First-principle Study on Half-metallic Ferromagnetism and Structural Stability Of C-doped Alkaline-earth Chalcogenides under Pressure

摘要

Three half-metallic ferromagnets with NaCl structure, X_4CS_3 (X = Mg, Ca and Sr) are investigated by the first principle calculations based on the density functional theory in thegeneralized gradient approximation. Non-spin and spin polarized calculations are done to obtain the lattice constants, the equilibrium cell volumes, the stable energies and the magnetic moments of X_4CS_3, and band structure and density of states for X_4CS_3 at high pressure are calculated. From the calculations it has been found that X_4CS_3 is stable in the FM state. The corresponding lattice constants and the equilibrium cell volumes in FM are greater than that in NM. The magnetic moment of X_4CS_3 decrease as pressure increases, and a second order magnetic phase transition of Sr_4CS_3 from FM to NM state at pressure of 140GPa, but a second order magnetic phase transitions of Mg_4CS_3 and Ca_4CS_3 have not been found. According to the band and the density of states, as the pressure increases the half-metallic nature of X_4CS_3 destroyed.