  We propose and develop a concept of magnonic logic gates enabling reversible
computing. The gates consist of passive elements: waveguides, cross-junctions
and phase shifters. Logical 0 and 1 are encoded in the relative phase of the
propagating spin wave packets (0 or {\pi}). The gates contain several possible
trajectories for each packet to propagate from the input to the output.
Re-direction of the spin wave packets among the possible trajectories is due to
the interference in the magnetic cross-junctions. Two wave packets coming to
the cross-junction in-phase propagate through the junction without reflection.
Two packets coming out-of-phase to the junction are completely reflected back.
The operation of the cross-junction is illustrated by numerical modeling. We
estimate the power dissipation in the proposed circuits and the feasibility of
cascading such magnetic devices in large circuits. The proposed gates may
potentially provide a route to magnetic reversible logic circuitry with power
dissipation less than kT per operation.
