Structural and magnetic properties of transition metal Co doped and III (B, Al, Ga) element co-doped Zn12Se12 clusters: A theoretical investigation

Abstract

To explore stable magnetic semiconductor clusters, Zn₁₂Se₁₂ was selected as the host material, Co doped and III (B, Al, Ga) element co-doped Zn₁₂Se₁₂ clusters were investigated with first principle all-electron calculations. Geometry optimization, frequency calculations and dynamics simulations were performed to determine stable clusters. The analysis revealed that in Co doped Co₂Zn₁₀Se₁₂ clusters, two Co atoms preferentially substituted for adjacent Zn atoms in opposite vertices of a rhombus, resulting in the shortest Co-Co distance. The introduction of III (B, Al, Ga) elements generated the most stable Co₂IIIZn₉Se₁₂ cluster, where two Co atoms replaced adjacent Zn atom sites, and III atoms replaced the Zn atom site nearest to the Se atom between the two Co atoms. Energy differences between ferromagnetic and antiferromagnetic states indicated that the Co₂Zn₁₀Se₁₂ clusters exhibited an antiferromagnetic coupling state, whereas the Co₂IIIZn₉Se₁₂ clusters exhibited ferromagnetic coupling states. A detailed analysis of electron density and electronic configurations for Co element was conducted to uncover the magnetic coupling mechanism. It was found that the introduction of III elements as donor doping decreased the Co-Se hybridization, which reduced the antiferromagnetic superexchange coupling while forming the Se-Co-Se-III bonds with an excess electron, thereby enhancing the Co-Co ferromagnetic double-exchange coupling. The strategy of III element co-doping facilitated ferromagnetic double-exchange coupling between Co atoms, providing valuable insights for the exploration of new dilute magnetic semiconductor materials.