  We study magnon transmission across gate-controlled junctions in the $n=0$
manifold of Landau levels in monolayer graphene, allowing for both spin and
valley Zeeman fields. We show that by tuning the external perpendicular
magnetic field, the phase in the intermediate region of a $1|\nu_m|1$ sandwich
geometry can be changed, due to which the magnon transmission can be switched
between fully transmitting and fully blocked. Our analysis, along with the
experimental measurements, can be used to determine the anisotropic couplings
in the sample.
