Effects of surface anisotropy on the energy barrier in cobalt-silver core-shell nanoparticles

We have used a combination of molecular dynamic and atomistic spin models to study the effective anisotropy in CocoreAgshell nanoparticles. Molecular dynamic simulations utilizing the Embedded Atom Method were used to calculate the structure of the particles. The simulation of the annealing process yields a clear segregation of the Ag atoms resulting in a Co core with a shape similar to a truncated octahedron. The surface anisotropy was simulated assuming the Neel model applied to an atomistic spin system with Heisenberg-type exchange. Energy landscapes were then calculated using the Lagrangian multiplier technique. The effective anisotropy of nanoparticles is strongly influenced by surface effects and the thermal motion of the atoms, causing an increase in the thermal stability. (c) 2007 Elsevier B. V. All rights reserved.