VO₂ thin films: Defect mediation in room temperature ferromagnetic switching characteristics

Abstract

Vanadium dioxide (VO₂) has tremendous potential in multifunctional device applications related to spintronics, switching, and magnetic recording. We have discovered that the room temperature ferromagnetism (RTFM) in undoped vanadium oxide epitaxial films can be switched on and off by altering the cooling ambient conditions which exhibit a sharp electrical transition at 341 K. By correlating the structural and ferromagnetic properties in VO₂, we envisage the potential for creation of novel multifunctional solid-state devices. High-quality epitaxial VO₂ thin films were grown on c-sapphire (0001) substrates, under different ambient conditions via the domain matching epitaxy paradigm. The observed RTFM has its origin in the valence charge defects with unpaired electrons in V⁺³ in VO₂ thin films, where the concentration of the defects could be varied with oxygen partial pressure. The VO₂ films-with a high ferro- to paramagnetic transition (Curie) temperature around 500 K estimated by fitting the magnetization data to the Bloch’s T^3/2 law, a saturated magnetization of 18 emu/cm³, and with a finite coercivity of 40 Oe at 300 K-can be useful for integrated smart sensors operable at room temperature.