Correlations, disorder, and multimagnon processes in terahertz spin dynamics of magnetic nanostructures: A first-principles investigation

Understanding the impact of electronic correlations and disorder is essential for an accurate description of solids. Here, we study the role of correlations, disorder, and multimagnon processes in THz spin dynamics. We reveal that a significant part of the electron self-energy, which goes beyond the adiabatic local spin density approximation, arises from the interaction between electrons and a virtual magnon gas. This interaction leads to a substantial modification of the exchange splitting and a renormalization of magnon energies, in agreement with the experimental data. Finally, we establish a quantitative hierarchy of magnon relaxation processes based on first principles.