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1
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Magnetic Anisotropy in (Ge,Mn)Te Layers

100%
Knoff W., Łusakowski A., Wołoś A., Story T.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
404-406
EN
Ferromagnetic resonance study of magnetic anisotropy is presented for thin layers of IV-VI diluted magnetic semiconductor (Ge,Mn)Te with Mn content of 12 and 21 at.% grown by molecular beam epitaxy on BaF₂ (111) substrates. The layers with low Mn content grow in the rhombohedral crystal structure and exhibit perpendicular magnetic anisotropy whereas the layers with Mn content higher than about 20 at.% are of cubic (rock-salt) structure and show regular easy-plane type magnetic anisotropy. The quantitative analysis of the angular dependence of the ferromagnetic resonant field is performed taking into account the magnetic energy contributions due to rhombohedral distortion (axial term along the (111) growth direction of the layer) and the crystal field terms allowed for ferromagnetic systems of rhombohedral symmetry.
2
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Magnetic Properties of (Zn,Mn)Te Semimagnetic Alloy Co-Doped with Chromium

100%
Avdonin A., Van Khoi L., Knoff W., Gałązka R.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
974-975
EN
Results of simultaneous doping of ZnTe with manganese and chromium are presented. An increase of magnetization of ferromagnetic Cr-related clusters with manganese concentration is observed. Phosphorus doping prevents the formation of ferromagnetic clusters.
3
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Magnetic Properties of ZMTO Alloys

100%
Avdonin A., Knoff W., Gałązka R.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
916-917
EN
The results of the magnetization and photoluminescence measurements of the ZMTO are presented. Under field cooling conditions a phase transition is observed. The dependence of the temperature of transition on oxygen concentration is analyzed. A model is proposed.
4
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Photoemission Study of Mn 3d Electrons in the Valence Band of Mn/GeMnTe

64%
Pietrzyk M., Kowalski B., Orłowski B., Knoff W., Osinniy V., Kowalik I., Story T., Johnson R.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
275-281
EN
We present the results of the electronic band structure study of Ge_{0.9}Mn_{0.1}Te epilayers, clean and modified in situ by deposition of manganese atoms. The sets of resonant photoemission spectra were measured for the photon energy range covering the energy of Mn 3p→3d transition (45
5
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A Comparison of the Valence Band Structure of Bulk and Epitaxial GeTe-based Diluted Magnetic Semiconductors

64%
Pietrzyk M., Kowalski B., Orlowski B., Knoff W., Story T., Dobrowolski W., Slynko V., Slynko E., Johnson R.
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issue 2
293-295
EN
In this work we present a comparison of the experimental results, which have been obtained by the resonant photoelectron spectroscopy for a set of selected diluted magnetic semiconductors based on GeTe, doped with manganese. The photoemission spectra are acquired for the photon energy range of 40-60 eV, corresponding to the Mn 3p → 3d resonances. The spectral features related to Mn 3d states are revealed in the emission from the valence band. The Mn 3d states contribution manifests itself in the whole valence band with a maximum at the binding energy of 3.8 eV.
6
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Magnetic Properties of EuS/Co Multilayers on KCl and BaF₂ Substrates

64%
Szot M., Kowalczyk L., Story T., Domukhovski V., Knoff W., Gas K., Volobuev V., Sipatov A., Fedorov A.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1397-1402
EN
Magnetic and structural properties of EuS/Co multilayers were studied by magnetic optical Kerr effect and SQUID magnetometry techniques and by X-ray diffraction method. The multilayers containing monocrystalline, ferromagnetic EuS layer (thickness 35-55 Å) and metallic Co layer (thickness 40-250 Å), were grown on KCl (001) and BaF₂ (111) substrates using high vacuum deposition technique employing electron guns for Co and EuS. All investigated EuS/Co multilayers exhibit ferromagnetic properties at room temperature due to Co layer with the ferromagnetic transition in EuS layer clearly marked upon cooling below 16 K. In EuS/Co/EuS trilayers grown on KCl substrate the antiferromagnetic alignment of magnetization vectors of Co and EuS layers was experimentally observed as a characteristic low field plateau on magnetization hysteresis loops and a decrease in multilayer magnetization below 16 K. In Co/EuS bilayers the characteristic temperature dependent shift of magnetization loops was found due to exchange bias effect attributed to the CoO/Co interface formed by the oxidation of the top Co layer.
7
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Studies of Diluted Magnetic Semiconductor Sn_{1-x-y-z}Ge_{x}Mn_{y}Gd_{z}Te

64%
Sichkovskyi V., Radchenko M., Lashkarev G., Slyn'ko V., Slyn'ko E., Knoff W., Domukhovski V., Dziawa P., Story T.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
911-912
EN
Magnetization, anomalous Hall effect, thermoelectric power, magnetoresistance, and resistivity of Sn_{1-x-y-z}Ge_{x}Mn_{y}Gd_{z}Te (x = 0.039÷0.597, y = 0.077÷0.125, z = 0.0014÷0.028) mixed crystals were studied over the temperature range 4.2-300 K. The ferromagnetic order with Curie temperature 18-24 K was revealed.
8
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Magnetization Studies of Antiferromagnetic Interlayer Coupling in EuS-SrS Semiconductor Multilayers

64%
Samburskaya T., Sipatov A., Volobuev V., Dziawa P., Knoff W., Kowalczyk L., Szot M., Story T.
Acta Physica Polonica A
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2013
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vol. 124
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issue 1
133-136
EN
Temperature and magnetic field dependence of magnetization of EuS-SrS multilayers grown epitaxially on KCl (001) substrate is experimentally studied by superconducting magnetometry technique. In these lattice-matched semiconductor heterostructures EuS layers are ferromagnetic quantum wells whereas SrS layers are nonmagnetic spacer barriers. The multilayers composed of EuS layers with thickness 3.5-5 nm and SrS layers (thickness 0.5-10 nm) exhibit ferromagnetic transition at 17 K. In the multilayers with ultrathin SrS spacers (0.5-1 nm) a nonmonotonic temperature dependence of magnetization as well as a characteristic switching in magnetic hysteresis loops is observed. These experimental findings are explained considering antiferromagnetic interlayer coupling between ferromagnetic EuS layers via nonmagnetic SrS spacers. The strength of this coupling is determined based on model magnetization calculations.
9
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Ferromagnetism of Narrow-Gap Ge_{1-x-y}Sn_xMn_yTe and Layered In_{1-x}Mn_xSe Semiconductors

52%
Lashkarev G., Sichkovskyi V., Radchenko M., Dmitriev A., Slyn'ko V., Slyn'ko E., Kovalyuk Z., Butorin P., Knoff W., Story T., Szymczak R., Jakieła R., Aleshkevych P., Dobrowolski W.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1219-1227
EN
Magnetic susceptibility, Hall effect and resistivity of narrow-gap Ge_{1-x-y}Sn_xMn_yTe single crystals (x = 0.083÷0.115; y = 0.025÷0.124) were investigated in the temperature range 4.2-300 K revealing a ferromagnetic ordering at T_C ≈ 50 K. Temperature dependence of magnetization indicates a superparamagnetic phase with magnetic clusters arranging in a spin glass state below the freezing temperature T_f. Magnetic structure of InSe ⟨Mn⟩ 2D-ferromagnetic single crystals was studied by SQUID magnetometry, neutron diffraction, secondary ion mass spectroscopy, and wave dispersive spectra. Hysteresis loops of magnetization were observed at least up to 350 K. The cluster model of ferromagnetism is considered. The formation of self-assembled superlattice ferromagnetic InSe:Mn/antiferromagnetic MnSe during growth process and further annealing was established.
10
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Magnetic and Structural Studies of GeMnSnTe Epitaxial Layers

52%
Grochot A., Knoff W., Taliashvili B., Wołkanowicz W., Minikayev R., Pieniążek A., Łusakowska E., Sawicki M., Jantsch W., Story T., Przybylińska H.
Acta Physica Polonica A
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2017
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vol. 132
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issue 2
340-342
EN
MBE grown Ge_{1-x-y}Mn_xSn_yTe layers with Mn content ranging from 10 to 30% and Sn content ranging from 2 to 5% have been characterized with X-ray diffraction, energy-dispersive X-Ray spectroscopy, atomic force microscopy, SQUID magnetometry, and ferromagnetic resonance. All layers (except the one with the highest Mn and Sn content) were found to be single phase rhombohedral, with the distortion axis perpendicular to the layer surface, and ferromagnetic. Ferromagnetic resonance studies have shown that co-doping with a few percent of tin makes the lattice more rigid and changes considerably the magnetocrystalline anisotropy, from purely uniaxial in GeMnTe to distorted cubic in Ge_{1-x-y}Mn_xSn_yTe at the same Mn content.
11
Content available remote

Physical Properties of ZnCoO Tetrapods and Nanofibers

52%
Gas K., Fronc K., Dziawa P., Knoff W., Wojciechowski T., Zaleszczyk W., Baranowska-Korczyc A., Morhange J., Paszkowicz W., Elbaum D., Karczewski G., Wojtowicz T., Szuszkiewicz W.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
868-870
EN
In this paper the physical properties of two types of Co-doped ZnO nanostructures: tetrapods and nanofibers grown by a rapid thermal evaporation process and prepared by the electrospinning technique, respectively, were investigated and analyzed. Surface morphology of the samples was examined using scanning electron microscopy. X-ray diffraction measurements showed hexagonal wurtzite crystal structure of both types of investigated nanostructures. Both X-ray diffraction and Raman scattering data confirmed high phase purity of the samples. The magnetic properties studied with the use of the SQUID magnetometer confirmed a presence of ferromagnetic order in analyzed nanostructures. The observed photoluminescence spectra exhibited two groups of lines. The first one, in the ultraviolet spectral range, is due to the optical transitions close to ZnO band gap, the second one in the red region is most probably related to the Co^{2+} d-d internal transitions. The influence of native defects on the optical properties is also shown and discussed. All results reported here lead us to the conclusion that in the mixed crystal nanostructures obtained, a fraction of the Zn^{2+} ions is substituted by Co^{2+} ions.
12
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Ferromagnetic Transition in Ge_{1-x}Mn_{x}Te Layers

52%
Knoff W., Domukhovski V., Dybko K., Dziawa P., Jakieła R., Łusakowska E., Reszka A., Świątek K., Taliashvili B., Story T., Szałowski K., Balcerzak T.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
904-906
EN
Ferromagnetic transition temperature in thin layers of diluted magnetic (semimagnetic) semiconductor Ge_{1-x}Mn_{x}Te was studied experimentally by SQUID magnetometry method and analyzed theoretically for a model Ising-type diluted magnetic system with Ruderman-Kittel-Kasuya-Yosida indirect exchange interaction. The key features of the experimentally observed dependence of the Curie temperature on Mn content (x ≤ 0.12) and conducting hole concentration p = (1-10) × 10^{21} cm^{-3} were reproduced theoretically for realistic valence band and crystal lattice parameters of p-Ge_{1-x}Mn_{x}Te taking into account short carrier mean free path encountered in this material and Ruderman-Kittel-Kasuya-Yosida mechanism with both delta-like and diffused character of spatial dependence of the exchange coupling between magnetic ions and free carriers.
13
Content available remote

Epitaxial Growth and Optical Properties of PbTe/CdTe Semiconductor Heterostructures

52%
Szot M., Kowalczyk L., Smajek E., Domukhovski V., Domagała J., Łusakowska E., Taliashvili B., Dziawa P., Knoff W., Wiater M., Wojtowicz T., Story T.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1391-1396
EN
Growth optimization, optical and structural properties of PbTe/CdTe multilayers grown by molecular beam epitaxy on GaAs (001) as well as on BaF_2 (111) substrates is reported. An intense photoluminescence in the mid-infrared region is observed from PbTe quantum wells excited with 1.17 eV pulsed YAG:Nd laser. The energy of the emission peak shows blue shift with decreasing PbTe well width and has a positive temperature coefficient. The influence of thermal annealing on photoluminescence spectra of PbTe/CdTe multilayers grown on BaF_2 substrate is discussed.
14
Content available remote

Magnetic Properties of Epitaxial (Ge,Mn)Te Thin Films with Varying Crystal Stoichiometry

52%
Knoff W., Domukhovski V., Dybko K., Dziawa P., Górska M., Jakieła R., Łusakowska E., Taliashvili B., Story T., Reszka A., Anderson J., Rotundu C.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1159-1165
EN
Magnetization of 1 μm thick ferromagnetic IV-VI (Ge, Mn)Te semiconductor layers with 10 at.% of Mn was studied by SQUID magnetometry method up to the magnetic fields of 70 kOe. The layers were grown on BaF₂ (111) substrates by molecular beam epitaxy with varying Te molecular flux, which permitted the control of layer stoichiometry and conducting hole concentration. X-ray diffraction and in situ electron diffraction characterization of layer growth and crystal structure revealed two-dimensional mode of growth and monocrystalline rhombohedral crystal structure of (Ge, Mn)Te layers. Controlling the layer stoichiometry influences the temperature dependence of magnetization with the ferromagnetic Curie temperature varying in Ge_{0.9}Mn_{0.1}Te layers from T_c=30 K (low Te flux) to T_c=42 K (high Te flux).
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