= Y, Ce, Nd, Sm, and Dy) compounds: Entropy-induced phase stabilization at finite temperature*

Up to now, phase stability problems of permanent magnets are still not yet entirely eliminated. Motivated by this, we report the dynamical and thermodynamic stability of the binary R_1−xFe_x (0< x <1) compounds (R= Y, Ce, Nd, Sm, and Dy) at finite temperature predicted by first-principles calculation based on density functional theory (DFT). We first demonstrate that thermodynamic stability problems cannot be elucidated when using the static DFT energy at T = 0 K. By considering the entropy contribution, including electronic and vibrational free energies, we obtained convex hull plots at finite temperatures, which successfully explain the phase stability of known compounds. Our results show a trend of stabilizing many R_1−xFe_x compounds studied here with increasing temperature. This entropy-induced stabilization mainly comes from the vibrational free energy, which decreases dramatically with temperature. We will discuss the origin of the stabilization and its rare-earth dependence.