Huanhuan Xu

Manipulation of morphology and magnetic properties in cobalt nanowires

Ferromagnetic metallic Cobalt nanowires are synthesized by the reduction of carboxylate salts of Co in 1, 2-butanediol using a solvothermal chemical process. In this process, the size and shape of the nanocrystals can be controlled via reaction parameters such as surfactant ratio, precursor concentration, and the temperature ramp. Synthesized Co nanocrystals exhibit the hexagonally close-packed phase favored the growth of anisotropic particles and the (002) crystalline direction is along the long axis of the nanowires. By varying the catalyst concentration in proper range, the effect of synthetic parameters on controlling Co nanoparticles with different length of 50 - 700 nm was systematically studied. Magnetic measurements and TEM images of the Cobalt nanowires indicate that the coercivity of the Co nanowires depends substantially on the morphology. The obtained highest coercivity of 8.4 kOe can be attributed to their small mean diameter and high crystallinity of nanowires for 200 - 300 nm.

A novel strategy to synthesize anisotropic SmCo5 particles from Co/Sm(OH)3 composites with special morphology

In this study, we report a new strategy for preparing magnetically anisotropic SmCo5 single crystal particles by reductive annealing of precursors with specially designed nanostructures. The precursors containing urchin-shaped Co clusters and Sm(OH)3 nanorods were synthesized by a hydrothermal process. Then we coated these precursors of Co/Sm(OH)3 nanocomposites with Ca(OH)2, and the following thermal reduction generated SmCo5 particles, where the original size and morphology of the precursor were basically preserved after undergoing high temperature annealing. The single crystalline SmCo5 particles exhibit strong magnetic anisotropy and excellent room temperature magnetic properties: remanence of 8.1 kG, coercivity of 25.7 kOe, and a maximum energy product of 15.8 MGOe, which is one of the highest maximum energy products for chemically synthesized nanostructured SmCo5 particles presently reported.

Effect of size distribution on magnetic properties in cobalt nanowires

Cobalt nanowires were synthesized by reduction of carboxylate salts of Co in 1, 2-butanediol using a solvothermal chemical process. These nanowires crystallize with the hcp structure and the growth axis is parallel to the crystallographic c-axis. The morphology of the nanowires that prepared with mechanical stirring during earlier stage of the reaction process exhibits a smaller averaged aspect ratio but narrow size distribution. The assembly of the nanowires that prepared with mechanical stirring shows almost same coercivity and remanent magnetization but 59% increase of magnetic energy product. This remarkable improvement of energy product has been further understood by micromagnetic simulations. The magnetic performance at variant temperatures of Co nanowires has also been presented. These ferromagnetic nanowires could be new ideal building blocks for permanent magnets with high performance and high thermal stability.