Magnetization dynamics in ferromagnetic, antiferromagnetic and superconducting systems
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- Institutt for fysikk 
The electron spin is an intrinsic property of the electron, just as its charge. Its spin is binary of nature, and is therefore well suited for encoding 0’s and 1’s in computers. The technology aiming to utilize the electron spin for conveying and storing information – spintronics – is in rapid development. Some spintronics components are already widely commercially available, some are approaching commercialization, while some are still in the idea phase. The hope is that spintronics based computer components can trigger a revolution in computer processing in the not-too-distant future, both in terms of energy efficiency and processing speed. There are several potential routes to making working spintronics components. Just to mention a few potential functionalities, the components may for instance store information in magnetic domains, read and write this magnetically encoded information, transport information as spin currents in magnets, metals or superconductors, or convert spin currents to voltages and vice versa. In the process of developing such components, it is of vital importance to understand how these mechanisms work, and how they are affected by material properties and interactions with the surroundings. A solid theoretical foundation facilitates for a more efficient screening for material candidates for use in spintronics applications, as well as it enables the discovery of new and potentially useful phenomena. This thesis represents a small step towards a better understanding of magnetization dynamics and interactions in ferromagnetic, antiferromagnetic and superconducting systems. The spine of the thesis is made up by the enclosed research papers, each of which aims to give answers to how magnetization dynamics in ferromagnets and antiferromagnets is affected by interactions with internal or external systems, or how the magnetization dynamics affects the surroundings. Three papers consider internal interactions between the magnetic subsystem and phonons or itinerant electrons. These interactions affect the magnetic modes, either by giving them finite lifetimes, or by mixing properties with the other excitations. Three papers consider spin pumping from ferromagnets or antiferromagnets, and spin-orbit torques in ferromagnets. Here, we show how magnetization dynamics can give rise to spin currents in different systems. The last two papers consider magnetic materials placed in cavities, either focusing on the interaction with a nearby superconductor, or on hybridization between magnon and cavity photon modes. The main body of this thesis aims to bind the research papers together, and give an introduction to the most important topics encountered in the research papers.