  Although the magnetoelectric effects - the mutual control of electric
polarization by magnetic fields and magnetism by electric fields, have been
intensively studied in a large number of inorganic compounds and
heterostructures, they have been rarely observed in organic materials. Here we
demonstrate magnetoelectric coupling in a metal-organic framework
[(CH3)2NH2]Mn(HCOO)3 which exhibits an order-disorder type of ferroelectricity
below 185 K. The magnetic susceptibility starts to deviate from the Curie-Weiss
law at the paraelectric-ferroelectric transition temperature, suggesting an
enhancement of short-range magnetic correlation in the ferroelectric state.
Electron spin resonance study further confirms that the magnetic state indeed
changes following the ferroelectric phase transition. Inversely, the
ferroelectric polarization can be improved by applying high magnetic fields. We
interpret the magnetoelectric coupling in the paramagnetic state in the
metal-organic framework as a consequence of the magnetoelastic effect that
modifies both the superexchange interaction and the hydrogen bonding.
