  We investigate the mean-field phase diagram of the Anderson impurity model
out of equilibrium. Generalising the unrestricted Hartree-Fock approach to the
non-equilibrium situation we derive and analyse the system of equations
defining the critical surface separating the magnetic regime from the
non-magnetic one. An exact analytic solution for the phase boundary as a
function of the applied voltage is found in the symmetric case. Surprisingly,
we find that as soon as there is an asymmetry, even small, between the
contacts, no finite voltage is able to destroy the magnetic regime which
persists at arbitrary high voltages.
