Publications

The nanocrystallization of two soft magnetic amorphous Finemet-type ribbons of the nominal composition Fe73.5Cu1Nb3Si13.5B9 and Fe73.5Cu1Gd1Nb2Si13.5B9 synthesized by a melt spinning technique is reported. The crystallization process was monitored by differential scanning calorimetry (DSC) that allows identification of the primary crystallization temperature as well as the other exothermic events occurring during crystallization process. The resulting phase structure of the properly annealed samples is investigated by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM) and is shown to consist of size-distributed body-centred cubic (bcc) alpha-Fe(Si) (rather than Fe3Si, DO3-type), nanograins, embedded into the amorphous Nb-rich residual matrix. The degree of dispersion of the nanograins in the amorphous matrix is estimated from the nanocrystalline volume fraction and the mean size of the nanograins obtained both from XRD data and TEM images. (C) 2003 Elsevier B.V. All rights reserved.

Magnetic behavior of the isolated ferromagnetic bimetallic nanoparticles is investigated in relation with the competition between exchange interaction and surface and bulk anisotropies. Experimental results on AgCo bimetallic nanoparticles are presented and correlated with Monte Carlo simulation of low temperature spin ordering. The nature of spin disorder at the surface, responsible for the reduction of the overall saturation magnetization is briefly discussed. (C) 2003 Elsevier B.V. All rights reserved.

Antiferromagnetic FeSn2(001) thin films with different thicknesses and relatively low Neel temperatures were grown on InSb(001)(4x2) surfaces by molecular-beam epitaxy. The Neel temperature could be increased to above room temperature by subsequent thermal annealing. In situ structural characterization was performed by high- and low-energy electron diffraction. The degree of the structural (001) texture as a function of the preparation and annealing conditions was investigated by x-ray diffractometry. The local magnetic properties and the spin structure were studied using Fe-57 conversion electron Mossbauer spectroscopy (CEMS) at different temperatures. The epitaxial FeSn2(001) thin films exhibit in-plane Fe spin orientation and appear to be suitable antiferromagnets for studying the interfacial spin structure in exchange-biased bilayers by CEMS. (C) 2003 American Institute of Physics.

Metal nanoparticles embedded in KCl crystals exhibit different forms and distributions, depending on the type of metal. The nanoparticles can be efficiently studied by optical absorption on these structures, calculated from Mie theory and comparison with Transmission Electron Mmicroscopy (TEM) measurements. The TEM images provide the detailed characteristics of the structures under study. Metal crystalline particle obtained by thermal treatments of negative indiurn ions are spherical. The particle size distribution was determined, the standard deviation was found 1.46, and the main statistical characteristics were calculated.

The influence of oxygen and carbon impurities on the concentrations of defects in silicon for detector uses, in complex fields of radiation (proton cosmic field at low orbits around the Earth, at Large Hadron Collider and at the next generation of accelerators as Super-LHC) is investigated in the frame of the quantitative model developed previously by the authors. The generation rate of primary defects is calculated starting from the projectile - silicon interaction and from recoil energy redistribution in the lattice. The mechanisms of formation of complex defects are explicitly analysed. Vacancy-interstitial annihilation, interstitial and vacancy migration to sinks, divacancy, vacancy and interstitial impurity complex formation and decomposition are considered. Oxygen and carbon impurities present in silicon could monitor the concentration of all stable defects, due to their interaction with vacancies and interstitials. Their role in the mechanisms of formation and decomposition of the following stable defects: VP, VO, V-2, V2O, C-i, CiOi and CiCs is studied. The model predictions could be a useful clue in obtaining harder materials for detectors at the new generation of accelerators, for space missions or for industrial applications.

Electron spin resonance investigations on polyethyleneterephtalate irradiated with a YAG-Nd laser are reported. The dependence of electron spin resonance spectra on the incident laser beam intensity (power) is studied. It is noticed that the concentration of free radicals has a sigmoidal dependence on the crystal current, presenting saturation at high incident powers. The nature of free radicals induced by laser irradiation is discussed. (C) 2003 Elsevier B.V. All rights reserved.

Temperature dependent EPR measurements on copper doped Rb2ZnCl4 single crystals allowed us to evidence and study the P2(1)cn ClcI structural phase transition that takes place in this compound at 74.6 K. From the two types Of Cu2+ centers localized at different anionic sites, called Cu2+(I) and Cu2+(II), which are formed in this compound, only the Cu2+(II) centers exhibit observable changes in their EPR spectra, attributable to the symmetry lowering. The observed changes have been related to the soft-mode responsible for the structural phase transition. (C) 2003 Elsevier Ltd. All rights reserved.

The Cu (3d-4s-->2p(3/2)) Lalpha X-ray emission band has been measured in Cu nanoclusters, present in a series of Cu/C-60 thin-film nanostructures. In comparison with bulk Cu, a negative shift and a narrowing of the Lalpha band have been noticed. These observations are mainly attributed to a size effect but charge transfer from metal to C-60 occurring at interfaces and causing a depletion of the Cu 3d band is also considered.

The melt spun nanocrystalline alloys such as Fe73.5Cu1Nb3Si13.5B9 (FINEMET) have attracted great deal of interest in recent years due to their excellent soft magnetic properties mostly related to the exchange coupling between nanograins, through the amorphous matrix. The microstructural evolution of both nanocrystalline and amorphous residual phases during annealing of the ribbons give rise to crystallization products that determine the expected magnetic properties for specific applications. Upon addition of the rare earth (RE), the evolution of the crystalline phases which emerge from metastable precursors during annealing is investigated. It is expected that the RE presence should strongly modify both the phase structure via new ternary metastable precursors and the magnetic properties of the ribbons by inducing enhanced exchange correlation due to novel ternary crystalline phases.

The backscattering of 100, 300, and 500 eV Ar atoms from the {100} and {110} planes of a Al crystalline target is investigated with a computer code based on the Molecular Dynamics(MD) method. The interactions between particles are described by a screened Coulomb type potential. The angular (both azimuthal and radial) distribution of the backscattered particles together with the distribution of the energy and of the energy loss of scattered particles are calculated using the Lindhard-Scharff parameterization. The azimuthal distribution shows high peaks for 300 and 500 eV incident energies and a cvasi-continuum for 100 eV incident energy in the case of {100} plane, and a single peak for the {110} plane. The radial. distribution of backscattered particles evidences the symmetry properties of the crystal. The relative energy loss decrease when increasing incident energy, and is compatible with the backscattered energy distribution. The results do not agree with the Binary Collision Approximation(BCA).