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1
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Charge and Spin Density Perturbation on Iron Nuclei by Non-Magnetic Impurities Substituted on the Iron Sites in α-Fe

100%
Błachowski A.
Acta Physica Polonica A
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2008
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vol. 114
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issue 6
1563-1571
EN
The paper is aimed at the review of the charge and spin density perturbation on the iron nucleus in the bcc iron-based binary alloys containing as the impurity either 4d (Nb, Mo, Ru, Rh, Pd) or 5d (Os, Ir, Au) metals. Additionally, Ga was used as such impurity as well. Measurements were performed by means of the ^{57}Fe transmission Mössbauer spectroscopy at room temperature. Powder X-ray diffraction data for alloys investigated show linear dependence of the lattice constant versus impurity concentration. The Mössbauer data were treated assuming random distribution of the impurity over the iron sites and additive effect for the charge density perturbation, and additive in the algebraic sense effect for the corresponding spin density perturbation. Hence, the effect of impurity depends solely on the distance between impurity and the iron nucleus under above assumptions. It has been found that impurities being further away than a third or in some cases as the second neighbor do not contribute directly to the charge and spin perturbation. On the other hand, they have usually some minor effect on the average charge and spin density. Generally, the perturbation to either charge or spin density has some oscillatory character versus distance from the impurity. The phase and period of the charge oscillation is vastly different from the phase and period of the spin oscillation in the majority of cases. Substitution of the impurities with the increasing number of 4d or 5d electrons leads to the lowering of the electron density on the iron nucleus and causes decreased band spin density on this nucleus. Subsequent impurities donate more and more d-type electrons to the band, and the latter screen more and more effectively s-like electrons. Hence, the density of the s-like electrons on the iron nucleus diminishes. Impurities with 5d electrons have generally stronger effect on the charge and spin density perturbation than impurities with 4d electrons.
2
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Impurity Effect on Charge and Spin Density in α-Fe - Comparison between Cellular Model, Ab Initio Calculations and Experiment

63%
Błachowski A., Wdowik U.
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2011
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vol. 119
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issue 1
24-27
EN
The influence of the impurity substituted on the regular site in the BCC α-Fe on charge and spin density on the adjacent iron nuclei has been studied by the ab initio method within framework of the full-potential linearized augmented plane-wave formalism applying density functional theorem. Results were correlated with the phenomenological cellular atomic model of Miedema and van der Woude and with the Mössbauer spectroscopy experimental data.
3
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Roughness Method to Estimate Fractal Dimension

63%
Błachowski A., Ruebenbauer K.
Acta Physica Polonica A
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2009
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vol. 115
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issue 3
636-640
EN
A method based on the pattern roughness was introduced for determination of the fractal dimension and tested for fractals like the Sierpiński carpet, the Sierpiński triangle, standard Cantor set, the Menger sponge and the Sierpiński tetrahedron. It was tested for non-fractal pattern like two- and four-dimensional gray scale random dust as well. It was found that for all these patterns the Hausdorff dimension is reproduced with relatively high accuracy. Roughness method is based on simple, fast and easy to implement algorithm applicable in any topological dimension. It is particularly suited for patterns being composed of the hierarchy of structures having the same topological dimension as the space embedding them. It is applicable to "fuzzy" patterns with overlapping structures, where other methods are useless. It is designed for pixelized structures, the latter structures resulting as typical experimental data sets.
4
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Mössbauer spectroscopy of iron-based superconductors

51%
Błachowski A., Ruebenbauer K., Żukrowski J.
Annales Universitatis Mariae Curie-Skłodowska, sectio AAA – Physica
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2011
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vol. 66
125-141
EN
A brief review concerned with the application of the Mössbauer spectroscopy to the investigations of iron-based superconductors is given. An introduction is devoted to the description of the most important features of the Mössbauer spectroscopy followed by the discussion of the basic properties of iron-based superconductors. Our results obtained for FeSe, LiFeP and parent compounds of the ‘122’ family, i.e., for AFe2As2 (A=Ca, Ba, Eu) are discussed later on with particular attention paid to the spin density wave (SDW) magnetism exhibited by the parents of the ‘122’ family. It is found that incommensurate SDW contain many harmonics in these layered structures and evolve from almost separated magnetic sheets through quasi-triangular forms to almost rectangular shape with the lowered temperature.
5
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Early Design Stage of the MsAa-4 Mössbauer Spectrometer

51%
Błachowski A., Ruebenbauer K., Żukrowski J., Górnicki R.
Acta Physica Polonica A
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2008
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vol. 114
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issue 6
1707-1713
EN
Entirely new Mössbauer spectrometer MsAa-4 is currently under design and construction. New features as compared to the basic features of the previous generation MsAa-3 spectrometer could be summarized as follows. Completely digital processing of the γ-ray detector signal beyond the Gaussian shape filter/amplifier is to be implemented. The spectrometer is going to be able to accommodate external multiple detector heads. One could collect simultaneously up to 128 γ-ray spectra in 16384 channels of 32-bit each and up to 512 Mössbauer spectra in 4096 channels of 32-bit each provided the proper external multiple detector head is used. The count-rate per single detector is limited to about 10^5 counts per second total. Improved precision of the reference function from 12-bit to 16-bit is to be provided. The reference function is stored in 8192 channels per complete cycle. Addition of the random noise to the reference corner prism of the Michelson-Morley calibration inteferometer is to be introduced to avoid spurious fringes due to the phase lock-up. Integrated universal temperature controller being able to use variety of the temperature sensors is to be interconnected with the proper spectrometer. The spectrometer is now a stand-alone network device as it is equipped with the Ethernet connection to the outside world. Modular design and use of the strict standards allows easy reconfiguration for other applications than the Mössbauer spectroscopy.
6
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Secondary Radiation Field Effects for the CEM Spectra

51%
Ruebenbauer K., Błachowski A., Żukrowski J.
Acta Physica Polonica A
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2010
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vol. 117
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issue 6
953-961
EN
The secondary resonant radiation field and resonant absorption thickness effects on the Conversion Electron Mössbauer Spectroscopy spectra are analyzed for highly enriched resonant targets. It is shown that secondary field effect is important for the thick α-Fe foil enriched in the resonant isotope. Even for the polycrystalline sample traces of the coherent resonant field have been detected as the distortion of lines. Secondary field is discussed in detail. Suitable approximations to treat spectra originating from targets with significant resonant thickness developing secondary field composed of the incoherent and coherent parts are introduced. Finally, the formalism is applied to the high quality spectrum recorded for the enriched iron foil and correlation between contribution due to the secondary field and experimental line shape is investigated.
7
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Interplay Between Spin Density Wave and Superconductivity in `122' Iron Pnictides: ^{57}Fe Mössbauer Study

39%
Błachowski A., Ruebenbauer K., Żukrowski J., Bukowski Z., Matusiak M., Karpinski J.
Acta Physica Polonica A
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2012
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vol. 121
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issue 4
726-729
EN
Iron-based superconductors Ba_{0.7}Rb_{0.3}Fe_{2}As_{2} and CaFe_{1.92}Co_{0.08}As_{2} of the `122' family have been investigated by means of the 14.41-keV Mössbauer transition in ^{57}Fe versus temperature ranging from the room temperature till 4.2 K. A comparison is made with the previously investigated parent compounds BaFe_{2}As_{2} and CaFe_{2}As_{2}. It has been found that Mössbauer spectra of these superconductors are composed of the magnetically split component due to development of spin density wave and non-magnetic component surviving even at lowest temperatures. The latter component is responsible for superconductivity. Hence, the superconductivity occurs in the part of the sample despite the sample is single phase. This phenomenon is caused by the slight variation of the dopant concentration across the sample (crystal).
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