  We study diffusive magnetic Josephson junctions with four superconducting
terminals in the weak proximity limit where the leads are arranged in cross
form. Employing the linearized Keldysh-Usadel technique, the anomalous Green's
function and Josephson current are analytically obtained based on a
quasiclassical theory using the Fourier series method. The derived results may
be reduced to non-magnetic junctions by setting the exchange field equal to
zero. We find that increments of the magnetic barrier thickness may cause a
reversal of the supercurrent direction flowing into some of the leads, whereas
the direction of current-flow remains invariant at the others. The reversal
direction can be switched by tuning the perpendicular superconducting phases.
In the non-magnetic case, we find that the supercurrent flowing between the
leads in one direction can be tuned by changing the superconducting phase
difference in the perpendicular direction. These findings suggest the
possibility of constructing a nano-scale superconducting phase transistor whose
core element consists of the proposed four-terminal Josephson junction with
rich switching aspects.
