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1
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The Study of the Electronic Structure of CrPt_{3} Alloy by the LMTO Method

100%
Szajek A.
Acta Physica Polonica A
|
1992
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vol. 82
|
issue 6
967-974
EN
The ab initio self-consistent linear muffin-tin orbital calculations in the atomic sphere approximation have been performed for the ordered CrPt_{3} (AuCu_{3}-type structure) alloy. The band structure and the densities of electronic states are presented. The para- and ferrimagnetic phases were considered. The spin-polarized calculations have confirmed the experimental observation of small antiparallel induced magnetic moment on a platinum atom.
2
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Content available

The Electronic and Magnetic Properties of the USn_2 Compound

100%
Szajek A.
Acta Physica Polonica A
|
2004
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vol. 105
|
issue 5
485-493
EN
The ab initio self-consis tent calculations were performed for USn_2 compound, which crystallizes in the ZrGa_2-type structure (Cmmm space group). The tight binding linear muffin-tin orbital method in the atomic sphere approximation was used in the calculations. The spin-polarized calculations confirmed the antiferromagnetic order in the USn_2 system. The magnetic moment is predominantly located on the uranium atoms and is formed mainly by the f electrons. The three types of Sn atoms may be treated as non-magnetic.
3
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Electronic and Magnetic Properties of ThCo_4B

100%
Szajek A.
Acta Physica Polonica A
|
2008
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vol. 113
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issue 1
283-286
EN
ThCo_4B compound crystallizes in the hexagonal CeCo_4B type structure. The electronic structure is calculated based on full-potential local-orbital full-relativistic method. The ab initio calculations showed that small magnetic moments (≈0.1 μ_B/atom) are formed on Th and B atoms, antiparallel to the moments on Co atoms equal to 1.55 and 0.43 μ_B/atom for Co(2c) and Co(6i), respectively. The densities of states at the Fermi level are equal to 1.3 and 5.4 states/(eV spin f.u.) for spin up and down, respectively. These values are predominated by Co(3d) electrons.
4
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Electronic Structure and Magnetic Properties of the UPdAs_2 Compound

64%
Werwiński M., Szajek A.
Acta Physica Polonica A
|
2012
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vol. 121
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issue 5-6
1148-1150
EN
The electronic band structure of UPdAs_2 is calculated using full potential linearized augmented plane wave implemented in the WIEN2k code. Calculations were started with the exchange-correlation potential in the form proposed by Perdew, Burke and Ernzerhof (PBE). We additionally studied PBE+U approach with the Coulomb repulsion energies U applied to the uranium 5f orbital and varying from 0 to 4 eV. PBE+OP with orbital polarization term was one more tested approach. To reproduce magnetic sequence ++- a doubled in c axis supercell is built. Initial magnetic moments on inequivalent uranium atoms are assumed to be opposite. The antiferromagnetic ground state is confirmed by comparison of total energies calculated for various magnetic configurations. Results of PBE+U(1.0 eV)+J(0.5 eV) and PBE+OP approaches are in the best agreement with the neutron scattering measurements of magnetic moments. The calculated total magnetic moment on uranium atoms is predicted to be equal to 1.47 μ_{B}.
5
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Effect of Al Substitution on the Electronic and Magnetic Properties of GdCo_5

64%
Szajek A., Malinowski W.
Acta Physica Polonica A
|
2002
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vol. 101
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issue 4
525-536
EN
Experimental data show that aluminium doped RCo_5 systems crystallize in CaCu_5-type structure for most of the rare-earth elements (R). Al impurities randomly occupy one of the two possible positions (2c and 3g) and there is a critical concentration of Al, x_c=2.0, for RCo_{5-x}Al_x when the Co sublattice becomes nonmagnetic. The ab initio self-consistent calculations show strong dependence of magnetic properties of GdCo_{5-x}Al_x on concentration of Al and position of the impurities in the unit cell, furthermore to fulfil experimental observation of existence of critical concentration, x_c=2.0, the Al impurities should prefer 3g positions otherwise the magnetic moments on Co atoms do not vanish.
6
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Band Structure of Dilute Metastable Co-Ag Alloys

64%
Morkowski J. A., Szajek A.
Acta Physica Polonica A
|
2000
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vol. 98
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issue 5
447-455
EN
Co-Ag systems have recently attracted considerable attention in application oriented research of ferromagnetic thin films and multilayers. Due to low miscibility of Ag in Co it is easy to fabricate thin Co-Ag films of granular structure, promising as a high magnetoresistance material. It was also shown that using modern technology it is possible to deposit thin films of Co-Ag forming metastable homogeneous alloys for compositions far exceeding the solubility limit. In the present paper results of electronic structure calculations by the tight-binding linear muffin-tin orbital method are reported. Computations were done for hypothetical uniform ordered Co_{100-x}Ag_{x} alloys assuming proper extended unit cells to simulate concentrations of x=25, 12.5, 6.25, 3.125 at.%. The results were used to calculate the photoemission spectra. The calculated photoemission spectra are in fair agreement with experimental data supporting the conclusion of existence of a homogeneous though metastable alloy in the dilute limit. On the contrary, superposition of pure Co and Ag spectra implied for precipitate of Ag in Co cannot explain the experimental data.
7
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The Electronic and Magnetic Properties of UGe Compound

64%
Werwiński M., Szajek A.
|
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issue 5
886-887
EN
The UGe system crystallizes in the orthorhombic ThIn-type structure. The uranium atoms occupy three crystallographic sites with interatomic U-U distances like below and above the Hill limit. The band structure has been calculated by using the density functional theory and generalized gradient approximation. Ab initio calculations were performed based on the full-potential local-orbital minimum-basis code. Calculations showed that all three types of uranium atoms are magnetically ordered with antiparallel alignment of the magnetic moments. For uranium atoms with an interatomic distance below the Hill limit magnetic moments are significantly reduced due to hybridization effects.
8
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Dynamic Crystal Field in CePb_{3}

64%
Lipiński S., Szajek A.
Acta Physica Polonica A
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2000
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vol. 97
|
issue 1
245-248
EN
The crystal field of valence fluctuating systems is time dependent due to f-electron transfers to the conduction band. We examine the effects of crystal field fluctuations on the neutron spectra, the specific heat and susceptibility of CePb_{3}.
9
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Electronic Structure and Magnetic Properties οf the UCoAs_{2} Compound

64%
Werwiński M., Szajek A.
Acta Physica Polonica A
|
2009
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vol. 115
|
issue 1
244-246
EN
The UCoAs_{2} compound crystallizes in the tetragonal HfCuSi_{2} type structure with space group P4/nmm. The compound orders ferromagnetically at 150 K with a spontaneous magnetic moment of about 1.8 μ_B per formula unit. We present results of fully relativistic band structure calculations based on the full-potential local-orbital minimum-basis scheme (FPLO-5.10-20) and compare magnetic moments obtained from calculations without and with orbital polarization corrections. The magnetic behavior of the Co atoms remains unknown.
10
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Ab initio Calculations of the Magnetocrystalline Anisotropy in UAuSb_2 Ferromagnet

64%
Morkowski J., Szajek A.
Acta Physica Polonica A
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2009
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vol. 115
|
issue 1
185-187
EN
The paper presents results of ab initio calculations of the magnetocrystalline anisotropy of UAuSb_2, a strongly anisotropic ferromagnet below 36 K. The total energy of the unit cell of UAuSb_2 was calculated by two methods: the full potential linear muffin-tin orbitals method and by the full-potential local-orbital minimum basis band structure code. The computations were done for the following quantization directions in the tetragonal unit cell (orientations of the magnetization vector M): [010], [001], [011], [110], [111], and [11½] . The anisotropic contribution to the total energy for various directions were fitted by the least-squares procedure to the expression for the magnetocrystalline energy suitable for tetragonal symmetry E_A=K(α_x^4 +α_y^4)+ K_2α_z^2, where (α_x,α_y,α_z) is a unit vector along the direction of magnetization M. The band structure calculations predict the direction [111] as the easy axis of magnetization. Values of the calculated anisotropy constants at T=0 are provided.
11
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Electronic Structure and Magnetic Properties of Intermetallic Alloys

52%
Jezierski A., Pugacheva M., Morkowski J. A., Szajek A.
Acta Physica Polonica A
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1997
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vol. 91
|
issue 1
151-159
EN
We present the influence of local ordering on the electronic and magnetic properties of Heusler-type alloys. The band structure and magnetic moments are calculated by ab initio spin-polarized tight binding linear muffin-tin orbital method. The calculated electronic density of states for Pd_{2}TiAl alloy is similar to ultraviolet photoelectron spectroscopy measurements. The self-consistent band calculations showed that the density of states at the Fermi level in Ni_{2}(Nb_{(1-x)}Ti_{x})Sn and Ni_{2}(Nb_{(1-x)}Ta_{x})Sn alloys decreased with the increase in Ti or Ta concentration. The total and local magnetic moments in ordered Rh_{2}TMSn (TM = Mn, Fe, Co, Ni, Cu) and Rh_{2}MnX (X = Al, Ga, In, Ge, Sb, Pb) Heusler-type alloys are calculated. The difference between theoretical and experimental results can be connected to the partial disorder in the samples.
12
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Electronic Structure of Mg_2Ni_{1-x}Cu_{x}

52%
Jezierski A., Jurczyk M., Szajek A.
Acta Physica Polonica A
|
2009
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vol. 115
|
issue 1
223-225
EN
Nanocrystalline Mg_{2}Ni doped alloys are good materials for hydrogen storage. In this work we present the influence of the chemical disorder on the electronic structure of Mg_{2}Ni_{1-x}Cu_{x} alloys for 0 < x < 0.2. The electronic structure was calculated by ab initio full potential scalar relativistic local-orbital method in the coherent potential approximation. We observe the change of the density of states near the Fermi energy.
13
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The Electronic and Magnetic Properties οf UNiAs_2 Antiferromagnet

52%
Werwiński M., Szajek A., Leśniak P., Malinowski W.
|
|
issue 2
413-416
EN
UNiAs_2 band structure has been calculated based on two full-potential methods: full potential linearized augmented plane wave implemented in WIEN2k code and full-potential local-orbital minimum-basis in FPLO code. Starting from the local (spin) density approximation (L(S)DA) we verified either the orbital polarization correction or the LSDA+U approach with the Coulomb repulsion energies U of 0-4 eV for the uranium 5f electrons. Calculated magnetic moments confirm antiferromagnetic ground state and collinear magnetic sequence. The best agreement with experimental results has been achieved by applying orbital polarization corrections, the magnetic moment on uranium amounts to 1.76 μ_{B} per U atom.
14
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Electronic Structure of UCo_{4}B Compound

52%
Szajek A., Smardz L., Szlaferek A., Kowalczyk A.
Acta Physica Polonica A
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2000
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vol. 98
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issue 5
599-603
EN
UCo_{4}B is a member of uranium intermetallic borides family which crystallizes in the hexagonal CeCo_{4}B structure. The experimental data suggest the occurrence of the spin-fluctuation behaviour of UCo_{4}B. In this paper we present the results of band structure calculations using the ab-initio tight binding linear muffin-tin orbital method. We found good agreement between the experimental X-ray photoemission spectroscopy valence band spectrum and the ab-initio results.
15
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Electronic Band Structure and Calculated Photoemission Spectra of USi_{3} Compound

52%
Morkowski J., Szajek A., Jezierski A.
Acta Physica Polonica A
|
1997
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vol. 92
|
issue 2
303-306
EN
The electronic band structure for USi_{3} was recalculated for varying ratios of the Wigner-Seitz radii, for U and Si atoms. The partial densities of states were used to calculate photoemission spectra which were compared with available experimental data.
16
Content available remote

The Electronic and Electrochemical Properties of the LaNi_5-Based Alloys

52%
Szajek A., Jezierski A., Nowak M., Jurczyk M.
Acta Physica Polonica A
|
2009
|
vol. 115
|
issue 1
247-250
EN
Mechanical alloying was used to synthesize LaNi_5-type hydrogen storage materials. X-ray diffraction analysis showed that, after 30 h milling, the starting mixture of the elements was decomposed into an amorphous phase. Following the annealing in high purity argon at 700°C for 0.5 h, X-ray diffraction confirmed the formation of the CaCu_5-type structures. The nanocrystalline materials were used as negative electrodes for a Ni-MH_x battery. A partial substitution o Ni by Al or Mn in LaNi_{5-x}M_x alloy leads to an increase in discharge capacity. On the other hand, the alloying elements such as Al, Mn and Co greatly improved the cycle life of LaNi_5 material. For example, in the nanocrystalline LaNi_{3.75}Mn_{0.75}Al_{0.25}Co_{0.25} powder, discharge capacities of up to 258 mA h g^{-1} (at 40 mA g^{-1} discharge current) were measured. The band structure ab initio calculations showed that 3g sites are preferred by Al, Co, and Mn atoms in the unit cell.
17
Content available remote

Magnetic Properties of the U_5Ge_4 Compound Based on Ab initio Calculations

52%
Szajek A., Werwiński M., Malinowski W., Leśniak P.
Acta Physica Polonica A
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2009
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vol. 115
|
issue 1
251-253
EN
U_5Ge_4 crystallizes in a hexagonal Ti_5Ga_4 type structure with two inequivalent crystallographic sites occupied by uranium atoms. The band structure calculations were performed by the full-potential local-orbital minimum basis band structure code. The calculations showed that on both types of uranium atoms small magnetic moments are formed and their values are equal to 0.08 and 0.15 μ_{B}/atom, respectively.
18
Content available remote

Electronic Properties of CeNiAl₄ Based on ab initio Calculations and XPS Measurements

52%
Werwiński M., Chełkowska G., Szajek A., Kowalczyk A.
Acta Physica Polonica A
|
2018
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vol. 133
|
issue 3
517-519
EN
The CeNiAl₄ compound crystallizes in an orthorhombic YNiAl₄-type structure with a Cmcm space group. The earlier susceptibility data and X-ray photoelectron spectroscopy (XPS) suggested a localized character of the 4f states in CeNiAl₄ with a valence state close to a Ce⁺³ ion. In this work we present a combined theoretical and experimental study of the electronic structure for the Kondo dense system CeNiAl₄ based on the XPS data and ab initio calculations. Using the band structure calculations the theoretical XPS valence band spectra are evaluated. Below the Fermi energy the total density of states contains mainly 3d states of Ni hybridized with Ce 4f states.
19
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Effect of Hydrogenation on the Electronic Structure of HoNiSn - Ab Initio Calculations

52%
Jezierski A., Szajek A., Jurczyk M.
|
|
issue 2
346-349
EN
The electronic and magnetic properties of HoNiSn alloy are studied by ab initio full relativistic full potential local orbital method within the local density approximation. The electronic structures are reported for two crystallographic structures: orthorhombic TiNiSi type and the hexagonal ZrNiAl-type structure. We also study the influence of hydrogenation on the electronic structure of HoNiSnH_{0.66}. Ab initio calculations have shown that in the both type of structures the Fermi level is located at the 4f peak of Ho, however we observed the modification of 3d peaks from nickel atoms below the Fermi energy. The hydrogenation leads to increase of the density of states at the Fermi level.
20
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XPS Valence Band Studies of LaNi_{5-x}Mₓ (M = Al, Co; x = 0, ,1) Alloy Thin Films

46%
Skoryna J., Marczyńska A., Pacanowski S., Szajek A., Smardz L.
Acta Physica Polonica A
|
2015
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vol. 127
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issue 2
430-432
EN
LaNi_{5-x}Mₓ (M = Al, Co) alloy thin films were prepared onto oxidised Si(100) substrates in the temperature range of 285-700 K using UHV magnetron co-sputtering. The surface chemical composition and valence bands of all the alloy thin films were measured in situ, immediately after deposition, transferring the samples to an UHV analysis chamber equipped with X-ray photoelectron spectroscopy. Results showed that the shape of the valence bands measured for the polycrystalline samples is practically the same compared to those obtained theoretically from ab initio band structure calculations. On the other hand, the X-ray photoelectron spectroscopy valence bands of the nanocrystalline thin films (especially LaNi₄Co) are considerably broader compared to those measured for the polycrystalline samples. This is probably due to a strong deformation of the nanocrystals. Therefore, the different microstructure observed in polycrystalline and nanocrystalline alloy thin films leads to significant modifications of their electronic structure.
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