Ti1−xCoxO2 polycrystalline films have been prepared on Si(0 0 1) substrates by the plasma enhanced chemical vapour deposition technique at 280 °C without using any carrier gas. All the films show room-temperature ferromagnetic behaviours and no ferromagnetic clusters are detected by x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy, Raman and superconducting quantum interference device measurements as the doping concentration is lower than 4%. In addition, the formation of non-ferromagnetic CoTiO3 under heavy doping is considered to be responsible for the degradation of magnetization in Ti1−xCoxO2 polycrystalline films. Furthermore, saturated magnetization of Ti1−xCoxO2 films is found to decrease with the increasing duration of oxygen-plasma processing, indicating that the oxygen vacancies in the films play an important role in the generation of ferromagnetic Ti1−xCoxO2 films.
The magnetic properties of anatase Ti1−xMnxO2 (0 < x < 0.06) films prepared by sol–gel spin coating annealed in air and vacuum have been investigated. Room temperature ferromagnetism was observed in all the films. Enhancement of ferromagnetism is revealed in the films annealed in vacuum. The magnetic moment of the films annealed in vacuum, at 300 K, is 0.285 ± 0.004 μB/Mn for Ti0.9618Mn0.0382 O2 and 0.366 ± 0.005 μB/Mn for Ti0.9409 Mn0.0591O2. It is believed that the enhanced ferromagnetism could be due to the formation of oxygen vacancies and/or defects.
Acetic acid molecule-coated Fe3O4 nanoparticles, 450–650 nm in size, have been synthesized using a chemical solvothermal reduction method. Fourier transform infrared spectroscopy measurements confirm one monolayer acetic acid molecules chemically bond to the Fe3O4 nanoparticles. The low-field magnetoresistance (LFMR) of more than −10% at room temperature and −23% at 140 K is achieved with saturation field of less than 2 kOe. In comparison, the resistivity of cold-pressed bare Fe3O4 nanoparticles is six orders of magnitudes smaller than that of Fe3O4/molecule nanoparticles, and the LFMR ratio is one order of magnitude smaller. Our results indicate that the large LFMR in Fe3O4/molecule nanoparticles is associated with spin-polarized electrons tunnelling through molecules instead of direct nanoparticle contacts. These results suggest that magnetic oxide-molecule hybrid materials are an alternative type of materials to develop spin-based devices by a simple low-cost approach.
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