The shape dependence of magnetic and microwave properties for Ni nanoparticles

The magnetic and microwave properties of Ni nanospheres and conical nanorods have been investigated through experimental and theoretical methods. Ni nanospheres and conical nanorods have the same crystal structure and close particle size, whereas the remanence ratio, coercivity, dynamic permeability and microwave absorbing properties show great dependence on their shape. Ni conical nanorods self-assembled into urchin-like structure have higher natural resonance frequency due to the large shape anisotropy compared to the Ni nanospheres. Supposing random spatial distribution of magnetic easy axes and using the Landau-Lifshitz-Gilbert equation associated with the Bruggeman's effective medium theory, we simulate the complex permeability of Ni nanoparticles, which agrees well with the experimental results.