  The effects of a local magnetic field on nonequilibrium stationary states
(NESS) of the open quantum $XXZ$ spin chain are investigated with a Lindblad
master equation approach in the limit of strong dissipation. The local magnetic
field is applied to a single bulk spin of the chain while the ends are kept at
fixed polarizations by dissipation. We show that suitable changes of the local
magnetic field permit to invert the spin current by switching pure NESS with
opposite chiralities, while preserving the state purity and achieving optimal
transport.
