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1
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D'yakonov--Perel Spin Relaxation Suppressed by an Applied Magnetic Field

100%
Wilamowski Z., Jantsch W.
Acta Physica Polonica A
|
2003
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vol. 103
|
issue 6
671-674
EN
We observe a strong anisotropy of spin relaxation and a decrease in the spin relaxation rate with increasing electron mobility in contrast to predictions of the classical D'yakonov-Perel spin relaxation model. We show that for high electron mobility the cyclotron motion causes an additional modulation of spin-orbit coupling, leading to an effective suppression of the spin relaxation rate.
2
Content available remote

Destruction of Antiferromagnetic Order by Localized Polarons

100%
Wilamowski Z., Hankiewicz E.
Acta Physica Polonica A
|
2000
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vol. 97
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issue 3
403-406
EN
Analysis of a finite spin cluster indicates a possibility of the formation of purely magnetic polarons in low-dimensional antiferromagnets. It is shown that for parameters characteristic of CuO_{2} based superconductors a strong antiferromagnetic polaron can occur. The destruction of antiferromagnetic order by the presence of a magnetic polaron is discussed.
3
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Impurity Self-Screening

100%
Wilamowski Z., Przybylińska H.
Acta Physica Polonica A
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1993
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vol. 84
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issue 4
832-834
EN
In a mixed valence impurity system the distribution of impurity charges can be adjusted to minimize the Coulomb energy of inter-impurity interactions. In this paper we discuss the possibility of extending the methods of analytical evaluation of the pair correlation function for classical liquids to apply to a system with a built-in disorder, where the occupation probability is governed by the Fermi-Dirac statistics.
4
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Ultra-Fast Spin Dynamics in Diluted Magnetic Semiconductors

81%
Wilamowski Z., Buczko R., Karczewski G., Jantsch W.
Acta Physica Polonica A
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1996
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vol. 90
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issue 5
969-972
EN
In nano-size antiferromagnetic systems a spatially inhomogeneous field leads to the formation of a staggered magnetization. Thereby the total magnetic moment does not change but the formation of a net magnetic moment at the border of the cluster leads to an energy gain. This type of magnetism is characterised by an ultra-fast dynamics. We suggest it is also responsible for the formation of the exciton magnetic polaron.
5
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Diluted Magnetic Semimetals - Beyond Heisenberg Coupling

81%
Wilamowski Z., Story T., Jantsch W.
Acta Physica Polonica A
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1995
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vol. 87
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issue 1
189-192
EN
We analyse effects which cannot be explained assuming the isotropic Heisenberg form of sp-d or of the indirect d-sp-d (RKKY) coupling. Resonance line broadening, a line shift and an enhancement of the magnetic anisotropy in diluted magnetic semimetals are discussed.
6
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Electrically Detected Magnetic Resonance

81%
Fedorych O., Wilamowski Z., Jantsch W., Sadowski J.
Acta Physica Polonica A
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2004
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vol. 105
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issue 6
591-598
EN
We compare the results of electrically detected magnetic resonance in a 2D electron gas in Si/SiGe quantum wells with transport and magnetic resonance measurements on ferromagnetic Ga_{1-x}Mn_xAs. The results lead us to the conclusion that observation of electrically detected magnetic resonance is possible only in the case of a slow spin relaxation, where the microwave resonant absorption leads to a noticeable change of spin magnetization.
7
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DX Puzzle: Where Are We Now?

81%
Wilamowski Z., Suski T., Jantsch W.
Acta Physica Polonica A
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1992
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vol. 82
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issue 4
561-571
EN
A brief review of the experimental data on the metastable DX-centers in AlGaAs is presented. The experimental proofs of the two-electron nature and of the intermediate, one-electron state of the DX-centers are discussed. We collect the available experimental data on the ground state, electron-emission and capture energies and we discuss the nature of the lattice barrier. The effect of splitting of these energies in AlGaAs alloys and the consequences of the splitting on the capture and emission kinetics are analyzed. The different character of the barrier and of the alloy splitting for donors of the IV and VI group is underlined. The necessity to consider the interdonor Coulomb interaction when discussing the experimental data is also pointed out.
8
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Spin Resonance Absorption in a 2D Electron Gas

81%
Ungier W., Jantsch W., Wilamowski Z.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
345-350
EN
We analyze the power absorption at electron spin resonance excited by the Bychkov-Rashba spin-orbit field in a 2D electron gas. We show that, as long as the absorbed power is dissipated by the usual spin lattice relaxation mechanisms, the resonance line shape is expected to be of pure absorption type, i.e., it can be described by the imaginary part of the dynamic magnetic susceptibility. Therefore, the Dysonian line shape observed in ESR of 2D electron gas cannot result from this type of the resonance signal.
9
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Quantum Phenomena in Small Antiferromagnets

81%
Wilamowski Z., Buczko R., Jantsch W.
Acta Physica Polonica A
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1997
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vol. 92
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issue 2
379-382
EN
We show that the most characteristic properties of mesoscopic antiferromagnets can be explained in terms of the response on a spatially inhomogeneous perturbation. This concept allows to explain the dynamic properties (quantum resonance, coherence and tunnelling rates) as well as static perturbations which, for increasing size of an antiferromagnet, leads to a transition from the quantum mechanical oscillating system to a classical antiferromagnet with well defined Néel vectors.
10
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Consequences of Spatial Fluctuation of Coulomb Potential in AlGaAs with DX Centers

81%
Wilamowski Z., Kossut J., Jantsch W., Ostermayer G.
Acta Physica Polonica A
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1991
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vol. 80
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issue 3
385-388
EN
Electric charges on randomly distributed impurities in semiconductors produce a spatially fluctuating potential. When the impurities are partially filled, their occupancy is not random but there appears a spatial correlation of the impurity charges appearing due to the inter-impurity Coulomb interactions. We show that when these interactions are taken into account then (i) the activation energy of the electron concentration, (ii) thermal emission kinetics, (iii) capture kinetics, (iv) persistent photoconductivity kinetics and (v) the electron mobility (in a steady state as well as during transients) in GaAlAs:Si can be explained in a consistent way. The energy diagram con cerning the DX center levels with respect to minima of the conduction band as well as the capture and emission barriers (including the effect of the alloy splitting) is constructed within an approach making use of the notion of the impurity self-screening.
11
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Monte Carlo Simulations of Spatial Correlations of Charged Centers in δ-Doped Layers

81%
Sobkowicz P., Wilamowski Z., Kossut J.
Acta Physica Polonica A
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1992
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vol. 82
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issue 4
645-648
EN
Results of Monte Carlo simulations of a 2D system of charged donors are presented. They enable to study the effects related to a spatial correlation of donor charges located on a random donor matrix. A qualitative difference between DX^{+} and DX¯ models is observed. In the first case, strong temperature dependence of the correlations and a "freezing-like" behaviour is found. The origin of the freezing is traced to the random distribution of donor sites by comparing the system with a liquid-like model where the charges may assume arbitrary positions within a plane. In the second case only nearest-neighbour correlations are observed. The simulations have direct application in analysis of the behaviour of the DX centers in the GaAs planarly doped with Si.
12
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Coulomb versus Madelung Gap: Ordering in a System of Point Charges

81%
Sobkowicz P., Wilamowski Z., Kossut J.
Acta Physica Polonica A
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1993
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vol. 84
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issue 3
515-518
EN
Spatial correlations of impurity charges in a mixed valence regime are studied with the use of Monte Carlo simulations. The influence of various kinds of disorder on the one-particle density of states is determined. A continuous transitions from a "soft" Coulomb gap (density of states vanishing only at the chemical potential) to a "hard" gap (with a finite range of energies with vanishing density of states) is found, driven by decreasing amount of built-in disorder in the system. The "hard" Coulomb gap resembles the Madelung gap, found in crystalline arrangements of charges. The similarity reflects the fact that both the Coulomb and Madelung gaps are manifestations of the same phenomenon, resulting from ordering of the positions of point charges, the only difference being the range of correlations.
13
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"Comb-Like" Polarons and Bipolarons in High-T_{c} Materials

81%
Hankiewicz E., Buczko R., Wilamowski Z.
Acta Physica Polonica A
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2000
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vol. 97
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issue 1
185-188
EN
Diagonalization of Hamiltonian composed from d-d exchange interactions between localized d spins of antiferromagnetic cluster and p-d interaction with the spin of carriers indicates a possibility of formation of pure magnetic polarons. The most energetically favorable solution occurs when the carrier density in CuO_{2} planes is distributed on every second spin. These "comb-like" polarons have a tendency to bind into pairs (bipolarons) "glued" by the antiferromagnetic medium.
14
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Potential Fluctuations in HgSe:Fe,Ga - a Numerical Study

81%
Sobkowicz P., Wilamowski Z., Kossut J.
Acta Physica Polonica A
|
1993
|
vol. 84
|
issue 4
645-648
EN
We study spatial correlation of donor charges in HgSe:Fe,Ga using a few simple quantities (mean electrostatic energy of various donor sites, fluctuations of the electrostatic potential). The study uses Monte Carlo simulation techniques. We are able to indicate general trends in the behavior of the correlation when proportion of correlating (Fe^{3+}) and noncorrelating (Ga) charged centers in the sample is changed.
15
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Small Antiferromagnetic Clusters

81%
Buczko R., Wilamowski Z., Jantsch W.
Acta Physica Polonica A
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1996
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vol. 90
|
issue 4
747-750
EN
The analysis of the quantum mechanical model of mesoscopic size antiferromagnets shows that small antiferromagnets are characterized by a stronger exchange coupling and by an oscillating character of spins polarizations. Experimental evidence of the quantum character is discussed. We interpret the interlayer coupling in antiferromagnet superlattices and a puzzling resonance observed in nano-size antiferromagnet grains.
16
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Spatial Correlation of Impurity Charges Induced by Coulomb Interactions - Application to DX Centers in GaAs

81%
Kossut J., Wilamowski Z., Dietl T., Świątek K.
Acta Physica Polonica A
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1991
|
vol. 79
|
issue 1
49-58
EN
The electron mobility enhancement observed in heavily doped GaAs under hydrostatic pressure is interpreted in terms of spatial correlation between the donor charges within partially occupied system of impurities induced by strong inter-donor Coulomb interaction. A simple analytic theory is given for both DX^{0} and DX^{-} models of the impurity state. The mobility is shown to increase together with pressure in both models. Estimates of the energy of the DX level are strongly perturbed by the inter-donor Coulomb interactions.
17
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Photoconductivity in GaAlAs:Si Proves Negative U of DX Centers

81%
Wilamowski Z., Jantsch W., Ostermayer G.
Acta Physica Polonica A
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1991
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vol. 80
|
issue 2
283-286
EN
The analysis of the temperature dependence of the photoconductivity, amplitude in doped GaAlAs, provides a simple and convincing proof of the negative sign of the Hubbard correlation energy U, strictly speaking of the two-electron nature of the thermal emission process from DX centers. The proof is based on a comparison of the emission activation energy measured per emission event (DLTS) with that measured per electron.
18
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Anisotropy of Magnetic Interactions in HgFeSe

81%
Wilamowski Z., Przybylińska H., Joss W., Guillot M.
|
EN
Magnetic properties (susceptibility, high-field torque and magnetization) of cubic HgFeSe are analyzed. Van Vleck magnetism of Fe^{2+} is well evidenced. The energy splitting of the Fe levels in HgSe is shown to differ considerably from that in other II-VI compounds.
19
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Oscillating Antiferromagnetism of Ultrathin EuTe Layers

81%
Wilamowski Z., Springholz G., Svrcek V., Jantsch W.
Acta Physica Polonica A
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1997
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vol. 92
|
issue 5
1051-1054
EN
We study magnetic resonance on EuTe/PbTe superlattices. Analysis of the magnetic dipole anisotropy in the superlattices and of the EPR amplitude of isolated Eu ions in the PbTe wells shows that the diffusion at interfaces is very small. The real thickness of EuTe can be evaluated with an accuracy better than one monolayer. Since for EuTe layers thicker than 2 monolayers there is no difference in the character of the antiferromagnetic resonance observed for even and odd numbers of monolayers, we conclude that there is no static magnetization of the antiferromagnetic sublattices. Nevertheless, long range antiferromagnetic order is clearly evident.
20
Content available remote

Localized Spin Relaxation Due To Coupling To Effective Mass States

81%
Wilamowski Z., Dmochowski J., Jantsch W.
Acta Physica Polonica A
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1997
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vol. 92
|
issue 5
1055-1058
EN
The EPR of residual Mn in CdF_{2} doped with Y, In and Ga is investigated. Although these donors are barely seen in EPR, they manifest themselves by a new effect: a drastic resonant reduction in the longitudinal relaxation rate of Mn which occurs only if the Zeeman splitting of the two subsystems coincide. In this situation, the saturation of those of the six Mn hyperfine lines is weakened which coincide with the shallow donor resonance.
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