Effects of particle size on the magnetic and microwave absorption properties of carbon-coated nickel nanocapsules

To study the effects of particle size on magnetic and microwave absorption properties, carbon-coated nickel (Ni/C) nanocapsules were prepared by an arc discharge method, where their particles size was adjusted by varying the arc current value from 40 to 100 A. The average particle size of the Ni/C nanocapsules increases from 25 to 53 nm while the thickness of carbon shells keeps independence with increasing the arc current value. The saturation magnetization and coercivity increase with increasing the particle size, due to the small size effect. The complex permittivity, dielectric loss and attenuation constant of paraffin-Ni/C composites are in inverse proportion to the particle size of Ni/C nanocapsules, ascribed to the larger interface area and more defects in the smaller nanocapsules. With the reduction of particle size of Ni/C nanocapsules, the peak of reflection loss (RL) at fixed absorber shifts to lower frequency and the bandwidth becomes broader, while the maximum RL of the composites can be achieved at thinner absorber layer. The phenomenon results from the bigger dielectric loss, larger attenuation constant and better impedance matching degree. The control of particle size is an effective way for adjusting the microwave absorption properties. (C) 2015 Elsevier B.V. All rights reserved.