Mn segregation at Fe grain boundaries is known to be a precursor for a variety of phenomena such as embrittlement, spinodal decomposition, and phase transformation. Therefore, various heat treatments are performed in experiments to control Mn decoration at grain boundaries for ‘segregation engineering’ [1], which could alter the local magnetic state. In this direction, a thorough understanding of the connection between the local magnetic state and segregation remains elusive. In the present work, we tackle this issue by studying segregation in both the ferromagnetic state (low-temperature) and paramagnetic state (high-temperature) using ab initio-based approaches [2]. We demonstrate that the Mn diffusion [3] and segregation profile is mainly modulated by local magnetic interactions, providing new opportunities for grain boundary segregation engineering. Finally, we show that grain boundary formation and Mn segregation can, in turn, tune the local magnetic transition temperature, thereby revealing an impressive coupling of magnetism, chemistry, and structure.

[1] A. Kwiatkowski da Silva, D. Ponge, Z. Peng, G. INden, Y. Lu, A. Breen, B. Gault, D. Raabe, Nature comm. 9, 1137 (2018).
[2] O. Hegde, M. Grabowski, X. Zhang, O. Waseda, T. Hickel, C. Freysoldt, J. Neugebauer, Phys. Rev. B 102, 144101 (2020).
[3] O. Hegde, V. Kulitchikii, A. Schneider, F. Soisson, T. Hickel, J. Neugebauer, G. Wilde, S. Divinski, C.-C. Fu, Phys. Rev. B 104, 184107 (2021).