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1
Content available remote Monte Carlo Simulations of Ferromagnetic Nanocomposites
100%
Woińska M. , Majhofer A. , Gosk J. , Szczytko J.
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nr 6
1019-1021
EN
We present results of Monte Carlo simulations of a model system of Co nanoparticles in an external magnetic field. In our simulations we take into account the interaction with the external magnetic field, the energy of crystallographic anisotropy and the dipole-dipole interactions between single domain nanoparticles. We apply the standard Metropolis algorithm to a cluster of 27 randomly distributed superparamagnetic Co nanoparticles. We investigate the dependence of blocking temperature T_{B} on particle and cluster size.
2
Content available remote Confocal Microscope Studies of MoS_{2} Layer Thickness
88%
Grzeszczyk M. , Gołasa K. , Piętka B. , Babiński A. , Szczytko J.
Acta Physica Polonica A
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2014
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tom 126
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nr 5
1207-1208
EN
We have been studying micro-luminescence of various exfoliated MoS_{2} flakes using a confocal microscope. A crucial issue is to determine thickness of the investigated layer. The common way - using atomic force microscopy, electron microscopy or the Raman spectroscopy - requires moving the sample out from the confocal microscope experimental setup and looking for a particular exfoliated flake hidden among thousands of others. In order to preliminarily determine thickness of investigated layers we have performed a study on optical reflectivity and compared the results with the Raman spectroscopy investigations. In this way we were able to calibrate our experimental setup. Optical measurements are much faster than the Raman spectroscopy and can give a good estimation of MoS_{2} thickness.
3
Content available remote Resonant Plasmon Response of a Periodically Modulated Two-Dimensional Electron Gas
88%
Sznajder P. , Piętka B. , Szczytko J. , Łusakowski J. , Bardyszewski W.
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nr 6
1090-1092
EN
We report the theoretical study of the optical response of a periodically modulated two-dimensional electron gas. The density of states is calculated within the first order of the perturbation theory and the effects of the short-range disorder are explained and discussed. We demonstrate that the magnetic field values corresponding to the characteristic narrowing of the density of states width are given by the zeros of the subsequent Laguerre polynomials. The observed increase of the density of states at the edges are interpreted as van Hove singularities. The broadening effects are shown to modify and smear out the observed effects with increasing temperature above 2 K. The plasmon dispersion relation is discussed in terms of the random phase approximation. Small changes in plasmon dispersion relation related to the periodic modulation were predicted.
4
Content available remote Hydrostatic Pressure Study of MBE CdMnTe Doped with Bromine
88%
Szczytko J. , Wasik D. , Przybytek J. , Baj M. , Waag A.
Acta Physica Polonica A
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1995
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tom 88
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nr 5
933-936
EN
We present Hall effect and resistivity measurements as a function of pressure performed on MBE-grown Cd_{1-x}Mn_{x}Te (with x = 0.14) layer (1 μm) doped with bromine. The experimental data were analysed using positive and negative U model of the Br centres. We found that both models could reproduce the experimental points, but in the case of positive U model - only under assumption that the sample was completely uncompensated.
5
Content available remote EPR Spectra of Multispin Systems. Application to Poly-m-p-Aniline
75%
Juszyński P. , Twardowski A. , Gosk J. , Kulszewicz-Bajer I. , Pawłowski M. , Dziatkowski K. , Szczytko J.
Acta Physica Polonica A
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2011
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tom 119
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nr 5
717-719
EN
In this communication we present NiceMagnetic, software for simulations and analysis of EPR spectrum and SQUID measurements. Systems of arbitrary number N of spin-only magnetic moments (S ≤ 0 and L = 0) were considered within the lines of the Heisenberg and Zeeman Hamiltonians. Effective algorithms used for the computations are discussed. This includes modified secant method adapted to calculate resonance fields with demanded precision. Finally, application of NiceMagnetic to experimental SQUID magnetization and EPR spectra of poly-m-p-aniline, one of recently synthesized high spin polymers containing unpaired electrons will be presented. As a result, exchange integral between electron and nitrogen nuclei spins (ligand hyperfine interaction) J = 6.3 × 10^{-4} cm^{-1} was estimated.
6
Content available remote Magnetic Field Induced Redistribution of Exciton-Polariton Density on Confined Modes
75%
Piętka B. , Szczytko J. , Łusakowski J. , Nardin G. , Léger Y. , Morier-Genoud F. , Deveaud-Plédran B.
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nr 6
1093-1095
EN
The influence of magnetic field on confined exciton-polariton modes inside a semiconductor microcavity is discussed. The three-dimensional confinement for exciton-polaritons is achieved by the mesa structures confining the photonic part of polaritons. We observe a strong increase of the polariton emission intensity and we argue that this effect is due to the change of the oscillator strength of the excitonic component of polaritons and the change of the excitonic content in polariton state as the magnetic field increases.
7
Content available remote Observation of Magnetic Anisotropy in GaN:Cr Single Crystals
75%
Gosk J. , Boćkowski M. , Kowalski G. , Grzegory I. , Szczytko J. , Twardowski A.
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nr 6
1007-1009
EN
Magnetic properties of bulk wurtzite GaN:Cr single crystals were studied with the magnetic field applied parallel and perpendicular to the crystal wurtzite c-axis. Structure of the crystal was examined by the X-ray diffraction method. Strong anisotropy of magnetization at low temperatures (2-10 K) was observed. The experimental data suggest Cr to be in nonspherical d^4 configuration.
8
Content available remote Influence of Epitaxial Strain on Magnetic Anisotropy in (Ga,Mn)As
75%
Juszyński P. , Wasik D. , Gryglas-Borysiewicz M. , Przybytek J. , Szczytko J. , Twardowski A. , Sadowski J.
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nr 6
1004-1006
EN
Two (Ga,Mn)As samples having different magnetic anisotropy (one with in-plane easy axis and another one with out-of-plane easy axis) were studied by means of magnetotransport experiments. Anisotropy field B_{A} was determined for both samples as a function of temperature. For the sample having in-plane easy axis, an inversion of the direction of planar Hall effect hysteresis was observed upon increase of temperature. This result was simulated using the Stoner-Wohlfarth model.
9
Content available remote On the Question of Ferromagnetism in Proton and He-Irradiated Carbon
75%
Szczytko J. , Juszyński P. , Teliga L. , Twardowski A. , Stonert A. , Ratajczak R. , Korman A.
Acta Physica Polonica A
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2008
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tom 114
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nr 5
1387-1390
EN
We tried to repeat the observation of the ferromagnetic response in proton and He-irradiated carbon made by the group of Esquinazi et al. We used He^+ and H^+ beams focused on graphite sample. The amount of charge deposited in the sample was comparable to the amount of charge used by Esquinazi. Magnetic measurements were performed in SQUID magnetometer. The magnetization of the samples before and after irradiation was compared. We did not observe any ferromagnetic enhancement of magnetization of our irradiated samples. Even if experiment was not the same as Esqinazi's one, we can exclude some of the mechanisms of ferromagnetism proposed by Esquinazi.
10
Content available remote Magnetooptical Properties of GaAs:Mn
75%
Szczytko J. , Stachow A. , Mac W. , Twardowski A. , Becla P. , Tworzydło J.
Acta Physica Polonica A
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1996
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tom 90
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nr 5
951-954
EN
Magnetoreflectance from GaAs:Mn was measured in the free exciton range for B ≤ 5 T and T = 2.0 K. Combining optical results with magnetization data the value for the exchange parameter N_{0}α-N_{0}β =-(2.3 ± 0.6) eV was obtained. Assuming that N_{0}α ≈ +0.2 eV, the ferromagnetic p-d exchange interaction was found with the magnitude N_{0}β ≈ +2.5 eV.
11
Content available remote Effect of the Sign of Anisotropy Constants on the Properties of the System of Interacting Ferromagnetic Nanoparticles
75%
Sadek M. , Marchwiany M. , Woinska M. , Majhofer A. , Gosk J. , Twardowski A. , Szczytko J.
Acta Physica Polonica A
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2016
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tom 129
|
nr 1a
A-53-A-55
EN
We use the Monte Carlo simulation method to investigate the influence of the signs of magnetocrystalline anisotropy constants and the magnetic dipole-dipole interactions on the zero field cooled-field cooled magnetization experiments and hysteresis curves of a system of magnetic nanoparticles. Positive first cubic anisotropy constant K₁ results in larger blocking temperatures and larger coercive fields of a system, while the second anisotropy constant K₂ is practically of negligible importance for the phenomena investigated. Magnetic dipole-dipole interactions are important only in the most dense systems of particles and their effects practically disappear for systems where the distance between the closest particles exceeds three particle diameters.
12
Content available remote Magnetoluminescence Studies of GaN:Fe
63%
Niedźwiadek A. , Wysmołek A. , Wasik D. , Potemski M. , Szczytko J. , Kamińska M. , Twardowski A. , Łucznik B. , Pastuszka B. , Grzegory I.
Acta Physica Polonica A
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2007
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tom 112
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nr 2
177-182
EN
We report on magneto-optical studies on iron doped GaN crystals grown using hydride vapor phase epitaxy method on bulk GaN substrate. The investigated samples showed an intensive 1.3 eV luminescence band, characteristic of Fe^{3+}(d^5) center in GaN. A high quality of the investigated samples allowed us to observe a well-resolved fine structure of intracenter transitions between ^4T_1(G) and ^6A_1(S) states, consisting of four sharp no-phonon lines. All the observed no-phonon lines showed pronounced splittings in magnetic field. From the analysis of the magneto-optical data, the structure of split ^4T_1(G) multiplet in the magnetic field applied along c-axis of GaN crystals was established.
13
Content available remote Carbon-Encapsulated Magnetic Nanoparticles Based on Fe, Mn, and Cr for Spintronics Applications
63%
Szczytko J. , Osewski P. , Bystrzejewski M. , Borysiuk J. , Grabias A. , Huczko A. , Lange H. , Majhofer A. , Twardowski A.
Acta Physica Polonica A
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2007
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tom 112
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nr 2
305-310
EN
We succeeded in the arc-plasma synthesis of carbon-encapsulated Fe, Cr, and Mn-based nanoparticles. The transmission electron microscopy, Mössbauer spectra (of iron) and SQUID magnetometry results demonstrate that the products of the synthesis contain metals and its carbides. The nanoparticles show ferromagnetic or superparamagnetic behavior at high temperatures, which is demanded for nano-spintronics applications.
14
Content available remote Relative Reflection Difference as a Method for Measuring the Thickness of the Exfoliated MoSe₂ Layers
63%
Łempicka K. , Norowski K. , Grzeszczyk M. , Król M. , Lekenta K. , Babiński A. , Piętka B. , Szczytko J.
Acta Physica Polonica A
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2017
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tom 132
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nr 2
316-318
EN
We propose a method for measuring the thickness of the exfoliated MoSe₂ layers deposited on Si/SiO₂ substrate, based on the reflectance measurements performed with laser light illumination at two different wavelengths: red and green from confocal microscope at room temperature. We demonstrate the correlation between the number of layers in a flake and the value of its relative reflection difference. We applied the transfer matrix method to calculate the reflectivity and verify our experimental results. The approach proposed by us allows for fast and automatic verification of the exfoliated MoSe₂ layers thickness on large areas of the substrate.
15
Content available remote THz Time Domain Spectroscopy of Thin Gold Layers on GaAs
63%
Szczytko J. , Adomavicius R. , Papis E. , Barańska A. , Wawro A. , Krotkus A. , Piętka B. , Łusakowski J.
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nr 6
1118-1120
EN
Thin layers of Au with the thickness of several nanometers were prepared on a semi-insulating GaAs substrate. The layers' thickness was determined by ellipsometry. THz time-domain spectroscopy was applied to determine a complex index of refraction of thin Au layers. The obtained results allow for a more precise modeling of the performance of semiconductor devices at THz frequencies.
16
Content available remote Magnetic Liquid Crystals for Molecular Spintronics
63%
Szczytko J. , Budzowski P. , Turski H. , Witek B. , Twardowski A. , Glebowska A. , Krówczyński A. , Pociecha D. , Szydlowska J. , Górecka E.
Acta Physica Polonica A
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2008
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tom 114
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nr 5
1383-1386
EN
The magnetic properties of Ni(II) and Cu(II) complexes were measured. In the case of Ni(II) samples strong enhancement of the magnetic susceptibility below 23 K was observed. The model of structural transition was proposed to explain this behavior.
17
Content available remote Optical Properties of Molybdenum Disulfide (MoS_2)
63%
Gołasa K. , Grzeszczyk M. , Korona K. , Bożek R. , Binder J. , Szczytko J. , Wysmołek A. , Babiński A.
Acta Physica Polonica A
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2013
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tom 124
|
nr 5
849-851
EN
Research of a monolayer and a bulk MoS_2 is reported. The room temperature Raman spectra of the natural MoS_2 crystals for the both resonant (632.8 nm) and the non-resonant (532 nm) excitation are presented. The apparent differences observed in the spectra from the bulk and the one monolayer MoS_2 are discussed. In particular, the feature due to a first order scattering involving the LA(M) phonon in the resonance Raman spectrum of the one monolayer MoS_2 was observed and explained in terms of the disorder in the natural crystal. The disorder is also documented by the line-shape of the room-temperature photoluminescence spectra observed from both the bulk and the one monolayer MoS_2.
18
Content available remote Magnetic Properties of Epitaxial Fe/(Ga,Mn)As Hybrids
51%
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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tom 124
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nr 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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