Room-temperature ferromagnetism properties of monoclinic VO2 (M1) nanobelts

• The unusual room temperature ferromagnetism of the VO2(M1) nanobelts is found in magnetic measurement.
• The oxygen vacancies induce the change of Bader charge of V atom from +2.34 to +1.84 (V+4 to V+3).
• The ferromagnetic nature is a result of the oxygen vacancies based on the calculations by DFT.

The magnetic properties of monoclinic VO2(M1) nanobelts synthesized by the hydrothermal method are investigated. The VO2(M1) nanobelts exhibit ferromagnetism at room temperature, which disagrees with previous literatures. The excessive oxygen vacancies induce the ferromagnetic nature of VO2(B) nanobelts, which is attributed to the fact that the Bader charge of V atom changes from +2.34 to +1.84 (V+4 to V+3) based on the calculations by using density functional theory (DFT). The calculations indicate that oxygen vacancy may induce the presence of V3+ atom, in agreement with experimental observations. The observed ferromagnetism should be a result of oxygen vacancies in VO2(M1) nanobelts.