Exchange Interaction in Gd $_4$ Bi $_3$ and Gd From First-Principles Calculations

Electronic structure and exchange interaction have been calculated for the Gd₄Bi₃ magnetocaloric compound and Gd metal by a local-spin-density- approximation + Hubbard U (LSDA+U) method. In Gd₄Bi₃ and Gd, the 4f states have little direct contribution to the ferromagnetic coupling. The higher Curie temperature is ascribed to the strong interaction between the Gd 5d and the Bi 6p electrons in the Gd₄Bi₃ compound. The estimated Curie temperatures from the calculated effective exchange coupling constants based on mean-field approximation are 337 K and 403 K for Gd metal and Gd₄Bi₃, respectively. These calculated values are comparable with the experimental values of Gd (T _C = 294 K) and Gd₄Bi₃ compound (T _C = 332 K).