Synthesis of single crystalline triangular and hexagonal Ni nanosheets with enhanced magnetic properties.

For the first time, single crystalline Ni nanosheets have been successfully synthesized with the aid of iron species. The as-prepared nanosheets are mainly triangular and hexagonal in shape, with edge lengths ranging from several tens to several hundreds of nanometres. The exposed sheet planes are assigned to be (111) planes of a face-centred cubic nickel crystal. The well defined geometry enhances the anisotropic energy of Ni nanosheets, and therefore increases its blocking temperature (TB) to room temperature. Notably, the coercive force of the Ni nanosheets is 172 Oe at 300 K, which is significantly higher than that of the bulk one (ca. 0.7 Oe at room temperature). A possible mechanism is proposed to explain the formation of the thermodynamically unfavorable morphology of nanosheets. We suggest that crystal twinning, which is formed by etching of the introduced iron species with oleic acid, lowers the system energy, and leads to the growth of these Ni nanosheets.