  The classical impact of electrical currents on magnetic nanostructures is
analyzed with numerical calculations of current-density distributions and
Oersted fields in typical contact geometries. For the Oersted field
calculation, a hybrid finite element / boundary element method (FEM/BEM)
technique is presented which can be applied to samples of arbitrary shape.
Based on the FEM/BEM analysis, it is argued that reliable micromagnetic
simulations on spin-tranfer-torque driven magnetization processes should
include precise calculations of the Oersted field, particularly in the case of
pillar contact geometries. Similarly, finite-element simulations demonstrate
that numerical calculations of current-density distributions are required,
e.g., in the case of magnetic strips with an indentation. Such strips are
frequently used for the design of devices based on current-driven domain-wall
motion. A dramatic increase of the current density is found at the apex of the
notch, which is expected to strongly affect the magnetization processes in such
strips.
