| 1. |
- Lawniczak-Jablonska, K., et al.
(författare)
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Structural and magnetic properties of GaAs:(Mn,Ga)As granular layers
- 2011
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Ingår i: Physica Status Solidi. B: Basic Research. - : Wiley. - 0370-1972. ; 248:7, s. 1609-1614
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Tidskriftsartikel (refereegranskat)abstract
- Granular GaAs:(Mn,Ga)As films were prepared by annealing the Ga0.92Mn0.08As/GaAs layer grown by the MBE method at low temperature. The annealing was performed at 500 or 600 degrees C. It is commonly accepted that this processing should result in formation of cubic zinc blende or hexagonal MnAs inclusions depending on the temperature. We demonstrate that such a priory assumption is not justified. The kind of formed inclusions depends not only on the annealing temperature but also on the number of defects and Mn atoms in the substitutional and interstitial positions in as grown sample. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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| 2. |
- Lawniczak-Jablonska, K., et al.
(författare)
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Structural and magnetic properties of nanoclusters in GaMnAs granular layers
- 2011
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596. ; 184:6, s. 1530-1539
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Tidskriftsartikel (refereegranskat)abstract
- Structural and magnetic properties of GaAs thin films with embedded nanoclusters were investigated as a function of the annealing temperature and Mn content. Surprisingly, the presence of two kinds of nanoclusters with different structure was detected in most of the samples independently of the thermal processing or Mn content. This proved that the presence of a given type of clusters cannot be assumed a priori as is reported in many papers. The fraction of Mn atoms in each kind of cluster was estimated from the extended X-ray absorption fine structure analysis. This analysis ruled out the possibility of the existence of nanoclusters containing a hypothetic MnAs cubic compound-only (Ga,Mn)As cubic and hexagonal MnAs clusters were detected. Moreover the bimodal distribution of Mn magnetic moments was found, which scales with the estimated fraction of Mn atoms in the cubic and hexagonal clusters. (C) 2011 Elsevier Inc. All rights reserved.
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| 3. |
- Lawniczak-Jablonska, K., et al.
(författare)
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The source of room temperature ferromagnetism in granular GaMnAs layers with zinc blende clusters
- 2011
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Ingår i: Physica Status Solidi. Rapid Research Letters. - : Wiley. - 1862-6254. ; 5:2, s. 62-64
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Tidskriftsartikel (refereegranskat)abstract
- Granular GaAs:(Mn,Ga) As films were prepared by annealing the Ga0.985Mn0.015As/GaAs layers at 500 degrees C or 600 degrees C. It is commonly accepted that this processing should result in the formation of cubic or hexagonal MnAs clusters, respectively. We demonstrate that such a priori assumption is not justified. If in the as grown sample there are not many defects with the interstitial Mn atoms, only small cubic clusters can be formed even after annealing at 600 degrees C. Moreover, in a sample containing solely cubic GaMnAs clusters, the Mn ions are ferro-magnetically coupled at room temperature. This fact was explained by the existence of GaMnAs solid solution in the clusters, with content of Mn close to 20% (higher than ever found in the layers) as was confirmed by experiment and theory. Extended X-ray absorption spectroscopy studies excluded the possibility of formation of the hypothetic zinc blende MnAs clusters. Not more than one Mn atom was detected in the second shell around central Mn atom. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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| 4. |
- Wagner, W, et al.
(författare)
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Europe ambivalent on biotechnology
- 1997
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Ingår i: Nature. - London : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 387, s. 845-847
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Tidskriftsartikel (refereegranskat)abstract
- The Eurobarometer on Biotechnology (46.1) was conducted during October and November 1996. The survey conducted in each EU (European Union) country used a multi-stage random sampling procedure and provided a statistically representative sample of national residents aged 15 and over. The total sample within the EU was 16,246 respondents (about 1,000 per EU country). The survey questionnaire was designed by the authors as part of a larger study involving the comparative analysis of public perceptions, media coverage and public policy in relation to biotechnology from 1973 to the present.
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| 5. |
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| 6. |
- Kwiatkowski, A., et al.
(författare)
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Magnetic properties of MnAs nanocrystals embedded in GaAs
- 2009
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 321:18, s. 2788-2791
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Tidskriftsartikel (refereegranskat)abstract
- A phenomenological model for explaining the magnetic properties of MnAs nanocrystals embedded in GaAs is proposed. It is shown that experimental data of DC magnetization as a function of temperature, obtained according to zero-field-cooled and field-cooled protocols, can be understood assuming a transition of the system from a low temperature state in which very slow dynamics is observed(frozen state) to a high-temperature state in which dynamics is fast(quasi superparamagnetic state). (C) 2009 Elsevier B. V. All rights reserved.
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| 7. |
- Kwiatkowski, A., et al.
(författare)
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MnAs Nanocrystals Embedded in GaAs
- 2008
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Ingår i: ACTA PHYSICA POLONICA A. - 0587-4246. ; 114:5, s. 1207-1211
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Konferensbidrag (refereegranskat)abstract
- Magnetic properties of MnAs nanocrystals embedded in GaAs are analyzed in the frame of phenomenological model proposed by Sasaki for ferritin superparamagnets. Our calculations explain qualitatively experimental data of magnetization versus temperature; obtained according to zero-field-cooled and field-cooled protocols. They show dynamics of magnetization of MnAs nanocrystals in range of temperature from 10 K to 320 K. There is transition from state in which very slow dynamics is observed (frozen state) to state in which dynamics is fast (quasi-superparamagnetic state).
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| 8. |
- Kwiatkowski, A., et al.
(författare)
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Structure and magnetism of MnAs nanocrystals embedded in GaAs as a function of post-growth annealing temperature
- 2007
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 101:11
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Tidskriftsartikel (refereegranskat)abstract
- Self-organized Ga(Mn)As nanoclusters, embedded in GaAs, were formed during post-growth thermal annealing of Ga1-xMnxAs layers. Structural and magnetic properties of such composites were systematically studied as a function of the annealing temperature. Small (similar to 3 nm) Mn-rich zinc-blende Mn(Ga)As clusters, coherent with the GaAs matrix, were formed at the annealing temperature of 500 degrees C. An increase of the annealing temperature of up to 600 degrees C led to the creation of 10-20 nm large NiAs-type hexagonal MnAs nanocrystals. Magnetization measurements showed that the MnAs nanoprecipitates were superparamagnetic, with a distribution of blocking temperatures that depended on the MnAs cluster size. Some intermediate paramagnetic clusters (structurally disordered clusters) were also observed. (c) 2007 American Institute of Physics.
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| 9. |
- Juszynski, P., et al.
(författare)
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Influence of Epitaxial Strain on Magnetic Anisotropy in (Ga,Mn)As
- 2012
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Ingår i: Acta Physica Polonica. Series A: General Physics, Physics of Condensed Matter, Optics and Quantum Electronics, Atomic and Molecular Physics, Applied Physics. - 0587-4246. ; 122:6, s. 1004-1006
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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