Magnetoelectric effects in an organo-metallic quantum magnet

TL;DR

This study demonstrates a significant magnetoelectric effect in an organo-metallic quantum magnet, where magnetic fields induce electric polarization through spin-lattice interactions in a polar crystal structure.

Contribution

It reports the first observation of magnetic field-induced electric polarization in an organo-metallic quantum magnet, highlighting the role of organic molecules in magnetoelectric coupling.

Findings

Magnetic field induces electric polarization of 50 μC/m^2 in DTN crystals.

Magnetization closely follows the electric polarization under applied magnetic fields.

The structure's polar organic molecules enable magnetoelectric effects in organo-metallic materials.

Abstract

We observe a bilinear magnetic field-induced electric polarization of 50 $\mu C/m^2$ in single crystals of NiCl$_2$-4SC(NH$_2$)$_2$ (DTN). DTN forms a tetragonal structure that breaks inversion symmetry, with the highly polar thiourea molecules all tilted in the same direction along the c-axis. Application of a magnetic field between 2 and 12 T induces canted antiferromagnetism of the Ni spins and the resulting magnetization closely tracks the electric polarization. We speculate that the Ni magnetic forces acting on the soft organic lattice can create significant distortions and modify the angles of the thiourea molecules, thereby creating a magnetoelectric effect. This is an example of how magnetoelectric effects can be constructed in organo-metallic single crystals by combining magnetic ions with electrically polar organic elements.