采用多元醇法在150～190℃合成了CoNi合金纳米粒子,利用SEM-EDX,XRD和VSM对所制备的CoNi纳米粒子形貌﹑成分﹑结构以及磁性能进行了研究,并进一步探讨了形核剂K_2PtCl_4对CoNi纳米粒子形貌及磁性能的影响.结果表明,在180℃用多元醇法制备的Co40Ni60(in at%)纳米粒子为FCC结构,Co~(2+)要易于Ni~(2+)被还原,导致最初10min内合成的CoNi纳米粒子中含有约78%(原子分数)Co,表现为高饱和磁化强度和高矫顽力,随着反应时间的延长,CoNi纳米粒子的Co含量﹑饱和磁化强度及矫顽力逐步下降.在150～190℃范围内,随着反应温度的提高,Ni~(2+)的被还原能力增强,高温下合成的CoNi纳米粒子具有较低的饱和磁化强度和较小的矫顽力.形核剂K_2PtCl_4的加入,并不影响CoNi合金纳米粒子的成分和晶体结构.但是,随着形核剂浓度的增加,CoNi纳米粒子平均直径明显减小,其矫顽力有所增大.通过设计形核剂的浓度,CoNi纳米粒子的直径可以在96～580nm范围内任意控制.
The morphology,composition,structure and magnetic properties of CoNi nanopartiles prepared at 150-190℃ for various times have been examined by using scanning electron microscopy assisted with energy dispersive spectropy of X-ray (SEM-EDX),X-ray diffraction (XRD) and vibrating sample magnetometer (VSM).The results show that all of the CoNi nanoparticles prepared above are of face centered cubic (FCC) structure.The Co~(2+) ions are easier to be reduced than Ni~(2+) ions,which results in about 78at%Co in the initial CoNi nanoparticles within 10 min at 180℃ with high saturation magnetization (M_s) and coercivity (H_c).With prolonging reaction time,the Co content in the CoNi nanoparticles decreases,together with the lower M_s and Hc.The reduction of Ni~(2+) ions can be enhanced by increasing temperature in the range of 150-190℃,and the CoNi nanoparticles prepared at higher temperature have low M_s and H_c.With the addition of nucleating agent K_2PtCl_4,the mean diameter of CoNi nanoparticles decreases rapidly but the H_c increases mildly.The addition of K_2PtCl_4 does not affect the composition and structure of CoNi nanoparticles,but the particle size can be tunable in the range of 96-580nm with the proper addition of K_2PtCl_4.The formation mechanism of CoNi nanoparticles has been finally discussed in detail based on the present results.
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