Magnetic exchange interactions in Mn doped ZnSnAs2 chalcopyrite

Accurate ab initio full-potential augmented plane wave (FP-LAPW) electronic calculations within generalized gradient approximation have been performed for Mn doped ZnSnAs2 chalcopyrites, focusing on their electronic and magnetic properties as a function of the geometry related to low Mn-impurity concentration and the spin magnetic alignment (i.e., ferromagnetic vs antiferromagnetic). As expected, Mn is found to be a source of holes and localized magnetic moments of about 4 mB per Mn atom are calculated which are sufficiently large. The defect calculations are firstly performed by replacing a single cation (namely Zn and Sn) with a single Mn atom in the pure chalcopyrite ZnSnAs2 supercell, and their corresponding formation energies show that the substitution of a Sn atom (rather than Zn) by Mn is strongly favored. Thereafter, a comparison of total energy differences between ferromagnetic (FM) and antiferromagnetic (AFM) are given. Surprisingly, the exchange interaction between a Mn pairs is found to oscillate with the distance between them. Consequently, the AFM alignment is energetically favored in Mn-doped ZnSnAs2 compounds, except for low impurity concentration associated with lower distances between neighboring Mn impurities, in this case the stabilization of FM increases. Moreover, the ferromagnetic alignment in the Mn-doped ZnSnAs2 systems behaves half-metallic; the valence band for majority spin orientation is partially filled while there is a gap in the density of states for the minority spin orientation. This semiconducting gap of 1 eV opened up in the minority channel and is due to the large bonding–antibonding splitting from the p–d hybridization. Our findings suggest that the Mn-doped ZnSnAs2 chalcopyrites could be a different class of ferromagnetic semiconductors.