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

Molybdenum selenide (MoSe) 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 remain controversial, but also the synthesis of MoSe 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 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) is achieved in the prepared MoSe thin films, about 5 times the previously reported record (1.39 emu g) obtained in 2H-MoSe nanoflakes. Meanwhile, the coercivity of the MoSe 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 (Vs) in the MoSe films. Our results give insights into the large-scale production and robust RTFM of MoSe thin films and may provide a platform for designing and fabricating spintronic materials and devices based on transition-metal dichalcogenides.