In physical systems simultaneously breaking time-reversal and spatial
inversion symmetries the strength of absorption for two
counter-propagating light beams can be different, which phenomenon is
termed as non-reciprocal directional dichroism. Until recent experiments
on multiferroic materials this effect was generally found to be weak.
The multiferroic Ni3TeO6 shows strong directional dichroism in its spin
excitations even for unpolarized light. The temperature- and magnetic
field dependence of these exotic resonances was followed up to the Néel
temperature and up to 30 T magnetic field, respectively.