  We have investigated microwave nonreciprocity in a noncentro-symmetric magnet
CuB2O4. We simultaneously observed differently originated nonreciprocities; the
classical magnetic dipolar effect and the magneto-chiral (MCh) effect. By
rotating magnetic field in a tetragonal plane, we clearly unveil qualitative
difference between them. The MCh effect signal reveals chiral transitions from
one enantiomer to the other via intermediate achiral state. We show
magnetoelectric effect plays an essential role for the emergence of microwave
MCh effect.
