  Recent x-ray absorption experiments have demonstrated the possibility to
accurately monitor the magnetism of metallic hetero-structures controlled via a
time-independent perturbation caused for example by a static electric field.
Using a first-principles, non-equilibrium Green function scheme, we show how
the measured dichroic signal for the corresponding steady-state situation can
be related to the underlying electronic structure and its response to the
external stimulus. The suggested approach works from the infinitesimal limit of
linear response to the regime of strong electric field effects, which is
realized in present experimental high sensitivity investigations.
