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Electronic Band Structure and Photoemission States of La_{2/3}Pb_{1/3}MnO_3

100%
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.
2
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Electronic Band Structure of La_{2/3}Pb_{1/3}Mn_{2/3}Fe_{1/3}O_3

100%
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
3
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Electronic Band Structures of La_{2/3}Pb_{1/3}Mn_{2/3}(Fe,Co,Ni)_{1/3}O_{3}

100%
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.
4
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Magnetic Polymer Nanocomposite for Medical Application

88%
Świętek M., Tokarz W., Tarasiuk J., Wroński S., Błażewicz M.
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vol. 125
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issue 4
891-894
EN
Magnetic sponges derived from biocompatible and resorbable polymers are promising materials for medical applications. These materials have been utilised extensively in research applications for the capture of biomolecules and cells, the construction of tissue scaffolds and in regenerative medicine. The object of this study was a polymer scaffold made of polycaprolactone (PCL) containing a 10 wt% amount of nanomagnetite, manufactured in a two-step method. The porosity and morphological parameters were characterised with the use of μ-computer-aided tomography and scanning electron microscopy. Furthermore, the magnetic properties were evaluated. The obtained results confirmed high porosity and the appearance of randomly oriented pores. Moreover, evaluations of the magnetic properties, of both the magnetite nanopowder and the prepared magnetic nanocomposite, were performed. The tests verified the ferromagnetic character of the materials under investigation.
5
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Inter- and Intragrain Magnetization of Thallium-Based Superconductors

88%
Tokarz W., Kąkol Z., Kołodziejczyk A., König W., Gritzner G.
Acta Physica Polonica A
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2000
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vol. 98
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issue 5
633-636
EN
We report on magnetization and magnetic hysteresis measurements for the (Tl_{0.6}Bi_{0.5})(Sr_{0.9}Ba_{0.1})_{2}Ca_{2}Cu_{3}O_{y} Ag-sheathed superconducting tape as well as for the powdered and bulk (Tl_{0.6}Pb_{0.5})(Sr_{0.9}Ba_{0.1})_{2}Ca_{2}Cu_{3}O_{y} superconductors. For the investigated tape and bulk specimens the low field magnetization showed a deviation from the ideal linear M(H) dependence, which was attributed to the superposition of inter- and intragrain superconducting currents. Fitting of the theoretical magnetization curves to the experimental data allowed for the independent determination of the intragrain critical current densities for the superconducting grains and intergrain critical current densities for the weak link system at 77K.
6
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Electronic Band Structure and Photoemission States of Bi_{1.96}Mg_{0.04}Se_3

76%
Tokarz W., Zalecki R., Kowalik M., Kołodziejczyk A., Kozłowski A., Miotkowski J.
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vol. 126
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issue 4a
A-127-A-129
EN
We present theoretical band structure calculations and ultraviolet electron photoemission spectroscopy of a topological insulator Bi_{1.96}Mg_{0.04}Se_3. Our calculations were based on the first-principles density functional theory with general gradient approximation using Wien2k package with the spin-orbit interaction included by a second-variation method. The R3̅m crystal structure was optimized. In consequence, 4% decrease of volume and 3% decrease of ratio c/a was obtained. This modified structure was multiplied three times in a and b direction in order to place proper amount of Mg. Final crystal structure P3m1 with 135 atoms was used for the calculations. As a result metallic band structure was obtained with conduction band extended from -5.6 eV up to 0.16 eV. It composes mostly from Se p states. Comparison of total DOS with ultraviolet photoemission spectrum shows similar features.
7
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Critical Currents, Magnetization and Microwave Absorption of (Tl_{0.5}Pb_{0.5})Sr_2(Ca_{0.8}Gd_{0.2})Cu_2O_{z} Superconductor

76%
Woch W., Niewolski J., Tokarz W., Kołodziejczyk A., Sudra H., Gritzner G.
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issue 2
319-322
EN
The bulk (Tl_{0.5}Pb_{0.5})Sr_2(Ca_{1 - x}Gd_{x})Cu_2O_{z} superconductors with x = 0.1, 0.2 and 0.3 have unique and very interesting magnetic and electrical properties. In this paper we focused our attention on the superconductor with gadolinium content x = 0.2. We measured the magnetic field dependences of the transport critical currents, the microwave absorption as well as the magnetization for different temperatures. The critical temperature of this sample is T_c = 105.3 ± 0.2 K and the transition width Δ T_{90% - 10%} = 3.6 ± 0.2 K. The critical current of this superconductor is J_c = 1 820 ± 10 A/cm^2 at 77 K. The data were analyzed within the frame of the Bean and Kim models as well as the percolation model.
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