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1

Study of Niobium Thin Films under Pressure

100%

Pristáš G., Gabáni S., Orendáč M., Komanický V., Gažo E.

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vol. 126

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issue 1

346-347

EN

Niobium is widely used in many important superconducting applications. At ambient pressure, bulk Nb has the highest critical temperature, T_c ≈ 9.25 K among the superconducting elements. Thin films of Nb show several differences in behavior in comparison with bulk Nb, e.g. substantial increase in the upper critical field (H_{C2}). Critical temperature of superconducting transition is usually lower for thin films than in bulk sample and depends on thickness of the film, size of grains etc. We prepared 100 nm thick niobium thin films in the high vacuum DC magnetron sputtering system, with T_c=8.95 K at ambient pressure. In this study, we performed measurements of superconducting transition temperature by electrical resistivity measurements of Nb thin film under hydrostatic pressure of up to 30 kbar. We observed an increase of T_c with increasing value of pressure (dT_c/dp=7.3 mK/kbar). On the other side in the case of bulk sample of Nb we observed a decrease of T_c value (dT_c/dp=-2.5 mK/kbar) with increasing applied pressure. Difference in superconducting properties between niobium bulk and thin film under pressure is discussed.

2

Heat Capacity of Heavy Fermion Compound CeCu_4Ga in High Magnetic Fields

86%

Kowalczyk A., Toliński T., Reiffers M., Zapotoková M., Falkowski M., Gažo E.

Acta Physica Polonica A

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2009

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vol. 115

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issue 1

123-125

EN

The heat capacity in the applied magnetic field up to 9 T, susceptibility and magnetization of polycrystalline CeCu_{4}Ga are presented. Magnetic ordering was not observed down to 2 K. For temperature T < 200 K a Curie-Weiss behavior is observable giving an effective magnetic moment μ_{eff} =2.53 μ_{B}/f.u. The experimental value of μ_{eff} is close to the calculated one for a free Ce^{3+} ion (μ_{eff} = 2.54 μ_{B}/f.u.), thus indicating the presence of well localized magnetic moments carried by the stable Ce^{3+} ions. At low temperatures the electronic heat capacity coefficient value depends strongly on the temperature range used for the extrapolation and applied magnetic field. We observe a typical heavy fermion behavior with γ value of about 380 mJ mol^{-1} K^{-2} obtained from extrapolation to T = 0 K of the temperature range above 7 K. However, extrapolation of the lowest temperatures range yields the γ value of 3.3 J mol^{-1} K^{-2}.

3

Heat Capacity Studies of NdNi_4Si Compound

86%

Falkowski M., Reiffers M., Zapotoková M., Kowalczyk A., Toliński T., Gažo E.

Acta Physica Polonica A

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2009

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vol. 115

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issue 1

126-128

EN

The study of the heat capacity of the intermetallic compound NdNi_{4}Si including the effect of the magnetic field is reported. This compound crystallizes in the hexagonal CaCu_5-type structure, space group P6/mmm. NdNi_{4}Si is ferromagnetic with T_C = 8 K and the saturation magnetic moment of 1.5 μ_{B}/f.u. at 4.2 K (in H = 9 T). The heat capacity was analyzed considering the electronic contribution, the Schottky anomaly, and the lattice contributions in the frames of the Debye model. The scheme of the energy levels created by the crystal electric field split is determined from the Schottky contribution to the specific heat. NdNi_{4}Si was characterized by the electronic heat capacity coefficient γ = 85 mJ/(mol K^2) and the Debye temperature Θp_D = 325 K.

4

Strong Electronic Correlations in a New Yb-Based Compound: YbCu_4Ni

86%

Čurlik I., Reiffers M., Giovannini M., Gažo E., Šebek J., Šantavá E.

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issue 5

919-921

EN

Heat capacity measurements performed on the new ternary compound YbCu_4Ni indicate for this compound strong electronic correlations with possible antiferromagnetic phase transition below 0.5 K. Susceptibility and magnetisation measurements above 2 K show no magnetic ordering.

5

Influence of Pressure on the Electron-Phonon Interaction in Superconductors

86%

Orendáč M., Gabáni S., Pristáš G., Gažo E., Shitsevalova N., Flachbart K.

Acta Physica Polonica A

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2017

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vol. 131

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issue 4

1039-1041

EN

The electron-phonon interaction is a very important and ubiquitous process in solids, affecting almost all their physical properties. In metals, where the relaxation processes depend on both electrons and phonons, all thermodynamic and transport properties are dictated by the electron-phonon interaction. A very strong manifestation of the electron-phonon interaction is related with the superconducting state. Here we report the effect of high pressure on the transport electron-phonon interaction, λ_{tr}, in superconducting systems such as YB_6 (T_c ≈ 7.5 K), Pb (T_c ≈7.2 K), Nb bulk or thin film (T_c ≈9.2 K), and in LaB_6 in which superconductivity was not yet observed. The expected pressure effect should correspond to the theoretically predicted negative pressure effect on T_c (except for Nb thin film and LaB_6). To determine the influence of pressure on λ_{tr}, we utilized the Bloch-Grüneisen fit (denoted also as "thermal spectroscopy") of the precise temperature dependence of resistivity measurements in the normal state up to a pressure of 2.8 GPa. Based on this fit the observed negative pressure effect on λ_{tr} values, dλ_{tr}/dp, are as follows: dλ_{tr}/dp ≈-0.045 GPa^{-1} for YB_6, dλ_{tr}/dp ≈-0.13 GPa^{-1} for Pb, dλ_{tr}/dp ≈-0.019 GPa^{-1} or -0.028 GPa^{-1} for Nb bulk or thin film, respectively, and dλ_{tr}/dp ≈-0.003 GPa^{-1} for LaB_6.

6

Influence of Pressure on the Electrical Transport Properties of Carbon-Doped EuB₆

73%

Pristáš G., Gabáni S., Baťko I., Baťková M., Orendáč M., Gažo E., Filipov V., Konovalova E., Diko P., Flachbart K.

Acta Physica Polonica A

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2017

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vol. 131

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issue 4

982-984

EN

We have studied the influence of hydrostatic pressure on the electrical resistivity of carbon-doped semimetal EuB₆ which orders ferromagnetically at T_{C}=3.9 K and is intrinsically inhomogeneous due to fluctuations of carbon content. We observed a shift of the low-temperature resistivity maximum from 4.6 K (at 1 bar) to 5.2 K (at 30.3 kbar) with increasing pressure. However, the maximum of the derivative dρ/dT(T), which reveals the temperature of ferromagnetic ordering, does not change its position with increasing pressure. This behaviour is different from stoichiometric EuB₆, where pressure increases the ferromagnetic ordering temperature. The origin of this discrepancy may lie in the increase of volume fraction of the non-ferromagnetic phase with increase of pressure. Additional magnetoresistance measurements at various pressures between 1.5 K and 30 K have shown that with increase of magnetic field the resistivity is monotonically decreasing, and above 1 T a transition to a monotonic resistivity behaviour (dρ/dT(T)>0) is observed. Our results support the picture that carbon-rich regions play a role of "spacers", which prevent the percolation of the ferromagnetic phase.

7

Heat Capacity and Susceptibility of CeCu_4Al

73%

Reiffers M., Gažo E., Timko M., Kowalczyk A., Toliński T., Andrzejewski B., Šebek J., Šantavá E.

Acta Physica Polonica A

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2008

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vol. 113

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issue 1

425-428

EN

The heat capacity in the applied magnetic field up to 9 T, susceptibility and magnetization of polycrystalline CeCu_4Al are presented. The determined electronic heat capacity coefficient γ= 210 mJ mol^{-1} K^{-2} confirmed heavy fermion character of this compound. Magnetic ordering was not observed down to 0.5 K. Magnetic properties confirm these observations.

8

Influence of Pressure on Superconductivity in YB_{6}

73%

Gabáni S., Pristáš G., Takáčová I., Flachbart K., Gažo E., Mori T., Braithwaite D., Samuely P.

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vol. 126

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issue 1

340-341

EN

Magnetoresistivity measurements on a superconducting system of YB_{6} (T_c ≈7.5 K) down to 60 mK at hydrostatic pressures up to 47 kbar are presented. The superconducting transition temperature, as well as the third critical field H_{c3} reveal a linear decrease with increasing pressure with slopes of d ln H_{c3}/dp=-1.1 %/kbar, and d ln T_c/dp=-0.59 %/kbar. From the latter a critical pressure, p_c ≈ 170 kbar, at which T_c vanishes, is determined.

Refine search results

Study of Niobium Thin Films under Pressure

Heat Capacity of Heavy Fermion Compound CeCu_4Ga in High Magnetic Fields

Heat Capacity Studies of NdNi_4Si Compound

Strong Electronic Correlations in a New Yb-Based Compound: YbCu_4Ni

Influence of Pressure on the Electron-Phonon Interaction in Superconductors

Influence of Pressure on the Electrical Transport Properties of Carbon-Doped EuB₆

Heat Capacity and Susceptibility of CeCu_4Al

Influence of Pressure on Superconductivity in YB_{6}