A series of Ti[Formula: see text]Co[Formula: see text]O[Formula: see text] ([Formula: see text] = 0.01, 0.03, 0.05, 0.07) nanoparticles were synthesized by sol–gel method. The X-ray diffraction, transmission electron microscopy, Raman analysis and X-ray photoelectron spectroscopy ruled out the signatures of Ti[Formula: see text], Co-clusters or any other oxides of Co. The ferromagnetic behavior was clearly observed at room temperature in doped samples with saturation magnetization [Formula: see text] of the order of 0.008–0.035 emu/g depending on doping concentrations. The saturation magnetization is found to be increased with the Co contents increasing from 1% to 7%. From the plot of the M–T curve, we obtain the [Formula: see text] as [Formula: see text][Formula: see text]515 K for 5% Co-doped TiO2. Oxygen vacancies were detected from the photoluminescence (PL) measurement. Magnetic properties analyses and PL analyses showed that oxygen vacancies probably played a major role in ferromagnetism of the Ti[Formula: see text]Co[Formula: see text]O2 system with Co substituting for Ti. The first-principles calculation was performed to investigate the magnetic properties of Co-doped TiO2 nanoparticles. It can be found that the major magnetic moment is from the 3d electron of Co. The experiment results are consistent with the first-principles calculation. The ferromagnetism derived from the spin-split of O-2p and Co-3d electron states caused by p–d orbit hybridization.
Electronic structure of β-Ta films from X-ray photoelectron spectroscopy and first-principles calculations
