Controlled synthesis of rice ear-like cobalt microcrystals at room temperature

In this work, we report a mild chemical procedure to synthesize rice ear-like cobalt microstructures using hydrazine hydrate as the reductive agent. The as-obtained products were characterized by X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry. The results show that the samples are hexagonal-close-packed (hcp) Co dendritic structures composed of a pronounced trunk and multiple ears. The length of the main trunk is tens of micrometers, and that of each ear is 3–5 μm with a width of about 1 μm. It was found that the chain length of surfactant PEG as directing agent drastically influenced the morphologies of the produced cobalt crystals. The morphologies of samples can be manipulated from cauliflower to flower and then to rice ear-like structures only by choosing PEG of different molecular weight as surfactant. These microstructures exhibited a ferromagnetic behavior at 300 K and might have potential applications in microdevices and other related magnetic devices.