Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, U.P., India.
J Colloid Interface Sci. 2010 Nov 15;351(2):323-9. doi: 10.1016/j.jcis.2010.07.065. Epub 2010 Aug 1.
Self-assembled monodisperse fcc Co(50)Ni(50) and Co(80)Ni(20) alloy nanoparticles with the average size of 25 and 8 nm respectively are synthesized by reductive thermal decomposition of Co(II)(acac)(2) and Ni(II)(acac)(2) in the presence of surfactants such as oleic acid, oleylamine and trioctylphosphine. The mechanism for formation of colloidal CoNi alloy nanoparticles is explored in this work. The CoNi nanoparticles with high atomic percentage of nickel are found to be more stable and non-interacting. The Co(50)Ni(50) nanoparticles are superparamagnetic at room temperature and exhibit superparamagnetic to ferromagnetic transition at the blocking temperature (T(b)) ∼130-160 K, whereas Co(80)Ni(20) nanoparticles are ferromagnetic at room temperature with low coercivity (∼20 Oe). The magnetization value of Co(80)Ni(20) nanoparticles is found to be high as compared to Co(50)Ni(50) nanoparticles due to high atomic percentage of cobalt. Interestingly, size of CoNi alloy nanoparticles with high nickel content is found to be large, which indicates that nickel nuclei act as catalysts for the growth of CoNi alloy nanoparticles in the reaction.
自组装单分散 fcc Co(50)Ni(50)和 Co(80)Ni(20)合金纳米粒子，平均尺寸分别为 25nm 和 8nm，是通过 Co(II)(acac)(2)和 Ni(II)(acac)(2)在表面活性剂如油酸、油胺和三辛基膦存在下还原热分解合成的。本工作探索了胶体 CoNi 合金纳米粒子的形成机制。研究发现，高镍原子百分比的 CoNi 纳米粒子更稳定且不相互作用。Co(50)Ni(50)纳米粒子在室温下呈超顺磁性，在阻塞温度（T(b)）130-160K 时表现出超顺磁到铁磁转变，而 Co(80)Ni(20)纳米粒子在室温下呈铁磁性，矫顽力低（20Oe）。与 Co(50)Ni(50)纳米粒子相比，Co(80)Ni(20)纳米粒子的磁化值较高，这是由于钴的原子百分比较高。有趣的是，高镍含量的 CoNi 合金纳米粒子的尺寸较大，这表明镍核在反应中充当了 CoNi 合金纳米粒子生长的催化剂。
