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1
Content available remote Diluted Magnetic III-V Semiconductors
100%
Twardowski A.
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nr 3
203-216
EN
During recent years diluted magnetic semiconductors based on III-V compounds have been of considerable interest. In this respect we review the basic properties of these materials, which are nearly exclusively Mn-based systems, such as GaMnAs, InMnAs, GaMnSb, and GaN:Mn. We discuss the nature of Mn impurity. Different Mn centers are considered and experimental pieces of evidence suggesting the dominating role of Mn (d^{5}) configuration are given. Then we analyze s, p-d exchange, together with resulting magnetooptical properties (in particular absorption edge slitting for heavily p-type GaMnAs). The coupling between Mn ions (d-d exchange) and ferromagnetic ordering observed in InMnAs and GaMnAs is the next subject. Some mechanisms responsible for this ordering are presented. Finally we discuss transport properties and some selected problems of quantum structures based on III-V diluted magnetic semiconductors.
2
Content available remote Influence of Local Potential on Exciton Splitting in Highly Diluted Cd_{1-x}Mn_{x}Te
45%
Kłopotowski L. , Herbich M. , Mac W. , Stachow-Wójcik A. , Twardowski A.
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nr 4
837-840
EN
We investigated magnetoreflectance and magnetization of highly diluted bulk Cd_{1-x}Mn_{x}Te crystals 0.2% ≤ x ≤ 10%. The exchange constant in terms of mean field approximation and virtual crystal approximation (the ratio of the heavy hole exciton splitting to mean spin per unit cell) was evaluated and found x-dependent. This deviation from the mean field approximation and virtual crystal approximation prediction is caused by the local potential introduced by Mn ions. We discuss the problem within a Wigner-Seitz approach and within a model of magnetic and chemical disorder based on the alloy theory.
3
Content available remote Magnetic Properties of EuS/PbS Semiconducting Structures
38%
Stachow-Wójcik A. , Twardowski A. , Story T. , Dobrowolski W. , Grodzicka E. , Sipatow A.
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nr 5
985-988
EN
We report results of magnetization study of EuS/PbS superstructures with different thicknesses of magnetic and nonmagnetic layers. Reduction of ferromagnetic phase transition temperature was found with decreasing EuS thickness. Reasonable description of this effect is obtained within the model based on the mean field approximation.
4
Content available remote Observation of Magnetic Anisotropy in GaN:Cr Single Crystals
38%
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.
5
Content available remote Influence of Epitaxial Strain on Magnetic Anisotropy in (Ga,Mn)As
38%
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.
6
Content available remote Ferromagnetic Resonance Study of Exchange Coupled (Ga,Mn)As/GaAs/(Ga,Mn)As Heterostructures
38%
Dziatkowski K. , Ge Z. , Liu X. , Furdyna J. , Clerjaud B. , Twardowski A.
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nr 2
227-232
EN
Ferromagnetic resonance study of the exchange coupled (Ga,Mn)As/ GaAs/(Ga,Mn)As heterostructures is reported. The measurements were performed on the series of samples with varying thicknesses d_{GaAs} of nonmagnetic GaAs spacer, established d_{GaAs}-dependent extent of weak and strong interlayer exchange coupling, judging on the observation of one or two ferromagnetic resonance modes.
7
Content available
38%
Kwiatkowski A. , Borysiuk J. , Bożek R. , Wasik D. , Kamińska M. , Sadowski J. , Twardowski A.
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tom 110
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nr 2
233-236
EN
We report on cross-sectional transmission electron microscopy and magnetic force microscopy studies performed on self-organized MnAs nanoclusters embedded in GaAs. It was found that 10÷20 nm large MnAs ferromagnetic nanocrystals were formed during rapid thermal annealing of Ga_{1-x}Mn_xAs layers at 600ºC, leading to magnetic contrasts in magnetic force microscopy images.
8
Content available Observation of Superconductivity in Highly Cr-Doped GaP Single Crystals
38%
Gosk J. , Strzelecka G. , Kowalski G. , Hruban A. , Kamińska M. , Twardowski A. , Gronkowski J.
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tom 110
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nr 2
189-193
EN
Studying bulk GaP, highly doped with Cr, and searching for possible ferromagnetic semiconductor in view of spintronic applications, we found superconducting behavior of this material unexpectedly. Magnetization techniques and X-ray diffraction were applied to study these crystals. Magnetization revealed superconducting features up to about 6 K and X-ray studies showed that superconductivity might be related to small size Cr precipitates.
9
Content available remote EPR Spectra of Multispin Systems. Application to Poly-m-p-Aniline
38%
Juszyński P. , Twardowski A. , Gosk J. , Kulszewicz-Bajer I. , Pawłowski M. , Dziatkowski K. , Szczytko J.
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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.
10
Content available remote Time-Resolved Studies of Gallium Nitride Doped with Gadolinium
38%
Witek B. , Wysmołek A. , Kamińska M. , Twardowski A. , Potemski M. , Boćkowski M. , Grzegory I.
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nr 5
1425-1430
EN
Time-resolved photoluminescence experiments on high quality bulk GaN doped with Gd are presented. It was found that the decay time of Gd-related transitions observed for 4.2 K around 1.78 eV is of about 3 ms. Such a long decay time strongly supports the identification of this emission band as due to transitions between Gd³+(4f⁷) levels. The decay time measured for Gd-related transitions observed in the UV spectral range, close to the GaN band-gap, was found to be much faster than 1 μs. This suggests that these emission lines could hardly be correlated with internal transitions within Gd³+(4f⁷). Possible origin of the Gd-related UV luminescence is discussed.
11
Content available Measurement of Very Small Zeeman Splittings in GaN:Mn,Mg by Faraday Rotation
32%
Wołoś A. , Kossacki P. , Golnik A. , Kamińska M. , Gaj J. , Twardowski A. , Grzegory I. , Boćkowski M. , Porowski S.
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nr 4-5
695-699
EN
In this work we demonstrate an application of Faraday rotation for measuring an extremely small Zeeman splitting of an Mn related absorption line placed at 1.417 eV in optical absorption spectrum of Mn and Mg doped gallium nitride. Analysis of the collected spectra allowed us to determine the value of the splitting as equal to 0.12±0.01 meV at 6 T. This data should help in establishing the nature of the observed absorption band.
12
Content available remote Magnetic Anisotropy in Eus-pbs Multilayers
32%
Story T. , Swüste C. , Swagten H. , de Jonge W. , Stachow-Wójcik A. , Twardowski A. , Arciszewska M. , Dobrowolski W. , Gałązka R. , Sipatov A.
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nr 3
435-438
EN
We present the results of ferromagnetic resonance studies of the thickness dependence of magnetic anisotropy in 2 series of EuS-PbS multilayers grown on (111) BaF_{2} and (100) KCl substrates with the EuS thickness varying in the range d=6-70 Å. The anisotropy constant K was found to follow the dependence K(d)=K_{V}+2K_{S}/d , with the surface term K_{S} larger for layers grown on BaF_{2} as compared to KCl. This difference is discussed in terms of different thermal stress-induced distortions of cubic crystal lattice of EuS. We found that the thickness of EuS layer required for the perpendicular (to the layer) magnetization is d ≤ 2-3 Å, i.e., it is below 1 monolayer.
13
Content available Photoluminescence and Electron Paramagnetic Resonance Studies of Bulk GaN Doped with Gadolinium
32%
Lipińska Z. , Pawłowski M. , Żołnierowicz H. , Wysmołek A. , Palczewska M. , Kamińska M. , Twardowski A. , Boćkowski M. , Grzegory I.
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tom 110
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nr 2
243-248
EN
Photoluminescence and electron paramagnetic resonance experiments on strain free GaN bulk crystals of wurtzite structure doped with gadolinium are reported. Efficient gettering of residual GaN donors by Gd was observed. Electron paramagnetic resonance showed that Gd ion incorporated into GaN lattice had Gd^{3+}(4f^7) configuration. The observed photoluminescence spectra were explained as due to intracenter Gd^{3+}(4f^7) transitions. No ferromagnetic behavior was detected.
14
Content available remote Carbon-Encapsulated Magnetic Nanoparticles Based on Fe, Mn, and Cr for Spintronics Applications
32%
Szczytko J. , Osewski P. , Bystrzejewski M. , Borysiuk J. , Grabias A. , Huczko A. , Lange H. , Majhofer A. , Twardowski A.
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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.
15
Content available remote Magnetoluminescence Studies of GaN:Fe
32%
Niedźwiadek A. , Wysmołek A. , Wasik D. , Potemski M. , Szczytko J. , Kamińska M. , Twardowski A. , Łucznik B. , Pastuszka B. , Grzegory I.
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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.
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