Magnetically induced electric polarization in an organometallic magnet

The coupling between magnetic order and ferroelectricity has been under intense investigation in a wide range of transition-metal oxides. The most direct coupling is obtained in so-called magnetically induced multiferroics where ferroelectricity arises directly from magnetic order that breaks spatial inversion symmetry. However, it has been difficult to find nonoxide-based materials in which these effects occur. Here we present a study of copper dimethyl sulfoxide dichloride (CDC), an organometallic quantum magnet containing S = 1/2 Cu spins, in which electric polarization arises from noncollinear magnetic order. We show that the electric polarization can be switched in a stunning hysteretic fashion. Because the magnetic order in CDC is mediated by large organic molecules, our study shows that magnetoelectric interactions can exist in this important class of materials, opening the road to designing magnetoelectrics and multiferroics using large molecules as building blocks. Further, we demonstrate that CDC undergoes a magnetoelectric quantum phase transition where both ferroelectric and magnetic order emerge simultaneously as a function of magnetic field at very low temperatures.