|
|
Relativistic spintronic effects in semiconductor structures
Nádvorník, Lukáš ; Jungwirth, Tomáš (advisor) ; Ramsay, Andrew (referee) ; Veis, Martin (referee)
The spin transport and dynamics of optically injected spin polarized carri- ers are studied with a high spatial and/or time resolution in semiconductor GaAs-based heterostructures in multiple transport regimes. An unexpectedly long-scale and high-speed spin diffusion transport is observed in a long-lived electron sub-system induced optically at an undoped single GaAs/AlGaAs heterointerface. A diffusion and drift-dominated spin transport is investi- gated using an electrical spin-detection via the inverse spin Hall effect in doped GaAs-based systems at room and low temperatures. It is shown that the inverse spin Hall signal and the spin transport parameters can be con- trolled by a direct application of an electric field or by expanding a depleted zone of a planar pn-junction.
|
|
|
Electronic Structure and Magnetic Properties of Antiferromagnetic Semiconductors and Metals
Železný, Jakub ; Jungwirth, Tomáš (advisor) ; Carva, Karel (referee) ; Gomonay, Helen (referee)
Antiferromagnets are common in nature and just like ferromagnets posses a long-range magnetic order. They have found little practical application so far, be- cause the magnetic order in antiferromagnets is hard to detect and to manipulate by external magnetic fields. This has become less of a problem due to the development of spintronics, which has motivated a new interest in antiferromagnets. In this thesis we first theoretically study the electronic and magnetic structure of certain class of antiferromagnetic compounds, which are related to common semiconductors. In the second part we focus on electrical manipulation of antiferromagnets. We show that the so-called spin-orbit torque, which has been studied extensively in ferromagnets, can efficiently manipulate the antiferromagnetic order. We calculate the spin-orbit torque in several antiferromagnets and study the symmetry of the spin-orbit torque in detail. Powered by TCPDF (www.tcpdf.org)
|
|
|
Magnetic anisotropies in (Ga,Mn)As and metallic multilayers with strong spin-orbit coupling
Zemen, Jan ; Jungwirth, Tomáš (advisor) ; Diviš, Martin (referee) ; Šob, Mojmír (referee)
The thesis presents a numerical study of magnetocrystalline anisotropies in dilute ferromagnetic semiconductors and transition metal systems intended to advance the current understanding of the microscopic origins of this relativistic effect and to contribute to the development of spintronic devices with new functionalities. The major part of the work surveys magnetocrystalline anisotropies in (Ga,Mn)As epilayers and compares the calculations to available experimental data. Our model is based on an envelope function description of the valence band holes and a spin representation for their kinetic-exchange interaction with localised electrons on Mn2+ ions, treated in the mean-field approximation. For epilayers with growth induced lattice-matching strains we study in-plane to out-of-plane easy axis reorientations as a function of Mn local-moment concentration, hole concentration, and temperature. Next we focus on the competition of in-plane cubic and uniaxial anisotropies. We add an in-plane shear strain to the effective Hamiltonian in order to capture measured data in bare, unpatterned epilayers, and we provide microscopic justification for this approach. The model is then extended by an in-plane uniaxial strain and used to directly describe experiments with magnetisation direction controlled by...
|
|
|
Topological band theory of relativistic spintronics in antiferromagnets
Šmejkal, Libor ; Jungwirth, Tomáš (advisor) ; Kuneš, Jan (referee) ; Shick, Alexander (referee)
Nanoelectronics and spintronics are concerned with writing, transporting, and reading information stored in electronic charge and spin degrees of freedom at the nanoscale. Past few years have shown that two spintronics effects discovered in the 19th century, namely anisotropic magnetoresistance and anomalous Hall effect, can be used also for sensing antiferromagnetism which opened the field of antiferromagnetic spintronics. The more than a century of controversial studies of these effects have shown their relativistic spin-orbit coupling and spin-polarisation symmetry breaking origin. However, a complete understanding of these effects and a fully predictive theory capable of identifying novel suitable antiferromagnetic materials are still lacking. Here, by extending modern symmetry and topology concepts in condensed matter physics, we have further developed the theory of anisotropic magnetoresistance and spontaneous Hall effect. Our approach is based on magnetic symmetry and topology analysis of antiferromagnetic energy bands, Bloch spectral functions, and Berry curvatures calculated from the state-of-the- art first-principle theory. This guided us to the prediction of two novel, previously unanticipated effects: relativistic metal-insulator transition from antiferromagnetic Dirac fermions, and crystal Hall...
|
|
|
Relativistic spintronic effects in semiconductor structures
Nádvorník, Lukáš ; Jungwirth, Tomáš (advisor) ; Ramsay, Andrew (referee) ; Veis, Martin (referee)
The spin transport and dynamics of optically injected spin polarized carri- ers are studied with a high spatial and/or time resolution in semiconductor GaAs-based heterostructures in multiple transport regimes. An unexpectedly long-scale and high-speed spin diffusion transport is observed in a long-lived electron sub-system induced optically at an undoped single GaAs/AlGaAs heterointerface. A diffusion and drift-dominated spin transport is investi- gated using an electrical spin-detection via the inverse spin Hall effect in doped GaAs-based systems at room and low temperatures. It is shown that the inverse spin Hall signal and the spin transport parameters can be con- trolled by a direct application of an electric field or by expanding a depleted zone of a planar pn-junction.
|
|
|
Electronic Structure and Magnetic Properties of Antiferromagnetic Semiconductors and Metals
Železný, Jakub ; Jungwirth, Tomáš (advisor) ; Carva, Karel (referee) ; Gomonay, Helen (referee)
Antiferromagnets are common in nature and just like ferromagnets posses a long-range magnetic order. They have found little practical application so far, be- cause the magnetic order in antiferromagnets is hard to detect and to manipulate by external magnetic fields. This has become less of a problem due to the development of spintronics, which has motivated a new interest in antiferromagnets. In this thesis we first theoretically study the electronic and magnetic structure of certain class of antiferromagnetic compounds, which are related to common semiconductors. In the second part we focus on electrical manipulation of antiferromagnets. We show that the so-called spin-orbit torque, which has been studied extensively in ferromagnets, can efficiently manipulate the antiferromagnetic order. We calculate the spin-orbit torque in several antiferromagnets and study the symmetry of the spin-orbit torque in detail. Powered by TCPDF (www.tcpdf.org)
|
|
|
Capability of international law to resolve an ethnic conflict: case of Bosnia and Herzegovina
Jungwirth, Tomáš ; Hofmannová, Mahulena (advisor) ; Bílková, Veronika (referee)
Title Capability of international law to resolve an ethnic conflict: case of Bosnia and Herzegovina Abstract The thesis deals with the complex issue of international law's capability to resolve an ethnic conflict, relying to a great extent on a case study of the Dayton system in Bosnia and Herzegovina. It aims to take an interdisciplinary approach, focusing not only on legal issues but also on sociological and other relevant aspects. The first chapters attempt to summarize peace proposals preceding Dayton and are followed by a legal analysis of the adopted documents and a subsequent thorough examination of the most significant and visible aspects of their implementation. The last chapter then reviews the topic from the standpoint of conflict resolution. Several key questions are formulated in the preface: Is international law able to deter the risk of yet another outbreak of armed conflict in Bosnia? Are its limits or flawed imposition the immediate cause of the present state? Has the international regime in Bosnia become completely dissasociated from the sociological substratum? Whilst seeking for answers, much attention is paid to the perception and reception of the Dayton system by various interest groups within Bosnia's society as well as to international community's ensuing engagement in the country....
|
|
| |
|
|
Magnetic anisotropies in (Ga,Mn)As and metallic multilayers with strong spin-orbit coupling
Zemen, Jan ; Jungwirth, Tomáš (advisor) ; Diviš, Martin (referee) ; Šob, Mojmír (referee)
The thesis presents a numerical study of magnetocrystalline anisotropies in dilute ferromagnetic semiconductors and transition metal systems intended to advance the current understanding of the microscopic origins of this relativistic effect and to contribute to the development of spintronic devices with new functionalities. The major part of the work surveys magnetocrystalline anisotropies in (Ga,Mn)As epilayers and compares the calculations to available experimental data. Our model is based on an envelope function description of the valence band holes and a spin representation for their kinetic-exchange interaction with localised electrons on Mn2+ ions, treated in the mean-field approximation. For epilayers with growth induced lattice-matching strains we study in-plane to out-of-plane easy axis reorientations as a function of Mn local-moment concentration, hole concentration, and temperature. Next we focus on the competition of in-plane cubic and uniaxial anisotropies. We add an in-plane shear strain to the effective Hamiltonian in order to capture measured data in bare, unpatterned epilayers, and we provide microscopic justification for this approach. The model is then extended by an in-plane uniaxial strain and used to directly describe experiments with magnetisation direction controlled by...
|
guest ::
