| 1. |
- Levchenko, K., et al.
(författare)
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Evidence for the homogeneous ferromagnetic phase in (Ga, Mn) (Bi, As) epitaxial layers from muon spin relaxation spectroscopy
- 2019
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 9, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- Ferromagnetic semiconductor thin layers of the quaternary (Ga,Mn)(Bi,As) and reference, ternary (Ga, Mn) As compounds, epitaxially grown under either compressive or tensile strain, have been characterized from a perspective of structural and magnetization homogeneity. The quality and composition of the layers have been confirmed by secondary-ion mass spectrometry (SIMS). A thorough evaluation of the magnetic properties as a function of temperature and applied magnetic field has been performed by means of SQUID magnetometry and low-energy muon spin relaxation (mu SR) spectroscopy, which enables studying local (on the nanometer scale) magnetic properties of the layers. The results testify that the ferromagnetic order builds up almost homogeneously below the Curie temperature in the full volume fraction of both the (Ga, Mn) As and (Ga, Mn)(Bi, As) layers. Incorporation of a small amount of heavy Bi atoms into (Ga, Mn) As, which distinctly enhances the strength of spin-orbit coupling in the quaternary (Ga, Mn)(Bi, As) layers, does not deteriorate noticeably their magnetic properties.
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| 2. |
- Andrearczyk, T., et al.
(författare)
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Bistability of (Ga,Mn)As Ferromagnetic Nanostructures Due to the Domain Walls Switching
- 2009
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Ingår i: Acta Physica Polonica A. - 0587-4246. ; 116:5, s. 901-903
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Konferensbidrag (refereegranskat)abstract
- We designed and investigated four-arm nanostructures, composed of two perpendicularly crossed stripes, fabricated from ferromagnetic (Ga,Mn)As layer by means of electron-beam lithography patterning and chemical etching. The nanostructures exhibit a bistable resistance behavior resulting from two configurations of magnetic domain walls in the central part of the structures. We demonstrate a possibility of switching between two stable resistance states in zero magnetic field by applying a pulse of either weak magnetic field or electric current through the structure.
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| 3. |
- Andrearczyk, T., et al.
(författare)
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Magneto-Transport Characterization of Four-Arm Nanostructure Based on Ferromagnetic (Ga,Mn)As
- 2008
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Ingår i: ACTA PHYSICA POLONICA A. - 0587-4246. ; 114:5, s. 1049-1054
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Konferensbidrag (refereegranskat)abstract
- We report on results of magneto-transport measurements performed on four-arm nanostructure fabricated from p-type ferromagnetic Ga0.92Mn0.08As layer. The results reveal hysteresis-like behaviors of low field magneto resistance. We interpret the magnetoresistance in terms of domain walls, which are expected to be trapped inside the nanostructure at some particular positions and which contribute to the total resistance.
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| 4. |
- Levchenko, K., et al.
(författare)
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Effect of misfit strain in (Ga,Mn)(Bi,As) epitaxial layers on their magnetic and magneto-transport properties
- 2016
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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. ; 129:1, s. 90-93
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Tidskriftsartikel (refereegranskat)abstract
- Effect of misfit strain in the layers of (Ga,Mn)(Bi,As) quaternary diluted magnetic semiconductor, epitaxially grown on either GaAs substrate or (In,Ga)As buffer, on their magnetic and magneto-transport properties has been investigated. High-resolution X-ray diffraction, applied to characterize the structural quality and misfit strain in the layers, proved that the layers were fully strained to the GaAs substrate or (In,Ga)As buffer under compressive or tensile strain, respectively. Ferromagnetic Curie temperature and magneto-crystalline anisotropy of the layers have been examined by using magneto-optical Kerr effect magnetometry and low-temperature magneto-transport measurements. Post-growth annealing treatment of the layers has been shown to enhance the hole concentration and the Curie temperature in the layers.
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| 5. |
- Levchenko, K., et al.
(författare)
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Impact of bismuth incorporation into (Ga,Mn)As thin films on their structural and magnetic properties
- 2015
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Ingår i: Physica Status Solidi C. - : Wiley. - 1610-1642 .- 1862-6351. ; 12:8, s. 1152-1155
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Konferensbidrag (refereegranskat)abstract
- Structural and magnetic properties of thin films of the (Ga,Mn)(Bi,As) quaternary diluted magnetic semiconductor grown by the low-temperature molecular-beam epitaxy technique on GaAs substrates have been investigated. High-resolution X-ray diffraction has been applied to characterize the structural quality and misfit strain in the films. Ferromagnetic Curie temperature and magnetocrystalline anisotropy of the films have been examined by using SQUID magnetometry and low-temperature magneto-transport measurements. Post-growth annealing treatment of the films has been shown to reduce the strain in the films and to enhance their Curie temperature. Significant increase in the magnitude of magneto-transport effects caused by incorporation of a small amount of Bi into the films is interpreted as a result of enhanced spinorbit coupling in the (Ga, Mn)(Bi, As) films. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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| 6. |
- Levchenko, K., et al.
(författare)
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Magnetic and Magneto-Transport Characterization of (Ga,Mn)(Bi,As) Epitaxial Layers
- 2014
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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. ; 126:5, s. 1121-1124
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Tidskriftsartikel (refereegranskat)abstract
- High-quality layers of the (Ga,Mn)(Bi,As) quaternary compound semiconductor have been grown by the low-temperature molecular-beam epitaxy technique. An effect of Si incorporation into the (Ga,Mn)As ferromagnetic semiconductor and the post-growth annealing treatment of the layers have been investigated through examination of their magnetic and magneto-transport properties. Significant enhancement of the planar Hall effect magnitude upon addition of Si into the layers is interpreted as a result of increased spin orbit coupling in the (Ga,Mn)(Bi,As) layers.
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| 7. |
- Levchenko, K., et al.
(författare)
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Novel Quaternary Dilute Magnetic Semiconductor (Ga,Mn)(Bi,As) : Magnetic and Magneto-Transport Investigations
- 2017
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Ingår i: Journal of Superconductivity and Novel Magnetism. - : Springer Science and Business Media LLC. - 1557-1939 .- 1557-1947. ; 30:3, s. 825-829
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic and magneto-transport properties of thin layers of the (Ga,Mn)(Bi,As) quaternary dilute magnetic semiconductor grown by the low-temperature molecular-beam epitaxy technique on GaAs substrates have been investigated. Ferromagnetic Curie temperature and magneto-crystalline anisotropy of the layers have been examined by using magneto-optical Kerr effect magnetometry and low-temperature magneto-transport measurements. Post-growth annealing treatment of the layers has been shown to enhance the hole concentration and Curie temperature in the layers. A significant increase in the magnitude of magneto-transport effects caused by incorporation of a small amount of Bi into the (Ga,Mn)As layers, revealed in the planar Hall effect (PHE) measurements, is interpreted as a result of enhanced spin-orbit coupling in the (Ga,Mn)(Bi,As) layers. A two-state behaviour of the planar Hall resistance at zero magnetic field provides its usefulness for applications in non-volatile memory devices.
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| 8. |
- Gluba, L., et al.
(författare)
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Band structure evolution and the origin of magnetism in (Ga,Mn) As : From paramagnetic through superparamagnetic to ferromagnetic phase
- 2018
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 97:11
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Tidskriftsartikel (refereegranskat)abstract
- The high-spectral-resolution optical studies of the energy gap evolution, supplemented with electronic, magnetic, and structural characterization, show that the modification of the GaAs valence band caused by Mn incorporation occurs already for a very low Mn content, much lower than that required to support ferromagnetic spin-spin coupling in (Ga,Mn) As. Only for n-type (Ga,Mn) As with the Mn content below about 0.3% the Mn-related extended states are visible as a feature detached from the valence-band edge and partly occupied with electrons. The combined magnetic and low-temperature photoreflectance studies presented here indicate that the paramagnetic <-> ferromagnetic transformation in p-type (Ga,Mn) As takes place without imposing changes of the unitary character of the valence band with the Fermi level located therein. The whole process is rooted in the nanoscale fluctuations of the local (hole) density of states and the formation of a superparamagnetic-like state. The Fermi level in (Ga,Mn) As is coarsened by the carrier concentration of the itinerant valence band holes and further fine-tuned by the many-body interactions.
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| 9. |
- Gluba, L., et al.
(författare)
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On the nature of the Mn-related states in the band structure of (Ga,Mn)As alloys via probing the E-1 and E-1 + Delta(1) optical transitions
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:3
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Tidskriftsartikel (refereegranskat)abstract
- The dilute (Ga,Mn)As became a model ferromagnetic semiconductor, however there is still a disagreement on the source of its magnetism. In this paper, we verify the ellipsometric results and compare them with more precise photoreflectance method, which gives an important insight into the interaction of the Mn-related states with the ones of GaAs valence band. No spectral shifts observed for the E-1 and E-1 + Delta(1) interband transitions in highly doped and annealed (Ga,Mn)As epitaxial layers indicate that the coupling between a detached Mn impurity band and the valence band does not occur. Our findings are supported by the characterizations of the (Ga,Mn)As epitaxial layers with the high resolution transmission electron microscopy and magnetization measurements. (c) 2014 AIP Publishing LLC.
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| 10. |
- Yastrubchak, O., et al.
(författare)
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Effect of low-temperature annealing on the electronic- and band-structures of (Ga,Mn) As epitaxial layers
- 2014
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 115:1
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Tidskriftsartikel (refereegranskat)abstract
- The effect of outdiffusion of Mn interstitials from (Ga,Mn) As epitaxial layers, caused by post-growth low-temperature annealing, on their electronic- and band-structure properties has been investigated by modulation photoreflectance (PR) spectroscopy. The annealing-induced changes in structural and magnetic properties of the layers were examined with high-resolution X-ray diffractometry and superconducting quantum interference device magnetometry, respectively. They confirmed an outdiffusion of Mn interstitials from the layers and an enhancement in their hole concentration, which were more efficient for the layer covered with a Sb cap acting as a sink for diffusing Mn interstitials. The PR results demonstrating a decrease in the band-gap-transition energy in the as-grown (Ga,Mn) As layers, with respect to that in the reference GaAs one, are interpreted by assuming a merging of the Mn-related impurity band with the GaAs valence band. Whereas an increase in the band-gap-transition energy caused by the annealing treatment of the (Ga,Mn) As layers is interpreted as a result of annealing-induced enhancement of the free-hole concentration and the Fermi level location within the valence band. The experimental results are consistent with the valence-band origin of itinerant holes mediating ferromagnetic ordering in (Ga,Mn) As, in agreement with the Zener model for ferromagnetic semiconductors. (C) 2014 AIP Publishing LLC.
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| 11. |
- Yastrubchak, O., et al.
(författare)
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Ferromagnetism and the electronic band structure in (Ga,Mn)(Bi,As) epitaxial layers
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:7
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Tidskriftsartikel (refereegranskat)abstract
- Impact of Bi incorporation into (Ga,Mn)As layers on their electronic-and band-structures as well as their magnetic and structural properties has been studied. Homogenous (Ga,Mn)(Bi,As) layers of high structural perfection have been grown by the low-temperature molecular-beam epitaxy technique. Post-growth annealing treatment of the layers results in an improvement of their structural and magnetic properties and an increase in the hole concentration in the layers. The modulation photoreflectance spectroscopy results are consistent with the valence-band model of hole-mediated ferromagnetism in the layers. This material combines the properties of (Ga,Mn)As and Ga(Bi,As) ternary compounds and offers the possibility of tuning its electrical and magnetic properties by controlling the alloy composition. (C) 2014 AIP Publishing LLC.
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| 12. |
- Yastrubchak, O., et al.
(författare)
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Photoreflectance study of the fundamental optical properties of (Ga,Mn) As epitaxial films
- 2011
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 83:24
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Tidskriftsartikel (refereegranskat)abstract
- Fundamental optical properties of thin films of the (Ga,Mn) As diluted ferromagnetic semiconductor with low (1%-2%) and high (4%-6%) Mn content and of a reference GaAs film, grown by low-temperature molecular-beam epitaxy, have been investigated by photoreflectance (PR) spectroscopy. In addition, the films were subjected to complementary characterization by means of superconducting quantum interference device magnetometry, Raman spectroscopy, and high-resolution x-ray diffractometry. Thorough full-line-shape analysis of the PR spectra, which enabled determination of the E-0 electronic transition in (Ga,Mn) As, revealed significant differences between the energy band structures in the vicinity of the Gamma point of the Brillouin zone in the investigated (Ga,Mn) As films. In view of the experimental results obtained, the evolution of the valence band structure in (Ga,Mn) As with increasing Mn content is discussed, pointing to a merging of the Mn-related impurity band with the host GaAs valence band for high Mn content.
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