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Dive into the research topics where Jovica Ivkov is active.

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Featured researches published by Jovica Ivkov.


Solid State Communications | 1978

Low temperature resistivities of FexNi80-xP14B6 metallic glasses

E. Babić; Ž. Marohnić; Jovica Ivkov

Abstract The resistivities of six FexNi80-xP14B6 alloys have been measured between 1.5 and 50 K. It is found that the resistivity variations both below and above the resistivity minima depend on the transition metal composition. The room temperature coefficients of the resistivity indicate the existence of the magnetic contribution to the resistivity.


Thin Solid Films | 1998

Preparation and structure of AlW thin films

Nikola Radić; Antun Tonejc; Milorad Milun; Petar Pervan; Jovica Ivkov; Mirko Stubičar

Abstract Thin films of AlW alloys were prepared by co-deposition of pure aluminum and pure tungsten, each sputtered by an independently controlled magnetron source. The deposition rate at the substrate (glass, fused quartz, and alumina ceramic), positioned 5 cm away from the target surface was 0.1–0.2 nm/s for pure metals, and the final film thickness was a few μ m. Completely amorphous films were obtained in the Al 80 W 20 –Al 67 W 33 composition range. At higher tungsten content, the W(Al) solid solution and pure tungsten phases appeared. The amorphous alloys exhibit a high negative temperature coefficient of the electric resistivity, increasing with the aluminum content up to −5.5·10 −4 K −1 . Finally, the amorphous AlW alloys exhibit a remarkable microhardness (6–7 GPa), and are structurally stable up to at least 400°C.


Journal of Physics: Condensed Matter | 2012

PdGa intermetallic hydrogenation catalyst: an NMR and physical property study

M. Klanjšek; A. Gradišek; A. Kocjan; M. Bobnar; P. Jeglič; Magdalena Wencka; Zvonko Jagličić; Petar Popčević; Jovica Ivkov; Ana Smontara; Peter Gille; Marc Armbrüster; Yuri Grin; J. Dolinšek

The PdGa intermetallic compound is a highly selective and stable heterogeneous hydrogenation catalyst for the semi-hydrogenation of acetylene. We have studied single crystals of PdGa grown by the Czochralski technique. The (69)Ga electric-field-gradient (EFG) tensor was determined by means of NMR spectroscopy, giving experimental confirmation of both the recently refined structural model of PdGa and the theoretically predicted Pd-Ga covalent bonding scheme. The hydrogenation experiment has detected no hydrogen uptake in the PdGa, thus preventing in situ hydride formation that leads to a reduction of the catalytic selectivity. We have also determined bulk physical properties (the magnetic susceptibility, the electrical resistivity, the thermoelectric power, the Hall coefficient, the thermal conductivity and the specific heat) of single-crystalline PdGa. The results show that PdGa is a diamagnet with metallic electrical resistivity and moderately high thermal conductivity. The thermoelectric power is negative with complicated temperature dependence, whereas the Hall coefficient is positive and temperature-dependent, indicating complexity of the Fermi surface. Partial fulfillment of the NMR Korringa relation reveals that the charge carriers are weakly correlated. Specific heat measurements show that the density of electronic states (DOS) at the Fermi energy of PdGa is reduced to 15% of the DOS of the elemental Pd metal.


Journal of Physics: Condensed Matter | 1990

On the origin of the positive Hall coefficient in disordered TE-TL alloys

Jovica Ivkov; E. Babić

The authors have collected and analysed the available data for the Hall effect and its dependence upon temperature in amorphous Zr-Co, Zr-Ni, Zr-Cu and Ti-Cu alloys. The differences between the measured Hall coefficients, Rh, and the suggested free electron values, R0, have very similar dependences on the number of electrons in the early transition (TE) metal d band. At temperatures higher than those at which quantum corrections are important, RH-R0 is either constant (within the experimental error) or decreases slowly with the increasing temperature as the resistivity does. These observations are consistent with the proposition that in these alloys the positive Hall coefficient is due to the spin-orbit effect.


Journal of Non-crystalline Solids | 2003

Structural relaxation of Al–W amorphous thin films

Jovica Ivkov; Nikola Radić; Antun Tonejc; Tihomir Car

Abstract The pronounced variation of the electrical resistivity of the amorphous Al–W thin films observed during initial heating above room temperature was examined. Both isochronal and isothermal treatments were performed in order to investigate the effects of the film composition, substrate material, and substrate temperature, on the magnitude of the relaxation phenomena. Regarding the isochronal heating, it was observed that the relaxation effects decreased with an increase of the heating rate, and decreased with the aluminum content in the film. The Al 78 W 22 amorphous thin films were subjected to isothermal annealing for 6 h at a temperature of 515 °C. The effects of the substrate material (alumina ceramic, glass and sapphire), and the deposition temperature (LNT, RT, 200 and 400 °C) were examined. The relaxation decreased in a sequence of: alumina ceramic–glass–sapphire substrates, as well as with an increase of the substrate temperature. An assumed dominant role of the aluminum in the effects observed, was tested by the corresponding investigation of Al–Ti and Cu–Ti amorphous thin films.


Journal of Physics: Condensed Matter | 1989

The Hall effect and the electrical resistivity in amorphous Ni-B-Si alloys

Jovica Ivkov; E. Babić; H H Liebermann

The values for the normal Hall coefficient, R0, electrical resistivity, rho , and the room-temperature coefficient of resistivity, alpha , for ten amorphous Ni-B-Si alloys, with metalloid concentration ranging from 20 to 39 at.% are reported. R0 and alpha continuously decrease with increasing metalloid content, or for the fixed metalloid content, with increasing silicon concentration; and alpha changes sign for rho >or=140 mu Omega cm. The value of the Fermi wavevector deduced from R0 (within the framework of the free-electron model) and its dependence on the composition of the alloy indicate that the transport properties of our alloys can be interpreted in terms of the Ziman-Faber theory. An alternative description of the variation of R0 is also discussed.


Physica C-superconductivity and Its Applications | 1994

Flux pinning in Ag-clad Bi-2223 tapes containing different fractions of Bi2212 phase

Ivica Kušević; E. Babić; Ž. Marohnić; Jovica Ivkov; Shi Xue Dou

Abstract Magnetoresistance, V-I curves and ac susceptibility of well-characterized Ag-clad (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O 10+y (Bi2223) tapes containing different Bi2212 contents (2–25%) have been measured (T) range 60–110K and magnetic fields B≤1T. The transport critical current densities J c (77K,0T) ranged up to 29000A/cm 2 whereas those deduced from ac susceptibility (J s ) were up to 39000A/cm 2 . For T≥76K J c and J s of all tapes show (1−T/T c ) n and initial B -0.5 variations with T and B respectively. Since the exponent n and the suppression of J c with B increase with increasing Bi2212 content, this phase deteriorates the performance of tapes. The pinning potentials (U) corroborate the above conclusion. Since U 0 (B≤1T) are larger then those of Bi2223 epitaxial films, a low fraction of a well-connected material limits J c in tapes.


Solid State Communications | 1994

FLUX PINNING IN AG-CLAD (BI,PB)2SR2CA2CU3O10+Y TAPE

Ivica Kušević; E. Babić; Jovica Ivkov; Ž. Marohnić; Hua-Kun Liu; Q.Y. Hu; Shi Xue Dou

Abstract The resistance of a well-characterized Ag-clad (Bi,Pb)2Sr2Ca2Cu3O10+y (hereafter Bi2223) tape containing about 2% of Bi2212 phase has been measured in the temperature (T) range 77–120K and magnetic field (B) up to 1T. The measurements were performed on two sections of the same tape showing very different critical current densities (Jct(77K,0T)=6 100 (SA) and 23 000 A/cm2 (SB), respectively as well as on a bare core of sample SB. All resistances showed an initial exp(-U(T,B)/kBT) variation enabling the determination of the pinning potential U(T,B). The values of U0(B)≡U(T→0,B) were nearly the same for all samples and showed rather modest anisotropy for B⊥c and B∥c consistent with the imperfect grain alignment in the studied tape. Since U0(B) of the tape is larger than those of the best Bi2212 and Bi2223 epitaxial films the intragranular flux pinning is not limiting Jc of Bi2223 tapes in low fields.


Journal of Physics: Condensed Matter | 1990

The hall effect and the conduction electron density in Ni-based amorphous alloys

Jovica Ivkov; E. Babić; H H Liebermann

New results for the normal Hall coefficient R0, the resistivity and the room-temperature coefficient of resistivity of five Ni-Bi-Si and six Ni-P amorphous (melt-quenched) alloys are reported. From these results, and results already reported, the authors have obtained rather detailed information on the variation in the conduction electron density with the metalloid concentration cm in the amorphous Ni-B-Si alloys. The results for the alloys with low cm extrapolate to those of liquid Ni, whereas the variation in the Fermi wavevector (deduced from R0) with cm supports the applicability of the Ziman-Faber theory for the explanation of the transport properties of these alloys. The contribution of the metalloid atoms to the conduction band is found to change at cm approximately=0.3, which is probably related to filling of the d band. This change occurs in the range of cm in which a significant change in the chemical short-range order has been observed. Although less detailed, the results for the Ni-P alloys follow the same trend as those for Ni-B-Si alloys and do not indicate any dramatic change in R0 at around cm approximately=0.24 as reported for electrodeposited Ni-P alloys.


Journal of Magnetism and Magnetic Materials | 1984

Critical behaviour of an amorphous ferromagnet close to the percolation threshold

E. Babić; Krešo Zadro; Z̆. Marohnić; Đuro Drobac; Jovica Ivkov

Abstract A detailed study of the magnetisation, electrical resistivity and ac magnetic susceptibility of the amorphous Fe 3 Ni 77 B 18 Si 2 alloy has been performed. This alloy is ferromagnetic with the Curie temperature T c = 19,5 K . Critical exponents δ = 4,9 and α = −0,51 were obtained from the experiment while γ = 1,66 and β = 0,43 were calculated from the scaling relations. However the effective critical exponent γ ∗ deduced from the initial magnetic susceptibility exhibits a non-monotonic variation with temperature reaching a maximum of about 1.8 around 43 K. The results are discussed in terms of recent theoretical predictions.

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Petar Popčević

Vienna University of Technology

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J. Dolinšek

University of Ljubljana

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Denis Stanić

Josip Juraj Strossmayer University of Osijek

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Ana Smontara

Joseph Fourier University

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Ana Smontara

Joseph Fourier University

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M. Feuerbacher

Forschungszentrum Jülich

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