National Institute Of Materials Physics - Romania

Publications

5914 articles found

3511. The influence of chemical composition on magnetic properties and magnetostriction coefficient of cobalt ferrites

Authors: Caltun, O; Dumitru, I; Feder, M; Diamandescu, L; Bibicu, I; Vasiliu, F; Lupu, N; Vilceanu, V

Published: JUL 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1778, DOI:

Four series of cobalt ferrites were prepared by conventional ceramic method. Calcined powders were analyzed by X-ray diffraction and Mossbauer spectroscopy to characterize the crystal structure. Green bodies were sinterized at temperatures between 1250 degrees-1300 degrees C, in air, for 5 hours. Chemical composition of samples and sintering parameters have a strong influence on the magnetic and magnetostrictive properties of the sintering bodies.

3512. The synthesis of doped manganese cobalt ferrites by auto combustion technique

Authors: Palamaru, MN; Iordan, AR; Aruxandei, CD; Gorodea, IA; Perianu, EA; Dumitru, I; Feder, M; Caltun, OF

Published: JUL 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1856, DOI:

CoMnxFe2-xO4 with x = 0; 0.10; 0.25; 0.40; 0.60 and 2.0 were prepared by low temperature combustion method. The samples were investigated using X-ray diffraction analysis at room temperature. All the synthesized samples exhibited XRD patterns specific for cubic spinel phase with a space group Fd3m. Infrared spectroscopic analysis, using KBr pellets in the range 400 - 4000 cm(-1) was carried out using a FTIR 600Plus Fourier transform infrared spectrometer. The magnetic properties of samples have been characterized at room temperature using a vibrating sample magnetometer, the magnetic properties measurements demonstrate an increase of the saturation magnetization with the increase of Mn content.

3513. Physical properties of the new ferromagnetic Kondo system CeAg1-xNixSb2

Authors: Popescu, B; Birsan, A; Galatanu, A; Royanian, E; Hilscher, G; Bauer, E

Published: JUL 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1629, DOI:

Structural, magnetic and transport properties of CeAg1-xNixSb2 compounds are investigated on polycrystalline samples. The experimental results show the formation of ferromagnetic compounds with sharp transitions decreasing from 9.5 K in the 100% Ag compound to 8.1 K for 33% Ni substitution, 7 K for 67% Ni substitution to 6 K for the 100% Ni compound. The characteristic temperatures, considered as the temperature of the resistivity maximum To increases from 26 K to 44 K, 54 K and 65 K, respectively. These results indicate Ce(AgNi)Sb2 compounds as a ferromagnetic Kondo system.

3514. Resonant Raman scattering and absorption spectroscopy studies on individual carbon nanotubes in surfactant solutions

Authors: Husanu, M; Baibarac, M; Preda, N; Baltog, I

Published: JUL 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1726, DOI:

Carbon Nanotubes are exotic low-dimensional systems, and due to their remarkable properties, are promising components for technological applications. The electronic and vibrational signatures raising from their existence as individual entities or associated in bundles, is still a controversed subject. A careful analysis of the G (similar to 1600 cm(-1)) and RBM (100-200 cm(-1)) band features as: profile, peak position and intensity in the Raman spectra may be a valuable indication about their dispersion state. The UV-VIS-NIR absorption spectrum comes to support this assumption. Observing the absorption spectra associated to resonant excitation of semiconducting and metallic nanotubes, may reveal complementary informations concerning the individualization procedure efficiency.

3515. Polaron activation energy as evidenced by EMR in colossal magnetoresistive nanowires

Authors: Popa, A; Toloman, D; Grecu, MN; Mihailescu, G; Darabont, A; Pop, CVL; Raita, O; Fardis, M; Idziak, S; Hoffmann, SK; Giurgiu, LM

Published: JUL 2008, APPLIED MAGNETIC RESONANCE, 34, 26, DOI: 10.1007/s00723-008-0097-5

In the present work an X-band electron magnetic resonance (EMR) investigation in the paramagnetic regime of colossal magnetoresistive manganite La2/3Ca1/3 MnO3 (LCMO) nanowires was carried out. The temperature dependence of the EMR line width has been analyzed in terms of the small polaron hopping scenario. From this analysis, the polaron activation energy E-a in LCMO nanowires was evaluated. A discussion is given concerning the factors which could explain the smaller value of E-a as compared with the corresponding ones for LCMO nanoparticles.

3516. Pressure response of Ce(Ag, Ni)Sb(2) compounds

Authors: Khan, RT; Galos, R; Bauer, E; Popescu, B; Galatanu, A

Published: JUL 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1615, DOI:

The pressure response of CeAg(1-x)Ni(x)Sb(2) is Studied by means of electrical resistivity measurements. The ferromagnetic ordering temperatures T(c) of this series decrease as pressure is applied, except CeNiSb(2), showing a pressure driven continuous increase of T(c). This refers to crystalline electric field effects originating distinct different magnetic ground states. Concomitantly, the pressure response of various material dependent parameters also behave in the opposite direction.

3517. The impact of the "memory effect" on the catalytic activity of Mg/Al; Mg,Zn/Al; Mg/Al,Ga hydrotalcite-like compounds used as catalysts for cycloxene epoxidation

Authors: Angelescu, E; Pavel, OD; Birjega, R; Florea, M; Zavoianu, R

Published: JUN 15 2008, , DOI: 10.1016/j.apcata.2007.12.022

3518. Thermally-induced self-assembling nanotechnology of gold nano-dots on CeO2-buffered sapphire for superconducting films

Authors: Crisan, A; Wordenweber, R; Hollmann, E; Kutzner, R; Button, TW; Abell, JS

Published: JUN 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1373, DOI:

A typical facility for fabrication of devices based on high temperature superconducting (HTS) films grown on the less-expensive CeO2-buffered sapphire substrates comprises a transfer chamber, a chamber for CeO2 growth, a chamber for YBa2Cu3Oy (YBCO) growth, and a chamber for Au deposition at room temperature. Here we present the adaptation of our previously-reported method to create artificial pinning centres in HTS films through self-assembled nano-scale islands for this type of facility without making any modifications. We succeeded to grow Au nano-dots from an ultra-thin layer of Au grown at room temperature subsequently annealed in the chamber for YBCO deposition, in the same conditions as for YBCO growth. AFM and RBS were used to investigate the formation of Au nano-dots, while XRD and susceptibility measurements were used to study the properties of nano-structured YBCO films.

3519. Potassium hydrogen phthalate (KAP) micro- and nano-rods prepared by a template approach

Authors: Enculescu, M

Published: JUN 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1504, DOI:

Micro and nanorods of potassium acid phthalate (KAP) with diameters ranging from a hundred nanometers to tens of microns were obtained by solution growth in polycarbonate (PC) ion track templates. The ion track templates were produced by swift heavy ion irradiation of PC foils (e.g. U with 11.4 MeV/nucleon specific energy) and subsequently etching. After the growth the host templates were partially dissolved in dichlormethane and imagined by scanning electron microscopy. The template approach allows the fabrication of arrays of uniform nanostructures with a controlled morphology.

3520. Size-broadening anisotropy in whole powder pattern fitting. Application to zinc oxide and interpretation of the apparent crystallites in terms of physical models

Authors: Popa, NC; Balzar, D

Published: JUN 2008, JOURNAL OF APPLIED CRYSTALLOGRAPHY, 41, 627, DOI: 10.1107/S0021889808012223

A new anisotropic size-broadening model based on a spherical-harmonics representation allowing determination of both volume-and area-averaged apparent crystallites and convenient for implementation into Rietveld programs is described. The model effectiveness is demonstrated on a ZnO powder pattern exhibiting strongly anisotropic size broadening and pronounced super-Lorentzian peak shapes. Moreover, it is shown how the apparent crystallites can be interpreted in terms of physical models by using ellipsoidal and cylindrical crystallites with lognormal size distributions. This interpretation is critically assessed and it is argued that both simplified physical models and a priori complementary information (obtained by transmission electron microscopy, for instance) are often needed to avoid unstable and non-unique solutions.