  Stability of ground magnetization state of a thin magnetic nanowire against
longitudinal spin-polarized current is studied theoretically with dipole-dipole
interaction taken into account. The critical current, minimum current at which
the instability of the ground state develops, is determined. Dependence of the
critical current on size and form of the transversal wire cross-section is
clarified. Theoretical predictions are confirmed by numerical micromagnetic
simulations.
