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Topological insulators and magnetic order
Šebesta, Jakub ; Carva, Karel (advisor) ; Hamrle, Jaroslav (referee) ; Železný, Jakub (referee)
The occurrence of various defects can strongly influence the physical properties of real materials. Depending on their type, new outstanding features can arise, but also charac- teristic behavior might be lost. This thesis is dedicated to the impact of diverse disorder's presence on the physical behavior of three-dimensional topological insulators, namely, the well-known Bi2Se3 compound. Despite possessing a band gap in the bulk, these materials host unique metallic surface states protected by the time-reversal symmetry. Thus, the surface states are robust against perturbation, which respects the protecting symmetry. Breaking the symmetry, e.g. by the magnetic field, can open the surface gaps. In this work, the influence of the magnetic as well as native chemical defects, occurring in the real samples, on the electronic structure is described. Notably, the dispersion of the sur- face metallic states is followed up. Since the surface gap can be opened by the magnetic field, magnetic exchange interactions and related Curie temperatures of magnetic defects are thoroughly studied. Particularly, the influence of disorder on the character of the exchange interactions and related Curie temperatures is described. Dealing with layered systems, the behavior of planar defects might be inspected. Therefore, the...
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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)
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Study of the effect of spin-orbit interaction in solids
Mrozek, Jan ; Carva, Karel (advisor) ; Šipr, Ondřej (referee)
One of the effects the spin orbit interaction leads to is the Anomalous Hall effect. In this thesis we describe the origins of the Anomalous Hall effect and its con- tribution to understanding the solid state physics. We introduce the formalism of linear response theory and other approximations needed to perform calcula- tions of the Anomalous Hall conductivity. We present two different models of the anomalous Hall conductivity - one based on the Kubo formalism and the other based on chemical potential difference. We then compare the models in a simple setting based on Strontium ruthenate. We show that in the case of Strontium ruthenate the models have very similar predictions. 1
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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)
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