First-principles investigation on the electronic and magnetic properties of cubic Be0.75Mn0.25X (X=S, Se, Te)

Abstract

The structural, electronic and magnetic parameters of Be0.75Mn0.25X (X = S, Se, Te) are investigated using first-principles calculations. The thermodynamic stability of these Mn-doped semiconductors can be confirmed by the negative energetic quantities of formation energy and cohesive energy, and the stability decrease from Be0.75Mn0.25S to Be0.75Mn0.25Te with the magnitude of energetic quantities decrease as the same order. Calculated from the band structures, Be0.75Mn0.25X have smaller band gaps (1.49 eV, 1.36 eV, 0.78 eV for X = S, Se, Te, respectively) than BeX. The density of states and valence electron distribution plots indicate that the atomic bonding of Be0.75Mn0.25X is mainly contributed from the interactions between Mn-d and X-p. And the electronic interaction weakens from Be0.75Mn0.25S to Be0.75Mn0.25Te. The local magnetic moment of Mn, the exchange splitting energies, and exchange constants can be obtained from the spin-polarized electronic structures and density of states plots, the splitting energy Δx(d) is positive while Δx(pd) is negative, the exchange constants N0α and N0β are negative. And all of them increase along with X atom radius increasing, which implies the effective potential for down-spin is more attractive than that for up-spin, and it decreases along with the X atom changing from S to Te. N0α and N0β suggest that the interactions of Be(2s)–Mn(3d) states and X(p)–Mn(3d) states are all attractive, and the interactions of s–d and p–d weakens with the same sequence.