The main phase of Nd-Fe-B permanent magnets is known as Nd_2Fe_(14)B, which was created from the idea of expanding the distance between Fe atoms in Nd_2Fe_(17) to improve its magnetic properties by adding B. We systematically investigated the role of not only B but also C, N, O, and F as candidates for improving the magnetic properties of the main phase of Nd-Fe-B permanent magnets through first-principles calculations. As predicted in previous theoretical studies, the magnetic moments of some Fe sites are improved by adding B. However, the total magnetic moment and magnetization of Nd_2Fe_(14)B and the magnetic anisotropy energy of Nd are decreased rather than increased by adding B. The formation energies of Nd_2Fe_(14)B and Nd_2Fe_(14)C are negative compared with those of Nd_2Fe_(17)B and Nd_2Fe_(17)C, respectively, indicating that the role of B is to stabilize the structure itself-this is consistent with experimental results.
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