  We show through non-equilibrium non-adiabatic electron-spin-lattice
simulations that above a critical current in magnetic atomic wires with a
narrow domain wall (DW), a couple of atomic spaces in width, the electron flow
triggers violent stimulated emission of phonons and magnons with an almost
complete conversion of the incident electron momentum flux into a phonon and
magnon flux. Just below the critical levels of the current flow, the DW
achieves maximal velocity of about $3\times 10^{4}$ m/s, entering a strongly
non-adiabatic regime of DW propagation, followed by a breakdown at higher
biases. Above this threshold a further increase of the current with the applied
bias is impossible -- the electronic current suffers a heavy suppression and
the DW stops. This poses a fundamental limit to the current densities
attainable in atomic wires. At the same time it opens up an exciting way of
generating the alternative quasi-particle currents, described above, once the
requisite electronic-structure properties are met.
