Atomistic modeling of nanocrystalline ferromagnets

A model nanocrystalline ferromagnet is investigated at the atomistic level using numerical simulations. The nanocrystalline microstructure is constructed using methods of stochastic optimization and Voronoi construction. The atomic structure of the grains is obtained by molecular dynamics. Nanostructures obtained in this way are characterized by the log-normal grain size distribution and the coordination number of defects at grain boundaries. An Ising model is employed to model the magnetic properties of nanostructured cobalt films with strong perpendicular anisotropy. Particular attention is paid to the effects of the grain boundary structure. We consider Jsimilar toexp(-alphar) on the grain boundary, where alpha is a parameter that represents grain boundary effects. The dependences of the Curie temperature, coercivity, and hysteresis loop on the grain-isolated parameter alpha are investigated. (C) 2003 American Institute of Physics.