Room-Temperature Ferromagnetic Ultrathin α-MoO3:Te Nanoflakes

We materialized room-temperature ferromagnetism in ultrathin alpha-MoO3:Te nanoflakes. The alpha-MoO3:Te nanoflakes, which had been grown by vapor phase epitaxy, clearly exhibited an Ag Raman band from symmetric stretching of v(Mo-O-3-Mo) in the 2D-like ultrathin alpha-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 alpha-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 alpha-MoO3:Te solid-state system. The results may move a step closer to the demonstration of spin functionalities in the wide bandgap semiconductor alpha-MoO3:Te.