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Wyszukujesz frazę "Hoffmann, M" wg kryterium: Autor


Wyświetlanie 1-11 z 11
Tytuł:
Vibronic Effects in EPR Spectra of (NH$\text{}_{4}$)$\text{}_{2}$Cu(BeF$\text{}_{4}$)$\text{}_{2}$·6H$\text{}_{2}$0 Single Crystal
Autorzy:
Hoffmann, S.
Gomółka-Marciniak, M.
Powiązania:
https://bibliotekanauki.pl/articles/1929355.pdf
Data publikacji:
1993-06
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
76.30.-v
71.70.Ej
Opis:
Angular variations of the g-factors and linewidth value were recorded at X-band, at room temperature, and at 77 K. The temperature dependence of the g-factors was measured along the principal g-tensor axes in the temperature range from 4.2 K to 300 K. The rigid lattice g-factors at 4.2 K are: g$\text{}_{z}$ = 2.428, g$\text{}_{y}$ = 2.138, and g$\text{}_{x}$ = 2.058. The g$\text{}_{x}$ value very slowly increases linearly on heating, whereas g$\text{}_{z}$ and g$\text{}_{y}$ nonlinearly tend towards their average value. This is a typical behaviour of Cu(II) EPR in Tutton salt crystals, however the g(T) dependence is much less pronounced in (NH$\text{}_{4}$)$\text{}_{2}$Cu(BeF$\text{}_{4}$)$\text{}_{2}$·6H$\text{}_{2}$0 as compared to the Cu(II) doped salts. The results are described in terms of the two vibronic coupling models of the strong Jahn-Teller effect. It is shown that the models are not adequate to describe the vibronic g-factor behaviour in paramagnetic Cu(II) crystals which is attributed to the cooperative Jahn-Teller effect existing in these crystals.
Źródło:
Acta Physica Polonica A; 1993, 83, 6; 817-830
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
EPR Dating of Hydroxyapatite from Fossil Bones. Transient Effects after γ and UV Irradiation
Autorzy:
Wencka, M.
Hoffmann, S. K.
Hercman, H.
Powiązania:
https://bibliotekanauki.pl/articles/2043612.pdf
Data publikacji:
2005-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
76.30.-v
65.90.+i
Opis:
ESR measurements at room temperature have been performed on fossil bones of cave bear (from Magurska Cave of the Tatra Mountains) and mammoth (from Dniestr River). Various paramagnetic centres related to defects in hydroxyapatite were identified. The ESR spectrum is dominated by Mn$\text{}^{2+}$ lines and free radical centres CO$\text{}_{2}^{-}$ and CO$\text{}_{3}^{-}$. Suitability of various EPR lines for the dating was evaluated. The spectra are affected by γ-ray and UV irradiation which produce new relatively unstable (transient) radical centres. From their decay curves we determined the delay period (waiting time) between irradiation and ESR dating measurements. For γ-rays the period is about 15 days and depends on the chosen ESR line. UV generates mainly surface O$\text{}^{-}$ centres which decay practically after a few days. The ESR dating of the bear bones using an additive dose method given the age t = 21.7 kiloyears (ky), whereas from radionuclide Th/U method t= 34 ky and from radiocarbon $\text{}^{14}$C method t > 33.1 ky.
Źródło:
Acta Physica Polonica A; 2005, 108, 2; 331-337
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Influence of Molecular Electric Fields on Elastic Properties of Perovskite-Like Substrates
Autorzy:
Hoffmann, T. J.
Drozdowski, M.
Kasprowicz, D.
Powiązania:
https://bibliotekanauki.pl/articles/1964365.pdf
Data publikacji:
1997-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
46.30.Cn
Opis:
The dynamics of ABCO$\text{}_{4}$ deformable crystals with electroelastic interacting was expressed by theoretical model with wave-linear approximation. The one-dimensional problem was considered assuming that the field variables are represented by plane electroelastic waves. As a result the dispersion equation for these crystals was obtained. Using this model the data concerning the elastic properties of SrLaGaO$\text{}_{4}$ are discussed.
Źródło:
Acta Physica Polonica A; 1997, 92, 1; 187-190
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Temperature Effects in ESR Spectra of Radical Centres in Dripstone Calcite Samples Used for ESR Dating
Autorzy:
Wencka, M.
Hoffmann, S. K.
Krzyminiewski, R.
Mielcarek, S.
Powiązania:
https://bibliotekanauki.pl/articles/2043694.pdf
Data publikacji:
2005-09
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
76.30.-v
65.90.+i
Opis:
Natural calcite samples were collected from the dripstone layers of the Black Cave of the Tatra Mountains. ESR spectra, thermal analysis, and thermoluminescence data were analysed to obtain a consistent picture of the calcite properties. The ESR spectra were analysed using computer enhanced resolution spectra and an influence of the thermal annealing on intensity of individual ESR lines was measured. These results together with the effects of γ-irradiation in ESR spectra allowed one to discriminate between ESR lines from various paramagnetic centres. A general conclusion of the paper is that in the ESR dating the outer ESR lines of CO$\text{}_{3}^{-}$ (g=2.0125) and CO$\text{}_{2}^{-}$ (g=1.9980) radicals should be used instead of the commonly used multicomponent central line.
Źródło:
Acta Physica Polonica A; 2005, 108, 3; 491-503
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Restricted Validity of the Two-State Model Describing a Vibronic EPR g-Factors Averaging in Cs$\text{}_{2}$Zn(SO$\text{}_{4}$)$\text{}_{2}$·6H$\text{}_{2}$O Tutton Salt Crystals Doped with Cu$\text{}^{2+}$ Ions
Autorzy:
Hoffmann, S. K.
Kaszyński, R.
Augustyniak, M. A.
Hilczer, W.
Powiązania:
https://bibliotekanauki.pl/articles/2011161.pdf
Data publikacji:
1999-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
63.90.+t
76.30.-v
Opis:
Single crystals and powder EPR spectra of Cu$\text{}^{2+}$ ions in Cs$\text{}_{2}$Zn(SO$\text{}_{4}$)$\text{}_{6}$·6H$\text{}_{2}$O were recorded in the temperature range of 4.2-300 K and the g-factor temperature variations were determined. The g$\text{}_{z}$ and g$\text{}_{y}$ have the values of 2.443 and 2.134, respectively, at the rigid lattice limit below 20 K, and then continuously tend to an average value on heating. This vibronic averaging produced by reorientations of Cu(H$\text{}_{2}$O)$\text{}_{6}$-complexes between Jahn-Teller distorted octahedral configurations is described in terms of a two-state Silver-Getz model which is known as a good model for diamagnetic non-ammonium Tutton salts. We found, however, that this model is only a crude approximation in Cs$\text{}_{2}$Zn(SO$\text{}_{4}$)$\text{}_{6}$·6H$\text{}_{2}$O below 150 K. Above this temperature the model works better and describes the vibronic dynamics between the two lowest energy potential wells in the adiabatic potential surface differing in the energy of δ$\text{}_{12}$=318(9) cm$\text{}^{-1}$=3.7 kJ/mol.
Źródło:
Acta Physica Polonica A; 1999, 96, 6; 733-740
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Role of Ferric(III) Oxide in Poly-(1,4-Phenylene Sulphide) Curing. EPR and X-ray Studies
Autorzy:
Wejchan-Judek, M.
Hoffmann, S. K.
Goslar, J.
Garbarczyk, J.
Powiązania:
https://bibliotekanauki.pl/articles/2043404.pdf
Data publikacji:
2005-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
76.30.-v
61.41.+e
Opis:
Commercially available poly-(1,4-phenylene sulfide) = PPS with trade names TEDUR and RYTON contain a great amount of Fe(III) (order of 10$\text{}^{20}$ Fe/gram) as shown by electron spin resonance spectra. The curing of the pure and Fe-doped (0.2% Fe$\text{}_{2}$O$\text{}_{3}$) PPS polymers proves that Fe(III) can be used for improvement of the PPS strength by increasing the polymer cross-linking and a decrease in the polymer crystallinity degree as shown by X-ray diffraction.
Źródło:
Acta Physica Polonica A; 2005, 108, 1; 107-112
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electron Spin Echo Envelope Modulation Analysis of SeO¯$\text{}_{3}$ Radical in (NH$\text{}_{4}$)$\text{}_{3}$H(SeO$\text{}_{4}$)$\text{}_{2}$ Single Crystal
Autorzy:
Tritt-Goc, J.
Goslar, J.
Hilczer, W.
Hoffmann, S.
Augustyniak, M. A.
Powiązania:
https://bibliotekanauki.pl/articles/1929835.pdf
Data publikacji:
1993-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
76.60.Lz
76.30.Mi
Opis:
A detailed computer analysis of the electron spin echo envelope modulations of SeO$\text{}_{3}$ radical in a suitable orientation of (NH$\text{}_{4}$)$\text{}_{3}$H(SeO$\text{}_{4}$)$\text{}_{2}$ single crystal is presented. It was found that the modulations are due to a weak dipolar coupling with nitrogens and protons of the only two neighbouring NH$\text{}_{4}$ groups among the five NH$\text{}_{4}$ groups surrounding SeO¯$\text{}_{3}$ center. Isotropic dipolar coupling constant is 1.7 MHz for nitrogens and 0.9 MHz for protons. It was shown that thermal reorientations of NH$\text{}_{4}$ groups observed by NMR have a negligible effect on the electron spin echo envelope modulation pattern but can be responsible for the same value of a$\text{}^{H}$$\text{}_{iso}$ for all protons in a NH$\text{}_{4}$ group. A good fit obtained between experimental spectra and theoretical calculations assuming nondisturbed crystal geometry indicates a small damage of the crystal by X-rays during the radical center formation.
Źródło:
Acta Physica Polonica A; 1993, 84, 6; 1131-1141
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Influence of the Grain Size on Polaron Transport in Nanostructured La$\text{}_{2}\text{}_{/}\text{}_{3}$ Ca$\text{}_{1}\text{}_{/}\text{}_{3}$ MnO$\text{}_{3}$ Evidenced by EPR
Autorzy:
Raita, O.
Grecu, M. N.
Filip, X.
Toloman, D.
Giurgiu, L. M.
Idziak, S.
Hoffmann, S. K.
Powiązania:
https://bibliotekanauki.pl/articles/2043406.pdf
Data publikacji:
2005-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.50.Tt
73.63.Bd
76.50.+g
Opis:
We report an electron paramagnetic resonance investigation of the grain size effects on the polaron transport in the paramagnetic regime of nanosized La$\text{}_{2}\text{}_{/}\text{}_{3}$ Ca$\text{}_{1}\text{}_{/}\text{}_{3}$ MnO$\text{}_{3}$ manganites. The temperature dependences of the EPR integral intensity were analyzed in terms of spin-spin exchange interaction and small polaron hopping scenarios. The polaron activation energy decreases with the reduction of the grain size. A discussion is given concerning the factors which could explain the observed change.
Źródło:
Acta Physica Polonica A; 2005, 108, 1; 113-118
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
EPR and Spectral Studies of a Molecular and Crystal Structure of Cu (3,5-dimethylpyridine)$\text{}_{3}$(NO$\text{}_{3}$)$\text{}_{2}$
Autorzy:
Hoffmann, S. K.
Goher, M. A. S.
Hilczer, W.
Goslar, J.
Hafez, A. K.
Powiązania:
https://bibliotekanauki.pl/articles/1930620.pdf
Data publikacji:
1994-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
33.20.Ea
61.66.-f
76.30.Da
Opis:
X-band single crystal EPR, IR and UV-VIS data are used to deduce a molecular and crystal structure of a new compound with a chemical formula Cu(3,5-dimethylpyridine)$\text{}_{3}$(NO$\text{}_{3}$)$\text{}_{2}$. EPR shows that four magnetically inequivalent molecules exist in the crystal unit cell of C$\text{}_{4v}$ symmetry. IR spectra suggested that both monodentate and bidentate NO$\text{}_{3}$-groups exist in the crystal. A most probable Cu(II) complex geometry with d$\text{}_{x²-y²}$ ground state is a square pyramid with three nitrogens from 3,5-dimethylpyridine molecules and one oxygen from monodentate nitrato group in a basal plane and an oxygen from NO$\text{}_{3}$-group in apical position. There exists a chemical contact between complexes as it is indicated by the exchange interaction with |J| ≤ 1 cm$\text{}^{-1}$. It suggests that square pyramid complexes are arranged in polymeric chains with semi-coordination of bidentate NO$\text{}_{3}$-group to the adjacent Cu(II) ion. An extended analysis of an exchange averaging effect between EPR lines from two and four Cu(II) sites is presented with equations relating molecular and crystal g-factors.
Źródło:
Acta Physica Polonica A; 1994, 85, 3; 517-530
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Influence of the Grain Size on the Magnetic Properties of $TbMnO_{3}$
Autorzy:
Bażela, W.
Dul, M.
Dyakonov, V.
Gondek, Ł.
Hoser, A.
Hoffmann, J.
Penc, B.
Szytuła, A.
Kravchenko, Z.
Nosalev, I.
Zarzycki, A.
Powiązania:
https://bibliotekanauki.pl/articles/1431251.pdf
Data publikacji:
2012-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
61.05.Cp
61.05.F-
61.05.J-
75.30.kz
75.50.Ee
75.50.-y
Opis:
The magnetic properties including magnetic structure of poly and nano samples of $TbMnO_{3}$ are determined. All the samples investigated are antiferromagnets. In these samples the Mn ad Tb moments order antiferromagnetically at different temperatures and form modulated magnetic structure described by the propagation vector k=($k_{x}$,0,0) with different value of $k_{x}$ for the Mn and Tb sublattices. Comparison of the data for poly and nano samples indicates the decrease of the moment and increase of the $k_{x}$ component of propagation vector in the nano specimens. The wide Bragg peak related to the Tb sublattice suggests that the magnetic order has the claster-like character. The magnetic moments value in both sublattices is smaller, whereas the $k_{x}$ values are larger for nano samples.
Źródło:
Acta Physica Polonica A; 2012, 121, 4; 785-788
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Magnetic and Neutron Diffraction Studies of the Polycrystalline and Nanoparticle $TbMnO_3$
Autorzy:
Bażela, W.
Dul, M.
Dyakonov, V.
Gondek, Ł.
Hoser, A.
Hoffmann, J.
Penc, B.
Szytuła, A.
Kravchenko, Z.
Nosalev, I.
Zarzycki, A.
Powiązania:
https://bibliotekanauki.pl/articles/1419577.pdf
Data publikacji:
2012-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.40.Cx
75.47.Lx
75.25.-j
75.50.Ee
Opis:
This paper reports on investigations of magnetic properties, crystal and magnetic structures on $TbMnO_3$ prepared in various ways, namely, as conventional polycrystalline sample and two nano particle specimens (synthesized with a sol-gel method at temperatures of 800 and 850°C). The X-ray and neutron diffraction data confirm the orthorhombic crystal structure (space group Pbnm, No. 62) without noticeable differences of the lattice parameters for poly- and nanocompounds. For the polycrystalline sample, a subsequent ordering of the Mn and Tb sublattices with decreasing temperature was observed. Namely, the Mn sublattice exhibits a modulated magnetic structure with the propagation vector k = (0, $k_{x},$ 0) in between 41-5 K. Below T = 21 K, a change from a collinear ($A_{y}$ mode) into non-collinear ($A_{y}G_{z}$ mode) structure was evidenced. Further decreasing of temperature below 10 K results in magnetic ordering of the Tb sublattice (modulated $G_{x}A_{y}F_{z}$ mode). For nanoparticle compounds, magnetic ordering in the Mn and Tb sublattices is described by propagation vector k = (0, $k_{y},$ 0), with $k_{y}$ components higher than observed for polycrystalline sample. The magnetic ordering in the Mn sublattice is described by a collinear $A_{y}$ mode down to 1.6 K where the Tb moment becomes ordered ($G_{x}A_{y}$ mode). The observed broadening of the Bragg peaks connected to the Tb sublattice suggests the cluster-like character of its magnetic structure.
Źródło:
Acta Physica Polonica A; 2012, 122, 2; 384-390
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-11 z 11

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