Control of Ferromagnetism of Vanadium Oxide Thin Films by Oxidation States

Abstract Vanadium oxide (VO x ) is a material of significant interest due to its metal‐insulator transition (MIT) properties as well as its diverse stable antiferromagnetism depending on the valence states of V and O with distinct MIT transitions and Néel temperatures. Although several studies reported ferromagnetism in the VO x , it is mostly associated with impurities or defects, and pure VO x has rarely been reported as ferromagnetic. The research presents clear evidence of ferromagnetism in the VO x thin films, exhibiting a saturation magnetization of ≈13 kA m −1 at 300 K. The 20‐nm thick VO x thin films via reactive sputtering from a metallic vanadium target in various oxygen atmospheres is fabricated. The oxidation states of ferromagnetic VO x films show an ill‐defined stoichiometry of V 2 O 3+ p , where p = 0.05, 0.23, 0.49, with predominantly disordered microstructures. The ferromagnetic nature of these VO x films is confirmed through a strong antiferromagnetic exchange coupling with the neighboring ferromagnetic layer in the VO x /Co bilayers, in which the spin configurations of the Co layer is influenced strongly due to the additional anisotropy introduced by VO x layer. The present study highlights the potential of VO x as an emerging functional magnetic material with tunability by oxidation states for modern spintronic applications.