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Opponent: Associate professor Richard Evans, University of York
Supervisor: Professor Anna Delin, Fysik, Tillämpad fysik; Associate professor Danny Thonig, Örebro University; Associate professor Anders Bergman, Uppsala University
Magnetic materials are fundamental to various information technological applications, from data storage devices to energy-efficient computing. As the demand for high-speed, efficient technologies grows, understanding the mechanisms of energy dissipation within these materials becomes increasingly important. This thesis explores the underlying mechanisms of energy dissipation in magnetic materials through multi-scale simulations, with a particular focus on the spin and lattice subsystems.
A primary objective of this thesis is to challenge and broaden the conventional understanding of energy dissipation in magnetic materials. Traditionally, damping in spin systems has been treated as a simple scalar quantity; however, recent developments suggest a more intricate, non-local behavior correlated with neighboring environments. Despite these advancements, experimental verification of damping non-locality remains elusive, as its influence on experimental observable is not yet fully explored. To address this gap, the thesis investigates the effects of non-local spin damping on the lifetimes and dynamics of magnetic excitations, using common metals such as Fe, Co, Ni, and Fe-Co alloys as model systems.
In further examining alloy systems, it becomes clear that traditional alloy theories often overlook the influence of short-range interactions, resulting in inaccuracies in predicting the dissipative properties of magnetic materials. To bridge this gap, the thesis applies this non-local spin damping model to explore how variations in local atomic environments and alloy compositions, particularly in Fe-Co systems, affect energy dissipation. The results demonstrate that even subtle changes in atomic arrangement and composition can significantly influence spin damping, underscoring the crucial importance of fine-tuning energy dissipation in spin systems at the atomic scale.
Expanding the scope beyond spin system, the thesis also investigates energy dissipation within the lattice subsystem. The interaction between electron and lattice reveals a parallel complexity in lattice damping, mirroring the non-local behavior observed in spin systems.
Collectively, these findings provide a comprehensive understanding of how both spin and lattice dynamics contribute to energy dissipation processes in magnetic materials. The insights obtained from this thesis not only offer theoretical clarity but also carry practical implications for the design of next-generation spintronic devices, where manipulating energy loss is essential for enhancing both speed and efficiency. By addressing these challenges, this thesis contributes to the development of more advanced materials and technologies that meet the increasing demands of modern computing and data storage.