This title appears in the Scientific Report : 2020 

First-principles study of collective spin excitations in noncollinear magnets
Dos Santos, Flaviano José (Corresponding author)
Quanten-Theorie der Materialien; PGI-1
Quanten-Theorie der Materialien; IAS-1
Jülich Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag 2020
Dissertation, RWTH Aachen University, 2019
Dissertation / PhD Thesis
Controlling Spin-Based Phenomena
Schriften des Forschungszentrums Jülich Reihe Schlüsseltechnologien / Key Technologies 212
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The pace of the current data revolution depends on the world's technological capabilityto store and process information. A great share of that is done by manipulatingmagnetic materials with astonishing speed and precision, which involves several dynamicalprocesses. Among the latter are the collective spin excitations known asspin waves. Just like the strings of a guitar, spin waves are the natural \tunes" ofa material's magnetization, and knowing their properties allows to predict, designand control technological devices.In this thesis, we study the properties of spin waves in complex magnets focusingon systems of low-dimensionality. The manifestation of spin waves in collinearmagnets, such as ferromagnets, has been extensively investigated. However, spinwaves in noncollinear magnets are not fully understood yet. For instance, no experimentaldata is available concerning large-wavevector spin waves in thin lmsand surfaces. Nevertheless, novel noncollinear spin textures, such as the topologicallynontrivial skyrmions, are at the heart of many recent proposals of informationnanotechnologies for the future.Therefore, we develop in this thesis an atomistic description of the spin wavesin noncollinear magnets applicable to real materials. We achieve that by combiningthe density functional theory, as implemented within the Korringa-Kohn-Rostokermethod, with the spin-wave adiabatic approximation. Eectively, we parametrizefrom rst-principles a generalized quantum Heisenberg Hamiltonian accounting forrelativistic eects of the spin-orbit coupling. Thus, besides calculating the magneticexchange interaction, we also have access to the Dzyaloshinskii-Moriya interaction(DMI) and the magnetocrystalline anisotropy. To further relate our results with experimentalworks, we calculate the inelastic-electron-scattering spectrum using timedependentperturbation theory. This led us to propose spin-resolved electron-energylossspectroscopy (SREELS) as an experimental tool to probe large-wavevector spinwaves in noncollinear magnets. [...]