  We calculate a nondissipative spin current and show that it can flow with or
without a charge current. We consider a two-band model which can be applied to
the description of Fe-based pnictides in coexistence regime of
superconductivity and spin-density wave. Using quasiclassical Green's functions
approach and tunneling Hamiltonian method we show that there exists a
possibility to switch off the Josephson current while leaving the spin current
finite. Moreover, it is possible to have the critical Josephson current and the
critical spin current being proportional to each other, thus giving a
possibility to measure the spin current via the Josephson current. The
underlying mechanism is the interfering hopping of electron--hole pairs between
different bands of the superconductors composing the junction. This is an
intrinsic property of the system and provides a unique and natural way to
utilize junctions made solely of pnictides in promising applications in
spintronics devices.
