缺陷诱导的Cr掺杂TiO2纳米粉末的铁磁性

用溶胶-凝胶法制备了金红石 Ti_1-xCr_xO₂ (x=0、0.04、0.08) 纳米粉末。磁性测量结果显示, 制备的 Cr 掺杂金红石 TiO₂ 纳米粉末具有室温铁磁性, 样品 x=0.04 和0.08 的饱和磁化强度M_s分别为 0.55×10^-3和 1.6×10^-3 emu/g, (emu/g=4π×10^-7Wb•m/kg)矫顽力H_c分别为 220和 40 Oe(Oe=10³/(4π)A/m)。Cr 掺杂量较大的样品的饱和磁化强度较大, 在 Ar 气中退火可以使粉末呈超顺磁性。Cr2p 区域的密集扫描 X 射线光电子能谱 (XPS)分析显示, 在所有的样品中 Cr都是以Cr³⁺存在。电子顺磁共振谱 (EPR)分析表明, 样品中的 Cr³⁺ 离子仅对其顺磁性有贡献。这些结果提示, 粉末微弱的室温铁磁性来源于掺杂引入的结构缺陷, 其中, 氧空位起重要作用。

Ferromagnetism Induced by Defects in Cr-doped TiO2 Nanopowders

Rutile Ti_1-xCr_xO₂ (x=0, 0.04, 0.08) nanopowders were synthesized by the Sol-Gel method. Magnetic measurements indicate that as-prepared Cr-doped rutile TiO₂ nanopowders exhibit room-temperature ferromagnetism with saturation magnetizations Ms of 0.55×10^-3 and 1.6×10^-3 emu/g, respectively, for samples x=0.04 and 0.08. And their coercive forces H_c are 220 and 40 Oe, respectively. The saturation magnetizations Ms increase with increasing Cr doping concentration. Annealed nanopowders in Ar atmosphere are superparamagnetic. The tight scan Cr2p by X-ray photoelectron spectroscopy spectra (XPS) indicates that Cr ions are in the +3 state for all samples. Electron paramagnetic resonance (EPR) spectra indicates that Cr³⁺ ions contribute only to paramagnetism. Based on above analysis, slight ferromagnetism of Cr-doped TiO₂ nanopowders at room temperature originates from structural defects introduced by doping Cr ions, where oxygen vacancies play an important role.