Forskningsseminarier i fysik

Next seminars:

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Friday, 4.April 2025, 13:00-14:00, room 21D302

Title: Atomistic spin dynamics and beyond 

Speaker: Danny Thonig, School of Science and Technology, Örebro University; Department of Physics and Astronomy, Uppsala University; LINXS Fellow in “Quantum Materials”, LINXS; WISE group of excellence, Örebro University 

Abstract: 

The majority of the world’s information is stored in magnetic media, making research on writing and retrieving data in magnetic materials increasingly important. Advancements in this field focus on achieving higher speeds, greater data transmission rates, and lower energy consumption, offering significant technological benefits. Over the years, sophisticated computational tools have been developed to characterize magnetic material properties and analyze magnetization dynamics from first principles. While density functional theory (DFT) can be used to calculate magnetization and atomistic exchange interactions, magnetization dynamics are often modeled using the Landau-Lifshitz-Gilbert (LLG) equation with parametrized energy models. However, recent studies [1] have highlighted serious limitations of these approaches, particularly at finite temperatures, ultrafast timescales, and in systems with strong coupling to other degrees of freedom, such as crystal lattice displacements. 

In my talk, I will introduce a spin-energy-parametrization-free approach to magnetization dynamics based on a self-consistent, fully relativistic Slater-Koster tight-binding (TB) method, implemented in the Cahmd software [2]. By employing a constraint formalism and comparing magnetization dynamics from both semi-classical and tight-binding formulations, I have identified cases where the semi-classical description breaks down. Additionally, an analysis of spin-spin exchange coupling and energy dissipation has revealed significant discrepancies from commonly used parametrized scalar models, such as the Heisenberg model and the Gilbert damping method. 

Furthermore, this TB formulation has been extended to incorporate lattice degrees of freedom, unveiling remarkable spin-lattice interaction effects—phenomena that are entirely absent in the semi-classical framework [3]. 

[1] J Mag. Mag. Mat. 324, 610 (2012), Phys. Rev. Lett. 111, 127204 (2013), Phys. Rev. B 105, 026401 (2022), Phys. Rev. B 103, L140408 (2021), etc. 

[2] Cahmd - Classical atomistic hybrid multi-degree dynamics https:// cahmd.gitlab.io/cahmdweb/ 

[3] Phys. Rev. B 99, 104302 (2019) 

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