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Dive into the research topics where T. Holubar is active.

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Featured researches published by T. Holubar.


Physica C-superconductivity and Its Applications | 1994

Superconductivity in Y-Ni-B base compounds

N.M. Hong; H. Michor; M. Vybornov; T. Holubar; P. Hundegger; W. Perthold; G. Hilscher; P. Rogl

Carbon introduced in Y-Ni-B ternary alloy material was shown to stabilise aquaternary compound YNi2B2C which is also responsible for the appearance of superconductivity in Y-Ni-B alloys YNi4−xB1+x. Rietveld refinement of a nearly single-phase material of YNi2B2C confirmed isotypism with the filled ThCr2Si2-type (zB=0.353(1)). Magnetic and specific heat measurements indicate type-II superconductivity in YNi2B2C with a Tc-onset of 15.2 K and a normalised specific heat discontinuity ΔC/γTc=1.57. We present a first estimate of the upper critical field μ0Hc2(0)=3.7 T, the coherence length ξGL=9.4 nm and the Ginzburg-Landau parameter κ=10.5 of this new compound.


Physica B-condensed Matter | 1995

Superconductivity and magnetism in quaternary borocarbides

G. Hilscher; H. Michor; N.M. Hong; T. Holubar; W. Perthold; M. Vybornov; P. Rogl

Abstract We present a status report of the new rare earth transition metal borocarbides and discuss in particular the magnetic properties, results of heat capacity measurements in connection with pressure experiments together with band structure calculations and properties of the superconducting state.


Physica C-superconductivity and Its Applications | 1994

Rare-earth magnetism and superconductivity in RBaSrCu3O7-x (R=Gd, Pr)

G. Hilscher; T. Holubar; G. Schaudy; J. Dumschat; M. Strecker; G. Wortmann; X.Z. Wang; B. Hellebrand; D. Bäuerle

Abstract We present specific-heat, susceptibility, X-ray absorption (EXAFS and XANES) and 155 Gd Mossbauer experiments of RBaSrCu 3 O 7−δ ( R = Gd , Pr ) in order to examine the effect of isoelectronic substitution of Ba by Sr upon superconductivity and magnetism with respect to the parent reference compounds RBaSrCu 3 O 7−δ . The RBaSrCu 3 O 7−δ compounds offer the possibility to vary the oxygen content without changing the long-range tetragonal structure. From 155 Gd Mossbauer spectroscopy a small local orthorhombic distortion is observed for tetragonal GdBaSrCu 3 O 7 with a superconducting transition at 69 K. The XANES spectra of PrBaSrCu 3 O 7−δ indicate that Pr is mainly trivalent with a considerable extent of hybridization, in agreement with a recent description of the specific-heat and susceptibility data in terms of Pr 3+ crystal-field effects. From the comparison of the isoelectronic Ba/Sr substitution with hole doping (oxygen removal or huydrogen absorption) we deduce that the hybridization of the Pr 4f states with the Cu-O valence bands appears to be important for the suppression of superconductivity and the high antiferromagnetic ordering temperature in these Pr compounds.


Journal of Magnetism and Magnetic Materials | 1992

Heat capacity of Sm2CuO4 and Sm1.85Ce0.15CuO4

T. Holubar; G. Schaudy; N. Pillmayr; G. Hilscher; M. Diviš; V. Nekvasil

Abstract We present specific heat measurements of Sm 2 CuO 4 and Sm 1.85 Ce 0.15 CuO 4 in external fields up to 11 T. Entropy considerations indicate that Ce is tetravalent in these systems.


Journal of Magnetism and Magnetic Materials | 1992

Heat capacity of (R1−xPrx)Ba2Cu3O7 (R=Y, Gd)

G. Schaudy; T. Holubar; N. Pillmayr; G. Leitenbauer; G. Hilscher; P. Rogl; A. Hanninger

Abstract We present specific heat measurements of (R, Pr)Ba 2 Cu 3 O 7 (R=Y, Gd) in external fields up to 11 T. The results are analyzed in terms of crystalline electric field (CEF) effects and indicate that in these systems Pr appears to be trivalent rather than tetravalent.


Solid State Communications | 1994

Specific heat and susceptibility of PrNi2

P. Javorský; G. Schaudy; T. Holubar; G. Hilscher

Abstract The specific heat of the cubic PrNi 2 , YNi 2 and LuNi 2 intermetallic compounds has been measured in magnetic fields up to 11 T in the temperature range 1.6–80 K and in zero field up to room temperature. The comparison of the measured susceptibility data with those of the static crystal field calculation yields an overall agreement but allows no decision with respect to a singlet or doublet ground state. Our specific heat data show that the singlet Γ 1 is the ground state in PrNi 2 . The excess specific heat observed below 20 K can be attributed to a broadening of the first excited level.


Solid State Communications | 1994

Magnetoelastic interactions in RE2CuO4 system

M. Diviš; V. Nekvasil; H. Müller; T. Holubar; C. Dusek; G. Schaudy; G. Hilscher; M. Vybornov; P. Rogl

Abstract We present thermal expansion data for R 2 CuO 4 (R = Pr, Nd, Sm, Gd, Eu) compounds and specific heat measurements of Sm and Eu compounds in the temperature range from liquid helium to room temperature. In the case of Pr, Nd, Gd, and Eu compounds the coefficient of thermal expansion (α) increases monotonously with rising temperature whereas α of the Sm compound shows a pronounced minimum at about 60 K. These findings are interpreted in terms of the crystal field induced electric quadrupole moment of the 4 f electrons.


Physica C-superconductivity and Its Applications | 1994

The effect of chemical pressure upon the magnetism of (Ba1−xSrx)2PrNbCu2O8

H. Michor; M. Vybornov; T. Holubar; W. Perthold; G. Schaudy; G. Hilscher; P. Rogl

Abstract We present specific-heat and susceptibility measurements and a structural analysis of (Ba1−xSrx)2PrNbCu2O8 in order to explore the effect of the chemical pressure on the magnetic properties of the Pr sublattice. These systems are similar to PrBa2Cu3O7−δ for which the Cu-O chain layers have been fully replaced by layers of Nb-O octahedra. The overall volume compression of - 5.5% across the series is found to be rather inhomogeneous yielding an anomalous expansion of the average Pr-O bond lenght of 3.8% which is accompanied by a reduction of TN from 11.6 K to 2.3 K. The variation of the magnetic properties across the solid solution is discussed in terms of hybridization of the Pr4f states with the Cu-O valence bands.


Physica C-superconductivity and Its Applications | 1994

Specific heat of (Y1−xErx)Ni2B2C

H. Michor; W. Perthold; T. Holubar; N.M. Hong; G. Hilscher

Abstract We present specific heat and magnetica measurements of Y1−xErxNi2B2C which provide evidence that superconductivity and antiferromagnetism coexist below TN = 5.9K of the Er sublattice.


Physica B-condensed Matter | 1994

Magnetic order in Sm2−xGdxCuO4

T. Holubar; H. Michor; G. Schaudy; G. Hilscher; M. Vybornov; P. Rogl

Abstract We performed specific heat and susceptibility measurements of the pseudoternary system Sm2−xGdxCuO4 in order to establish the magnetic phase diagram of the Rare Earth sublattice.

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G. Hilscher

Vienna University of Technology

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G. Schaudy

Vienna University of Technology

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P. Rogl

University of Vienna

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H. Michor

Vienna University of Technology

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W. Perthold

Vienna University of Technology

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N. Pillmayr

Vienna University of Technology

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N.M. Hong

Vienna University of Technology

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B. Hellebrand

Johannes Kepler University of Linz

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D. Bäuerle

Johannes Kepler University of Linz

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