  This article discusses the spin-torque effect in a spin-valve made out of two
ferromagnetic leads connected through a coherent nanoconductor (NC), in the
limit where a single channel of the NC lies near the Fermi energy of the leads.
Due to quantum interferences inside the NC, the spin-torque presents clear
qualitative differences with respect to the case of a multichannel disordered
spin-valve. In particular, it can be modulated with the NC gate voltage. In
principle, this modulation can be observed experimentally, assuming that the
spin-torque affects a ferromagnetic nano-domain in direct contact with the NC.
