We materialized room-temperature ferromagnetism in ultrathin α-MoO3:Te nanoflakes. The α-MoO3:Te nanoflakes, which had been grown by vapor-phase epitaxy, clearly exhibited an Ag Raman band from symmetric stretching of υ(Mo-O3-Mo) in the 2D-like ultrathin α-MoO3:Te layer. Due to the intentional incorporation of smaller Te ions into bigger Mo sites, the pentacoordinated Mo5+ bonds were created inside the orthorhombic α-MoO3:Te lattice system. Since Mo5+ ions have magnetic moments from unpaired electron spins, a large number of overlapped bound magnetic polarons could be formed via ferromagnetic coupling with charged oxygen vacancies that are inevitably generated at pentacoordinated [Mo5+O5] centers. This gives rise to the increase in long-range ferromagnetic ordering and leads to room-temperature ferromagnetism in the entire α-MoO3:Te solid-state system. The results may move a step closer to the demonstration of spin functionalities in the wide bandgap semiconductor α-MoO3:Te.
Keywords: 2D-like layered structure; bound magnetic polaron; orthorhombic α-MoO:Te; room-temperature ferromagnetism; ultrathin nanoflake.