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  1. 195 Acta Physica Polonica A

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  1. 19 Sadowski J.

  2. 19 Twardowski A.

  3. 18 Story T.

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1
Content available remote

Direct Measurements of Bound Magnetic Polaron Magnetization in Ga-Doped Cd_{1-x}Mn_{x}Te

100%
Stankiewicz J., Palacio F., Villuendas F.
Acta Physica Polonica A
|
1997
|
vol. 92
|
issue 5
976-980
EN
Light induced remanent changes in magnetization of n-type Cd_{1-x}Mn_{x} Te (x=0.01, 0.05) single crystals have been measured at T=2 and 5 K and in magnetic fields of up 0.5 T. The effect observed gradually saturates with increasing magnetic field. It also correlates with light induced increase in shallow donor concentration measured on the same samples. The bound magnetic polaron theory accounts for the temperature and magnetic field variations of the persistent magnetization. There are no fitting parameters.
2
Content available remote

Magnetic Properties of EuS/PbS Semiconducting Structures

100%
Stachow-Wójcik A., Twardowski A., Story T., Dobrowolski W., Grodzicka E., Sipatow A.
Acta Physica Polonica A
|
1997
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vol. 92
|
issue 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.
3
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Temperature Dependence of the Energy Gap in Cd_{1-x}Fe_{x}Se

100%
Gaj J., Nguyen K., Arciszewska M., Lebecki K.
Acta Physica Polonica A
|
1991
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vol. 80
|
issue 3
405-407
EN
The energy gap and magnetic susceptibility of Cd_{0.85}Fe_{0.15}Se were measured in function of temperature. Experiments showed that the magnetic contribution to the variation of the energy gap in Cd_{1-x}Fe_{x}Se is not proportional to the product of magnetic susceptibility and temperature as it has been observed in Mn^{++}-containing semiconductors.
4
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Magnetic Susceptibility and Charge State of Gd Impurity in Pb_{1-x}Sn_{x}Te⟨Gd⟩ Crystals

100%
Zayachuk D., Ivanchuk R., Kempnyk V., Mikityuk V.
Acta Physica Polonica A
|
1996
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vol. 90
|
issue 5
985-988
EN
The effective magnetic momentum p_{eff} of Gd-impurities in the Pb_{1-x}Sn_{x}Te⟨Gd⟩ crystals as a function of crystal composition x with 0 ≤ x ≤ 0.25 is studied. It is shown that with the increase in tin content in the crystals from 0 to 0.15, p^{2}_{eff}(Gd) increases slowly from 37 to 43. Then p^{2}_{eff}(Gd) increases abruptly to 63 value when x = 0.16±0.01. For subsequent increase x ≥ 0.17 p^{2}_{eff}(Gd) remains constant at 63. Possible reasons of observed changes of p_{eff}(Gd) and possible mechanisms of influence of the Pb_{1-x}Sn_{x}Te crystal field on the effective magnetic momentum value of Gd-impurities in the crystals under study are analysed.
5
Content available remote

Second-Order Phase Transitions in Magnetic Ca₃Al₂(SiO₄)(Oₕ¹⁰) and Non Magnetic Cubic ZnO

100%
Kunert H.
Acta Physica Polonica A
|
2015
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vol. 127
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issue 2
439-441
EN
Possible symmetry of modes those may cause transitions in magnetic and non magnetic crystals as well as lower space subgroup symmetries of the crystals have been found. The Landau-Lifshitz theory for non magnetic crystals has been reformulated for magnetic crystals and has been applied to Ca₃Al₂(SiO₄)(Oₕ¹⁰). Some experimental data confirm our results.
6
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Second-Order Phase Transitions in Non-Magnetic Wurtzite ZnO and Magnetic Doped with Co

100%
Kunert H., Niyongabo P.
Acta Physica Polonica A
|
2015
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vol. 127
|
issue 2
400-403
EN
We investigate the second-order phase transitions in non-magnetic wurtzite ZnO and magnetic doped with cobalt. Using reformulated Landau-Lifshitz theory of second-order phase transitions and our computer program, we have found all possible lower space group symmetries of ZnO and ZnO doped with Co as well as symmetries of vibration modes which may cause structural phase transitions. We interpret the Raman phonon modes of magnetic doped ZnO according to corepresentations of the magnetic space group P6'₃m'c (ZnO magnetic). Some experimental techniques like X-ray diffraction, reflectivities and Raman spectroscopies can verify our theoretical results.
7
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Exchange Interaction in ZnCrSe Semimagnetic Semiconductor

100%
Mac W., Nguyen K., Twardowski A., Gaj J., Demianiuk M.
Acta Physica Polonica A
|
1992
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vol. 82
|
issue 5
902-904
EN
Magnetoreflectance and magnetization of ZnCrSe were measured for B ≤ 5 T and T = 2 K. A linear dependence between exciton splitting and magnetization was found. The s, p-d exchange parameter was estimated: N_{0}α-N_{0}β=0.67eV.
8
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Content available

High Temperature Ferromagnetism and Nano-Scale Phase Separations in Diluted Magnetic Semiconductors and Oxides

100%
Dietl T.
Acta Physica Polonica A
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2007
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vol. 111
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issue 1
27-46
EN
In this paper the present understanding of the origin of ferromagnetic response that has been detected in a number of diluted magnetic semiconductors and diluted magnetic oxides at room temperature is outlined. It is argued that in these systems, owing to a typically small solubility of magnetic ions, crystallographic or chemical phase separation into regions with a large and a small concentration of magnetic component takes place. The ferromagnetic signatures then come from the regions with a large concentration of magnetic ions, which show non-zero spontaneous magnetization up to the blocking temperature, whose magnitude is proportional to the nanocrystal volume and magnetic anisotropy. Novel methods enabling a control of nano-assembling of magnetic nanocrystals in non-conducting matrices as well as possible functionalities of these spatially modulated magnetic systems are described. We also discuss phase separations into paramagnetic and ferromagnetic regions, which are driven by the Anderson-Mott localization and/or competing ferromagnetic and antiferromagnetic interactions. Finally, the question whether the high temperature ferromagnetism is possible in materials without magnetic ions is addressed.
9
Content available remote

A Photoluminescence Study in PbS-EuS Superlattices

100%
Kowalczyk L., Sadowski J., Gałązka R., Stachow-Wójcik A., Sipatov A., Volobuev V., Smirnov V., Dugaev V.
Acta Physica Polonica A
|
1998
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vol. 94
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issue 3
397-400
EN
Investigations of the photoluminescence of PbS-EuS superlattices deposited on (111)BaF_{2} substrates are presented. Quantum-size and deformation effects in photoluminescence spectra are observed. The strain-induced gap shift and valence-band offset is determined from experimental results. A strong stimulated photoluminescence with relatively low threshold was observed. It was found that the photocarriers generated in EuS barrier strongly affect the population of PbS subbands.
10
Content available remote

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

100%
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).
11
Content available remote

Defect-Related Origin of the Ferromagnetism in ZnO:Co

100%
Hanafin R., Pemmaraju C., Archer T., Sanvito S.
Acta Physica Polonica A
|
2009
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vol. 115
|
issue 1
263-265
EN
In recent years transition metal ion doped ZnO has been the focus of intense scientific enquiry. ZnO:Co is by far the most studied member of this family. However, despite the many experimental claims for ferromagnetism, a definitive theoretical explanation for long range magnetic interaction has so far been lacking. Here we present a mechanism which describes not only the origin of this previously inexplicable magnetism but also explains the experimental findings to date and in addition, suggests a recipe for tailoring the magnetic properties. We demonstrate that the magnetism originates from a Co^{2+} oxygen vacancy pair with a partially filled level close to the ZnO conduction band minimum. The long range coupling then occurs via conduction electrons at moderate n doping. This however is not sufficient for room temperature ferromagnetism due to the prohibitive concentrations of O vacancies needed. The experimental findings may then be explained by a combination of our proposed mechanism and the formation of blocked superparamagnetic clusters.
12
Content available remote

Faraday Rotation and Photoionization of ZnCrSe Semimagnetic Semiconductor

100%
Mac W., Nguyen K., Gaj J., Twardowski A., Demianiuk M., Stachow-Uciakowska A.
Acta Physica Polonica A
|
1993
|
vol. 84
|
issue 3
567-570
EN
The magnetoabsorption and the Faraday rotation of ZnCrSe were measured for B ≤ 5 T and T = 2 K in the region of photon energies lower than the fundamental absorption edge. The circular dichroism of the photoionization absorption bane was observed and analyzed. The Faraday rotation was interpreted as due to the sum of contributions from interband and photoionization optical transitions.
13
Content available remote

Magnetization of Pb_{1-x}Cr_{x}Te Semimagnetic Semiconductor

63%
Mac W., Story T., Twardowski A.
Acta Physica Polonica A
|
1995
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vol. 87
|
issue 2
492-494
EN
We present experimental studies of magnetization of Pb_{1-x}Cr_{x}Te (x ≤ 0.01) crystals. The reasonable description of the data is obtained for a composition of x ≤ 0.001 using Cr^{+++} model (Brillouin type paramagnetism S = 3/2).
14
Content available remote

Kinetic Exchange in Diluted Magnetic Semiconductors of Wurtzite Structure

63%
Blinowski J., Kacman P.
Acta Physica Polonica A
|
1993
|
vol. 84
|
issue 4
693-696
EN
Kinetic exchange between valence electrons and paramagnetic ions in diluted magnetic semiconductors of wurtzite structure is examined and compared with the results obtained previously for zinc-blende type diluted magnetic semiconductors. Two limiting electron configurations of the impurity ion, d^{5} and d^{1}, are discussed. For the former, it is shown that the exchange constant anisotropy, experimentally observed in CdMnSe, results from the anisotropy of the hybridization matrix elements. In the latter case, apart from the similar anisotropy of the ferromagnetic exchange constant, additional, antiferromagnetic corrections should be expected, since for this particular symmetry the hybridization between the ground state of the ion and valence band becomes allowed.
15
Content available remote

Magnetic Anisotropy in Eus-pbs Multilayers

63%
Story T., Swüste C., Swagten H., de Jonge W., Stachow-Wójcik A., Twardowski A., Arciszewska M., Dobrowolski W., Gałązka R., Sipatov A.
Acta Physica Polonica A
|
2000
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vol. 97
|
issue 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.
16
Content available remote

Resonant Photoemission Study of Sn_{0.96}Gd_{0.04}Te

63%
Orlowski N., Janowitz C., Müller A., Manzke R., Kowalski B. J., Orłowski B. A.
Acta Physica Polonica A
|
1997
|
vol. 91
|
issue 5
847-850
EN
Sn_{0.96}Gd_{0.04}Te has been studied by means of the resonant photoemission spectroscopy in the constant final states, constant initial states and energy distribution curves modes. In the constant final states spectrum of the well-known giant resonance at the 4d-4f threshold around 150 eV we were able to resolve a peak of the multiplet structure that has not previously been found. Spectra were also taken at the 4p-5d threshold around 280 eV revealing a double structure with antiresonating behaviour.
17
Content available remote

Impact of Exchange-Correlations Effects (+U Corrections) on the Energy Levels of Mn and Fe Impurities in GaN and AlN: A Comparison with Experiment

63%
Zakrzewski T., Bogusławski P.
Acta Physica Polonica A
|
2013
|
vol. 124
|
issue 5
898-900
EN
Electronic structure of Mn and Fe impurities in GaN and AlN are calculated within the density functional theory in the generalized gradient approximation without and with the +U corrections. The comparison with the available experimental data shows that the results obtained with U = 0 are in good agreement with experiment. Inclusion of +U corrections makes the agreement worse.
18
Content available remote

Static and Dynamic Spin Organization in Magnetic Semiconductor Nanostructures

63%
Samarth N., Luo H., Furdyna J., Giebultowicz T., Awschalom D.
Acta Physica Polonica A
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1992
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vol. 82
|
issue 4
573-584
EN
We describe experiments which study static and dynamic aspects of Mn spin organization in magnetic semiconductor superlattices and quantum wells. Neutron diffraction studies of ZnSe/MnSe and ZnTe/MnSe superlattices show how static Mn spin organization in these antiferromagnetic layers may be modified by strain and lowered dimensionality. We also use a novel form of femtosecond magnetic spectroscopy to examine magnetic polaron dynamics in diluted magnetic semiconductor quantum wells, and show how the organization of Mn spins by a spin-polarized carrier population may be directly viewed in the time domain.
19
Content available remote

Scattering Dynamics of Free Excitons on Fe^{++} Ions in Cd_{1-x}Fe_{x}Se

63%
Gaj J., Nguyen K., Nawrocki M., Golnik A., Lebecki K.
Acta Physica Polonica A
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1991
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vol. 80
|
issue 3
409-412
EN
Inelastic scattering of excitons on Fe^{++} ions in Cd_{1-x}Fe_{x}Se was studied by resonant Raman scattering. Polarization measurements were done using a modulation technique, allowing for the first time to determine the full polarization state of the detected light. The obtained results were compared to a simple calculation in an incoherent model of scattering on Fe^{++} ions.
20
Content available remote

Concentration Dependence of Photo-Induced Magnetization in Diluted Magnetic Semiconductor Cd_{1-x}Mn_{x}Te

63%
Yamaguchi Y., Kawai H., Sato T.
Acta Physica Polonica A
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1997
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vol. 91
|
issue 2
479-482
EN
The photo-induced decrease in magnetization ΔM_{photo} was observed in Cd_{1-x}Mn_{x}Te (0.25 < x < 0.42) under unpolarized light illumination whose photon energy is smaller than the band gap of the sample. The photo-induced magnetization decreases with increasing Mn content through Mn^{2+}-Mn^{2+} antiferromagnetic interaction, which supports our idea for origin of it based on the flipping of Mn spins in the bound magnetic polarons accompanied by the spin-flip Raman scattering.
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