Room temperature ferromagnetism in non-magnetic doped TiO2 nanoparticles

Abstract

Room-temperature ferromagnetism in non-magnetic doped TiO2 semiconductor nanoparticles is analyzed in the present work. Undoped and N-doped TiO2 nanoparticles were obtained employing sol-gel procedure using urea as the nitrogen source. The obtained gels were first dried at 70 °C and afterwards calcined in air at 300 °C. A residual carbon concentration was retained in the samples as a consequence of the organic decomposition process. Post-annealing treatments at 300 °C under air and vacuum conditions were also performed. The crystallographic structure of nanoparticles was analyzed by X-ray diffraction, obtaining a single anatase crystalline phase after the calcinations (mean nanoparticle diameters around 5–8 nm). SQUID magnetometry was employed to analyze the magnetic response of the samples. Whereas for the undoped samples synthesized with hydrolysis rate h = 6, paramagnetic like behavior is observed at room temperature, the N-doped nanoparticles (h = 3) show a weak ferromagnetic response (saturation magnetization ≈10−3 emu/g). Moreover, a clear reinforcement of the room-temperature ferromagnetism response is found with the post-annealing treatments, in particular that performed in vacuum. Thus, the results indicate the dominant role of the oxygen stoichiometry and the oxygen vacancies in the room temperature ferromagnetic response of these TiO2 nanoparticles.

Structural and magnetic properties of irradiated SiC

“…It challenges the mJ paradigm for magnetism, where m refers the local moment and J stands for the interaction between the local moments. Experimentally, defect-induced ferromagnetism was observed in many materials, including graphite [2][3][4][5] and various oxides [6][7][8][9][10][11][12]. SiC single crystals are emerging as another candidate for this investigation and have been shown to be ferromagnetic after particle irradiation [13,14] or after aluminum doping [15].…”

Magnetic Properties of N- and (Cr, N)-Doped TiO₂ Nanoparticles

“…3 shows the hysteresis loops of the calcined nanoparticles at room temperature. For comparison, the hysteresis loop of non-doped TiO 2 nanoparticles obtained under similar synthesis conditions is also displayed [22]. While nearly paramagnetic behavior is found in the non-doped TiO 2 sample, a weak ferromagnetic response characterizes the room temperature response of the N-TiO 2 nanoparticles (see fig.…”

Bandgap Engineering and Signature of Ferromagnetism in Ti1−xMnxO2­ Diluted Magnetic Semiconductor Nanoparticles: A Valence Band Study

“…[5] Gomez-Polo et al reported RTFM in N-doped (non-magnetic) TiO 2 NPs mainly due to the dominant role of oxygen vacancies concentration with doping. [24] Santara et al observed strong ferromagnetic behavior at room temperature in Co-doped TiO 2 . [25] The saturation magnetization is found to decrease when the samples were post-annealed at 300 C in air atmosphere, which might be due to the reduction of oxygen vacancies in TiO 2 .…”