Structural stability, band structure and magnetic properties of ZnS and Zn_0.75Cr_0.25S under pressure

Due to the significant luminescent properties of ZnS and the half metallic features of Cr doped ZnS (Zn_0.75Cr_0.25S), many researches have been done to make possible the use of these materials in optical and spintronic devices. The environmental conditions, such as, high pressure and high temperature, are crucial for the device service, however, it is difficult to exploit this issue from the experimental aspect. Therefore, spin-polarized first-principle calculations were performed to study the structural stability, band structure and magnetic properties of zincblende ZnS and Zn _0.75Cr_0.25S under pressure. It is shown that ZnS can exist stably under pressure up to 10 GPa, while Zn_0.75Cr_0.25S becomes unstable under a pressure of 5GPa or so. The bulk modulus (B _H), Poisson ratio (v) and anisotropic parameter (A) of ZnS and Zn_0.75Cr_0.25S increase with pressure, but the shear modulus (G_H) decreases. B_H and G_H of Zn _0.75Cr_0.25S are smaller than those of ZnS, while v and A of Zn_0.75Cr_0.25S are larger than those of ZnS. Both ZnS and Zn_0.75Cr_0.25S behave in a ductile manner, while Zn_0.75Cr_0.25S is more anisotropic and is easier to induce deformation than ZnS. As for ZnS, the direct band structure is kept but the band gap increases gradually with the pressure. As for Zn_0.75Cr _0.25S, the half metallic features are maintained up to a pressure of 10 GPa, but both the band gap for minority spin and the half metallic band gap have the largest values under 6 Pa. The spin exchange splitting energy Δ_x(d) and Δ_x(pd) decrease with the increase of pressure. The negative values of Δ_x(pd) under pressure imply that the effective potential (E_ep) of the minority spin is more attractive than that of majority spin.