National Institute Of Materials Physics - Romania

A novel nanocomposite FePt-based exchange-coupled magnet has been synthesized and structurally and magnetically characterized. We report for the first time the direct formation of the L1(0) FePt phase without the need for post-synthesis annealing procedures in Fe-Pt-based melt-spun ribbons, obtained by a conventional melt spinning method. The structure and magnetic properties are investigated and the occurrence of the L1(0) ordered phase in the as-cast state of Fe-Pt-Ag-B melt-spun ribbons is confirmed by XRD and magnetic measurements. A microstructure consisting of fine, uniformly dispersed, 22-24 nm FePt grains dispersed within a soft magnetic matrix is observed by scanning transmission electron microscopy imaging. Coercive fields as high as 727 kAm(-1), saturation magnetization of about 1.2 T and energy product around 87 kJm(-3) are determined from 270 K hysteresis loops of the as-cast ribbons, making one of the best FePt-based nanocomposite magnet ribbons even without further annealing treatments.

The difficulties in synthesizing phase pure BaTiO3 doped-(Na0.5Bi0.5)TiO3 are known. In this work, we reporting the optimized pulsed laser deposition (PLD) conditions for obtaining pure phase 0.92(Na0.5Bi0.5)TiO3-0.08BaTiO(3), (BNT-BT0.08), thin films. Dielectric, ferroelectric and piezoelectric properties of BNT-BT0.08, thin films deposited by PLD on Pt/TiO2/SiO2/Si substrates are investigated in this paper. Perovskite structure of BNT-BT0.08 thin films with random orientation of nanocrystallites has been obtained by deposition at 600 degrees C. The relative dielectric constant and loss tangent at 100 kHz, of BNT-BT0.08 thin film with 530 nm thickness, were 820 and 0.13, respectively. Ferroelectric hysteresis measurements indicated a remnant polarization value of 22 mu C/cm(2) and a coercive field of 120 kV/cm. The piezoresponse force microscopy (PFM) data showed that most of the grains seem to be constituted of single ferroelectric domain. The as-deposited BNT-BT0.08 thin film is ferroelectric at the nanoscale level and piezoelectric. (C) 2011 Elsevier B.V. All rights reserved.

Abnormal anti-Stokes Raman emission (AASRE) is defined by an anti-Stokes/Stokes intensity ratio much greater than expected on the basis of the equilibrium population of excited vibration states provided by the Boltzmann law. Using nonlinear optical materials such as LiNbO(3) and CdS in powder form, we demonstrate that under continuous single beam excitation it presents AASRE whose properties are similar to a single beam pumped Coherent Anti-Stokes Raman Scattering. We explain AASRE as resulting from a wave-mixing mechanism of the incident laser light with a Stokes shifted Raman light produced by a spontaneous Raman light scattering process, both strongly scattered inside the sample. (C) 2011 American Institute of Physics. [doi:10.1063/1.3633936]

We show that the optical infrared magneto-refractive effect can be used to probe magneto-resistance effects in absolute terms. A spin valve sample with synthetic anti-ferromagnet has been studied using non-contact infrared reflection spectroscopy measurements. Direct experimental comparison shows excellent agreement between electrical and optical measurements in both shape of the magneto-resistance curves and absolute values. This opens the possibility of developing fast and efficient tests of magneto-resistive samples and sensors using an in situ, non-contact, non-destructive optical approach, without the need to determine a calibration factor between the electrical and optical measurements. [doi:10.1063/1.3631778]

Fine and well dispersed Pt-Cu bimetallic nanoparticles stabilized by polyvinyl pyrrolidone (PVP) were synthesized by alkaline polyol method. The molar ratio of Pt to Cu was 1 : 1. Further, the Pt-Cu bimetallic nanoparticles were supported on alumina and their catalytic behavior in methane combustion was investigated. The as-prepared as well as the supported Pt-Cu nanoparticles were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), fractal analysis and X-ray diffraction (XRD). The dependence of methane combustion on the morphology and surface composition of Pt-Cu nanoparticles was analyzed based on the experimental results.

Thin films of Mg (x) Zn1-x O and Mg (x) Zn1-x O doped with nitrogen were deposited by Radio Frequency plasma beam assisted Pulsed Laser Deposition (RF-PLD) in oxygen or oxygen-nitrogen discharge with different nitrogen/oxygen ratios. A Nd:YAG laser working at a wavelength of 266 nm, having a 10 Hz repetition rate was used for the depositions. The energy density of the incident beam was 3 J/cm(2) and the RF power was set to 100 W for all the samples. X-ray Diffraction (XRD) and Spectroscopic Ellipsometry (SE) were employed to investigate the samples. The degree of crystallinity is fount to decrease with increasing the Mg concentration, while the solubility of Mg in ZnO increases by 30% in the N-doped Mg (x) Zn1-x O thin films grown by RF-PLD. Segregation of MgO phase at a Mg concentration of 30% for Mg (x) Zn1-x O thin film is detected both by XRD and SE. The band gap of the samples increases from 3.37 up to 3.57 eV with increasing the Mg concentration and the nitrogen/oxygen ratio for each Mg concentration. A dependence of the dielectric function (refractive index) on both stoichiometry and degree of crystalinity is also found, the refractive index having values between 1.7 and 2 in visible spectral range.

In this study, we present the deposition of ZnPc, Alq3, and PTCDA thin films using Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique. We also report the realisation of multilayer structures, made by the successive application of MAPLE. The films have been characterized by spectroscopic (UV-VIS and Photoluminescence) and microscopic (SEM and AFM) methods, and the effect of different deposition conditions such as fluence, number of pulses, and target concentration on the properties has been analysed. This paper also presents some investigations on the electrical conduction in sandwich type structures ITO or Si/organic layer/Au or Cu and ITO/double organic layer/Cu, emphasising the dominant effect of the height of the energetic barriers at the inorganic/organic and organic/organic interfaces.

The relaxation of the irreversible magnetic moment m(t) in YBa(2)Cu(3)O(7) (YBCO) films was investigated as a function of temperature T and the external magnetic field H along the c axis applied in zero-field cooling conditions, for the determination of vortex creep parameters. The data analysis was performed using the T and current density dependence of the normalized vortex creep activation energy, or by the fit of the m(t) data with the well known interpolation formula in the framework of the general vortex creep equation. It was found that (i) even for specimens with strong static pinning the characteristic pinning energy remains small in the low-T range, where the vortex creep appearing in standard magnetization measurements is elastic, (ii) the observed strong increase of the time scale for creep and the decrease of the creep exponent with increasing H beyond the theoretical predictions can be attributed to the crossover elastic-creep-plastic-creep generated by the macroscopic currents induced in the specimen during magnetization measurements, and (iii) the creep parameters extracted with the interpolation formula are highly affected by the m(t) data registered at short t, which may lead to unphysical creep parameter values.

The corrosion inhibition of carbon steel in 1.0 mol L(-1) HCl in the presence of an antibacterial sulfa drug Sulfathiazole, IUPAC name 4-amino-N-(1,3-thiazol-2-yl) benzene sulfonamide (TBSA) was investigated using mass loss and electrochemical measurements such as: potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Surface chemistry was analyzed by X-ray photoelectron spectroscopy (XPS). For the study of the surface morphology scanning electron spectroscopy (SEM) was used. The results showed that TBSA acts as a corrosion inhibitor in 1.0 mol L(-1) HCl solution by suppressing simultaneously the cathodic and anodic processes via adsorption on the carbon steel surface and that the inhibition efficiency increases with increasing concentration. XPS analysis revealed that the corrosion product consists of an oxyhydroxide/oxide mixture and that the iron oxyhydroxide proportion is higher than the iron oxide proportion.

The structural changes of cubic ZnS (cZnS) nanocrystals (NCs) doped with 0.2 at.% Mn2+ pulse annealed in vacuum and in air, up to 500 A degrees C, were investigated by multifrequency electron paramagnetic resonance (EPR), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The samples, prepared by a surfactant (Tween20)-assisted liquid-liquid reaction at pH = 6, consist of NCs with a tight size distribution around 3 nm and high crystallinity self-assembled into a stable mesoporous structure. The EPR spectra of the as prepared samples contain only the characteristic lines of the substitutional Mn2+(I) centers. No spectra from Mn2+ ions localized in (hydro)oxidized regions of the NCs surface were observed. The absence of such a surface layer could explain the stability of the cubic (sphalerite) structure observed by XRD and TEM in the investigated cZnS:Mn NCs annealed in vacuum up to 500 A degrees C. The observation of the cubic-hexagonal transformation for the same NCs annealed in air supports the role of such layer in promoting this structural transformation. The narrowing of the EPR spectral lines above 200 A degrees C with the increase in the average size of the cZnS:Mn crystallites was observed. The effect was more pronounced for the sample annealed in air. EPR also revealed the formation of minute amounts of substitutional Mn2+-type centers in a hexagonal ZnO structure at T similar to 300 A degrees C, corresponding to the early stages of the thermally induced oxidation of the cZnS:Mn NCs.