Srikala D, Singh V N, Banerjee A, Mehta B R, Patnaik S
School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067, India.
J Nanosci Nanotechnol. 2009 Sep;9(9):5627-32. doi: 10.1166/jnn.2009.1157.
We report the synthesis of cobalt nanoparticles with different shapes and sizes by rapid pyrolysis of cobalt carbonyl in the presence of various surfactants. The size and shape of the nanoparticles were influenced by reaction conditions, such as type of the surfactant, molar ratio of surfactant to precursor, reflux temperature and reaction time. The shapes that we have achieved include spherical, nearly spherical, disc and cube. The presence of linear amine yielded nanodiscs and they spontaneously self-assembled into long ribbons. The effect of shape anisotropy on magnetic nanoparticles has been investigated. Spherical nanoparticles of diameter 14.5 nm show strong ferromagnetic behavior at low temperature and superparamagnetism at room temperature. On the other hand the cubic nanoparticles of 45 nm sides showed negligible coercive field at T=10 K and ferromagnetism that persisted above T=300 K. The cobalt nanospheres were oxidized to grow cobalt oxide shell of varying thickness to study exchange bias effect. A pronounced exchange bias and a strong temperature dependant magnetization were observed in oxidized cobalt nanospheres.
我们报道了在各种表面活性剂存在下，通过快速热解羰基钴来合成不同形状和尺寸的钴纳米颗粒。纳米颗粒的尺寸和形状受反应条件影响，如表面活性剂的类型、表面活性剂与前驱体的摩尔比、回流温度和反应时间。我们得到的形状包括球形、近球形、盘状和立方体。线性胺的存在产生了纳米盘，并且它们自发地自组装成长条带。研究了形状各向异性对磁性纳米颗粒的影响。直径为14.5 nm的球形纳米颗粒在低温下表现出强铁磁行为，在室温下表现出超顺磁性。另一方面，边长为45 nm的立方纳米颗粒在T = 10 K时矫顽场可忽略不计，在T = 300 K以上表现出持续的铁磁性。钴纳米球被氧化以生长不同厚度的氧化钴壳，以研究交换偏置效应。在氧化钴纳米球中观察到明显的交换偏置和强烈的温度依赖性磁化。
