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Spin Transition Diagram of (2Me-5Et-PyH)[Fe(Th-5Cl-Sa)_2] Studied by EPR

100%
Krupska A., Augustyniak-Jabłokow M., Yablokov V., Zelentsov V.
Acta Physica Polonica A
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2005
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vol. 108
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issue 2
291-296
EN
The high-spin↔ low-spin transition in (2Me-5Et-PyH)[Fe(Th-5Cl-Sa)_2] was studied by EPR under hydrostatic pressure in the temperature range of 80-310 K. Two modifications of the low-spin complexes: low-pressure (LS-1) and high-pressure (LS-2) ones were revealed. The low-spin complexes are associated in domains. Under atmospheric pressure LS-1 appears or disappears at 220 K. The hydrostatic pressure shifts the transition to high temperatures. Above 410 MPa the abrupt changes of the g-factor and width Δ B of the EPR line are observed. The pressure-induced transition LS-1 ↔ LS-2 is almost independent of T up to 275 K where under pressure 420 MPa a triple point is observed. When the pressure has been decreased the reverse transition from LS-2 to LS-1 or to high spin phase (at T>260 K) occurs with a large hysteresis about 95 MPa.
2
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Electron Paramagnetic Resonance Study of Organic Radicals in Some Herbal Plants

100%
Krupska A., Wojtowicz E., Augustyniak-Jabłokow M.
Acta Physica Polonica A
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2016
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vol. 129
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issue 6
1201-1204
EN
In this work we show the impact of the roasting process on the properties of organic radicals in some herbal products added to cereal coffee. The EPR study shows the presence of radicals in dried herbal products, both natural and roasted. Changes in the relative intensity of the EPR signal and in the g-factor for unroasted and roasted plant material can be observed. This indicates to the recombination processes of radicals. Roasting process increases the number of radicals. The analysis of EPR spectra show that they consist of two Gaussian lines which indicate that there are at least two different kinds of radicals. The values of g-factor about 2 may be derived from a number of very different radicals. For this reason the identification of such radicals is not strictly possible.
3
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Magnetic Centres in Functionalized Graphene

100%
Majchrzycki Ł., Augustyniak-Jabłokow M., Strzelczyk R., Maćkowiak M.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
540-542
EN
Discussion of the origin of paramagnetic centres observed by electron paramagnetic resonance in graphene oxide (GO) and reduced graphene oxide (rGO) is done on the assumption that GO can be considered as a functionalized graphene. This leads to the conclusion that the narrow signal with g close to 2, observed for GO and thermally reduced GO, is due to paramagnetic centres localized on defects and exchange coupled to conduction electrons. Randomness of graphene modification results in variety of parameters of EPR signals. The broad signals observed in GO and rGO and ascribed to magnetic clusters on the zig-zag edge states indicate that the edge magnetism can be preserved by functionalization.
4
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FMR Evidence of Stable Ferromagnetic Correlations at Zigzag Edge States in Graphene

100%
Augustyniak-Jabłokow M., Maćkowiak M., Tadyszak K., Strzelczyk R.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
537-539
EN
We studied magnetic properties of a composite of paraffin and graphene flakes. Magnetic properties of this composite were investigated by ferromagnetic resonance/electron spin resonance technique. The ferromagnetic resonance signal from graphene suspension in paraffin is broad and shifted from magnetic field corresponding to g ≈ 2 to the low magnetic field. The temperature dependence of the spectra shows that magnetic ordering in the studied system is sensitive to thermal fluctuations. These features are expected for the 1D ferromagnetism and the obtained results are analyzed in the frame of the theoretical predictions concerning magnetic correlations at graphene edges. Therefore, based on our investigation we can conclude the existence of the magnetic edges in graphene and presence of the ferromagnetic correlations between edge spins.
5
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Intramolecular and Lattice Dynamics in V_{6-n}^{IV}V_ n^V O_7(OCH_3)_{12} Crystal

88%
Yablokov Y., Augustyniak-Jabłokow M., Borshch S., Daniel C., Hartl H.
Acta Physica Polonica A
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2005
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vol. 108
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issue 2
271-281
EN
Multi-nuclear mixed-valence clusters V_4^{IV}V_2^VO_7(OCH_3)_{12} were studied by X-band EPR in the temperature range 4.2-300 K. An isotropic exchange interactions between four V^{IV} ions with individual spin S_i=1/2 determine the energy levels structure of the compound with the total spin states S=0, 1, and 2, which are doubled and split due to the extra electron transfer. The spin-Hamiltonian approach was used for the analysis of the temperature dependences of the EPR spectra parameters and the cluster dynamics. Two types of the electron transfer are assumed: the single jump transfer leading to the splitting of the total spin states by intervals comparable in magnitude with the exchange parameter J≈100-150 cm^{-1} and the double jump one resulting in dynamics. The dependence of the transition ratesν_{tr} on the energy of the total spin states was observed. In particular, in the range 300-220 K theν_{tr} ≈0.7×10^{10} cm^{-1} and below 180 K the ν_{tr}≈1×10^{10} cm^{-1} was estimated. The g-factors of the spin states were shown to depend on the values of the intermediate spins. A phase transition in the T-range 210-180 K leading to the change in the initial V^{IV} ions localization was discovered.
6
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The Origin of EPR Signals in SrCuO_2 Ceramics

88%
Augustyniak-Jabłokow M., Yablokov Y., Ivanova T., Jacyna-Onyszkiewicz I., Shustov V.
Acta Physica Polonica A
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2005
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vol. 108
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issue 2
345-351
EN
The origin and thermal evolution of the EPR signals in SrCuO_2 ceramics are studied. It has been shown that the EPR signals observed in this ceramic material are due to contamination with other phases. The axial signal is due to SrCu(OH)_4·H_2O, which is a product of water reactions with SrCuO_2.
7
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EPR Study of Water Induced Decomposition of the SrCuO_2 and Sr_2CuO_3 Ceramics Surface. The Role of Carbon Dioxide

88%
Augustyniak-Jabłokow M., Yablokov Y., Jacyna-Onyszkiewicz I., Ivanova T., Shustov V.
Acta Physica Polonica A
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2007
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vol. 112
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issue 3
525-536
EN
Processes of SrCuO_2 and Sr_2CuO_3 ceramics decomposition induced by contact with water and carbon dioxide were studied by EPR. The dominant signals in the spectra were found to originate from Sr_2Cu(OH)_6 (for Sr_2CuO_3) and SrCu(OH)_4·H_2O (for SrCuO_2) compounds. The thermally induced conversion of SrCu(OH)_4·H_2O into Sr_2Cu(OH)_6 was analysed, and its product CuO was found to exist in the nanocrystalline form. The presence of CO_2, reacting with Sr(OH)_2, was shown to modify the decomposition process leading to the appearance of SrCu(OH)_4·H_2O, some hydroxycarbonates and Cu(OH)_2 on the surface of ceramics studied. At temperatures higher than 300ºC CuO reacts back with Sr(OH)_2. For the samples being in contact with atmospheric moisture this compound, deposited on a surface of SrCuO_2, decomposes to Sr_2Cu(OH)_6. The presence of the antiferromagnetic compounds Cu(OH)_2, CuO, and Cu_2[(OH)_2CO_3] in the samples can influence the results of magnetic measurements of the studied ceramics.
8
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EPR Discovery of a New Pressure-Induced Low-Spin Phase in (2Me-5Et-PyH)[Fe(Th-5Cl-Sa)_2]

76%
Krupska A., Augustyniak-Jabłokow M., Yablokov Y., Zelentsov V., Ulanov V., Mroziński J.
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EN
Electron paramagnetic resonance studies of the high-spin (HS) ↔ low-spin (LS) transition in 2-methyl-5-ethyl-pyridine-5-chloro-salicylalt hiosemicarbazonatoferrate(III) performed under hydrostatic pressure up to 500 MPa in a temperature range of 80-310 K have revealed two modifications of the low spin complexes: low-pressure (LS1) and high-pressure (LS2) ones. Under atmospheric pressure LS1 appears on cooling and disappears on heating at 220 K. The hydrostatic pressure shifts the transition to higher temperatures. Below 275 K an increase in pressure to 410 MPa results in abrupt changes in the g-factor and widthΔ B of the EPR line indicating a transition to a new phase. The pressure-induced transition LS1 ↔ LS2 is almost independent of T up to 275 K, where at a pressure of 420 MPa a triple point is observed. The LS1↔ LS2 and HS↔ LS2 (at T>260 K) transitions occur with a large hysteresis of about 95 MPa. The process of the spin transition has been shown to begin with the formation of domains of LS complexes in the matrix of HS ones. The response of the domains to external factors has been studied.
9
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Delocalization of the Cu^{2+} Unpaired Electron on the Next Nearest Ligands in Sr_2Pd_{0.99}Cu_{0.01}O_3 Ceramics

76%
Augustyniak-Jabłokow M., Yablokov Y., Jacyna-Onyszkiewicz I., Ivanova T., Shustov V., Polovniak V.
Acta Physica Polonica A
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2008
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vol. 114
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issue 1
197-201
EN
Supertransferred hyperfine interactions between the Cu^{2+} unpaired electron and the ^{105}Pd nuclei in the Sr_2Pd_{0.99}Cu_{0.01}O_3 ceramic were studied by the EPR method. The spectrum of isolated -Pd-O-CuO_2-O-Pd- units (g_∥ = 2.280±0.001; g_⊥ = 2.040±0.001; A_∥(^{63}Cu) = 13 mT±0.1; A_∥(^{65}Cu) = 13.9 ±0.1 mT; A_⊥(^{63,65}Cu) = 0.0 mT) overlaps the signal from small groups of exchange coupled Cu^{2+} ions (g_∥ = 2.278±0.002; g_⊥ = 2.041±0.001). The isotropic contribution was shown to dominate in the Cu-Pd supertransferred interactions (A_∥(^{105}Pd) = A_⊥ (^{105}Pd) = 1 mT = a_{iso} Pd).
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