Publications

The Fe-57 Mossbauer spectroscopy on alpha-iron(II) phthalocyanine (FePc) as a function of temperature (1.3 < T < 295 K) and applied field (0 < B < 10 T) has been used to study the peculiar magnetic properties of this ferromagnetic quasilinear chain type compound. One sextet with an internal hyperfine field B-int=66.2 T was observed at 1.3 K, a very large value for a bivalent iron with S=1 pointing to the existence of large positive orbital and dipolar contributions in the investigated FePc. Under an applied field, the experimental spectra exhibited two nonequivalent Fe positions, due to spin canting, with the values for the hyperfine fields of the split sextets increasing with increasing field, an indication that unlike most cases, B-int in alpha-FePc is positive, i.e., parallel to the magnetic moment of iron. Therefore, the origin of the large hyperfine field is the orbital moment rather than the Fermi's contact interaction. This fact is ascribed to the orbital degeneracy of the ground state of Fe(II) in the present configuration, where an unpaired hole occupies the orbital doublet (d(xz), d(yz)). This feature supports and explains the magnetization and susceptibility data as well as the anomalously high hyperfine field observed at Fe-57 nucleus. The relaxational behavior in the ac susceptibility and Mossbauer spectra found in the region 5-20 K was ascribed to solitonlike motion of domain walls within the magnetic chains, with a single-kink activation energy of 72 K.

Polycarbonate templates of ( 30 +/- 1) mu m thickness containing cylindrical etched-track nanochannels of ( 500 +/- 50) nm diameter were used for electrodeposition of Ni nanowires. Using 10(4) channels per cm(2), the most favourable deposition potential of -1.0 V was determined in a potentiostatic mode by varying the deposition potential with respect to an Ag/AgCl reference electrode over a range between -0.1 V and -1.5 V. The deposition efficiency at -1.0 V was estimated around 10%. The resulting single wires had a resistance around 200 W and showed an anisotropic magnetoresistance (AMR) effect of 1%, applicable to directionally sensitive magnetic field sensors.

We review the current status of the growth, characterization and applications of Bi-Sr-Ca-Cu-O (BSCCO) whiskers from the materials science point of view. Our analysis leads to the conclusion that reconsideration of the importance of the whisker studies is necessary; whiskers can play a major role in studies of the growth mechanism and defects, properties control and their understanding, and new devices and applications. Arguments favourable to the idea that BSCCO whiskers can possibly have a significant impact on future synthesis of nano-objects in this system or other high-T-c superconducting systems, as well as in investigation and understanding of the growth processes under elevated magnetic fields, are discussed. Emphasis is made on superconducting whiskers, but non-superconducting ones are also briefly addressed.

The structure of bulk glassy As2Se3 has been investigated by X-ray diffraction. The structure was compared with that of bulk glass As2S3 measured in the same conditions. Similarities and differences have been pointed out.

Barium tetratitanate (BaTi4O9) ceramic prepared by coprecipitation method was analyzed by Raman spectroscopy and by X-ray photoelectron spectroscopy (XPS). The orthorhombic crystalline structure of BaTi4O9 ceramic sintered at 1300 degrees C for 2h in air was identified on the Raman spectrum. The sample was etched in argon plasma and then analysed by XPS. The etching process did not influence significantly the XPS spectra of barium and titan suggesting a good compositional homogeneity of the BaTi4O9 ceramic prepared by oxalate method.

The structure of low coordinated disordered materials can be understood in the frame of basically different theories: the formation of a continuous random network with all the valence bonds satisfied, the formation of small clusters (amorphites) having all the bond at the margins satisfied (closed clusters) or open clusters with many dangling bonds that are partially compensated due to the formation of valence alternation pairs, and last but not least the formation of so-called nanoparacrystalline structures, i.e. deformed nano-crystalline structures. We show that an intermediate model based on a mixture of closed and open clusters as well as layer like configurations can explain the structure and properties of the binary arsenic chalcogenide glasses.

Ceria-zirconia supported (10 and 20 wt.% EuCoO3) versus bulk EuCoO3 perovskite were prepared via citrate decomposition at 700 degrees C and tested for toluene complete oxidation. S-BET, XRD, XPS, H-2-TPD and in situ Eu-151 Mossbauer investigations were performed. Electron delocalization processes around the Eu cations are induced by the reaction, as proved via the evolution of the Mossbauer parameters. All characterization data indicate the formation of a well-dispersed EuCoO3 at the surface of Ce0.9Zr0.1O2 for the 10 wt.% loading and larger crystallite formation for 20 wt.% loading. In terms of intrinsic activity for toluene combustion, supported catalysts were more active than bulk EuCoO3. All structural changes during operation time are reversible. (C) 2006 Elsevier B.V. All rights reserved.

The crystallization processes that occur in amorphous melt-spun ribbons of nominal composition Fe73.5Cu1Nb3Si13.5B9 with Gd addition in different concentrations are studied by differential scanning calorimetry (DSC). The aim of Gd addition is to study the changes induced in the calorimetric behavior of Finemet alloys, the crystallization sequences at intermediate stages of annealing as well as the nature of obtained crystallization products. The nature and structural properties of the phases formed at the end of the calorimetric process are investigated using X-ray diffraction (XRD) and Mossbauer spectrometry (MS). The crystallization sequence and also the phase composition at different stages of annealing were investigated for the Fe68.5Gd5Cu1Nb3Si13.5B9 alloy. Structure and magnetic properties of resulting crystallized samples have been thoroughly investigated. It is shown that in the above-mentioned composition, the decomposition at around 690 degrees C of the metastable Gd3Fe62B14 phase formed at incipient stages of crystallization leads to the co-existence of Gd2Fe14B, Fe2B and alpha-Fe(Si) phases. Magnetic measurements of as-cast and annealed samples are in good agreement with the XRD and MS results and with the proposed crystallization sequences and decomposition of intermediate metastable phases. (c) 2005 Elsevier B.V. All rights reserved.

Results are reported on the characterization of 200-250 nm thick TiO(x) transparent films grown at temperatures of 150 degrees C and 500 degrees C by reactive pulsed-laser ablation of a metallic Ti target under 0.13-13.3 Pa oxygen atmosphere. Film structure and composition were investigated by X-ray diffraction and X-ray photoelectron spectroscopy. The samples deposited at 150 degrees C reveal a mixture of amorphous TiO(2) and Ti(2)O(3), irrespective of oxygen pressure. The O:Ti atomic ratio fluctuates in their surface around 1.83 for oxygen pressure ranging between 0.13 Pa and 2.66 Pa. The samples deposited at 500 degrees C feature different characteristics, as a function of oxygen pressure: (a) below 2.66 Pa of O(2) the films contain a mixture of significant amount of anatase and rutile TiO(2) phases, along with titanium suboxides; (b) above this threshold, the rutile phase vanishes, the anatase TiO(2) phase remaining dominant along with small amounts of nanocrystalline suboxides. The size of the anatase nanocrystallites decreases with the increase of oxygen pressures. The samples deposited at 500 degrees C feature a slight improvement of surface stoichiometry, from roughly TiO(1.8) to TiO(1.9). The films deposited at high substrate temperature and oxygen pressure are highly hydrophilic. (c) 2006 Elsevier B.V. All rights reserved.

Thin layers of Fe are deposited at 100 degrees C on GaAs(1 0 0) and InAs(1 0 0) substrates by molecular beam epitaxy. These structures are characterized by photoelectron spectroscopy (PES), in order to derive their chemical composition and interface reactivity, and by X-ray magnetic circular dichroism (XMCD) recorded at room temperature in remanence mode, in order to derive the atomic magnetic moment of Fe. As previously reported, Fe/GaAs(1 0 0) exhibits a strong and complicated interface reactivity, with considerable intermixing of Fe with Ga and As. Unlike the above structure, Fe/InAs(1 0 0) exhibits a much lower interface reactivity, whereas the Fe magnetic moment increase is much more pronounced as function of Fe thickness. The total atomic ferromagnetic moment reaches at room temperature 2.0 Bohr magnetons by about I nm Fe effective thickness, which is almost the Fe bcc bulk value (2.2 Bohr magnetons). The novelty of the present study is a direct comparison of the two interfaces prepared and measured in the same experimental arrangements. (c) 2006 Elsevier B.V. All rights reserved.