Search

Experiments were performed on Co67Fe4Cr7Si8B14 metallic glass in which the transverse magnetic anisotropy was induced by a proper annealing process. Measurements of the magnetic permeability μ at high frequency of 20 and 200 kHz were performed versus tensile stress applied to the sample. It was found that for the low-stress region the value of the initial permeability increases with the stress but at higher stress, depending on the induced anisotropy, the behavior of μ can be significantly modified. The results obtained are interpreted as an influence of the stress-dependent modification of the domain pattern, as shown by the observation of the Kerr effect domain structure.

A theoretical model describing the surface magnetoelastic properties (`surface magnetostriction') in nanocrystalline materials is proposed. The model is based on the magnetic dipole–dipole interactions. The nonuniform medium consisting of perfect spherical crystalline grains in a magnetic environment of two structures (amorphous and crystalline) is considered. The calculations are limited to simple ferromagnets of high symmetry such as body centered cubic (BCC) and face centered cubic (FCC) crystals.

It is shown that gradual devitrifiation of non-magnetostrictive Co-based metallic glass leads to a giant, five orders of magnitude, increase of its coercivity. This magnetic hardening is due to the pinning of domain walls by growing fine crystallites much smaller than the domain wall width, the number and size of which increase with an increase of the annealing temperature.

et al., A new iron-based T 1 contrast agent consisting of a complex of iron ions coordinated to phosphate and amine ligands (Fe(phos) in short) has been characterized by spectroscopic and magnetic measurements. NMR relaxation studies showed r 1 values to be dependent on the phosphate salt concentration, K2HPO4, present in the medium. r 1 reaches a maximum value of 2.5 mM-1 s-1 for measurements carried out at 7 T and 298 K. 31P MRS, Mössbauer spectroscopy and magnetic measurements of Fe(phos) solutions suggest paramagnetic Fe3+ ions present in the studied iron-phosphate complex. In vitro and in vivo toxicity experiments with C6 cells and CD1 mice, respectively, demonstrated lack of toxicity for Fe(phos) at the highest dose tested in the MRI experiments (12 mM iron for C6 cells and 0.32 mmol iron/kg for mice). Finally, T 1 weighted images of brain tumours in mice have shown positive contrast enhancement of Fe(phos) for tumour afflicted regions in the brain. © 2007 ESMRMB., This work was funded by: Ministerio de Ciencia y Tecnología (MCYT SAF 2002-0440 and MCYT MAT 2003-01052), Ministerio de Educación y Ciencia (MEC SAF 2005-03650), Fondo de Investigaciones Sanitarias (2003-0467), Fundação para a Ciência e a Tecnologia (SFRH/BD/17643/2004).

We present studies of structural, magnetic and electrical properties of Zn/1-x-y/Cd/x/Mn/y/GeAs/2/ nanocomposite ferromagnetic semiconductor samples with changeable chemical composition. The presence of MnAs clusters induces in the studied alloy room temperature ferromagnetism with the Curie temperature, TC, around 305 K. The chemical composition of the chalcopyrite matrix controls the geometrical parameters of the clusters inducing different magnetoresistance effects in the crystals. The presence of ferromagnetic clusters in the alloy induces either negative or positive magnetoresistance with different values. The Cd-content allows a change of magnetoresistance sign in our samples from negative (for x = 0.85) to positive (for x = 0.12). The negative magnetoresistance present in the samples with x = 0.85 is observed at temperatures T < 25 K with maximum values of about -32% at T = 1.4 K and B = 13 T, strongly depending on the Mn content, y. The positive magnetoresistance present in the samples with x = 0.12 is observed with maximum values not exceeding 50% at B =13 T and T = 4.3 K, changing with the Mn content, y., 8 pages, 7 figures

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.

Co66Nb9Cu1Si2B12 metallic glass is used as a parent material for nanocrystalline magnets exhibiting low Curie temperature of the amorphous matrix (100–140 K). Precipitation of Co nanoparticles destroys the ferromagnetic ordering in the amorphous alloy and leads to a low-temperature cluster-glass state. At higher temperatures, the grains embedded in the paramagnetic matrix exhibit a superparamagnetic behaviour. In the fully crystallized state the magnetic properties of the material, composed of two crystalline phases with their Curie points above the room temperature, are mainly governed by the inter- and intra-phase magnetic interactions which lead to a preferential ferromagnetic ordering.

8 pages, 12 figures, 1 table.-- PACS: 75.50.Tt; 75.30.Kz; 82.70.Rr; 75.30.Cr; 68.35.Dv; 81.40.Gh.-- et al., The production and structural characterization of gas-evaporated nanoparticles in the Fe1–xCrx system, with 0, This research has been supported by a NATO fellowship (OTSF03-074) and the CSIC-PAS exchange program (2004PL0009). C. Rovira (ICMAB-CSIC), for facilitating DSC measurements and E. Snoeck (CEMES-CNRS), for performing the HRTEM measurements, are acknowledged.

The correlation between structure and magnetic properties of Fe particles with core-shell structure (with the ratio of their linear dimensions of around 11:2 nm) has been investigated. In the as-prepared particles the surface layer, composed of small clusters of iron oxide, causes suppression of the exchange interactions and strong pinning of the core moments. Annealing leads to reconstruction of the surface layer and formation of big islands of good quality stoichiometric magnetite with sharp Verwey transition at 122 K. The exchange couplings between Fe particles across ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ interfaces are enhanced leading to long-range ferromagnetic correlations, reduction of the local anisotropy, and magnetic softening.

This paper studied the synthesis, characterization and use of the magnetic chitosan nanogel for carrying meleimidic compounds. The hydrogel polymer was prepared using O-carboxymethylchitosan, which was crosslinked with epichlorohydrin for subsequent incorporation of iron oxide magnetic nanoparticles. The characterization revealed that the magnetic material comprises about 10% of the hydrogel. This material is comprised of magnetite and maghemite and exhibits ferro-ferrimagnetic behavior. The average particle size is 4.2 nm. There was high incorporation efficiency of maleimides in the magnetic nanogel. The release was of sustained character and there was a greater release when an external magnetic field was applied. The mathematical model that best explained the process of drug release by the magnetic hydrogel was that of Peppas-Sahlin. The magnetic nanogel proved to be an excellent candidate for use in drug-delivery systems.

The experimental results of the magnetic anisotropy induced during annealing under tensile stress and/or longitudinal magnetic field in FeCrSiB metallic glasses are presented. The possible origins of the induced anisotropies are connected with the type of 3d metal atoms arranging into pairs during annealing.

It is shown that stress-anneal-induced magnetic anisotropy is created during annealing, prior to not after stress release. It is argued that the commonly used model of anelasticity, based on the microscopic mechanism of local bond reorientation gives a description which is inconsistent with the experimental results obtained.

Fe 81 P 1 Si 23 Nb 3 Cu 1 metallic glass is used as the parent alloy for a new soft magnetic nanocrystalline material. Two structural transformations of the as-cast alloy are identified during the annealing process. The microstructures created are related to magnetic properties of the nanocrystalline samples.

An existence of effects connected with the surface of grains in nanocrystalline FINEMET-like Fe 72 Cu 1.5 Nb 4 Si 13.5 B 9 alloy was verified by investigation of hyperfine and magnetoelastic properties. In the Mossbauer spectra (collected both at room temperature and close to T c of amorphous matrix) a broad, high field component was found, which could be attributed to the grains surface and interface region. Such interpretation is confirmed in magnetostrictive experiment pointing to a high value of surface magnetostriction constant.

The nanocrystalline Fe66Cr8Cu1Nb3Si13B9 metallic glass with relatively low Curie temperature of the amorphous matrix has been proposed as a particulate medium showing superparamagnetic behavior at elevated temperatures. The samples of this material with different volumetric fractions of the crystalline phase, were characterized by differential thermal analysis, X-ray diffraction and transmission electron microscopy as well as by temperature dependencies of saturation magnetization and isothermal magnetization curves. The correlation between the structural parameters determined by direct measurements and those estimated from the magnetic studies is shown and discussed in terms of a new algorithm which allows to determine a distribution of the particle magnetic moments.

The expectation that the nanocrystalline Fe-based metallic glasses may show the richness of magnetic phases with a change of the temperature has experimentally been confirmed. It has been shown that, depending on the annealing conditions (resulting in controlled crystallite size as well as the volumetric fraction) the particles exhibit superparamagnetic or "superferromagnetic" behavior at elevated temperatures. In these cases, the amorphous matrix, into which the particles are embedded, is in paramagnetic state. In order to confirm the occurrence of these phases, magnetization characteristics measured at different temperatures were analyzed in terms of the well-known Langevin approach. At sufficiently low temperature (e.g., at room temperature), lower than the Curie points of both, the amorphous matrix and the particles, the sample behaves ferromagnetically in a way as it does for the typical commercial material.

Investigation of soil on the surface of Mars by means of the Mossbauer spectrometer is proposed. Two main goals that can be achieved by Mossbauer spectroscopy are discussed: identification of iron containing coumpounds and determination of the Fe2+/Fe3+ ratio. The parameters of the spectrometer to be sent on the surface of Mars are given. Various objects in the martian regolith that can be investigated by Mossbauer spectroscopy are indicated.

The temperature dependencies of the coercivity in Fe 87 Zr 7 Si 4 B 2 nanocrystalline samples with various contents of α-Fe crystallites have been investigated and interpreted in terms of intergranular distances and interactions between the grains separated by paramagnetic matrix.