LABORATORY
LOW TEMPERATURE PHYSICS

HEAD: Prof. Nikolay Tonchev, Ph.D., Dr.Sc.
tel: 7144-276 or 677; e-mail: tonchev@issp.bas.bg

TOTAL STAFF: 20
RESEARCH SCIENTISTS: 17
Prof. V.Kovachev, Ph.D., D.Sc.
Assoc. Prof. V.Lovchinov, Ph.D.
Assoc. Prof. M.Bushev, Ph.D.
Assoc. Prof. E.Vlakhov, Ph.D.
Assoc. Prof. B.Terziiska, Ph.D.
Assoc. Prof. D.Dimitrov, Ph.D.
Assoc. Prof. K.Kalaydjiev, Ph.D.
Assoc. Prof. N.Balchev, PhD
Assoc. Prof. E Nazarova, Ph.D.
Assist. Prof. K.Nenkov
Assist. Prof. N.Todorov
Assist. Prof. Chr.Popov
Assist. Prof. M.Kirov
Assist. Prof. M.Baychev
Assist. Prof. A.Stoianova-Ivanova
K.Zalamova, Ph.D.student
G.Mihova, chemist
P.Simeonova, chemist
K.Lovchinov, technologist


RESEARCH ACTIVITIES:

1. SUPERCONDUCTING AND NEW MATERIALS

    ÌgB2 superconductor with critical temperature Òñ = 39.6 K obtained by two different methods were investigated. The series differ in the superconducting phase quantity and superconducting grain size. This reflects in the width of the superconducting transition.
    AC magnetic susceptibility and transport properties of bulk HTSC samples were investigated. The effect of hole doping on the transport and magnetic properties of Ca substituted YBCO bulk samples Y1-xCaxBa2Cu3Oz (0≤x≤0.4) has been investigated. The existence of bulk pinning (established by measurements of third harmonics of ac magnetic susceptibilities) and increasing of critical current density is found for x=0.3 Ca substitution.
    Ag -sheated Y0.7Ca0.3Ba2Cu3O7-δ superconducting tapes has been obtained by OPIT technology. The influence of temperature and deformation treatment on the Tc and Jc of the tapes was investigated.
    Single phase samples of nominal composition Pr0.5Sr0.5Mn0.5Cu0.5O3 and Pr0.5Sr0.5Mn0.5Ru0.5O3 were synthesed and their magnetic and transport properties studied at low temperatures for the first time.
    Application problems of high-current superconducting materials and AC losses of super-conducting accelerator magnets were apprehensively discussed.
    Low Temperature (4,2-300K) thermal properties of a ternary GeXAs40-XS60 (x=4-38) system were studied. The found peculiarities, proved to be controlled by the compositions of these very perspective for optoelectronic chalcogenide glasses, were related to- and correlated with the results by the structural study as: the basic structural units, the percolative 2D-3D phase transition at x= 27 and a Boson peak in a Raman spectra, an indication for the increased vibrational density of states within 2-10 K.

2. MAGNETIC AND TRANSPORT PROPERTIES OF MANGANITES

    The transport of spin polarized current via the double-exchange mechanism makes manganite perovskites perspectively for application in spin electronics especially as thin films. Magnetron sputtered thin films of La0.7Sr0.3MnO3 and La0.7Ñà0.3MnO3 were systematicaly investigated and optimized in order to be included in tunnel junctions and heterostructures.
    Structural and magnetotransport properties of single crystal samples of Pr0.7Sr0.28Pb0.02MnO3 and Pr0.5Sr0.05Pb0.45MnO3 were characterized in wide temperature region. Measurements of DC magnetization, AC susceptibility and Hall effect of Pr0.7Sr0.3MnO3 single crystal were reported. The various features were discussed in terms of competing electronic and spin ordering phase transitions, in particular concerning the eg and teg competition and its effect on spin ordering.

3.THE PROBABILISTIC APPROACH OF DYNAMIC SYSTEMS AND INTERPRETATION OF RELATIVISTIC QUANTUM MECHANICS

    The work concerning the development of interpretation of the relativistic quantum mechanics has continued. This theory is based on the assumption of existence of non-zero size ~ h / mc of elementary particles (electrons, etc).

4. ENVIROMENTAL AND ECOLOGY RESEARCH

    In the frame of ecology foundation " Human, Ecology, Universe" a scientific programme on ecometric estimation and monitoring of river water ( Kavala region, North Greece; Rivers Sahle, Unstrut and Ilm located in Germany ) has been succesively completed.


PUBLICATIONS:
  1. E.S.Vlakhov, T.I.Donchev, A.Y.Spasov, K.Doerr, K.A.Nenkov, A.Handstein, S.Pignard, H.Vincent, Structure and magnetotransport properties of magnetron sputtered La0.7Sr0.3MnO3 thin films, Vacuum 69 (2003) 255 -259.
  2. E.S.Vlakhov, K.A.Nenkov, T.I Donchev, A.Y.Spasov, Influence of Misfit stress on Structure and Magnetoresistive Properties of Magnetron Sputtered La0.7Sr0.3MnO3 Thin Films on LaAlO3 (100) Substrate, Vacuum 69 (2003) 249 -254.
  3. E.S.Vlakhov, E.Wieser, K.A.Nenkov, R.Groetzschel, Effect of Fe and Ni - Ion Implantation on Magnetoresistance of La0.7Sr0.3MnO3 Thin Films, Physica Status Solidi (a) 196 No1, 125 -128 (2003).
  4. W.Haessler, C.Rodig, C.Fischer, B.Holzapfel, O.Perner, J.Eckert, K.Nenkov, G.Fuchs, Low temerature preparation of MgB2 tapes using mechanically alloyed powder, Superconductor Science and Technology 16 (2003) Nr. 2, S. 281-284.
  5. Z.Drzazga, G.Fuchs, A.Handstein, K.Nenkov, K.-H.Mueller, The interplay of magnetic order and superconductivity in GdxY1-xNi2B2C, Physica C 383 (2003) Nr. 4, S. 421-430.
  6. M.Kalvius, D.R Noakes, R Waeppling, E.Schreier, N.Marcano, U.K.Roessler, K.Nenkov, K.-H.Mueller, B.Idzikowski, Spin dynamics in granular CoxCu1-x by MySR, Physica B 326 (2003) Nr. 1-4, S. 489-493.
  7. M.Sahana, A.Venimadhav, M.S.Hegde, K.Nenkov, U.K.Roessler, K.Doerr, K.-H.Mueller, Magnetic properties and specific heat of LaMn1-xTixO3+delta(0<x≤0.2), Journal of Magnetism and Magnetic Materials 260 (2003), S. 361-370
  8. N.V.Tristan, K.Nenkov, T.Palewski, K.P.Skokov, S.A.Nikitin, Specific heat of the R3Co (R=heavy rare earth or Y) compounds, Physica Status Solidi (a) 196 (2003) Nr. 1, S. 325-328
  9. N.V.Tristan, S.A.Nikitin, T.Palewski, K.Nenkov, K.Skokov, Specific heat of the Gd3Co and Gd3Ni compounds, Journal of Magnetism and Magnetic Materials 258-259 (2003), S. 583-585
  10. T.Palewski, N.V.Tristan, K.Nenkov, K.Skokov, S.A.Nikitin, Magnetization and specific heat of the Ho3Co compound, J. of Magnetism and Magnetic Materials 258 (2003), S. 561-563
  11. N.Balchev, K.Nenkov, B.Kunev, J Pirov, A.Souleva, Synthesis and Phase Composition of FeSr2YCu2Oz, Journal of Superconductivity: Incorporating Novel Magnetism 16 (2003) Nr. 3, S. 513-516.
  12. G.Fuchs, S.-L.Drechsler, K.H.Mueller, A.Handstein, S.V.Shulga, G.Behr, A.Gumbel, J.Eckert, K.Nenkov, V.N.Narozhnyi, L.Schultz, H.Eschrig, S.Otani, H.Rosner, W.E.Pickett, A comparative study of MgB2 and other diborides, Journal of Low Temperature Physics 131 (2003) Nr. 5-6, S. 1159-1163.
  13. D.Lipp, S.-L.Drechsler, J.Freudenberger, G.Fuchs, K.Nenkov, K.-H.Mueller, M.Schneider, A.Gladun, Specific heat in the mixed state of non-magnetic borocarbides, Physica C 388-389 (2003), S. 183-184
  14. H.Rosner, M.D.Johannes, W.E.Pickett, G.Fuchs, A.Waelte, S.-L.Drechsler, S.V.Shulga, K.-H.Mueller, A.Handstein, K.Nenkov, J.Freudenberger, L.Schultz, Superconductivity and electronic structure in MgCNi3, Physica C 388-389 (2003), S. 563-564.
  15. A.Guembel, O.Perner, J.Eckert, G.Fuchs, K.Nenkov, K.-H.Mueller, L.Schultz, High density nanocrystalline MgB2 bulk superconductors with improved pinning, IEEE Transactions on Applied Superconductivity 13 (2003) Nr. 2, S. 3064-3067.
  16. Tristan, T.Palewski, K.Nenkov, K.P.Skokov, S.A.Nikitin, Magnetic properties and specific heat of the Dy3Ni intermetallic compound, Journal of Physics- Condensed Matter 15 (2003) Nr. 35, S. 5997-6004
  17. C.Fischer, C.Rodig, W.Haessler, O.Perner, J.Eckert, K.Nenkov, G.Fuchs, H.Wendrock, B.Holzapfel, L. Schultz, Preparation of MgB2 tapes using a nanocrystalline partially reacted precursor, Applied Physics Letters 83 (2003) Nr. 9, S. 1803-1805.
  18. L.Shlyk, G.Krabbes, G.Fuchs, K.Nenkov, P.Verges, Melt-textured YBa2Cu3O7 based material doped with Li: high trapped fields and pinning, Physica C 392-396 (2003) Nr. 1, S. 540-544
  19. T.Hopfinger, R.Viznichenko, G.Krabbes, G.Fuchs, K.Nenkov, Joining of multi-seeded YBCO melt-textured samples using YBCO/Ag composites as welding material, Physica C 398 (2003), S. 95-106
  20. D.Dimitrov, L.Vassilev, V.Lovchinov, M.Gospodinov, S.Dobreva, Hall effect investigations of Pr0.7Sr0.3MnO3 compound, Proc. 12 ISCMP, Varna 2002, Eds. J. M.Marshall, A. G.Petrov, A.Vavrek, D.Nesheva, D.Dimova-Malinovska, J.M.Maud, J. of Matt. Sci.: Matter. In Electronics, v.14, (2003) p.765-766.
  21. V.D.Parvanova, S.K.Andreev, D.A.Dimitrov, Microwave properties of ceramic compositions M2+Ti4+1-xMe4+O3, Proc. 12 ISCMP, Varna 2002, Eds. J.M.Marshall, A.G.Petrov, A.Vavrek, D.Nesheva, D.Dimova-Malinovska, J.M.Maud, J. of Matt. Sci.: Matter. In Electronics,v.14, (2003).
  22. Z.Milosavlevski, V.Micevski, V.Lovchinov, S.Stoimenov, D.Dimitrov., The superconductive properties of multilayered tapes (BiPb)2Sr2Ca2Cu3O10+x prepared by cold pressing method., Fifth General Conference of the Balkan Physical Union (BPU-5), August 25-29, 2003, Vrnjacka Banja, Serbia and Montenegro, Section 6: Cond. Matter. Physics, p. 759-762.
  23. I.Stanimirova, P.Simeonova, V.Simeonov, Assessment of Atmospheric Pollution in the Industrial Region of Devnia, Bulgaria, Chem. Eng. Ecol., v.10, 5 (2003) p.381-388.
  24. P.Simeonova, V.Simeonov, G.Andreev, Environmetrical Analysis of the Struma River Water Quality, Central European J. Chem., v.2 (2003) 121-136.
  25. M.Bushev. Science at culturological Crossroads. "Divinatio" v.18 (2003) 87.
  26. K.Kalaydjiev, M.Gospodinov, S.V.Dobreva, M.Kirov, M.Baychev, Chr.Popov, M.Bushev, Growth of Pr0.7Sr0.28Pb0.02MnO3 single crystals and determination of the phase transition temperature, J. of Matt. Sci.: Matter. In Electronics, v.14, (2003) 763 - 764.
  27. K.Kalaydjiev, M.Gospodinov, M.Kirov, M.Baychev, Chr.Popov, Electrical Resistance of Pr0.5Sr0.05Pb0.45MnO3 Single Crystals in Ferromagnetic and Paramagnetic State, J.of Phys. Studies, 7, ¹1 (2003) 98 - 100.
  28. V.Kovachev, Application problems of high-current superconducting materials, J. of Matt. Sci.: Matter. In Electronics, 14 (2003) 665-669.
  29. V.Kovachev, AC losses of superconducting accelerator magnets, Mod. Phys. Lett. B, v.17, N5&6 (2003) 175-198.

ONGOING RESEARCH PROJECTS:
  1. Joint Research Project between BAS and Forschungszentrum Rossendorf e.V., (FZR), Institute of Ion Beam Physics and Materials Research, No6 "Tailoring of Magnetotransport Properties of Thin and Ultra-Thin La0.7Sr0.3MnO3 Layers Employing Nondestructive Structural Characterisation and Ion Implantation.
  2. Obtaining and investigations of high temperature superconductors, Ss"Cyril and Methodius" University, Skopje, Makedonia.
  3. Mounting the experimental set-up for thermal diffusivity measurements of thin samples at low temperature and high magnetic fields, ILHMFLT, Wroclaw, Poland.
  4. Tailoring of manganite thin films structures, Joint Research Project between BAS (ISSP-Sofia, Bulgaria) and PAS (IP- Warsaw, Poland).
  5. Thermal Properties of HTSC Tapes for Practical Applications, Universite de Liege, Institute d'Electricite - SUPRATECS, Liege, Belgium.
  6. Low temperatures' investigations of electrical and thermal properties of HTSC and new materials, Joint Research Project between BAS (ISSP-Sofia, Bulgaria) and PAS (ILTSR- Wroclaw, Poland).

INTERNATIONAL COLLABORATION:
  1. Universite de Liege, Institute d'Electricite - SUPRATECS, Liege, Belgium.
  2. Forschungszentrum Rossendorf e.V., (FZR), Institute of Ion Beam Physics and Materials Research, Germany.
  3. Institute of Low Temperatures and Structural Research (ILTSR), Polish Academy of Sciences, Wroclaw, Poland.
  4. Institute of Physics, Polish Academy of Sciences, Warshaw, Poland.
  5. International Laboratory for High Magnetic Fields and Low Temperatures - Wroclaw, Poland.
  6. Ss "Cyril and Methodius" University, Skopje, Makedonia.

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