Madhu G, Maniammal K, Biju V
Department of Physics, University of Kerala, Kariavattom Campus, Thiruvananthapuram, Kerala Pin 695581, India.
Phys Chem Chem Phys. 2016 Apr 28;18(17):12135-48. doi: 10.1039/c5cp03710g.
Nanostructured nickel oxide samples with crystallite sizes in the range 32-45 nm are synthesized through a facile chemical route using nickel chloride and ethanol amine as the starting materials. The analysis of the antioxidant activity and DC conductivity of the NiO samples confirmed the presence of both Ni(2+) and O(2-) vacancies. The temperature dependent magnetization studies of the samples are done using a Vibrating Sample Magnetometer in the range 20-300 K. The core-shell magnetic structure of the NiO nanoparticles with an antiferromagnetic core and a spin-glass shell is revealed from the zero field cooled and field cooled magnetization studies of the samples. The dependence of uncompensated moments on total spins contradicts Neel's models and is found to vary directly with O(2-) vacancy concentration. The ferromagnetic response of NiO samples due to the interaction between the antiferromagnetic core and the ferromagnetic shell is evident from the magnetic hysteresis studies in the temperature range 20-300 K. The ferromagnetic response is traced to the concentration of O(2-) vacancies, which act as donor impurities and mediate the alignment of magnetic moments associated with Ni(2+) vacancies. The decrease of ferromagnetic contribution upon annealing is explained by the decrease in the concentration of O(2-) vacancies which caused a reduction in the number of magnetic polarons and hence the effective magnetization.
采用氯化镍和乙醇胺作为起始原料，通过简便的化学路线合成了微晶尺寸在32 - 45纳米范围内的纳米结构氧化镍样品。对氧化镍样品的抗氧化活性和直流电导率分析证实了Ni(2+)和O(2-)空位的存在。使用振动样品磁强计在20 - 300 K范围内对样品进行了温度依赖磁化研究。从样品的零场冷却和场冷却磁化研究中揭示了具有反铁磁核心和自旋玻璃壳的氧化镍纳米颗粒的核壳磁结构。未补偿磁矩对总自旋的依赖性与尼尔模型相矛盾，并且发现其与O(2-)空位浓度直接相关。在20 - 300 K温度范围内的磁滞研究表明，由于反铁磁核心与铁磁壳之间的相互作用，氧化镍样品呈现出铁磁响应。铁磁响应可追溯到O(2-)空位的浓度，这些空位充当施主杂质并介导与Ni(2+)空位相关的磁矩排列。退火后铁磁贡献的降低是由于O(2-)空位浓度的降低，这导致了磁极化子数量的减少，从而有效磁化强度降低。
