Coupled spin dynamics and ab initio molecular dynamics approach for paramagnetic materials

Magnetic semiconductors like YMnO₃[1] and CrN [2] show an anomalous temperature dependence of the thermal conductivity in their paramagnetic phase: A strong suppression is observed right above the magnetic transition, followed by an almost constant conductivity at higher temperatures.

At high temperature lattice vibrations and spin fluctuations occur simultaneously. As local effective moments still exist above the magnetic transition temperature, they interact with each other and with the lattice vibrations.

By treating both lattice vibrations and spin fluctuations in a combined atomistic spin dynamics (ASD) – ab initio molecular dynamics (AIMD) approach, we are able to ascribe this experimentally observed effect to a mutual and dynamic spin-lattice coupling [3]. This coupling shows a strong influence on the phonon life times right above the magnetic transition.

[1] Sharma et al., Phys. Rev. Lett. 93, 177202 (2004).
[2] Jankovský et al., J. Eur. Ceram. Soc. 34, 4131 (2014).
[3] Stockem et al., Phys. Rev. Lett. 121, 125902 (2018).