  We propose emergent time-reversal switching responses in antiferromagnets,
which is triggered by an accompanying magnetic toroidal monopole, i.e.,
time-reversal odd scalar distinct from electric and magnetic monopoles. We show
that simple collinear antiferromagnets exhibit unconventional responses to
external electric and/or magnetic fields once magnetic symmetry accommodates
the magnetic toroidal monopole. We specifically demonstrate that the emergence
of the magnetic toroidal monopole in antiferromagnets enables us to control
rotational distortion by an external magnetic field, switch vortex-type
antiferromagnetic structure by an external electric field, and convert
right/left-handedness in chirality by a composite electromagnetic field. We
also present the symmetry conditions to induce the magnetic toroidal monopole
and exhibit candidate materials including noncollinear antiferromagnets in
order to stimulate experimental observations.
