Role of typical elements in Nd2Fe14X (X = B, C, N, O, F)

The magnetic properties and structural stability of Nd2Fe14X (X = B, C, N, O, F) aretheoretically studied by first-principles calculations focusing on the role of X.We find that Breduces the magnetic moment (per formula unit) and magnetization (per volume) in Nd2Fe14B.The crystal-field parameter A02 r2 of Nd is not enhanced either, suggesting that B has minorroles in the uniaxial magnetocrystalline anisotropy of Nd. These findings are in contrast to thelong-held belief that B works positively for the magnetic properties of Nd2Fe14B. As Xchanges from B to C, N, O, and F, both the magnetic properties and stability vary significantly.The formation energies of Nd2Fe14X and α-Fe relative to that of Nd2Fe17X are negative forX = B and C, whereas they are positive when X = N, O, and F. This indicates that B plays animportant role in stabilizing the Nd2Fe14B phase.

 We thank Dr. S. Hirosawa, Dr. T. Nakamura, and Dr. T. Fukazawa for his fruitful and stimulating discussion. This work was supported by the Elements Strategy Initiative Project under the auspices of MEXT, by the “Materials research by Information Integration” Initiative ( ${\mathrm{MI}}^{2}I$ ) project of the Support Program for Starting Up Innovation Hub from Japan Science and Technology Agency (JST), and also by MEXT as a social and scientific priority issue [Creation of new functional Devices and high-performance Materials to Support next-generation Industries (CDMSI)] to be tackled by using post-K computer, as well as JSPS KAKENHI Grant No. 17K04978. The calculations were partly carried out by using supercomputers at ISSP, The University of Tokyo, and TSUBAME, Tokyo Institute of Technology, the supercomputer of ACCMS, Kyoto University, and also by the K computer, RIKEN (Projects No. hp160227, No. hp170100, and No. hp170269).