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1
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Preparation and Characterization of Nano Ferrites

100%
Lazarević Z., Jovalekić Č., Milutinović A., Romčević M., Romčević N.
Acta Physica Polonica A
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2012
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vol. 121
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issue 3
682-686
EN
Nickel ferrite (NiFe_2O_4) and manganese ferrite (MnFe_2O_4) have been prepared by a soft mechanochemical route from mixture of (1) Ni(OH)_2 and α-Fe_2O_3 and (2) Mn(OH)_2 and α-Fe_2O_3 powders in a planetary ball mill. The mixture was activated for varying duration. Soft mechanochemical reaction leading to formation of the NiFe_2O_4 and MnFe_2O_4 spinel phases were followed by X-ray diffraction, Raman and infrared spectroscopy, scanning and transmission microscopy. The spinel phase formation was first observed after 4 h of milling (case 1) and after 3 h (case 2) and its formation was completed after 25 h in both cases. The synthesized NiFe_2O_4 and MnFe_2O_4 ferrites have a nanocrystalline structure with a crystallite size of about 30 and 40 nm for cases (1) and (2), respectively. There are five Raman and four IR active modes. In order to understand better the whole process of phase formation, the Mössbauer measurements were done.
2
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Resonant Raman Spectra of CdTe/ZnTe Self Assembled Quantum Dots

86%
Romčević N., Romčević M., Kostić R., Stojanović D., Abolmasov B., Karczewski G., Galazka R.
Acta Physica Polonica A
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2009
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vol. 116
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issue 1
88-90
EN
In this paper we present Raman scattering and photoluminescence spectra measured on CdTe/ZnTe self assembled quantum dots. The photoluminescence spectrum has shown two main emission peaks, both connected with existing of quantum dots. One presents direct deexcitation to ground state and the other is optical phonon (οmega = 207.3 cm^{-1})-assisted deexcitation. The registered multiphonon emission process depends on temperature. At low temperature phonon spectra shows line at 450 cm^{-1} (TA + 2LO in ZnTe) and 595 cm^{-1} (2LO + TO(Γ) in ZnTe).
3
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Ellipsometric Measurements of Plastically Deformed Copper

86%
Mirić M., Rudolf R., Anžel I., Hadžić B., Romčević M., Trajić J., Romčević N.
Acta Physica Polonica A
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2009
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vol. 116
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issue 4
715-717
EN
Chemically pure copper (99.99) prepared in the sample of square cross-section (10×10 mm^{2}) and length about 50 mm was extremely plastically deformed with the repeated application of equal channel angular pressing. Equal channel angular pressing was applied as an effective technique for producing bulk nanoscaled structures. It is well known that severe plastic deformation of metallic materials often leads to microstructure with ultrafine grains and cross-sections which remain about equal before and after deformation. Optical properties of the sample were studied using spectroscopic ellipsometry in UV-VIS range. The parameters of the sample like copper oxide and surface roughness overlayer were calculated using two-film model together with the Bruggeman effective medium approximation.
4
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Characterization of Barium Titanate Ceramic Powders by Raman Spectroscopy

86%
Lazarević Z., Romčević N., Vijatović M., Paunović N., Romčević M., Stojanović B., Dohčević-Mitrović Z.
Acta Physica Polonica A
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2009
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vol. 115
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issue 4
808-810
EN
Barium titanate, BaTiO_3 ceramic powders were prepared by mechanochemical synthesis and by the Pechini method. A powder mixture of BaO and TiO_2 was treated in a planetary ball mill in an air atmosphere for up to 1 h, using zirconium oxide vial and zirconium oxide balls as the milling medium. After 60 min BaTiO_3 phase was formed. In both ways BaTiO_3 ceramics were sintered after 2 h on 1300°C without pre-calcinations step. The heating rate was 10°C min^{-1}. The formation of phase and crystal structure of BaTiO_3 was approved by X-ray diffraction analysis and the Raman spectroscopy. The morphology and microstructure of obtained powders were examined by scanning electron microscopy method. Sharp phase transition from ferroelectric to paraelectric state was observed. The hysteresis loop is very well performed with regular sharp characteristic of ferroelectric materials.
5
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Far-Infrared Study of DX-Like Centers in Pb_{0.95}Mn_{0.05}Te(Ga)

86%
Stojanović D., Trajić J., Hadžić B., Romčević M., Ivanchik I., Khokhlov D., Romčević N.
Acta Physica Polonica A
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2007
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vol. 112
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issue 5
959-962
EN
We present far-infrared reflection spectra of Pb_{0.95}Mn_{0.05}Te single crystal doped with gallium between 10 and 300 K. The analysis of the far-infrared reflection spectra was made by a fitting procedure based on the model of coupled oscillators. Together with the strong plasmon-phonon coupling we obtain three local modes of gallium at about 122 cm^{-1}, 166 cm^{-1}, and 192 cm^{-1}. The position of these modes depends on impurity center charge, and their intensity depends on temperature.
6
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Nanocrystalline ZnO Doped with Fe_2O_3 - Magnetic and Structural Properties

73%
Kuryliszyn-Kudelska I., Hadžić B., Sibera D., Kilanski L., Romčević N., Romčević M., Narkiewicz U., Dobrowolski W.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
689-691
EN
We have studied the magnetic properties of ZnO nanocrystals doped with Fe_2O_3 in the magnetic dopant range from 5 to 70 wt%. The nanocrystals were synthesized by wet chemical method. The detailed structural characterization was performed by means of X-ray diffraction and micro-Raman spectroscopy measurements. The results of systematic measurements of magnetic AC susceptibility as a function of temperature and frequency are presented. We observed different types of magnetic behavior. For ZnO samples doped with low content of Fe_2O_3, the results of low-field AC susceptibility are satisfactorily explained by superparamagnetic model including inter-particle interactions. With the increase of magnetic Fe_2O_3 content, the spin-glass-like behavior is observed.
7
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Raman Spectroscopy of Multiphonon Emission Process in Ni-Doped PbTe

73%
Romčević N., Trajić J., Hadžić B., Romčević M., Stojanović D., Lazarević Z., Kuznetsova T., Khokhlov D., Rudolf R., Anžel I.
Acta Physica Polonica A
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2009
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vol. 116
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issue 1
91-92
EN
In this paper, we present room temperature unpolarized Raman scattering spectra of Ni doped PbTe single crystal sample. Crystal of PbTe(Ni) was grown by the Bridgman method. The Ni concentration in the sample used here was 1× 10^{19} at./cm^{3}. Well resolved peaks appear at about 126, 143, 181, 362 and 724 cm^{-1}. The modes at 126 and 143 cm^{-1}, which are also observed in other telluride compounds, originate from vibrations in TeO_2. We assume that the mode at about 181 cm^{-1} is connected to excitations of a local phonon mode in the vicinity of an impurity atom (donor Ni^{3+} state). Modes at about 362 cm^{-1} and 724 cm^{-1} are the second and fourth harmonic of a local phonon mode, registered here due to multiphonon emission.
8
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Optical Properties of Plastically Deformed Copper

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Trajić J., Rudolf R., Anžel I., Romčević M., Lazarević N., Mirić M., Lazarević Z., Hadžić B., Romčević N.
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issue 5
791-793
EN
Pure copper (99.99), prepared in the sample of square cross-section (10 × 10 mm^{2}) and length about 50 mm, was extremely plastically deformed with the repeated application of Equal Channel Angular Pressing (ECAP). ECAP was applied as an effective technique for producing bulk nano-scaled structures. Optical properties of the sample were investigated using Raman spectroscopy. Two types of lines: narrow (with width of ≈ 7 cm^{-1}) and wide ( ≈ 40 cm^{-1}) are registered. Existence of two types of lines indicates that in the specimen exists nano-sized crystal structures of both Cu and CuO related with three dimensional amorphous boundary spaces, which indicates that plastic deformation of the sample did not lead to total amorphisation of the specimen.
9
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Raman Scattering from ZnO(Fe) Nanoparticles

73%
Romčević N., Kostić R., Romčević M., Hadžić B., Kuryliszyn-Kudelska I., Dobrowolski W., Narkiewicz U., Sibera D.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1323-1328
EN
Nanocrystalline samples of ZnO(Fe) were synthesized by wet chemical method. Samples were characterized by X-ray diffraction to determine composition of the samples (ZnO, Fe₂O₃, ZnFe₂O₄) and the mean crystalline size (8-52 nm). In this paper we report the experimental spectra of the Raman scattering (from 200 to 1600 cm¯¹). Main characteristics of experimental Raman spectrum in 200 to 1600 cm¯¹ spectral region are: sharp peak at 436 cm¯¹ and broad two-phonon structure at ≈ 1150 cm¯¹, typical of ZnO;broad structure below 700 cm¯¹ that has different position and shape in case of ZnFe₂O₄ or Fe₂O₃ nanoparticles.
10
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Low-Frequency Raman Scattering from ZnO(Fe) Nanoparticles

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Kostić R., Romčević N., Romčević M., Hadžić B., Rudolf R., Kuryliszyn-Kudelska I., Dobrowolski W., Narkiewicz U., Sibera D.
Acta Physica Polonica A
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2009
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vol. 116
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issue 1
65-67
EN
Nanocrystalline samples of ZnO(Fe) were synthesized by wet chemical method. Samples were characterized by X-ray diffraction to determine the sample composition and the mean crystalline size. Low-frequency Raman modes were measured and assigned according to confined acoustic vibrations of spherical nanoparticles. Frequencies of these vibrational modes were analyzed in elastic continuum aproximation, which considers nanoparticle as homogeneous elastic sphere.
11
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Optical and Magnetic Properties of PbTe(Ni)

73%
Romčević N., Trajić J., Romčević M., Stojanović D., Kuznetsova T., Khokhlov D., Dobrowolski W., Rudolf R., Anžel I.
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EN
Far-infrared and magnetic properties of Ni doped PbTe (Z_Ni = 1× 10^{19} at./cm^{3}) single crystal are investigated in a broad range of temperature and magnetic fields. Far-infrared reflection spectra were analyzed using a fitting procedure based on the modified plasmon-two phonon interaction model. Together with the strong plasmon-two longitudinal optical phonon coupling we obtained a local mode of Ni at about 180 cm^{-1}. This mode intensity depends on temperature. Magnetic measurements shows that PbTe alloys doped with Ni reveals weak ferromagnetic interaction between magnetic ions.
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