnetic phase which is created by relatively large Co-rich regions.

Magnetocaloric effect in slightly crystallised Co–Nb–Cu–Si–B alloy

Abstract Temperature dependence of the entropy variation Δ S M was calculated from the magnetisation data. A considerable magnetic entropy change was observed in nanocrystalline and amorphous samples even for relatively small field changes. The maximum of Δ S M was found to appear in the vicinity of the cluster glass–superparamagnetic transition which occurs around the Curie temperature of the amorphous phase.