National Institute Of Materials Physics - Romania

Publications

5781 articles found

3261. Magnetic Temperature Transducers Made from Copper Based Soft Ferrite

Authors: Miclea, C; Tanasoiu, C; Miclea, CF; Spanulescu, I; Cioangher, M; Miclea, CT

Published: 2009, SMART MATERIALS & MICRO/NANOSYSTEMS, 54, 69, DOI:

Soft ferrites in the CuZnTi system, having the chemical composition Cu1-x-yZnxTiyFe2O4 with 0.5 <= x <= 0.7 and 0.00 <= y <= 0.05 were investigated as a function of composition, sintering temperature and cooling speed, in order to obtain materials with different Curie temperatures, between 30 and 180 degrees C and very high change rate of permeability with temperature around their Curie points. Such materials are well suited to use as high sensitive magnetic temperature sensors and transducers for temperature control. Zn and Ti additions to copper ferrite change the Curie temperature in a controllable manner, thus being possible to produce ferrite material with a fine control of the Curie point at any desired temperature. Most important was the behavior of magnetic permeability with temperature around the Curie point, where it may change with about 60 %/degrees C by a proper choice of the cooling speed of samples from the sintering temperature to room temperature. This makes such materials extremely attractive as magnetic temperature sensors of high sensitivity. Two applications Of Such materials as temperature sensors, namely an ultrathermostat and an on-off switch type relay were designed. Their functionality and performances are presented and discussed.

3262. Efficient Laser Emission of Nd-vanadates on the 1.34-mu m (4)F(3/2)->(4)I(13/2) Transition under Pumping with Diode Lasers Directly into the Emitting Level

Authors: Pavel, N; Dascalu, T; Vasile, N; Lupei, V

Published: 2009, 2009 CONFERENCE ON LASERS AND ELECTRO-OPTICS AND QUANTUM ELECTRONICS AND LASER SCIENCE CONFERENCE (CLEO/QELS 2009), VOLS 1-5, 2604, DOI:

Efficient 1.34-mu m laser emission is realized in Nd-vanadates under pumping with diode lasers at 0.88 mu m. A Nd:YVO(4) crystal yielded 3.4-W output power for 9.3-W absorbed pump power, at a slope efficiency of 0.43. (C) 2009 Optical Society of America

3263. Possible influence of two-band superconductivity on the behaviour of the second magnetization peak in La2-xSrxCuO4 single crystals

Authors: Miu, L

Published: AUG-OCT 2009, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 469, 1139, DOI: 10.1016/j.physc.2009.05.200

An anomalous temperature T dependence of the field H-on for the onset of the second magnetization peak (SMP) in La1.81Sr0.19CuO4 single crystals (with the external magnetic field H oriented parallel to the c axis) is discussed. While the peak field H-p and the magnetization at H-p have a continuous variation with T, H-on exhibits a sudden decrease with increasing T for T similar to 11 K-15 K. The analysis of the nature of the SMP in La2-xSrxCuO4 single crystals in terms of a simple dynamic energy balance relation suggests that the observed behaviour Could be related to the particular T dependence of the superfluid density in the case of two-band Superconductivity, affecting the T variation of the elastic energy of the vortex system at low H (C) 2009 Elsevier B. V. All rights reserved.

3264. Peak-dip crossover of the differential conductance in mesoscopic systems with quantum impurities

Authors: Aldea, A; Tolea, M; Dinu, IV

Published: 2009, 25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 2, 150, DOI: 10.1088/1742-6596/150/2/022001

We investigate the differential conductance dI/dV for the interacting T-shape model, using an approach based on the Keldysh formalism and the Lacroix solution for the equation of motion. A peak-dip crossover has been noticed by changing the hybridization between the two dots. For the same model, the combined interaction and interference processes give rise to the Fano-Kondo effect with an interesting crossing point of the isoterms below the Kondo temperature A tentative explanation of these effects is given in terms of the many-body spectral properties of the system.

3265. Polymer functionalization with manganites

Authors: Sandu, V; Popa, S; Ivan, I; Plapcianu, C; Sandu, E; Hurduc, N; Nor, I

Published: 2009, SECOND INTERNATIONAL CONFERENCE ON SMART MATERIALS AND NANOTECHNOLOGY IN ENGINEERING, 7493, DOI: 10.1117/12.843221

We investigated the transport properties of a series of composites made of La2/3Sr1/3MnO3 and different copolymers. The temperature dependence of the electrical resistance of the samples is strongly dependent on the nature of the polymers. We found four types of temperature dependences of the electrical resistance: i) simple current dependence of resistivity for poly(methyl-methacrylate-co-styrene) copolymers, ii) single peaked characteristics for poly(acryl amide-co-vinyl acetate), iii) multipeaked dependence found in poly(methyl-methacrylate-co-butadiene) and star type polysiloxane-g-styrene, and iv) current independent characteristics visible in the samples made with linear polysiloxane-based composites.

3266. COMMUTON - A NEW CONCEPT IN SWITCHING MATERIALS

Authors: Popescu, M; Velea, A; Lorinczi, A; Sava, F

Published: MAR-APR 2009, JOURNAL OF OVONIC RESEARCH, 5, 34, DOI:

A switching unit can be defined as the smallest unit that preserves the property of switching in memory materials. Atomic switching unit is discussed, molecular switching units are described and supramolecular units in phase change materials are evidenced and discussed. The "commuton", as basic switching unit, could give more insight into the particular properties of the switching phenomena in various solid materials.

3267. Enhancing critical current in YBCO thick films: Substrate decoration and quasi-superlattice approach

Authors: Sarkar, A; Mikheenko, P; Dang, VS; Abell, JS; Crisan, A

Published: AUG-OCT 2009, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 469, 1553, DOI: 10.1016/j.physc.2009.05.242

For power applications of superconducting films. the critical current density (J(c)) and the thickness of the film (d) should be as high as possible. Since J(c) decreases with both thickness and magnetic field, artificial pinning centres in addition to natural ones are required to keep J(c) high. The earliest cost-effective method used for introducing artificial pinning centres was the so-called substrate decoration, i.e., growing nanoscale islands (nano-dots) of certain materials on the substrate prior to the deposition of the superconducting thin film. Later on another version of this approach proved to be successful: building up a layered distribution of a second phase using a multilayer deposition (quasi-superlattices). Several materials have been used for the Creation of artificial pinning centres. Here we report on the artificial pinning centres induced in YBCO thick films by substrate decoration and quasi-superlattice approaches using nano-dots of Pd and non-superconducting YBCO. The cross-sectional AFM images show evidence of c-axis correlated columnar defects. These defects significantly contribute to the pinning of magnetic flux and increase critical current in the films. We observed an important shift of the position of the maximum in the thickness dependence of J(c)(B) towards higher thicknesses compared with pure YBCO films by both approaches. A high J(c)(B) in our quite thick films provides a very high total critical current per cm of the film width. Critical current as high as 800 A/cm width was achieved in a 2.4 mu m thick quasi-superlattice film with non-superconducting YBCO nano-dots. (C) 2009 Elsevier B.V. All rights reserved.

3268. Nanostructured Ferrite Formation in Borosilicate Glass

Authors: Sandu, V; Popa, S; Pasuk, I; Enculescu, I; Nicolescu, MS; Radicescu, S

Published: 2009, MULTI-FUNCTIONAL MATERIALS AND STRUCTURES II, PTS 1 AND 2, 79-82, +, DOI: 10.4028/www.scientific.net/AMR.79-82.445

We present the preparation, structural, and magnetic properties of a series of Fe-containing borosilicate glasses as a function of the ratio SiO2/Fe2O3 which is ranging from 1.49 to 2.68. The role of nucleators (Cr2O3 and P2O5) was also investigated. X-Ray diffraction has revealed the formation of magnetite as the major or unique crystalline phase. As SEM micrographs have revealed, the addition of P2O5 give rise to a finer structure as compared with Cr2O3. In addition, the same oxide decreases the temperature of structural transition with almost 100 degrees C. The magnetization data reveal a two step transition at low temperatures: a high temperature transition at T-v = 128 K, which we attribute to the Verwey transition, and a low temperature transition at T-s = 48 K which, most likely, is the result of change in the dynamic of the domain motion.

3269. ENERGY DEPOSITED BY RADIATION IN SOLIDS: REGISTRATION PHYSICS

Authors: Lazanu, I; Lazanu, S

Published: 2009, ROMANIAN REPORTS IN PHYSICS, 61, 699, DOI:

General aspects of the interactions of ions in silicon are investigated: energy lost in electronic and nuclear processes, as well as their consequences, creation of point and extended defects in the crystal structure. The correlations between irradiation ions, their energy, ionization and nuclear energy loss per atom, radius of interaction and spatial extension of the primary damaged region are also investigated.

3270. CATALYTIC COMBUSTION OF METHANE OVER UNSUPPORTED AND gamma-Al2O3 SUPPORTED Sr2FeTaO6 and Sr2Fe0.7Co0.3TaO6 DOUBLE PEROVSKITES

Authors: Popescu, I; Redey, A; Marcu, IC; Popescu, B; Mako, E; Sandulescu, I

Published: NOV-DEC 2009, REVUE ROUMAINE DE CHIMIE, 54, +, DOI:

Sr2FeTaO6 and Sr2Fe0.7Co0.3TaO6 double perovskites, unsupported and supported on gamma-Al2O3 were prepared, characterized and studied in the catalytic combustion of methane, as a test reaction for volatile organic compounds (VOCs) destruction. These mixed oxides, with double perovskite structure, present good catalytic activities, and after their dispersion - 5 % (wt.) - on gamma-Al2O3 support, the reaction rates increased compared with the unsupported samples.