  The electric field effect on magnetism was examined in the multiferroic
conical magnet Mn$_2$GeO$_4$, which shows a strong coupling between
ferromagnetic and ferroelectric order parameters. The systematic evaluation of
the electric polarization in the multiferroic phase below 5.5 K under various
field cooling conditions reveals that small magnetic fields of 0.1 T
significantly reduce the required electric fields needed to reach saturation.
By applying electric fields during magnetic field dependent hysteresis
measurements of magnetization M and polarization P an electrically controllable
exchange bias was observed, a phenomenon exceedingly rare in single phase
multiferroics. Furthermore, non-reversible electric switching of P and M
domains was achieved under specific magnetic field conditions.
