| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- Sawicki, M., et al.
(författare)
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Cubic anisotropy in (Ga,Mn) As layers : Experiment and theory
- 2018
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 97:18
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Tidskriftsartikel (refereegranskat)abstract
- Historically, comprehensive studies of dilute ferromagnetic semiconductors, e.g., p-type (Cd,Mn) Te and (Ga,Mn) As, paved the way for a quantitative theoretical description of effects associated with spin-orbit interactions in solids, such as crystalline magnetic anisotropy. In particular, the theory was successful in explaining uniaxial magnetic anisotropies associated with biaxial strain and nonrandom formation of magnetic dimers in epitaxial (Ga,Mn) As layers. However, the situation appears much less settled in the case of the cubic term: the theory predicts switchings of the easy axis between in-plane < 100 > and < 110 > directions as a function of the hole concentration, whereas only the < 100 > orientation has been found experimentally. Here, we report on the observation of such switchings by magnetization and ferromagnetic resonance studies on a series of high-crystalline quality (Ga,Mn) As films. We describe our findings by themean-field p-d Zener model augmented with three new ingredients. The first one is a scattering broadening of the hole density of states, which reduces significantly the amplitude of the alternating carrier-induced contribution. This opens the way for the two other ingredients, namely the so-far disregarded single-ion magnetic anisotropy and disorder-driven nonuniformities of the carrier density, both favoring the < 100 > direction of the apparent easy axis. However, according to our results, when the disorder gets reduced, a switching to the < 110 > orientation is possible in a certain temperature and hole concentration range.
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