National Institute Of Materials Physics - Romania

Lithium ferrites have been obtained by combustion reaction of ureate precursors. Various physico-chemical techniques: IR spectra, XRD, magnetic determinations, Mossbauer spectra have been employed to characterize the precursors and end products. The single spinel phase alpha-Li(0.5)Fe(.2.5)O(4) with saturation magnetization of similar to 56 Am(2)/kg were achieved from ureate precursor with ratio 2.5Fe(3+) : 0.5Li(+) : 7urea after a thermal treatment at 800 degrees C/1h.

In the early days of amorphous research, Romania was deeply involved in the development of the field of amorphous semiconductors within a close collaboration with Boris Kolomiets. The first researches in this field are discussed and further rapid developments up to the present are shown. The latest results in the field of amorphous semiconductor:, with special emphasis on chalcogenide glasses are presented. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Experimental results for the temperature dependence of the density of propyl - cyanobiphenyl (3CB), butyl - cyanobiphenyl (4CB) and hexyl - cyanobiphenyl (6CB) are presented. The results arc compared with previous results for temperature dependence of other members of the alkyl cyanobiphenyl series (nCB). The deviation of the density from linear temperature dependence is discussed in terms of the recently discovered corresponding rule for nematic liquid crystals. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Two soft chemistry routes - complexation and solution combustion - are explored to obtain the zinc gallate spinel ZnGa2O4. Three types of complexes, namely: (NH4)(2)[ZnGa2(C4O6H4)(4)(OH)(2)]center dot 4H(2)O, [ZnGa2(NH2CH2COOH)(4.5)](NO3)(8)center dot 4H(2)O and [ZnGa2(CO(NH2)(2))(7)](NO3)(8)center dot 9H(2)O have been synthesized and characterized by IR and UV-vis spectroscopy. Zinc gallate spinels obtained by decomposition of these compounds have been investigated by XRD spectra, analytic electronic microscopy and photoluminescence spectroscopy. Zinc gallate spinels exhibited blue emission spectra in the wavelength range of 400 nm-450 nm. (C) 2009 Elsevier B.V. All rights reserved.

A multifrequency electron paramagnetic resonance (EPR) investigation of Nd3+ impurities in PbWO4 single-crystals at the conventional microwave frequency (MF) 9.43 GHz, and at the 95, 190, and 285 GHz high frequencies was carried out. The resulting spectra are well described at all frequencies by an axial spin-Hamiltonian corresponding to an effective electron spin of one-half and to a tetragonal symmetry. For the magnetic field along the tetragonal axis, the g(-)factor and the hyperfine constant A of the lowest doublet of the ground multiplet decreases with frequency increase. For the magnetic field perpendicular to the tetragonal axis, the g(perpendicular to)-factor exhibits a small azimuthal angular dependence that increases with increasing the frequency due to the S-4 site symmetry. The azimuthal angular dependence allows to clearly distinguish between different local axial symmetries. These properties are interpreted as high field/frequency (HF) effects associated with the mixing by the large Zeeman interaction of some of the upper-lying doublets of the ground multiplet into the lowest-lying doublet states. We show that from the combined analysis of the multifrequency MF- and HF-EPR spectra and of the optical data, an accurate description of the ground multiplet of the Kramers rare earth ions in solid matrices can be derived.

We report measurements of critical current in YBa2Cu3Ox films deposited on SrTiO3 substrates decorated with silver and gold nanodots. An increase in critical current in these films, in comparison with the films deposited on non-decorated substrates, has been achieved. We argue that this increase comes from the c-axis correlated extended defects formed in the films and originated from the nanodots. Additionally to creating extended defects, the nanodots pin them and prevent their exit from the sample during the film growth, thus keeping a high density of defects and providing a lower rate of decrease of the critical current with the thickness of the films. The best pinning is achieved in the samples with silver nanodots by optimising their deposition temperature. The nanodots grown at a temperature of a few hundred degrees C have a small diameter of a few nanometres and a high surface density of 10(11)-10(12) particles/cm(2). We give evidence of c-axis correlated extended defects in YBa2Cu3Ox films by planar and cross-sectional atomic force microscopy, transmission electron microscopy and angle-dependent transport measurements of critical current. (C) 2009 Elsevier B.V. All rights reserved.

Nonstationary and steady-state transport through a mesoscopic sample connected to particle reservoirs via time-dependent barriers is investigated by the reduced density operator method. The generalized master equation is solved via the Crank-Nicolson algorithm by taking into account the memory kernel which embodies the non-Markovian effects that are commonly disregarded. The lead-sample coupling takes into account the match between the energy of the incident electrons and the levels of the isolated sample, as well as their overlap at the contacts. Using a tight-binding description of the system, we investigate the effects induced in the transient current by the spectral structure of the sample and by the localization properties of its eigenfunctions. In strong magnetic fields, the transient currents propagate along edge states. The behavior of populations and coherences is discussed, as well as their connection to the tunneling processes that are relevant for transport.

Samples of LaNi5-xFex were prepared by arc melting and subsequent melt spinning procedure. Structural, magnetic and Mossbauer investigations were performed for physical characterization while the hydrogen storage properties were carefully analyzed. Detailed discussions concerning the sample's quality, the site assignment, the effect of temperature and applied fields on hyperfine parameters and the related Debye temperatures were provided. (C) 2008 Elsevier B.V. All rights reserved.

Six tetranuclear complexes [Fe(III)(3)Ln(mu(3)-O)(2)(CCl3COO)(8)(H2O)(THF)(3)]center dot THF center dot C7H16 [Ln=Gd(III) (1), Tb(III) (2), Dy(III) (3), Ho(III) (4), Y(III) (5), and Lu(III) (6)] have been studied by magnetic susceptibility and Moumlssbauer spectroscopy. These isostructural molecules have a "butterfly" structure core consisting of two Fe(2)Ln(mu(3)-O) triangular "wings" which share a common Ln-Fe "body"; the dihedral angle between the wings is ca. 148 degrees. The coordination spheres of the iron ions are essentially distorted octahedral. The lanthanides are eight-coordinate with coordination polyhedra that may be described as distorted tetragonal bipyramids. Variable-temperature solid-state magnetic susceptibility in the temperature range 1.8-300 K and magnetization at 1.8 K for compounds 1-6 were measured. The spin state of Fe is S=5/2 in all cases. In compounds 5 and 6, where Ln(III) (Y and Lu, respectively) is diamagnetic, the three Fe atoms form an obtuse isosceles triangle with antiferromagnetic interactions J(Fe-Fe)=-50 K between the wing-tip Fe-w and body Fe-b atoms, and negligible interaction between the Fe-w's, resulting in a ground state of effective spin S=5/2 per cluster. In the complexes with paramagnetic lanthanide ions, the interaction between the Fe-3 triangle and the Ln(III) center is described by an effective exchange constant which is antiferromagnetic and 1 order of magnitude weaker. Besides, at 3 K incipient spin blocking, characteristic of single molecule magnets, was found to occur in the out-of-phase component of the ac susceptibility in {Fe3TbO2}, {Fe3DyO2}, and {Fe3HoO2}. The activation energy of a Debye process describing the magnetization reversal has been determined to be, E-a approximate to 8, 9, and 10 K for the Ln=Tb, Dy, and Ho, respectively, and the prefactor tau(0)approximate to 10(-7) s. The high spin states of the Fe(III) centers were confirmed by the Moumlssbauer spectra, in which two distinguishable Fe sites could be resolved above 80 K, corresponding to the Fe-w and Fe-b sites, respectively. Relatively larger values of the quadrupole splitting of the Moumlssbauer spectra were observed for the Fe-w pair as compared with that for the Fe-b, and both quadrupole splittings diminished with increasing temperature. At 3 K the Moumlssbauer spectra showed a state with blocked spins (sextets) for the {Fe3TbO2} and {Fe3DyO2} cases. From the E-a and tau(0), determined in the ac susceptibility, the relaxation time at 3 K is estimated as tau approximate to 10(-5)-10(-6) s much longer than the time window of Moumlssbauer spectroscopy and compatible with the single molecule magnet behavior. In the presence of a strong magnetic field the moments of the Ln(III) cation and the Fe-3 triangle are polarized. For some compounds at low temperature a magnetic pattern (sextet) for each of the three Fe sites appeared, and the antiferromagnetic coupling within the Fe-3 cluster was directly proved by the opposite trend of the field dependence of the two Fe-w sextets as compared with the Fe-b third one.

PbI2, BiI3, CdI2 and AgI crystalline samples intercalated with pyridine have been studied by Raman spectroscopy. Comparing the Raman spectra of pristine metal iodides with those of intercalated samples we have shown the coexistence, in the host crystalline lattice, of two adsorbed forms: a physisorbed one, featured by weak forces of van der Waals type and a chemisorbed one, involving stronger forces related to an electrostatic interaction. The physisorbed form is consistent with the molecules inserted into the interlayer spaces while the chemisorbed form is represented by the molecules forming coordination complexes with the crystalline lattice cations. The crucial role in the formation of such complexes is played by the lone pair of nitrogen atom belonging to the molecules.