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1
Content available remote Temperature study of magnetic resonance spectra of co-modified (Co,N)-TiO2 nanocomposites
Guskos N., Typek J., Zolnierkiewicz G., Guskos A., Berczynski P., Dolat D., Mozia S., Aidinis K., Kruk K., Morawski A. W.
Materials Science Poland
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2016
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Vol. 34, No. 2
242--250
EN
The (nCo,N)-TiO2 (n = 1, 5 and 10 wt.% of Co) nanocomposites were investigated by magnetic resonance spectroscopy in 4 K to 290 K range. Analyses of ferromagnetic/electron paramagnetic resonance (FMR/EPR) spectra in terms of four Callen lineshape components revealed the existence of two types of magnetic centers, one derived from metallic cobalt nanoparticles in superparamagnetic (SPM) phase and the other from cobalt clusters in the TiO2 lattice. Additionally, at low temperature the EPR spectrum arising from Ti3+ ions was also registered. Both relaxations of the Landau-Lifshitz type and the Bloch-Bloembergen type played an important role at high temperature in determining the linewidths and the latter relaxation was prevailing at low temperature. Analysis of the integrated intensity showed that the SPM signal is due to small size FM cobalt nanoparticles while the paramagnetic signal from Co clusters originates from those nanoparticles in which the concentration of magnetic polarons is below the percolation threshold.
2
Content available Magnetic resonance study of co-modified (Co,N)-TiO2 nanocomposites
Guskos N., Zolnierkiewicz G., Guskos A., Typek J., Berczynski P., Dolat D., Mozia S., Aidinis C., Morawski A. W.
Nukleonika
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2015
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Vol. 60, No. 3, part 1
411--416
EN
Three nCo,N-TiO2 nanocomposites (where cobalt concentration index n = 1, 5 and 10 wt %) were prepared and investigated by magnetic resonance spectroscopy at room temperature. Ferromagnetic resonance (FMR) lines of magnetic cobalt agglomerated nanoparticle were dominant in all registered spectra. The relaxation processes and magnetic anisotropy of the investigated spin system essentially depended on the concentration of cobalt ions. It is suggested that the samples contained two magnetic types of sublattices forming a strongly correlated spin system. It is suggested that the existence of strongly correlated magnetic system has an essential infl uence of the photocatalytic properties of the studied nanocomposites.
3
Content available remote Ferromagnetic and spin wave resonances in thin layer of expanded austenite phase
Typek J., Guskos N, Zolnierkiewicz G., Berczynski P., Guskos A., Baranowska J., Fryska S.
Materials Science Poland
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2014
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Vol. 32, No. 2
198—205
EN
Four samples of austenite coatings deposited by reactive magnetron sputtering on silicon substrate at four different temperatures and pressures were investigated by ferromagnetic resonance (FMR) method at room temperature. The expanded austenite phase S (gN) layers with thickness in the 160 – 273 nm range and concentration of magnetic atoms: 72 % Fe, 18 % Cr and 10 % Ni, were obtained. The coatings with nanometric size grains were strongly textured and grown mostly in [100] direction, perpendicular to the sample surface. Intense FMR spectra were recorded at various angles between the static magnetic field direction and the sample surface. A strong magnetic anisotropy of the main uniform FMR mode was observed and the effective magnetization 4πMe f f determined. Spin wave resonance (SWR) modes were observed in all investigated samples in out-of-plane geometry of the magnetic field. The resonance fields of SWR modes in our samples varied linearly with the spin wave mode number. The value of the effective magnon stiffness constant was determined assuming a parabolic shape of the magnetization variation across the sample thickness.
4
Content available remote Gaussian beam evolution in longitudinally and transversely inhomogeneous nonlinear fibres with absorption
Berczynski P.
Opto-Electronics Review
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2013
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Vol. 21, No. 3
303-319
EN
The method of complex geometrical optics (CGO) is presented, which describes Gaussian beam (GB) diffraction and self-focusing in smoothly inhomogeneous and nonlinear Kerr type and saturable fibres. CGO reduces the problem of Gaussian beam evolution in inhomogeneous and nonlinear media to the system of the first order ordinary differential equations for the complex curvature of the wave front and for GB amplitude, which can be readily solved both analytically and numerically. As a result, CGO radically simplifies the description of Gaussian beam diffraction and self-focusing effects as compared to other methods of nonlinear optics such as variational method approach, method of moments and beam propagation method. The power of CGO method is presented on the example of Gaussian beam propagation in saturable fibres with either focusing and defocusing refractive profiles. Besides, the influence of initial curvature of the wave front, phenomenon of weak absorption and effect of either transverse and longitudinal inhomogeneity on GB propagation in nonlinear fibres is discussed in this paper.
5
Content available Gaussian beam evolution in inhomogeneous nonlinear media with absorption
Berczynski P.
Optica Applicata
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2013
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Vol. 43, nr 3
583--595
EN
The method of complex geometrical optics (CGO) is presented, which describes Gaussian beam (GB) diffraction and self−fo− cusing in smoothly inhomogeneous and nonlinear Kerr type and saturable fibres. CGO reduces the problem of Gaussian beam evolution in inhomogeneous and nonlinear media to the system of the first order ordinary differential equations for the complex curvature of the wave front and for GB amplitude, which can be readily solved both analytically and numerically. As a result, CGO radically simplifies the description of Gaussian beam diffraction and self−focusing effects as compared to other methods of nonlinear optics such as variational method approach, method of moments and beam propagation method. The power of CGO method is presented on the example of Gaussian beam propagation in saturable fibres with either focu− sing and defocusing refractive profiles. Besides, the influence of initial curvature of the wave front, phenomenon of weak ab− sorption and effect of either transverse and longitudinal inhomogeneity on GB propagation in nonlinear fibres is discussed in this paper.
6
Content available remote Study of magnetic properties of two samples from FeVO4-Co3V2O8 system
Guskos N., Zolnierkiewicz G., Typek J., Szymczak R., Guskos A., Berczynski P., Blonska-Tabero A.
Materials Science Poland
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2013
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Vol. 31, No. 4
601--610
EN
Two samples containing phases formed in the FeVO4–Co3V2O8 system were prepared by a conventional sintering method. The sample designated as H5 was one-phase with the howardevansite-type structure, while the sample designated as HL7 contained a mixture of H-type and lyonsite-type structures. The temperature dependence of the electron paramagnetic resonance (EPR) spectra and static magnetic susceptibility c was investigated in the temperature range from liquid helium to room temperature. Both the EPR spectra and the dc magnetic susceptibility showed anomalous behavior indicating that the magnetic competition process may be responsible. A comparison of the obtained results with previous studies on related compounds with the same structure, i.e. M3Fe4V6O24 (M = Mg(II), Zn(II), and Cu(II)) revealed that the observed anomaly shifted to lower temperatures on replacing the non-magnetic ions by magnetic Co(II) ions. The temperature dependence of the inverse susceptibility c􀀀1 indicates the existence of antiferromagnetic interactions between Fe(III) and Co(II) spins in sample H5. The obtained values of the Curie-Weiss temperatures are lower than for the Mn3Fe4V6O24 compound and comparable to compounds from M3Fe4V6O24 systems with M diamagnetic cations. The introduction of cobalt cations intensifies the magnetic frustration what is reflected in the temperature dependence of the magnetic susceptibility at low temperatures.
7
Content available remote Magnetic resonance study of γ-Fe2O3 nanoparticles dressed in oxygen based free radicals
Guskos N., Typek J., Zolnierkiewicz G., Wardal K., Guskos A., Berczynski P., Petridis D.
Materials Science Poland
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2013
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Vol. 31, No. 4
587--594
EN
Two composites consisting of g-Fe2O3 (maghemite) nanoparticles covered by two different oxygen-based free radicals derived from a 4-(methylamino)phenol sulphate and 8-hydroxy-1,3,6-trisulfonic trisodium salt acid were prepared and investigated by the magnetic resonance method in the 4 – 300 K range. Both composites displayed broad and very intense ferromagnetic resonance (FMR) lines originating from g-Fe2O3 agglomerated nanoparticles. The FMR spectrum was fitted satisfactorily at each temperature by two Landau-Lifshitz functions reflecting the existence of magnetic anisotropy in the investigated system. The temperature dependence of the obtained FMR parameters (resonance field, linewidth, integrated intensity) was studied and the results were interpreted in terms of magnetic interactions between free radicals and nanoparticle agglomerates. A comparison with previously studied similar systems containing maghemite nanoparticles was made and conclusions about the role of free radicals were drawn.
8
Content available remote Effect of annealing on EPR spectra of Ti-Si-C-N samples
Guskos N., Anagnostakis E. A., Zolnierkiewicz G., Typek J., Biedunkiewicz A., Guskos A., Berczynski P.
Materials Science Poland
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2012
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Vol. 30, No. 1
23--31
EN
Two nanocrystalline samples of TiC+SiC+20%C (sample 1) and Si3N4+Si(C,N)+Ti(C,N)+1%C (sample 2) were prepared by non-hydrolytic sol-gel method. The latter sample was produced from sample 1, by subjecting it to additional annealing at high temperature. XRD measurements showed the presence of aggregates of cubic SiC+TiC nanoparticles (10 to 30 nm in size). In both samples, a very narrow electron paramagnetic resonance (EPR) line originating from localized magnetic centers was centered at geff2. At T = 130 K, we registered the linewidths DHpp = 1.41(2) G and DHpp = 2.92(2) G for the sample without and with thermal annealing, respectively. For the non-annealed sample, the resonance line was fitted by a Lorentzian line in the low temperature range, and by a Dysonian line above 70 K, which indicates a significant change in electrical conductivity. Therefore, thermal annealing can significantly improve the transport properties of samples. An analysis of the temperature dependence of the EPR parameters (g-factor, linewidth, integrated intensity) showed that thermal annealing has a significant impact on the reorientation processes of localized magnetic centers.
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