Berlin 2018 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 7: Focus Session: Magnetism in Materials Science: Thermodynamics, Kinetics and Defects I (joint session MM/MA)
MA 7.3: Vortrag
Montag, 12. März 2018, 11:00–11:15, TC 010
Modeling the high-temperature paramagnetic state of magnetic materials from first-principles - coupling of lattice vibrations and disordered magnetism — •Björn Alling1,2 and Irina Stockem1,2 — 1Linköping University, Sweden — 2Max-Planck-Institut für Eisenforschung, Düsseldorf, Germany
The paramagnetic state of magnetic materials lack global magnetization and long range order between moments. However, in most cases there still exist important local magnetic moments. Also, lattice vibrations are important for properties and stability of materials at high temperature. Simultaneous presence of disorder of magnetic and vibrational nature poses a severe challenge for first-principles theory.
I present our recently developed method combining atomistic spin dynamics with ab-initio molecular dynamics (ASD-AIMD) treating the magnetic and vibrational degrees of freedom on an equal, first-principles based footing. It allows us to explicitly study the coupled dynamics of magnetism and lattice in the paramagnetic state.
We use it to study paramagnetic CrN. Phonon life times are obtained from the AIMD part of the simulations. At 300 K, we see dramatically lower phonon lifetimes as compared to an adiabatic, fast-magnetism, approximation. Further, the phonon lifetime does not decrease in the normal manner with increasing temperature which could explain anomalys thermal conductivity observed experimentally for many materials in the paramagnetic state. These results underline the importance of allowing for a dynamical coupling between magnetism and lattice vibrations in theoretical studies of the paramagnetic state.