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1
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Transition from Mixed-Valence to Trivalent Cerium State in Ce(Ni,Cu)Al Series

100%
Čermák P., Javorský P., Šantavá E.
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issue 5
926-928
EN
In this work we present the study of the part of Ce(Ni,Cu)Al series from the pure CeNiAl to 30% of copper concentration, which illustrates the transition from mixed-valence state of CeNiAl to the trivalent state in CeCuAl. The work is based on X-ray diffraction, magnetization and specific heat measurement. The results indicate smooth transition between the mixed-valence and trivalent cerium state. The specific-heat data reveal increase of the Sommerfeld γ coefficient with copper concentration.
2
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Specific Heat and Magnetism of LuFe_6Al_6

100%
Svoboda P., Andreev A., Šantavá E., Šebek J.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
307-310
EN
Here we present the results of the zero-field specific heat study of the LuFe_6Al_6 single crystal. The specific heat data were analyzed as a sum of the phonon, electronic, and magnetic contributions, respectively. The analysis of the phonon part involves three acoustic and 36 optical branches, respectively, all of them corrected for the anharmonicity. The magnetic part of the specific heat was obtained by subtracting the electronic and the phonon part from the experimental specific heat and the magnetic entropy was calculated.
3
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Magnetic Properties of γ-Fe₂O₃ Nanopowder Synthesized by Atmospheric Microwave Torch Dischargie. Acta Physica Polonica A 122, 9 (2012), ERRATUM

100%
David B., Schneeweiss O., Šantavá E., Jašek O.
Acta Physica Polonica A
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2016
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vol. 129
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issue 1
168
EN
A nanopowder containing γ-Fe₂O₃ particles was synthesized by adding a gas mixture of H₂/Fe(CO)₅ into a microwave torch discharge at 1 bar. The presence of γ-Fe₂O₃ phase was confirmed by powder X-ray diffraction (mean crystallite size d_{XRD}=24 nm). The dominating characteristic sextets of γ-Fe₂O₃ were identified in the Mössbauer spectrum taken at 5 K. The presence of pure Fe₃O_4 in the nanopowder was excluded. The Mössbauer spectrum taken at 5 K exhibited six times larger total spectrum area than the Mössbauer spectrum taken at 293 K. Zero field cooled/field cooled curves measured down to 4 K in the magnetic field of 7.9 kA/m are reported.
4
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Low-Temperature Magnetic Properties of Nanocomposites Containing Superparamagnetic Fe_3C Particles

100%
David B., Schneeweiss O., Šantavá E., Morjan I.
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issue 5
766-767
EN
Two nanopowders containing superparamagnetic Fe_3C particles, superparamagnetic Fe_3O_4/γ-Fe_2O_3 particles and carbon black phase were synthesised by the method of laser-induced homogeneous pyrolysis of gaseous precursors. Both were characterised by X-ray diffraction, Mössbauer spectrometry and standard magnetic measurements. The mean crystallite size of Fe_3C was 3 nm for the first sample and 10 nm for the second sample. Mössbauer spectra measured at 27 K and zero-field cooled/field cooled curves measured down to 4 K are reported.
5
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Magnetic Anisotropy of Lu_2Co_{17-x}Si_x Single Crystals

100%
Tereshina E., Andreev A., Šantavá E., Daniš S.
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EN
Magnetic anisotropy of Lu_2Co_{17-x}Si_x single crystals grown by the Czochralski method was investigated. The homogeneity range of Si substitution for Co extends up to x = 3.4 in Lu_2Co_{17-x}Si_x solid solutions. The unit cell volume, Curie temperature, and spontaneous magnetic moment decrease monotonously with increasing Si content. Lu_2Co_{17} has the easy-plane type of magnetic anisotropy in the ground state, which changes into the easy-axis type by two spin-reorientation transitions of the second-order, the easy-plane-easy-cone at T_{SR1}~680 K and the easy-cone - easy-axis at T_{SR2}~730 K. Upon Si substitution, the observed spin-reorientations shift towards the lower temperatures for Lu_2Co_{17-x}Si_x (T_{SR1}~75 K and T_{SR2}~130 K in Lu_2Co_{16}Si) and vanish for compounds with 1
6
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Magnetic Phase Transitions in TbNi(Al,In) Compounds

100%
Klicpera M., Javorský P., Šantavá E.
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issue 5
881-883
EN
The magnetic phase transitions in TbNiAl_{1-x}In_{x} compounds were investigated by ac-susceptibility measurements. Our data reveal magnetic ordering with transition temperatures between 40 and 70 K, depending on the In concentration. All the studied compounds exhibit two or more phase transitions accompanied by distinct anomalies in the real and imaginary part of the ac-susceptibility. The paramagnetic Curie temperatures remain positive in the whole series.
7
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Magnetic Properties of γ-Fe_2O_3 Nanopowder Synthesized by Atmospheric Microwave Torch Discharge

100%
David B., Schneeweiss O., Šantavá E., Jašek O.
Acta Physica Polonica A
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2012
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vol. 122
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issue 1
9-11
EN
A nanopowder containing γ-Fe_2O_3 particles was synthesized by adding a gas mixture of H_2/Fe(CO)_5 into a microwave torch discharge at 1 bar. The presence of γ-Fe_2O_3 phase was confirmed by powder X-ray diffraction (mean crystallite size d_{XRD}=24 nm). The dominating characteristic sextets of γ-Fe_2O_3 were identified in the Mössbauer spectrum taken at 5 K. The presence of pure Fe_3O_4 in the nanopowder was excluded. The Mössbauer spectrum taken at 5 K exhibited six times larger total spectrum area than the Mössbauer spectrum taken at 293 K. Zero field cooled/field cooled curves measured down to 4 K in the magnetic field of 7.9 kA/m are reported.
8
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Structural and Magnetic Properties of the PrNi_{1-x}Cu_{x}Al Series

100%
Fikáček J., Javorský P., Klicpera M., Šantavá E.
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issue 5
884-885
EN
Polycrystalline samples of PrNi_{1-x}Cu_{x}Al series were studied by X-ray diffraction, magnetization and specific heat. The hexagonal ZrNiAl-type structure is preserved in the whole series. Compounds with x up to 0.4 order antiferromagnetically with the Néel temperatures between 3 and 5 K. The rest of the compounds (x = 0.5-0.9) exhibits a transition into a spin glass state below the freezing temperatures around 4 K. The analysis of the specific heat data reveals a quasi-doublet ground state well separated from higher crystal field levels in the whole series.
9
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Low-Temperature Magnetic Properties of Nanometric Fe-Based Particles

88%
David B., Schneeweiss O., Šantavá E., Alexandrescu R., Morjan I.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
561-564
EN
Fe-based nanoparticles were prepared by laser-driven pyrolysis. The as-synthesised powder consists ofα-Fe and Fe_3O_4/γ-Fe_2O_3 nanoparticles embedded in a pyrolytic carbon matrix. The crystallite size of 1.8 nm forα-Fe was calculated using the Scherrer formula. The as-synthesised nanopowder was superparamagnetic. The maximum of the zero-field cooling curve was observed at 32 K and the distribution of blocking temperatures g(T_B) peaked at 11 K. As a result of small particle sizes and the soft matrix, the Lamb-Mössbauer factor f was significantly higher at 4 K than at 293 K.
10
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Lattice Heat Capacity in RTAl (R = Y, Lu;T = Ni, Cu, Pd) Compounds

88%
Daniel P., Javorský P., Prchal J., Daniš S., Šantavá E.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
331-334
EN
We present analysis of the specific heat of the RTAl (R = Y, Lu;T = Cu, Ni, Pd) compounds. We focus on the lattice contribution and analyze the dependence of all the characteristic parameters in the Debye and Einstein models on the atomic masses and interatomic distances.
11
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Low Temperature Properties of the Ce_{1-x}La_{x}NiAl_4

76%
Toliński T., Kowalczyk A., Reiffers M., Šebek J., Šantavá E., Curlik I., Ilkovič S.
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issue 5
933-935
EN
Measurements of the heat capacity in ultralow temperatures (down to 350 mK) have been carried out for Ce_{1-x}La_{x}NiAl_4. The paramagnetic behavior above about 30 K can be well described by the Curie-Weiss magnetic susceptibility. The undoped CeNiAl_4 compound is a known heavy fermion system with a large electronic specific heat coefficient (γ = 0.5 J mol^{-1} K^{-2}) and the Kondo temperature in the range 30-80 K. In the case of the Ce_{0.8}La_{0.2}NiAl_4 and Ce_{0.6}La_{0.4}NiAl_4 compounds a peak in C/T appears below 2 K, which is strongly damped by the magnetic field. It is probably connected with the Kondo and/or magnetic interactions and the electronic specific heat coefficient is 0.19 J mol^{-1} K^{-2} (0.43 J mol^{-1} K^{-2}) for x = 0.2 (x = 0.4) at T → 0. The value determined above the peak, at temperature for which the magnetic field starts to decrease γ ( ≈ 3 K), is about 0.5 J mol^{-1} K^{-2} and the effect of the magnetic field can be well analyzed in frames of the single-ion Kondo model.
12
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Strong Electronic Correlations in a New Yb-Based Compound: YbCu_4Ni

76%
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.
13
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Magnetotransport Properties of CaTi_xRu_{1-x}O_3 (x=0, 0.07)

76%
Zorkovská A., Baran A., Feher A., Šebek J., Šantavá E., Bradarić I.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
351-354
EN
Electrical resistance, transversal magnetoresistance and the Hall effect were studied on polycrystalline CaTi_xRu_{1-x}O_3 (x=0, 0.07) samples using a conventional Quantum Design PPMS-9 equipment in the temperature range 2-300 K and magnetic field up to 9 T. Substantial differences were found between the two samples: (i) opposite to the metallic character of CaRuO_3, the substituted sample has insulating-like electrical resistance;(ii) the magnetoresistance of the substituted sample changes the sign from negative to positive values with increasing temperature. The magnetoresistance of CaRuO_3 is negative, the sign reversal is induced by magnetic field and only at temperatures below 15 K, such a behaviour is predicted for clustered systems;(iii) the Hall voltage in pure CaRuO_3 also changes sign from negative to positive values above 35 K. This temperature coincides with the observed magnetic transition temperature, indicating that the magnetic state and the carrier character interrelate.
14
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Ti-Induced Ferromagnetism and the Specific Heat of CaTi_xRu_{1-x}O_3 (x=0, 0.005, 0.03)

76%
Zorkovská A., Baran A., Kajňaková M., Feher A., Šebek J., Šantavá E., Bradarić I.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
355-358
EN
The influence of Ti substitution on the specific heat of the CaTi_xRu_{1-x}O_3 system at low concentrations x=0, 0.005, and 0.03 was studied in the temperature range of 2-300 K at magnetic fields up to 9 T. Small peak was revealed in the C/T vs. T^2 dependence at around 3 K, which are field sensitive (the electronic specific heat coefficient γlinearly decreases with the increase in magnetic field), and might be connected to some kind of magnetic ordering. The coefficient γis suppressed also by Ti substitution.
15
Content available remote

Magnetic Properties of UFe_{2+x} Prepared by Splat Cooling

64%
Havela L., Miliyanchuk K., Pešička J., Gonçalves A., Waerenborgh J., Pereira L., Šantavá E., Šebek J.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
247-250
EN
A series od UFe_{2+x} materials was prepared using splat cooling. The Laves phase structure can accommodate up to 0.3 Fe excess, while T_C is enhanced from 172 K to approximately 240 K. Higher Fe concentration leads to the segregation of α-Fe. ^{57}Fe Mössbauer spectroscopy indicates higher Fe magnetic hyperfine fields on Fe nuclei occupying the U sublattice than for the regular Fe sites.
16
Content available remote

Low Temperature Anomalies in the Specific Heat and Magnetic Susceptibility of Na_{0.7}CoO_2 Samples

64%
Baran A., Zorkovská A., Feher A., Šebek J., Šantavá E., Hejtmánek J., Veverka M., Bradarić I., Ružička M.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
495-498
EN
We present a comparative study of Na_{0.7}CoO_2 samples obtained from three different sources and prepared by different methods. The specific heat and magnetic susceptibility measurements in the temperature range 2-300 K show substantial influence on the observed anomalies, which underlines that the system is extremely sensitive to preparation protocols.
17
Content available remote

Heat Capacity and Susceptibility of CeCu_4Al

64%
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.
18
Content available remote

Anomalous Transport Properties of Carbon-Doped EuB_6

64%
Batkova M., Batko I., Filipov V., Flachbart K., Sechovský V., Shitsevalova N., Šantavá E., Šebek J.
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issue 5
893-894
EN
In the presented work we report electrical, magnetic and thermal properties of EuB_{6-x}C_{x} single crystals with an estimated value of x ≈ 0.07. Our studies reveal an antiferromagnetic phase transition at T_{N} ≈ 6.7 K. Electrical resistivity at zero magnetic field shows a pronounced resistivity maximum at T_{M} ≈ 7 K, just above the antiferromagnetic phase transition temperature. With increasing applied magnetic field the maximum moves to lower temperature and becomes totally suppressed at the field of 9 T. Observed magnetoresistance is negative in the whole studied temperature range 2-20 K, yielding a ratio of ρ(0 T, 7 K)/ρ(9 T, 7 K) ≈ 2.5. The origin of such magnetoresistance is associated with formation of mixed magnetic structure in the system due to fluctuation of carbon concentration.
19
Content available remote

Magnetic Field Influence on the Thermal Conductivity of PrB_6

64%
Priputen P., Reiffers M., Gabáni S., Flachbart K., Šantavá E., Šebek J., Alekseev P., Nefeodova E., Sadikov I., Shitsevalova N.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
383-386
EN
Results of thermal conductivity measurements on single crystalline PrB_6 sample in the temperature range of 2-30 K and in magnetic field up to 14 T are presented. The obtained results are discussed in order to estimate the electron, phonon, and magnetic contributions to thermal conductivity. Taking into account the results of electrical resistivity of this compound the temperature dependence of the reduced Lorentz function is determined.
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