Large-scale fabrication and Mo vacancy-induced robust room-temperature ferromagnetism of MoSe 2 thin films.

Molybdenum selenide (MoSe 2 ) has recently attracted particular attention due to its room-temperature ferromagnetism (RTFM) and related spintronic applications. However, not only does the FM mechanism of MoSe 2 remain controversial, but also the synthesis of MoSe 2 thin films with robust RTFM is still an unmet challenge. Here it is shown that using polymer-assisted deposition under appropriate growth conditions, large-scale (4 cm × 4 cm) synthesis of MoSe 2 thin films with robust RTFM and a smooth surface (roughness average ∼0.22 nm) is possible. A new record-high saturation magnetization (6.69 emu g -1 ) is achieved in the prepared MoSe 2 thin films, about 5 times the previously reported record (1.39 emu g -1 ) obtained in 2H-MoSe 2 nanoflakes. Meanwhile, the coercivity of the MoSe 2 films can be tuned down to a new record-low value (5.0 Oe), one-tenth of the previously reported record. Notably, detailed analysis combining the experimental findings and calculation results shows that the robust RTFM mainly comes from the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction between the magnetic moments induced by abundant Mo vacancies (V Mo s) in the MoSe 2 films. Our results give insights into the large-scale production and robust RTFM of MoSe 2 thin films and may provide a platform for designing and fabricating spintronic materials and devices based on transition-metal dichalcogenides.