Synthesis and magnetic properties of nickel micro urchins

• Loose nickel micro urchins were synthesized by a wet chemical method.
• The synthesis was heated from 25 °C to 85 °C and stayed 25 min at this final temperature.
• The slow heating rate allowed a relative decoupling between nucleation and growth.
• Increasing the final plateau temperature increase both urchins size and spike size.
• The nickel micro-urchins showed higher coercivity and remanence than the bulk nickel.

Urchin-like nickel micro particles were produced in aqueous solution through a simple auto-catalytic chemical reduction method without any complexant or surfactant by slowly increasing the temperature of the bath from 25 °C to an aging plateau at 85 °C. The overall time of synthesis is around 40 min. The micro urchins are nanostructured, formed by only one fcc-Ni phase with mean crystallite size of 27.6 nm; they have mean diameter of 1.36 μm with spherical core and blade shaped spikes rising from its surface. In order to study the nucleation and growth process, we also repeated the synthesis changing its plateau temperature and aging time. Based on the reaction temperature and time investigations, a scheme for the micro urchins formation was proposed and discussed. Vibrating sample magnetometry measurements of the particles present coercivity (Hc = 107.12 Oe) and relative remanence (Mr/Ms = 0.15) much higher than the nickel bulk and lower saturation magnetization (Ms = 50.8 emu/g) due to their shape and nanosized structure.

Figure optionsDownload as PowerPoint slide