Curie temperature of Sm${}_2$Fe${}_{17}$ and Nd${}_2$Fe${}_{14}$B: a first-principles study

We calculate intersite magnetic couplings for Sm${}_2$Fe${}_{17}$, Nd${}_2$Fe${}_{14}$ and Nd${}_2$Fe${}_{14}$X (X = B, C, N, O, F) using Liechtenstein’s formula on the basis of first-principles calculation, and analyze them to investigate the Curie temperature of Sm${}_2$Fe${}_{17}$ and Nd${}_2$Fe${}_{14}$B. We find that the magnetic coupling in the dumbbell bond is strongly ferromagnetic in our calculation, which is against a previous conjecture explaining the low Curie temperature for Sm${}_2$Fe${}_{17}$. The calculated values of the couplings explain the experimentally observed difference in the Curie temperature of Sm${}_2$Fe${}_{17}$ and Nd${}_2$Fe${}_{14}$B. We also address boron’s effects on the Curie temperature of Nd${}_2$Fe${}_{14}$B, especially in connection with Kanamori’s theory of cobaltization.