Coexisting Ferromagnetic and Ferroelectric Order in a CuCl₄-based Organic–Inorganic Hybrid

We investigate the structural, magnetic, and dielectric properties of the organic–inorganic hybrid material CuCl4(C6H5CH2CH2NH3)2 and demonstrate that spontaneous ferroelectric order sets in below 340 K, which coexists with ferromagnetic ordering below 13 K. We use X-ray diffraction to show that the electric polarization results from the spatial ordering of hydrogen bonds that link the organic block comprised of phenylethylammonium cations to the inorganic copper chloride block. The hydrogen bond ordering is driven by buckling of the corner-linked copper chloride octahedra. Because the magnetic exchange pathways are also determined by this octahedral buckling, a potentially large magnetoelectric coupling is induced. Our results imply that such hybrids form a new family of multiferroic materials.