| 1. |
- Gryglas-Borysiewicz, Marta, et al.
(author)
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Hydrostatic-pressure-induced changes of magnetic anisotropy in (Ga, Mn) As thin films
- 2017
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In: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 29:11
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Journal article (peer-reviewed)abstract
- The impact of hydrostatic pressure on magnetic anisotropy energies in (Ga, Mn) As thin films with in-plane and out-of-plane magnetic easy axes predefined by epitaxial strain was investigated. In both types of sample we observed a clear increase in both in-plane and out-of-plane anisotropy parameters with pressure. The out-of-plane anisotropy constant is well reproduced by the mean-field p-d Zener model; however, the changes in uniaxial anisotropy are much larger than expected in the Mn-Mn dimer scenario.
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| 2. |
- Islam, Rajibul, et al.
(author)
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Engineering axion insulator and other topological phases in superlattices without inversion symmetry
- 2023
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 107:12
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Journal article (peer-reviewed)abstract
- We study theoretically the interplay between magnetism and topology in three-dimensional HgTe/MnTe superlattices stacked along the (001) axis. Our results show the evolution of the magnetic topological phases with respect to the magnetic configurations. An axion insulator phase is observed for the antiferromagnetic order with the out-of-plane Néel vector direction below a critical thickness of MnTe, which is the ground state among all magnetic configurations. Defining T as the time-reversal symmetry, this axion insulator phase is protected by a magnetic twofold rotational symmetry C2⋅T. We find that the axion insulator phase evolves into a trivial insulator as we increase the number of the magnetic MnTe layers, and we present an estimate of the critical thickness of the MnTe film above which the axion insulator phase is absent. By switching the Néel vector direction into the ab plane, the system realizes different antiferromagnetic topological insulators depending on the thickness of MnTe. These phases feature gapless surface Dirac cones shifted away from high-symmetry points on surfaces perpendicular to the Néel vector direction of the magnetic layers. In the presence of ferromagnetism, the system realizes a magnetic Weyl semimetal and a ferromagnetic semimetal for out-of-plane and in-plane magnetization directions, respectively. We observe large anomalous Hall conductivity in the presence of ferromagnetism in the three-dimensional superlattice.
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| 3. |
- Pournaghavi, Nezhat, et al.
(author)
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Realization of the Chern-insulator and axion-insulator phases in antiferromagnetic MnTe/Bi2(Se, Te)3/MnTe heterostructures
- 2021
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In: Physical review B (PRB). - : American Physical Society. - 2469-9950 .- 2469-9969. ; 103:19
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Journal article (peer-reviewed)abstract
- Breaking time-reversal symmetry in three-dimensional topological insulator thin films can lead to different topological quantum phases, such as the Chern insulator (CI) phase and the axion insulator (AI) phase. Using first-principles density functional theory methods, we investigate the onset of these two topological phases in a trilayer heterostructure consisting of a Bi2Se3 (Bi2Te3) TI thin film sandwiched between two antiferromagneticMnTe layers. We find that an orthogonal exchange field from the MnTe layers, stabilized by a small anisotropy barrier, opens an energy gap of the order of 10 meV at the Dirac point of the TI film. A topological analysis demonstrates that, depending on the relative orientation of the exchange field at the two interfaces, the total Chern number of the system is either C = 1 or C = 0, characteristic of the CI and AI phases, respectively. Nontopological surface states inside the energy-gap region, caused by the interface potential, complicate this identification. Remarkably though, the calculation of the anomalous Hall conductivity shows that such nontopological surface states do not affect the topology-induced transport properties. Given the size of the exchange gap, we estimate that gapless chiral edge states, leading to the quantum anomalous Hall effect, should emerge on the sidewalls of these heterostructures in the CI phase for widths > 200 nm. We also discuss the possibility of inducing transitions between the CI and the AI phases by means of the spin-orbit torque caused by the spin Hall effect in an adjacent conducting layer.
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| 4. |
- Sadowski, Janusz, et al.
(author)
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Formation process and superparamagnetic properties of (Mn,Ga)As nanocrystals in GaAs fabricated by annealing of (Ga,Mn)As layers with low Mn content
- 2011
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 84:24, s. 245306-
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Journal article (peer-reviewed)abstract
- X-ray diffraction, transmission electron microscopy, and magnetization measurements are employed to study the structural and magnetic properties of Mn-rich (Mn,Ga)As nanocrystals embedded in GaAs. These nanocomposites are obtained by moderate-temperature (400 degrees C) and high-temperature (560 degrees C and 630 degrees C) annealing of (Ga,Mn)As layers with Mn concentrations between 0.1% and 2%, grown by molecular beam epitaxy at 270 degrees C. Decomposition of (Ga,Mn)As is already observed at the lowest annealing temperature of 400 degrees C for layers with initial Mn content of 1% and 2%. Both cubic and hexagonal (Mn, Ga) As nanocrystals, with similar diameters of 7-10 nm, are observed to coexist in layers with an initial Mn content of 0.5% and 2% after higher-temperature annealing. Measurements of magnetization relaxation in the time span 0.1-10 000 s provide evidence for superparamagnetic properties of the (Mn,Ga)As nanocrystals, as well as for the absence of spin-glass dynamics. These findings point to weak coupling between nanocrystals even in layers with the highest nanocrystal density.
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