Here, we report a phase-solution annealinginduced structural transition of 7 nm-Co nanocrystals from the fcc polycrystalline phase to the hcp single-crystalline phase. For any annealing temperature, contrary to what was down in our previous paper (Langmuir 2011 , 27 , 5014), the same solvent (octyl ether) is used preventing any change in adsorbates related to various solvents on the nanocrystal surface. A careful transmission electron microscopy study, combined with the electron diff raction, confi rms the nanocrystal recrystallization mechanism. The annealing process results in neither coalescence nor oxidation. The converted nanocrystals can be easily manipulated and due to their low size dispersion self-organize on an amorphous-carbon-coated grid. Magnetic property investigations, keeping the same nanocrystal environment, show that the structural transition is accompanied by a signifi cant increase in both the blocking temperature (to a near room-temperature value) and the coercivity.
Source : A phase-solution annealing strategy to control the Co nanocrystal anisotropy: Structural and magnetic investigations. Z.Yang, M.Cavalier, M. Walls, P. Bonville, I. Lisiecki, M.P Pileni J.Phys.Chem.C. , 2012, 116, 15723-15730.