Frustration-induced multiferroicity in hauerite MnS2

Pyrite-type mineral hauerite MnS${}_2$ is a magnetic insulator with localized $S=\frac{5}{2}$ moments. Below 48 K, it develops a collinear antiferromagnetic order, accompanied by unit-cell doubling and breaking the inversion symmetry. We demonstrate that the latter gives rise to a ferroelectric polarization of up to 360 $\mu$C/m${}^2$ rendering MnS${}_2$ a type-II multiferroic. Microscopically, the electronic polarization originates from S${}_2$ dimers that acquire a dipole moment induced by the frustrated magnetic ordering of neighboring Mn sites. We show that time-reversal symmetry leaves ferroelectric domains intact, and that domain switching necessitates overcoming a high energy barrier set by the magnetic exchange energy scale.