Competitive coexistence of ferromagnetism and metal-insulator transition of VO₂ nanoparticles

We investigated the magnetic and electric properties of nanometer-sized vanadium dioxide (VO₂) particles. VO₂ nanoparticles were formed by milling VO₂ powder. We measured the magnetic field dependence of the magnetization of the VO₂ powder and nanoparticles. The VO₂ powder did not exhibit ferromagnetism, whereas the VO₂ nanoparticles exhibited ferromagnetism. In addition, we fabricated samples by bridging between electrodes with the VO₂ nanoparticles, and the temperature dependence of their resistance was measured. Metal-insulator transitions (MITs) were observed, and the temperature range where the MIT occurred was wider than that in a typical bulk VO₂. The VO₂ nanoparticles exhibited these properties of ferromagnetism and MIT possibly because of the surface and size effects of the VO₂ nanoparticles. These results indicate the first observation of the competitive coexistence of ferromagnetism and MIT of VO₂ nanoparticles.