He Xuemin, Xu Yingru, Yao Xiujuan, Zhang Chuangwei, Pu Yong, Wang Xingfu, Mao Weiwei, Du Youwei, Zhong Wei
New Energy Technology Engineering Laboratory of Jiangsu Province, Research Center of Information Physics, School of Science, Nanjing University of Posts and Telecommunications Nanjing 210023 P. R. China
National Laboratory of Solid State Microstructures, Nanjing University Nanjing 210093 P. R. China
RSC Adv. 2019 Sep 24;9(52):30195-30206. doi: 10.1039/c9ra03242h. eCollection 2019 Sep 23.
In this study, Ni/NiO binary nanoparticles are synthesized utilizing a reflux method combined with a calcination process. The average size of the nanoparticles is 5-20 nm and the Ni content is 3.55%. Both the microstructures of the Ni/NiO interface and the states of different phases have significant impacts on the magnetic properties. By tuning the temperature and the cooling field during the loop measurement, the change rule of several critical parameters such as coercivity and exchange bias was complicated in nature. Both large (482 Oe) and enhanced (1335 Oe) were observed at 5 K, mainly due to the strong coupling interaction between Ni and NiO components. For current studies of the Ni/NiO binary nanoparticles, the complex magnetic behaviors are related to (i) the ferromagnetic contribution of Ni nanoparticles, (ii) the intrinsic antiferromagnetism of the volume phase of NiO, and (iii) the spin-glass-like characteristic corresponding to the frozen disordered state at the surface of partial NiO particles. The comprehensive effect of these three magnetic structures promotes the generation of a strongly-coupled Ni/NiO binary system, and improves the magnetic performance.
在本研究中，采用回流法结合煅烧工艺合成了Ni/NiO二元纳米颗粒。纳米颗粒的平均尺寸为5 - 20 nm，Ni含量为3.55%。Ni/NiO界面的微观结构和不同相的状态对磁性能都有显著影响。在循环测量过程中，通过调节温度和冷却场，矫顽力和交换偏置等几个关键参数的变化规律本质上较为复杂。在5 K时观察到了较大的矫顽力（482 Oe）和增强的交换偏置（1335 Oe），这主要归因于Ni和NiO组分之间的强耦合相互作用。对于当前对Ni/NiO二元纳米颗粒的研究，复杂的磁行为与以下因素有关：（i）Ni纳米颗粒的铁磁贡献；（ii）NiO体相的本征反铁磁性；（iii）部分NiO颗粒表面对应于冻结无序态的自旋玻璃状特征。这三种磁结构的综合作用促进了强耦合Ni/NiO二元体系的产生，并提高了磁性能。
