Curie Temperature of Sm2Fe17 and Nd2Fe14B: 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.