A new method for investigating the
dynamics of atomic magnetic moments in current-carrying magnetic point
contacts under bias is presented. This combines the non-equilibrium
Green s function (NEGF) method for evaluating the current and the
charge density with a description of the dynamics of the magnetization
in terms of quasistatic thermally-activated transitions between
stationary configurations. This method is then implemented in a
tight-binding (TB) model with parameters chosen to simulate the main
features of the electronic structures of magnetic transition metals. We
investigate the domain wall (DW) migration in magnetic monoatomic
chains sandwiched between magnetic leads, and for realistic parameters
find that collinear arrangement of the magnetic moments of the chain is
always favorable. Several stationary magnetic configurations are
identified, corresponding to a di erent number of Bloch walls in the
chain and to a di erent current. The relative stability of these
configurations depends on the geometrical details of the junction and
on the bias, however we predict transitions between di erent
configurations with activation barriers of the order of a few tens of
meV. Since di erent magnetic configurations are associated to di erent
resistances, this suggests an intrinsic random telegraph noise at
microwave frequencies in the I-V curves of magnetic atomic point
contacts at room temperature. Finally, we investigate whether or not
current induced torques are conservative.