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1
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Electron Paramagnetic Resonance Study of the [(CH_3)_2NH_2]_5Cd_3Cl_{11} Monocrystal Doped with Cu^{2+} ion

100%
Ostrowski A., Bednarski W., Waplak S., Czapla Z.
Acta Physica Polonica A
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2002
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vol. 101
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issue 6
893-899
EN
The paper reports the electron paramagnetic resonance investigation of Cu^{2+} doped [(CH_3)_2NH_2]_5Cd_3Cl_{11} (DMACC) monocrystal. DMACC:Cu^{2+} was studied in the temperature range (6÷293) K. We did not observe any anomalies of spin-Hamiltonian parameters of Cu^{2+} ion corresponding to the temperature anomalies observed in dielectric studies. The electron paramagnetic resonance anomaly recorded at about 40 K results from the subtle changes in bonds angles and Cu-Cl distances and suggests the smooth second order transition.
2
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Microwave X-Band Resonances in Doped Cd₂Nb₂O₇ Monocrystals

100%
Waplak S., Ostrowski A., Wencka M., Bednarski W.
Acta Physica Polonica A
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2017
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vol. 132
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issue 1
7-11
EN
Cadmium pyroniobiate (CNO) is the ferroic material with unusual diffuse phase diagram which includes both relaxor and nanocluster domains. We present the data for CNO crystals with several admixtures of paramagnetic ions studied on X and S microwave bands at zero-external magnetic field and classical EPR conditions. Our results lead to an assertion of a ferroelectric resonance effect due to "electronic ferroelectricity". The data fit well to the Falicov-Kimball theoretical model applicable to strongly-correlated-electron or mixed-valence systems.
3
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EPR Study of VO^{2+} Center in Fast Proton Conductor K_3H(SO_4)_2

100%
Ostrowski A., Waplak S., Bednarski W.
Acta Physica Polonica A
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2005
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vol. 108
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issue 1
127-135
EN
The pretransitional phenomena of superprotonic phase transition (T_{sp}=471 K) were studied in detail by X-band continuous wave EPR spectra of K_3H(SO_4)_2 crystal doped with VO^{2+} ions. Three kinds of VO^{2+} complexes (magnetically equivalent but structurally non-equivalent) denoted as VO^{2+}(I), VO^{2+}(II), and VO^{2+}(III) were found. "Smearing out" of the superhyperfine structure was observed as a result of interbond proton motion. VO^{2+} impurity replaces K^+ ion and experiences the same average crystal field gradient at T_{sp}=471 K for I- and II-type complexes. The increase in interbond proton frequency hopping above 360 K is a reason of significant line broadening.
4
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Pretransition Phenomena in Fast-Proton Conductors

100%
Waplak S., Bednarski W., Ostrowski A.
Acta Physica Polonica A
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2005
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vol. 108
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issue 2
261-270
EN
In this paper we present recent experimental results related to nonlinear crystal field fluctuations and current flow in K_3H(SO_4)_2 fast-proton conductor far below the transition temperature T_g. The results for crystalline and powdered samples are quantitatively explained in the framework of soliton model of charge transport.
5
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EPR Study of Cu^{2+} Doped Fast-Proton Conductor K_3H(SO_4)_2 in the Temperature Range 100-450 K

100%
Ostrowski A., Bednarski W., Waplak S.
Acta Physica Polonica A
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2003
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vol. 104
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issue 6
549-558
EN
The K_3H(SO_4)_2 doped with Cu^{2+} ion was studied in detail by X-band CW EPR. Two kinds of Cu^{2+} complexes (magnetically and structurally nonequivalent) denoted as Cu^{2+}(I) and Cu^{2+}(II) were found. Spin-Hamiltonian parameters, direction cosines, and coordination of Cu^{2+} ion were determined at room temperature. The superhyperfine structure was observed below 250 K as a result of interacting of Cu^{2+} ion with four equivalent protons (I=1/2). Temperature studies of K_3H(SO_4)_2 crystal show that interbond motion as a precursor of superprotonic phase transition occurs at above≈250 K.
6

Importance of eps genes from Bacillus subtilis in biofilm formation and swarming

88%
Nagorska K., Ostrowski A., Hinc K., Holland I. B., Obuchowski M.
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vol. 51
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issue 3
369-381
EN
Unicellular organisms naturally form multicellular communities, differentiate into specialized cells, and synchronize their behaviour under certain conditions. Swarming, defined as a movement of a large mass of bacteria on solid surfaces, is recognized as a preliminary step in the formation of biofilms. The main aim of this work was to study the role of a group of genes involved in exopolysaccharide biosynthesis during pellicle formation and swarming in Bacillus subtilis strain 168. To assess the role of particular proteins encoded by the group of epsI-epsO genes that form the eps operon, we constructed a series of insertional mutants. The results obtained showed that mutations in epsJ-epsN, but not in the last gene of the eps operon (epsO), have a severe effect on pellicle formation under all tested conditions. Moreover, the inactivation of 5 out of the 6 genes analysed caused total inhibition of swarming in strain 168 (that does not produce surfactin) on LB medium. Following restoration of the sfp gene (required for production of surfactin, which is essential for swarming of the wild-type bacteria), the sfp+ strains defective in eps genes (except epsO) generated significantly different patterns during swarming on synthetic B medium, as compared to the parental strain 168 sfp+.
7
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Magnetic Properties of Epitaxial Fe/(Ga,Mn)As Hybrids

52%
Kalbarczyk K., Dziatkowski K., Szczytko J., Gosk J., Tokarczyk M., Kowalski G., Twardowski A., Bednarski W., Ostrowski A., Waplak S., Martinek J., Liu X., Furdyna J.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
873-876
EN
Thin-film structures composed of two kinds of ferromagnetic material - metallic Fe and semiconducting (Ga,Mn)As - were investigated by means of SQUID magnetometry and ferromagnetic resonance spectroscopy. Dependence of remnant magnetic moment on temperature showed unexpected anisotropic features when recorded along two orthogonal in-plane directions. For one of these orientations, the change in sign of the slope of m(T) curve at the Curie point of (Ga,Mn)As was observed, while for the other, an analogous m(T) curve retained monotonic character. Based on the comparison with ferromagnetic resonance data, the apparent non-monotonicity was attributed to the temperature-induced change of balance between the external magnetic field and uniaxial magnetic anisotropy in the plane of Fe layer.
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