last update: 01 nov. 2004

 Volume 5, No. 1, March 2003

Content:

 

Review Paper

1

Comparison of Photoinduced Atom Displacements in Glasses and Polymers

 H. Jain  

  Scientific and Technological Researches
2 Chalcogenide glasses – survey and progress  

D. Lezal

3

Microhardness of Pb modified chalcogenide glasses  

 A. K. Pattanaik, P. S. Robi, A. Srinivasan

4

On fabrication of large format optoelectronic elements  

P. Sharlandjiev, B. Markova  

5

Optoelectronic properties of spray deposited SnO2:F thin films for window materials in solar cells  

E. Elangovan, K. Ramamurthi  

6

Effect of temperature annealing on periodically poled rare-earth  doped lithium niobate crystal  

 V. Bermúdez, D. Callejo, E. Diéguez  

7

Periodically poled structures in lithium niobate crystals: growth and photoelectric properties  

I. A. Ghambaryan, R. Guo, R. K. Hovsepyan, A. R. Poghosyan, E. S. Vardanyan, V. G. Lazaryan  

8 Some optical properties of BaO - PbO - B2O3 glasses  

J. Schwarz, H. Tichá

9

Growth and characterisation of InGaAs(P) by CBE technique  

 M. Udhayasankar, J. Kumar, P. Ramasamy  

10 Application of microtechnology in biotechnology. Microarray analytical systems – an overview  

 G. De Bellis , G. Caramenti,  M. Ilie, E. Cianci, V. Foglietti  

11

Numerical study of the growth conditions in a MOCVD reactor: application to the epitaxial growth of CdTe 

R. Tena-Zaera, I. Mora-Seró, C. Martinez-Tomas, V. Muñoz-Sanjosé

12

Methylene - blue modified polypyrrole film electrode for optoelectronic applications

 R. M. Ion , F. Scarlat, Fl. Scarlat, V. I. R. Niculescu

13

The effective pair potential calculations of molten NaCl and AgI  

 S. Dalgiç

  Short Communications
14

Grown periodically poled lithium niobate crystal: period stabilization  

N.F. Evlanova, I. I. Naumova, S. A. Blokhin, T. O. Chaplina, G. D. Laptev, A. A. Novikov

   

Proceedings of AMS Conference 2002

15 Soft Magnetic Nanocrystalline alloys  

 J. M. Grenèche  

16

New ferromagnetic and functionally graded shape memory alloys  

 C. M. Craciunescu, M. Wuttig  

17

Spectroscopic characterisation of crystalline phases development from amorphous precursors  

 S. Simon 

18

MAS NMR and SEM study of local structure changes induced by heat treatment in La2B4Al2O12

 M. Vasilescu, G. Borodi, S. Simon  

19

Structural and magnetic investigations of transition metal ions in TeO2 based glasses  

 I. Ardelean, S. Filip  

20

Structural and magnetic investigations of manganase ions in 2B2O3×As2O3 glass matrix

 I. Ardelean, M. Flora

21

Local structure and metal-metal interaction in some phosphate glasses

O. Cozar, I. Ardelean

22

Fast ion conduction in silver molybdenum phosphate glasses  

A. Latia, C. Vancea

23

Calcium influence on dissolution rates of potassium phosphate glasses  

D. Cacaina, S. Simon  

24

Transverse susceptibility of  single-domain particle systems  

 A. Stancu, L. Spinu  

25 Chain-of-spheres approximation in micromagnetic modelling of magnetic recording media  

 D. Cimpoesu, A. Stancu  

26

Magnetic properties of g-Fe2O3 nanoparticles  

 D. Predoi, V. Kuncser, M. Nogues, E. Tronc, J. P. Jolive, G. Filoti, G. Schinteie  

27

Easy axis distribution in modern nanoparticle storage media: a new methodological approach

 V. Kuncser, W. Keune, M. Vopsaroiu, P. R. Bissell, B. Sahoo, G. Filoti  

28

Study of the interparticle magnetic interaction effect on magnetic resonance line in ferrofluids  

 C. N. Marin, I. Mălăescu, V. Socoliuc

29

A new method for determination of the effective anisotropy constant of the particles within ferrofluids

 I. Mãlãescu

30

Formation of the nanocrystalline cubic (FeNi)23B6 phase in the nickel-rich FeNiZrB alloys and its magnetic behaviour   

B. Idzikowski, A. Szajek  

31

Structural relaxation in Fe70Cr10.5P11.5Mn1.5C6.5 amorphous alloy  

 I. Mihalca, A. Ercuta  

32

Nanocrystalline Ni-Zn ferrites prepared by sol-gel method  

M. Popovici, C. Savii, D. Niznansky, J. Subrt, J. Bohacek, D. Becherescu, C. Caizer, C. Enache, C. Ionescu  

33

Preparation and magnetic properties of Ni80Fe20 nanowire arrays  

 H. Chiriac, T. A. Óvári, A. E. Moga, M. Urse  

34

Non-linear behaviour of the spin transition compounds during photo-excitation and relaxation  

C. Enachescu, J. Linares, E. Codjovi, K. Boukheddaden, F. Varret  

35 The quantum efficiency of the photo-excitation in a Fe (II) spin-crossover compound  

C. Enachescu, U. Oetliker, A. Hauser  

36 Stress and temperature effect on the FMR response of nearly zero magnetostrictive amorphous microwires  

 F. M. Tufescu, T. A. Óvári, H. Chiriac, A. Stancu  

37

Spin dynamics investigated by magnetic resonance in colossal magnetoresistive materials

 L. V. Giurgiu  

38

Effects of In doping investigated by ESR in colossal magnetoresistive manganite La2/3Ca1/3MnO3

O. Raita, M. N. Grecu, X. Filip, Al. Darabont, D. Gavre, J. Blasco, L. V. Giurgiu

39

Modeling the multi-crystalline SIlicon ingot solidification process in a vertical square furnace  

F. Barvinschi, C. Stelian, Y. Delannoy, N. Mangelinck, T. Duffar  

40

Identification of nonlinearties in anelastic polycrystalLine materials using Volterra - Fourier Transform  

Gh. E. Drăgănescu, A. Ercuţa

41

Manganase activated (2-x)ZnO×xCdO×1.1SiO2 phosphors obtained by solid state synthesis   

C. Enache, R. Turcin, C. Savii, M. Popovici, R. M. Jurca, V. Socoliuc  

42 Microstructural evolution and thermo-mechanical response of Ni ion irradiated TiNi SMA thin films  

 T. B. Lagrange, R. Gotthardt  

43

Computer simulation of magnetization curves in magnetic thin films  

 M. Volmer, J. Neamtu  

44

Thermoionic Vacuum Arc – a new method of thin film deposition  

 R. Vladoiu, G. Musa, I. Mustata

45

Optical and electronic properties of metal doped polymers for integrated optics  

 M. Bulinski, V. Kuncser, D. Cristea, C. Plapcianu, S. Krautwald, H. Franke, F. E. Wagner, G. Filoti

46

Strontium-doped LaCoO3 perovskites in solid oxide fuel cells   

V. V. Srdic, L. Nikolic, V. Pejovic  

47

Synthesis of LiMn2O4 by glycine-nitrate method

 D. Jugović, N. Cvjetićanin, V. Kusigerski, S. Mentus  

48

Conduction electron spin resonance of Pt-nanoparticles in porous Al2O3 membranes

D. Gavre, G. Mihailescu, O. Raita, E. Indrea, S. Pruneanu, J. Rahmer, L. V. Giurgiu

49

Identification of the generalised preisach  model parameters for systems with magnetostatic interactions  

 M. Cerchez, L. Stoleriu, Al. Stancu  

50 A Preisach-Néel model with thermal variable variance: sensibility to the parameters  

I. D. Borcia, L. Spinu, Al. Stancu  

51 Bar-configuration in Hall measurements with GaAs  

 R. V. Ghita, C. Logofatu, C. Negrila, M. F. Lazarescu, A. S. Manea, V. Ciupina  



 

Abstracts:

Review Paper

1. Comparison of Photoinduced Atom Displacements in Glasses and Polymers

 H. Jain

When exposed to visible-UV light, photoinduced atom displacement (PAD) may occur in certain inorganic glasses as well as polymers, leading to similar changes in their opto-electronic and structural properties. An understanding of PAD is important for the use of these materials in photonic applications such as optical storage, CD-RW, opto-mechanical transducers, etc. In both classes of materials, PAD is caused by a combination of electronic excitation and subsequent response of the structure to the excited state configuration. There are indications of photoinduced localized atomic restructuring as well as long-range diffusion, which require bond-breaking. In spite of the initially homogeneous, isotropic structure, the photoinduced effects can be anisotropic, depending on the direction of polarization and/or the direction of light propagation. In general, the PAD in polymers is much larger but less stable than that in glasses, presumably due the greater adaptability of polymer structure to the optically created polarization and other stresses. A combination of these characteristics in a single glass-polymer or organic-inorganic material is likely to yield superior photoinduced properties. A comparative overview of PAD in inorganic glasses and polymers is presented in this paper.  

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Scientific and Technological Researches

2. Chalcogenide glasses – survey and progress

D. Lezal

Chalcogenide glasses are reviewed. The physical properties are discussed in relation to the purity of the glass. The photo-luminescence properties and the state-of-art of applications are presented.  

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3. Microhardness of Pb modified chalcogenide glasses

 A. K. Pattanaik, P. S. Robi, A. Srinivasan

Microhardness of bulk PbxGe42-xSe58(3 ≤ x ≤ 15), Pb20GexSe80-x(17 ≤ x ≤ 24), PbxGe42-xSe48Te10(3 £ x £ 15) and Pb20GexSe70-xTe10 (17 £ x £ 24) glasses was measured at room temperature. In Pb20GexSe80-x and Pb20GexSe70-xTe10 glasses, microhardness attained a maximum value at the composition with 21 at. wt. % Ge. In the case of PbxGe42-xSe58 and PbxGe42-xSe48Te10 glasses, the microhardness decreased with the addition of Pb. The variation in microhardness with composition and the effect of Te substitution on the microhardness of these glasses are discussed in the light of the change in the average bond energy of the glasses.  

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4. On fabrication of large format optoelectronic elements

P. Sharlandjiev, B. Markova

We discuss different methods for synthesis and analysis of large format optical elements with predetermined reflectance or/and transmittance characteristics. Chemical vapor deposition, electron beam evaporation and ion beam sputter deposition are well-established techniques for production of optical coatings and multilayers. There are some intrinsic limitations for the quality of such elements, i.e. position of source, target and substrate. Holographic techniques are an alternative to “classical” optical elements fabrication. We compare different methods for analysis of the optical response of large “classical” and holographic elements (Abélès characteristic matrix and Lorenz – Mie theory) as well as some possible applications, related to solar concentrators and holographic Fabry – Perrot elements.

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5. Optoelectronic properties of spray deposited SnO2:F thin films for window materials in solar cells

E. Elangovan, K. Ramamurthi

Spray pyrolysis technique has been employed to prepare ~1.2 µm thick pure and fluorine doped tin oxide films from SnCl2 precursor. The electrical and optical studies on the as prepared films were carried out. The sheet resistance was found to decrease with increasing doping concentration to a minimum of 1.75 W/ÿ for 15 wt. % of NH4F, but increased thereafter. The minimum sheet resistance observed in the present study is the lowest among the reported values for SnO2:F films prepared from SnCl2 precursor. The transmittance was found to increase with the increase in fluorine concentration. The highest optical transmittance obtained is 85 % (at 800 nm). The calculated reflectivity in the infrared region is in the range of 94 - 98 % (for 5-30 wt% NH4F). On fluorine doping, the figure of merit values of the tin oxide films were found to increase to a maximum of 5.67 ´ 10-2 (15 wt. % of NH4F) from 4.73´10-6 (at 800 nm) for undoped ones. The obtained values of figure of merit and reflectivity are discussed in the context of the suitability of this material for transparent and conducting window materials in heterojunction thin film solar cells.

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6. Effect of temperature annealing on periodically poled rare-earth  doped lithium niobate crystal

 V. Bermúdez, D. Callejo, E. Diéguez

Rare earth doped Periodic Poled Lithium Niobate crystals prepared by the off-centered Czochralski growth technique have been submitted to several annealing proceses either at T>Tc as T<Tc. It is shown that an annealing process at T>Tc eliminates the periodic domain structure in the surface but not in the bulk crystal, where the periodic structure is not damaged for a low cooling rate, while it is strongly damaged for a quenching process. When the annealing process is performed at temperatures very close to the Curie temperature but below, the periodic domain structures do not disappear even from the surface, but they are strongly damaged when temperature is cooled down following a quenching procedure. When temperature is reduced following a low cooling rate process the surface domain structure is not affected.  

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7. Periodically poled structures in lithium niobate crystals: growth and photoelectric properties

 I. A. Ghambaryan, R. Guo, R. K. Hovsepyan, A. R. Poghosyan, E. S. Vardanyan, V. G. Lazaryan

The advantages of producing a periodically poled lithium niobate (PPLN) structure during crystal growth process are the possibility to get thicker and wider structures that leads to greater useful surfaces in addition to the elimination of the subsequent poling process.  We report in this paper a new technology of creating bulk periodically poled LiNbO3 single crystals with antiparallel ferroelectric domains, by direct electric field poling during growth processes. Growth system configuration, crystal composition and geometry selection are explored to allow successful control of the direction of spontaneous polarisation using external electric field. PPLN crystal samples with periodicity 10 - 200 mm were grown using this electric field modulated growth technique. The photoelectric and photorefractive properties of PPLN crystals were investigated.  

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8. Some optical properties of BaO - PbO - B2O3 glasses

J. Schwarz, H. Tichá

Glasses from the system PbO-BaO-B2O3 with the value of the molar ratio R (= PbO/B2O3) in the interval 0.125 £ R £ 2.0, were prepared. The hydrostatic density, the softening temperature, Raman and infrared reflectivity spectra and transmittivity in the UV-VIS region of prepared glasses have been measured. The compositional dependence of experimental values of optical gap and refractive index were compared with the values calculated using the assumption of the additivity of the “local gaps” and Maxwell-Garnet theory, resp. The agreement is satisfactory.  It is suggested also that in the region where 0.125 £ R £ ~ 0.6 the lead atoms behave rather as a network modifier, while at higher values of R the lead atoms behave as network formers.

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9. Growth and characterisation of InGaAs(P) by CBE technique

 M. Udhayasankar, J. Kumar, P. Ramasamy

Growth and evaluation of InGaAs(P) epilayers grown on InP by CBE technique for optical telecommunication applications is discussed.  The grown InP epilayers have HALL mobility values of 70.000 and 2800 cm2/V.s with background impurities as low as 1 ´ 1014  cm-3 and       2 ´ 1015 cm-3 at 77 K and 300 K respectively. FWHM of the (004) Bragg reflection peak as narrow as 17 arcsec was obtained for these samples by HRXRD measurements. RT PL measurements also show typical spectra with a peak FWHM of about 19 nm. Lattice matched In0.53Ga0.47As was grown on InP and the strain value of 0.34 µm thick layers was about 6.7 ´ 10-4. The mobilities of the thick undoped ternary layer were 5970 (300 K) and 37,550 cm2/V.s (77 K) with carrier concentration in the range of 1.2 ´ 1015 – 4.2 ´ 1014 cm-3. Be-doped In0.53Ga0.47As layers with p300K = 9 ´ 1018 cm-3 and  µ300K = 58 cm2/V.s were also grown on InP which exhibits a line width (HRXRD) of nearly 25-30 arcsec. In1-xGaxAsyP1-y quaternary epilayers (x = 0.24, y = 0.52) closely lattice matched to InP have also been grown. The HRXRD pattern of the quaternary layers shows a lattice mismatch of 2.4 ´ 10-3 and a luminescence peak FWHM of 8 meV. Further, the homogeneity of these layers was checked using FTPL study at different positions of the full wafer and it was extremely good.  MQWs structures were also grown for the fabrication of SOA devices and are characterised by PL, absorption, ECV measurements.  

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10. Application of microtechnology in biotechnology. Microarray analytical systems – an overview

 G. De Bellis , G. Caramenti,  M. Ilie, E. Cianci, V. Foglietti

 The evolution of modern biology, that recently entered the genome era, requires faster and cheaper analytical systems. Techniques as microlithography, micromachining, laser induced fluorescence detection, microfluidics contributed to the development of the DNA microarray technology, having as result complex analytical systems able to perform hybridization of nucleic acids in an array format on small bidimensional surfaces, and also to process huge quantities of information. The most significant achievements worldwide obtained are presented illustrating the state of the art in this domain. In order to automate the fluidic process involved in the DNA hybridization three micromachining techniques, slightly differing from each other have been approached by the authors team. Reservoirs with volumes ranging from 1nl to 2 ml in different materials have been obtained by means of reactive ion etching of polyimide, anisotropic etching of silicon respectively an optimised wet etching of borosilicate glass as well as a low temperature bonding of borosilicate glass on silicon nitride.  One obtained device has been tested in a Laser Induced Fluorescence detection set-up.

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11. Numerical study of the growth conditions in a MOCVD reactor: application to the epitaxial growth of CdTe

 R. Tena-Zaera, I. Mora-Seró, C. Martinez-Tomas, V. Muñoz-Sanjosé      

A 2-D model to simulate the gas flow in a horizontal MOCVD reactor has been developed. This model takes into account the conservation equations coupled with heat transfer and mass transport of the chemical species. For the mathematical solution a commercial solver, that can be run in a conventional personal computer, has been used. The influence of different parameters such as total flow, partial pressures of precursors, reactor pressure and substrate temperature on the gas flow and growth rate has been studied. Diisopropyltelluride (DIPTe) and dimethylcadmium (DMCd) have been used as precursors and H2 as carrier gas. The capabilities of the used model for the numerical study in a conventional research or production laboratory will be shown. The main goal of this paper is both to offer a valuable tool for the numerical simulation of the MOCVD system and to suggest some practical reflections for the MOCVD experimental grower in order to facilitate the optimization process in a reduced time.

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12. Methylene - blue modified polypyrrole film electrode for optoelectronic applications

 R. M. Ion , F. Scarlat, Fl. Scarlat, V. I. R. Niculescu

Organic semiconductors have been the objects of considerable attention in recent years, both as electrodes and photoelectrods in different applications. Radiation-induced and electrochemical modification of polypyrrole film by incorporating of large electro-active organic molecules is investigated in this paper. Introduction in the polypyrrole (PPy) of methylene blue as counterion has a strong effect on the electrochemical performance of PPy films. The UV - VIS spectra of the films (fitted with Gauss type function) are also evaluated. IR spectra are measured in order to proof the incorporation of MB into polypyrrole film.

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13. The effective pair potential calculations of molten NaCl and AgI

 S. Dalgiç

In this work, we have calculated effective pair potentials for different Z values of molten NaCl and AgI. We used the Huggins-Mayer potential form parametrised by Fumi and Tosi for NaCl and the Vashishta-Rahman potential form for AgI. The interionic interactions in this last system have been modelled with the use of a semi-empirical rigid ion potential based on the functional form originally proposed by Vashishta and Rahman in 1978. The results show excellent agreement with those reported in other works.

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Short Communications

14. Grown periodically poled lithium niobate crystal: period stabilization

 N. F. Evlanova, I. I. Naumova, S. A. Blokhin, T. O. Chaplina, G. D. Laptev, A. A. Novikov


High degree of the period stabilization and homogeneity of the regular domain structure of the Nd:Mg:LiNbO3 crystals was obtained in the growth process by the Czochralski method from melt with lithium dioxide excess, in the direction along the normal to the { } close packed face.

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Proceedings of AMS Conference 2002

15. Soft Magnetic Nanocrystalline alloys

 J. M. Grenèche

During the last decade, nanocrystalline alloys have received a great interest because of their unusual structural and magnetic properties. Their soft magnetic features stimulated the fundamental research. This paper reports some general structural, microstructural and magnetic aspects of soft magnetic nanocrystalline alloys and reviews the different tools which are commonly used to characterize these alloys. The state of art in research and applications is assessed.  

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16. New ferromagnetic and functionally graded shape memory alloys

 C. M. Craciunescu, M. Wuttig

 

The paper summarizes recent advances in shape memory alloy investigation with focus on the path used to find new ferromagnetic shape memory alloys and on the improvement of micro-actuation by thermoelastic control of the phase transformation in graded shape memory alloy films. The first part of the paper describes experimental results and theoretical considerations concerning the search, fabrication and characterization of new Co-based Heusler-type ferromagnetic shape memory alloys with focus on the CoNiGa system. It is shown that CoNiGa alloys undergo a reversible thermoelastic martensitic transformation in a wide temperature range, depending on the composition and displaying a nickel-like saturation magnetization. The second part of the paper takes into consideration the case of layered and functionally graded microlayered films constructed by continuously changing the temperature during the deposition process of NiTi alloys on heated Si cantilever-type substrates. It is shown that – depending on the deposition temperature and sequence of deposition - high actuation can be achieved. The discussion takes into consideration the martensitic transformation in layers under constraints from the substrate and/or the neighboring microlayers. The best actuation can be obtained when transformation starts and develops gradually from the top microlayer. This was achieved in NiTi films deposited continuously on heating.  

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17. Spectroscopic characterisation of crystalline phases development from amorphous precursors

 S. Simon 

The development of LaAl2.03B4O10.5 (124) lanthanum aluminoborate crystalline phase from amorphous xerogels is characterised by Magic Angle Spinning Nuclear Magnetic Resonance (MASNMR), Electron Paramagnetic Resonance (EPR) and Fourier Transform Infrared (FTIR) spectroscopies. The crystallisation of amorphous xerogels takes place between 760 and 860 oC. The major changes are evidenced both in the boron and aluminium surrounding. These structural results are correlated with those obtained from 27Al and 11B MAS NMR spectra. The boron environment is changed from three-coordinated in amorphous samples to tetra-coodinated in the crystalline samples. Aluminium occurs in amorphous samples as hexa-, penta- and tetra-coordinated by oxygens while in the crystalline ones it appears preponderantly penta-coordinated. From FTIR measurements it results, also, that the local structure dramatically changes when in amorphous matrices are developed crystalline phases. Three different sites for Fe3+ ions in crystalline samples were identified by EPR measurements.

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18. MAS NMR and SEM study of local structure changes induced by heat treatment in La2B4Al2O12

 M. Vasilescu, G. Borodi, S. Simon

 Xerogels of composition La2B4Al2O12, treated between 200 and 1100°C, are investigated by magic angle spinning nuclear magnetic resonance (MAS NMR) and scanning electron microscopy (SEM). The 11B MAS NMR results indicate the presence of tetra coordinated boron in all investigated samples. For three coordinated boron, two sites were observed one of them being present only after heat treatment above 860 °C when the sample become crystalline. The mean values of the NMR parameters like chemical shift, asymmetry parameter and quadrupolar coupling constant are strongly influenced by the heat treatment temperature. SEM results are correlated with them obtained by NMR.

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19. Structural and magnetic investigations of transition metal ions in TeO2 based glasses

 I. Ardelean, S. Filip

Electron paramagnetic resonance (EPR) and magnetic susceptibility measurements are performed on xMnOm×(100-x)[70TeO2×25B2O3×5PbO] glasses with MnOm Þ Cr2O3 (0 < x £ 20 mol %), Fe2O3 (0 < x £ 20 mol %), MnO (0 < x £ 40 mol %) or  CuO (0 < x £ 40 mol %). The EPR absorption spectra due to paramagnetic ions (Cr3+, Fe3+, Mn2+ and Cu2+) in vitreous matrix revealed the structural details of the diamagnetic host, the coordination, distribution and valence states of the paramagnetic ions, the EPR parameters being sensitive to the local symmetry, the character of the chemical bonds, as well as to structural factors. EPR and magnetic susceptibility data have shown that the  magnetic ions are present in the glasses as isolated species, coupled by dipole-dipole and negative superexchange interactions. The strength of interaction that involves magnetic ions was determined as a function of concentration and the valence states of magnetic-active ions were revealed. The particular behaviour of the transition metal ions in the glassy matrix depends on the nature and concentration of the paramagnetic ions.

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20. Structural and magnetic investigations of manganase ions in 2B2O3×As2O3 glass matrix

 I. Ardelean, M. Flora

Glasses of the xMnO×(100-x)[2B2O3×As2O3] system with 0 < x £ 50 mol % were investigated by means of electron paramagnetic resonance (EPR) and magnetic susceptibility measurements,. EPR of Mn2+ ions revealed their distribution on different structural units of 2B2O3×As2O3 glass matrix doped with MnO. Distorted octahedral sites were detected. The progressive clustering of Mn2+ ions was evidenced for x ³ 5 mol %. Magnetic data revealed both 2+ and 3+ valence states for the manganese ions simultaneously present in the vitreous matrix for x > 1 mol %. The transition from isolated ions (x < 1 mol %) to those involved in dipole-dipole interactions  (x < 5 mol %) and to antiferromagnetically coupled pairs (x ³ 5 mol %) was revealed.

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21. Local structure and metal-metal interaction in some phosphate glasses

O. Cozar, I. Ardelean

The local symmetry and the interactions between metallic ions in some soda-phosphate glasses with copper, vanadium, molybdenum and tungsten ions were investigated by ESR spectroscopy. It was evidenced the presence of Cu2+, V4+, Mo5+ and W5+ ions which are used as spectroscopic ESR probes. The appearance of other valence states of these ions in the studied glasses is possible, too. The obtained ESR data suggest different local symmetry of these ions, which determine specific metal-metal interaction between them.

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22. Fast ion conduction in silver molybdenum phosphate glasses

 A. Latia, C. Vancea

Investigation of the transport phenomena in silver molybdenum phosphate glasses has revealed that the observed fast ionic transport is due to silver ions. The structure of these glasses, investigated using infrared spectra, shows that MoO3 and P2O5 are the glass formers, the role of the last one being more important as the MoO3 content decreases. The densities of the glasses, measured using the displacement method show that the addition of Ag2O to the binary MoO3-P2O5 system causes a constant increase in the density of the glasses. AC conductivity measurements of the glasses were conducted in open atmosphere from 5 Hz to 100 kHz by use of a HP 4142 impedance-meter in the temperature range of 303 - 423 K.  The glasses exhibited high ion conductivities in the range of 10-4 to 10-1 Sm-1 at room temperature. The conductivities of the glasses increase and the activation energies of the conduction process decrease with the Ag2O content. The total conductivity of the glasses was recorded using the two electrodes method. The investigated glasses have a very similar behavior in direct and alternative current, respectively, the activation energies being close. The obtained values for the transport number, very close to unity, shows that the Ag+ ions are the charge carriers in these glasses, the contribution of the electronic conductivity being negligible.

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23. Calcium influence on dissolution rates of potassium phosphate glasses

D. Cacaina, S. Simon

The dissolution behaviour of xCaO·(90-x)P2O5·10K2O glasses  with 0 £ x £ 35% mol% in decationized water, physiological serum and chlorine acid, considered as simulated biological media was investigated at room temperature, in static regime. The dissolution behaviour of the samples depends on the hydrogen concentration in solutions and on glass composition and local structure. The lowest release rate is observed for the potassium-phosphate matrix (x = 0) in decationized water. One also remarks that the dissolution rate is higher in the first four hours, then decreases up to seven hours and is again intensified in the corrosion stage from 7 to 24 hours.

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24. Transverse susceptibility of  single-domain particle systems

 A. Stancu, L. Spinu

Simulations of the Transverse Susceptibility (TS) signal for single-domain and for systems of ferromagnetic particles are presented. When calculating the TS for single domains, details are provided concerning the uniaxial and cubic anisotropies. For the uniaxial single-domain particles a 2D critical approach can be used. The TS for cubic anisotropy is essentially a 3D problem that was solved with a micromagnetic Landau-Lifsith-Gilbert algorithm. Since the TS experimental method is extensively used in the laboratories for the anisotropy evaluation, the importance of this study consists in the fact that it offers a tool for understanding the problems and errors in the correct interpretation of the TS curves.

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25. Chain-of-spheres approximation in micromagnetic modelling of magnetic recording media

 D. Cimpoesu, A. Stancu

The behavior of prolate spheroidal particles, corresponding to the acicular particles found in magnetic recording media is analyzed. Both experimental and theoretical investigations have been carried out to understand and optimize magnetic materials. A problem is the magnetization reversal mode for even the simplest system, a particle small enough consisting in a single magnetic domain.  

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26. Magnetic properties of g-Fe2O3 nanoparticles

 D. Predoi, V. Kuncser, M. Nogues, E. Tronc, J. P. Jolive, G. Filoti, G. Schinteie

The g-Fe2O3  nanoparticles with different surface states are investigated by X-ray Diffraction, Electron Microscopy, Differential Thermal Analysis and magnetic measurements in low applied field. The influence of the adsorbed species (H2O and sulphate complexes) on the inter-particle magnetic interactions is analysed in relation to both the magnetic states of the surface and the inter-particle distance.

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27. Easy axis distribution in modern nanoparticle storage media: a new methodological approach

 V. Kuncser, W. Keune, M. Vopsaroiu, P. R. Bissell, B. Sahoo, G. Filoti

 Easy axis distribution in metal particle magnetic tapes for linear digital data storage were studied by Mössbauer spectroscopy and magnetometry, for comparison. Qualitative and quantitative agreement between the distribution parameters deduced at room temperature via the two different techniques was found. The proposed methodology based on the interpretation of the Mössbauer data has the advantage that it can be applied at different temperatures and for very thin films. Moreover, angular spin distribution at low temperatures were obtained by Mössbauer spectroscopy and discussed with respect to the room temperature results. There was evidenced that the room temperature easy axis angular distribution contains both static orientation and dynamical components.

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28. Study of the interparticle magnetic interaction effect on magnetic resonance line in ferrofluids

 C. N. Marin, I. Mălăescu, V. Socoliuc

The dipolar magnetic interaction effect on magnetic resonance line in ferrofluids is analyzed. Starting from a ferrofluid with magnetite particles dispersed in kerosene and stabilized with oleic acid, three samples were obtained by successive dilution with kerosene. Magnetic resonance and light scattering measurements were performed for each sample of ferrofluid. The experimental results revealed that the resonance line has a two-line feature for all samples, the magnetic field at resonance slowly increases and the magnetic resonance linewidth decreases by dilution of the samples. In accordance with the light scattering measurements, this behaviour is interpreted as a magnetic interparticle interaction and particle agglomeration effect.  

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29. A new method for determination of the effective anisotropy constant of the particles within ferrofluids

 I. Mãlãescu

A new method for determination of the effective anisotropy constant (magnetocrystalline, shape and surface), Keff, of the colloidal particles within ferrofluids, from ferromagnetic resonance measurements and based on the theoretical values computed for the Lande factor (g) of the ferrite molecule, is described. Two ferrofluids samples (denoted F1 and F2), with magnetite particles dispersed in kerosene and stabilized with oleic acid, were used. In the proposed method only one measurement (magnetic resonance) is necessary in order to determine Keff. The Lande factor of the magnetite molecule, having the chemical formula, , was computed that the weight mean value of the Landé factors corresponding to the three ions in the tetrahedral positions (A) and in the octahedral positions (B). The values obtained in this way for Keff are compared to the ones determined from other measurements.

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30. Formation of the nanocrystalline cubic (FeNi)23B6 phase in the nickel-rich FeNiZrB alloys and its magnetic behaviour 

B. Idzikowski, A. Szajek

Nickel-rich amorphous precursor with nominal chemical composition of Ni64Fe16Zr7B12Au1 was produced by melt-spinning technique and then heat-treated at temperatures ranged from 420 to 465°C for one hour, to form nanostructure. The transformation from the amorphous state into the nanocrystalline state was investigated by DSC and XRD techniques. Due to annealing in amorphous matrix appear grain fraction (5-50 nm in diameter) of magnetically ordered cubic FexNi23-xB6 phase, as was identified by XRD measurements. The magnetic behaviour of pure Ni23B6 and Fe23B6 phases was studied theoretically using the spin polarized tight binding linear muffin-tin orbital (TB-LMTO) method. Anomalously high magnetic moments of Fe atoms were found in some nonequivalent positions in the crystal structure.  

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31. Structural relaxation in Fe70Cr10.5P11.5Mn1.5C6.5 amorphous alloy

 I. Mihalca, A. Ercuta

The changes in the Curie temperature and magnetostriction subsequent to structural relaxation by isothermally annealing amorphous ribbons of nominal composition Fe70Cr10.5P11.5Mn1.5C6.5 were examined. The alloy is low magnetostrictive in both native and relaxed states, but significant enhancement, from 0.5 ppm to 10.4 ppm, of the saturation magnetostriction coefficient was observed. The relaxation was attributed to free volumes annealing out and short range order changes, both topological and chemical. A value ~ 0.85 eV of the effective activation energy resulted from the analysis of the process kinetics.

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32. Nanocrystalline Ni-Zn ferrites prepared by sol-gel method

M. Popovici, C. Savii, D. Niznansky, J. Subrt, J. Bohacek, D. Becherescu, C. Caizer, C. Enache, C. Ionescu

Nanocrystalline Ni-Zn ferrites have been synthesized in silica matrix by sol-gel processing and thermal treatment at 1100 oC. Samples with weight fraction of 20 % Ni1-xZnxFe2O4 in silica matrix were obtained for x = 0.15, 0.35, 0.50, 0.65 and characterized by X-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM), Mössbauer spectroscopy (MS) at room temperature and vibrating sample magnetometry (VSM) measurements. The cubic spinel structure is proved both by XRD and Mössbauer spectroscopy. The ferrites embedded in the matrix have nanoparticles in the range 5-13 nm. The obtained composites, display superposed superparamagnetic and ferrimagnetic behavior, as a function of Zn/Ni ratio. Both lattice constant parameter and average hyperfine fields vary with the degree of substitution of nickel ions with zinc ones.  

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33. Preparation and magnetic properties of Ni80Fe20 nanowire arrays

 H. Chiriac, T. A. Óvári, A. E. Moga, M. Urse

Arrays of Ni80Fe20 nanowires were prepared by electrodeposition into nanosized pores of anodic alumina and polycarbonate membranes, using a two-electrode electrochemical cell. Nanoporous anodic alumina membranes were prepared in a two-step anodizing process of aluminium foils. The morphology of the samples was investigated by means of scanning electron microscopy (SEM). The structural characteristics of the samples were examined using X-ray diffraction (XRD). Magnetic measurements were performed at room temperature, using a vibrating sample magnetometer (VSM) and showed the as-made samples to be magnetically soft. The magnetization curves are reversible indicating a high saturation field and low remanence. Magnetic anisotropy along the axis of the wire is present.

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34. Non-linear behaviour of the spin transition compounds during photo-excitation and relaxation

 C. Enachescu, J. Linares, E. Codjovi, K. Boukheddaden, F. Varret

Spin-crossover solids are photo-excitable materials, which are studied for future applications as optical memories or numerical display. The spin transition is a first order phase transition produced by variations of temperature, pressure or light. Cooperative effects constitute the basic mechanism for the spin crossover transition. They induce instability in the thermodynamic competition between the two states of the spin-crossover molecules: high-spin (HS) and low spin (LS).We investigate here the photo-excitation process and the relaxation of the photo-excited state in photo-switchable solids, such as spin transitions systems  [(FexM1-x)(btr)2(NCS)2] H2O, with M=Co, Ni, Zn. We follow the competition between the relaxation and the photo-excitation processes (up and eventually down). The experimental kinetics gives evidence for a non-linear character of the relaxation at all temperatures, including the tunnelling regime, and for non-linear behaviours of the photo-excitation rates.  

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35. The quantum efficiency of the photo-excitation in a Fe (II) spin-crossover compound

C. Enachescu, U. Oetliker, A. Hauser

In this paper we discuss on the quantum efficiency in spin crossover compounds. Spin crossover solids are text-book examples of photo switchable materials that present a thermal spin transition from the diamagnetic low-spin state, thermodynamically stable at low temperatures, to the paramagnetic high-spin state becoming the thermodynamically stable state at elevated temperature. By irradiating them with an appropriate wavelength, they can pass from the stable low spin state to the metastable high spin state at temperatures below the thermal transition temperature. For the compound [Fe(pic)3]Cl2·EtOH, the question regarding the quantum efficiency of the photo-conversion process that is the number of molecules converted by one single photon and its possible dependency on irradiation intensity gave rise to a controversy. The experimental results presented in this paper demonstrate that the quantum efficiency of the photo-conversion at 11 K is on the order of unity, with no noticeable dependency of the quantum efficiency on light intensity. It does, however, depend to a small extent on the fraction of complexes already converted to the high-spin state.  

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36. Stress and temperature effect on the FMR response of nearly zero magnetostrictive amorphous microwires

 F. M. Tufescu, T. A. Óvári, H. Chiriac, A. Stancu

Results on the ferromagnetic resonance (FMR) investigation of the effect of applied tensile stresses and different temperatures during measurements on the surface magnetic anisotropy of Co68.25Fe4.5Si12.25B15 amorphous glass-covered microwires are reported. Axial stresses determine a decrease of the resonance field and an increase of the absorption intensity that correspond to the resonance peak, indicating a reinforcement of the circumferential magnetoelastic anisotropy from the microwire’s surface region. An increase of the temperature during measurements up to 160 °C leads to a significant increase of the resonance field that corresponds to a decrease of the circumferential magnetoelastic anisotropy.

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37. Spin dynamics investigated by magnetic resonance in colossal magnetoresistive materials

 L. V. Giurgiu

The spin dynamics in colossal magnetoresistive manganites La2/3Ca1/3Mn1-xDixO3 (Di = Al, In;     x 0.05) has been analysed by ESR spectroscopy. The effect of the partial substitution of Mn by closed shell ions was evidenced. The temperature and x dependence of the resonance linewidth and integral intensity of the ESR signal have been investigated and disscused in terms of the bottlenecked spin relaxation and small polaron hoping models. The exchange coupling integral between Mn3+ and Mn4+ ions shows a decrease with increasing x due to the weakening of the double exchange interaction upon doping. A strong variation of the polaron activation energy with the doping level was also found and discussed in terms of the Mn - O distortion and the Mn3+ content.

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38. Effects of In doping investigated by ESR in colossal magnetoresistive manganite La2/3Ca1/3MnO3

 O. Raita, M. N. Grecu, X. Filip, Al. Darabont, D. Gavre, J. Blasco, L. V. Giurgiu

The effects of the substitution for Mn with In in the colossal magnetoresistive manganites La2/3Ca1/3Mn1-xInxO3 (x £ 0.05) have been investigated by ESR. The temperature and  x dependence of the resonance linewidth have been investigated and discussed in terms of the spin–spin (exchange) interaction scenario. In the paramagnetic regime, the exchange coupling integral, J, between Mn3+and Mn4+ spins shows a decrease with increasing x. It could arise from the weakening of the double - exchange interaction upon doping, which reduces the exchange field at the Mn sites. The high temperature limit of the ESR linewidth does not depend on the doping level.

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39. Modeling the multi-crystalline SIlicon ingot solidification process in a vertical square furnace

F. Barvinschi, C. Stelian, Y. Delannoy, N. Mangelinck, T. Duffar

Large-scale production of multi-crystalline silicon for high-efficient solar cells is a very important task of today’s photovoltaic technology. The efficiency of crystalline silicon solar cells depends on both the crystallization process and the solar cell processing sequence. As far as the crystallization process is concerned, it is very important to know the temperature distribution during the solidification of silicon ingots, to predict the solidification structure obtained and thus the materials properties. In this study the transient 2D and stationary 3D numerical simulation of the solidification process of large square mc-Si ingots is investigated, by using the software FIDAP and FluentTM. Some geometrical approximations of the real furnace and specific approaches for the radiation modelling are used in order to solve the difficulties related to numerical analysis.  The results are compared to the experimental data, in order to calibrate the numerical model.  

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40. Identification of nonlinearties in anelastic polycrystalLine materials using Volterra - Fourier Transform

Gh. E. Drăgănescu, A. Ercuţa

A nonlinear rheological model built on the basis of structural properties of polycrystalline solids is presented. A Fourier - Volterra series method of model parameters identification from the experimental data is proposed.  

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41. Manganase activated (2-x)ZnO×xCdO×1.1SiO2 phosphors obtained by solid state synthesis 

C. Enache, R. Turcin, C. Savii, M. Popovici, R. M. Jurca, V. Socoliuc

The aim of the work was to study the evolution of luminescence emission properties of some Mn2+ activated phosphors in the ZnO – CdO – SiO2 system in correlation with both the cadmium oxide/zinc oxide mole ratio and the activator concentration. A number of phosphors corresponding to the mole target composition of (2-x)ZnO×xCdO×1.1SiO2:yMn, where 0 £ x £ 0.15, and y = 0.021; 0.042; 0.085, were obtained by firing the mixed powders of precursors (oxides and carbonates), at 1250 ºC or 1350 ºC temperatures, in air, for 60 minutes. Thermal analysis technique was used in order to elucidate the oxide system behaviour during thermal treatment. Structural and optical properties were investigated by X-ray diffraction and spectrofluorometry techniques All obtained samples show a green luminescence emission, as it was expected for manganese-activated willemite. The emission intensity of the synthesised phosphors seems to be influenced by host matrix composition and activator amount, as well. It was observed that, in the domain of relatively low CdO/ZnO mole ratio, regardless the activator concentration, the emission intensity is favourable influenced by CdO content, the maximum being reached for the composition 1.975ZnO×0.025CdO×1.1SiO2×0.085Mn.  

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42. Microstructural evolution and thermo-mechanical response of Ni ion irradiated TiNi SMA thin films

 T. B. Lagrange, R. Gotthardt

The present study focuses on the effect of 5 MeV Ni ion irradiation of plastically strained (e ~ 4 %) martensitic TiNi thin films, which is used as a processing technique for a novel out of plane bending actuator. Conceptually, the frustration of the martensitic transformation due to ion beam damage in a 2 mm surface layer of a 6 mm thick film will create a sharp differential latent strain on reverse transformation. This latent strain causes a two-way bending motion during cyclic heating and cooling, and in addition, this thermal actuator can be used to do useful mechanical work on both heating and cooling. To better understand the behaviour of these ion irradiated thin films, TEM observations and motion experiments were conducted.  Results are presented and discussed as they relate to the ion induced microstructure and its influence on the martensitic transformation and the shape memory effect.

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43. Computer simulation of magnetization curves in magnetic thin films

 M. Volmer, J. Neamtu

Computer simulation based on Stonner-Wolfarth model is used to investigate magnetization flop in magnetic thin films of Ni80Fe20 (Py) and magnetic multilayers with the structure Py/Cu/Py. The results of computer simulations are compared with the magnetic measurements made with a commercial Vibrating Sample Magnetometer (VSM).  

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44. Thermoionic Vacuum Arc – a new method of thin film deposition

 R. Vladoiu, G. Musa, I. Mustata

New equipment for the technology of thin film deposition using thermoionic vacuum arc is presented. Advantages of this system are underlined: extended application possibilities for the increase of the microhardness of the pieces, decrease of the friction of moving pieces, change of the chemical reactivity of the pieces (corrosion resistant components). The new technique can be used for the development of nanostructural materials.

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45. Optical and electronic properties of metal doped polymers for integrated optics

 M. Bulinski, V. Kuncser, D. Cristea, C. Plapcianu, S. Krautwald, H. Franke, F. E. Wagner, G. Filoti

The electronic mechanism responsible for the optical behavior of the mixed Fe and Sn doped polymers were studied in comparison with the correspondent single doped (Fe or Sn)  ones. Optical absorption as well as 57Fe and 119Sn Mössbauer measurements were performed on different UV exposed films. The new data provided the role of each element from the pair on the involved electronic mechanism induced by irradiation.

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46. Strontium-doped LaCoO3 perovskites in solid oxide fuel cells 

V. V. Srdic, L. Nikolic, V. Pejovic

Cathode-electrolyte structures, for solid oxide fuel cells, are prepared by deposition of porous (La,Sr)CoO3 film on the surface of dense nanocrystalline 3 mol% Y2O3 stabilized zirconia electrolyte. The perovskite powder is prepared by a wet-chemical synthesis technique using metal-nitrates, mixed with a resin and organic solvents to form a paste that is deposited as a thick film by screen-printing technique. The characteristics of the synthesized powders, sintered samples and cathode-electrolyte structures are investigated.

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47. Synthesis of LiMn2O4 by glycine-nitrate method

 D. Jugović, N. Cvjetićanin, V. Kusigerski, S. Mentus

Glycine-nitrate method was used to synthesize lithium manganese oxides. For the molar ratio of lithium-to-manganese in precursor solution equal to 1:2 spinel LiMn2O4 was obtained. For molar ratio of 1:1 a mixture of Li2MnO3 and spinel phase different from LiMn2O4 was observed.

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48. Conduction electron spin resonance of Pt-nanoparticles in porous Al2O3 membranes

 D. Gavre, G. Mihailescu, O. Raita, E. Indrea, S. Pruneanu, J. Rahmer, L. V. Giurgiu

An electron spin resonance (ESR) investigation of Pt-nanoparticles electrodeposited in the channels of porous Al2O3 membranes has been performed in the temperature range 6 – 50 K. Pt – particle mean size was evaluated by means of Kawabata theory that relates ESR linewidth to metal particle size. A comparison with the effective crystallite mean size obtained from the X – ray diffraction analysis is given.

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49. Identification of the generalised preisach  model parameters for systems with magnetostatic interactions

 M. Cerchez, L. Stoleriu, Al. Stancu

This paper presents the testing of a recently developed Preisach identification algorithm. The algorithm uses the properties of the Integral Generalized DM plot that is very sensitive to interactions and thus produces a more accurate choice of parameters. The parameters obtained in the identification produce simulations that fit first and second order magnetization processes with reasonable precision.  For some of the metal particle recording media studied with negative DM curves, a good fit can only be obtained using negative mean field interactions. This is different from most acicular systems where a positive mean term is usually required.

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50. A Preisach-Néel model with thermal variable variance: sensibility to the parameters

I. D. Borcia, L. Spinu, Al. Stancu

We performed simulations of magnetization curves in field, remnant and also with variable temperature. The simulations were done using a Preisach-Néel model for nanoparticulate media. The model includes the reversible and the irreversible part of the magnetization. There are taken into account the variations of the Preisach distribution due to the mean field and to the thermals effects as well as the movements of the thermal boundary in processes with variable field and temperature. Because the identification problem is a very important point in our simulations, the study of the model sensibility to the parameters can allow for choosing a better identification procedure.

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51. Bar-configuration in Hall measurements with GaAs

 R. V. Ghita, C. Logofatu, C. Negrila, M. F. Lazarescu, A. S. Manea, V. Ciupina

The electrical and transport properties of GaAs crystals such as resistivity (r), mobility (m) and carrier concentration (n) depend on the purity and defects of a particular crystal. These parameters are normally obtained by performing a simple Hall effect analysis in a bar configuration.  The technical procedure is connected with the design of appropriate contacts for Hall bar configuration. In order to ensure good ohmic contacts on GaAs, thin metal layers of Au-Ge-Ni have been deposited in high vacuum followed by heat treatment in low vacuum. Hall effect measurement is important for checking the quality of the GaAs wafers. We analyzed various GaAs wafers with (100) and (110), orientation obtained by LEC and HB methods. The resistivity of the wafers varied from low resistivity, n-type doped crystals (n = 1018 cm-3), to high resistivity crystals (n = 1014 cm-3). This paper presents the data of Hall characterization of wafers cut from GaAs crystals grown by different methods (LEC, HB).

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