Morphology-controlled fabrication and magnetic properties of nickel assemblies

In this study, nickel assemblies with various morphologies, including nanospheres, pinecone structures, microspheres, and necklace chains, were synthesized in ethylene glycol solution by adjusting the experimental conditions. We propose a possible growth mechanism for the formation of different structures, which involves the rapid nucleation of primary particles followed by slow aggregation and Ostwald ripening crystallization of the primary particles. The saturation magnetization (M_s) of the nickel assemblies decreased as the particle size declined. We found that the coercivity (H_c) of the necklace chains appeared to be higher than that of other structures due to their shape anisotropy. The results of our study indicated that the magnetic properties of the nickel assemblies were morphology-dependent. The coercivities of the nickel samples with different structures prepared in this study were two orders of magnitude higher than that of bulk nickel (0.7 Oe).