  We explore the impact of a magnetic field on the ferroelectric domain pattern
in polycrystalline hexagonal ErMnO3 at cryogenic temperatures. Utilizing
piezoelectric force microscopy measurements at 1.65 K, we observe modifications
of the topologically protected ferroelectric domain structure induced by the
magnetic field. These alterations likely result from strain induced by the
magnetic field, facilitated by intergranular coupling in polycrystalline
multiferroics. Our findings give insights into the interplay between electric
and magnetic properties at the local scale and represent a so far unexplored
pathway for manipulating topologically protected ferroelectric vortex patterns
in hexagonal manganites.
