Singh Akash, Price Christopher C, Shenoy Vivek B
Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
ACS Nano. 2022 Jun 28;16(6):9452-9460. doi: 10.1021/acsnano.2c02387. Epub 2022 May 26.
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-MoS and 2D-WS 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-MoS doped with Mn atoms at sulfur site (Mn), at two Mo sites (2Mn), on top of a Mo atom (Mn-top), and at a Mo site (Mn). While the majority of the Mn-defect complexes provide trap states, Mn and Mn 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-Mn (2Mn) and Mn-Mn (2Mn) clusters are found to be stable in ferromagnetic (FM) ordering. Interestingly, we observed the defect charge state dependent magnetic behavior of 2Mn and 2Mn clusters in 2D-TMDs. We investigate that the FM coupling of 2Mn and 2Mn clusters is stable in only a neutral charge state; however, the antiferromagnetic (AFM) coupling is stable in the +1 charge state. 2Mn clusters provide shallow donor levels in AFM coupling and deep donor levels in FM coupling. 2Mn clusters lead to trap states in the FM and AFM coupling. We demonstrate the AFM to FM phase transition at a critical electron density = 3.5 × 10 cm in 2D-MoS and 2D-WS. At a 1.85% concentration of Mn, we calculate the Curie temperature of 580 K in the mean-field approximation.
二维（2D）稀磁半导体（DMS）由于有望在纳米级半导体中嵌入可控磁序，是多功能纳米自旋电子学应用中极具吸引力的材料平台。确定候选主体材料和掺杂剂系统需要考虑掺杂形成能、磁序以及掺杂剂形成聚集畴的趋势。在这项工作中，我们将具有Mn磁掺杂剂的二维-MoS和二维-WS的缺陷热力学和稀磁性质作为二维-DMS的候选系统，研究其不同电荷态的情况。使用杂化密度泛函计算，我们研究了这些系统在具有热力学有利缺陷的构型下的磁学和电学性质：在硫位点掺杂Mn原子的二维-MoS（Mn）、在两个Mo位点掺杂的（2Mn）、在Mo原子顶部的（Mn-top）以及在一个Mo位点的（Mn）。虽然大多数Mn缺陷复合物提供陷阱态，但Mn和Mn是两性的，尽管之前预测为施主缺陷。还考虑了这些两性缺陷的团簇形成对磁序的影响；发现Mn-Mn（2Mn）和Mn-Mn（2Mn）团簇在铁磁（FM）序中都是稳定的。有趣的是，我们观察到二维过渡金属二卤化物中2Mn和2Mn团簇的缺陷电荷态依赖磁行为。我们研究发现，2Mn和2Mn团簇的FM耦合仅在中性电荷态下稳定；然而，反铁磁（AFM）耦合在+1电荷态下稳定。2Mn团簇在AFM耦合中提供浅施主能级，在FM耦合中提供深施主能级。2Mn团簇在FM和AFM耦合中导致陷阱态。我们证明了二维-MoS和二维-WS在临界电子密度 = 3.5 × 10 cm时从AFM到FM的相变。在Mn浓度为1.85%时，我们在平均场近似下计算出居里温度为580 K。
