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1
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Thermoelectric Power and Thermal Conductivity of Heavy Fermion CeCu_4Al

100%
Falkowski M., Kowalczyk A.
Acta Physica Polonica A
|
2012
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vol. 121
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issue 5-6
1056-1058
EN
The thermal conductivity and thermopower are discussed for the heavy fermion CeCu_4Al compound. CeCu_4Al is paramagnetic and follows the modified Curie-Weiss law with μ_{eff} = 2.53 μ_{B}/f.u. and θ_{P} = - 10 K indicating on the presence of well localized magnetic moments of Ce^{3+} ions. The determined electronic specific heat coefficient γ = 2.2 J mol^{-1}K^{-2} confirms the heavy fermion character of this compound. Thermopower is positive over the whole temperature range and below T_{max} = 25 K falls rapidly. Based on a simple band model the position and width of the 4f peak nearest to the Fermi level have been estimated. The measured total thermal conductivity of the CeCu_4Al compound increases almost linearly with increasing temperature.
2
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Thermal Conductivity of Ce₂Ru₃Ga₉ Compound

100%
Falkowski M., Strydom A.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
240-242
EN
The Ce-based 2:3:9 series of compounds are known for strongly correlated 4f-electron behaviour. Here, we report for the first time a study of the thermal conductivity κ(T) in zero and 9 T magnetic field for Ce₂Ru₃Ga₉ across the temperature range 2 K ≤ T ≤ 300 K. The zero-field temperature dependence of κ(T) exhibits a pronounced maximum, characteristic for metals with large electronic mean free path and towards room temperature κ(T) starts behaving in a manner usually attributed to the enhanced electron-phonon coupling. Based on the Wiedemann-Franz law the electronic and lattice contributions to the thermal conductivity were estimated. In high temperature region a distinct step-like anomaly at T* = 203 K has been observed which signals a putative phase transition, probably of phononic or lattice origin. We furthermore discuss the effect of applied magnetic fields on the thermal transport in Ce₂Ru₃Ga₉.
3
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Magnetocaloric Effect in NdNi_4Si Compound

81%
Falkowski M., Toliński T., Kowalczyk A.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1290-1292
EN
On the basis of the thermodynamic approach, we report the magnetocaloric properties of the ternary ferromagnetic NdNi_4Si compound with magnetic phase transition temperature T_{C} at 8 K. The saturated magnetic moment in H = 9 T is equal to 1.5 μ_{B}/f.u. at 4.2 K and the compound crystallizes in the hexagonal CaCu_5-type structure (space group P6/mmm). The magnetocaloric effect was calculated in terms of the isothermal magnetic entropy change Δ S_{M} as well as the adiabatic temperature change Δ T_{ad} using the specific heat data and magnetization measurements. Within the second order phase transition significant values of these parameters have been observed.
4
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Thermoelectric Properties of CeCu_4Ag Compound

81%
Kowalczyk A., Toliński T., Falkowski M., Timko M.
Acta Physica Polonica A
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2010
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vol. 118
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issue 5
936-937
EN
The magnetic and electronic properties including electrical resistivity, thermal conductivity and thermopower are discussed for the heavy fermion CeCu_4Ag compound. The electrical resistivity shows a Kondo-like logarithmic increase up to a maximum at T = 75 K. Thermopower is positive over the whole temperature range and below T_max = 25 K falls rapidly. The measured thermal conductivity of the CeCu_4Ag compound increases with increasing temperature.
5
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Specific Heat of YbNi_4Si Compound

81%
Falkowski M., Kowalczyk A., Toliński T.
Acta Physica Polonica A
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2008
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vol. 113
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issue 2
641-644
EN
The specific heat of YbNi_4Si has been analyzed considering the electronic contribution and the lattice contributions in frames of the Debye model. Based on the specific heat measurements, the electronic specific heat coefficient γ = 25 mJ mol^{-1} K^{-2} and the Debye temperature θ_D = 320 K were derived. This small value shows that YbNi_4Si cannot be classified as a heavy fermion system. These studies are completed by magnetic susceptibility, X-ray photoemission spectroscopy, and electrical resistivity.
6
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Thermoelectric Power of CeNi_4Si and YbNi_4Si Compounds

81%
Falkowski M., Kowalczyk A., Tran V., Miiller W.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
303-306
EN
The thermoelectric power was measured from 4.2 to 300 K for CeNi_4Si and YbNi_4Si. The thermoelectric power was analysed in the framework of the phenomenological resonance model. According to the model the dominant contribution to thermopower is caused by scattering between electrons of a broad s-band and a narrow f-band with the Lorentzian shape. The electron-hole analogy is reflected in the thermoelectric power behaviour of the investigated compounds.
7
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New Method of Measurement of the Magnetoelastic Characteristics for Tensile Stresses

71%
Salach J., Szewczyk R., Bieńkowski A., Kolano-Burian A., Falkowski M.
Acta Physica Polonica A
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2010
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vol. 118
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issue 5
775-777
EN
The paper presents a novel method of measurements of tensile stress dependence of the magnetic characteristics of ring-shaped cores made of soft amorphous alloys. In the presented method, the uniform tensile stress was applied perpendicularly to the magnetizing field direction. Magnetoelastic core with closed magnetic circuit was fixed on the non-magnetic backings enabling the conversion of compressive force into tensile stresses as well as it enables the core to be winded by magnetizing and sensing windings. Magnetoelastic characteristics measured under tensile stress, for Fe_{25}Ni_{55}Si_{10}B_{10} alloy annealed in temperature 350°C for 1 h, are presented in this paper. The presented results indicate high tensile stress sensitivity of Fe_{25}Ni_{55}Si_{10}B_{10} alloy. Moreover, together with magnetoelastic characteristics for compressive stresses (presented previously in the literature), the describes results create possibility of further development of models of the magnetoelastic effects in amorphous alloys.
8
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Magnetic Properties and Magnetocaloric Effect of DyNi_{4}Si

71%
Synoradzki K., Kowalski W., Falkowski M., Toliński T., Kowalczyk A.
Acta Physica Polonica A
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2014
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vol. 126
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issue 1
162-163
EN
The magnetic properties and magnetocaloric effect (MCE) in DyNi_{4}Si have been studied by the magnetization and specific heat measurements. The saturation magnetic moment in μ_{0}H=9 T is equal to 7.9 μ_{B}/f.u at 4.2 K. A significant MCE has been observed around the second order phase transition at T_{C}=11 K. The maximum magnetic entropy change is -Δ S_{M}=14.5 J kg^{-1}K^{-1} for the magnetic field change of 9 T.
9
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Heat Capacity Studies of NdNi_4Si Compound

62%
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.
10
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Heat Capacity of Heavy Fermion Compound CeCu_4Ga in High Magnetic Fields

62%
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}.
11
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From Heavy Fermion and Spin-Glass Behavior to Magnetic Order in CeT_4M Compounds

62%
Toliński T., Kowalczyk A., Falkowski M., Synoradzki K., Chełkowska G., Hoser A., Rols S.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1014-1018
EN
We report on the transitions between the ferromagnetic order, spin-glass behavior, heavy fermion and fluctuating valence state in a series of isostructural compounds CeT_4M (T = Ni, Cu; M = Al, Ga, Mn). The dilution of Ce or the T and M elements allowed us to follow the physical properties evolution employing the measurements of the heat capacity, dc magnetic susceptibility, frequency dependent ac magnetic susceptibility, magnetization relaxation, inelastic neutron scattering and also the X-ray photoemission spectroscopy. It is shown that the Mn rich compounds lean towards the spin glass behavior. For the compounds governed by the close to localization Ce 4f states the effect of the crystal electric field has been studied. It has been shown that the spin glass-like behavior can significantly influence the physics of the CeT_4M compounds.
12
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Content available

Superconductivity and Electronic Structure of the W_7Re_{13}B Compound

62%
Kowalczyk A., Andrzejewski B., Jezierski A., Toliński T., Szlaferek A., Falkowski M., Chełkowska G.
Acta Physica Polonica A
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2006
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vol. 109
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issue 4-5
597-600
EN
The superconductor W_7Re_{13}B has been studied by the magnetic measurements and microwave absorption. The crystal structure of W_7Re_{13}B is cubic (β-Mn type). This compound exhibits a sharp superconducting transition at a temperature of T_c=7.2 K. The electronic structure of W_7Re_{13}B has been studied by X-ray photoelectron spectroscopy and the band structure has been calculated by the full-potential local-orbital minimum-basis method using the scalar-relativistic mode. The main contribution to the density of states at the Fermi level is from 5d electrons of W and Re. The W and Re bands are similar and substituting W by Re does not change the total density of states.
13
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The Electronic Structure and Specific Heat of YNi_4Si

52%
Pugaczowa-Michalska M., Falkowski M., Kowalczyk A., Timko M., Reiffers M., Mihalik M., Šebek J., Šantava E.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
323-326
EN
The studies of the electronic structure and the specific heat of YNi_4Si are reported. Below the Fermi energy (E_F) the density of states contains mainly the 3d states of Ni, which hybridized with 4d states of Y and 3p states of Si. The theoretical electronic specific heat coefficient (12.32 mJ/(mol K^2)) obtained for equilibrium lattice parameters and the experimental value (13 mJ/(mol K^2)) are in a reasonable agreement.
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