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1
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XANES Experiments for High-Temperature Superconductors

100%
Kołodziejczyk A.
Acta Physica Polonica A
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1992
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vol. 82
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issue 2
273-281
EN
The paper presents the results of XANES (X-ray Absorption Near Edge Structure) experiments, of the high-temperature superconductors of Y-Ba-Cu-O-type carried out at the Cu L_{II,III}- and O K_{I}-edges using synchrotron radiation and the KMC double monochromator and SX-700 grading monochromator beamlines of BESSY/Berlin synchrotron storage ring. The aim of the paper is to show that the XANES studies are well suited for characterization of the local electronic structure of the high-temperature superconductors.
2
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Electronic Band Structure and Photoemission States of La_{2/3}Pb_{1/3}MnO_3

52%
Tokarz W., Kowalik M., Zalecki R., Kołodziejczyk A.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1151-1153
EN
We present the theoretical study of electronic and magnetic properties in a manganese perovskite La_{2/3}Pb_{1/3}MnO_3. The calculations were carried out in frame of the first-principles density functional theory with the general gradient approximation using the WIEN 2K package. The P3c1 crystal structure was taken from the detailed X-ray diffraction data for the perovskite. The exact exchange energy was utilized for Mn d electrons. Density of states was determined by the modified tetrahedron method. As a result we get a valence band for the spin up and down density of states with the gap for the latter of 1.85 eV. We noticed that conduction band is mainly dominated by d spin up manganese electrons and Mn (d_{xz}, d_{yz}) states have twice larger contribution than (d_{x^2 - y^2}, d_{xy}). We attribute this to Mn-O_6 octahedral tilting. From the same reason d_{3z^2 - r^2} state has no contribution to the density of states at the Fermi energy (E_{F}). Comparison of total density of states with the ultraviolet photoemission spectroscopy measurements shows similar features especially as far as the lead spectral intensity from the 6s electrons at about - 10 eV is concerned. The calculated total magnetic moment per formula unit is 3.66 μ_{B}, the measured one 3.48 μ_{B}/f.u.
3
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Analysis of Resistive Superconducting Transition of a (Tl_{0.6}Pb_{0.24}Bi_{0.16})(Ba_{0.1}Sr_{0.9})_2Ca_2Cu_3O_{y} Film

52%
Woch W., Chrobak M., Kołodziejczyk A.
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issue 2
389-392
EN
In this paper we analyze the resistive transition as a function of both the temperature and the dc applied magnetic field. We use the two models: first, based on the Ambegaokar and Halperin theory that describes the resistive transitions by the modified Bessel function and second, based on the Anderson and Kim theory represented by the exponential formula. The fits of the models to experimental results show that the freezing into superconducting vortex-glass phase takes place at the same temperature that does not practically depend on the applied magnetic field.
4
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Temperature and Magnetic Field Dependences of Critical Current of Thallium-Based Superconducting Films

52%
Zalecki R., Kołodziejczyk A., Heiml O., Gritzner G.
Acta Physica Polonica A
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2006
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vol. 109
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issue 4-5
669-674
EN
The critical current densities of three superconducting thallium-based films, prepared by screen printing, were measured as a function of temperature and applied magnetic field. The degradation of critical current densities was investigated for two different magnetic field orientations with respect to the sample plane - parallel and perpendicular.
5
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Study of Resistive Superconducting Transition of Bulk (Bi_{0.6}Pb_{0.4})_2Sr_2Ca_2Cu_{3}O_{x}

52%
Woch W., Chrobak M., Zalecki R., Kołodziejczyk A.
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vol. 126
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issue 1
328-329
EN
The temperature widths of the resistive transition as well as the thermal fluctuations of bulk (Bi_{0.6}Pb_{0.4})_2Sr_2Ca_2Cu_{3}O_{x} superconductor with T_{c,50%} = 107.1 K were studied. The applied magnetic field widens the resistive transition according to the following formula: ΔT = CH^{m} + ΔT_{0}. The value of exponent m = 0.44 suggests that there is strong pining of vortices, especially at lower temperatures. The critical exponents λ of the conductivity were calculated using the following equation: Δσ = Kε^{-λ}, with the λ_1 = 1.75 close to the zero critical temperature and λ_2 = 3.77 at higher temperatures. These values were discussed within the available theoretical models.
6
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Photoemission Electronic States of Thallium- and Bismuth-Based Superconductors

52%
Zalecki R., Kołodziejczyk A., König J. W., Gritzner G.
Acta Physica Polonica A
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2000
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vol. 98
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issue 5
513-524
EN
X-ray photoemission spectra the core-levels as well as the X-ray photoemission spectra and ultraviolet photoemission spectra from the valence bands of the (Tl_{0.6}Pb_{0.5})(Sr_{0.9}Ba_{0.1}) Ca_{2}Cu_{3}O_{y} and (Bi_{1.75}Pb_{0.35})Sr_{1.9}Ca_{2.05}Cu_{3.05}O_{y} superconductors were measured and analyzed. Special attention was paid to the valence band X-ray photoemission spectra and ultraviolet photoemission spectra, the Cu 2p core-level X-ray photoemission spectra and the Cu L_{2,3}-M_{4,5}M_{4,5} and O K-L_{2,3}L_{2,3} Auger spectra. Both Cu 2p_{3/2} and Cu 2p_{1/2} core-level lines consisted of two spin-orbit split main lines accompanied with the two satellite lines. The charge transfer energy Δ from the oxygen ligand to the copper 3d^{9} states and the hopping integral t were estimated from the energy separation between the main line and the satellite line taking advantage of the local cluster model calculations and their extension to high-temperature superconductors. The Coulomb correlation on-site energy U_{dd} of two electrons in the same copper orbital and U_{pp} of two electrons in the oxygen orbital as well as the correlation energy U_{cd} of the 2p core hole - 3d electron interaction have been estimated from the Auger electron spectra and the valence band spectra. They are: U_{dd}=6.0±0.5eV, of U_{pp}≅ 10±1eV and of U_{cd}≅ 8.0±0.5eV nearly the same for both the Tl- and Bi-compounds. We conclude that these compounds are the charge transfer strongly-correlated metals.
7
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Electronic Band Structure of La_{2/3}Pb_{1/3}Mn_{2/3}Fe_{1/3}O_3

52%
Tokarz W., Kowalik M., Kołodziejczyk A.
Acta Physica Polonica A
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2012
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vol. 121
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issue 4
876-878
EN
We present theoretical studies of electric and magnetic properties in manganese perovskite La_{2/3}Pb_{1/3}Mn_{2/3}Fe_{1/3}O_3. The calculations were carried out by means of the first-principles density functional theory (DFT) with general gradient approximation GGA+U using Wien2K package. The P-3c1 crystal structure was chosen from the detailed X-ray diffraction data for the perovskite. For Mn and Fe d electrons exact exchange energy was utilized. Different orientation of magnetic moments on Mn and Fe atoms was considered. The computed density of states display band gap for both spin orientations in accord with our previous work, indicating that this compound should show an insulating ground state
8
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Electronic States of Collosal Magnetoresistive Manganites La_{0.67}Pb_{0.33}Mn_{1-x}Fe_{x}O_{3} from Photoemission Spectroscopy

52%
Kowalik M., Zalecki R., Kołodziejczyk A.
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issue 2
277-280
EN
The electron photoemission spectra of valence bands and core-level states of manganese perovskite La_{0.67}Pb_{0.33}(Mn_{1-x}Fe_{x})O_{3} with x = 0, 0.01, 0.03, 0.06, 0.10 and 0.15 were measured by the X-ray and Ultraviolet Photoemission Spectroscopy (XPS and UPS) below and above the metal-insulator transition. From analysis of the Mn 2p core-level spectra the ratio Mn^{3+}/Mn^{4+} was calculated as a function of the iron content. Comparison of the valence band spectrum with band structure calculations and with the high-resolution spectra measured at synchrotron radiation for Ca-, Ba- and Ce- substituted manganites revealed the strong hybridisation of Mn 3d and of O 2p states between -3 eV and -7 eV, and no estimated oxygen states between 0 eV and -2 eV where the Mn-3d states play a predominant role. The composition dependent insulating energy gaps were measured at room temperature. Reasons for the behaviour were discussed taking into account previous analysis of XPS/UPS spectra of other manganese perovskites.
9
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Resistance and AC Susceptibility of YBCO 1:2:3 Films on Silver Substrates

52%
Zalecki R., Woch W., Chrobak M., Kołodziejczyk A.
Acta Physica Polonica A
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2012
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vol. 121
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issue 4
850-853
EN
The YBa_{2}Cu_{3}O_{δ} films were obtained directly on the polished silver substrates by the sedimentation process. Thickness of these films is of the order of several tens micrometers. The temperature dependences of the resistance and the AC susceptibility of the films were measured and analyzed. The critical temperatures of these specimens vary from 89 K to 91 K and they do not depend on the annealing temperatures. The critical currents were calculated from AC susceptibility measurements using the Bean's model.
10
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Thermal Fluctuations of Bismuth Based 1G Tape

52%
Chrobak M., Woch W., Zalecki R., Kołodziejczyk A.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
306-308
EN
The thermal fluctuations of bismuth based commercial 1G tape were studied near the critical temperature T_{c}=110.2 K. The detailed analysis of the temperature dependence of resistivity measurements was made in the temperature region from the zero resistance critical temperature up to 300 K. The thermal fluctuations of conductivity were analysed using the Aslamazov-Larkin microscopic approach and the critical exponents were calculated close to the transition temperature.
11
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Thermal Fluctuations of (Tl_{0.5}Pb_{0.5})Sr_2(Ca_{0.9}Gd_{0.1})Cu_2O_{z} Bulk Superconductor

52%
Woch W., Chrobak M., Kołodziejczyk A., Gritzner G.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1059-1062
EN
We report on the critical fluctuations from the magnetoresistance measurements in polycrystalline (Tl_{0.5}Pb_{0.5})Sr_2(Ca_{0.9}Gd_{0.1})Cu_2O_{z} superconductor. The critical exponents have been calculated above the critical temperature T_{c} as well as in the temperatures interval close to the zero resistance critical temperature. Above T_{c} only Gaussian fluctuations have been observed in a three-dimensional fluctuating system. Additionally, far above T_{c} the applied magnetic field induces the crossover from 3D to 2D fluctuating system. At the temperatures range close to the zero critical temperature the properties of the weak links are dominating and the fluctuating phase in each grain becomes long-range ordered as a consequence of the activation of weak links between grains.
12
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Critical Currents of Bismuth 1G Tape

52%
Woch W., Zalecki R., Chrobak M., Kołodziejczyk A.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
315-317
EN
The critical currents of commercial bismuth based superconducting tape were determined in the two ways. In the first one the transport critical current density was measured by the four points method using the dc current power supply at the liquid nitrogen temperature. In the second one the critical current densities were obtained from the absorption part of ac susceptibility measurements using the Bean model near the critical temperature. The temperature dependence of the critical current densities was fitted to take advantage of the Ginzburg-Landau strong-coupling limit approach. Using the fit parameters the critical current density at 77 K was calculated. The critical temperature of this tape (T_{c}= 110.5 K) was determined from the ac susceptibility measurements.
13
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AC Susceptibility of YBCO 1:2:3 Films on Silver Substrates

52%
Zalecki R., Woch W., Chrobak M., Kołodziejczyk A.
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vol. 126
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issue 4a
A-13-A-16
EN
The YBa_2Cu_3O_δ films were obtained directly on silver substrates by the sedimentation processes. The thicknesses of these films are of the order of several tens μ. The temperature dependences of the AC susceptibility of the films were measured and analyzed. The critical temperatures of these specimens obtained from the dispersion part of AC susceptibility vary from 89.2 K to 92.5 K. The critical currents were calculated from the absorption part of AC susceptibility using the Bean model. The temperature dependences of the critical currents were fitted using the Ginzburg-Landau strong coupling limit approach.
14
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Penetration Depth of Magnetic Field into YBa₂Cu₃Oₓ Film on Polycrystalline Ag Substrate

52%
Zalecki R., Woch W., Chrobak M., Kołodziejczyk A.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
272-274
EN
The magnetic field penetration depth into YBa₂Cu₃Oₓ film on polycrystalline Ag substrate with the critical temperature of 90.4 K was determined from the AC susceptibility measurements. The 95 μm thick YBCO film was deposited directly on Ag substrate by the sedimentation process. When the sample is in the Meissner state, the dispersive component of the AC susceptibility as well as its temperature dependence reflects the changes of the penetration depth with the temperature. The penetration depth of this film is found to be 5.4 μm.
15
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Electronic Band Structures of La_{2/3}Pb_{1/3}Mn_{2/3}(Fe,Co,Ni)_{1/3}O_{3}

52%
Kowalik M., Tokarz W., Kołodziejczyk A.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
251-253
EN
We present calculations of the electronic band structures of La_{2/3}Pb_{1/3}Mn_{2/3}(Fe,Co,Ni)_{1/3}O_{3} colossal magneto-resistance manganites. The calculations are based on first-principles density functional theory with general gradient approximation GGA+U using WIEN2k package. The calculations show that electronic structures of these compounds consist mainly of Mn 3d, O 2p, and (Fe,Co,Ni) 3d states, which are hybridized over whole valence bands. Substitution Mn ion by Fe, Co, or Ni ions reduces the Mn and O contributions to the valence bands and weakens the double exchange interaction. The results are in good agreement with available experimental data.
16
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Content available

Superconductivity, Weak Itinerant Ferromagnetism and Electronic Band Structure of Y_9Co_7

46%
Kołodziejczyk A., Wiendlocha B., Zalecki R., Toboła J., Kaprzyk S.
Acta Physica Polonica A
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2007
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vol. 111
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issue 4
513-526
EN
The paper presents experimental results for the intermetallic compound Y_9Co_7 which is the first very weak itinerant ferromagnetic superconductor. The measurements of electrical resistivity, susceptibility, magnetization, specific heat, nuclear magnetic resonance, and other properties show the magnetic transition at T_C≈ 4.5 K and the onset of superconductivity at about T_S≈ 2.5 K, revealing the coexistence state within a temperature interval below T_S. A few of the results are shortly reviewed and discussed. We focus attention on our recent ultraviolet photoemission spectroscopy and their comparison with our band structure calculations. Interpretations are considered which take into account the characteristic structure of the compound and different possible types of magnetic ordering.
17
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Bismuth Valence in a Tl_{0.7}Bi_{0.3}Sr_{1.6}Ba_{0.4}CaCu_{2}O_{y} Superconductor from X-Ray Photoemission Spectroscopy

46%
Zalecki R., Woch W., Kowalik M., Kołodziejczyk A., Gritzner G.
|
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issue 2
393-395
EN
The X-ray electron photoemission spectra of a Tl_{0.7}Bi_{0.3}Sr_{1.6}Ba_{0.4}CaCu_2O_{y} superconductor were measured with Al K_{α} and Mg K_{α} radiation at room temperature. The Bi 4f spectrum was compared to the same spectra of Bi_{1.75}Pb_{0.35}Sr_{1.9}Ca_{2.05}Cu_{3.05}O_{y} and Tl_{0.6}Pb_{0.4}Sr_{1.6}Ba_{0.4}Ca_2Cu_3O_{y} superconductors. In Bi,Pb-based superconductor only one type of Bi^{3+} ions is present. The Bi 4f spectrum in the Tl,Bi-superconductor consists of two contributions due to the different valences. The component from Bi^{5+} lines is in higher binding energy than from Bi^{3+}. The ratio of trivalent Bi^{3+} to pentavalent Bi^{5+} bismuth ions was calculated from decomposition of the spin-orbit split spectrum of the Bi 4f photoelectrons. The conclusion is that Bi is present in trivalent and in pentavalent form and the ratio of Bi^{3+} to Bi^{5+} is 1.87 ± 0.02.
18
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Specific Heat and Magnetoresistance of Y-, Tl- and Bi-Type High-Temperature Superconductors

46%
Zalecki R., Kozłowski A., Kołodziejczyk A., Gritzner G., Mair M.
Acta Physica Polonica A
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1997
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vol. 91
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issue 2
431-434
EN
Specific heat of polycrystalline DyBa_{2}Cu_{3}O_{7} and Tl_{0.58}Pb _{0.42}Sr_{1.6}Ba_{0.4}Ca_{2}Cu_{3}O_{9} samples, as well as the single crystal of Bi_{2}Sr_{2}CaCu_{2}O_{8} have been measured within the temperature interval from 50 to 250 K. For Dy- and Tl-specimens the pronounced jump in specific heat and apparent contribution from Gaussian fluctuations of superconducting order parameter close to T_{c} have been observed. In contrary, for Bi-specimen only a rounded maximum within a broad interval around T_{c} has been detected. Magnetoresistance measurements as a function of temperature just below T_{c} have been carried out for Dy- and Tl-samples and the slopes of upper critical fields have been determined. The data have been analysed within a frame of Ginzburg-Landau-Abrikosov- Gorkov theory with additional Gaussian-like fluctuation term. The electronic specific heat coefficients γ, and the coherence length χ have been obtained.
19
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Penetration Depth of Tl_2Ba_2Ca_2Cu_3O_y and Tl_{0.58}Pb_{0.4}Sr_{1.6}Ba_{0.4}Ca_2Cu_3O_y Bulk Superconductors

46%
Zalecki R., Woch W., Kołodziejczyk A., Konig W., Gritzner G.
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vol. 126
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issue 4a
A-133-A-136
EN
The penetration depths of bulk Tl_2Ba_2Ca_2Cu_3O_y and Tl_{0.58}Pb_{0.4}Sr_{1.6}Ba_{0.4}Ca_2Cu_3O_y superconductors with the critical temperatures 112 K and 114 K, respectively, were determined from the AC susceptibility measurements. When the samples are in the Meissner state, the dispersive components of AC susceptibility as well as their temperature dependences reflect the changes of the penetration depths at various temperatures. In these bulk ceramic superconductors the penetration depths are of the order of few μm and they are comparable to the grains sizes in the ceramics.
20
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Study of Resistive Superconducting Transition of Thallium Based Superconductors

46%
Woch W., Zalecki R., Chrobak M., Kołodziejczyk A., Gritzner G.
Acta Physica Polonica A
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2012
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vol. 121
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issue 4
789-795
EN
A width and shape of resistive transition as well as thermal fluctuations of the thallium based superconductors were analyzed theoretically. The applied magnetic field widens the resistive transition according to the following formula: ΔT=CH^{m}+ΔT_{0}. The exponent m fluctuates around 2/3 and depends on vortex structure and strength of the pinning force. The shape of the resistive transition was fitted by two models: the first one based on Ambegaokar-Halperin theory and the other one based on Anderson-Kim theory expressed by the exponential formula. Critical fluctuations were analyzed on the basis of magnetoresistance measurements results. The critical exponents have been calculated above the critical temperature T_{c} as well as for temperatures close to the zero resistance critical temperature.
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