Researchers report that the common mineral hauerite (MnS2) becomes ferroelectric at low temperature because of the way its magnetic moments order. Ferroelectricity means the crystal develops a permanent electric polarization that can point one way or the other. In MnS2 this electric polarization appears below about 48 K (−225 °C) at the same temperature where the manganese spins form a collinear antiferromagnetic pattern. Because the electric order appears as a direct consequence of magnetic order, MnS2 is classified as a type‑II multiferroic.

The team combined experiments on a natural single crystal with electronic structure calculations. They measured electric polarization using a charge‑collection electrometer inside a Physical Property Measurement System and saw a clear jump in polarization at the magnetic transition. Low poling fields produced measured values of about 120 microcoulombs per square meter. Field‑cooled measurements gave a projection of 210 μC/m2 along the [111] crystal axis; from this the authors estimate a saturation polarization of about 360 μC/m2. Dielectric measurements showed a sharp peak at the transition and a broad hysteresis, consistent with a first‑order change. They also measured thermal expansion and used the Clausius–Clapeyron relation to estimate that the magnetic transition shifts by about 0.7(1) K per GPa of uniaxial pressure.

To explain how magnetism produces electric polarization, the researchers point to the crystal structure. Mn atoms form a frustrated face‑centered cubic sublattice and pairwise sulfur atoms (S2 dimers) sit between them. When the manganese spins order in the observed pattern, the arrangement breaks inversion symmetry (the symmetry that would make left and right equivalent). This lets the two atoms of certain S2 dimers develop small dipole moments. The unequal magnetic environment of the two sulfur atoms makes the dimer electrically polar. In microscopic terms, frustration of competing magnetic interactions gives rise to two interacting antiferromagnetic sublattices and that interplay creates the net polarization.