Seminar über die Physik der kondensierten Materie (SFB/TRR173 Spin+X und SFB/TR288 Kolloquium, TopDyn-Seminar)

Jan. 24, 2019 at 2 p.m. in MEDIEN-Raum, Staudinger Weg 7, 03-431Univ-Prof. Dr. Jure Demsar

Univ.-Prof. Dr. Hans-Joachim Elmers

Univ.-Prof. Dr. Mathias Kläui

Univ.-Prof. Dr. Thomas Palberg

Joseph Barker (University of Leeds)

Atomistic spin dynamics is a formalism based on the classical Heisenberg model which is often used to study the dynamics and thermodynamics of spin models. An often-touted advantage is the inclusion of temperature by thermostating the spin system with a Langevin equation. However, this has generally been applied in the classical limit—using the classical fluctuation dissipation theorem. We will argue that this is almost never the correct limit for magnets below their ordering temperature and instead the quantum fluctuation dissipation theorem should be used. Applying such a thermostat we should that thermodynamics can now be calculated which agree with analytic results such as Bloch’s law. We also show complex spin models such as yttrium iron garnet and display quantitative agreement with experimental measurements.