  The research on multiferrocity and magnetoelectric coupling in metal-organic
system is rare. Very few hybrid organic-inorganic frameworks (HOIF) exhibit
direct magnetoelectric coupling (coupling between spins and dipoles) and also
restricted to particular COOH-based system. We show how one can design a hybrid
system to obtain such coupling based on the rational design of the organic
ligands. The layered phosphonate, MnO3PC6H5.H2O, consisting of perovskite
layers stacked with organic phenyl layers, is used as a starting potential
candidate. To introduce dipole moment, a closely related metal-phosphonate,
MnO3PC6H4-m-Br.H2O is designed. For this purpose, this phosphonate is prepared
from 3-bromophenylphosphonic acid that features one electronegative bromine
atom directly attached on the aromatic ring in meta position, lowering the
symmetry of precursor itself. Thus, bromobenzene moieties in MnO3PC6H4-m-Br.H2O
induce a finite dipole moment. This new designed compound exhibits complex
magnetism, as observed in layered alkyl chains MnO3PCnH2n+1.H2O materials,
namely, 2D magnetic ordering around 20 K followed by weak ferromagnetic
ordering below 12 K(T1) with a magnetic field (H)-induced transition around 25
kOe below T1. All these magnetic features are exactly captured in T and
H-dependent dielectric constant, epsilon(T) and epsilon(H). This demonstrates
direct magnetodielectric coupling in this designed hybrid and yields a new path
to tune multiferroic ordering and magnetodielectric coupling.
