Anisotropic magnetic molecular dynamics of cobalt nanowires

An investigation of thermally induced spin and lattice dynamics of a cobalt nanowire on a (111) Pt substrate is presented via magnetic molecular dynamics. This dynamical simulation model treats each atom as a particle supporting a classical spin. A coordinate dependent on both exchange and anisotropic functions ensures a minimal coupling between the spin and the lattice degrees of freedom to translate the magnetostrictive behavior of most magnetic materials. A spin-pair model of anisotropy is proposed to connect to the lattice thermodynamics. In order to solve linked spin-coordinate equations of motion, the efficiencies of algorithms based on Suzuki-Trotter decompositions are compared. The temperature dependence of the magnetic behavior of Co nanowires is investigated through thermal stochastic connections with mechanical and spin Langevin noises. From a magnetic Hamiltonian parametrized on ab initio calculations, the size dependence of the energy barriers and characteristic time scales of the magnetization relaxation are computed. In the superparamagnetic limit, it is shown that all spins in a nanowire evolve in a coherent rotation. When the size of the single nanowire increases, nucleations of domain walls let the activation energy be independent of the length of the wire.