Ferromagnetic effects on non-Arrhenius diffusion of single interstitial helium solute in BCC Fe

Helium diffusion in metals is one of the key atomic processes for bubble nucleation. Ferromagnetic effects play important roles on microstructural evolution in BCC iron. The spin-lattice dynamics simulations are performed to study the ferromagnetic effects on the non-Arrhenius diffusion behavior of single interstitial helium solute in BCC iron. It is found that the ferromagnetic effects significantly reduce the helium diffusivity at low temperatures, but give rise to a statistically negligible influence at high-temperatures. In addition, we propose a coarse-grained formula to describe the non-Arrhenius behavior, and three diffusion modes are well-defined depending on the competition between thermal energy of helium gained from the host atoms’ collisions and its migratory barrier, for instant, helium diffusion reveals Arrhenius- and Einstein-diffusion modes in the low- and high-temperature limits, respectively. Further, the effects of quantum statistics of both phonons and magnons in BCC Fe are also discussed, which is found to give rise to the non-linear temperature dependent thermal energy thus the strong non-Arrhenius behavior in the region of Arrhenius-diffusion mode. The above-mentioned non-Arrhenius diffusion feature of helium in BCC Fe is consistent with the cases of helium diffusion in BCC W [Wen et al., J. Nucl. Mater. 493 (2017) 21; Woo et al., Phys. Rev. E 96 (2017) 032133], and the diffusion parameters are in agreement with the experimental measurement and other calculations results. The current work could help to get a complete understanding of ferromagnetic effects on irradiation damage accumulation in structural materials of fusion reactors.