  Long-range non-collinear all-in/all-out magnetic order has been directly
observed for the first time in real space in the pyrochlore Cd$_2$Os$_2$O$_7$
using resonant magnetic microdiffraction at the Os L$_3$ edge. Two different
antiferromagnetic domains related by time-reversal symmetry could be
distinguished and have been mapped within the same single crystal. The two
types of domains are akin to magnetic twins and were expected - yet unobserved
so far - in the all-in/all-out model. Even though the magnetic domains are
antiferromagnetic, we show that their distribution can be controlled using a
magnetic field-cooling procedure.
