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1
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Magnetic Anisotropy and Exchange Interactions in R_{n+1}Co_{3n+5}B_{2}n Compounds

100%
Kowalczyk A.
Acta Physica Polonica A
|
1994
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vol. 85
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issue 3
623-626
EN
The individual Co site contributions to the magnetocrystalline anisotropy in RCo_{5}, RCo_{4}B and R_{3}Co_{11}B_{4} compounds have been studied. An analysis is given of the room temperature anisotropy constants of these compounds by using a model of Streever. The values of the rare earth-transition metal exchange coupling J_{RCo}/k_{B} derived by mean field analysis of the Curie temperatures are -11.2 K, -15 K and -20.9 K, respectively. In general, a decrease in J_{RCo}/k_{B} with increasing Co concentration is observed.
2
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Electronic Structure of DyCo_5 and DyCo_3B_2 Compounds

64%
Jezierski A., Kowalczyk A.
Acta Physica Polonica A
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2001
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vol. 100
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issue 4
565-572
EN
We study the electronic structure of the hexagonal DyCo_5 and DyCo_3B_2 compounds. The magnetic moments and the band structures were calculated by ab initio self-consistent tight binding linear muffin-tin orbital method within the atomic sphere approximation. These compounds crystallize in a hexagonal structure having the P6/mmm space group. The substitution of cobalt by boron atoms changes the local environment of remaining Co atoms and leads to the decrease in the local magnetic moments as well as in the Curie temperature.
3
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Non-Destructive Characterization, Inspection, Failure Analysis of Advanced Components and Sensors with a High Resolution and High Contrast Micro XCT System

64%
Lau S., Kowalczyk A.
Acta Physica Polonica A
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2009
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vol. 116
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issue S
S-192-S-193
4
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Role of Boron in Nd(Co_{1-x}B_{x})_{5} System

64%
Kowalczyk A., Smardz L.
Acta Physica Polonica A
|
1997
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vol. 92
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issue 2
285-289
EN
The influence of boron atoms on the magnetic properties of Νd(Co_{1-x}B_{x})_{5} (i.e. ΝdCo_{5}, NdCo_{4}B, Νd_{3}Co_{11}Β_{4} and Νd_{2}Co_{7}Β_{3}) compounds has been studied. These structures are based on the well-known CaCu_{5} structure. They all have the hexagonal symmetry and belong to the space group of P6/mmm. The experimental values of the Curie temperatures (T_{c}) of Nd(Co_{1-x}B_{x})_{5} are used to calculate the effective intersublattice exchange interactions (J_{NdCO}) between Nd and Co sublattices. As the Β content increases, a tendency to decrease in J_{NdCO} and T_{c} is found. This variation is compared with that observed for the Co magnetic moment.
5
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Thermoelectric Power and Thermal Conductivity of Heavy Fermion CeCu_4Al

64%
Falkowski M., Kowalczyk A.
Acta Physica Polonica A
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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.
6
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Thermoelectric Properties of CeCu_4Ag Compound

52%
Kowalczyk A., Toliński T., Falkowski M., Timko M.
|
|
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.
7
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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.
8
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Frequency Domain Optical Coherence Tomography Techniques in Eye Imaging

52%
Wojtkowski M., Kowalczyk A., Targowski P., Gorczyńska I.
Acta Physica Polonica A
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2002
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vol. 102
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issue 6
739-746
EN
This contribution presents an application of frequency-domain optical tomography to ophthalmology. Essential theoretical foundations of time-domain and frequency-domain optical tomography are presented. Images of sections through the anterior chamber, the corneo-scleral angle and fundus of the eye are reconstructed from the spectral fringes. The morphological information gained by tomograms is important for diagnosing and planning of a treatment of glaucoma.
9
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Negative Magnetisation and Absence of Superconductivity in RFe_4Al_8 (R=Lu, Yb) Compounds

52%
Andrzejewski B., Kowalczyk A., Toliński T.
Acta Physica Polonica A
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2006
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vol. 109
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issue 4-5
561-564
EN
We report researches for superconductivity and the effect of negative magnetisation in the RFe_4Al_8 (R = Lu, Yb) compounds by means of magnetic measurements and microwave absorption. Contrary to the earlier reports we do not confirm the existence of any traces of superconductivity in these compounds. Instead of the superconductivity and the Meissner effect, the YbFe_4Al_8 compound exhibits the effect of negative magnetisation, whereas the LuFe_4Al_8 compound shows an exact antiferromagnetic behaviour.
10
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Superconducting Properties of Mo_2Re_3B_x-Mo_3Re_2B_x Eutectic

52%
Andrzejewski B., Guilmeau E., Kowalczyk A., Jurga W.
Acta Physica Polonica A
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2007
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vol. 111
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issue 5
727-735
EN
We synthesized, for the first time, superconducting eutectic composed of two new superconducting phases, namely of Mo_2Re_3B_x and of Mo_3Re_2B_x (where x≈1) and investigated its basic transport, magnetic, and microwave properties. The transition temperatures T_c were equal to 6.6 K and to 8.7 K for Mo_3Re_2B_x and Mo_2Re_3B_x compound, respectively. The phases present in the eutectic were identified by means of energy dispersion spectroscopy analyses. It was also shown that the two phases in the eutectic were separated by thin boron interface and formed regular network of the Josephson junctions which very effectively absorbed microwave energy.
11
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Electronic, Magnetic and Transport Properties of YCo_{3}B_{2} Compound

52%
Kowalczyk A., Jezierski A., Smardz L., Baszyński J.
Acta Physica Polonica A
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2000
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vol. 97
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issue 5
803-806
EN
We studied the electronic, magnetic and transport properties of the hexagonal YCo_{3}B_{2} compound. The electronic structure was studied by X-ray photoemission spectroscopy and ab initio self-consistent tight binding linear muffin tin orbital method. We found a good agreement between the experimental X-ray photoemission spectroscopy valence band spectra and theoretical calculations. Theoretical calculations showed that the YCo_{3}B_{2} is a paramagnet in agreement with experimental results. Electrical resistivity at low temperatures shows a T^{2} dependence, implying that the scattering by the spin fluctuactions is dominant in this temperature range.
12
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Magnetocaloric Effect in NdNi_4Si Compound

52%
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.
13
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Electronic Structure and X-Ray Photoelectron Spectra of YNi_4B Compound

52%
Pugaczowa-Michalska M., Chełkowska G., Kowalczyk A.
Acta Physica Polonica A
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2003
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vol. 104
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issue 5
487-494
EN
The electronic structure of the ternary YNi_4B compound, crystallizing in the hexagonal CeCo_4B structure (P6/ mmm space group), was studied by X-ray photoelectron spectroscopy and ab initio calculations. Core levels and the valence band were investigated. The X-ray photoelectron spectroscopy valence band is compared with that obtained from ab initio calculations. The valence band spectrum at the Fermi level exhibits the domination of the Ni(3d) states, which are hybridized with 4d states of Y and 2p states of B. The theoretical electronic specific heat coefficientγ derived from N(E_F) is about 11.33 mJ/(mol K^2) for experimental lattice parameters. The calculated bulk modulus is B_0=1.61632 Mbar.
14
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Magnetic Transition in La_{1/3}Nd_{1/3}Ca_{1/3}MnO_{3} Perovskite Induced by Electric Field at a Given Magnetic Field

52%
Baszyński J., Kowalczyk A., Kováč J.
Acta Physica Polonica A
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2000
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vol. 97
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issue 5
879-882
EN
We report the discovery of new effect in La_{1/3}Nd_{1/3}Ca_{1/3}MnO_{3} - the jump of magnetization induced by external electric field E (2.5-4)V/cm at a given magnetic field H (18-25) kOe at T=4.2 K. This effect is large when compared with a metamagnetic transition induced by the magnetic field in many substances. The origin of the magnetization jump induced by external electric field has not yet been explained. We assume that this transition is induced by the hopping of E-excited e_{g} electrons and that this is a source of a jumpwise increase in magnetization in the non-collinear magnetic phase within the perovskite. This effect can be attributed to a strong coupling between carriers induced by the electric field (the conduction electrons e_{g}), and the local magnetic moments (t_{2g}-localized spins) through a mechanism of the Zener double exchange.
15
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Thermoelectric Power of CeNi_4Si and YbNi_4Si Compounds

52%
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.
16
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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.
17
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Specific Heat of YbNi_4Si Compound

52%
Falkowski M., Kowalczyk A., Toliński T.
Acta Physica Polonica A
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2008
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vol. 113
|
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.
18
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Magnetic Properties and Magnetocaloric Effect of DyNi_{4}Si

46%
Synoradzki K., Kowalski W., Falkowski M., Toliński T., Kowalczyk A.
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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.
19
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X-Ray Magnetic Circular Dichroism Studies on CeNi_4B

46%
Toliński T., Cezar J., Wende H., Kowalczyk A., Baberschke K.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
129-131
EN
The CeNi_4B compound is a mixed-valence system. It is a paramagnet with μ_{eff}= 0.52 μ_{B}/f.u. and the paramagnetic Curie temperature θ= -10.7 K. In the present research we complete our previous magnetic susceptibility and X-ray photoemission measurements with new studies by the X-ray magnetic circular dichroism method. The observation of the Ce M_{4,5} edges carried out with X-ray magnetic circular dichroism confirms the mixed-valence state deduced previously from X-ray photoemission spectroscopy. Moreover, we report on the measurements of the Ni L_{2,3} edges, which enable verification of the Ni contribution to the magnetism of this compound.
20
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Spin Reorientation and Exchange Coupling in the Dy_{1-x}Er_{x}Fe_{10}Si_{2} Compounds

46%
Stefański P., Kowalczyk A., Skoryna D., Szlaferek A., Wrzeciono A.
Acta Physica Polonica A
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1994
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vol. 85
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issue 2
259-262
EN
The structural and magnetic properties of Dy_{1_{x}}Er_{x}Fe_{10}Si_{2} are investigated. X-ray analysis reveals that these compounds are of the tetragonal ThMn_{12} structure. In this structure the rare earth atoms occupy one crystallographic position 2(a). The unit cell contains 26 atoms. The spin reorientation temperature, T_{SR}, was measured from the temperature dependence of the initial susceptibility using an ac bridge of mutual inductance of the Harsthorn type. Dy^{+3} and Er^{+3} have opposite contributions to the entire magnetic anisotropy. The spin reorientation temperature is found to be about 271 K in DyFe_{10}Si_{2} and 48 K in ErFe_{10}Si_{2}. The values are discussed applying the crystal field model. The value of the rare earth-transition metal exchange coupling constant J_{RFe}/k_{B} derived from the mean-field model analysis of the Curie temperature is about -13 K. The Fe-Fe exchange integral is much higher and is equal to about 75 K.
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