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MM: Fachverband Metall- und Materialphysik

MM 25: Transport (Diffusion, conductivity, heat)

MM 25.7: Vortrag

Mittwoch, 3. April 2019, 12:00–12:15, H46

Impact of paramagnetic excitations and relaxations on diffusion in Fe-Mn alloys — •Omkar Hegde, Osamu Waseda, Tilmann Hickel, Christoph Freysoldt, and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung, Düsseldorf, Germany

Understanding the impact of paramagnetism on defect kinetics is, though conceptually and computationally challenging, important for designing Fe-based alloys. Since magnetic degrees of freedom change faster than atomic degrees of freedom in the paramagnetic state, the atoms move according to an averaged force instead of instantaneous forces attained from each spin configuration. Therefore, a new computationally efficient method based on spin-space averaging (SSA) has been developed to handle magnetic disorder next to defects. The method uses the spin constraint tool developed and implemented in the DFT code S/PHI/nX. The performance of the method is demonstrated for local atomic relaxations next to point defects. For α-Fe, we show that both magnetic disorder and local relaxations significantly affect vacancy formation and migration energies. Next, we focus on the FeMn system, for which the vacancy formation energy as a function of Mn concentration for both ferromagnetic and paramagnetic cases is presented. We demonstrate that paramagnetism significantly affects atomic relaxations as well as diffusion barriers and thereby explain why Mn diffusion shows a different temperature dependence than Fe-self diffusion in α-Fe.