Large-scale fabrication and Mo vacancy-induced robust room-temperature ferromagnetism of MoSe₂ thin films

Molybdenum selenide (MoSe₂) has recently attracted particular attention due to its room-temperature ferromagnetism (RTFM) and related spintronic applications. However, not only does the FM mechanism of MoSe₂ remain controversial, but also the synthesis of MoSe₂ 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 MoSe₂ 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 MoSe₂ thin films, about 5 times the previously reported record (1.39 emu g^-1) obtained in 2H-MoSe₂ nanoflakes. Meanwhile, the coercivity of the MoSe₂ 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_Mos) in the MoSe₂ films. Our results give insights into the large-scale production and robust RTFM of MoSe₂ thin films and may provide a platform for designing and fabricating spintronic materials and devices based on transition-metal dichalcogenides.