Tunable electrical properties and multiple-phases of ferromagnetic GdS₂, GdSe₂ and Janus GdSSe monolayers

With the continuous miniaturization and integration of spintronic devices, the two-dimensional (2D) ferromagnet coupling of ferromagnetic and diverse electrical properties has become increasingly important. Herein, we report three ferromagnetic monolayers: GdS₂, GdSe₂ and Janus GdSSe. They are bipolar magnetic semiconductors and demonstrate ferroelasticity with a large reversible strain of 73.2%. Three monolayers all hold large magnetic moments of about 8μ_B f.u.^-1 and large spin-flip energy gaps in both the conduction and valence bands, which are highly desirable for applications in bipolar field effect spin filters and spin valves. Our calculations have testified to the feasibility of the experimental achievement of the three monolayers and their stability. Additionally, intrinsic valley polarization occurs in the three monolayers owing to the cooperative interplay between spin-orbit coupling and magnetic exchange interaction. Moreover, we identified square lattices for GdS₂ and GdSe₂ monolayers. The new and stable square lattices of GdS₂ and GdSe₂ monolayers show robust ferromagnetism with high Curie temperatures of 648 and 312 K, respectively, and the characteristics of spin-gapless semiconductors. Overall, these findings render GdS₂, GdSe₂ and Janus GdSSe monolayers promising candidate materials for multifunctional spintronic devices at the nanoscale.