Evidence for a magnetic metallic R phase in Vanadium dioxide VO2

Vanadium dioxide VO$_{\mathrm{2}}$ has garnered extensive research interests for over decades due to its metal-insulator transition (MIT) around 340 K (Ref. 1). Much is known for the physics behind the MIT (including a correlated structural transition and the involvement of several intermediate states). On the other hand, the magnetic property across the MIT is much less known. Although there are no fundamental arguments against the possibility of forming local magnetic moments in VO$_{\mathrm{2}}$. So far, only the M2 phase has been confirmed to possess local magnetic moments. However, our temperature-dependent magnetic susceptibility measurements of VO$_{\mathrm{2}}$ show a sudden jump at the MIT that cannot be attributed to a simple Pauli susceptibility from conducting electrons. In a recent paper$^{\mathrm{2}}$, we pointed out local magnetic moments may form in the metallic R phase. The formation of local moment would naturally explain the extremely high magnetic susceptibility of VO$_{\mathrm{2}}$ above the phase transition temperature. We further discuss the magnetoresistance (MR) measured across the MIT, which shows different magnitude and field dependence in M1 and R phase, including the MR in the metallic phase suppressed to lower temperature in a VO$_{\mathrm{2}}$ electric double layer transistor device using ionic liquid as gate dielectrics. 1. F. J. Morin, Phys. Rev. Lett. 3, 34 (1959). 2. Xun Yuan et al., Phys. Rev. B 86, 235103 (2012).