Magnetic Order, Electrical Doping, and Charge-State Coupling at Amphoteric Defect Sites in Mn-Doped 2D Semiconductors

Two-dimensional (2D) dilute magnetic semiconductors (DMSs) are attractive material platforms for applications in multifunctional nanospintronics due to the prospect of embedding controllable magnetic order within nanoscale semiconductors. Identifying candidate host material and dopant systems requires consideration of doping formation energies, magnetic ordering, and the tendency for dopants to form clustered domains. In this work, we consider the defect thermodynamics and the dilute magnetic properties across charge states of 2D-MoS₂ and 2D-WS₂ with Mn magnetic dopants as candidate systems for 2D-DMSs. Using hybrid density functional calculations, we study the magnetic and electronic properties of these systems across configurations with thermodynamically favorable defects: 2D-MoS₂ doped with Mn atoms at sulfur site (Mn_S), at two Mo sites (2Mn_Mo), on top of a Mo atom (Mn-top), and at a Mo site (Mn_Mo). While the majority of the Mn-defect complexes provide trap states, Mn_Mo and Mn_W are amphoteric, although previously predicted to be donor defects. The impact of cluster formation of these amphoteric defects on magnetic ordering is also considered; both Mn_Mo-Mn_Mo (2Mn_2Mo) and Mn_W-Mn_W (2Mn_2W) clusters are found to be stable in ferromagnetic (FM) ordering. Interestingly, we observed the defect charge state dependent magnetic behavior of 2Mn_2Mo and 2Mn_2W clusters in 2D-TMDs. We investigate that the FM coupling of 2Mn_2Mo and 2Mn_2W clusters is stable in only a neutral charge state; however, the antiferromagnetic (AFM) coupling is stable in the +1 charge state. 2Mn_2Mo clusters provide shallow donor levels in AFM coupling and deep donor levels in FM coupling. 2Mn_2W clusters lead to trap states in the FM and AFM coupling. We demonstrate the AFM to FM phase transition at a critical electron density n^c_e = 3.5 × 10¹³ cm^-2 in 2D-MoS₂ and 2D-WS₂. At a 1.85% concentration of Mn, we calculate the Curie temperature of 580 K in the mean-field approximation.